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  • 1.
    Akram, Shazad
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Sidén, Johan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Capacitive and optical sensing for automatic detection and characterization of cleaning sponges in fiber optic microduct installations2019In: Proceedings - 2019 8th International Workshop on Advances in Sensors and Interfaces, IWASI 2019, IEEE, 2019, p. 274-278, article id 8791315Conference paper (Refereed)
    Abstract [en]

    Optical fiber duct installation requires blowing of cleaning sponges for dirt and moisture removal before blowing the fiber cables. The traditional method requires one operator that blows the sponge and one operator in the receiving end that manually evaluate the sponges until a dry sponge is received. The proposed system eliminates the need of a second operator by introducing a solution for automatic sponge detection and characterization of moisture in sponges at the receiving end. An optical sensor is used for detection and a capacitive sensor is developed to measure the sponge's wetness. Sensor data is automatically transmitted back to the operator at the feeding end via a mobile phone. The system is characterized to work with sponges ranging from saturated with wetness to what is deemed as dry. 

  • 2.
    Akram, Shazad
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Sidén, Johan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    LTspice electro-thermal model of joule heating in high density polyethylene optical fiber microducts2019In: Electronics, E-ISSN 2079-9292, Vol. 8, no 12, article id 1453Article in journal (Refereed)
    Abstract [en]

    At present, optical fiber microducts are joined together by mechanical type joints. Mechanical joints are bulky, require more space in multiple duct installations, and have poor water sealing capability. Optical fiber microducts are made of high-density polyethylene which is considered best for welding by remelting. Mechanical joints can be replaced with welded joints if the outer surface layer of the optical fiber microduct is remelted within one second and without thermal damage to the inner surface of the optical fiber duct. To fulfill these requirements, an electro-thermal model of Joule heat generation using a copper coil and heat propagation inside different layers of optical fiber microducts was developed and validated. The electro-thermal model is based on electro-thermal analogy that uses the electrical equivalent to thermal parameters. Depending upon the geometric shape and material properties of the high-density polyethylene, low-density polyethylene, and copper coil, the thermal resistance and thermal capacitance values were calculated and connected to the Cauer RC-ladder configuration. The power input to Joule heating coil and thermal convection resistance to surrounding air were also calculated and modelled. The calculated thermal model was then simulated in LTspice, and real measurements with 50 µm K-type thermocouples were conducted to check the validity of the model. Due to the non-linear transient thermal behavior of polyethylene and variations in the convection resistance values, the calculated thermal model was then optimized for best curve fitting. Optimizations were conducted for convection resistance and the power input model only. The calculated thermal parameters of the polyethylene layers were kept intact to preserve the thermal model to physical structure relationship. Simulation of the optimized electro-thermal model and actual measurements showed to be in good agreement. 

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  • 3.
    Akram, Shazad
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Sidén, Johan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Battery powered inductive welding system for electrofusion joints in optical fiber microducts2021In: Electronics, E-ISSN 2079-9292, Vol. 10, no 6, article id 743Article in journal (Refereed)
    Abstract [en]

    Optical fiber microducts are joined together by mechanical joints. These mechanical joints are bulky, require more space per joint, and are prone to air pressure leakage and water seepage during service. A battery powered electrofusion welding system with a resistive-type joint has been recently developed to replace mechanical joints. These resistive-type electrofusion joints require physical connectors for power input. Due to a different installation environment, the power input connectors of resistive optical fiber microduct joints may corrode over time. This corrosion of connectors will eventually cause water seepage or air pressure leakage in the long run. Moreover, due to connector corrosion, resistive-type optical fiber microduct joints cannot be re-heated in future if the need arises. In this study, an inductively coupled electrofusion-type joint was proposed and investigated. This inductive-type electrofusion joint is not prone to long-term corrosion risk, due to the absence of power connectors. Inductive-type electrofusion joints can be re-heated again for resealing or removal in the long run, as no metal part is exposed to the environment. The battery powered inductive welding system can be easily powered with a 38 volts 160 watt-hour battery. The inductive-type electrofusion joint was welded within one second, and passed a 300-newton pull strength test and a 10-bar air pressure leakage test. It was demonstrated that the power input requirement for inductive electrofusion joints is 64% higher than that of resistive electrofusion joints. However, these inductive joints are relatively easy to manufacture, inexpensive, have no air leakage, and no water seepage risk in highly corrosive environments. 

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  • 4.
    Akram, Shazad
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Sidén, Johan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Duan, Jiatong
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Design and Development of a Battery Powered Electrofusion Welding System for Optical Fiber Microducts2020In: IEEE Access, E-ISSN 2169-3536, Vol. 8, p. 173024-173043Article in journal (Refereed)
    Abstract [en]

    At present, optical fiber microducts are coupled together by mechanical types of joints. Mechanical joints are thick, require a large space, and reduce the installation distance in multi-microduct installation. They may leak or explode in the blown fiber installation process. Mechanical joints are subjected to time dependent deterioration under long service times beneath the earth's surface. It may start with a small leakage, followed by damage due to water freezing inside the optical fiber microduct. Optical fiber microducts are made up of high-density polyethylene, which is considered most suitable for thermoelectric welding. For thermoelectric welding of two optical fiber microducts, the welding time should be one second, and should not cause any damage to the inner structure of the microducts that are being coupled. To fulfill these requirements, an LTspice simulation model for the welding system was developed and validated. The developed LTspice model has two parts. The first part models the power input to joule heating wire and the second part models the heat propagation inside the different layers of the optical fiber microduct and surrounding joint by using electro-thermal analogy. In order to validate the simulation results, a battery powered prototype welding system was developed and tested. The prototype welding system consists of a custom-built electrofusion joint and a controller board. A 40 volt 4 ampere-hour Li-Ion battery was used to power the complete system. The power drawn from the battery was controlled by charging and discharging of a capacitor bank, which makes sure that the battery is not overloaded. After successful welding, a pull strength test and an air pressure leakage test were performed to ensure that the welded joints met the requirements set by the mechanical joints. The results show that this new kind of joint and welding system can effectively replace mechanical joints in future optical fiber duct installations.

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  • 5.
    Alishah, Rasoul Shalchi
    et al.
    Univ Tabriz, Tabriz, Iran.
    Hasani, Mir Yahya
    Islamic Azad Univ Tabriz, Tabriz, Iran.
    Hosseini, Seyed Hossein
    Univ Tabriz, Tabriz, Iran.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Babalou, Milad
    Univ Tabriz, Tabriz, Iran.
    Analysis and Design of a New Extendable Sepic Converter with High Voltage Gain and Reduced Components for Photovoltaic Applications2019In: 2019 10th International Power Electronics, Drive Systems and Technologies Conference (PEDSTC), IEEE, 2019, p. 492-497, article id 8697249Conference paper (Refereed)
    Abstract [en]

    This paper presents a high step-up DC-DC converter which is appropriate for Photovoltaic systems. This topology has been combined from an extended switched-capacitor and a common SEPIC converter. Low components and high-voltage-gain are the main benefits of the introduced topology. Low rate current ripple, easy control and continuous input current are other advantages of the presented structure. Integrating the switched-capacitor with the SEPIC converter leads to increase the output voltage with variable conversion ratio which can be used for a wide range of loads. The switched-capacitor converter provides a constant dc output voltage while the SEPIC converter extracts maximum power of PV panels because it operates under control of duty cycle. Continuous input current is highly suitable for PV applications. The operating principles and steady-state analysis of the suggested topology are discussed in detail. In order to assess the effectiveness of the presented topology, it has been simulated on PSCAD/EMTDC software.

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  • 6.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Comparison of Two Layered and Three Layered Coreless Printed Circuit Board Step-Down Power Transformers2011In: 2011 INTERNATIONAL CONFERENCE ON INSTRUMENTATION, MEASUREMENT, CIRCUITS AND SYSTEMS (ICIMCS 2011), VOL 2: FUTURE COMMUNICATION AND NETWORKING, Shenzhen: IEEE conference proceedings, 2011, p. 59-62Conference paper (Refereed)
    Abstract [en]

    In this paper the comparative results of two layered and three layered coreless Printed Circuit Board (PCB) step down 2:1 power transformers operating in MHz frequency were addressed. The  two different step down transformers approximately having same self inductances, one in two layer and the other in three layer were designed and evaluated for the given power transfer application. The performance characteristics of these transformers under similar conditions were measured and the comparative parameters of these transformers in terms of their resistances, self, leakage, mutual inductances, and coupling coefficient are analyzed. For the given output power, the measured energy efficiency of the three layered transformer is improved by 3% and the area is reduced by 32% compared to two layered transformer. The efficiency of the three layered transformer is 94.5% approximately for an output power level of 25W at an operating frequency of 2.5MHz

  • 7.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Coreless Printed Circuit Board (PCB) StepdownTransformers for DC-DC ConverterApplications2010In: PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY, ISSUE 70, OCTOBER 2010, ISSN:1307-6892, France: World Academy of Science Engineering and Technology , 2010, p. 380-389Conference paper (Refereed)
    Abstract [en]

    In this paper, multilayered coreless printed circuit board (PCB) step-down power transformers for DC-DC converter applications have been designed, manufactured and evaluated. A set of two different circular spiral step-down transformers were fabricated in the four layered PCB. These transformers have been modelled with the assistance of high frequency equivalent circuit and characterized with both sinusoidal and square wave excitation. This paper provides the comparative results of these two different transformers in te rms of their resistances, self, leakage, mutual inductances, coupling coefficient and also their energy efficiencies. The operating regions for optimal performance of these transformers for power transfer applications are determined. These transformers were tested for the output power levels of about 30 Watts within the input voltage range of 12-50 Vrms. The energy efficiency for these step down transformers is observed to be in the range of 90%-97% in MHz frequency region.

  • 8.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Effect of Air Gap on the Performance of Hybrid Planar Power Transformer in High Frequency (MHz) Switch Mode Power Supplies (SMPS)2012In: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Conference paper (Refereed)
    Abstract [en]

    A half bridge transformer with novel winding strategy was designed and tested up to the output power level of 50W with a maximum energy efficiency of 98% in 1-6 MHz frequency region. In this paper, the effect of air gap on the performance of the designed transformer for high frequency (MHz) Switch Mode Power Supplies (SMPS) was studied and analyzed. The air gap of the transformer was varied from 0 – 2mm and the effect on self, leakage, mutual inductances, coupling coefficient and power transfer capability was recorded in 1 - 6MHz. The parameters of the transformer with different air gaps were extracted using network analyzer. The transformer was excited with sinusoidal voltages using power amplifier and the performance characteristics such as input impedance, power transfer capability and hence the energy efficiency was measured. At a particular operating frequency of 3MHz, the maximum power transferred for the given excitation voltage with 0mm air gap was found to be 22W whereas it is only 8W with the 2mm air gap . The measured energy efficiency of the transformer at 3MHz with 0mm and 2mm air gap was found to be 93% and 79% respectively. With this study, for the given power transfer application, at a particular high frequency operation of converter, an optimum air gap without sacrificing the energy efficiency and core saturation was proposed

  • 9.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Effect of Dielectric Material on the Performance of Planar Power Transformers in MHz Frequency Region2012In: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Conference paper (Refereed)
    Abstract [en]

    In this paper, the effect of two different dielectric materials in planar printed circuit board (PCB) transformers applicable for power transfer applications in MHz frequency region is discussed. The 2-D model of the planar transformer was developed and the effect of the dielectric material on the magnetic field and the current distribution in the transformer was analyzed. Based on the FEA analysis, the power transformers of two different dielectric materials were designed, manufactured and characterized by using ‘S’ parameters obtained from network analyzer in order to determine the performance of dielectrics at high frequencies. The electrical parameters such as inductances, capacitances and resistances of the transformers were obtained and the changes in these parameters with the variation of the dielectric material were analyzed in the MHz frequency. This paper discusses the effect of dielectric material on the magnetic field distribution and the current density which results in the variation of the coupling coefficient and the eddy current losses of the transformer. By changing the dielectric material from a traditional FR-4 to a Rogers, the coupling coefficient was improved by a maximum of 5% and the copper losses of transformer were also decreased in the MHz frequency region. The power gain/energy efficiency obtained from the network analyzer with a resonant capacitor is verified with those obtained using a power amplifier and the simulations. An overall energy efficiency improvement of about 2-5% was achieved with a Rogers’s material in MHz frequency region compared to traditional FR-4 laminate.

     

  • 10.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    High Performance Planar Power Transformer with High Power Density in MHz Frequency Region for Next Generation Switch Mode Power Supplies2013In: 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference And Exposition (APEC 2013), IEEE conference proceedings, 2013, p. 2139-2143Conference paper (Refereed)
    Abstract [en]

    The authors report the utilization of the core based transformer for power transfer applications with high power density and high energy efficiency in the MHz frequency region. A custom made POT core center tapped transformer of 4:1:1 turn’s ratio using novel winding strategy with the core diameter of 16mm is designed and evaluated. The designed transformer has been characterized using sinusoidal excitation for a given output power in the frequency range of 1 – 10MHz and determined the operating frequency region of the transformer. The power tests of the transformer has been carried out up to the power level of 62W at an operating frequency of 6.78MHz with a peak energy efficiency of 98.5% resulting in the record power density of ~1100W/in3. The designed transformer has been characterized using class E isolated DC-DC converter topology at an output power of approximately 18W. The simulated energy efficiency of the converter is 88.5% under the full load condition. This work provides the significant step for the development of next generation high power density isolated converters (both AC/DC and DC/DC) in MHz frequency region

  • 11.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Radiated Emissions of Multilayered Coreless Printed Circuit Board Step-Down Power Transformers in Switch Mode Power Supplies2011In: 8th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2011-ECCE Asia 2011, IEEE conference proceedings, 2011, p. 960-965Conference paper (Refereed)
    Abstract [en]

    This paper addressesradiatedEMI issues in Coreless PCB step-down transformers used for power transfer applications. In case of SMPS circuits, since the waveforms are not sinusoidal in nature, most of theradiatedemissionsare not only from fundamental frequency component but also from harmonic contents. According to antenna theory,radiatedEMI for three different power transformers of different radii were estimated for fundamental frequency of 2MHz to 300MHz. The computations were made for both sinusoidal and square wave excitations and at a load power of 20W. The calculatedradiatedpower obtained for simulated waveforms and for practical measured current waveforms are in good agreement with each other up to certain bandwidth. These computational results confirm thatradiatedpower can be reduced in three layered 2:1 transformer compared to two layered 2:1 transformer. Also theradiatedemissionsare negligible in case of sinusoidal excitations compared to square wave excitations. © 2011 IEEE.

  • 12.
    Andersson, Henrik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Processing and Characterization of a MOS Type Tetra Lateral Position Sensitive Detector with Indium Tin Oxide Gate Contact2008In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 8, no 9-10, p. 1704-1709Article in journal (Refereed)
    Abstract [en]

    A 2-D tetra lateral position sensitive detector (PSD) based on the metal-oxide-semiconductor (MOS) principle has been manufactured and characterized. The active area of the device is 5 nun x 5 mm and the intention is to use the central 4 nun x 4 nun for low nonlinearity measurements. The gate contact is made of indium tin oxide (ITO) that is a degenerate electrically conducting semiconductor, which, in addition, is also transparent in the visible part of the spectrum. The use of a MOS structure results in a processing with no necessity to use implantation or diffusion in order to make the resistive p-layer as in a conventional p-n junction lateral effect PSD. Position measurements show good linearity in the middle 4 nun x 4 mm area. Within the middle 2.1 mm x 2.1 mm, the nonlinearity is within 1.7% of the active area with a position detection error of maximum 60 mu m. Measured MOS IV characteristics are compared to a level 3 spice model fit and show good agreement. The threshold voltage is determined to be -0.03 V. Responsivity measurements show a high sensitivity in the visible spectral region.

  • 13.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Barg, S
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    A 2x3 Reconfigurable Modes Wide Input Wide Output Range dcdc Power ConverterIn: IEEE Access, E-ISSN 2169-3536Article in journal (Refereed)
  • 14.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    A phase shifted full bridge converter with novel control over the leakage inductance2016In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 7695545Conference paper (Refereed)
    Abstract [en]

    The electronics industry is progressing towards the high density board solutions due to the requirement of compact and intelligent electronic systems. In order to meet the industry demands, the power system is required to be of high power density. This article proposes one of the solution to improve the power density for the medium power applications. In phase shifted full bridge converter, the intrinsic leakage inductance of the main transformer is not high enough to obtain the zero voltage switching of the power switches for the entire operating conditions. An additional shim inductor is usually connected in series with the primary winding of the main transformer to increase the collective leakage inductance. This additional shim inductor degrades the power density of the converter. This paper proposes a method to embed and control the resonance inductance inside the main transformer. In addition to the increased inter-winding spacing, this paper proposes a practical approach to integrate the ferrite rods inside the main transformer for further increase in the leakage inductance. A power transformer is constructed and investigated by using the modelled equations to estimate the leakage inductance. A prototype phase shifted full bridge converter is also developed to investigate the performance of the proposed transformer. The converter is designed for the switching frequency of 400kHz, and tested up to 600watts output power at the input voltage of 200Vdc. The performance of the proposed converter is also compared with the converter of using an external inductor. The investigations show that, in addition to the improved power density, the converter with the proposed transformer is more efficient than the converter with the traditional transformer.

  • 15.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Modeling and Characterization of Series Connected Hybrid Transformers for Low-Profile Power Converters2020In: IEEE Access, E-ISSN 2169-3536, Vol. 8, p. 53293-53306Article in journal (Refereed)
    Abstract [en]

    Compact and low profile power converters are the main business of today's power industry. A significant volume of a power converter is occupied by the power transformer. This article proposes a unique solution that would make the power converters low profile. Instead of designing a power converter by using a single bulky transformer, the solution proposed is to split the main bulky transformer into a number of low profile transformers. This not only reduces the total weight and volume of the converter but also the total transformer losses. The use of more than one transformer in series reduces the applied voltage on the transformers, which minimizes the required turns ratio and decreases the stress on the secondary rectifiers and filter elements. Moreover, the decrease in the applied voltage reduces the proportional loss per transformer and makes it possible to design a hybrid transformer by combining Litz wire and traces of a printed circuit board. The reduced copper loss and lower heat dissipation per transformer simplify thermal management. An analytical comparison is made between the utilization of a single transformer or a number of transformers. The procedure of splitting a volume of a single transformer into a number of small transformers has been comprehensively discussed. The idea is investigated both experimentally and in computer simulation for an example application of a phase shifted full bridge dc-dc converter. The converter is characterized up to a load power of 2.2 kW at Vin = 400 Vdc and Vout = 48 Vdc. To make the approach more practical, the transformers are modeled using the traditional analytical method. The design of the example application using the split transformer approach reduces the total transformer weight by 45%, compared to the traditional approachwith a single transformer. The converter also shows good performance with a maximum efficiency of 96%.

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  • 16.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Das, Moumita
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Barg, Sobhi
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Reconfigurable three state dc-dc power converter for the wide output range applications2019In: IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, Lisbon: IEEE, 2019, p. 4911-4916Conference paper (Refereed)
    Abstract [en]

    Improving the dc voltage gain of power converters has been the primary focus of the current and past research in the area of power electronics. This work presents another solution to widen the range of the output voltage. It proposes three reconfigurable steps for the output voltage. The range of theoutput voltage varies up to four times the base level. These configurations together vary the output voltage from 15 to 96 volts. A soft switched dc-dc power converter is built with the traditional topology of phase shifted full bridge converter along with improved characteristics. For better management of thetransformer loss, a configuration of four transformers has been employed. The proportional gate drive approach is implemented to obtain four similar isolated blocks of the output voltage. This makes it possible to either configure these blocks all in series,parallel or in series/ parallel combination of two. The concept is verified in a low-profile prototype. The hardware is characterized up to the load power of 1kW for the input voltage of 400Vdc. The converter reports better efficiency over the complete range of output voltage.

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  • 17.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Majid, Abdul
    COMSATS University Islamabad.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Dual-mode stable performance Phase-Shifted Full-Bridge converter for wide-input and medium power applications2021In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 36, no 6, p. 6375-6388Article in journal (Refereed)
    Abstract [en]

    Power converters with an extended range of line voltage are the main requirement in today's industrial applications like photovoltaic and supercapacitors based energy systems. The variation in the line voltage severely degrades the performance of power converters, because of the extended freewheeling interval, more circulation current, narrow range of zero voltage switching and increased EMI. This work suggests a modified Phase-Shifted Full-Bridge converter that cuts the freewheeling interval and minimizes these problems. It extends the input voltage range by keeping the operational duty cycle of the converter high over the wide range of input voltage while maintaining the performance stable. The proposed converter consists of four low profile transformers having reconfigurable interconnection structure. There are two distinct reconfigurable modes, a series mode and a parallel mode, which can be configured with changes in the operational conditions. The operation of the proposed converter with high switching frequency improves power density. Additionally, the use of multiple transformers minimizes heat management efforts and reduces the overall volume of the converter. The proposed work is validated in hardware characterization for a wide range of input voltage 100-400Vdc and up to the load power of 1kW. The measured energy efficiency of the proposed converter remains stable over the complete range input voltage 100-400Vdc.

  • 18.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Shalchi Alishah, Rasoul
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Characterization of phase shifted full bridge converter along with GaN devices and series-connected hybrid transformers for medium power applications2020In: / [ed] IEEE, 2020, p. 1058-1064Conference paper (Refereed)
    Abstract [en]

    Compact power converters are the major concern of today’s power industry. This article proposes GaN devices based isolated dc-dc phase shifted full bridge converter along with the configuration of four series-connected hybrid transformers. The series connection of transformers reduces the applied volt-second on each transformer which reduces the proportional losses and simplify thermal management. This configuration also reduces the required turn’s ratio as well as bringing down the stress on the secondary devices and filters. The converter is characterized in a compact prototype up to the load power of 2.2 kW for Vout=48 Vdc at Vin=400 Vdc. The converter reports satisfactory performance with a maximum efficiency of 96%.

  • 19.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Wårdemark, Mats
    Powerbox International AB, SWEDEN.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    A 2x3 Reconfigurable Modes Wide Input Wide Output Range DC-DC Power Converter2021In: IEEE Access, E-ISSN 2169-3536, Vol. 9, p. 44292-44303Article in journal (Refereed)
    Abstract [en]

    There is an increasing demand for efficient and low-profile power converters in almost all industrial applications. Some require stable performance over a wide range of input voltages, whereas others require converters with a stable performance over a wide range of output voltages. In this regard, little work has been done to combine both requirements into one solution. This work suggests a unique solution that addresses both requirements at once. A power converter with 2x3 reconfigurable modes has been presented, able to operate with DC gains of 1, 2 and 4, which can be further extended to 8. The converter shows stable performance for the extended range of both input and output voltage. The flexible reconfigurable feature of the proposal can be applied in a variety of applications. Two reconfigurable modes on the input side can be configured following the variation in the line voltage to maintain a stable performance, and three reconfigurable modes for the output voltage, which raises the output voltage from 24V to 48V and 96V. The proposal is applied in an example application of a phase shifted full bridge converter. The converter is characterized for Vin = 100-400Vdc, Pout = 1kW. CCBY

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  • 20.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    A Modified Higher Operational Duty Phase Shifted Full Bridge Converter for Reduced Circulation Current2020In: IEEE Open Journal of the Industrial Electronics Society, ISSN 2644-1284, Vol. 1, p. 82-96Article in journal (Refereed)
    Abstract [en]

    Besides many advantages, the reduction in the operational duty of traditional phase shifted full converter limits its scope in applications where a wide range of input voltage is the main requirement. Operation with low duty cycle extends freewheeling interval, which results in degraded performance such as more circulation current, increased conduction loss in power devices, narrow range of zero voltage switching and increased EMI. To overcome these drawbacks, this work suggests a modified phase shifted full bridge converter that keeps the operational duty of the converter high for a wide range of input voltage. This cuts the freewheeling interval and improves performance. The proposed converter consists of four low profile transformers having reconfigurable interconnection structure. There are two distinct reconfigurable modes, a low gain mode and a high gain mode, which can be adopted in accordance with the variation in line voltage. The proposed work is validated in LTspice simulation and hardware characterization for a wide range of input voltage 100-400Vdc/12Vout and up to the load power of 1.2kW.

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  • 21.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    An improved modelling and construction of power transformer for controlled leakage inductance2016In: Environment and Electrical Engineering (EEEIC), 2016 IEEE 16th International Conference on, IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    In this work, a transformer with increased leakage inductance for the soft switched power applications is presented as a practical solution by constructing a transformer with good control over the leakage inductance. An analytical reluctance based model is presented, which accurately predicts the leakage inductance. With the presented approach, a transformer is designed with a leakage inductance varying between 3-7μH. Increasing the efficiency and improving the power density has been the main focus of power electronics researchers in the recent years. In this regards, transformers with increased leakage inductance are becoming more popular in order to accomplish different soft switching concepts and for improving the power density.

  • 22.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    High frequency (MHz) soft switched flyback dc-dc converter using GaN switches and six-layered PCB transformer2016In: IET Conference Publications, UK: Institution of Engineering and Technology, 2016, Vol. 2016, p. 1-6, article id CP684Conference paper (Refereed)
    Abstract [en]

    The increased switching losses with increasing switching frequency are the biggest concerns in designing high power density converters. This paper presents the investigation of an energy efficient DC-DC flyback converter in combination with six layered printed circuit board transformer. The recorded efficiency of the low profile transformer for the frequency range of 1-5MHz is 98% at power density of 770W/in3. The proposed converter is characterized for frequencies up to 4MHz by using possible soft switching techniques such as Boundary Mode and Quasi Resonant Mode. The emerging Gallium Nitride (GaN FET) devices are used as power switch. The control is incorporated with Digital Signal Processor (dsPIC) for both the Boundary and Quasi Resonant Modes of operations. The proposed flyback DC-DC converter is tested on a prototype Printed Circuit Board (PCB). The performance of the proposed converter is investigated for the telecom input voltage range of 36-72Vdc. The maximum obtained energy efficiency of the converter is about 94%. According to the authors' knowledge, this is the maximum efficiency ever achieved in flyback converters switching in MHz frequency range. The results are very encouraging for the development of high frequency, high power density and low cost isolated power converters.

  • 23.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Haller, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Contribution of Leakage Flux to the total Losses in Transformers with Magnetic Shunt2021In: International journal of electronics (Print), ISSN 0020-7217, E-ISSN 1362-3060, Vol. 108, no 4, p. 558-573Article in journal (Refereed)
    Abstract [en]

    To execute soft switching methods in resonant power converters, transformers with larger leakage inductance are getting more attention. Many papers have constructed various concepts in this regard. However, a discussion about, how the transformer efficiency is affected is lacking in the literature. This paper analyses the effects of the increased leakage inductance on the performance of the transformer. A transformer for increased leakage inductance is modelled and constructed to investigate the losses. The model discusses the effects of increased leakage inductance either by increasing the inter-winding spacing or by integrating the magnetic shunt within the transformer. The investigations show that increasing the leakage inductance by inserting a magnetic shunt can have severe degrading effects on the performance of the transformer, if not designed adequately. Additional losses are also calculated and the effects are verified by the experiments.

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  • 24.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Modeling of the Geometry Effect on the Core Loss and Verification with a Measurement Technique Based on the Seebeck Effect and FEA2019In: IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society / [ed] IEEE, IEEE, 2019, p. 1832-1837Conference paper (Refereed)
    Abstract [en]

    In this paper, the effect of the core geometry of non-toroidal magnetic cores on the magnetic loss is investigated. A frequency dependent core material-geometry loss factor is developed. This factor is function of the change in the non-toroidal core section and the Steinmetz parameter “β”. In addition, the temperature effect is included in the developed loss model for wide range of frequency and magnetic flux density. The model is applied for ER core and 3C92 ferrite material. The core loss measurements are performed using a Peltier cell. The principle of operation of the Peltier cell is based on the Seebeck effect, which convert the heat flow due to the temperature difference into electric power.  The calibration of the Peltier cell is validated with a resistive load and a relative error lower than 1% is achieved. The accuracy of the developed model is assessed with FEA and the experimental results. A maximum error of 10% is registered of the developed core loss model.

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  • 25.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Optimization of High Frequency Magnetic Devices with Consideration of the Effects of the Magnetic Material, the Core Geometry and the Switching Frequency2020In: 2020 22nd European Conference on Power Electronics and Applications, EPE 2020 ECCE Europe, IEEE, 2020, article id 9215860Conference paper (Refereed)
    Abstract [en]

    This paper presents an optimization approach of high frequency transformers based on the calculation of the optimum number of turns. The relationship between the volume, the power and the frequency is also investigated. The design approach considers the skin and proximity effects, the core geometry and the magnetic material. 

  • 26.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Computer and Electrical Engineering (2023-).
    Barg, Souhaib
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Computer and Electrical Engineering (2023-).
    High Performance Planar Magnetics Based on an Unbalanced-Flux Approach2023In: IEEE Open Journal of Power Electronics, E-ISSN 2644-1314, Vol. 4, p. 283-292Article in journal (Refereed)
    Abstract [en]

    This paper presents a new design concept to increase the efficiency and the power density of planar magnetics. In contrast to the existing magnetics, which are built using the balanced magnetic flux density design, the proposed design concept generates unbalanced magnetic flux density across the different parts of the magnetic core. The theoretical analysis shows that the core loss of the unbalanced-flux design can be reduced by more than 50% compared to the existing one. The core loss reduction brings several benefits to planar magnetics such as: high power capability, better thermal performance and wider safe operating area (SOA). The proposed design is experimentally evaluated and compared with the balanced-flux design. The experimental results are in good consistency with its theoretical counterparts. The measured core loss are decreased by more than 50% and the power density is increased by more than 250%.

  • 27.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Core Loss Calculation of SymmetricTrapezoidal Magnetic Flux Density Waveform2021In: IEEE open Journal of Power Electronics, E-ISSN 2644-1314, Vol. 2, p. 627-635Article in journal (Refereed)
    Abstract [en]

    Existing empirical core loss models for symmetric trapezoidal flux waveform (TzFW) stillsuffer some issues such as the inaccuracy and the complexity. These issues are mainly due to the lack ofan accurate model of the relaxation loss generated during the off-time. This paper aims to understand therelaxation loss and develop an accurate model using the superposition technique. The developed model givesan accurate prediction of the on-time loss and the relaxation loss and shows the dependency of each on theduty cycle. The research shows that the core loss at low duty cycle is several times the core loss at full dutycycle. The developed model is verified with experimental results and compared to the Improved Steinmetzequation (ISE). The model error is reduced to lower than 15% compared to 50% of the ISE. Finally, an easymethod using multiplication factors with the ISE model is given to simplify the developed model.

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    Core Loss Calculation of SymmetricTrapezoidal Magnetic Flux Density Waveform
  • 28.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Core Loss Modeling and Calculation for Trapezoidal Magnetic Flux Density Waveform2021In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, E-ISSN 1557-9948, Vol. 68, no 9, p. 7975-7984Article in journal (Refereed)
    Abstract [en]

    This paper proposes a novel approach in order to understand the different kinds of core loss of the trapezoidal flux waveform. The proposed approach is based on the theory of magnetism and assessed with the experimental results to show that the total loss is composed by two terms: the effective triangular loss during the on-time resulting from the flux variation and the relaxation loss during the off-time which is due to the magnetic after-effect phenomenon. The study shows that the relaxation loss depends on the off-time and it has a maximum at a particular off-time-to-on-time ratio which depends on the magnetic material. In addition to that, two models with accuracy higher than 96% and with reduced number of parameters compared to the existing models were developed to predict the relaxation loss. The models are verified with previous experimental results and new experiments performed in this work.

  • 29.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Multi‑objective Pareto and GAs nonlinear optimization approach for fyback transformer2019In: Electrical engineering (Berlin. Print), ISSN 0948-7921, E-ISSN 1432-0487, Vol. 101, no 3, p. 995-1006Article in journal (Refereed)
    Abstract [en]

    Design and optimization of high-frequency inductive components is a complex task because of the huge number of variables to manipulate, the strong interdependence and the interaction between variables, the nonlinear variation of some design variables as well as the problem nonlinearity. This paper proposes a multi-objective design methodology of a 200-W flyback transformer in continuous conduction mode using genetic algorithms and Pareto optimality concept. The objective is to minimize loss, volume and cost of the transformer. Design variables such as the duty cycle, the winding configuration and the core shape, which have great effects on the former objectives but were neglected in previous works, are considered in this paper. The optimization is performed in discrete research space at different switching frequencies. In total, 24 magnetic materials, 6 core shapes and 2 winding configurations are considered in the database. Accurate volume and cost models are also developed to deal with the optimization in the discrete research space. The bi-objective (loss–volume) and tri-objective (loss–volume–cost) optimization results are presented, and the variations of the design variables are analyzed for the case of 60 kHz. An example of a design (30 kHz) is experimentally verified. The registered efficiency is 88% at full load.

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  • 30.
    Barg, Sobhi
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Torrico, Grover
    A Novel Concept to Optimize Core Loss in Planar Magnetic Based on an Unbalanced-Flux-Approach2022In: 2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), IEEE conference proceedings, 2022Conference paper (Refereed)
    Abstract [en]

    This paper presents a new method to design planar magnetics. Unlike existing magnetics which have a balanced-flux distribution, the proposed method is based on the principle of unbalanced-flux distribution. The Steinmetz model, derived for this design principle, shows that the unbalanced-flux method reduces the core loss by more than 50%. The core loss reduction brings several benefits to planar magnetics such as: high magnetic power factor, better thermal performance and larger safe operating area (SOA). The proposed method is experimentally evaluated and compared with the balanced-flux method. The obtained results confirmed the advantages of the unbalanced-flux method found from the theoretical study. The core loss is decreased by more than 50%, the magnetic power factor is increased by 73% and the SOA is much larger.

  • 31.
    Bertilson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo Simulation of 4H and 6H-SiC short channel MOSFETs2001In: High Temperature Electronics Network. HITEN ; 4 (Oslo) : 2001.06.05-08: Proceedings of the International Conference on High Temperature Electronics : held in Oslo, Norway, 5th - 8th June 2001, Oxford: Oxford Applied Technology Ltd, , 2001, p. 199-Conference paper (Refereed)
  • 32.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nästa generations kompakta spänningsomvandlare2012In: Thule, Kungl. Skytteanska Samfundets Årsbok 2012, ISSN 0280-8692, Vol. 1, no 1, p. 153-157Article in journal (Other (popular science, discussion, etc.))
  • 33.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation and Optimization of SiC Field Effect Transistors2004Doctoral thesis, monograph (Other scientific)
  • 34.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Transformer2010Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A printed circuit board transformer comprises at least one primary winding and one secondary winding, each in the form of at least one layer of turns inside or at the surface of a printed circuit board. The transformer is designed for a step-up/down-operation. Each of the two layers (10, 11) has an elongated winding element (12, 13, 13′) substantially following an elongated winding element of the other layer while being in an overlapping relationship therewith as seen perpendicularly to said printed circuit board over substantially the entire extension of said winding elements. A second (11) of the layers belonging to the secondary winding has a fewer number of turns than the first (10) of said layers belonging to said primary winding.

  • 35.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC2001In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, no 3-7, p. 1283-1286Article in journal (Refereed)
    Abstract [en]

    The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device

  • 36.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 183-187Article in journal (Refereed)
    Abstract [en]

    A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.

  • 37.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Harris, C
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Calculation of lattice heating in SiC RF power devices2004In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 48, no 12, p. 1721-1725Article in journal (Refereed)
    Abstract [en]

    Silicon carbide MESFET devices are suitable for high-speed and high-power applications. In this paper we are studying thermal effects in 4H-SiC RF power devices. The simulations are based on a combination of 2D device simulations for the electrical transport, and 3D thermal simulations for the lattice heating. We show that the method gives good accuracy, efficiency, flexibility and capacity dealing with tasks, where a 2D coupled electrical-thermal simulation is not sufficient. We also present an improvement of Roschke and Schwierz mobility model, based on Monte Carlo simulations for the temperature dependencies of the mobility parameters beta and v(sat).

  • 38.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Harris, C.I.
    Comparison of bipolar and unipolar SiC switching devices for very high power applications2007In: Silicon Carbide and Related Materials 2006, Trans Tech Publications Inc., 2007, Vol. 556-557, p. 975-978Conference paper (Refereed)
    Abstract [en]

    Both unipolar and injection SiC devices can be used for high voltage switching applications; it is not determined, however, for which applications one approach is preferred over the other. In this paper, simulation studies are used to compare the suitability of unipolar devices, in this case a JFET (Junction Field Effect Transistor) against an equivalent FCD (Field Controlled Diode) configuration up to very high voltages. The calculations are performed in a finite element approach, with commercial drift-diffusion software. Numerous drift layers have been simulated in a Monte-Carlo approach to ensure that the optimal design of the drift layers for different breakdown is used. In a static case, purely conductive losses in the drift layer in both unipolar and injection configuration are compared. Additionally the total losses are studied and compared in switched applications for different switching frequencies and current levels.

  • 39.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Optimization of 2H, 4H and 6H-SiC high-speed vertical MESFETs2002In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 11, no 3-6, p. 1254-1257Article in journal (Refereed)
    Abstract [en]

    Silicon carbide vertical MESFET devices are well suited for high speed and high power electronic devices. In this work we have optimized the geometry of vertical MESFETs for microwave applications, using iterative two-dimensional simulations. Relevant parasitics are included in the simulations to investigate the performance of realistic devices. The state of the art device has f(T)=7 GHz and we show that vertical MESFETs fabricated with traditional technology are totally limited by parasitics. Two different approaches to reduce the parasitics in the vertical MESFET are proposed where f(T) increases significantly.

  • 40.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Optimization of 2H, 4H and 6H-SiC MESFETs for High Frequency Applications2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, p. 75-77Article in journal (Refereed)
    Abstract [en]

    Silicon carbide MESFET devices are well suited for high speed, high power and high temperature electronics due to high saturation velocity, high critical electrical field, good thermal conductivity and large band-gap. Optimization of a high performance device demands a substantial number of numerical simulations, where several different design parameters have to be investigated thoroughly. In this work, we optimize the geometry of lateral MESFETs for maximal unity current-gain frequency (fT) using iterative 2-dimensional simulations. We also present a comparison of performance for individually optimized devices, realized with lithographic resolutions ranging from 0.2 to 2 μm in different SiC polytypes.

  • 41.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    The power of using automatic device optimization, based on iterative device simulation, in design of high-performance devices2004In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 48, no 10-11, p. 1721-1725Article in journal (Refereed)
    Abstract [en]

    An automatic optimization tool for semiconductor devices based on iterative device simulations is developed. The tool is used for optimization of different kinds of semiconductor devices using various performance measures. High performance optimization algorithms, both local and global, are used to achieve an efficient design in shortest possible time. In this paper the effects of different optimization algorithms, performance measures, and number of variables in the optimization are studied. Both the computational efficiency and the devices achieved with different performance measures are studied. We give a demonstration of the usefulness of this method in a comparison between different device topologies, which have been optimized for best performance.

  • 42.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    The power of using automatic device optimization, based on iterative device simulations, in design of high-performance devices2003In: 2003 International Semiconductor Device Research Symposium, ISDRS 2003 - Proceedings, 2003, p. 152-153, article id 1272038Conference paper (Refereed)
    Abstract [en]

    Device design is a time consuming work, where the influence of many design parameters has to be investigated carefully. In advanced devices optimal performance is often achieved taking multiple trade-off into consideration, and manual device optimization is often insufficient. In this paper we present the feasibility of using device optimization for design on electronic devices. An optimization tool is developed, which runs device simulations and automatically changes the design parameters, searching for optimal performance according to a specified performance measure. This has been shown to be a very time and cost efficient way for device design, as the search for optimal performance is fuily automatic working in a systematic way 24 hours 7 days a week. From an industrial point of view this is very important as it can reduce the evaluation and optimization cost for new devices considerably. It is impossible to give a fair comparison between different devices unless these are designed to give optimal performance. We give a demonstration of the usefulness of this method in a comparison between different device topologies which individually have been optimized for best performance.

  • 43.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Käckell, P.
    Persson, C.
    The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs2001In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 45, no 5, p. 645-653Article in journal (Refereed)
    Abstract [en]

    A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations

  • 44.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation of anisotropic Breakdown in 4H-SiC Diodes2000In: IEEE Workshop on Computers in Power Electronics: COMPEL 2000, IEEE , 2000, p. 118-120Conference paper (Refereed)
    Abstract [en]

    The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. Our numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams if one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in design and characterization of 4H-SiC power devices.

  • 45.
    Das, Moumita
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Barg, Sobhi
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Haller, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bakar, Muhammad Abu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Rezaee, Ali
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    State of Art of Designing Power Electronics Converter for Low Voltage Motor Drives for Electric Vehicle2020In: 2020 IEEE International Conference on Power Electronics, Smart Grid and Renewable Energy (PESGRE2020), IEEE, 2020Conference paper (Refereed)
    Abstract [en]

    In recent times, the boom in electric vehicle (EV) is increasing due to the development of highly efficient power converters and to reduce the fossil fuel dependency. Hence, the progress in both electric and hybrid vehicles are rising. However, the safety become an issue in EVs for operating at high voltage level. Therefore, the application of the low voltage motor in EVs is proposed. This helps to increase the safety in the vehicle and reliability of the system. The proposed voltage for such low voltage motor drives is 48V. This voltage level is also beneficial for integration of battery and ultra-capacitors (UCs). This paper proposes the state of art of designing power converters for low voltage motor drives. Additionally, a novel bi-directional DC-DC converter with reconfigurable transformer is proposed for driving low voltage motors. The proposed bi-directional converter can operate with wide input (12V-4SV) and wide output voltage (1.5V-24V) ranges for power level of 1. 2kW. Analysis of this system and operating principle of the novel converter are also included for different output voltage and current levels. The presence of UCs in the system helps to improve the control response required during accelerating and braking. The simulation results of the system are included in the paper for different voltage and speed levels. The preliminary experiment result is included in the paper.

  • 46.
    Das, Moumita
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    GaN Based Converters for Battery Charging Application of Electric Vehicle2019In: IECON2019: 45th Annual Conference of the IEEE Industrial Electronics Society, IEEE, 2019Conference paper (Refereed)
    Abstract [en]

    The high frequency capability and low on-state losses of Gallium Nitride (GaN) transistors offer the potential to increase converter efficiency and/or reduce heatsink and passive component size. This paper investigates the use of GaN technology to enhance the performance of power factor correction (PFC) and LLC converters for battery charging applications. First the efficiency performance of non-isolated PFC converters using GaN transistors is compared by simulation, the asymmetric bridgeless PFC converter is shown to achieve the best efficiency, with a predicted figure of 99% in a 1MHz, 200W design. The predictions are validated by an experimental prototype using a GS66502B, GaN Systems E-mode GaN transistor. Then the efficiency comparison of the PFC and LLC converter using GaN devices for battery charging applications is included in the paper. The experimental results of the PFC converter with GaN devices are also included. Additionally, this paper includes the analysis and design of a common mode input filter for the GaN-based high frequency converters for battery charging application. The size of both the converters using GaN devices is reduced by 40% than the converters based on Si devices. The switching loss comparison of GaN and Si devices are also included in the paper.

  • 47.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulations of Submicron MOSFETs in 2H, 4H and 6H-SiC2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, p. 14-17Article in journal (Refereed)
    Abstract [en]

    In this paper, we present numerical studies of the high frequency performance of a submicron MOSFET in 2H-, 4H- and 6H-SiC. The studies are based on simulations where commercial two-dimensional drift-diffusion and hydrodynamic carrier transport models have been used. The results have been compared with those obtained from full band Monte Carlo simulations. The Monte Carlo carrier transport model is based on data from a full potential band structure calculation using the Local Density Approximation to the Density Functional Theory. In 6H-SiC the bulk transport properties in the direction perpendicular to the c-axis, are slightly lower than in 2H- and 4H-SiC. However, in the direction parallel to the c-axis the transport properties are considerably less favourable than in the other two polytypes. The effects of these differences, on surface mobility device performance and carrier energy, have been studied.

  • 48.
    Döhlen, Viktor
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Direct integration of supercapacitors in CHB converter with low voltage components for Fast Frequency Reserve and enhanced response from Kaplan turbines2022In: Proceedings, International Conference on Electrical, Control and Instrumentation Engineering, ICECIE, IEEE conference proceedings, 2022Conference paper (Refereed)
    Abstract [en]

    The paper investigates the feasibility, cost and performance of a Cascaded H-Bridge converter using low-voltage components and direct integration of supercapacitors to deliver short duration frequency regulatory services. Through coordination with a Kaplan turbine hydro power plant, the system may qualify for a further palette of regulatory power. Parallel MOSFET switches are considered as a low voltage alternative to high voltage IGBTs. Suitable configurations of supercapacitors in each submodule, number of submodules and configurations of switches are proposed to meet requirements for Fast Frequency Reserve with a nominal power of 5 MW within the limits of component ratings. A Matlab model is used to validate the function and performance of the converter. The system proposed meets criteria for supercapacitor balancing, temperature over semiconductor junctions while supplying Fast Frequency Reserve. The energy needed from the energy storage to meet activation time requirements for FCR-D when coordinated with the Kaplan turbine is quantified for two Kaplan turbine responses. A comparison of conduction and switching loss in the converter show that conduction loss from the internal resistance of the supercapacitors are the largest driver of loss in the system. 

  • 49.
    Haller, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Reconfigurable Battery for Charging 48 V EVs in High-Voltage Infrastructure2022In: Electronics, E-ISSN 2079-9292, Vol. 11, no 3, article id 353Article in journal (Refereed)
    Abstract [en]

    48 V is emerging as a safe-to-touch alternative voltage level for electric vehicles (EVs). Using a low- instead of a high-voltage drive train reduces isolation efforts, eliminates the risk of electric shock, and thus increases the system safety. In contrast, fast charging of a 48 V battery would require very high currents and is incompatible with the widely established high-voltage electric vehicle charging infrastructure. Instead of employing additional on board power converters for fast charging, the concept of a reconfigurable battery is presented. A small-scale prototype system is designed consisting of eight 48 V lithium iron phosphate battery modules. In series configuration, they can be charged at 460 V with up to 25 A. In 48 V parallel configuration, the peak discharge current is up to 800 A. The MOSFET-based reconfiguration system also operates as a module charge balancer during high-voltage charging. The cost overhead for the reconfiguration system is estimated to 3% for a scaled-up full size EV. Due to the additional reconfiguration switch resistances, the simulation of a 48 V 75 kW electric vehicle in the World harmonized Light-duty vehicles Test Procedure showed a performance reduction of 0.24%.

  • 50.
    Haller, Stefan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bakar, Muhammad Abu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Kennel, Ralph
    Technical University of Munich.
    Cpld and dspic hybrid-controller for converter prototyping driving a reconfigurable transformer phase-shifted full-bridge2020In: PCIM Europe Conference Proceedings, VDE Verlag GmbH, 2020, p. 1552-1558Conference paper (Refereed)
    Abstract [en]

    The development of recent high-efficient power converters leads to novel multi-switch topologies. To allow precise control of multiple switches, high-resolution PWM signals are required. Today, DSCs already provide PWM signal generation with 250 ps resolution. Nevertheless, limitations prevent them from meeting new converter topologies. Still, they are a promising choice for prototyping compared to FPGAs in terms of cost, footprint and complexity. To overcome these limitations, a hybrid-controller with a dual core dsPIC DSC and a CPLD was designed. The presented controller is optimized for a wide-range converter with reconfigurable transformer configuration. Since it is very versatile, easy to configure and fabricate, it can also be used for prototyping of many other converter topologies. In addition to the regular DSC features, it adds dynamic signal routing, logic and synchronization capabilities. The proposed hybrid-controller is described, experimentally verified and compared to a purely DSC based controller when driving a phase-shifted full-bridge with reconfigurable transformer. To estimate the component stress, the generated PWM waveforms were captured and fed into a spice simulation of the converter. 

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