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  • 1.
    Abrahamsson, Curt Johan David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bladh, Johan
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic thrust bearing for a 10 MW hydropower generator with a Kaplan turbine2018Conference paper (Refereed)
  • 2.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    An experimental approach to energy storage based synthetic inertia and fast frequency regulation for grid balancing2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing interest in renewable energy has significantly increased in the last decades. The increasing amount of variable renewable energy resources in the grid, which are connected via power electronics, reduces the total mechanical system inertia. Frequency-regulating resources such as hydropower will become more important in balancing variable renewable energy resources, setting higher requirements on stability and performance to maintain a stable electrical grid. This thesis concerns the decreased mechanical inertia from non-directly electrically coupled generation units. The thesis starts with a description of the grid system inertia situation today and presents two methods for estimating the grid frequency derivative used to provide synthetic inertia and one method used to enhance the mechanical inertia response of a synchronous generator. The synthetic inertia and enhanced inertia methods are tested in a small-scale experimental setup and compared with results from tests in the Nordic grid. A full-scale hybrid energy storage system was designed and built using a split frequency method as a power controller. The results show that a power-frequency derivative controller-based synthetic inertia method achieved an improved grid frequency quality during regular operation in the nano-grid experimental setup. The results are evaluated both via simulations and experimental tests. The results from the hybrid energy storage solution showed the possibility of increasing frequency quality by using a slow run of the river hydroelectric power plants and a battery energy storage system for frequency containment reserve.

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  • 3.
    Fregelius, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Albuquerque, Vinicius
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Enhanced Inertia using amplified power response from synchronous machines compared with frequency derivative-based inertiaIn: Article in journal (Refereed)
    Abstract [en]

    Two approaches for delivery of inertia-like grid services are described and compared. Voltages and currents are measured and logged from two synchronous generators during large grid disturbances. The data is used in Matlab Simulinkfor comparison and evaluation of control strategies. A novel enhanced inertia control strategy is proposed and compared with two synthetic inertia controllers utilizing frequency derivative estimators, a frequency locked loop and a Savitzgy Golay finite impulse response filter. Both inertia delivery approaches naturally rely on that the properties of the surrounding grid are such that the frequency variations due to power imbalances are large compared to other variations. Furthermore, the synthetic inertia controllers face the usual software signal filtering problems if the signal-to-noise ratio is low. The other approach, to enhance a physical Inertialresponse from a real machine, is a way to avoid such filtering challenges. However, the physical properties of the machine, mainly rotor angle oscillations, might call for software filtering anyway, adding phase shift to the otherwise low latency shown to be achievable

  • 4.
    Fregelius, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Hardware Implementation of A Synthetic Inertia System for Grid Stability2019In: 2019 8th International Conference on Renewable Energy Research and Applications (ICRERA), 2019, p. 186-190Conference paper (Refereed)
    Abstract [en]

    The frequency in the electrical grid is, on the short time-scale, stabilized by the total rotational mass given predominantly by synchronously connected devices. These devices include the generators themselves and, on slightly longer timescales, the control system acting on turbine governors. As the inverter-connected technologies increase their share of total power, the total inertia in the grid is significantly reduced. One way to stabilize the frequency and reduce low frequency oscillations is to add synthetic inertia provided by a small energy, high power, storage devices combined with a fast control system. This paper describes a possible hardware topology for linear synthetic inertia. It uses an inverter coupled to a local energy storage unit comprised of supercapacitors. The paper presents the implementation and some selected experimental results. The system response is fast enough on a small test grid to act as inertia.

  • 5.
    Fregelius, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Performance Evaluation of a Supercapacitor Based Synthetic Inertia System Using Frequency Locked Loop and Real-Time Frequency Derivative Estimation2023In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 144, article id 108554Article in journal (Refereed)
    Abstract [en]

    The installation of intermittent renewable energy sources (RESs) are now fast increasing, reducing fossil fuel use. Due to the fact that RESs are typically grid-connected to the power-system via grid following fast-response voltage source converters, the amount of mechanical inertia synchronised in the power system is decreasing. As a result, the power system will be more sensitive to load and generation variations, causing larger frequency fluctuations which, in turn, could result in undesirable load-shedding, or large-scale blackouts. This paper presents a performance evaluation of a concept of emulating virtual inertia via power-electronics and a energy storage unit in terms of a supercapacitor connected to the DC-bus. Simulation and experimental results are presented to validate the proposed combination of frequency estimation and frequency derivative estimation. The paper shows the feasibility of using virtual inertia and how it could be implemented.

  • 6.
    Fregelius, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Full scale hybrid hydroelectric lithium-ion energy storage for supplying frequency containment reserveIn: ISSN 1687-5257Article in journal (Refereed)
    Abstract [en]

    A full scale hybrid energy storage system consistingof two 14.5 MVA bulb hydro turbines and a 1.1 MWh lithium-ion battery energy storage system was designed, built andcommissioned in the North of Sweden. A hybrid power controllerwas designed and tested were grid frequency disturbances weresimulated in the programmable logic controllers and voltagesand currents were logged from each generating unit. Responsetimes and rise times were measured for each generating unit. Itwas shown that the battery energy storage has the capability ofchanging output power fast to meet new grid services require-ments such as fast frequency response. The hybrid energy storagecontroller was shown to be able to divide the frequency of thegrid frequency disturbances into slow and fast changes for eachgenerating unit and letting the battery energy storage handle fastpower responses and the bulb hydro turbines the slow and longterm power responses to fulfil frequency control requireme

  • 7.
    Lundin, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Pérez, José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Nøland, Jonas Kristiansen
    NTNU, Norwegian University of Science and Technology.
    Start of a synchronous motor using rotor field polarity inversion and rotor back-emf sensing2020In: 2020 International Conference on Electrical Machines (ICEM), 2020, Vol. 1, p. 338-344Conference paper (Refereed)
    Abstract [en]

    Synchronous motors are hard to line start due to torque pulsations at zero rotor speed and low starting torque when started using induced current in a damper squirrel cage. By inverting the rotor pole polarity at appropriate times it is possible to, in principle, achieve uniform torque, albeit pulsating with twice the line frequency at zero initial rotor speed. This has been demonstrated in an earlier work. In this paper we demonstrate that high torque starting using the back-emf in the field winding as triggering signal for the rotor polarity inversion is possible. We further discuss the origin of the rotational energy and active and reactive power pulsations. Finally, we show that it is possible to operate a synchronous motors at continuous asynchronous speed by inverting the polarity of the rotor current and adjusting the field current accordingly, although down rated.

  • 8.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Almeida, Pedro
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control ApplicationIn: International Marine Energy Journal, ISSN 2631-5548Article in journal (Refereed)
    Abstract [en]

    The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.

  • 9.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cardosa Silva, Dalmo
    Department of Electrical Engineering, Universidade Federal de Juiz de Fora, Juiz de Fora, Brazil.
    Potapenko, Tatiana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hjalmarsson, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kelly, James
    MaREI―Centre for Marine and Renewable Energy Ireland, University College Cork, Cork, Ireland.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goncalves de Oliveira, Janaína
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Department of Electrical Engineering, Universidade Federal de Juiz de Fora, Juiz de Fora, Brazil.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids2019In: Energy and Power Engineering, ISSN 1949-243X, E-ISSN 1947-3818, Vol. 11, no 3, p. 99-131Article in journal (Refereed)
    Abstract [en]

    Renewable energy sources, such as photovoltaicwind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous ge-nerators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is imple-mented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed con-troller uses a current synchronous detection scheme to emulate a virtual iner-tia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power manage-ment control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.

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    fulltext
  • 10.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chatzigiannakou, Maria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grid Integration and a Power Quality Assessment of a Wave Energy Park2019In: IET Smart Grid, ISSN 2515-2947, p. 1-14Article in journal (Refereed)
    Abstract [en]

    This study presents a step toward the grid connection of a wave-energy park through an electric power conversion system (EPCS) developed and installed for the wave-energy harvesting in Lysekil, Sweden. The EPCS comprises a rectifier, a DC bus, and an inverter followed by a harmonic filter (HF). The higher- and lower-order harmonics injected by the inverter in a power quality context are investigated. The lower-order voltage harmonics partially distort the voltage-source inverter output grid current. A phase-locked loop-based (PLL) grid-phase tracking is used to attenuate the lower-order harmonics by reflecting the grid harmonics in the inverter output. An expression for the grid-current harmonics as a function of the grid-voltage harmonics has been derived and implemented. A mathematical model is derived to obtain a transfer function for the PLL, and finally, proportional–integral gains are tuned for stable system operation. An HF for mitigating the higher-order harmonics has been implemented. The total harmonic distortion is evaluated experimentally, and the results fulfil the grid-code requirements at various frequencies and harmonic orders.

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    fulltext
  • 11.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chatzigiannakou, Maria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Fed Juiz De Fora, Juiz De Fora, Brazil.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Chalmers Univ Technol, Dept Elect Engn, Gothenburg, Sweden.
    Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System2018In: 2018 5th International Conference on Electric Power and Energy Conversion Systems (EPECS), 2018Conference paper (Refereed)
    Abstract [en]

    This paper provides an overview of electric power conversion system installed at the Lysekil research site, located at the west coast of Sweden. The electric power conversion system consists of rectifiers, rectifying the power from the wave energy converters, a DC-link and a grid-tied inverter. The paper focuses on the performance of the inverter and the filter and presents experimental results obtained during the grid integration.

  • 12.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universidade Federal de Juiz de Fora, Brazil.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Chalmers University of Technology.
    Energy management for a grid-connected wave energy park through a hybrid energy storage system2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 231, p. 399-411Article in journal (Refereed)
    Abstract [en]

    The concern for climate change and energy consumption has increased the demand for renewable energy production considerably. Marine energy sources attract attention because of their high energy density. Wave energy is an attractive renewable energy source with large potential. Due to the nature of the ocean waves, a linear wave energy converter generates intermittent power. It is therefore crucial to regularize the power before connecting to the grid. Energy storage systems present effective ways to minimize the power fluctuations and deliver a steady power to the grid. In this paper, we present an energy management control system with a dynamic rate limiter. The method is applied to control a hybrid energy storage system, combining battery and supercapacitor, with a fully active topology controlled by the power converters. The results show that the method is able to control the charging and discharging states of the battery and the supercapacitor, and minimize the power fluctuation to the grid. The algorithm ensures low losses by shifting the required power and the stored power smoothly over the energy storage system.

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