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Study of Induction Machines with Rotating Power Electronic Converter
KTH, School of Electrical Engineering (EES), Electric power and energy systems. (Electrical Machines and Drives Laboratory)ORCID iD: 0000-0003-2398-8528
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates a novel induction machine topology that uses a rotating power electronic converter. Steady-state and dynamic performance of the topology is studied to understand its operational principle. Furthermore the potential of improving its efficiency and power factor is investigated. The topology is referred to as wound rotor induction machine with rotating power electronic converter (WRIM-RPEC).

    The WRIM-RPEC topology offers the possibility to magnetize the induction machine from the rotor side by introducing a reactive voltage in the rotor. Thus, the power factor of the machine can be improved. Constant speed variable load operation can be achieved by setting the frequency of the introduced voltage. Two options of rotor winding and converter configuration in the WRIM-RPEC system are investigated. The wound rotor windings can either be open-ended and fed by a three-phase back-to-back converter or Y-connected and fed by a single three-phase converter. The dc-link in both converter configurations contains only a floating capacitor. These two configurations give different dc-link voltages at the same torque and speed.

    Two analytical steady-state models of the topology are developed in this thesis. The first model can be used to analyze the operating condition of the motor at specific speed and torque. Particularly, the operating range of speed and torque of the topology is investigated. The second model is used to analyze variable power factor operation, including unity power factor operation. Analytical calculations and measurements are carried out on a 4-pole, 1.8kW induction machine and the results are compared.

     A dynamic mathematic model is then developed for the WRIM-RPEC system for the back-to-back converter configuration. The mathematic model is then applied in Matlab/Simulink to study the dynamic performance of the system including starting, loading and phase-shifting. The simulation results are compared with measurements on the 4-pole, 1.8kW induction machine. Moreover, the simulation model using the existing Simulink blocks are studied to compare with the results obtained from the mathematic model. Furthermore, the dynamic performance of the WRIM-RPEC system with the single converter configuration is investigated. In addition, harmonic spectra analysis is conducted for the stator and rotor currents.

    In the last part of the thesis, efficiency improvement is investigated on the 4-pole induction machine when it is assumed to drive a pump load. It is shown that the efficiency can be further improved by decreasing the rotor resistance. Due to space constraints it is however difficult to decrease the rotor resistance in a 4-pole induction machine. An investigation is thus carried out on a standard 12-pole, 17.5kW squirrel-cage induction machine with inherent low power factor. The cage rotor is redesigned to a wound rotor to enable the connection of converter to the rotor windings. An analytical model is developed to design the wound rotor induction machine. The machine performance from calculations is then compared with FEM simulations with good agreement. The analytical model is further used to design several WRIMs with different dimensions and rotor slot numbers. Power factor and efficiency improvement is then explored for these WRIMs. A promising efficiency increase of 6.8% is shown to be achievable.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2016. , 59 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:168
Keyword [en]
Brushless induction machine, efficiency improvement, optimum efficiency, rotating power electronic converter, unity power factor, variable power factor, wound rotor induction machine
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-196054ISBN: 978-91-7729-166-4OAI: oai:DiVA.org:kth-196054DiVA: diva2:1045804
Public defence
2016-12-09, Kollegiesalen, Brinellvägen 8, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20161111

Available from: 2016-11-11 Created: 2016-11-10 Last updated: 2016-11-11Bibliographically approved
List of papers
1. Analysis of an induction machine using a rotor integrated converter with a floating capacitor
Open this publication in new window or tab >>Analysis of an induction machine using a rotor integrated converter with a floating capacitor
2015 (English)In: Electrical Machines and Systems (ICEMS), 2015 18th International Conference on, IEEE , 2015, 1851-1857 p.Conference paper (Refereed)
Abstract [en]

A novel topology of induction machine with a rotor integrated converter with a floating capacitor is investigated in this paper. The stator windings of the induction machine are directly connected to the grid. While the rotor windings are connected to a converter with a floating capacitor. The steady state mathematical model is presented and used to predict the operating range of the induction machine. The result shows that the induction machine can operate in a wide torque and speed range instead of working on the original torque-speed curve. In addition, the relationship between capacitance and capacitor voltage is studied for the constant speed and variable load operation. It is shown that it is possible to choose a low volume and high capacitance capacitor since the average DC-link voltage is quite low.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-185009 (URN)10.1109/ICEMS.2015.7385342 (DOI)000380616300355 ()2-s2.0-84966601409 (ScopusID)978-1-4799-8805-1 (ISBN)
Conference
Electrical Machines and Systems (ICEMS), 2015 18th International Conference, 25-28 Oct. 2015, Pattaya, Thailand
Note

QC 20160408

Available from: 2016-04-08 Created: 2016-04-08 Last updated: 2016-11-29Bibliographically approved
2. Investigation on the dynamic performance of an induction machine using a novel concept of a rotating converter with a floating capacitor
Open this publication in new window or tab >>Investigation on the dynamic performance of an induction machine using a novel concept of a rotating converter with a floating capacitor
2015 (English)In: Industrial Electronics Society, IECON 2015 - 41st Annual Conference of the IEEE, IEEE , 2015, 2944-2949 p.Conference paper (Refereed)
Abstract [en]

This paper explores a topology of induction machine drive with a novel concept of a wound rotor fed by a converter with a floating DC-link capacitor. The Y-connected stator windings are connected to the grid, while Y-connected rotor windings are connected to a three phase converter with a floating DC-link capacitor. By integrating the converter into the wound rotor, the slip-rings and the brushes becomes unneeded. Constant speed operation can be achieved at various loads by controlling the fundamental frequency of the converter. The stator power factor can be effectively improved over a wide range of load at constant speed. Particularly, unity power factor can be obtained within ±25% of the rated load. Moreover, harmonic spectra of the stator and rotor currents are presented.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-185011 (URN)10.1109/IECON.2015.7392550 (DOI)000382950702169 ()2-s2.0-84973138040 (ScopusID)978-1-4799-1762-4 (ISBN)
Conference
Industrial Electronics Society, IECON 2015 - 41st Annual Conference of the IEEE, November 9-12, 2015, Yokohama, Japan
Note

QC 20160408

Available from: 2016-04-08 Created: 2016-04-08 Last updated: 2016-11-29Bibliographically approved
3. Power Factor Improvement and Dynamic Performance of an Induction Machine With a Novel Concept of a Converter-Fed Rotor
Open this publication in new window or tab >>Power Factor Improvement and Dynamic Performance of an Induction Machine With a Novel Concept of a Converter-Fed Rotor
2016 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 2, 769--775 p.Article in journal, Editorial material (Refereed) Published
Abstract [en]

This paper investigates an induction machine with a novel concept of the rotor fed by a converter. The stator is Y-connected and directly connected to the grid, while the rotor windings are open-ended and fed by a back-to-back converter with a floating capacitor. Power factor and efficiency improvements of the induction motor are studied with different settings of phase-shift angle between the two converters. Moreover, the dynamic performance of the induction machine is explored in MATLAB/Simulink and verified experimentally on a 1.8-kW induction machine in the laboratory. The result shows good agreement between simulation and experiment. At a constant speed, variable load operation of the induction machine is obtained by setting the frequency of the rotor voltage.

Place, publisher, year, edition, pages
IEEE, 2016
Keyword
unity power factor, Back-to-back converter, dynamic performance, induction machine drives, open-end winding
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-196049 (URN)10.1109/TEC.2015.2505082 (DOI)2-s2.0-84949980797 (ScopusID)
Note

QC 20161111

Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2016-11-18Bibliographically approved
4. Optimum operating point of an induction machine using a rotor integrated converter with a floating capacitor
Open this publication in new window or tab >>Optimum operating point of an induction machine using a rotor integrated converter with a floating capacitor
2016 (English)In: 2016 IEEE 8th International Power Electronics and Motion Control Conference, IPEMC-ECCE Asia 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, 98-103 p., 7512268Conference paper (Refereed)
Abstract [en]

This paper investigates an induction machine using a novel concept of rotating converter. The stator is directly connected to the grid while the rotor is fed by a rotating converter with a floating capacitor over the dc-link. An analytical method to find the operating point at specific power factor and torque is proposed in this paper, which is verified by the good agreement between calculation and experimental results. It is found that when the considered machine topology is operated at rated torque and unity power factor, the efficiency can be improved by 0.74% compared with the standard induction machine with short-circuited rotor. Moreover, the effect of reducing the rotor resistance on efficiency improvement of the induction machine at unity power factor is explored. A further efficiency improvement of 2.36% can be achieved by decreasing the rotor resistance by 30%. Furthermore, optimum efficiency of the induction machine is studied when it drives a pump and operates near the rated operation point. The result shows that an optimum efficiency, which is 3.13% higher than the standard machine, can be obtained by operating the machine at a new operation point other than the rated condition. Decreasing the rotor resistance by 30% will further increase the optimum efficiency by 1.47%. The corresponding output power will also increase with higher operation speed and load torque.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2016
Keyword
floating capacitor, Induction machine, unity power factor, rotor integrated converter, steady state model, operating range
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-196050 (URN)10.1109/IPEMC.2016.7512268 (DOI)2-s2.0-84983371596 (ScopusID)978-150901210-7 (ISBN)
Conference
8th IEEE International Power Electronics and Motion Control Conference, IPEMC-ECCE Asia 2016; Hefei; China; 22 May 2016 through 26 May 2016
Note

QC 20161111

Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2016-11-24Bibliographically approved
5. Efficiency Improvement of a 12-Pole 17.5 kWInduction Motor Using Converter-fed Wound Rotor
Open this publication in new window or tab >>Efficiency Improvement of a 12-Pole 17.5 kWInduction Motor Using Converter-fed Wound Rotor
(English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059Article in journal, Editorial material (Other academic) Submitted
Abstract [en]

This paper investigates an induction machine usinga novel concept of a converter-fed rotor. The stator is directlyconnected to the grid while the rotor is fed by a converter with afloating capacitor over the dc-link. In earlier work this topologyhas shown to be capable of improving the power factor andefficiency of a 4-pole induction machine. This paper exploresthe possibility to improve the power factor and efficiency of asquirrel-cage 12-pole 17.5 kW induction machine by redesigningthe cage rotor to a wound rotor to enable connection of therotor windings to the converter. A standard 12-pole squirrelcageinduction machine (SCIM) with an inherent low powerfactor is studied. An analytical model to design the wound rotorinduction machine (WRIM) is then developed. The performanceof the designed WRIM using the analytical model is shown toagree with the results from the finite element (FEM) simulations,thus verifying the correctness of the model. The analyticalmodel is then further used to design different WRIMs withdifferent dimensions and rotor slot numbers. Performances ofthese designed WRIMs show good potential for power factorand efficiency improvement. Particularly, an optimum efficiencyimprovement of 6.8%, compared with the original SCIM, hasbeen achieved.

Keyword
Converter-fed rotor, efficiency improvement, induction machine drives, power factor improvement
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-196051 (URN)
Note

QCR 20161111

Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2016-11-11Bibliographically approved
6. Construction of a rotating power electronic converter for induction machine operation
Open this publication in new window or tab >>Construction of a rotating power electronic converter for induction machine operation
2015 (English)Conference paper (Refereed)
Abstract [en]

This paper describes the construction of the rotating power electronic converter. By mounting the power electronics on the rotor of an induction machine, the rotor winding can be made easily accessible without the use of slip-rings and brushes. This offers certain advantages regarding motor control. However, it is evident that the rotating mass, communication with the converter and maintaining the mechanical stability and reliability of the system are huge challenges that must be overcome. This paper describes some solution that are partly investigated and some solutions that still needs to be investigated in more detail.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-185014 (URN)10.1109/ICEMS.2015.7385087 (DOI)000380616300100 ()2-s2.0-84966681585 (ScopusID)
Conference
Electrical Machines and Systems (ICEMS), 2015 18th International Conference on
Note

QC 20160425

Available from: 2016-04-08 Created: 2016-04-08 Last updated: 2016-11-29Bibliographically approved

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