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Optimum operating point of an induction machine using a rotor integrated converter with a floating capacitor
KTH, School of Electrical Engineering (EES), Electric power and energy systems. (Electrical Machines and Drives Laboratory)ORCID iD: 0000-0003-2398-8528
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. 98-103 p., 7512268
Keyword [en]
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: urn:nbn:se:kth:diva-196050DOI: 10.1109/IPEMC.2016.7512268ScopusID: 2-s2.0-84983371596ISBN: 978-150901210-7OAI: oai:DiVA.org:kth-196050DiVA: diva2:1045763
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
In thesis
1. Study of Induction Machines with Rotating Power Electronic Converter
Open this publication in new window or tab >>Study of Induction Machines with Rotating Power Electronic Converter
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
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:nbn:se:kth:diva-196054 (URN)978-91-7729-166-4 (ISBN)
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

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