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Efficiency Improvement of a 12-Pole 17.5 kWInduction Motor Using Converter-fed Wound Rotor
KTH, School of Electrical Engineering (EES), Electric power and energy systems. (Electrical Machines and Drives Laboratory)ORCID iD: 0000-0003-2398-8528
(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 [en]
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: urn:nbn:se:kth:diva-196051OAI: oai:DiVA.org:kth-196051DiVA: diva2:1045783
Note

QCR 20161111

Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2016-11-11Bibliographically 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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Citation style
  • apa
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