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Title:Efficient operation of variable-pole induction machines and drives
Author(s):Libbos, Elie
Advisor(s):Banerjee, Arijit
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Induction machine
multiphase drives
power electronics
electric machines
electric drives
loss minimization
electric vehicles
Abstract:Transportation electrification is a necessary step for a sustainable and clean energy future. As land vehicles and trucks are responsible for 82% of transportation emissions, electric vehicles (EVs) must become more affordable to replace conventional cars and reduce emissions. High power density, high efficiency, inexpensive drivetrains operating over a wide torque/speed range are critical for EVs. Most modern EVs use permanent magnet (PM) motors which rely on rare-earth material to achieve high energy efficiency. However, rare-earth magnets are expensive, have low recycling rates, and have high risk of price volatility. An induction machine (IM) is a magnet-free motor which offers a cost-effective, rugged and reliable alternative to permanent magnet motors. IMs have been widely established in EVs and are still used in modern designs. The magnetic pole count of an IM can be electronically varied by controlling a high number of stator currents as the cage-rotor naturally follows the stator. Variable-pole operation extends the speed range of an IM, a feature which is attractive in EV applications. Conventionally, pole count has been linked only to the machine operating speed, with a high pole at low speed and low pole at high speed. In this thesis, we show that pole count is a degree of freedom that can be used to improve drivetrain efficiency. Pole count must be selected based on both the required torque and operating speeds if the goal is to minimize losses or stator current. Low pole counts are more efficient than high pole counts at producing low and intermediate torque levels. By exploiting this property, experimental average power loss reduction and torque-per-ampere improvements of 1/3 and 2X were achieved at partial loading condition, where an EV operates for a predominant period of the time. We also show that power electronics converters for variable-pole IMs are more efficient than 3-phase fixed-pole converters.
Issue Date:2020-05-11
Rights Information:Copyright 2020 Elie Libbos
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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