Three-Phase 24/16 Switched Reluctance Machine for Hybrid Electric Powertrains: Design and Optimization

Abstract

This thesis studies the method of optimizations of conduction angles for switched reluctance motors (SRMs) and presents an optimization and design of a three-phase 24/16 SRM used in the powertrain of hybrid electric vehicles (HEVs). The electrified powertrains, especially the power-split powertrain used in the Toyota Prius, are studied in this thesis. Different types of electric machines used as traction motors in HEV are compared. Results show that SRMs can be an alternative to replace interior permanent magnet synchronous machines (IPMSMs) commonly used as the traction motors in HEVs and EVs. The mechanism, operation, and electromagnetic energy, and control of SRMs are presented. Studies show that conduction angles affect SRMs’ performances, such as output torque, torque ripple, and efficiency. In this thesis, a fast optimization-based procedure for automatically characterizing SRM performances is proposed. Within the procedure, four optimization problems, including two single-objective and two multi-objective, are formulated in order to optimize the conduction angles for SRMs. The objectives used in these optimization problems are aimed towards maximizing average output torque, maximizing the ratio of average torque to RMS value of phase current, and maximizing RMS value of net torque ripple. One multi-objective optimization, which employs maximizing average output torque, and maximizing RMS value of net torque ripple as the objectives, is chosen in the optimization of conduction angles for priority operating points and over the entire operating range, because this method balances output torque and torque ripple. It also has highly competitive performances in motor efficiency. The procedure is then used to obtain the motor’s performances, such as torque-speed profile, loss map, and efficiency. Experimental results from a 12/8 SRM at three operating points are carried out to verify the results from the procedure. This procedure is used in the design of a 60 kW three-phase 24/16 SRM as well. The motor is targeted to replace an IPMSM as the traction motor in the HEV powertrain of the 2010 Toyota Prius. In this thesis, the optimized results for motor designs with different stator pole height, stator taper angle, rotor pole arc angle, and stator pole shoe shape, are presented and compared in terms of output torque, RMS value of phase current, normalized torque ripple, and optimized conduction angle. The finalized motor design is characterized using the optimized turn-on and turn-off angle lookup table obtained from the same optimization. The motor performances, such as torque-speed profile, torque ripple, copper losses, core losses, etc., over the entire operating range are studied. At the end of this thesis, the sub-assemblies of the frame, the rotor-shaft, and stator-winding, are designed and discussed. Thermal analyses on the finalized motor are also studied. The SRM’s torque-speed profile matches that of the IPMSM used in the 2010 Toyota Prius. The SRM has competitive motor efficiency over the entire operating range when compared with the Prius motor.