Advanced Control Methods for Torque Ripple Reduction and Performance Improvement in Switched Reluctance Motor Drives

Abstract

In this thesis, advanced control methods are presented for torque ripple reduction and performance improvement in switched reluctance motor (SRM) drives. Firstly, a comparative evaluation of power electronic converters including asymmetric, N+1, C dump, split AC, and split DC converters is presented for three-phase SRMs in terms of cost, efficiency and control performance. Secondly, two methods are proposed using torque sharing function (TSF) concepts for torque ripple reduction of SRM over a wide speed range. An offline TSF is proposed to minimize the copper loss and the absolute rate of change of flux linkage (ARCFL) with a Tikhonov factor. Then an online TSF is proposed by adding a proportional and integral compensator with torque error to torque reference of the phase with lower ARCFL. Therefore, the total torque of online TSF is determined by the phase with lower ARCFL rather than the phase with higher ARCFL as in conventional TSFs. The maximum torque-ripple-free speed (TRFS) of the offline TSF and online TSF is validated to be 7 times and 10 times as high as the best case in these conventional TSFs, respectively. Thirdly, two methods are proposed to eliminate mutual flux effect on rotor position estimation of SRM drives without a prior knowledge of mutual flux, one is the variable-hysteresis-band current control for the incoming-phase self-inductance estimation and the other is variable-sampling outgoing-phase self-inductance estimation. Compared with the conventional method which neglects the mutual flux effect, the proposed position estimation method demonstrates an improvement in position estimation accuracy by 2º. Fourthly, a fixed-switching-frequency integral sliding mode current controller for SRM drives is presented, which demonstrates high dynamics, strong robustness and none steady-state error. All the proposed control methods are verified by both simulations and experiments with a 2.3 kW, 6000 rpm, three-phase 12/8 SRM operating in both linear magnetic and saturated magnetic regions.