Research On Power Converter Technique For Multi-phase Switched Reluctance Motor

Multi-phase switched reluctance motor(SRM) not only has the advantages like simple structure, flexiable control, low manufacture cost, strong fault tolerance, and etc., but also can weaken the conventional three-phase SRM’s shortcomings such as low power density and high torque ripple, and increase the system’s reliability and fault tolerance. However, the required power devices’ number and cost of multi-phase SRM power converter would be raised with phase number increased. Therefore, it is quite significant to develop and research on the new-type power converter for SRM, of which the performance is good and the cost is low.To slove the problem that the current power converters for SRM cannot satisify simultaneously all the requirement i.e. less compenent, flexiable control, strong fault torlerance and good applicability, the novel multi-phase N+2 power converter is proposed in the paper and its topology structure, work pricinple, control scheme and performance are investigated deeply. The performances at standstill, rated and fault condition are all compared with conventional power converter. Also, optimized control based on the N+2 power converter is achieved.To analyse and verify the novel power converter’s performance in the application of multi-phase SRM, a six-phase SRM is used as applied objective and nonliner MATLAB/SINKLINK model of SRM based on finite analysis results is established. The different conditions of the novel power converter are simulated and analysed under current chopped control(CCC), angle position control(APC), voltage chopped control and open circuit fault. By the contrast with asymmetric half bridge(AHB) and split phase(SP) power converters, the novel N+2 power converter is proved to be equivalent to the AHB power converer with half input DC voltage and superior to the SP power converter in all condition.With the novel N+2 power converter employed, there exist high torque ripple and low efficiency at the rated condition of the six-phase SRM. According to the theoretical analysis based on the linear inductance model, it is discovered that beacause the phase current has high value during the beginning of the magnetic stage and drop dramatically at the later, the fixed duty PWM(FDPWM) control of which the equivalent implemented voltage is constant DC would lead to the efficiency fall and torque ripple rise. Hence, the DC-biased SPWM(DSPWM) control of which the equivalent implemented voltage is sinusoidal wave with DC voltage biased is proposed. The rational parameters selection i.e. ampltitude, phase angle and frequence and the effects to motor’s perfomances are analysed. By comparsion with FDPWM control, DSPWM control is demonstrated to be better in terms of efficiency, torque ripple, torque current density and etc..Finally, the novel N+2 power converter is used and the six-phase SRM general control is developed based on dSPACE1104. With the existing six-phase SRM prototype in laboratory as control object, the feasibility and effectiveness of the multi-phase N+2 power converter and thereof DSPWM control have been verified.