Effect of the Back-EMF Limiting of Broad Adjustable Speed Synchronous Reluctance Permanent Magnet Motors

A back-electromotive force (EMF) limiting design strategy is proposed to avoid damage to the inverters caused by the excessively high level back-EMF of the synchronous reluctance permanent magnet (SR-PM) motors with high field-weakening capability. Performance analysis and the parameter optimization of this strategy are compared with the conventional design strategy without back-EMF limitation. The results show that the cost trade-off between inverters and motors is the main consideration under the conventional design strategy. On the other hand, the bottleneck of the design with back-EMF limitation is how to produce enough torque at low speed with smaller current. Consequently, the reluctance characteristics of SR-PM motors must be fully utilized. However, there is also an upper bound of this utilization.