High performance analysis of permanent magnet synchronous motor of changing PM flux for EV/HEV applications

In order to solve the contradiction between high torque below base speed and the wide expanding-speed range above base speed, this paper focuses on this kind of permanent magnet synchronous motor with the different winding connections. This motor can change PM flux, so motor efficiency is even higher. Firstly, design principle of windings-changing is studied in detail. The winding connections are researched to realize maximization of PM flux at low speed and minimization of PM flux at high speed. High efficiency of WC-PMSM is also researched. Then, motor performances in no-load and on load are analyzed by FE. Small stator current produces the equivalent electromagnetic torque by alternately using MTPA and FWC. Critical speed of switching MTPA and FWC is determined. Unlike the traditional method of flux weakening by increasing the bigger negative d-axis current, the negative d-axis current is always small and stator current is almost used to produce torque in this paper. It is proven that efficiency of WC-PMSM is even higher in the entire speed range. A 15-kW prototype for test is manufactured. The experimental results show that PMSM with the different winding connections can obtain high performance.