Loss Analysis of a High-Speed IPMSM using Different Trajectory Control

This paper investigates the loss performances of a high-speed interior permanent magnet synchronous motor under three different trajectory controls: maximum torque per ampere (MTPA) with and without considering core loss and maximum efficiency (ME) trajectories. The paper considers the variation of the equivalent core loss resistance by representing it using a function of currents and speed instead of the constant value used in conventional methods. An equation of MTPA considering variable core-loss-resistance was derived based on the equivalent circuit. The trajectories, efficiencies, and loss maps of the three control methods were compared and analyzed. The methods were applied to a high-speed IPMSM to compare their experimental efficiency improvements. Both analytical and experimental results show that ME and MTPA with variable core loss resistance make minor efficiency improvements when the core loss relative to the total loss is small in a well optimized high-speed IPMSM. Detailed analyses were carried out to identify the reasons behind the insignificant efficiency gain with the ME compared to the MTPA. It will be shown that the existing ME trajectory, which assumes constant core loss resistance, does not give the real maximum efficiency operating points. In the paper, the real maximum efficiency trajectory of the motor was found using a statistical method which was used to assess the effectiveness of ME over the MTPA for a high-speed IPMSM.