Study of Reactance Evaluation Methods in Saturated Magnetic Field for Permanent Magnet Synchronous Motor

In order to speculate motor performance with high precision, it is important to understand correctly motor parameters, such as reactance, in an actual operation state. The design of Interior Permanent Magnet Synchronous Motor (IPMSM), the rotor of which has complicated magnetic circuit, necessitate accurate estimation of reactance that makes it possible to calculate the proportion of magnet torque and reluctance torque. Permanentmagnet ac line-start motor, which is directly connected to an electric power system and is desired to operate under high power factor, also requires the exact reactance in a design stage because the power factor is calculated with vector diagram including reactance. This paper presents a study of three reactance evaluation methods: Dalton-Cameron method, the method applying the direct magnetic field and the method considering cross-magnetizing reactance under actual-operation state. The work deals with a permanentmagnet ac line-start motor. Though Dalton-Cameron method and the method applying the direct magnetic field are superior in simplicity of measurement, the reactance under saturated magnetic field could not be calculated correctly, because magnetic saturation in actual operation state is not taken into consideration. Especially, Dalton-Cameron method treats the alternative magnetic field with locked rotor, which will result in the reactance widely different from that of an actual operation state. Figure 1 shows errors between the reactance with DaltonCameron method (shown as DCM) and the reactance with direct magnetic field applied (shown as IdIq). Figure 2 shows the reactance under actual-operation state that is corresponded with the load torque. Comparison of Fig. 1 and Fig. 2 indicates that the reactance achieved by each method is different. In order to verify the