Generalized Analysis of Operating Limits of PM Motor and Suitable Machine Parameters for Constant Power Operation

Abstract

Permanent magnet synchronous motor (PM motor) is widely used for several industrial applications. Some applications such as an electric vehicle and a compressor drive require a constant power operation. The available maximum power considering the voltage and current constraints can be obtained by the optimal current vector control such as the maximum torque control and the flux-weakening control. The operating limits, however, deeply depend on the machine parameters. This paper examine the relationships between the machine parameters and the output characteristics, and it is clarified that the speed versus power characteristics depend only on the difference between the magnet flux-linkage and the maximum d-axis armature reaction flux-linkage. The maximum torque, the constant power operating range are given as a function of this difference value. The optimal machine parameters and the design of PM motor for the constant power operation are discussed based on the generally analyzed results and the examinations considering both copper loss and core loss in the light load operation.