Generalized analysis of operating limits on PM motors and suitable machine parameters for constant-power operation

Abstract

Permanent magnet synchronous motors (PM motors) are widely used in industrial applications. Some applications such as electric vehicles and compressor drives require constant-power operation. The available maximum power under specified voltage and current constraints can be obtained by optimal current vector control, such as maximum torque control and flux-weakening control. The operating limits, however, strongly depend on the machine parameters. This paper examines the relationships between the machine parameters and the output characteristics. It is shown that the power-versus-speed characteristic depends only on the difference between the magnet flux linkage and the maximum flux linkage of the d-axis armature reaction. The maximum torque and the constant-power operating range are obtained as functions of this difference. The optimal machine parameters and the design of PM motors for constant power operation are discussed based on the overall analytical results and on analyses that takes into account both copper loss and core loss in light-load operation. © 1998 Scripta Technica. Electr Eng Jpn, 123(3): 55–63, 1998