Variable Speed Drive System of Permanent Magnet Synchronous Motors with Flux-weakening Control

Abstract

Permanent magnet synchronous (PM) motors are widely used for industrial applications. In traction and spindle drives, the constant power operation and wide speed range are desirable. With DC motor drives, these are achieved by the appropriate reduction of the field current as the speed increases. In the PM motor, the direct control of magnet flux is not available. The air-gap flux, however, can be weakened by the direct axis armature reaction. This control technique is called “flux-weakening” instead of “field-weakening”. This paper describes a variable speed drive system of PM motor for the constant power and wide speed range operations. In the proposed control system, a novel flux-weakening technique is applied. The current vector is controlled so that the maximum torque per armature current can be obtained at low speeds and the terminal voltage is kept within its limited value at high speeds. The control performances are examined by the simulations and the experimental results.