EXPANSION OF OPERATING LIMITS FOR PERMANENT-MAGNET MOTOR BY CURRENT VECTOR CONTROL CONSIDERING INVERTER CAPACITY

Permanent magnet (PM) motors are attracting growing attention for a wide variety of industrial applications. In traction and spindle drives, 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, direct control of the magnet flux is not available. The air-gap flux, however, can be weakened by the direct axis armature current. In this operation, magnet demagnetization due to the direct axis armature reaction must be prevented, because the magnet torque decreases irreversibly if this demagnetization is very large. The current vector control method of PM motors is examined to expand the operating limits considering the inverter capacity. This control method is optimum in the sense of deriving maximum output torque within the voltage and current constraints. The effects of motor parameters are examined by the computer simulation. The operating limits are examined considering the demagnetization of the permanent magnet. © 1990 IEEE