Expansion of operating limits for permanent magnet motor by current vector control considering inverter capacity

The current vector control method of PM (permanent magnet) motors is examined to expand the operating limits associated with 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 computer simulation. The operating limits are greatly expanded by controlling the d- and q-axis components of the armature current according to the rotor speed. The operating limits are examined considering the demagnetization of the permanent magnet. If the permanent magnet has a straight demagnetization curve, like a rare-earth permanent magnet, the PM motor can be safely operated until the demagnetizing coefficient becomes 1.0. If wide speed range or constant power operation is desirable, a permanent magnetic with a high coercivity and a linear demagnetization curve must be used for the PM motor