Design of variable flux permanent magnet machine for reduced inverter rating

The paper presents a design procedure for tangentially magnetized variable flux machines that aims to reduce the machine inverter rating. The proposed design can achieve high torque density at low speeds, and high efficiency at an extended speed range, as armature d-axis current pulses are applied at high speeds to reduce the magnet flux, thus avoiding the flux weakening current in conventional permanent magnet synchronous (PMSMs) machines. In order to regain the full torque capability when the motor slows down, a magnetizing current pulse has to be applied. The amplitude of the magnetizing current is usually larger than the machine rated current. Therefore, the machine might need an oversized inverter in order to be able to re-magnetize the magnets. The impact of different machine design parameters on the magnetization current requirement is investigated in order to reduce the inverter cost.