Interior Permanent-Magnet Synchronous Motors for Adjustable-Speed Drives

TLDR

IPM synchronous motors are robust, high‑power‑density machines that offer adjustable‑speed operation with high efficiency over wide speed ranges while minimizing magnet cost due to low magnet weight. The study examines how the buried‑magnet configuration affects the motor’s electromagnetic characteristics and outlines its electrical excitation requirements. The authors describe how rotor saliency raises quadrature‑axis inductance and adds a reluctance torque term, and they detail a feedforward current‑vector control algorithm that regulates sinusoidal phase currents for smooth torque while addressing high‑speed regulator saturation. Simulation and prototype drive measurements confirm the predicted electromagnetic behavior and control performance of the IPM motor.

Abstract

Interior permanent-magnet (IPM) synchronous motors possess special features for adjustable-speed operation which distinguish them from other classes of ac machines. They are robust high powerdensity machines capable of operating at high motor and inverter efficiencies over wide speed ranges, including considerable ranges of constant-power operation. The magnet cost is minimized by the low magnet weight requirements of the IPM design. The impact of the buried-magnet configuration on the motor's electromagnetic characteristics is discussed. The rotor magnetic circuit saliency preferentially increases the quadrature-axis inductance and introduces a reluctance torque term into the IPM motor's torque equation. The electrical excitation requirements for the IPM synchronous motor are also discussed. The control of the sinusoidal phase currents in magnitude and phase angle with respect to the rotor orientation provides a means for achieving smooth responsive torque control. A basic feedforward algorithm for executing this type of current vector torque control is discussed, including the implications of current regulator saturation at high speeds. The key results are illustrated using a combination of simulation and prototype IPM drive measurements.