Optimum Current Control for a High Speed Axial Gap Permanent Magnet Synchronous Motor

A high-speed (20,000 r/min) axial-gap permanent magnet (PM) synchronous motor constructed and controlled using a novel algorithm is described. An optimization algorithm using the Newton-Raphson method is proposed to solve the maximum torque/amp problem for salient-type PM motors. The optimum voltage and torque angle for different speeds are further derived from optimum dq-axes currents so that decoupled control can be applied to a six-step inverter. The complete drive system can be implemented using open-loop optimum voltage and torque angle trajectories or closed-loop control with one variable controlled by a lookup table and the other variable controlled by a closed-loop controller. The open-loop and closed-loop control systems are simulated. Although torque pulsation cannot be avoided with a six-step inverter, acceleration is quite smooth due to high load inertia.