Optimum torque control of permanent-magnet AC Machines in the field-weakened region

This paper presents a novel current regulation algorithm for permanent-magnet ac (PMAC) machines that provides maximum torque-per-ampere capability in the entire field-weakened region. The algorithm provides robust current regulation with maximum efficiency and torque capability for PMAC machines despite significant changes in the voltage source and machine parameters. The algorithm identifies when the current regulator starts to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined from the torque command and d-axis current feedback. When the voltage angle reaches the maximum angle, the current magnitude is decreased to provide maximum torque per ampere. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation.