Optimum torque control of induction machines in the field-weakened region

This paper presents a novel current regulation algorithm for induction machines that enables maximum torque-per-ampere capability over the entire field-weakened region. The algorithm enables robust current regulation with maximum efficiency and torque capability despite significant variation in voltage source and machine parameters. The algorithm identifies when the current regulator begins to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined as a function of the torque command and the d-axis current feedback. When the voltage angle reaches the maximum allowable angle, the output of the q-axis and the d-axis current regulators are clamped, and the slip frequency that provides maximum torque is maintained. 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