Current control of induction machines in the field-weakened region

This paper presents a novel current regulation algorithm for induction machines that enables smooth operation and maximum torque-per-ampere capability over the entire field-weakened region. The algorithm enables robust current regulation with maximum 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. In the field-weakened region, the q-axis current is monitored not to exceed the maximum q-axis current. The maximum q-axis current is calculated based on the maximum slip frequency, which is a function of rotor frequency. q-axis current >= maximum q-axis current (in motoring mode) indicates that the machine entered field-weakened region II, and the q-axis current is limited to its maximum value. 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 quadrant, of operation.