A simple potential balancing strategy for neutral-point-clamped inverter fed direct torque control induction machines

This paper presents a simple and robust potential balancing strategy for Direct Torque Control (DTC) of induction machines. In the proposed method, a two-level hysteresis comparator is used to restrict the error voltage, i.e. difference of upper and lower capacitors voltage, within the hysteresis band. The comparator will produce suitable digitized output status to be indexed into a look-up table for selecting appropriate switching states to compensate the mismatch voltages. In doing so, the variation of two capacitors voltages can be controlled, consistently, as compared to that of using the common SVM approaches where the variation (or error of ripple) is not strictly maintained. Some experimental results are presented to highlight the improvements of DTC performances as well as the robustness of control balancing strategy for steady state and dynamic conditions.