Direct Torque Control in a Flying Capacitor Inverter with Reduction of Common Mode Voltage

Bearing current in inverter-fed induction motors can result in premature bearing failure. This paper gives a detailed analysis of common mode voltage as the main source of bearing currents. Moreover, it presents an algorithm to reduce the common mode voltage in multilevel DTC drive. Based on the given analysis, the common mode voltage is reduced to about 33 percent of the initial value. The simulation results in MATLAB/SIMULINK confirm the capability of the algorithm in common mode voltage reduction without degrading the electromagnetic torque and the speed response. The results of real world experiments using TMS320F2812 DSP processor are also provided.