A simple control circuit for a three-level hysteresis current controlled voltage source converter

Hysteresis current control (HCC) is common in applications such as active power filters and high-precision drives where a reference current has to be followed very closely. The main disadvantages of the classical two-level HCC are related to the switching frequency of the devices. The switching periods vary significantly and the average witching frequency is relatively high. Some papers have shown that the latter problem can be reduced with a three-level HCC. However, the implementations employed yielded unbalanced switching stress on the converter legs or required an offset compensation with an analog switch. This paper discusses the main issues behind operation with balanced switching, namely the alternation of the zero states, and proposes a simple control circuit that does away with the need for offset compensation. Simulation and experimental results show that the proposed control circuit results in a line current with low THD while the converter operates with balanced switching stress and low switching frequency.