Voltage balancing control of a three-phase hybrid-clamped five-level inverter based on optimal zero-sequence voltage injection

As the society pursuing for a more efficient way of using energy, the technology of multilevel converter, which aims at the field of large-power high-voltage, has been widely studied. In this paper, a newly released single phase hybrid-clamped five-level inverter has been extended to three phases. The characteristics of this topology and the switching states have been analyzed. To solve the voltage balance problem of the DC-bus capacitors and flying capacitors, a control strategy based on optimal zero-sequence voltage injection has been proposed. The strategy selects the optimal switching combinations according to their influences on the voltages of capacitors. With the injection of zero-sequence voltage, we can extend the voltage balance region of this topology compared to the existing control method. The proposed control strategy has been verified in simulations and experiments. Furthermore, the control strategy is a universal strategy which can be applied into other multilevel converters.