This paper investigates the fault-tolerance control of a multilevel cascaded NPC/H-bridge (CNHB) inverter. The fault-tolerance control method has been widely used for multilevel inverters, such as the neutral-point voltage-shifting control, which can operate for a certain period of time by compensating for the phase voltage of a faulty stack even if one stack is broken. Even though the three-phase equilibrium is maintained in the case of failure by using the conventional neutral-point voltage-shifting control, an imbalance in the output power occurs between each stack, which causes problems for maintenance and lifetime. Therefore, this paper proposes a fault-tolerance control that can maintain three-phase equilibrium in a case of stack failures and minimize power imbalances between the stacks. The problem of the conventional neutral-point voltage-shifting control is presented based on the output power. In addition, the power imbalance is improved by performing selective neutral-point voltage-shifting control according to the reference voltage range. To verify the principle and feasibility of the proposed neutral-point voltage-shifting control method, a simulation and an experiment are implemented with the CNHB inverter.
Improved Neutral-Point Voltage-Shifting Strategy for Power Balancing in Cascaded NPC/H-Bridge Inverter
