Predictive load voltage and capacitor balancing control for a four-leg NPC inverter

This paper presents a predictive voltage control strategy to control the three-phase four-leg neutral-point-clamped (NPC) inverter with an output LC filter. The four-leg NPC converter is developed to deliver power to the unbalanced/nonlinear three-phase loads and it can produce three output voltages independently with one additional leg. The proposed method uses the discrete model of the inverter and load to predict the future load and capacitor voltage behavior for each valid switching state of the converter. The control method chooses a state which generates minimum error between the output voltages and their references and as well as between the capacitor voltages. The feasibility of the proposed predictive voltage control scheme is verified by computer simulations, showing good performance and the capacity to compensate disturbances while maintaining the balance of the dc-link capacitor voltages.