Virtual Flux DPC of a Three-Level NPC Inverter with DC Bus Neutral Point Voltage Balancing

This paper investigates the virtual-flux direct power control (VF-DPC) of a three-level neutral point clamped (NPC) inverter with and without DC bus neutral point voltage (NPV) balancing. This strategy aims to achieve the control of the active and reactive powers under a unity power factor operation and commonly balance the two DC-link capacitor voltages. In a first step, the VF-DPC of the three-level NPC inverter is discussed without considering the NPV balancing problem. The appropriate switching table is designed after studying the effect of different voltage vectors of the inverter in the P and Q powers. In a second step, the VF-DPC approach is developed using the redundant states method with the aim to balance the DC-link voltages at the desired level. The numerical results demonstrate the effectiveness of the studied DPC approach in terms of the output power signals, the output current and the capacitor voltages under a unity power factor operation.