Model Predictive Control Method With NP Voltage Balance by Offset Voltage Injection for Three-Phase Three-Level NPC Inverter

This paper proposes a predictive control method with offset voltage injection for achieving a neutral point (NP) voltage balance of three-phase three-level neutral point clamped (NPC) inverter, without employing a weighting factor. In order to ensure the proper and reliable operation of the NPC inverter, the NP voltage balance should be regulated in addition to the sinusoidal output current. The conventional predictive control methods for NPC has suffered from tedious weighting factor selection. Besides, when the converter's parameters value and control condition changes, it is cumbersome to empirically redesign the weighting factor. Therefore, the proposed predictive control method without the weighting factor can successfully maintain the balance of NP voltage by utilizing an offset voltage, which is determined according to the difference between the upper and lower capacitor voltages. As a result, the proposed algorithm using the offset voltage injection can control the output currents and maintain the balance of NP voltage. Simulation and experiments are presented to prove the validity of the NP voltage balancing of the proposed control method.