A Control Strategy for T-Type Three-Level Converter to Suppress Midpoint Voltage Fluctuation

T-type three-level converter is widely used in high-current and low- voltage fields owing to its small number of power devices, low on state loss and high power density. Midpoint potential balance control of T-type converter is one of its key technologies. The neutral point potential imbalance increases harmonic distortion rate of output voltage and current, and reduce service life of DC side capacitor. This paper proposes midpoint potential balance control strategy in view of PIR-controlled zero-sequence voltage to control offset and fluctuation of midpoint potential. Functional model between midpoint current, reactive current and active current and the functional link between SPWM and SVPWM are established. The control strategy is simple in calculation and fast in dynamic response. It can realize midpoint potential balance domination under different power factors and the suppression of low-frequency voltage pulsation. Ultimately, simulations verify the effectiveness and correctness of proposed domination tactics.