A neutral point voltage regulation method with SVPWM control for single-phase three-level NPC converters

This paper deals with the analysis, design and operation of a control system for the single phase three-level converter with a neutral-point diode-clamped (NPC) topology. The mathematic model of the converter in D-Q reference frame is derived. Two closed control loops are adopted in the control scheme to achieve line current command tracking and DC-link voltage regulation. The traditional control method in the inner loop is transient current control and SPWM method in electrical locomotive. In this paper, Predictive current control and SVPWM method is presented in the inner loop to draw a sinusoidal line current from the wire. A voltage controller based on a proportional-integral scheme is used in the outer loop to obtain a constant DC-link voltage. A neutral point voltage compensator is proposed in the system to balance the capacitor voltages on the DC side. Based on the presented control scheme, a three-level pulse-width modulated waveform is generated on the AC terminal of the converter. Computer simulation results are provided to verify the performance of the control scheme.