A neutral-point potential balancing technique implemented at the front end in back-to-back-connected three-level converter

This paper presents a neutral-point potential balancing (NPB) technique which is implemented only at the front end in back-to-back-connected three-level converter. The converter is a three-level inverter fed by a front end with a three-level rectifier. Hysteresis current control and optimized SVPWM algorithm are used for the rectifier and the inverter respectively. The proposed NPB technique is implemented only in the rectifier by injecting compensation currents into input currents according to the neutral-point potential deviation. This control scheme can achieve unity power factor, balanced and sinusoidal input currents and output voltages, and balanced neutral-point potential. Compared with the conventional NPB technique which is implemented in inverter, the proposed NPB technique does not modify the inverter modulation algorithm, and optimized modulation algorithm can be adopted for inverter, then output voltage harmonics are lower. The basic principles of the control scheme and NPB technique are introduced and verified by simulation in this paper. The proposed NPB technique is also compared with a conventional NPB technique which implements NPB in inverter. Simulation results show that the proposed control scheme and NPB technique are correct and effective.