Suppression strategy of neutral-point potential fluctuation in VIENNA rectifier based on zero-sequence voltage component injection

Abstract

The neutral-point potential fluctuation in the VIENNA rectifier is one of the key factors affecting the charging performance of DC charging systems. To address this issue, the charging and discharging behavior of the DC-link capacitors under different switching states is analyzed, revealing that the neutral-point potential fluctuation mainly consists of an AC fluctuation component and a DC offset component. A time-domain expression for the neutral-point potential fluctuation is derived, showing that its amplitude is proportional to the modulation index and the input current amplitude, and inversely proportional to the grid frequency and the DC-link capacitance. Based on this analysis, a zero-sequence voltage component injection strategy based on neutral-point charge balance is proposed. The strategy regulates the switching-period-averaged neutral-point current, divides the modulation cycle into different intervals according to the polarities of the three-phase input currents, and analytically determines the AC-compensation zero-sequence voltage in each interval. A DC-offset correction component is then superimposed to simultaneously suppress the low-frequency AC fluctuation and DC offset of the neutral-point potential. To verify the proposed strategy, a three-phase VIENNA rectifier experimental platform is built. Experimental results demonstrate that the proposed strategy reduces the voltage ripple of each DC-link capacitor from ±2.5% to ±1.0%, thereby confirming its effectiveness.