Analysis of DC-link Current of Parallel Three-phase Inverters under Unbalanced Output Currents

Analysis and calculation of DC-link current of three-phase inverter is one of significant part of the selection of de capacitors, system life expectation and the stability of converter control. However, almost all DC-link current analysis have focused on balanced three-phase ac output currents so far. For applications of four-wire power quality improvement, like the active power filter (APF) and the static VAR generator (SVG), unbalanced output current are required. In this paper, considering unbalanced output currents, the analysis and calculation of the de-link current for three-phase inverter are firstly presented and the sideband harmonic orders are derived subsequently. Then, for parallel three-phase inverters with a shared dc bus, the effect of interleaved carrier phase shift PWM on DC-link current is studied and the optimal interleaving angle is derived. Finally, the analysis and calculation of the dc-link current is verified by simulation, which shows the good accuracy of the analysis results under unbalanced output currents.