Imbalance Compensation of the Grid Current Using Effective and Reactive Power for Split DC-Link Capacitor 3-Leg Inverter

Abstract

Unbalanced loads cause the imbalance of the grid current and the resulting imbalance of the grid voltage when the imbalance rate of the grid current increases considerably. To cope with this problem flexibly at low cost, we modify the circuit structure from previously installed \Delta -Y transformer 3-phase 3-leg inverter to split dc-link capacitor 3-leg inverter eliminating the transformer. And then we propose two kinds of compensation algorithms for balancing the grid current that can basically utilize a preinstalled control board. It is divided into reactive compensation, where dc-link of the inverter does not supply effective power to the grid but compensates for the imbalance of grid current, and effective compensation, where dc-link of the inverter supplies effective power to the grid for compensating the unbalanced grid current. We design an additional power calculator board to obtain power information, and apply it to a 10kW prototype, and then verify its validity through PSIM simulation and experiments.