Zero-Axis Virtual Synchronous Coordinate Based Current Control Strategy for Grid-Connected Inverter

Abstract

Unbalanced power has a great influence on the safe and stable operation of the distribution network system. The static power compensator, which is essentially a grid-connected inverter, is an effective solution to the three-phase power imbalance problem. In order to solve the tracking error problem of zero-sequence AC current signals, a novel control strategy based on zero-axis virtual synchronous coordinates is proposed in this paper. By configuring the operation of filter transmission matrices, a specific orthogonal signal is obtained for zero-axis reconstruction. In addition, a controller design scheme based on this method is proposed. Compared with the traditional zero-axis direct control, this control strategy is equivalent to adding a frequency tuning module by the orthogonal signal generator. The control gain of an open loop system can be equivalently promoted through linear transformation. With its clear mathematical meaning, zero-sequence current control can be controlled with only a first-order linear controller. Through reasonable parameter design, zero steady-state error, fast response and strong stability can be achieved. Finally, the performance of the proposed control strategy is verified by both simulations and experiments.