Zero-Sequence Voltage Injection-Based Grid Impedance Estimation Method for Three-Phase Four-Wire DC/AC Grid-Connected Inverter

In this article, a novel method based on zero-sequence voltage injection to estimate grid impedance is proposed. The target of the proposed method is to inject a third harmonic before space vector pulse width modulation in order to generate zero-sequence voltage on the output side of the inverter. Then, the voltage response of the point of common coupling is measured to estimate the grid impedance. The main advantage of this method is that it minimizes the impact on the operation of the grid-connected inverter, without complex signal processing calculations. A three-phase four-wire dc-ac inverter configuration interconnected with the electric grid has been used to verify the effectiveness of the proposed method experimentally.