A Configurable Virtual Impedance Method for Grid-Connected Virtual Synchronous Generator to Improve the Quality of Output Current

There are two significant problems for the virtual synchronous generator (VSG) under the nonideal grid, including power coupling and current distortion. Although the virtual impedance (VI) is often used to decouple the control of active power and reactive power, it can neither suppress current harmonics nor solve current imbalance caused by the nonideal grid. Therefore, this paper proposes the configurable virtual impedance (CVI) approach to improve both the power coupling and the output current quality. The proposed methodology could aid the independent design of the virtual sequence impedance (VSI) for any harmonics, of which the virtual fundamental positive sequence impedance can be used to realize power decoupling, and the other VSI is designed to mitigate current aberration. Due to the requirements of VSI, the novel harmonic extraction algorithm (NHEA) based on the state space model is presented to separate the positive-sequence component (PSC), negative-sequence component (NSC), and zero-sequence component (ZSC) in the fundamental and harmonic current. Then, under this harmonic extractor, 90° phase lead for each SC can be easily achieved by means of simple vector rotation. Excellent extraction performance of the NHEA and remarkable ability of current quality control and power decoupling regarding CVI are demonstrated by simulations and experiments.