Virtual External Perturbance-Based Impedance Measurement of Grid-Connected Converter

The impedance of grid-connected converter (GCC) is crucial for the small-signal stability analysis of the renewable-energy system. Traditionally, the impedance of the power-electronic device is measured by primary-side perturbance method, connecting a real perturbance source in the main circuit, which is high in cost and complex in operation. Thus, without actual perturbance sources, the secondary-side perturbance impedance measurement method that perturbances are injected into the control loops has attracted more attention. This article proposes a virtual external perturbance-based impedance measurement method of GCC, injecting perturbances into the voltage and current sampling values at the point of common coupling (PCC). Taking into account the impact of the grid impedance, an equivalent calculation model of GCC is established, and the impedance can be calculated through the perturbance responses of GCC. In addition, the differences between primary-side and secondary-side perturbance method are compared, and the design approach for the amplitude of perturbances rooted in the size of grid impedance is proposed. The effectiveness of the proposed method is verified by both simulation and hardware-in-the-loop (HIL) experiments.