Voltage-source converters (VSCs) are widely used in renewable energy sources as the grid interface, e.g., wind turbine generators and photovoltaics. These VSCs control the dc-link capacitor voltage and the reactive power output to track the reference values, which generally apply phase-locked loop (PLL) for grid synchronization. However, the dynamic performance of the conventional PLL can be deteriorated when the VSC is integrated into weak grids, which may even cause instability of the VSC. In this paper, a virtual synchronous control (ViSynC) is proposed for VSCs, which utilizes the dynamics of the dc-link capacitor to realize self-synchronization. Grid synchronization mechanism of the ViSynC-based VSC is particularly analyzed in this paper. The ViSynC-based VSC can provide inertial responses to the grid, and has the advantage that it can operate normally under weak grid conditions without any modification of the grid synchronization unit. Furthermore, virtual impedance and Q-V droop control can be easily implemented in the control structure of the ViSynC. Simulations based on MATLAB/ Simulink and hardware-in-the-loop real-time simulations based on RT-LAB verify the effectiveness of the proposed ViSynC.

A Virtual Synchronous Control for Voltage-Source Converters Utilizing Dynamics of DC-Link Capacitor to Realize Self-Synchronization