An Inrush Current Limiting Strategy for Virtual-Oscillator-Controlled Grid-Forming Inverters

Grid-forming (GFM) inverters refer to the ones that can regulate inverter voltages and frequencies instantaneously and simultaneously. In this paper, we focus on a recent time-domain GFM controller based on the virtual oscillator control realized by the Andronov-Hopf dynamics. Due to the features of voltage source inverters, GFM inverters are susceptible to damage if their controllers are not properly initialized prior to inverters' start-up operation. Generally, an effective pre-synchronization strategy is required to achieve a seamless and safe connection. This paper proposes an inrush current limiting strategy applicable to virtual-oscillator-controlled inverters in electric power systems where voltages and frequencies are unknown and off-nominal. Parameters of the proposed controller are properly designed and selected to satisfy the transient requirements. A small-signal model is then established to analyze the stability of the proposed strategy. Finally, experimental results on an ac system consisting of multiple GFM inverters validate the theoretical developments and demonstrate that inverter inrush currents can be effectively mitigated through the proposed pre-synchronization method.