A Novel Control Strategy for Enhancing System Stability in Weak Grids by Mitigating Additional Disturbance Components from PLL

Wind and photovoltaic power plants connected to weak grids can bring stability problems. The grid-connected inverter is an important connection port between the renewable energy and the grid. Some studies have indicated that the phase-locked loop (PLL) controller of the inverter can play a significant role in causing stability issues in weak grids. In this paper, a small-signal model of a phase-locked loop with complex variables is established. Then, the influence of phase-locked loop on system stability is analyzed. It is found that the presence of the PLL introduces additional disturbance components into the inverter control loop, resulting in a decrease in system stability. To mitigate the influence, a control strategy is proposed that involves injecting opposite disturbance components into the control loop to counteract the additional disturbance components. The proposed control strategy effectively improves the system stability. In addition, when compared to existing methods for enhancing stability, such as reducing the bandwidth of the PLL, the proposed method demonstrates a good dynamic response. The simulation and experimental results are presented to demonstrate the effectiveness of the proposed method.