Adaptive hybrid synchronization control of grid-connected converters in renewable power plants and its small-signal stability analysis

As the capacity of renewable power plants connected to the grid increases year by year， optimizing the control strategies for their converters becomes crucial for enhancing system stability. Currently， the primary control strategies in renewable power plants focus on grid-following （GFL） and grid-forming （GFM） converters. The former tends to exhibit poor stability in weak grids， while the latter may lose stability in strong grids. To address this challenge， the paper first proposes a hybrid synchronous control structure for grid-connected converters that incorporates adaptive coefficients. This structure combines the phase-locked loop （PLL） commonly used by GFL converters with the power-synchronization loop （PSL） utilized by GFM converters， creating a hybrid synchronous control loop through a proportional coefficient. Subsequently， the corresponding small-signal model is developed， and based on the analysis results of small-signal stability， a method for determining adaptive parameter values is introduced. Finally， simulation results validate that the converter-connected system employing adaptive hybrid synchronous control maintains good stability in weak grids with a short-circuit ratio of 1 and in strong grids with a short-circuit ratio of 30. This provides a new control scheme suitable for the stable operation of grid-connected converters in renewable power plants under varying grid conditions.