Pre-Synchronization Control Strategy for Virtual Synchronous Generator Grid Connection Based on Voltage Mathematical Relationships

Conventional pre-synchronization control strategies for grid-connected virtual synchronous generator typically involve phase-locked loops, coordinate transformations or other non-linear computations, which may lead to substantial hardware resource consumption, pre-synchronization failures, even potential system instability. Hence, the mathematical relationships between voltage differences and angle differences on both sides before grid-connecting are analyzed. Based on those relationships, a pre-synchronization control strategy is proposed. It achieves smooth grid connection only by simple linear calculations using the filter capacitor voltage and the grid voltage. The difference between the effective values of these two voltage components is processed through a PI controller, with the result serving as a correction value for the output voltage command of the reactive power loop. The instantaneous value difference of the corresponding phase voltages is summed in absolute terms and processed through another PI controller, with the resulting output serving as a correction value for the frequency command of the active power loop. The cutoff frequencies of the two PI controllers are staggered to achieve decoupling. Control parameters are designed through stability analysis. Finally, experimental results validate the effectiveness of the proposed control strategy.