Adaptive Low-Voltage Ride-Through Control Strategy for VSG Based on Three-Phase Voltage Equivalent Amplitude

In virtual synchronous generator (VSG) systems, positive and negative sequence compound control in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i>–<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> axis rotating coordinate system is a mainstream approach for low-voltage ride-through (LVRT) due to its effective suppression capability of unbalanced components. However, the time delay caused by sequence decomposition leads to serious transient overcurrent during voltage sag/recovery. To solve this issue, this article analyzes the characteristics of three-phase voltage equivalent amplitude <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u_gm </i> under various voltage sag conditions, and proposes a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u_gm </i>-based rapid fault diagnosis method to distinguish symmetrical and asymmetrical sag faults. Based on the theoretical analysis, an adaptive LVRT control strategy was proposed. Specifically, the strategy determines whether to introduce positive–negative sequence decomposition at the appropriate time point, which significantly mitigates the delay influences caused by sequence decomposition during voltage sag and recovery. Ultimately, this smooths the transient response of the VSGs grid-side current. Finally, the correctness and effectiveness of the control strategy are experimentally verified.