Transient Stability Enhancement Control for VSGs Based on Active-Power Deviation and Angle-Feedback Compensation

Deep grid-voltage depressions may simultaneously induce transient power-angle instability and excessive fault current in VSGs, thereby compromising the operational security of grid-connected converters. To address this coupled challenge, an active-power deviation and angle-feedback compensation (APDAFC) strategy is developed. A fault-on power-angle model incorporating virtual damping and reactive-power-loop dynamics is first established to characterize the transient behavior of the VSG. The respective effects of grid-voltage-sag severity and power-angle variation on fault-current amplitude are subsequently identified. APDAFC introduces a compensation signal derived from the active-power deviation and power angle into the active-power–frequency loop, enabling online regulation of the equivalent active-power command. This regulation reverses the continued increase in the power angle and establishes a stable fault-period operating point whose power angle is lower than the prefault value. The resulting reduction in power-angle deviation decreases the magnitude of the voltage-phasor difference between the VSG and the grid. Consequently, transient synchronization stability and steady-state fault-current suppression are achieved simultaneously, while voltage-source operation is retained without imposing explicit current saturation. Simulations under different grid-voltage-sag severities corroborate the theoretical findings and demonstrate the effectiveness of the proposed strategy.