A Real-time Enhanced Thevenin Equivalent Parameter Estimation Method for PLL Synchronization Stability Control in VSC

The real-time estimation of the AC power system equivalent parameters enables the grid-connected voltage source converter (VSC) to achieve more effective stability control during a short-circuit fault. In this paper, a novel Thevenin equivalent (TE) parameter estimation method based on local PMUs is proposed and applied to the phase-locked loop (PLL) synchronization stability control of VSC. First, the relationship between the variation of the measured voltage and the error of the estimated impedance is strictly derived based on the rules of norm inequality. Then, according to the analysis of the upper bound of the system voltage change, a voltage threshold is proposed to select the PMU measurements to ensure the accuracy of the estimation during the large disturbance. Finally, using the estimated TE parameters, the current control instruction of VSC during the fault is calculated in real-time to ensure a synchronous and stable operation. The simulations reveal that the proposed estimation method can accurately track the TE parameters after a fault. Furthermore, the associated current control actions during a fault can ensure the PLL synchronization stability of VSC.