Suppression to Angular Oscillation among Synchronous Generators by Optimizing Parameters and Set-Points of Synchronous Condenser and High-Voltage DC

Abstract

After losing one or two poles of the high-voltage DC (HVDC) line, power systems may experience angular oscillations among the synchronous generators (SGs), possibly followed by tripping of the SGs and blackouts of the loads. To suppress the oscillations, the difficulty lies in the optimization methods and the countermeasures. For the former, parameter optimization based on the eigen-analysis for a given scenario is not suitable for angular oscillation after a large disturbance lasting for several seconds or longer. For the latter, adjusting the active power of the SGs is effective but responds slowly. Adjusting the excitation system of the synchronous condensers (SCs) is seldom studied since the relation of the power angle with the reactive power is not clearly described. Adjusting the control parameters of the remaining HVDC has limited effect and is not enough. The set-points for the controller of the HVDC are adjusted to suppress the oscillation but are to be restored after the oscillation, which is different from optimization of the control parameters. In this paper, coordinated optimization of the control parameters and the set-points of the SC and the HVDC is proposed to suppress the angular oscillations among the SGs. At first, the relation of the reactive power of the SC with the power angles is validated to provide the basis for optimizing the control parameters and the set-points of the SC. Since the analytical expression between the power angle and the control parameters or the set-points related to the reactive power is not explicit and the optimization periods of different parameters are different, an improved analytical model of the trajectory sensitivity (TS) is proposed. Based on the indication indices, the control parameters and the set-points of the constant current controller and the excitation system to be optimized are decided. The gradients of the objective function are extended to derive a coordinated multiparameter optimization model to suppress the angular oscillation among the SGs. The numerical results validate the accuracy of the improved TS by comparing it with the perturbation method. The time-domain analysis in different scenarios shows that the angular oscillations in the AC/HVDC system are effectively suppressed with the proposed optimization model.