State-feedback-based Low-Frequency Active Damping for VSC Operating in Weak-Grid Conditions

Voltage source converters (VSCs) are nowadays widely integrated in the power grid, nevertheless they can induce low frequency stability problems under weak grid conditions. The interaction of PLL, dc-link voltage control, and ac voltage control generates a positive feedback which threatens the power system stability. The existing researches mainly focus on modeling strategies and stability analyses tools, however still few studies dealt with active damping in the low frequency range. In this paper, a nonlinear state space model of a VSC is presented and linearized around the operating point. From the model, a linear state feedback control law is designed and incorporated in the dc-link and ac voltage control in order to increase the system damping. Eigenvalue analysis is used to investigate the performance of the proposed controller. The simulation results based on a 2 MW grid connected wind generation unit, clearly show the effectiveness of the proposed solution. Experimental results with a 4 kW scaled-down setup validate the analytic and simulation results.