Analysis and Damping of Low-Frequency Oscillation for DC-Link Voltage-Synchronized VSCs

The power-synchronization control has been proven effective to enhance the stability of voltage-source converters (VSCs) in weak grids. This method can be realized with the dc-link voltage control for VSCs with regulated dc-link dynamics, which leads to the dc-link voltage-synchronization control. This paper analyzes the small-signal stability of dc-link voltage-synchronized VSCs, considering the effect of constant power load/source at the dc link. It is found that low-frequency oscillations may arise with dc-link constant-power dynamics. To dampen the oscillation, an active damping control method based on the active power feedforward (PFF) control is proposed. A notch filter tuned at the synchronous frequency is embedded in the PFF loop to avoid the adverse effect on synchronous oscillation. Design guideline for the PFF control parameters is formulated. Experimental tests of VSC operating in the rectifier and the inverter modes are performed. The results validate the theoretical analysis and the effectiveness of the control approach.