Damping Analysis of Outer Control Loops and Impacts on Stability of Grid-Connected VSC

This paper conducts damping analysis of grid-connected Voltage Source Converter (VSC) with the outer control loops based on the corrected complex torque coefficient method. An 8th-order small-signal model with active and reactive power control loops is developed, and the impacts of outer control loops on system damping are quantitatively evaluated. The damping generated by outer control loops can be divided into four parts: d/q-axis damping component of active/reactive power control loop, respectively. Results shows that d-axis damping component is mainly generated by active power control loop, while q-axis damping component is mainly generated by reactive power control loop. It can be drawn that outer control loops mainly contribute positive damping to system. Moreover, the impacts of outer controller parameters are also analyzed. Small Proportional-Integral (PI) controller parameters of outer control loops will deteriorate system damping. The electromagnetic transient simulations have verified the theoretical analysis.