This article presents a small signal analysis of an offshore AC network to integrate offshore wind energy with the main AC grid at shore through more than one VSC-HVDC transmission system. The offshore AC network reference frequency and voltage are controlled by VSC-HVDC systems using frequency and voltage droop schemes. Droop scheme establish a closed loop control with reference frequency and voltage hereby affecting the system stability. An impedance based modeling approach has been proposed to formulate the network small signal model in order to analyze the influence that the droop gain exerts on the voltage and current control. An eigenvalue analysis has been performed to determine the system stability. It is further demonstrated how the frequency and voltage droop gains influence the overall system stability. In addition, the active and reactive power low pass measurement filters effects on the system stability is addressed. In the end, the performance of the developed system is evaluated through nonlinear dynamic simulation.

Peer Reviewed