DC Inertia Support Scheme for MMCs in HVDC Transmission System Integrating Offshore Wind Farm

This paper presents dc inertia support scheme for MMCs used for integrating offshore wind farm based on HVDC system. The proposed mechanism has two energy buffering paths: through the energy controller and the zero sequence circulating current (ZSCC) controller. The first path is used to support the dc system when ac disturbances happen inside the offshore wind farm. For this purpose, the gains of the energy controller are tuned online based on the dc voltage deviation and the ac power change. On the other hand, the function of the second path is to make the MMC engage in the supporting the dc system when disturbance occurs in ac system of other side of the HVDC system. To achieve this, the ZSCC reference is modified by the time derivative of the dc voltage amplified by a virtual capacitor. Furthermore, in the provision of dc inertia support, the energy deviation is contained within the defined range. Also, the deviation is at the transient stage only. The effectiveness of the proposed scheme has been verified using simulation analysis based on the nonlinear model developed in MATLAB/SIMULINK.