Distributed optimal voltage control strategy for AC grid with DC connection and offshore wind farms based on ADMM

A distributed optimal voltage control (DOVC) strategy based on the alternating direction method of multipliers (ADMM) is proposed for the AC grid with voltage source converter (VSC) DC connection and offshore wind farms (OWFs). The proposed DOVC strategy achieves global optimal power distribution inside the AC grid with DC connection to minimize the power losses while minimizing the bus voltage deviation from the rated value as well as power losses inside several OWFs. The optimal power flow (OPF) of the AC grid with VSC DC connection combined with model predictive control (MPC) is relaxed by using the semidefinite programming (SDP) relaxation technique. The MPC-based voltage optimization problem for the OWF is formulated by considering the dynamics of WTs. The ADMM is used to decompose the large-scale strongly coupled optimization problem, which is calculated in AC-DC grid and OWF controllers in parallel while guaranteeing global optimality. Compared to conventional control methods, the control performance of the system is enhanced. A modified IEEE-30 bus system with DC connection incorporating three OWFs consisting of 288 wind turbines (WTs) is used to evaluate the proposed DOVC strategy.