Decentralized Communication Based Two-Tier Volt-Var Control Strategy for Large-Scale Centralized Photovoltaic Power Plant

Long-distance power transmission makes a large-scale centralized photovoltaic (PV) power plant (CPPP) integrated into a weak power grid with a low short circuit ratio. Under this condition, small fluctuations in PV power are likely to cause significant fluctuations in system-wide voltage. To overcome this problem, a novel CPPP Volt-Var control (VVC) strategy is proposed. Unlike the conventional VVC strategy achieved in a centralized manner, the realization of the proposed VVC is mainly based on decentralized communication. The control framework for the proposed VVC has two tiers. In the upper-tier “optimal control”, a distributed VVC optimization model is formulated. Analysis target cascading (ATC) and alternating direction method of multipliers (ADMM) are combined to provide 15-minute-ahead optimal VVC scheduling, considering voltage deviation and active power losses together. In the lower tier “emergency control”, local droop control is applied to respond to the unexpected voltage deviation in real time. The final simulation results indicate that the proposed VVC strategy has good performances on the algorithm convergence in the upper tier and the control stability in the lower tier. The entire two-stage VVC could effectively maintain the system-wide voltage within the safe range and perform well on active power losses reduction, without the central controller.