Reactive-power and voltage control for large-scale grid-connected photovoltaic plants

The active-power output fluctuation of large-scale grid-connected photovoltaic plant causes not only the PCC voltage violation but also the higher internal voltage, resulting in the protective action to trip off the inverters. The factors influencing the PCC voltage and the grid-connecting voltage of photovoltaic unit are analyzed and a strategy of reactive-power and voltage control considering the in-station voltage distribution is proposed. It detects the PCC voltage in real time, compares it with the reference, adopts a PI controller to automatically obtain the reactive-power needed for maintaining the PCC voltage, and realizes the dynamic adjustment of PCC voltage; it also regulates the reactive-power output of inverters in real-time to realize the uniform distribution of in-station voltage. The sensitivity analysis is applied to indicate the relationship between reactive-power and voltage, the design of PI controller parameters is given, and the reactive-power optimization with the uniform distribution of in-station voltage as its objective is converted to a nonlinear programming model with constraints, which can be quickly and accurately solved to obtain the reactive-power references for the reactive-power compensation devices and photovoltaic units. The in-station voltage distribution is improved to ensure the stable operation of photovoltaic power station while the stability of PCC voltage is guaranteed. The correctness and feasibility of the proposed control strategy are verified by the simulative results. © 2016, Electric Power Automation Equipment Press. All right reserved.