Study on the Coordination of V-Q Control in Grid Connected System of Renewable Energy Stations

In view of the growing proportion of renewables and power electronics, the operation characteristics of the power system have changed significantly, and the problem of voltage stability is becoming more and more prominent. As the grid connection interface of renewable energy stations (RES), voltage source inverters (VSCs) play a vital role in the progress of voltage-reactive power(V-Q) regulation. The mathematical model of the grid-connected VSC system is established in MATLAB/Sinmulink in the beginning. And then the system’s stability is studied concerning the influence of the outer loop control and different reactive control (QC) strategies by means of root luci analysis. It is concluded that the outer loop impacts the static stability margin of the system deeply, and the small disturbance stability of constant voltage control (CVC) has better preformance than that of constant reactive power control (CQC) under the weak grid. This paper further constructs Thevenin equivalent circuit of grid connected system of RES, analyzes the sensitivity of key electrical quantities according to the mathematical equations, and reveals the mechanism why the stability of the CQC is inferior to the CVC in weak grids and the limitation of outer loop control structure.