Optimal reactive power management for transmission connected distribution grid with wind farms

This work presents an optimal reactive power management strategy for the operation of a transmission connected distribution grid with high share of wind power. Main control objective is minimizing reactive power exchange with the overlaying transmission grid. For this purpose, a mixed integer non-linear optimal power flow (MINLP-OPF) problem is formulated utilizing reactive power capabilities of wind farms and transformer tap-changer positions whilst respecting voltage limitations. Loss minimization and flat voltage profile are possible secondary sequential optimization objectives. The proposed control is evaluated for a real German 110-kV distribution grid with 1.6 GW installed wind power and yearly time series. Throughout a year, reactive power exchange with the transmission grid can be reduced by 96.8% while minimizing the increase in active power losses to 11.1%. Choosing voltage profile as secondary objective, reactive power exchange is reduced by 96.5% while quadratic deviation from nominal voltage is reduced by 30.8%.