A study of power flow control and optimization by UPFC

The control action of FACTS on power system transients has been extensively recognized. But its function on system steady-state operation should be further studied. In this paper, the power controlling characteristics of the UPFC power injection model is firstly analyzed with the aid of a three-dimensional diagram thus the scope of the UPFC on power flow control can be clearly displayed. With this model, the power flow control problem can be transformed into an optimization problem. Then the optimal power flow is undertaken and the power transmitted via interconnecting lines can be obtained. The computation results of the two IEEE sample systems reveal that UPFC has quite powerful capability of controlling the local area power flow, but has only limited capability of reaching the objective of optimal operation of the whole system. This demonstrates the dependence of the steady-state controllability of UPFC on the operational objective of the system. The computation results also show that the optimal control strategy of UPFC under steady state should be the optimal control of the local area power flow incorporating with the corresponding operating conditions. This conclusion can also be referred during UPFC placement. This project is supported by National Natural Science Foundation of China for National Outstanding Young Investigators (No. 59825104) and National Natural Science Foundation of China for Oversea Young Scientists (No. 59928705).