Research on multi-objective coordinated control strategy of UPFC

Unified power flow controller (UPFC) has a number of functions, including controlling power flows, regulating bus voltages, enhancing power system transient stability and suppressing sub-synchronous resonance (SSR), etc. Unfortunately, the above goals are not completely uniform. This paper analyzes the control principle and method of each goal and their interrelationships and potential contradictions. In order to satisfy the different requirements of power system and guarantee the major performances under varied operating conditions, the multi-objective coordinated control strategy is proposed, in which fuzzy logic is applied in designing the auxiliary controller. And PSCAD/EMTDC simulations verify its feasibility and effectiveness. During steady operation of power system, the bus voltage and power flow are made to track their references strictly. And during transient process, the strategy transfers to improve the transient stability limit and damp oscillation rapidly while keeps the bus voltage and power flow within their allowed range. Furthermore, SSR, if occurred, could be suppressed as well.