With the successive emergence of such new technology as large-scale new energy power generation and large power and efficiency inverter etc.

the requirement of wide area balance of power supply and demand to the flexible AC transmission technology is proposed. For solving the issue of eliminating grid connection of fluctuating and intermittent new power

balance source

power fluctuation of load and increasing system stability and power transmission capability

a new type of FACTS named UPFC/BESS is proposed on the basis of unified power flow controller（UPFC） and battery energy storage system（BESS）. The dynamically balancing both active and reactive power of new energy by UPFC/BESS in case of most critical power imbalance is obtained by way of setting up mathematical model of the new power system of big grid and designing such strategy of short time balance

intermediate and long term peak valley

abrupt rise and reduction control. The simulation model including UPFC/BESS device is set up based on PSCAD/EMTDC platform. It is shown by the simulation result that UPFC/BESS has strong active power adjustment and balance capability

can adjust quickly power imbalance of load and power

can balance power fluctuation of new power and has importance significance in strengthening safe margin of high power grid and reducing investment of back up capacity of power supply.