Along with the fast development of Yunnan electric power system

tie line overload has become an increasingly serious problem. But

traditional automatic generation control (AGC) only takes the regulation abilities of the generation units into account during the arrangement of generation units output

without regarding to the security restriction of the whole system. So

the power flow of tie line exceeds the limit frequently by normal adjustment of AGC. This paper proposes that by integrating the AGC with security constrained dispatch (SCD) and network sensitivity analysis (NSA) and supershortterm load forecasting (SSTLF) to constitute a closedloop control system

the active power control of tie lines is implemented. The approach has been implemented in the energy management system (EMS) of Yunnan Province and the results demonstrate that it’s practical and valid.