A decoupled unified power flow controller model for power flow considering limit resolution

A decoupled UPFC model is used for power flow. Both ends of UPFC may be assigned as PV buses or PQ buses with the desired values. Then the power flow of the power system with UPFC is performed without modifying any conventional power flow program by the model only with the addition of two buses per one UPFC. After power flow, the equations to obtain the internal UPFC states are derived. The UPFC states calculated by the power flow may not be allowed because of the UPFC limit due to the rating of inverters. In this case, the UPFC parameter values should be revised to resolve the limit. In this paper, when the series voltage magnitude and/or the shunt current magnitude are violated, the iterative methods to resolve the limits are proposed. When resolving the series voltage magnitude, three strategies are proposed according to the priority of the active power and the voltage magnitude.