Security Constrained Optimal Power Flow with Optimally Allocated UPFC Based on Technical and Economic Criteria

The Unified Power Flow Controller (UPFC), which is the most versatile and suitable Flexible AC Transmission Systems (FACTS) device, can maintain a stable and secure operation of modern deregulated power systems as it can control power flow and power flow variables independently or simultaneously. In this paper, MiPower software is used to find the optimal placement of UPFC considering practical constraints. In order to reduce the search space and computation time, performance assessment of the device is executed only at the weaker lines of the system. The weaker buses and weaker lines are identified using Fast Voltage Stability Index (FVSI). The losses of UPFC itself such as switching losses of converters, losses due to coupling transformers and power transmission losses in UPFC are taken into account for power flow calculation. Considering practical upper and lower limits of voltage magnitude, an innovative voltage profile enhancement index (VPEI) is formulated. In this paper, objective functions, namely, overall improvement in FVSI, VPEI, reduction in losses and expenditure of UPFC are considered altogether in order to determine the optimal location of UPFC on IEEE 30-bus test system.