Available Transfer Capability Calculation Considering UPFC

The modern power system has been developed into a large scale AC-DC hybrid power system. The higher and higher challenges to the reliable and economic operation of power grid have been posed. This is restricted by many conditions, such as complexity of system structure, onerous operating task, and stringent requirements of power quality, as well as market and environment protection. But traditional mechanical controlling methods have a limitation which leads to the difficulty of flexible regulation in transmission of electricity and transmission equipment can not be fully used. While Flexible AC Transmission System (FACTS) is for a new solving method, it brings an unprecedented turning point in power flow controlled, stability and transmission capacity and improves power system. In this complicated large-scale power system, how to seek the best system operating method between economy,safety and reliability undoubtedly becomes the most concerned issue to the operator of system. Available Transfer Capability (ATC) not only can display the margin of safe and stabilization in power system operating, but also provide accurate information of power system's state for operator and electricity market participants in order to guide its marketable behavior. Therefore, it seems especially important to study and calculate ATC considering FACTS devices.GUPFC will not only control the bus voltage, but also to control the power flow of many transmission lines or even a sub-network. But, if want to control the power flow between two lines, IPFC is generally adopted. The mathematical model of the Generalized Unified Power Flow Controller (GUPFC) and the Interline Power Flow Controller (IPFC) are established based on power injection method. The available transfer capability(ATC) calculation model taking GUPFC and IPFC into account is built according to add the controlling constraints, operating constraints and power injection model of GUPFC and IPFC into the optimal power flow analysis model.The central path-following interior point algorithm is applied to calculate the ATC. Numerical results with various FACTS devices based on IEEE-30 bus system not only demonstrate the capability that controlling bus voltage and power flows of more than one line or even a sub-network of GUPFC and the capability that reasonable distributing power flows among two lines, but also demonstrate the feasibility as well as the effectiveness of the model established and the algorithm proposed.