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Power Electronic Handbook P20

An electric power system is an interconnection of generating units to load centers through high-voltage electric transmission lines. It consists of generation, transmission, and distribution subsystems, which used to belong to the same electric utility in a given geographical area. But, | 20 Unified Power Flow Controllers Ali Feliachi 20.1 Introduction West Virginia University 20.2 Power Flow on a Transmission Line Azra Hasanovic West Virginia University 20.3 UPFC Description and Operation Series Converter Four Modes of Operation Automatic Power Control Karl Schoder West Virginia University 20.4 UPFC Modeling UPFC Steady-State or Load Flow Model UPFC Dynamic Model Interfacing the UPFC with the Power Network 20.5 Control Design UPFC Basic Control Design Power System Damping Control through UPFC Using Fuzzy Control 20.6 Case Study Test System Tracking Real and Reactive Power Flows Operation under Fault Conditions 20.7 Conclusion 20.1 Introduction An electric power system is an interconnection of generating units to load centers through high-voltage electric transmission lines. It consists of generation transmission and distribution subsystems which used to belong to the same electric utility in a given geographical area. But currently the electric power industry is in transition from large vertically integrated utilities providing power at regulated rates to an industry that will incorporate competitive companies selling unbundled power at possibly lower rates. With this new structure which will include separate generation distribution and transmission companies with an open-access policy comes the need for tighter control strategies. The strategies must maintain the level of reliability that consumers not only have taken for granted but expect even in the event of considerable structural changes such as a loss of a large generating unit or a transmission line and loading conditions such as the continuous variations in power consumption. The deregulation of electricity that is taking place now will affect all business aspects of the power industry as known today from generation to transmission distribution and consumption. Transmission circuits in particular will be stretched to their thermal limits because existing transmission lines are loaded close