| The power system has entered the new stage of large system, ultra high voltagelong distance transmission, cross regional networking. The development of the socialeconomy changes the mode of operation and management of modern power grid, therequirements of the safe, stable, efficient, flexible power control improves day by day.With the presentation and development of flexible AC transmission system (FACTS),the realization of various compensation techniques greatly improve the capability ofpower flow control. As the most complex and attractive compensator in FACTS, unifiedpower flow controller (UPFC) can obtain any combination of control for line impedance,phase angle, active and reactive power with strong flexibility, which has gained wideattention since it was proposed. In this paper, UPFC is studied from improving powerflow controller of its series converter, finding its optimal location and capacity.Firstly, the present situation of application and study of UPFC were brieflyintroduced, the basic structure and working principle of UPFC were discussed. Inaddition, decoupling the system contained UPFC device based on the d-qtransformation, the mathematical model was established and the control principle wasanalyzed. Afterwards, selecting principle for UPFC parameters was summarized,especially for DC-link capacitor.Then in order to improve the control effect of series controller of UPFC, its activeand reactive power flow were analyzed. A PI self-tuning controller with variableparameters based on particle swarm optimization algorithm(PSO) is designed in thispaper. Using Matlab/Simulink to found a model of single machine infinite bus powersystem and comparing the proposed control strategy with the traditional PI controlstrategy. Simulation results show that the proposed control method has quick adjustmentin changing active and reactive power flow, and also can effectively reduce the poweroscillation caused by the three-phase short-circuit fault, improve the system dampingand transient stability.Finally, the concept of the active power flow performance index was introduced,which sensitivity with respect to the voltage magnitude and phase angle has been usedas a measure to decide optimal location in the IEEE14node system. Then the methodof establishing UPFC investment income and cost function were introduced, in whichthe total economic benefit of UPFC was maximized to find the optimal capacity byusing artificial fish-swarm algorithm. |
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