A Var/Volt Closed Loop Control System For Regional Power Grid Based On Hierarchical Coordination

The main objectives of daily Var/voltage control to a power grid are to reduce system losses and to improve the voltage profile. In general, there are two different types of control devices in regional power grid in China: the shunt capacitors and under load tap changer(ULTC) of main transformers, which both contribute to the two objectives above. Coordination between capacitor switching and tap adjustment of ULTC is necessary in order to reach satisfactory integrated control of reactive power and voltage at lower operation cost.With the remarkable improvements on automation technology for power grid operation, the practice to make an optimal reactive power/voltage control decision and to perform a closed loop control directly to capacitors and ULTCs via a computerized system, is now coming feasible.In this thesis, the mathematical modeling and the practical constraints of Var/Volt control problem for regional power grid are analyzed, and a heuristic Var/Volt optimal algorithm based on hierarchical coordination is proposed. Two-level hierarchy is adopted in the algorithm. Firstly, the whole regional power grid is decomposed into several control zones with radial network configuration. Based on an algorithm to alternately execute a recursive equivalence and an optimal matching injection flow searching, the regional-level control strategy is realized. Secondly, based on an improved "nine-area-graph" control strategy, substation-level control is implemented which is started up once the regional-level control does not work normally, ensuring the robustness of the algorithm.Additionally, a practical Var/voltage closed loop control system for regional power grid is developed in this thesis. Several advanced computer techniques, such as client/server architecture, C/C++ OOP, and QT, are adopted by this control system, making this system transplantable between Unix and Windows. The control system presented in this thesis has been implemented and put into practical operation and the operation results show that this system is robust and effective.