Voltage / Reactive Power Coordination Control Of Interconnected Power Network

With the development of the world economy and the promotion of the people’s living standard, the world’s demand for electric power is increasing, and higher requirements for electric power industry has been put forward. The index such as voltage qualified rate and voltage stability index should remain at a level as high as possible when the grid is operating economically. The grid interconnection, which realize the sustainable development of the electric power industry, provides favorable conditions for the grid security and stability, cost saving and resources optimization configuration. The developing and scale expanding of the grid interconnection form the hierarchical and divisional independent control centers for voltage/reactive power. When controlling the voltage/reactive power, it is necessary to adopt the coordinate control means for the control centers among the interconnected grid, in order to realize the reasonable distribution of reactive power and avoid control oscillation.The operation of interconnected power grid should realize the optimization of network loss and the voltage stability control at the same time, but it is not limited to all the subnet control centers, for the whole network is connected together. Aiming at the matter of reasonable allocation of reactive power and coordinated control of regional voltage/reactive power, according to the thought that "the promotion of regional voltage/reactive power regulation level should not be at the expense of the loss of global or interconnected grid control ability", an interconnected grid voltage/reactive power coordinated control method which takes both voltage stability and economic operation into account has been designed. The main research content is as follows:(1) Aiming at the coordinated control of the interconnected grid, the interactional relationships among interconnected areas during the regional voltage/reactive power control have been derived, based on the interconnected network equation of voltage and reactive power after decoupling the active and reactive power.(2)To reduce the amount of calculation and speed up the reaction rate of the reactive power control, according to the functional relationship between active power loss and reactive power injection, the definition of convex sets and convex function and the minimum criterion theorem are brought in, after which the parsing algorithm of optimal reactive power injection is derived, and then the optimal injected reactive power of the boundary notes in associated regions is obtained on condition that the network active power loss is minimum.(3) The L-index, which has the characteristic of online monitoring, is selected as the index for voltage stability evaluation. According to the functional relationship between L-index and injected reactive power, the analytical algorithm of solving optimal injected reactive power based on the minimum L-index is derived analogically, and the optimal injected reactive power is obtained on condition that the voltage of associated region is optimum, which verified the superiority of L-index evaluating the network voltage stability.(4) A multi-objective coordinated control model of voltage/reactive power for interconnected grid has been designed, which give consideration to both voltage stability and economic operation. Four optimization targets are included in the model, namely, the active power loss of the local regulatory region Ploss, L-index, the impacts of reactive power regulation in local region on boundary nodes in associated region△Qe,△Qs. As there may be contradictories among the four optimization targets, the solving model of multi-objective evolutionary algorithm (MOEA) based on the thought of Pareto-optimal solution set is selected.Finally, two interconnected grids are selected for the simulation verification, i.e., a24nodes network which is composed of the active and large capacity IEEE-14nodes network and a passive10nodes distribution network, and a IEEE-118nodes network which is comprised of two active networks with roughly equal capacity. The result shows that the proposed coordinated control can realize the grid optimization objective of economic operation and voltage stability in the whole region and local region via a small amount of key information exchange among regions, which verifies the correctness and effectiveness of the proposed coordinated control mechanism and method.