Research On Voltage Self-healing Strategy Of Regional Power Network

Self-healing is an important feature and symbol of smart grid. And "voltage and reactive power control" is one of self-healing functions of smart grid, so the research on voltage self-healing strategy is necessary. Especially, as the gradual realization of power system wide-area interconnected and the deep development of power market in current, the problem of voltage stability becomes serious day by day. Once voltage instability accident happens, a series of problems will bring about wide influence and severe losses, It has certain realistic significance and practical value for preventing grid cascade accident to research reliable and efficient voltage self-healing strategy. According to voltage stability index, this paper divided the operating condition of power grid into three conditions:fault condition, fragile condition and normal condition, then voltage self-healing strategy for different conditions was researched. The main research results were summarized as follows:Under fault condition, to guarantee voltage stability and maintain system voltage, this paper divided the process of voltage self-healing into two steps: recover system stability and enhance node voltage according to load power margin and voltage amplitude. Then for each step, based on graph theory, the load which will be shed was get according to the power flow before fault and the power flow after fault respectively. Then load was shed successive until the system recovers voltage stability and maintains system voltage meeting a certain level using dichotomy.Under fragile condition, to coordinate multiple objectives in self-healing control, this paper took control cost minimization, control amount minimization and load shedding minimization as optimization objectives, using MOPSO to solve the optimal voltage control strategy. It not only made the load power margin and voltage amplitude meet standards, but also got the voltage self-healing strategy which can achieve optimum both in economics and security. Meanwhile, to improve converging speed of PSO, this paper using voltage sensitivity to filter effective control equipments, initialize particle and adjust infeasible particle and out-limited particle. Under normal condition, based on the reactive power optimization algorithm, the voltage control strategy was get via getting voltage variation of each node with voltage sensitivity, taking the minimum variance between node voltage and voltage expectation as objective function and using dynamic programming to solve the sequence of control actions. The method can guarantee the transition of the voltage smooth during the process of grid self-healing and it can avoid bus voltage beyond limits.All of the above methods have been tested on IEEE30-bus system and a regional17-bus system. The simulation results show that these methods are valid.