Research On Network Reconfiguration Methods Of Smart Distribution System

The permeability of distributed generation represented by wind power and photovoltaic and electric vehicle has increased gradually in the distribution system,which has brought new challenges to the safe and economic operation of the distribution system.By switching opening-closing state of tie switches and section switches,the economy can be optimized and the risk can be reduced for distribution system under normal state.The fault area can be isolated and the power supply of the non fault area can be restored under the fault condition.In this paper,the methods for network reconfiguration and service restoration reconfiguration of smart distribution system are researched.A continuous algorithm for distribution network reconfiguration based on efficient encoding of solution space is proposed in the paper.By reducing the exchange range of switch exchange through deduced approximate formula of network loss,the solution space is compressed and the efficiency of optimization is improved.To avoid solving discrete variables directly,a double-population solution space including discrete variables and continuous variables solutions is established,which can reduce the amount of calculation and is suitable to apply continuous variable optimization method to solve distribution network reconfiguration problem.After reducing the radius of the interval variables,two kinds of non-effective solutions are avoided and the number of times of power flow calculation is also decreased.The improved crisscross optimization algorithm improves convergence speed and precision.Simulation results verified the correctness and effectiveness of the proposed algorithm.To guarantee both the speediness and global optimization of service restoration of distribution network simultaneously,a new phased service restoration strategy based on network reconfiguration is proposed.Firstly,partial reconstruction using heuristic rules for non-islanding operation is implemented for fast restoration of distribution network connectivity with fewer switching times.Secondly,the optimal solution is searched in the feasible region for global reconstruction while the state variables are over-limit.Finally,if the state variables are still over-limit,part of non-critical load is shed in the order of the importance index of the load until back to a new safe operation state.To improve the speediness of global reconstruction,an optimization rule to avoid infeasible solutions is proposed,which avoids frequent topology analysis,and service restoration reconfiguration is based on the improved dual population crisscross optimization algorithm.The effectiveness of the proposed method is verified by simulation results.Voltage stability of distribution system is under certain challenges with large-scale electric vehicle Integration.A distribution network reconfiguration model based on maximum static voltage stability margin is proposed to improve voltage stability margin of distribution network,and a smooth solution algorithm based on distribution network complementary constrains is proposed for the model.Firstly,the assessment index of voltage stability margin for distribution network is proposed through the analysis of static voltage stability conditions of distribution network nodes.Secondly,the probabilistic load models of typical EV charging stations established and the load model with full consideration of static voltage characteristic adapted in power flow calculation,the reconfiguration model is established targeting at maximum voltage stability margin of the distribution network.Finally,to reduce the decision-making time of network reconfiguration,discrete variables are slacked to continuous variables using complementary constraints,and a gradient optimization algorithm is applied for solution with good numerical stability.Simulation results show that the reconfiguration method for distribution network in this paper can help to improve the level of the voltage stability for the distribution network,numerical stability being good,solving speed being high,and load static voltage characteristic being fully consideration.