Study On Zonal-voltage Control Method Of Distribution Network With Distributed Generation

With the increasing severity of environmental issues and energy crisis,distributed generation(DG)based on renewable energy has developed rapidly.DGs accessed to distribution network can improve the stability and reliability of the power grid,but massive DGs grid-connected also brings a significant impact on the voltage control of regional power grid.The local control of the distribution network with the DGs can not only improve the capacity of the distribution network to access DGs,but also can use the reactive power capacity of DGs to carry out the continuous adjustment of the regional voltage and improve the stability of the local voltage.so this thesis studies on the zonal-voltage control method of distribution network with DG.At present,the voltage zoning control methods of power system mainly focus on the transmission network,and they are biased to reactive voltage control.DGs are usually connected to low voltage grade of power distribution network.The impedance characteristics of the distribution network(especially low voltage power distribution network)are different from the transmission network.The resistance(R)is usually greater than the reactance(X).Therefore,the voltage partition control methods only consider the impact of reactive power on the grid voltage are no longer suitable for the distribution network with DGs.This thesis uses the concept of comprehensive voltage sensitivity which considering both voltage/active sensitivity and voltage/reactive sensitivity.Based on the comprehensive voltage sensitivity,the DG output is changed to obtain the voltage increment matrix,and the distribution network is partitioned by cluster analysis.In the cluster analysis methods,the K-means clustering algorithm has the characteristics of simple and rapid,but there is a disadvantage that the "correct" number of clusters is difficult to determine.At the same time,the strong coupling in the region and the weak coupling between regions are considered in the partition principle.This thesis adopts a CFK-means(K-means Based on Comprehensive Fitness),which based on the comprehensive fitness evaluation function considering intra-class distance and inter-class distance.However,there is still a disadvantage that is easily trapped in the local optimal solution.Therefore,this thesis adopts an MPSO(Modified Particle Swarm Optimization)algorithm based on improved inertia weight and learning factor,which has strong global search capability.Then,this thesis combines the MPSO algorithm with the CFK-means,and proposes an MP-CFK clustering algorithm with the advantages of both algorithms.The feasibility of the MP-CFK clustering algorithm proposed in this thesis is verified by the IEEE-33 distribution system with DGs.The partition results obtained by the PSO-K clustering algorithm,the MP-CFK clustering algorithm,the K-means clustering algorithm and the hierarchical clustering method are compared with the MP-CFK clustering algorithm to further verify the effectiveness and superiority of the voltage partition control method for distribution networks with DGs which proposed in this thesis.Finally,the partitioning situations that simultaneously changing the reactive power of multiple DGs are discussed.