Voltage Risk Analysis And Optimal Access Capacity Planning Of Distribution Network Considering Photovoltaic Access

Under the background of large-scale connection of photovoltaic(PV)system to the distribution network,the intermittent and uncertainty of PV output will affect the stable operation of the power system.At the same time,the system structure and power flow distribution of the distribution network are changed by connecting the PV to cause the risk of system voltage over the limit potentially.Therefore,in the planning stage of PV station,the risk of system voltage over the limit is considered,and a suitable scheme is selected,which can not only meet the low risk of system voltage over the limit,but also increase the economic benefits by connecting the maximum PV capacity.The main contents of this dissertation are as follows:(1)The risk assessment model of voltage over limit in power system is proposed,and the risk index is determined by calculating the probability and severity of node voltage over limit.The output random model and load random model of photovoltaic power generation are constructed,and the PV output random model and load random model are expanded by series expansion method,and the semi invariants of each order of PV output and load are obtained.The probability distribution data of node voltage is obtained by random power flow calculation,and the probability distribution of voltage exceeding the limit is substituted into the risk assessment model to obtain the system The risk of voltage out of limit.(2)The IEEE 34 distribution network model is constructed,and the two objective functions with the lowest risk of system voltage exceeding the limit and the best overall economy are established,and the planning model with the system power flow and photovoltaic access capacity of nodes as constraints is established.The multi-objective function planning problem is transformed into single objective function planning problem by using efficiency coefficient method,which simplifies the planning steps and calculation amount,and improves the efficiency coefficient method by determining the weight of each objective function by AHP,so that the result of efficiency coefficient method is more in line with the actual situation.By adding the addressing idea of genetic algorithm into particle swarm optimization algorithm,a new improved particle swarm optimization algorithm is formed,and the optimization result is improved.The photovoltaic access capacity and access location planning results are obtained by using this algorithm.Simulation experiments show that the planning results obtained by using the improved particle swarm optimization algorithm to calculate the model are better than those obtained by using the traditional genetic algorithm and the traditional particle swarm optimization algorithm The result of the sub group algorithm is more excellent.(3)In order to further optimize the risk of system voltage exceeding the limit,considering the access of energy storage device to improve the risk of system voltage exceeding the limit,according to the idea of energy storage balancing photovoltaic output,the output probability model of photovoltaic is modified,the probability model of combined output of photovoltaic storage is proposed,and two objective functions are established,which are the lowest risk of system voltage exceeding the limit and the best overall economy of energy storage,The simulation results show that the access of energy storage elements improves the risk of system voltage exceeding the limit,but the risk of power system voltage exceeding the limit is lower when more photovoltaic capacity is connected,so the energy storage elements play a good role in regulating.