Reactive Voltage Control Strategy For Distribution Networks With High Proportion Of Distributed Photovoltaics

With the increasing development of distributed photovoltaic power generation technology,the number of distributed photovoltaic access in the distribution network has increased significantly,which also affects the safe operation of the distribution network when it brings convenience to users.On the one hand,distributed photovoltaic grid connection has changed the power flow characteristics of traditional distribution networks,and the increasing proportion of distributed photovoltaic access has made the problem of voltage exceeding the limit of the distribution network more and more serious.On the other hand,distributed photovoltaics are affected by factors such as light intensity and temperature,and there are fluctuations and uncertainties in the output power.Due to the large-scale access of distributed photovoltaics to the distribution network,the large number,scattered locations,and the uncertainty of its output power,which greatly increases the difficulty of voltage control in the distribution network,this dissertation focuses on the reactive voltage control strategy with high proportion of distributed photovoltaics,and the research content mainly includes the following aspects:(1)Analysis of the influence of distributed photovoltaic grid connection on distribution network voltageAiming at the problem of voltage exceeding the voltage at the grid-connected point caused by the distributed photovoltaic access to the distribution network,the distributed photovoltaic gridconnected model is first established to lay the foundation for subsequent research.Then,the influence of distributed photovoltaic single-point and multi-point access on distribution network voltage is theoretically analyzed.Finally,the reliability of the analysis is verified by simulation,which paves the theoretical foundation and basic research for the voltage control work after the subsequent distributed photovoltaic grid connection.(2)Distributed photovoltaic reactive power droop control strategy considering probability distributionAiming at the difficulties and challenges brought by the volatility and uncertainty of distributed photovoltaic output to the reactive voltage control of the distribution network system,a distributed photovoltaic reactive power droop control strategy considering the probability distribution is proposed.Firstly,the probability distribution characteristics of photovoltaic output are analyzed.Then,a probabilistic model of reactive power droop gain is established,the expected value of reactive power sag gain is solved,and it is applied to the distributed photovoltaic reactive voltage droop control link.Finally,simulation verifies that the control strategy has a good voltage control effect in the scene of constant light intensity and light intensity change.(3)Distributed photovoltaic reactive voltage control strategy based on cluster divisionAiming at the limitations of the reactive voltage control effect with nodes as the unit caused by the high-proportion and large-capacity distributed photovoltaic access,a distributed photovoltaic reactive voltage control strategy based on cluster division is proposed.Firstly,on the basis of the modularity index,the modularity index based on reactive voltage sensitivity is proposed,and the reactive power balance and coupling degree in the cluster are considered to obtain the improved modularity index,and the improved modularity index is used to divide the cluster.Then,the reactive voltage control strategy in the over-limit cluster and the coordinated control strategy between the clusters are proposed,and when the reactive power adjustable capacity in the cluster is insufficient,the remaining reactive power adjustable capacity is allocated to the over-limit cluster through the safety cluster to restore the voltage level of the over-limit cluster.Finally,through simulation,it is verified that this control strategy can restore the voltage level to the range of safe and stable operation in the scenarios of mild voltage limit and severe voltage limit.