Analysis And Control Of Active Distribution Network Voltage Stability Based On HELM

With the global non-renewable energy facing the energy crisis,the demand for renewable energy is increasing.Distributed generation(DG)is widely used in the power grid because of its green,clean,high reliability and good flexibility.The access of DG will also have a great influence on the power flow,voltage level,voltage stability and network loss of system,which is closely related to the configuration of DG in the distribution network.Therefore,it plays an important role to study the voltage stability of distribution network and the optimal configuration of DG in distribution network to improve the utilization and consumption of DG.In addition,with the increasing proportion of DG grid connection,the risk of voltage over-limit will occur in the distribution network,so it is necessary to take effective voltage control strategy to ensure the safe and stable operation in distribution network.This paper works from the following aspects:Firstly,in view of the dependence on the initial value selection in the traditional power flow calculation method and the problem that the ill-conditioned power flow cannot converge,and the problem that the PI node is not considered in the HELM power flow calculation algorithm,the Holomorphic Embedding Load Flow Method(HELM)including PI nodes and considering the static characteristics of the load is proposed.It is non-iterative and does not depend on the initial estimation value,overcomes the non-convergence problem in the traditional power flow calculation,and can consider various types of DG.The HELM power flow calculation process including different DG types(PQ,PV and PI nodes)and considering load static characteristics is realized by Matlab programming.The effectiveness of the power flow algorithm in this paper is verified by case analysis.Secondly,aiming at the problem that the traditional voltage sensitivity cannot be calculated when encountering ill-conditioned power flow and approaching the voltage stability limit,a HELM voltage sensitivity calculation method including PQ,PV and PI nodes is proposed.The calculation process of HELM voltage sensitivity is deduced in detail,and the correctness of the method is verified.Based on the voltage sensitivity of HELM,a new voltage stability index is proposed.Compared with the load margin index,it is faster and more suitable for the power grid with DG.Compared with the L index and VSI index,it is more accurate and can judge the voltage collapse point.Then,the IEEE 33 distribution system is taken as an example to study the influence of the capacity,location,number,type and power factor of accessing DG on the voltage stability of the distribution system and compare it with the existing voltage stability criteria.Thirdly,in order to ensure the economy and reliability of the distribution network in the operation process,aiming at the problem that the L index and VSI can not effectively judge whether the system reaches the voltage collapse state,this paper adds the voltage stability index based on HELM to the objective function and constraint conditions,and establishes a multi-objective optimization model based on the comprehensive cost of configuring DG,the system network loss and the voltage stability judgment index based on HELM.Combined with the IEEE 33 distribution system example and the genetic algorithm,the model is solved to determine the installation position and capacity of DG.The results indicate that the model can ensure the economy,reduce the network loss and improve the voltage stability of system.Finally,in order to solve the problem of voltage over-limit caused by the increasing proportion of distributed photovoltaics grid-connection,this paper introduces the voltage stability index based on HELM into the objective function,and constructs a voltage control optimization model based on photovoltaic active power reduction,network loss of system and HELM voltage stability determination index,then uses genetic algorithm to solve it.Finally,the IEEE 33 node system is used to analyze the example.The results indicate that the proposed method can solve the problem of voltage over-limit,reduce the network loss and improve the voltage stability of the distribution network,and ensure the safe and stable operation of the system.