Study On Optimal Allocation Of Distributed Generators And Vanadium Redox Flow Battery Energy Storage System In Active Distribution Networks

With the development of renewable energy sources,distributed generators and energy storage systems are widely connected to active distribution networks(ADNs).Vanadium redox flow battery(VRB)energy storage system,as a large-scale energy storage technology with the best overall performance,can participate in the power regulation of active distribution network and achieve the consumption of renewable energy.In order to achieve the optimal operation of active distribution networks,it is necessary to reasonably optimize the access of the distributed generators and vanadium redox battery energy storage system.Focused on the planning of distributed generators and VRB energy storage systems in ADNs,this paper researched the optimization models,optimization algorithms,dynamic characteristics of VRB energy storage systems and the absorption of new energy sources.The main content of the paper is as follows:(1)Focusing on the optimal configuration of distributed generators in active distribution networks,an optimization configuration method for distributed generators considering the operational risks is proposed.Firstly,stochastic models are constructed for distributed generators such as photovoltaic and wind power generators.And then,a point estimation method is used to discretize the output of distributed generators based on the stochastic models and a risk assessment method for distribution networks with distributed generators based on 2m+l point estimation method is constructed.Finally,a multi-objective mathematical model for the optimal configuration of distributed generators is proposed taking into account the index of operational risk assessment as well as the economic benefits of photovoltaic and wind power generators,network loss,investment costs,maintenance costs,etc.An improved genetic algorithm is used for the siting and sizing of distributed generation planning in distribution networks and test results show that it is more reasonable and accurate to sit and size distributed generation planning in distribution networks considering the index of operational risk assessment.(2)For the research of the connection way to ADNs and the dynamic characteristics of grid-connected energy storage systems for vanadium redox flow battery,a grid-connected design method for energy storage systems of vanadium redox flow battery considering the simplified model was proposed and the dynamic models of efficiencies and maximum absorption power were constructed.Firstly,the equivalent circuit model of vanadium redox flow battery considering the charge and discharge characteristics of vanadium redox flow battery(VRB).Correspondingly,a grid-connected design method for energy storage systems of vanadium redox flow battery considering the simplified model was proposed which simplified the controller parameters designing of VRB energy storage system and greatly improved the response speed of VRB energy storage system.In addition,the charge and discharge control performances of VRB energy storage system are largely improved.Then,on the basis of the designed VRB energy storage system,the simulation of VRB energy storage system under different charge and discharge power was set to fit the dynamic characteristics model of VRB.The dynamic efficiencies and maximum absorption power of VRB were quantitatively simulated which reveals the internal dynamic performance of VRB and makes a basis for the application of VRB.(3)Aiming at the optimal configuration of VRB energy storage system in distribution network,an optimal configuration method for VRB energy storage system was proposed considering dynamic characteristics of VRB and the maximum absorption of photovoltaic and wind power.Firstly,for the uncertainties of photovoltaic&wind power generators,load requirements,the price of electricity and fuel prices,the corresponding probability prediction models were constructed.And then,for the the maximum consumption of photovoltaic and wind power,an operating strategy for VRB energy storage system to achieve the maximum consumption of photovoltaic and wind power was built.Under the premise of reliable loads supplying,the maximum consumption of photovoltaic and wind power is realized.By this operational strategy of VRB energy storage system,the operational strategies of VRB energy storage system under various working modes are acquired and the power output of VRB energy storage system was obtained.Finally,on the basis of the dynamic efficiency and maximum absorption power model of VRB,an optimal configuration method for VRB energy storage system was proposed considering dynamic characteristics of VRB and the maximum absorption of photovoltaic and wind power.The total costs of VRB ESS,the direct economic benefits,environmental benefits,the consumption of wind and solar energy and network loss reduction costs were used as objective functions.This proposed mathematical framework was solved by a dynamic programming optimisation algorithm and the optimal VRB power and energy ratings were determined.The case studies verified the effectiveness of the proposed method and the optimal operational characteristics as well as the parameters of the optimal model were analyzed.(4)Aiming at the optimal configuration of the hybrid supercapacitors-VRB ESS in distribution networks,a multi-objective optimization configuration method for VRB-supercapacitor hybrid ESS considering both the economy index and the reliability index is proposed.Firstly,Fourier transform is applied for the imbalanced power caused by the randomness of the wind power generators and the load requirements in distribution networks and a net load power spectrum analysis method based on dividing the variations of imbalanced power was used to obtain the optimal capacity of supercapacitor ESS.The high-frequency component of net load power was restrained by the designed supercapacitor energy storage system.And then,for the maximum consumption of wind&photovoltaic power and the regulation of load requirements,an operating strategy for VRB-supercapacitor energy storage system was constructed.Simultaneously,the economical index such as total costs of ESS,the total benefits of ESS,loads interruption loss and the costs of abandoned wind energy were analyzed as well as the voltage fluctuations of nodes.Based on these,a multi-objective optimization configuration model for hybrid supercapacitors-VRB ESS considering both the economy and reliability of distributed power systems associated with VRB’ dynamic operation characteristics is proposed and a hybrid PSO and GA optimization algorithm is used to solve the proposed model.The optimal sizing and siting of hybrid supercapacitors-VRB ESS were acquired and the effectiveness of the proposed optimal method was verified by a modified IEEE 33-bus system.At the end of the paper,the main achievements and conclusions are summarized,and expectation on future work is given.