Research On Service Restoration Of Active Distribution Networks Under The Background Of Renewable Energy

With the development of national economy,the demand for electric power is increasing rapidly,which leads to the operation mode of traditional power system becoming more and more complex,which makes the prevention of large-area chain fault become very difficult.Under the background of system security,the construction of smart grid in the future,if it can be more inclined to the technology of distributed generation and grid connection,intelligent power distribution and other technologies close to the user side,it can ensure the power reliability of local load and reduce the harm of large-scale blackout.As the key power transmission system on the user side,distribution network is an important infrastructure for the development of national economy and society.With the improvement of power supply quality and technical level of distribution network in China,as well as the construction of advanced measurement equipment and remote control device,the function of passive power distribution in traditional distribution network is further expanded to "active" control power and develop into active distribution network.Active distribution network has the characteristics of all-round observability and controllability,which can meet the needs of micro distributed generation,electric vehicles,active load and other energy equipment access under the new energy situation.In the case of a major power outage in the main network,the active distribution network can effectively control the distributed energy through advanced measurement and control functions,so as to quickly recover the local power load,ensure the power supply of the local load,improve the reliability of power supply,and reduce the economic losses caused by the major power outage in the main network.Based on this background,this dissertation studies several key technologies of active distribution network fault recovery under the background of multi energy,and obtains the following results:1)The active distribution network contains various distributed generation,electric vehicles,energy storage equipment and flexible loads,which pose challenges to the operation and maintenance plan of the grid enterprise due to its uncertainty in the domain of time and space.From the point of service restoration after a blackout,this paper considers the uncertain factors of wind and photovoltaic in active distribution networks and uses electric vehicles as emergency dispatching resources.A three-layer robust islanding recovery mathematical model in the form of min-max-min is established which ensures the minimum load shedding in the worst case.In terms of solving method,the three-layer robust optimization model is converted to a relaxed main problem and a max-min sub-problem using the Column & Constraint Generation(CCG)method.By adding feasible cuts and optimal cuts iteratively into the relaxed main problem,the optimal solution of the original problem is obtained.Considering the non-convexity of the Distflow power flow equations in the max-min sub-problem,the sub-problem is converted into a MISOCP programming model by using relaxation techniques.Meanwhile,the duality theory is utilized to transform the max-min subproblem into a single-layer max problem.Finally,the effectiveness of the proposed model and method is verified by the simulations of PG&E 69 distribution network system.2)Based on the theory of distributed robust optimization and transient stability analysis of diesel generator,a fault recovery method for distribution network is proposed.Compared with the traditional robust optimal recovery method,it improves the conservatism of the original method in dealing with the output uncertainty of distributed generation,and gets better load recovery.At the same time,the frequency stability constraints in the recovery process are incorporated into the fault recovery model,which ensures the safe and reliable operation of the system in the process of power supply restoration in fault sequence.In addition,the topology constraints in the fault recovery model are improved to make the network topology more flexible after fault reconstruction,so that the load with high recovery importance can be recovered first,thus further improving the flexibility of the fault recovery scheme.3)The service restoration is a vital measurement to enhance the resilience of the electrical distribution network.With the integration of Distributed Generations(DGs)in the distribution network,the uncertainties are introduced,which have a considerable impact on the service restoration.Meanwhile,the Soft Open Points(SOPs)are electronic devices installed in the tie-line of the distribution networks.They have the ability to control the branch power flow,which can be utilised to assist the service restoration.This paper proposes a data-driven stochastic and robust service restoration method to handle the uncertainties of DGs outputs,which is modelled as a two-stage conic optimisation programming problem.The non-parametric estimation method is introduced to estimate the probability density function of forecasted error based on historical data.Furthermore,the nonlinear constraints of the SOPs are reformulated into conic forms so that the proposed model could be solved efficiently.Numerical tests are carried out on the IEEE 33-bus and 123-bus distribution networks to show the effectiveness of the proposed method,and the results show the superiority of the proposed method.4)Power system and natural gas networks can achieve high reliability operation through two-way coupling.In or-der to solve the problem of recovery of electric-gas integrated energy system after failure,this paper proposes a timing fault recovery method.On the one hand,considering the bidirectional coupling characteristics of gas turbines and P2 G equipment,the complementary mutual aid of the power-gas network is realized by scheduling the output of the gas turbine during the recovery process;on the other hand,considering that most of the equipment in the recovery process has timing characteristics,such as energy storage.The battery capacity,load size,wind turbine output and network topology change,a multi-time fault recovery mixed integer programming problem is established,and the model is easily solved by piecewise linearization,and the fault recovery process is obtained.The optimal sequence of topology switch operations.Finally,the effectiveness of the proposed method is proved by the joint simulation of 13-node distribution network and 6-node distribution network.