Optimal Scheduling Of Active Distribution Networks Based On Flexible Loads On Multiple Time Scales

Under the dual crisis of fossil energy and environmental pollution,vigorously developing and utilizing renewable energy is an effective way to solve this problem.The distribution of resources and the center of load in China are not synchronous.It is difficult to transport renewable generation resources in a long distance,and the loss is great.Due to close to load,small installed capacity,convenient control and flexible characteristics,distributed power supplies have received a lot of support and development.However,the intermittent and fluctuating characteristics of distributed renewable energy will have an enormous impact on the dispatching and operation of traditional distribution networks,when large-scale access to the power grid.Distribution network is developing from single "source" to multi "source".With the improvement of battery energy storage technology,the popularity of electric vehicles and the development of smart home,the load side can also reflect the flexible characteristics to participate in the power market scheduling.The flexible load as a crucial resource of demand response,has played a vital role to promote renewable energy consumption,to clip peak and fill valley and to improve flexible adjustment of the distribution network,is also an important part of the active distribution network's the source network load scheduling.The response characteristics of flexible load in active distribution network are studied in this paper.The flexible load of the whole network is divided into four categories:electric vehicle load,industrial load,commercial load and resident load.According to the four kinds of schedulable potential types and the way to participate in response,load models are established,and the mechanism of different load participating in the power grid dispatching is formulated.The centralized and based on load aggregator's control forms are adopted to participate in the power grid dispatching.Based on the improved IEEE33 node model,the paper considers the impact of flexible loads on the distribution of economic and renewable energy for distribution network dispatch.With the addition of transferable load,interruptible load,translatable load,and load reduction added to IEEE33 node model,an economic dispatch model is established in the premise of renewable energy consumptive maximization.In consideration of four cases:renewable energy in low permeability without flexible load;renewable energy in low permeability with flexible load;renewable energy in high permeability without flexible load;renewable energy in high permeability with flexible load.Simulation results show that flexible load participating in grid scheduling can reduce the operation cost of distribution network and promote renewable energy consumption.Considering the forecasting errors of wind power distributed generation and photovoltaic distributed generation on different time scales:the closer the time is,the higher the prediction accuracy is,a“day-ahead-day-real-time”multi-time scale scheduling strategy is proposed in this paper.Multi-time scheduling will stabilize the fluctuation of renewable energy sources and allow the grid to absorb more renewable energy.According to factors such as the flexible load's response speed,schedulable duration,and notice time when participating in the grid scheduling,the flexible load can be divided into low-quality flexible load,general flexible load and high-quality flexible load.In addition,a multi-objective optimization scheduling model for active distribution networks with flexible loads is proposed,which aims to maximize renewable energy consumption,optimize economic efficiency,minimize power line fluctuations,and minimize network losses.A multi-objective particle swarm optimization algorithm is used to solve the high-dimensional,multi-constraint mixed-integer nonlinear multi-objective optimization model,and the overall performance of the algorithm is enhanced by using dynamic step size and increasing weight coefficient,so that the solved model obtains a better Pareto frontier.The effectiveness of the proposed multi-time-scale scheduling model is verified using the improved IEEE33 node model in this paper.Getting the Pareto optimal solution set,and it proves that under the coordinated scheduling of active distribution network with multiple time scales and flexible load,the fluctuation of the equivalent load and the active power loss of the line decreases when the economic cost increases.So,the expansion pressure can be decreased,and resource utilization can be improved.At the same time,it can also guarantee the high-permeability renewable energy power generation situation,stabilize the fluctuation of renewable energy,track the scheduling of power grid dispatching plans,and ensure that the optimal scheduling is achieved within the acceptable fluctuations of the plan.