Study Of Aggregated Flexibility Evaluation Methods For Flexible Loads In Distribution Networks

With the reform of the power supply structure of the power system,the penetration rate of new energy sources such as wind power in the power system is increasing,and its randomness and volatility bring serious challenges to the supply and demand balance of the power system.At the same time,the proportion of traditional regulating units such as thermal units is decreasing,and the regulating resources of the power system are becoming more and more scarce,so it is urgent to find new flexible resources.Compared with traditional loads,there are many controllable loads in the distribution network that can actively adjust their own power consumption behavior according to incentives,which are often called flexible loads.These flexible loads can change the electricity consumption within a certain range and have higher controllability compared with traditional loads,and can participate in peak and valley reduction,renewable energy fluctuations,and auxiliary services of the power grid,which is an important supplement to the regulation capacity of the power system.Before regulating the flexible load,it is necessary to know the range of adjustable capacity of the flexible load.In this paper,we first take the typical load of flexible load-flexible load as the research object and propose a method to construct the flexibility of thermostatic controlled loads into a virtual battery model.This chapter proposes an enhanced sufficient battery model for describing the aggregation flexibility of temperature-controlled load clusters by modifying the in-approximation and out-approximation models based on the aggregation flexibility of thermostatic controlled loads.Compared with the previous model,the enhanced sufficient battery model proposed in this paper further narrows the gap between the in-approximation and out-approximation models of aggregation flexibility and can avoid over-conservatism of the model while retaining the advantage of sufficiency.In addition,the present method adequately considers multiple coupling constraints that may significantly limit the aggregation flexibility of thermostatic controlled loads,and ignoring these coupling constraints will lead to erroneous results.Simulation results show that the method proposed in this paper is a significant improvement over the internal approximation model and can more accurately describe the dispatchable flexibility of thermostatic controlled loads clusters.The evaluation method is then extended to multiple types of flexible loads,and a robust evaluation method of aggregation flexibility with multiple time granularities including intraday rolling time windows-dispatch period-minute level is proposed.The evaluation framework with multiple temporal granularities is described,and a robust evaluation model for maximizing aggregation flexibility over multiple time periods is constructed by considering the effects of power network congestion,load operating states changing during the dispatch cycle,and time delay response.An iterative solution strategy based on nested columns and constraint generation algorithms is designed for the binary variables present in this problem.The proposed method is verified to be more accurate in evaluating the aggregation flexibility of flexible loads than the existing common methods,and the necessity of considering the power network constraints when evaluating the aggregation flexibility is verified through the analysis of arithmetic cases.In order to evaluate the effect of flexible load participation in grid dispatch,a rolling robust economic dispatch method applicable to flexible load participation is proposed.A two-stage robust rolling economic dispatch model is developed,in which the first stage considers only the state at the current moment,while the second stage considers the fluctuations of wind power generation,load demand,and flexible load in the future period,and is optimized with the objective of worst-case economic optimality for the system in the entire rolling time domain.The two-stage problem is solved based on a heuristic C&CG algorithm.Simulations are performed to analyze the effect of flexible load participation in economic dispatch on enhancing wind power consumption under different evaluation methods.Finally,the paper is summarized and analyzed,and the shortcomings and further research directions of this paper are discussed.