Research On Dispatch Of Power System Considering Large-scale Electrochemical Energy Storage Participating In Dual Ancillary Services

With the high proportion of renewable energy sources connected to the grid and the rapid development of ultra-high voltage transmission technology,the peak-to-valley difference of equivalent load of power system has increased,and the risk of low-frequency caused by major power deficit also increases steeply.Conventional thermal power units in traditional power grids have frequency response capability and undertake the main task of peak shaving.However,wind and optical power generation with the characteristic of anti-peak shaving occupy the grid-connected space of conventional thermal power units in the power grid with high proportion of renewable energy,resulting in the frequency response capability and peak shaving capability of power system is continuous weakened.Following which,in the power system,the pressure of peak shaving is rising and the frequency response posture is increasingly grave,so the power grid urgently needs to increase the flexibility of regulation resources and regulation capacity.Electrochemical energy storage is a high quality regulation resource with flexibility.In particular,large-scale electrochemical energy storage,which has advantages of both power and capacity,should be involved in multiple ancillary services at the same time to give full play to its regulation and protection roles on the grid side as well as its supporting role for the construction of new power system.In view of the above problems,this paper carried out the establishment,simplification and calculation of the day-ahead joint optimization model of the dispatch considering large-scale electrochemical energy storage participating in dual ancillary services of peak shaving and frequency response,and realized the comprehensive coordination of dual ancillary services output between large-scale electrochemical energy storage and conventional thermal power units at the same time.Based on the deep understanding of the difference between the output characteristics of conventional thermal power units and large-scale electrochemical energy storage,as well as the difference between the time scale of dual ancillary services of peak shaving and frequency response,the principle of joint optimization dispatch is designed for thermal power units and large-scale electrochemical energy storage participating in dual ancillary services of peak shaving and frequency response at the same time.Then,the joint optimization model is established with the objective of ’’taking into account the economy of system operation under the premise of ensuring the frequency safety of system’’,with various factors such as the cost of deep peak shaving of units,the cost of calling energy storage and the punishment cost of wind curtailment are considered comprehensively,while taking the safety constraint of system frequency into account,also considering the characteristics of large-scale electrochemical energy storage such as the fast adjustment speed,large adjustment capacity and the output affected by the state of charge.In view of the problem that the constraints related to frequency response in the model involve many control parameters and decision variables,in order to reduce the calculation difficulty,the influences of three control parameters on the overall frequency response ability of the system are analyzed with the help of analytical calculation and simulation analysis,and a practical frequency response control strategy of energy storage with only virtual droop control is proposed.Accordingly,the joint optimization model is simplified.For the solution of the nonlinear mixed integer programming problem with differential equations,the original problem is decomposed into the main-problem for linear unit commitment and the sub-problem for differential calculation of frequency nadir by using the two-stage iterative idea,and the solution of the joint optimization model is realized while retaining the application of CPLEX solver to supplement the calculation,which takes into account the efficiency and accuracy of the solution.Three schemes are used to conduct the day-ahead joint optimization dispatch considering large-scale electrochemical energy storage participating in dual ancillary services at the same time for 10 types of wind power scenarios obtained by clustering.The results show that the participation of large-scale electrochemical energy storage in dual ancillary services at the same time can not only effectively improve the peak shaving and frequency response ability of the system,but also make full use of its resources,and comprehensively improve the security and economy of the system operation.The results of this paper also provide reference for the subsequent researches on large-scale electrochemical energy storage participating in ancillary services dispatch on the grid side.