Evaluation Of Pumped Storage Units For Frequency Regulation Auxiliary Service And Variable Speed Operation Performance

With the acceleration of energy structure reform and low-carbon power transformation,renewable energy has been integrated into the grid in a higher proportion.As the regulator and stabilizer of power system,the development of pumped storage faces both opportunities and challenges.Accelerating market construction of pumped storage ancillary service can promote the solution of problems such as fluctuation of power grid in the process of renewable energy absorption.The market benefit is the key to restricting the development of pumped storage industry,and it is necessary to explore the performance and benefit of frequency regulation(FR)ancillary service.Variable-speed pumped storage unit(VSPSU)has superior operation advantages,but there is no VSPSU put into operation in China,so it is urgent to explore its variable-speed operation performance.This paper aims to evaluate the FR auxiliary service and variable speed operation performance of pumped storage units,and to focus on the analysis of primary frequency regulation(PFR)and secondary frequency regulation(SFR)in auxiliary service function as well as pressure pulsation during variable speed operation,to provide reference for technical development and practical application of pumped storage.The main work of this paper is as follows:(1)Quantitative evaluation of PFR performance of fixed-speed pumped storage unit(FSPSU)is carried out,and an evaluation method reflecting PFR performance with an intuitive score is constructed based on fuzzy analytic hierarchy process(FAHP),which lays a foundation for evaluation of SFR performance and benefit of FSPSU and VSPSU in the following text.Five important evaluation indexes are selected based on the auxiliary service compensation in electricity markets in China and the USA,including average value and standard deviation of power difference,energy penalty,regulation mileage and power delay time.A refined numerical model of FSPSU is established,taking a plant in China as an example.Different types of frequency disturbance signals are inputted into the model,and the PFR performance of each scheme is evaluated by changing governor parameters(K_p,K_i,b_p,and frequency dead zone)and time constants(T_w,T_s,T_y).This work reveals the influence mechanism of governor parameters,matching rules among time constants,and frequency dead zone on dynamic response of PFR and auxiliary service performance.The results show that this method provides analysis means and intuitive reference basis for guiding multi-parameter matching problems in the system and promoting the coordination between power plants and power grids.(2)Evaluation of SFR benefit of pumped storage unit is carried out.Based on the selected FR performance indexes and proposed evaluation steps,an evaluation method is constructed to quantify the economic benefits generated by SFR,and the SFR benefit of FSPSU and VSPSU is compared.The average benefit of pumped storage plant with each MW capacity per day under the best FR response state is analyzed based on the current market research at home and abroad,and the value is determined to be(?)15.56.Taking a variable-speed pumped storage plant(VSPSP)in China as an example,the FSPSU model and the VSPSU models in power priority mode and speed priority mode are constructed.The wind power deviation signals of different distribution types are input,and the power response signals are simulated and analyzed,and the benefit values of these three models are compared.The governor parameters(K_p,K_i,K_d,b_p)of the VSPSU model in speed priority mode are optimized,and the SFR benefit value can be increased by about 65.94%.The result shows that VSPSU model in power priority mode can better meet the regulation requirements of power grid.The benefit value of SFR is the highest,(?)544,400 per day,215.16%higher than VSPSU model in speed priority mode and 398.34%higher than FSPSU model.This method is helpful to explore the benefit of SFR and provides reference for clarifying the development potential of domestic FR auxiliary service market.(3)Quantitative evaluation of pressure pulsation intensity under both fixed and variable speed operating conditions is carried out,and an evaluation method reflecting pressure pulsation intensity of VSPSU with an intuitive score is constructed.Amplitude distribution diagrams of pressure pulsation are plotted by processing model test results with fitting function,taking a real VSPSP in China as an example,including double-amplitude contour and three-dimensional surface.The total pressure during transient processes is predicted by simulation of a numerical model.Emergency shutdown conditions(change initial speed)and large-amplitude load regulation conditions(change speed command)are simulated.The influence of operating trajectory on pressure pulsation during variable speed operation is specified,and the intensity of pressure pulsation is quantitatively evaluated.The results show that with the increase of initial speed or speed command,the value of pressure pulsation increases;the trajectory passes through more high-amplitude pressure pulsation region and gradually shifts to the S-shaped region,causing the oscillation of pressure and worsening the operation safety.When speed command reduces,maximum pressure pulsation at volute inlet and draft tube can be reduced by 82.18%and 63.24%at most,and the evaluation score can be increased by 28.77%.This study could help to explore the variable speed operation characteristics and provide theoretical reference for the operation of VSPSUs.