Mathematical Model And Dynamic Regulation Characteristics Of Doubly-fed Variable Speed Pumped Storage Unit

In order to achieve the goal of carbon peaking and carbon neutrality,China is currently accelerating the transformation of energy structure and the construction of new power systems,and pumped storage faces unprecedented development opportunities.Variable speed pumped storage unit(VSPSU)has the advantages of flexibility,rapidity,and efficiency,and it is a new orientation of the pumped storage industry."How to develop large-scale VSPSUs" was selected into the "Ten Industrial Technology Issues" in the field of science and technology in 2022 released by the China Association for Science and Technology.However,there is no VSPSU currently in operation in China,and there is little research on the mathematical modeling and control strategy of VSPSU.Hence,relevant research on VSPSU needs to be carried out.Doubly-fed induction machine(DFIM)is currently the most commonly used technology for VSPSU.It can achieve continuous variable speed operation,expand the operating range,and improve unit efficiency.In this thesis,a mathematical model of a variable speed pumped storage plant(VSPSP)using DFIM is established,and the numerical simulation under typical transient processes is carried out.The main contents of this thesis are as follows:1.The mathematical model of(VSPSP)is established,and different modules of VSPSP are developed on MATLAB/Simulink.The VSPSP model can be conveniently built through the combination of these modules,which greatly simplifies the modeling process.Three constraints of the speed variation of the VSPSU are proposed,and these constraints are applied in the numerical simulation of this thesis.The simulation of the VSPSP model is compared with onsite measurements and other simulation software,and the comparison results show good consistency,which verifies the accuracy of the VSPSP model.The VSPSP model established in this thesis can also provide technical support for the design and operation of VSPSPs in China.2.The dynamic characteristics of VSPSU under small disturbances are studied.In this paper,numerical simulation of VSPSU under fast power control strategy and fast speed control strategy is carried out.For the fast power control strategy,the unit can achieve a fast and stable power response,but the speed may fluctuate,which is mainly influenced by the governor.To avoid speed exceeding the allowable range,the speed pulling-back control(SPBC)is taken into consideration,but the SPBC could also cause fluctuations of the active power of the VSPSU,and sensitivity analysis of the SPBC is conducted.For the fast speed control strategy,the unit speed can achieve a fast and stable response,but the active power takes longer to stabilize to the power command,and the stabilization time is mainly affected by the governor.Through the quantitative comparison of these two control strategies,it can be concluded that the response speed and stability of active power under the fast power control strategy are much better than the fast speed control strategy.Therefore,the fast power control strategy will be mainly discussed in the following simulation research of this thesis.3.The dynamic characteristics of VSPSU under large disturbances are studied.For the load rejection condition,although the VSPSU operating at the super-synchronous speed could achieve higher efficiency,the indicators of the transient process are slightly worse than the situation when the VSPSU operates at the sub-synchronous speed,but the indicators are still within the allowable control standards.For large-scale load adjustment,not only can adjusting the speed command improve the efficiency of the VSPSU at different power commands,but it can also improve the rapidity of active power response and avoid oscillation in the S-shaped region.However,there is a certain paradox between the rapidity and the safety of the VSPSU,and the speed command needs to be further determined after comprehensively considering the balance between rapidity and safety.4.The dynamic characteristics of VSPSU under hydraulic disturbances are studied.Compared with the conventional fixed-speed unit,the VSPSU under the fast power control strategy has better anti-interference characteristics.However,due to the effect of the SPBC,the VSPSU still faces active power fluctuation.Two typical factors that affect the active power fluctuation of the VSPSU are analyzed.The results show that the problem of active power fluctuation cannot be solved by prolonging the closing time of the guide vane of the disturbing unit or optimizing the governor parameters of the disturbed unit.For this reason,a useful countermeasure,adjusting the speed command of the disturbed unit,is proposed to eliminate active power fluctuations.After adjusting the speed command of the disturbed VSPSU,it can achieve stable active power output even under hydraulic disturbances.