| Pumped storage is a green,low-carbon,clean and flexible regulating power supply of the power system with the most mature technology,the best economy and the most large-scale drevelopment conditions.It is an important support for the safe and stable operation of the new power system and an important guarantee for the large-scale development of renewable energy.Variable speed technology can further improve pumped storage units’ peak regulation and frequency regulation capability,but its technology is monopolized by foreign countries.It is still in its initial stage in China.The development of large variable speed pumped storage units（VSPSUs）has been listed as 10 major industrial technical problems at the 24th Annual Conference of the Chinese Association of Science and Technology in 2022.Variable speed technology has fundamentally changed the structure of regulation system of the pumped storage unit and brought a series of new problems,such as optimization of operation efficiency,imperfect analysis of regulation system model and stability,influence of hump area after variable speed operation of pump condition,etc.Therefore,this paper takes the doubly-fed variable speed pumped storage unit（DVSPSU）as the research object,deeply probes into the key scientific problems such as efficiency optimization method,electromechanical transient modeling,small fluctuations stability,hump area stability and improvement method,and studies the application of DVSPSU in suppressing wind power fluctuation over shout-time scale.The specific research work is as follows:（1）In view of the problem that the efficiency optimization method for VSPSUs under pump mode is incomplete,an optimization method（Method 1）based on the complete characteristic curves of pump turbine and the test data of pump operating efficiency is put forward from the optimizing principle and raw data.The process of this method is clear but the steps are complicated.For this reason,an optimization method（Method 2）based on the pump on-cam curves is put forward,which is simple and efficient,and its effectiveness is verified by the Method 1.At the same time,the efficiency optimization method under turbine mode is improved,and an optimization method based on the complete characteristic curves of pump turbine is proposed.This method has fewer interpolation times,which effectively improves the optimization efficiency and can cover all operating conditions under turbine mode.（2）Aiming at the problems that the common transient process models of DVSPSU are not conducive to the study of dynamic process of pump turbine regulating system,the electromechanical transient model of DVSPSU is established,which is suitable for the study of pump turbine regulating system.The model simplifies the electromagnetic transient and reactive power related parts in converter,DC bus,doubly-fed induction generator（DFIG）,and vector control.The number of formulas for DFIG and its control systems has been reduced from 24 to 6 and the simulation step size from 5×10-6s up to 1×10-3 s,greatly reducing the complexity of the model and calculation time.The electromechanical transient model is validated by numerical simulation.The results show that the electromechanical transient model not only accurately reflects the electromechanical dynamic characteristics of the system,but also greatly saves the calculation cost.（3）Aiming at the incomplete analysis of small fluctuations stability of double-fed variable speed pump turbine regulating system,the regulating system is analyzed by using high-order Hopf bifurcation theory,and the stability region of speed regulation system under turbine and pump mode and the influence rule of power controller adjustment parameters are obtained.The results show that the stability region of speed regulation system under pump mode is much larger than that under turbine mode.The regulation parameters of power controller have no influence on the stability region of speed regulation system under turbine mode but have a greater influence on that under pump mode,and the reasons for this result are pointed out.（4）Countering the problem of unstable operation of VSPSU in the hump area,the unstable mechanism is revealed and a correction method of on-cam curves based on operation safety margin is proposed.The relationship between the optimum efficiency point of pump mode and the hump area is analyzed,and a non-linear model of pump-turbine reflecting the characteristics of the hump area is established,the mechanism of operation instability in the hump area is revealed by analyzing the trace of transition the process,and a method of setting operation safety margin to modify the on-cam curves before efficiency optimization is put forward,so as to avoid the operation in the hump area.Compared with the method of setting hump limit line,the method greatly increases the adjustment range of the unit under pump mode.（5）Based on the researches above,the DVSPSU is used to suppress wind power fluctuation over short-time scale.According to the operating characteristics of the unit,the power stabilization strategies for turbine mode and pump mode are designed respectively.The simulation results show that the DVSPSU can use rotor inertia to release or absorb active power quickly to realize fast regulation of unit power,thus effectively suppressing wind power fluctuation over short-time scale.The power fluctuation of the system under turbine mode is reduced from 7.96%to 0.13%,and the power fluctuation of the system under pump mode is reduced from 7.96%to 0.37%. |
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