Countercurrent Phenomenon Of Pump Condition In Variable Speed Pumped Storage Unit And Its Suppression Strategy

At present,the research of variable speed pumped storage technology is the hot spot in the industry,and has been listed by the China Association for Science and Technology as one of the "10 major industrial technology problems in 2022".Compared with the conventional fixed-speed pumped-storage unit,doubledfed variable speed pumped-storage unit has the advantage of adjustable speed under pump conditions,which can realize continuous change of input power.However,when the unit is running at variable speed under pump condition,there may be countercurrent phenomenon,which threatens the safe and stable operation of the unit.Therefore,this paper takes doubledfed variable speed pumped storage unit as the research object,explores the occurrence mechanism of countercurrent phenomenon in pump working conditions and puts forward corresponding suppression strategies.Specific research work is as follows:(1)This dissertation has established the electromechanical transient model of pump condition in doubled-fed variable speed pumped storage unit.The full characteristic curve of the pump turbine is supplemented by the experimental data of pump efficiency and the nonlinear model of the pump turbine is established by logarithmic projection method.Combined with the optimization method considering the operating safety margin,the optimal speed and optimal opening generator of the pump is established.Combining the electromechanical transient model of doubly-fed motor control system,pump turbine control system model and elastic water hammer model,the electromechanical transient model of variable speed pump is established.Finally,the electromechanical transient model is verified by numerical simulation.(2)This dissertation has revealed the mechanism of countercurrent phenomenon.Through the sensitivity analysis of input power change,guide vane change rate and speed controller parameters,the influencing factors and mechanism of countercurrent phenomenon were revealed.The results show that the premise of countercurrent phenomenon is that the input power of the variable speed unit decreases rapidly and greatly,and the main reason is that the change of speed and opening does not match.The larger the variation range of input power is,the faster the rate is,the slower the closing rate of guide vane is,the smaller the initial operating point opening is,and the more likely the countercurrent phenomenon will occur.(3)This dissertation has proposed two suppression strategies for countercurrent phenomena.The suppression strategy proposed by limiting the change rate of the incoming force is simple and clear,but it will reduce the unit’s rapidness.Therefore,the suppression strategy of improving the optimal speed generator by replacing the reference value of the incoming force with the real-time opening is proposed.The simulation shows that the control strategy makes the unit closer to the optimal operating curve in the transient process,and effectively inhibits the occurrence of counter-current phenomenon while ensuring the rapidness.It is conducive to the safe and stable operation of the new power system.