Study On Dynamic Performance Of Pump Working Conditions Of Variable Speed Pump Storage Units

With the large-scale integration of wind power,photovoltaic and other renewable energy into the large power grid,the stability of the power grid has been greatly affected.Peak shaving and frequency regula,tion of pumped storage units in the power grid is particularly important.The operation mode of conventional pumped storage units is usually peak load generatio.n and low load pumping.When the units are operating under pump conditions,they can only start and shut down the whole unit.The input power of the units can not be continuously changed,and the input power of the units can not be continuously adjusted according to the demand of the power grid.Variable-speed pumped storage unit can change the input power of the unit by changing the speed according to the frequency change of the power grid,and then adjust the frequen cy of the power grid,which can increase the frequency control resources of the power grid.Therefore,this paper studies the operating characteristics of pumps of reversible variable speed pumped storage units,mainly completing the following aspects:(1)Modeling.AC excitation motor is used as generator/motor of pumped storage unit to realize variable speed operation of pumped storage unit under pump operation condition.Based on the analysis and summary of the mathematical models of diversion system,electro-hydraulic servo system,pump turbine,AC excitation motor,converter and its control mode,power regulator and frequency regulator,the mathematical model of variable speed pumped storage unit is established.(2)Study on power response of unit under pump condition.Through the excitation system to regulate the speed of the unit,the input power of the pump can be continuously adjusted within the allowable range of load.The power response of the pump is studied by simulating the step disturbance at the given end of the power command.Because the power response index of pumping units is not stipulated in the relevant criteria of power grid operation,the simulation results are analyzed by referring to the AGC operation index of other grid-connected units.The results show that the adjusting speed of the pump power response of variable speed pumped storage units is much faster than the prescribed requirements,and the response time and steady-state error are much smaller than the prescribed requirements(3)Participating in the primary frequency modulation capability research under pump condition.In this paper,the frequency response control method with PI link is adopted,and the open-loop characteristic simulation test is carried out by the step disturbance of input frequency sudden increase and decrease at the given frequency end,and the primary frequency modulation characteristic of pump operation is studied.Because the primary frequency regulation index of pumping unit is not stipulated in the relevant criteria,the simulation results are analyzed by referring to the primary frequency regulation index of hydroelectric unit.The results show that the variable speed pumped storage unit can not only participate in primary frequency regulation,but also the primary frequency regulation indexes are better than those of hydroelectric unit.