Stability Analysis And Parameter Optimization Of Variable-speed Pumped Storage AC Excitation System

With the world energy crisis becoming more and more serious,many countries begin to pay attention to renewable energy.However,with the increasing proportion of wind power,photovoltaic and other new energy in the power grid,the problems of power fluctuation,grid connected wind and light abandonment are becoming increasingly prominent.In order to suppress the power fluctuation caused by wind power and photovoltaic,it is necessary to build some energy storage power sources while increasing the transmission capacity of power grid.State Grid Corporation of China plans to build 10 conventio nal pumped storage units and 2 300 MW variable speed pumped storage units in Fengning of Zhangbei flexible DC demonstration project.In view of the power structure characteristics of Beijing Tianjin Hebei Power Grid,the urgent need for safe and stable opera tion,and the special political guarantee status,variable speed pumped storage units,as the supporting power supply of flexible direct power grid connected to AC power grid,have never had relevant research on the coordinated operation characteristics of network source,so they have become the focus of attention of all parties.In this paper,the working principle of doubly fed variable-speed pumped storage unit is described,and the mathematical models of doubly fed induction machine,phase-locked loop and frequency converter are established respectively.The working principle of PLL and the reduction of time constant are analyzed,which lays a theoretical foundation for the later linearization and small signal system modeling of variable speed pumped storage AC excitation system.Secondly,the control strategy of the rotor side converter is analyzed,and the normalized model of the inner loop control system and the motor of the rotor side converter is proposed.The mathematical model of the variable-speed pumped storage AC excitation system is linearized,and the variable-speed pumped storage AC excitation system is transformed into a current source,which acts on the power grid in the form of a voltage source through the motor effect,On this basis,the variable speed pumped storage AC excitation system of single machine infinite bus system is established.Finally,the small signal model of variable speed pumped storage AC excitation system is built on the Simulink simulation platform,and the stability of the small signal model is analyzed.The influence of the inner and outer loop parameters on the small signal stability of subsynchronous oscillation is analyzed,and the direction of parameter optimization is given.