Research On Low Voltage Ride Through Control Strategy Of Variable Speed Pumped Storage Generation-Motor Unit

With the development of high-power devices and modern control technology,the technology of DVSPSGM(Doubly-Fed Variable Speed Pumped Storage GenerationMotor)to realize continuous variable speed operation of large-capacity pumped storage units has attracted more and more attention.However,as its capacity continues to expand,when the grid voltage drops,the unit is disconnected from the grid,which will cause greater disturbances in the subsequent power system.LVRT(Low Voltage Ride Through)capability has gradually become an inevitable requirement of DVSPSGM,that is,within a certain voltage drop range,the unit is required to operate continuously without off-grid,and at the same time,reactive power is issued to support voltage recovery.This paper focuses on the related issues of DVSPSGM low voltage ride through.Aiming at the complex modeling problem of DVSPSGM under multi-control objectives and multi-system coupling,the mathematical models of hydraulic,mechanical and electrical parts are established respectively,and the control strategies and control parameters of each part are determined.Then,the correctness and dynamic performance of the control model are verified by the simulation of the dynamic response ability of the system.The grid voltage sag will excite a series of electromagnetic transient and energy conversion processes inside the unit.In order to provide the design basis of LVRT strategy,the transient characteristics of EMF(Electromotive Force)and energy flow under different operating conditions of electric and power generation are analyzed.In order to offset the EMF to the maximum extent to meet the rotor voltage and current constraints while accelerating the stator flux attenuation,a virtual inductance control strategy based on software optimization is proposed.In order to break through the limitation of typical hardware topology,a cooperative control strategy combining hardware and software is proposed.The strategy adds a bidirectional DC/DC +supercapacitor hardware branch on the DC side of the unit,and cooperates with the software control of RSC virtual inductance and GSC reactive power priority to improve the LVRT capability and energy utilization of the unit during severe voltage drop.From the different dimensions of DC-link voltage,rotor side voltage and current,electromagnetic torque stability,the simulation results show that compared with the stator current feedback control method and the demagnetization control method,the proposed method can better maintain the DC-link voltage and improve the energy recovery rate,while meeting the system ’s demand for reactive power,so as to more effectively solve LVRT-related problems when the voltage drops seriously.According to the principle of proportional reduction,the experimental platform is built,and Lab VIEW is used to centrally monitor and manage the pumping storage system platform to realize the system process control,as well as the control,data acquisition,analysis,storage,display and other functions of various instruments in the system.Through experimental verification,the rationality of the platform construction and the effectiveness and applicability of the proposed control strategy are proved.