| In recent years,the state has paid more and more attention to the utilization of renewable energy,at the same time,the demand for the quality of electricity and the demand for the supply of electrical energy are increasing gradually.Therefore,it is necessary to consider the problems of power quality such as transmission line loss,system reactive power shortage,power frequency overvoltage,operation overvoltage and so on in the construction of Extra-High Voltage(EHV)and Ultra-High Voltage(UHV)transmission lines.This requires that a large number of reactive power sources with fast response are installed on the system to maintain reactive power flow balance,reduce losses and improve power supply reliability.The MCR(Magnetically Controlled Reactor)is a static reactive power compensation equipment to maintain the voltage stability of the transmission line.It is showed that the winding structure of MCR is closely related to the transition time from empty load to full load and from full load to empty load.To achieve the dual functions of limiting overvoltage and compensating reactive power,this thesis proposes a new type of self-excited MCR.Then through mathematical modeling,MATLAB simulation,prototype experiment to provide theoretical guidance and further performance of MCR.Secondly,by building the simulation model of 500 k V EHV transmission line in MATLAB/Simulink,the limitation of MCR on different kinds of overvoltage in power system is studied.It turns out to be the case that MCR can play a good role in both limiting power frequency overvoltage and operation overvoltage.Finally,by designing the hardware circuit and writing the software program,a MCR control system is completed.The specific contents of this study are as follows:(1)Firstly,the influence of different winding structures on the response speed of MCR is analyzed qualitatively,and a new self-excited MCR is proposed.Later,based on multi-winding transformer model,the response speed of the traditional self-excited MCR and new type self-excited MCR are compared in MATLAB/Simulink.Finally,the correctness of the theoretical analysis and simulation experiment is verified by the experiment on the prototype.(2)Secondly,a 500 k V EHV long-distance transmission line model,an MCR model based on equivalent circuit,a typical PI control system model are built in MATLAB/Simulink,the control of power frequency overvoltage by MCR during heavy and light load switching of EHV long distance transmission lines is studied.Then,the operation overvoltage of 500 k V EHV long-distance transmission line during no-load closing and circuit breaker reclosing are simulated.The over-voltage waveforms with and without MCR and MCR working current waveforms are given respectively.The result proves that MCR can not only control the power frequency overvoltage well,but also have a significant limitation on the operation overvoltage.(3)At last,a hardware of MCR control system based on DSP is finished and various schematics of peripheral circuits are designed,such as signal acquisition circuits,signal conditioning circuits,level conversion circuits,device protection circuits,pulse drive circuits and so on.Then the design,manufacture and test of PCB board are completed.Afterwards,the DSP software program in the main control board is completed,including the acquisition of voltage,current,frequency,zero crossing and other electrical parameters,the calculation of other electrical parameters and trigger angles,the communication between upper and lower computers,failure detection and alarm function.Then open loop control,closed-loop control and multi parameter mode control are achieved.Finally,a touch-screen PC interface for monitoring is designed and open-loop and closed-loop experiments are performed on the MCR prototype to verify the availability of the control system. |
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