Research On Grid Connected Control System Of High Speed Power Generation Based On Z-source Inverter

Traditional high speed permanent magnet synchronous generation grid-connected system has two kinds of topologies,one is uncontrollable rectifier and PWM inverter,the other is back-to-back dual PWM converter.The former has the problem of excessive voltage stress of switch when HSPMSG working in wide speed range,the latter has the problem of high harmonic content when rectifying high frequency current,so it is necessary to find a new topo logy to overcome these shortcomings.Z-source inverter is a low cost,high reliability topology,with unique characteristics of boost and buck,allowing the bridge arm of the inverter to shoot-through instantaneously,which can effectively overcome the sho rtcomings of traditional voltage-source inverter.Therefore,it has higher transmission efficiency and better economy,and has been widely concerned and applied since it was proposed.This paper applies it to the grid connected system of high speed permane nt magnet synchronous generation,and studies the grid connected control system of high speed permanent magnet synchronous generation based on Z-source inverter.Firstly,the working principle of the HSPMSG system is described,and the mathematical model of the HSPMSG is established,and simplified the mathematical model by coordinate transformation,at the same time,the relationship between the speed of the generator and the output voltage of the uncontrollable rectifier is obtained.The working principle of Z-source inverters is introduced in detail,the relationship between input voltage and output voltage of Z-source network and shoot-through duty ratio is deduced,on this basis,the design formula of Z-source network parameters and the network optimiza tion method to avoid Z-source network working in an abnormal state are given.Mathematical models of Z-source inverters and Z-source networks are built,and simplified by means of small signal analysis.Secondly,several modulation methods for Z-source inverter used in high-speed power generation systems are analyzed in detail.Aiming at the problems of high harmonic content,high voltage stress of switch and limited maximum modulation factor of inverters in high-speed power generation system,a detailed comparison of these modulation methods is made by building relevant simulation on MATLAB/Simulink,and a modulation strategy which is most suitable for high-speed power generation system is obtained.Finally,on the basis of the above mathematical model,in order to reduce the harmonic content of grid side current and improve the stability of Z-source network capacitance voltage,the double closed-loop control strategy of Z-source network capacitance voltage outer loop and grid side current inner loop is adop ted for Z-source inverters of high-speed power generation system,the control strategy can stabilize the grid side current and Z-source network capacitance voltage,realize unit power factor grid connected.At the same time,in order to control the speed o f HSPMSG and make it work in a wide speed range,the double closed-loop control of Z-source network output voltage peak outer loop and inductance current inner loop is adopted to control Z-source network,indirectly control the speed of HSPMSG by controlli ng the output voltage peak of Z source network.A complete grid connected control system of high-speed power generation base on Z-source inverters is established,and the validity and correctness of the control system are verified by establishing relevant simulation in MATLAB/Simulink.