级联型多电平逆变器控制策略的研究

重庆大学硕士学位论文级联型多电平逆变器控制策略的研究姓名：徐曦申请学位级别：硕士专业：电气工程指导教师：侯世英2010-05中文摘要I摘要级联型多电平逆变器通过将多个低压H桥功率单元级联的方式实现了高压领域的电能转换，同时有效降低了电压变化率，显著改善了电磁环境，在中高压调速领域、交流柔性输电系统等场合中获得了广泛的应用。作为直接决定逆变器控制效果的重要因素——多电平脉宽调制(Pulse-WidthModulation，PWM)方法，更是受到了国内外学者的广泛关注。多电平脉宽调制法可分为三角载波调制法和空间矢量调制法(SpaceVectorPulse-WidthModulation，SVPWM)两类。当前，级联型多电平逆变器的主流调制方式为三角载波调制法，它计算简单、容易实现，但由于其基于平均值理论，且直流电压利用率低、因而造成逆变器输出性能差，难以与高性能电机控制策略相融合。空间矢量调制法的直流电压利用率高、电流纹波小并且输出电压形式丰富，但计算十分复杂，且在电平数较多时难以实现实时控制，适用性受到很大限制。为此，对级联型多电平逆变器的PWM控制技术进行优化改进，必能有效提高逆变器的输出性能。论文首先讨论了级联型多电平逆变器现有的控制方式，主要包括三角载波调制法和空间矢量调制法，深入分析了这几类PWM控制方法的基本原理及各自特点。并以三电平逆变器为例，推导了三角载波调制法和空间矢量法的本质联系。随后，针对传统的三角载波PWM技术电压调制深度低、基波幅值小的问题，结合单载波调制法及梯形波调制法各自的优势，提出了基于单载波的梯形波PWM调制方式。分析了该调制法的调制原理，并在对三相三电平级联型逆变器输出线电压进行双重傅里叶分析的基础上，得出了昀佳梯形调制波的取值。将不同调制方式下三相十三电平级联型逆变器输出电压的频谱特性进行比较分析后，证实了梯形波PWM调制法的优越性。提出了基于两电平的通用多电平空间矢量调制法以解决传统算法复杂，难以实现的问题。确定了线性调制模式下参考矢量所对应的基本矢量及其作用时间；并提出了极值法对冗余开关状态进行优化选择以降低开关频率。为进一步提高逆变器直流侧电压利用率，按照JoachimHoltz的经典双模式过调制理论，将该算法的过调制模式分为两个区间，并分别进行了讨论。由给出的算法流程图可知，该算法简单易行，且复杂程度不随电平数的增加而增大，可扩展性强。仿真研究验证了该算法的正确性。昀后，论文在系统分析异步电机矢量控制的基本原理，并推导异步电机在静止坐标系和同步旋转坐标系下的数学模型后，总结出矢量控制的基本方程，同时推导出电压解耦控制方程，从而实现了电机定子电流励磁分量和转矩分量的解耦控制。并按照控制器重庆大学硕士学位论文II参数工程设计方法，对控制系统的PI调节器参数进行了设计。在此基础上，将本文提出的通用SVPWM算法用于转子磁场定向电压解耦型矢量控制系统中，并进行了仿真研究，结果表明，该算法控制下三电平级联型逆变器供电的异步电动机有效地实现了矢量控制，并且具有良好的动态和静态性能。关键词：级联型多电平逆变器，脉冲宽度调制，空间矢量调制，矢量控制英文摘要IIIABSTRACTBycascadingseverallow-voltageH-bridgepowerunits,cascadedmultilevelinverterachievesthepowerconversioninhigh-voltagefield,atthesametime,reducestherateofvoltagechangeeffectively,improvestheelectromagneticenvironmentsignificantly.SoithasbeenwidelyconcernedinapplicationssuchasmediumvoltagedriveandflexibleACtransmissionsystem.Asanimportantfactorindecidingtheeffectofinvertercontrol,multilevelpulse-widthmodulation(PWM)methodisreceivedextensiveattentionsfromscholarsathomeandabroad.Themodulationmethodcanbedividedintotriangular-carriermodulationandspacevectormodulationtypes.CascadedMultilevelInverterusuallyuseatriangular-carriermodulationmethodcurrently.Itiseasytobecomputedandimplemented.However,becauseitisbasedontheaveragetheory,andhasalowDCvoltageutilizationrate.Soitcausespoorperformanceofinverteroutput,anddifficultlymixeswithhigh-performancemotorcontrolstrategy.SpacevectormodulationhasahighDCvoltageutilizationandalowCurrentripple.Anditsoutputvoltageformisdiversiform.However,itscalculationisverycomplicated.Andwhenlevelsaremore,itisdifficulttoachievereal-timecontrol.Sothatitsapplicabilityislimited.Inthisrespect,doingoptimizingimprovementforPWMcontroltechniquesofmultlevelcascadedinverterwillbeabletoeffectivelyimproveitsoutputperformance.Firstly,thecurrentcontrolmodeofcascadedmultilevelinverterisdiscussed,mainlyincludingtriangular-carriermodulationandspacevectormodulation.Moreover,theirrespectivecharacteristicsandbasicprinciplesareanalyzed.Andtothree-levelinverterasanexample,thenaturecontactofthetriangular-carriermodulationmethodandspacevectormethodisderived.Forthisissuethatthetraditionaltriangular-carrierPWMtechniqueshasalow-voltagemodulationdepthandsmallfundamentalamplitude.Therespectiveadvantagesofsingle-carriermodulationmethodandtrapezoidalwavemodulationiscombinedtoproposeanewtypePWMcontrolmethod,whichisTrapezoidalwavePWMbasedonsingle-carrier.Anditsmodulationprincipleisanalyzed.OnthebasisofdoubleFourieranalyzingthree-phasethree-levelcascadedinverteroutputlinevoltage,thebestvaluesoftrapezoidalmodulationwaveisobtained.Analyzingthespectralcharacteristicsofthree-phase13-level重庆大学硕士学位论文IVcascadedinverteroutputvoltagewaveformunderdifferentmodulationmethod,superiorityoftrapezoidalwavePWMcontrolmethodisverified.GeneralmultilevelSVPWMbasedontwo-levelSVPWMisproposedinthispapertosolvetheproblemsthattraditionalalgorithmsbecomecomplex,anddifficulttoachieve.Thereferencevectorcorrespondingtobasicvectoranditsroletimeunderlinearmodulationmodeisdecided.Aswellasredundantswitchesareoptimizationselectedbyextremevaluemethodtoreducetheswitchingfrequency.TofurtherenhancetheutilizationofinverterDCsidevoltage,thisalgorithmwillbeextendedtoovermodulationmodeanddiscussedintworangesaccordingtotheclassicaltheorydual-modeovermodulationofJoachimHoltz.Fromthealgorithmflowchartwecanseethatthealgorithmisverysimple.Anditscomplexityisnotincreasingfollowingtheadditionoflevel.Simulationconfirmsthecorrectnessofthealgorithm.Finally,aftersystematicanalyzingthebasicprincipleofinductionmotorvectorcontrolandderivingthemathematicalmodelofasynchronousmotorunderthestationarycoordinatesystemandsynchronouslyrotatingcoordinatesystem,thebasicequationofvectorcontrolissummarized,atthesametime,voltagedecouplingcontrolequationsarederived.Sothedecouplingcontrolofmotorstatorcurrentexcitationandtorqueisachieved.Inaccordancewithengineeringdesignmethods,theparametersofPIcontrollerinthecontrolsystemisdesignedThenthegeneralSVPWMalgorithmproposedinthispaperisusedintherotor-flux-orientedcontrolofavoltage-sourceinverter-fedinductionmotordrive.Simulationshowsthegoodperformanceofthethree-levelinverterfeddrivewithvectorcontrolunderthisalgorithm.Keywords:Cascadedmultilevelinverter,Puls