Research On Three-phase Voltage-fed Cascaded Quasi-Z Source AC-AC Converter

In recent years,China has vigorously developed new energy power generation and UHV AC and DC transmission projects.The implementation of these projects is inseparable from the transformation of electric energy.In this environment,power electronics technology has gradually become the focus and hotspot of research in the medium and high voltage field.The traditional AC voltage regulator has the disadvantages of poor waveform quality,large filter volume,low power factor and low boosting capability,while the quasi-Z source AC-AC converter has high boosting capability,low harmonic content and high waveform quality.In this thesis,based on quasi-Z source network,a three-phase voltage-fed cascaded quasi-Z source AC-AC converter is proposed.The converter has the characteristics of high boosting capacity and low harmonic content.Firstly,this thesis analyzes the working principle of phase-controlled AC voltage regulator,chopper AC voltage regulator and traditional quasi-Z source AC-AC converter,With the combination of various voltage regulator circuit topologies,a three-phase voltage-fed cascaded quasi-Z source AC-AC converter is proposed based on the quasi-Z source network in this thesis.Compared with the traditional AC voltage regulator,the converter has the following advantages:the boosting and the buck functions can be realized at the same time by changing the duty ratio D,the boosting ratio is higher,the output waveform quality is higher,and the harmonic content is small,the circuit has soft start function,etc.The thesis then makes a detailed theoretical analysis of the working principle of the improved converter.The relationship between input and output voltage and duty cycle D is obtained by formula derivation,and the quasi-Z source network and filtering in the improved converter hardware circuit are obtained.The component parameters such as the circuit were designed and selected.Then introduces two modulation methods,complementary modulation method and non-complementary modulation method of AC voltage regulator circuit,then compares and analyzes the two modulation methods.Finally,the complementary modulation method is adopted as the improved AC-AC converter modulation method.Several control methods of AC voltage regulating circuit are briefly introduced,including current mode control,voltage mode control,non-linear control method,etc.The output voltage regulation control of the three-phase voltage-fed cascaded quasi-Z source AC-AC converter is realized by the constant frequency single-cycle control theory.The relevant formulas are theoretically deduced and calculated.Finally,modeling of three-phase voltage-fed cascaded quasi-Z source AC-AC converter by Matlab/Simulink software The correctness of the three-phase voltage-fed quasi-Z source AC-AC regulator proposed in this thesis is verified by simulation analysis.And completed the corresponding prototype physical production,through the experiment to verify the correctness of theoretical analysis and simulation analysis.