Research On Wide Frequency Domain Modeling Of Cascaded H-Bridge Converter

In recent years,with the rapid development of semiconductor technology and modern control technology,power electronic converters have been widely used.The power levels of power electronic equipments are gradually increasing.The traditional average model can only analyze the low-frequency characteristics of the system,but it cannot analyze the characteristics of the system at the switching frequency and above.Therefore,it is necessary to find a mathematical model that can describe the full-band characteristics of power electronic converter.In this paper,the cascaded H-bridge converter is taken as the research object,and the wide frequency domain model of the converter is studied.Firstly,the topology and working principle of the H-bridge converter are introduced,and the conditions of the cascade of H-bridge converters are analyzed.After that,the structure and characteristics of the cascaded H-bridge inverter are analyzed,and the expression of output voltage is derived.Based on the average method,the average model of H-bridge inverter is established.Its voltage and current control strategies are introduced.Secondly,commonly used modeling methods are introduced.The advantages and disadvantages of these methods are compared.Starting with the Buck converter with simple structure,the sampling model of the PWM comparator is established.The matrix model and the output impedance model of the Buck converter are derived.For more complex H-bridge converters,the analogy method is first used to establish the sampling model of the PWM comparator.After that,the matrix model of the H-bridge converter is derived.The MATLAB / Simulink simulation is used to verify the established model.Thirdly,the modulation strategies of the multilevel converters are introduced,including carrier phase shifting technology,carrier stacking technology and space vector pulse width modulation technology.The advantages and disadvantages of natural sampling method and regular sampling method are introduced.Based on the matrix model of H-bridge,the mathematical model of the single-phase five-level cascaded H-bridge is derived and then the model is extended to the case of N H-bridge cascades.After that,the model of the three-phase five-level cascaded H-bridge converter is derived.The characteristics of its output voltage are analyzed,and then the theoretical analysis is verified.Finally,the experimental platform of the five-level cascaded H-bridge inverter is built.The structure and composition of the experimental platform are introduced.The platform is described from both software and hardware aspects.The experimental results prove that the wide frequency domain model established in this paper has certain accuracy.The paper has 72 pictures,7 tables,and 113 references.