SVPWM Algorithm And Voltage Balance Boundary Of Single-phase Multi-level Cascaded H-bridge Converter

The power electronic traction transformer without power frequency transformer has a modular circuit structure,and the existing modulation method of its front cascade rectifier is more complicated and difficult to apply.In this thesis,to solve the problem of DC-link voltage imbalance in the single-phase three-level H-bridge cascaded rectifier part of the power electronic traction transformer system,a single-phase one-dimensional space vector pulse width modulation(SVPWM)voltage equalization algorithm and its voltag eequalization boundary are studied.Firstly,the minimum energy characteristics of the single-phase cascaded rectifier is analyzed,that is,after the total DC-link voltage is determined,if the dc-link voltages of all modules are balanced,the system energy can reach the minimum level.By combining the minimum energy characteristics and the working principle of the single-phase cascaded rectifier,the optimal redundant vectors for voltage equalization SVPWM algorithm is derived.And then after analyzing the implementation of the voltage balancing strategy in the twomodule and three-module cascade rectifier in details,the unified implementations trategy of the single-phase one-dimensional voltage equalization SVPWM algorithm in the single-phase multi-module cascaded rectifier is established.The unified implementation strategy of the proposed voltage balancing algorithm only requires sorting,a small amount of logic cell,addition and subtraction cell,therefor,the algorithm is fast and can be extended to cascaded rectifiers with arbitrary number of modules.Secondly,according to the voltage balancing essence of the proposed voltage balancing SVPWM algorithm,the vector analysis method is used to quantitatively analyze the voltage balancing boundary for the proposed SVPWM voltage balancing algorithm.When the proposed voltage balancing algorithm is applied and run stably on the cascaded rectifier,the function relationship between the no-load module number limit and degree of balance limit with the number of cascaded modules,modulation index,and power factor can be obtained.The proposed voltage balancing boundary function provides a reference for parameter design of single-phase cascaded rectifiersFinally,based on Matlab / Simulink,the simulation verification of two-module,threemodule and six-module single-phase cascaded rectifiers is completed respectively.At the same time,the small capacity experimental platform of two-module and three-module single-phase cascaded converter based on FPGA controller and the voltage-sharing SVPWM algorithm program based on VerilogHDL are designed Then on this cascaded converter small capacity experimental platform,the inverter experiment,rectifier experiment and the verification of the voltage balancing boundary experiments of proposed voltage balancing SVPWM algorithm are completed respectively.The simulation and experimental results validates the correctness and effectiveness of the proposed voltage balancing SVPWM algorithm and the voltage balancing boundary in this thesis.