级联三相桥并网逆变器的调制策略研究

发布时间：2018-04-08 20:10

本文选题：多电平　切入点：级联三相桥　出处：《重庆大学》2014年硕士论文

【摘要】：级联多电平逆变器已成为电力电子技术领域的研究热点之一，它广泛应用于新能源发电并网系统、高压直流输电、大容量电机驱动等场合。目前应用较为广泛的是以单个H桥逆变器为基本单元构成的级联H桥(Cascaded H-Bridge, CHB)多电平逆变器，其调制策略及控制方法的研究已经比较成熟。近年来，有学者提出了一种以三相桥为基本单元构成的级联三相桥多电平逆变器，与级联H桥逆变器相比，它更加适合三相大功率场合以及新能源发电并网系统。本文以级联三相桥多电平逆变器为研究对象，对其调制策略、控制方法及并网技术等方面进行了研究。首先建立了级联三相桥多电平逆变器的数学模型，从数学角度分析了其级联关系及控制方式，并分析了二级级联结构的电压、电流及功率等电量关系，，同时分别研究了逆变器二级级联结构和耦合变压器结构的电压、电流矢量图及电压空间矢量描述，并且对后者更多级的扩展方式进行了分析研究。本文在载波相移PWM(Carrier Phase-shifted PWM, CPS-PWM)调制策略的基础上，提出一种新的调制方法——载波相移分配PWM （Carrier Phase-shifted-distributed PWM,CPSD-PWM）调制策略，并推导出不同调制策略下逆变器交流侧输出的线电压谐波数学表达式。研究表明，CPSD-PWM的本质是在线电压的各次谐波分量表达式中加入了数学因子ejm。然后，研究了基于LCL滤波器结构的级联三相桥逆变器的并网控制策略，给出了连接逆变器模块的抑流电感的折算方法，并建立了并网逆变器等效电路模型。通过仿真验证了级联三相桥多电平逆变器二级级联结构和耦合变压器结构的并网控制策略，表明了新调制策略的正确性。同时，通过对比两者的仿真结果，得出各模块交流侧输出电流的负序分量是影响其直流母线电压波动的原因之一。最后，搭建了级联三相桥逆变器实验平台，通过升压模块构造了三组独立的直流母线，采用DSP和FPGA数字控制器实现了CPSD-PWM调制策略，实验结果证实了新调制策略的正确性。综上，本文对级联三相桥多电平逆变器的数学模型、拓扑扩展、调制策略及并网控制方法等方面进行了详细的分析和研究，并通过仿真和实验验证了理论分析的正确性。
[Abstract]:Cascaded multilevel inverter has become one of the research hotspots in the field of power electronics. It is widely used in new energy generation grid connection system, high voltage direct current transmission, large capacity motor drive and so on.At present, the cascade H-bridge Cascaded H-Bridge( CHB) multilevel inverter, which is composed of a single H-bridge inverter as its basic unit, has been widely used. Its modulation strategy and control methods have been well studied.In recent years, some scholars have proposed a cascaded three-phase bridge multilevel inverter with three-phase bridge as the basic unit. Compared with the cascaded H-bridge inverter, it is more suitable for three-phase high-power occasions and new energy generation grid-connected system.In this paper, the modulation strategy, control method and grid-connected technology of cascaded three-phase bridge multilevel inverter are studied.Firstly, the mathematical model of cascaded three-phase bridge multilevel inverter is established, the cascade relation and control mode are analyzed from the point of view of mathematics, and the relationship between voltage, current and power of two-stage cascade structure is analyzed.At the same time, the voltage, current vector diagram and voltage space vector description of the two-stage cascade structure and the coupling transformer structure of the inverter are studied respectively, and the more multistage expansion mode of the latter is analyzed and studied.Based on the carrier phase shift PWM(Carrier Phase-shifted PWM (CPS-PWM) modulation strategy, a new modulation method, the carrier phase shift assignment (PWM) carrier Phase-shifted-distributed PWM (CPSD-PWM) modulation strategy, is proposed in this paper.The mathematical expressions of linear voltage harmonics of AC side output of inverter with different modulation strategies are derived.It is shown that the essence of CPSD-PWM is to add the mathematical factor ejm. into the expressions of each harmonic component of the on-line voltage.Then, the grid-connected control strategy of cascaded three-phase bridge inverter based on LCL filter structure is studied, the conversion method of current suppression inductance connected with inverter module is given, and the equivalent circuit model of grid-connected inverter is established.The grid-connected control strategy of cascaded three-phase bridge multilevel inverter with two-stage cascade structure and coupled transformer structure is verified by simulation, and the correctness of the new modulation strategy is demonstrated.At the same time, by comparing the simulation results, it is concluded that the negative sequence component of the output current of the AC side of each module is one of the reasons that affect the voltage fluctuation of the DC bus.Finally, the experimental platform of cascaded three-phase bridge inverter is set up, three groups of independent DC bus are constructed through the boost module, and the CPSD-PWM modulation strategy is realized by using DSP and FPGA digital controller. The experimental results prove the correctness of the new modulation strategy.In summary, the mathematical model, topology extension, modulation strategy and grid-connected control method of cascaded three-phase bridge multilevel inverter are analyzed and studied in detail, and the correctness of the theoretical analysis is verified by simulation and experiment.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464

【参考文献】