模块化多电平双PWM变频器拓扑机理与控制研究

Now the high voltage multilevel level inverter have the problems of the output voltage level is not high enough, large harmonic, and cannot realize the four quadrant operation, etc.. Thorough the research of this project, the inverter which has green power alternation and run in four quadrant is builded. The main contents are as follows: ① The back-to-back symmetry topology structure of the converter based on modular multilevel converter(MMC) is constructed. The precise static and dynatic mathematical model based on fractional-order modeling theory is established. ②By using the instantaneous power theory, the load current feed-forward control, the capacitive current inner loop control, and the coordination control strategy of rectifier and inverter are finished. The system reliability is raisied.The smooth and fast transition between power-driven and braking state is realized.The dynamic characteristic of the system is improved. .③ The sub-module voltage predict based on the rough set theory and sorting algorithm are presented. Then the balance control of sub-module voltage is achieved. The project research will provide theoretical foundation and systemic analysis method for dual-PWM high voltage converter technique. And the project research also can provide a theoretic guide for the engineering application of the presented converter.

目前高压多电平变频器存在输出电压等级不够高、网侧谐波含量较大、无法实现四象限运行等问题。通过本项目的研究，构建具有“绿色电能变换”的高压四象限运行变频器。研究内容包括：①构造基于模块化多电平变流器(MMC)的背靠背对称变频器拓扑结构，结合分数阶建模理论，建立精确的静态和动态数学模型。②采用瞬时功率理论、负载电流前馈控制和电容电流内环控制方法，研究网侧和负载侧变换器协调控制策略，实现电动状态和制动状态之间的平滑和快速过渡，提高系统可靠性和动态特性。③提出基于粗糙集理论的子模块电压预测和排序算法，实现子模块电容电压的均衡控制。本课题的研究成果，将为双PWM高压变频器技术提供理论支持，为变频器的设计和工程应用提供方法和技术指导。

模块化多电平变流器(MMC)秉承了H桥级联结构模块化的优点，弥补了诸多传统多电平变流器的缺陷，其在多电平变频器中应用具有重要的应用价值。本项目对基于MMC的双PWM变频器拓扑构建、控制策略和调制方法等进行了相关理论研究，并搭建了基于MMC的新型高压变频器半实物实验仿真平台。首先，提出了一种双PWM变频器一体化协调控制系统，在负载电流前馈的基础上，采用基于分数阶控制和电容电流反馈的协调控制技术。推导了基于开关函数的MMC数学模型，对同相层叠、正负反向层叠(POD-PWM)和交替反向层叠三种载波层叠调制方法进行了分析，通过推导其理想条件下的正弦波分量表达式，得出了可获得任意多电平载波PWM输出量的精确表达式，并对三种调制算法的输出电压进行了比较研究；经实验验证，POD-PWM调制效果最好。其次，提出了基于排序法的电容电压平衡方法，实现了MMC变流器各子模块电容电压排序的实时检测和子模块电容电压的平衡控制。采用延时叠加SVPWM调制方法，将SVPWM调制方法应用到高压多电平变频器系统中。然后，提出了一种基于静止坐标系的正负序分量计算方法——T/4延迟法，将这种方法成功地应用到电网不平衡时的三相PWM整流器控制系统中。最后，以Matlab-Simulink 及RT- Lab半实物仿真设备为实验平台，搭建了MMC变频器系统，实际的实验结果显示变流器运行正常、电容电压稳定平衡，且输出电能质量高、谐波含量小，表明了所提出的载波正负反相层叠与电压稳定平衡控制相结合的控制策略的有效性，并得出了实验条件下的最佳三角载波频率；T/4延迟法能够有效的抑制直流母线电压波动和交流侧电流谐波，保证网侧高功率因数和输入电流正弦化。