由于PWM变换器具有功率因数高、可同时实现变频变压及抑制谐波的特点，因此在交流传动及其它能量转换系统中得到广泛应用。最常用的一种PWM技术SPWM，这种PWM的脉冲宽度按正弦规律变化，可以有效的抑制低次谐波，使电机工作在近似正弦的交变电压下，转矩脉冲小，大大的扩展了交流电机的调速范围。 本文在阐述并分析了单元串联中压变频器两种载波移相PWM调制方法（水平移相和垂直移相）的基础上，分析了它们的优缺点。它们虽然能输出多电平电压波形，波形接近于正弦波，且能够减少谐波污染，降低对电网和电机的冲击，但却存在各自的缺点：（1）垂直移相：当调制度较小时，单元间出力不同，还需要动态分配各功率单元的输出功率；（2）水平移相：当三角波之间的距离非常远时，采样精度大大降低，达不到要求。本文正是基于上述缺点，在着力解决水平移相和垂直移相PWM的缺点的基础上，提出了基于CPLD的矢量旋转法产生多路SPWM的理论，该方法不但继承了水平移相和垂直移相的优点，而且具有运算简便、输出波形完美，系统响应速度快、可靠性强等优点。 本文主要论述了以下几方面内容： （1）详细阐述了单元串联中压变频器两种载波移相的PWM调制方法，分析了各自的优劣，并对载波水平移相和垂直移相PWM调制进行了仿真，分析了在不同调制度下的输出波形。仿真和系统实验表明，载波水平移相和垂直水平移相PWM调制可以提高等效开关频率，使输出波形电平数增加，减小谐波，改善输出波形。但是由于有各自的缺点，所以本文提出了采用矢量旋转法解决中压变频器多路SPWM的产生方法，并给出了详细的理论分析。 （2）采用光纤通信，能很好的解决光电隔离，并提高了系统的抗干扰能力。在信号传输中减少了误码率，提高了信号传输的准确率。 （3）系统中采用了CPLD芯片进行系统设计，并采用了VHDL语言进行了编程。CPLD的强大功能使其能很好的把主控芯片（DSP）计算出的脉宽准确的分配到系统内部各单元控制器中，叠加出系统所需要的接近于正弦的波形，减少了谐波的污染。 最后，给出了系统仿真和实验。仿真和试验表明，本控制器软硬件设计合理，控制方法正确、可行，系统运行可靠、平稳。

Since the power-factor of the PWM's transforming exchanger is higher and can achieve the variable voltage variable frequency(VVVF) and harmonious wave,so it can be using in alternating current drive and other energy transformation system. One kind of PWM's technique is SPWM,this kide’s feature is pulse lenger is changing according to the sine regular ,can valid repressing the low wave,then the electrical machinery can working below the similar sine alternating voltage , The torque impulse is little,but the limit of the alternating current generator velocity modulated is extensived. This essay mainly analysised the two forms of phase-shift in PWM of level phase-shift and vertical phase-shift in serial units mid-voltage frequency converter, and concluded both the benefits and shortcomings of them. Both of them can output multi-levels voltage waves that approximated to the sine wave ,and light the harmonic pollution to the net and light the impulse to the net and motors, but with some shortcomings in itselves，(a) in case of vertical phase-shift when the modulate amplitude is smaller, the outputs between the units is different, need to distribute every power unit’s output dynamically; (b) in case of level phase-shift, when the distance between the tri-angle waves is larger, the sample precision is lower and cannot meet the requirment. On basis of overcoming these shortcomings, we suggested a theory producing multi-paths SPWM by using vector rotating method that based on CPLD, this method keeps the benefits of the level phase-shift and vertical phase-shift but with simpler calculation and better output wave forms and faster response and better reliability. The essay discussed in detaily the following contents: (1) Described the two kinds of PWM modulation methods of carrier phase-shift in serial units mid-voltage frequency converter, and done simulation to the PWM modulation of carrier level phase-shift and vertical phase-shift ,analysised the output wave forms that under different modulation. The simulation and the system tests showed that both the carrier level phase-shift and vertical phase-shift PWM modulation can enhance the switching frequencies, and increase the numbers of output levels, and light the harmonics and promote the output wave forms, but with shortcomings in itselves. Due to this reason, suggested one method of vector rotating to resolve the problem of producing multi-paths SPWM in mid-voltage frequency converter, and given a detailed theoretically analysis. (2) Adopted light fibre to communicate, resolved the problem of isolation of light and electric, and promoted the anti-disturb ability, and light the error code rate in signal transmission and increased the correctness of the code in transmission. (3) Adopted the CPLD chips in the system, and programmed them with VHDL language, the strong functions of the CPLD made it finely distribute the DSP calculated pulse width to each unit's controller inner the system, and add out the approximated sine wave that needed by the system, and light the pollution of the harmonics. Finally done the system simulation and test, the result shows that both the hardware and the software are in good designed, the control method is correct and can be used in practice, the system runs stably and reliably.