随着现代控制理论与微机控制技术的成熟，电子软起动器在工业领域中的应用更加广泛，而电子软起动器的控制方式主要是控制功率器件的导通与关断。触发方式的不同导致电动机的起动方式也不同，单一的限流起动和斜坡电压起动的控制方式已经不能满足工业生产的要求，而离散变频软起动具有电子软起动器相同的主电路结构和电力电子器件，通过新的控制算法使异步电动机在降低起动电流的同时增加起动转矩。因此，离散变频软起动可以应用电子软起动器所不能胜任的重载场合。 本文首先介绍了晶闸管三相调压的基本原理，在此基础上研究和分析了离散变频软起动的控制方法，阐述了离散变频基本原理；其次分析了分频后的各频段的电压相序，如何通过对称分量法求出非正序分量的最佳相位组合；然后对初始子频段和过渡频段进行选择，并总结了各频段之间的切换原则，而且对不同子频段的脉冲触发方式做了详细的研究；最后将功率因数角作为反馈信号，以抑制异步电动机在额定转速附近地抖动。 在理论分析之后，通过MATLAB/Simulink仿真软件搭建离散变频软起动控制系统的仿真模型。将13分频和7分频作为初始起动子频率，通过转矩波形、转速波形和电流波形的对比分析得出最适合重载起动的初始子频率。最后将离散变频软起动控制方法与斜坡电压起动和限流起动的控制方法进行对比，发现离散变频软起动控制方式具有其他起动方式所不具有的优势。 最后，本文以DSP TMS320F28335芯片为控制核心芯片设计了离散变频软起动系统的硬件电路和软件流程图，并通过物理实验平台对离散变频软起动的理论分析和仿真研究进行实验验证，得出实验波形与仿真波形基本一致，进一步验证了离散变频软起动控制方法的优越性和可行性。

With the development of modern control theory and computer control technology, electronic soft starter has been used in industrial production. The main control method is to change the trigger angle of the thyristor to complete the motor starting. Triggering pulses in different ways lead different starting ways. Single limited current starting and ramp voltage starting control modes have gradually been eliminated. The discrete variable frequency soft starter has same topological structure with electronic soft starter, which increase torque while reducing the starting current of the asynchronism motor through the new control algorithm. Therefore, the discrete variable frequency soft starter can be applied in high-load occasions which the electronic soft starter can not be competent. This thesis introduces the basic principle of three-phase pressure regulating thyristor, and proposes the control method of discrete variable frequency soft starter, and introduces how to change power frequency into different subbands using the symmetrical component method to calculate the maximum positive phase combination of non positive component. Secondly, we analyzed the selection of the initial and the transition frequency band. Then, we studied the distribution of pulse trigger signal in each sub frequency band in detail. Finally, the power factor angle is used as the feedback signal, which can restrain asynchronism motor chattering near the rated speed. After theoretical analysis, we did simulation analysis of discrete frequency soft starting by MATLAB/Simulink simulation software, and by comparing the frequency of 13 and 7 frequency divider, summarized the most suitable initial sub bands of high-load starting. We also compared the discrete variable frequency soft starter with the ramp voltage starter and the limited current starter, and then we can see the discrete variable frequency soft starting control method has advantages the others do not have. At last, the thesis introduces software and hardware design of the discrete frequency soft starting based on digital signal processor DSP28335 made by TI company, and proves the discrete frequency soft starting the oretically and simulate through the physical experiment pla tform. We found the experimental waveforms and simulation waveforms are basically the same, so verified the feasibility of discrete variable frequency soft starting.