电子软起动器是伴随功率电子器件发展而出现的一种电机辅助起动工具，其核心组件是由六组反并联晶闸管构成的交流调压装置，通过控制这些晶闸管的触发角来达到调节电压的目的，从而轻易的改变异步电机的运行特性。加之现代控制理论与微机控制技术的发展，新的晶闸管触发策略应运而生。现在交流调压除了单一的调压功能之外，可以引入双斜坡，构成双斜坡电压软起动，可以引入电流闭环，构成限流软起动，而最新颖最实用的莫过于分级变频软起动。分级变频技术具有间接起动方法和传统软起动方法无法比拟的优势，因此分级变频对三相异步电动机的起动有很重要的研究意义。 本文先对晶闸管调压器的工作原理进行了简单的介绍，以此为依据引出了分级变频技术，并对分频原理进行了叙述，通过分析分频后的各频段的电压相序，以对称分量法确定各频段下的正序分量最大的相位组合；而且，结合工程实际对电机起动过程中遇到的问题进行了研究，总结了如何选取分级变频的起动频段，和各频段之间切换的原则。其次，为了降低电机分级起动时产生的大量谐波，使电机的起动转矩平稳，应用了基于等效正弦的VVVF的控制策略。并通过对电机续流角的检测，实现功率因数角的补偿控制，大大的降低了电机在轻载下的抖动现象。 在理论研究的基础之上，利用MATLAB/Simulink软件搭建仿真模型，并介绍了仿真模型的主要模块。而后，分别对斜坡电压，限流及分级变频软起动的起动过程进行了仿真研究，通过各种仿真结果对比，验证了分级变频软起动方案的可行性及正确性。 最后，本文以TI公司的一种高性能DSP（TMS320F28335）为核心设计了一款三相异步电动机软起动器，这款软起动器集多种控制方法于一身包括本文研究的分级变频软起动技术，可以针对不同负载及起动要求，切换起动模式、调整起动参数，使电机达到最好的起动效果。设计的主要工作包括软起动器的硬件设计和分级变频软起动的软件实现。通过对硬件调试，以及相关的电机软起动实验，所得到的实验结果与仿真基本一致，从而再次验证了分级变频软起动控制技术在电机重载甚至满载时起动时的优越性，不得不说这又是晶闸管软起动应用范围的一次扩展。

Electronic soft starter, a motor-assist tool with the development of power electronics device, the core component of which consists of AC voltage regulation device composed of six sets anti-parallel thyristors. By controlling the firing angle of thyristor, we can regulate the voltage so as to easily change the operating characteristics of asynchronous motor. Because of the development of modern control theory and computer control technology, the new strategy of thyristor trigger came into being. Now apart with AC voltage regulation’s single function of voltage regulating, we can bring in dual-ramp which constitutes dual-ramp voltage soft starter. Current closed loop can be also introduced into the function and constitutes current-limiting soft starter. The technology of discrete frequency soft starter has incredible advantages that indirect starting method and traditional method of starting cannot even match. Therefore, discrete frequency soft starter is so vital to the research on starting of three-phase asynchronous motor. This thesis first gives a brief introduction of operating principle to thyristor regulator, based on which brings discrete frequency technology and describes principle of discrete frequency. By analyzing the voltage phase sequence of sub frequency band after it was divided, we can nail down the maximum phase combination under each phase sequence by using symmetrical components method. Besides, applying to project practice, I do the research on specific problems of motor starting in process. I summarize how to select the start frequency band among all frequencies and switch principle covered each frequency band. Secondly, in order to reduce a large number of harmonic wave generated by the division starting of motor and make the starting torque stable, I put forward the VVVF control strategy based on equivalent sine. And by detecting the follow current of motor, closed loop control of the power factor angle is achieved, which greatly reduces jitter under the circumstances of under loading. Based on theoretical research and by using MATLAB/Simulink software to set up simulation models, I introduce the main modules of simulation model. After the introduction, I do the simulation study on the starting process of soft starter of ramp voltage, limited current and discrete frequency. By comparing various simulation results, I verify the feasibility and correctness of the discrete frequency soft starter program. Last but not least, I work out a three-phase asynchronous motor based on high-performance digital signal processor TMS320F28335 made by TI company. This soft starter has numerous variety control method which includes discrete frequency soft starter technology mentioned in this thesis. To different load and starting requirements, this soft starter can switch start mode, adjust the starting parameters to achieve the best effect. The main task of design includes hardware and software design of this new soft starter. At the meantime, I regulate the hardware and make some relevant starting experiment of motor soft starter. It turns out that the experiment results are consistent with simulation results, which again verify the superiority of control technology of discrete frequency soft starter applying to heavy load even full load motor. I have to say that this is another expanding application range of thyristor soft starter.