【作者】 刘庆利；

【导师】 李冬辉；

【作者基本信息】 天津大学 ， 控制理论与控制工程， 2005， 硕士

【摘要】 在工、矿业应用中,有许多重载运输设备,比如皮带输送机、矿山刮板输送机等。这些设备一旦出现故障停车,再重新起动就比较困难。直接起动会产生很大的冲击电流,影响电动机的使用寿命;采用降压起动装置或常规软起动器起动又不能提供足够大的起动转矩,无法实现重载起动;而采用变频器起动投入成本又太大。针对这些矛盾,本文寻求了一种新的起动方案,即利用晶闸管斩波技术进行离散变频,以降压-降频的方式实现高起动转矩、低起动电流的重载软起动,且使投入成本大为降低。离散变频是指通过控制晶闸管的触发脉冲序列,有选择地让工频信号的某些半周波通过,而另一些半周波截止,由此达到变频的目的,所得到的频率只能是工频的整数分之一。本文对单相离散变频技术进行了分析,确定了各离散频率下基波信号的初始相位角与原信号之间的关系,给出了通用公式;进一步研究了如何通过三组反并联的晶闸管实现三相变频,找出能够使电动机获得最大电磁转矩的离散变频方式,给出了相应算法;之后,本文对离散变频软起动的控制方案进行了设计,提出了相应的控制策略,包括如何进行电压调节,如何选择频率等级,如何进行频率切换以及如何控制晶闸管的触发脉冲序列等,并在由低频切换到工频过程中引入模糊控制策略实施恒流控制,实现真正意义上的软起动;最后,本文利用MATLAB/SIMULINK构建了系统模型,对三相异步电动机离散变频软起动进行仿真,验证了方案的可行性,并与其它起动方式进行比较,证明了离散变频软起动在重载起动方面所具有的优势。更多还原

【Abstract】 There are lots of over-loading transport equipment in mineral industry, such as ebelt conveyer and drawing conveyer, etc. It is more difficult to restart once those equipments appear to break down. Starting directly will produce big dash current, which will shorten the service life of the electromotor. Traditional soft starter can not provide enough starting torque to carry out overloading starting. Starting by using inverter will make high cost. Aiming at those problems, a new resolution is represented in this paper and the exact scheme is to make discrete frequency-control by controlling the triggering instants of thyristors, and realizes over-loading soft starting with high start torque by using VVVF method. This resolution also immensely cuts the cost.After Analyzing discrete frequency-control technology and taking further research on how to realize three-phase frequency-control by using three groups of inversely parallel-connecting thyristors, I give the general equation of initial phase angle. Then I provide the algorithm to get the best combination after three-phase frequency-control, introduce the control strategy which can realize over-loading soft start by using discrete frequency-control technology, and point out how to realize switch among different frequency. This control strategy also leads into fuzzy control method to carry on the constant current control in the process of low frequency switch to line frequency and it realizes the real soft start.Finally, this paper sets up the system model by using MATLAB/ SIMULINK, makes simulation for this system and verifies the feasibility of this control strategy, and, by simulating experiment, compares discrete variable frequency soft start with other starting ways and verifies the advantages of the former in over-loading start area.更多还原