Research On Soft Starting Based On Switch Transformer

The high voltage high power motors’ nominal voltage is usually up to10kV. Whenthey start directly, the current can be5-7times of rating and the electromagnetic torquecan be2times of rating. And it will damage equipments, so soft starting is usually used.The soft starting based on switch transformer can improve starting performance. It alsoavoid thyristors’ series connection to improves system’s reliability. So this paperresearches the soft starting based on switch transformer.Switch transformer is a equivalent switch that be constituted by switching deviceand transformer. It is also the core of the soft starting system researched in this paper.So this paper firstly researches switch transformer’s working principle andcharacteristics. The excitation inrush current’s and the special operative mode of ironcore’s principle and impacts on system are researched in this paper. The designprinciples of transformer capacity based on short time temperature rise and short circuitimpedance is given in this paper, and it lays the foundation of using switch transformermore widely and more deeply.This paper then researches the soft starting based on switch transformer usingphase-control adjusting voltage’s fundamentals. The mathematical model of motor andthree-phase AC voltage regulation circuit is built and the operating principle of switchtransformer is analysed. According to analysis and simulation, it proves that the startingperformance can be improved, but it also has the disadvantages of high thd, low powerfactor and low response speed.For the disadvantages of phase-control adjusting voltage, this paper proposes thechopper circuit based on switch transformer that combining switch transformer andPWM technology. Its operating principle is analysed. The control strategy is researchedand this paper proposes a cnotrol strategy that rejecting the instantaneous perturbationbased on instantaneous perturbation offset. According to analysis and simulation, itproves that the chopper circuit can improve the thd, power factor and response speedwith high starting performance when the chopper circuit is used in soft starting.Finaly, according to the theoretical analysis, this paper designs and makes a softstarting prototype based on switch transformer. The experiment results show that thesoft starting can reduce the starting current and torque effectively to protect equipmentand improve starting performance in its practical application.