Research On Control System Of Asynchronous Motor Soft Starter

Since the 21 st century, great changes have taken place to human life, and the asynchronous motor has also made great contribution to the change. With the maturing of power electronic technology, the starting technology of asynchronous motor is also more and more get the attention of many scholars. The direct starting and traditional step-down starting technology already cannot meet the demand of the increasing production. In order to get smaller current and larger torque, the paper puts forward the soft starting control technology of asynchronous motor, which is based on discrete variable frequency.Firstly, the paper introduces the disadvantage of direct starting and the aim of the starting solutiones, namely, decreasing the starting current and adjusting the starting torque. The paper simply describes the history and development of the soft starter, which detailedly analyses the advantages and disadvantages of soft starter in step-down and frequency. According to the study of asynchronous motor and the analysis of the principle of the thyristor adjusting voltage, we can get the conclusion that the decreasing starting frequency could increase the starting torque. The paper analyses serveral starting ways of common soft starter, which puts forward the advantages of starting way of discrete variable frequency. The paper detailedly expound the theory of discrete variable frequency, which can get better starting performance by triggering thyristor selectively and controlling the semi-periodic of power supply regularly. In the paper, the third chapter respectively builds the models of direct starting, full-frequency starting and discrete variable frequency soft starter by using SIMULINK toolbox in MATLAB simulation software. Through the contrast of three kinds of starting current and starting torque in oscilloscope, which could found that the discrete variable frequency soft starter is more advantageous to reduce impulse current, starting current and increase the starting torque of motor. The paper design the hardware circuit of controlling system of discrete variable frequency soft starter by using chips of USA Microchip company, which includes the whole system construction, the main circuit, the detective circuit, triggering circuit, communicating circuit and the design of display circuit. The paper introduces the design of software program and the flow chart of programming strategy. Finally, according to the debugging and the experiment, which could prove the algorithm is effective and feasible.Compared with the traditional soft starter, this system has the following advantages: simple hardware circuit, small volume, stable and reliable system operation, low starting current and so on. Users can easily control the motor by display board to start or stop. Thus it is widely applied to industry, agriculture and many fields of drives, have a certain application value.