Research Of Soft Starting Control System Based On DSP For Three-Phase Induction Motors

With the development of power electronics, the progress of electronic soft starting technology for three phase induction motor is made, which becomes the preferable technique for dealing with starting, stopping, saving-energy and protection for three phases induction-motor, and the technique has widely applying prospect and development space.Firstly, the dissertation introduces the development of AC motor soft starting, and analyses the start process of motor in theory. Then based on the selecting of trigger methods and ascertaining of the phase shift range of AC voltage-regulate soft starter, reliability of each trigger method is researched.Secondly, research about control strategy of soft starting system was made. After analyzing the relationship between non-conducted thyristors voltage, power factor angle and motor speed, simulation research based on MATLAB about the mode of soft starting proves this way of good control effect. Oscillation of current, electromagnetic torque and speed appears during soft-starting of three-phase induction motor.According to the mathematical model of the induction motor,a common simulation model of induction motors is established.The design and implementation of soft starting control system for three phase ac induction motor and the experimental research are given. The system adopts the high speed DSP-TMS320F2812 as main control unit, and the main circuit, driving circuit, detecting circuit were designed. This method makes the current zero-crossing as the reference.During the starting process of induction motor,the hold-off angle of current has gradually decreased from initial value to zero.This paper verifies the correctness of the method by simulation.The problem of extracting synchronizing signal of the system was solved by means of the advantage of the ideal phase-locked loop characteristics,frequency control and narrow-band tracking and as a result,real-time tracking of the synchronizing signal of three phases power supply was realized. Finally the software of control system was designed, and the experiment results are given in the end. Furthermore,it presents experimental facility based on hold-off angle control and experiments on a prototype induction motor.Then experiment results validate the correctness of theory analyses. It proves closed loop control method of combining the non-conducted thyristors voltage with power factor angle can eliminate current fluctuation and improve starting performance, has wide application foreground.