Research Of The Soft Starter With Pump-control Function Based On All-digital Torque Measurement

To reduce the high starting current as asynchronous motors start up directly and eliminate the negative influence to electrical equipment and mechanism that brought about by asynchronous when it starts up with reduced-voltage means, a new method based on power electronics technology for improving the starting characteristics of asynchronous motor is presented.The paper introduce a new-style soft starter which based on DSP(TMS320 LF2407).It has three start modes: the ramp voltage start, the limit current start, and the pump-control start which is different from the traditional soft starter. The soft starter can reduce the water hammer when a pump is started or stopped, and release the vibration of transfer system.Firstly, on the basis of the research of the structure and the operation principle of the asynchronous, the basic principle and control method of the soft starter are established, the water hammer can be decreased or avoided by using the soft starter with torque closed-loop control function.Secondly, the control circuits of the soft starter are improved. A chip of TMS320LF2407 made by TI Company is the core of the soft start controller. A detail introduction of the controller, such as the power supply circuits, the AC sample circuits, the communication circuits and so on, is given in the following passages. The software adopts C and Assemble languages to realize modularized programming. It introduce several programs of the controller, such as the main program, the different control programs of different start modes, A/D program, and the communication program and so on.Lastly, the three-phase regulating circuit of asynchronous motor system is analyzed and simulated by MATLAB. Also the experiments have made with the soft starter which is designed .Both the results of the simulation and the experiment show that the system based on torque closed-loop circuit can reduce the high starting current as asynchronous motors start up directly, reduce the water hammer, and also improve the performance of the motor.