Research On Intelligent Soft Starter Of Asynchronous Electromotor Based On PIC

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 stats up with reduced-voltage means, a new method based on power electronics technology for improving the starting characteristics of asynchronous motor is presented.This paper designed and introduced a soft starter of asynchronous electromotor which is controlled by PIC18F4550, analyzed the working principle, function and application. This system optimized the traditional voltage ramping technique and current limit technique. The mode of torque close-loop control was designed, which can start pump load more smoothly. It can also reduce the water hammer and the vibration of pipeline. At the same time, oscillation of current, electromagnetic torque and speed appears during soft-stating.Some influencing factors of the oscillation are analyzed and the cause of oscillation is derived.Than, a method of controlling hold-off angle is proposed to reduce the oscillation.Firstly, on the basis of the research of the structure and the operation principle of the asynchronous motor, the basic principle and control method of the soft starter are established. Soft starter with torque closed-loop control function to restrain water hammer and the hold-off angle of current method to reduce oscillation are available.Secondly, the control circuits of the soft starter are improved. A chip of PIC18F4550 made by microchip Company was used as the core of the soft start controller. A detail introduction of the hardware design, such as the AC sample circuits, the communication circuit and so on. The software adopts C and Assemble languages to realize modularized programming, including the main program, A/D sampling program and the different control programs of different start modes.Lastly, the system is analyzed and simulated by MATLAB. The results of the simulation show that the system based on torque closed-loop circuit can reduce the high starting current as asynchronous motors start up.