Study And Application Of Torque Control Soft Starter

Squirrel-cage three-phase asynchronous motor because of its relatively cheap price andmaintenance cost is low, become the market mainstream motor. However, the instantaneousinrush current of direct motor starting can be up to4~8times the rated current of the motor,which will have great impact to the grid, directly affect the normal operation of otherelectrical equipment in the power grid; in the meanwhile, the excessive starting torque willshorten the longevity of the motor itself and its dragged equipment. The impact of direct stopwill also shorten the longevity and stability of the entire system, especially for pump system.In order to improve the starting characteristics of motor and eliminate the impact on thesystem, in this paper, a torque control soft starter based on microcontroller is introduced.This paper first introduces the development status and prospect of soft startingtechnology at home and abroad. Then based on the comprehensive comparison of the startingcharacteristics of different methods, thyristor based soft starting with torque control isproposed, as well as its working principle and different starting modes. Then it introduces thehardware design of the soft starter, including the main circuit, chip selection, power supplycircuit, current and voltage detection circuit, communication and HMI circuit; the softwaredesign of the control system is also introduced, including the main program, self-test program,electrical parameter acquisition module, power supply frequency detection subroutine,keyboard and display subroutine, soft start control algorithm subroutine modules. Test on thesoft starter is done, test result shows that the soft starter can effectively limit the startingcurrent and the motor can drive the load smoothly. Finally, it introduces the application of softstarter in various fields, especially in pump system.