Research On Soft Starting Of AC Motor Based On Speed Estimation

High voltage AC motor in the process of direct starting will cause great current and torque impact, so the high power motor must use the soft starter system to ease the impact of torque and electric. And the starting of synchronous motor is more complex, because of the difficulty of direct starting, asynchronous starting method is the general selection. In the starting process of synchronous motor asynchronous starting and asynchronous motor starting, their principle is similar. For asynchronous motor, if adding speed information into the soft start process can shorten the starting time, and for synchronous motor, whether the detection of motor’s sub synchronous speed information is accurate or not will directly affects the starting’s successful, so speed information’s obtaining and precision is very important. But it is very difficult to install and use the speed sensor in the starting process of high power AC motor. In this paper, the speed estimation of AC motor in soft start is studied, and a soft start method based on speed estimation is designed and implemented according to the estimated speed information.The full order state observer is chosen to estimate the speed of motor in soft start process. Firstly, this paper prove that the full order state observer can complete the speed estimation mission of phase controlled voltage regulation. And the concept of power network access speed is introduced to shorten starting time.And the soft starting process of asynchronous motor is improved.Due to the synchronous asynchronous motor soft starting process requires the accurate sub synchronous speed information, design damping winding of motor flux observer.And for the speed estimation in the vicinity of the sub synchronous speed appeared ultra,to solve the problem introducing the concept of equivalent rotor. A new method of speed estimation is obtained by combining the idea of equivalent rotor with the speed estimation of induction motor, and the correctness of the method is verified by the simulation analysis.Finally, this paper designs and makes a prototype of the motor soft starter system based on the switch transformer. Through the prototype experiment, the accuracy of the speed estimation method is verified; the host computer can accurately monitor the state of the motor starting process; the soft starter can complete the motor start task.