A method of speed measurement without sensor in motor soft starting control system

At motor start-up process, the motor speed is constantly changing, the input voltage adjustments should follow the changes of motor speed timely, or it is difficult to achieve the desired objectives, but the traditional way increased the cost of maintaining, complexity, and made the reliability lower, which would certainly affects the usage and scope of the controller. This paper presents a new method of speed detection according to conventional soft starter, and in heavy soft starter system, according to discrete variable frequency features, the new method based on the residual voltage after current dump is been selected. These method are only in accordance with characteristics of soft-start controller main circuit, the speed information can be got without additional speed sensor, the stator voltage is regulated according to running status so that the parameters of motor speed, current change in accordance with the expected curve.