SOFT STARTER CONTROL METHOD CAPABLE OF CONTROLLING LOW-SPEED FORWARD ROTATION AND LOW-SPEED BACKWARD ROTATION OF MOTOR

The present invention relates to the technical field of motor control, in particular to a control method for a soft starter for controlling low-speed forward rotation and low-speed reverse rotation of a motor. A forward rotation frequency division coefficient KF of the low-speed forward rotation of the motor and a reverse rotation frequency division coefficient KR of the low-speed reverse rotation of the motor are determined through an improved method; and then, by controlling a trigger time sequence of thyristors and a time point at which the trigger signal is inputted to the thyristor each time, a frequency and a phase sequence of a three-phase input current of the motor are reduced without changing an input phase sequence of a power grid, the grid frequency and a main circuit of a transmission motor soft starter. Therefore, the motor is controlled for low-speed forward rotation at a rotating speed of VF or low-speed reverse rotation at a rotating speed of VR.