Control method and device of sensorless permanent magnet motor used for pump

The invention provides a control method and device of a sensorless permanent magnet motor used for a pump, belongs to the technical field of motor driving, and solves the problem in the prior art that the motor starting success rate is low. The control method of the sensorless permanent magnet motor comprises the steps of; A, positioning an initial position of a permanent magnet motor rotor; B, setting a target rotation speed of the starting of the permanent magnet motor, the time for speeding up to the target rotation speed, and a second PWM duty ratio; C, powering on the permanent magnet motor according to a phase change sequence after the initial position of the permanent magnet motor rotor is positioned so as to enable the rotation speed of the permanent magnet motor to reach the target rotation speed; and D, a control module judges whether the rotation speed of the permanent magnet motor is normal according to a phase change signal output by a back electromotive force detection module, if yes, the starti