METHOD OF AND SYSTEM FOR CONTROLLING A PERMANENT MAGNET MOTOR
摘要:
The present invention provides a method of controlling a permanent magnet motor (101). The permanent magnet motor may be a brushless direct-current (BLDC) motor or a permanent magnet synchronous motor (PMSM). The method comprises applying closed-loop control (301) to the speed of the motor to match it to a reference speed (ω ref ) by comparing a measured q-axis stator current of the motor with a reference q-axis stator current of the motor and deriving a difference therebetween. This difference represents the current error. The current error is compared (302) to a threshold value at which a phase current amplitude of the motor starts to exhibit distortions. If the current error is not greater than this threshold value, the reference speed (ω ref ) of the motor is set (303) equal to an application reference speed of the motor for its particular application and the closed-loop control is continued. If, on the other hand, the current error is greater than the threshold value, the reference speed (ω ref ) is set (304) equal to a temporary reference speed, which is then compared (305) to the application reference speed. If the temporary reference speed is not less than the application reference speed, the reference speed (ω ref ) is set (306) equal to the application reference speed and the closed-loop control is continued. If, on the other hand, the temporary reference speed is less than the application reference speed, a phase offset angle (theta) between stator and rotor magnetic fields of the motor is changed (307), in order to adjust the actual speed of the motor by flux weakening, before the closed-loop control continues. In this way, the actual speed of the motor may be made to approach the reference speed (ω ref ) without inducing periodical variations in the amplitude of the motor phase current waveform. The invention also provides a system for performing such a method and computer program product or a program code for executing such a method.
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