Brushless direct current motor back electromotive force zero crossing point detection method

Abstract

The invention discloses a brushless direct current motor back electromotive force zero crossing point detection method, which comprises the following steps: synchronizing PWM period interruption through a timing unit, starting to collect A, B and C three-phase phase voltages in a brushless direct current motor by an ADC module, and calculating the number of times of collecting the three-phase phase voltages by the ADC module in a PWM-ON stage; and according to the acquisition times and the two-conduction phase voltage and the third-phase counter electromotive force acquired by the ADC module, comparing the third-phase counter electromotive force with half of the two-conduction phase line voltage in a PWM rising edge or falling edge, and judging whether the third-phase counter electromotive force crosses a zero point or not. According to the method, whether the third-phase counter electromotive force crosses the zero point or not is detected in the PWM-ON stage, and a counter electromotive force zero-crossing pre-judgment program is introduced in the PWM-OFF stage, so that the problem that the third-phase counter electromotive force zero-crossing point cannot be detected in the PWM-OFF stage is well solved, the commutation precision of the brushless direct current motor is greatly improved, and the reliability of the brushless direct current motor is improved. And the efficiency and stability of the motor are improved.

Description

【Technical field】 [0001] The invention relates to the field of brushless motors, in particular to a method for detecting a zero-crossing point of a counter electromotive force of a brushless DC motor. 【Background technique】 [0002] In the technical field of brushless DC motor sensorless drive control, the operation process of the brushless DC motor may include a rotor pre-positioning stage, a low-speed operation stage and a medium-high speed operation stage. In the prior art, the commutation operation is generally performed by detecting whether the floating opposite electromotive force crosses zero: the ADC module is used to sample the phase voltage of the floating phase of the brushless DC motor once in each PWM control cycle, and then compare the sampling result with the reference voltage Compare to determine whether zero-crossing occurs. [0003] Since the back electromotive force obviously exists in PWM-ON, the ADC module only collects it in the PWM-ON phase. Once the ...

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Problems solved by technology

[0003] Since the back electromotive force obviously exists in PWM-ON, the ADC module only collects it in the PWM-ON phase. Once the real zero crossing point of the back electromotive force occurs in PWM-OFF, there will be a lag in judging the time of zero crossing, especially in brushless DC. During the high-speed operation of the motor (above 100,000 revolutions), the number of PWM cycles in a commutation interval is small, and the lag in back EMF zero-crossing detection may cause the commutation lag of the brushless DC motor, which can easily cause a reduction in motor efficiency Even cause the motor to stop abnormally after out of step

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