Basic principles and driving waveforms of BLDC six-step commutation method

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Basic principles and driving waveforms of BLDC six-step commutation method [Copy link]

The most classic driving method for brushless DC motors (BLDC) is the three-phase six-step commutation method. During the debugging these days, I used an oscilloscope to capture the gate drive waveforms of the next six MOS tubes.

The basic driving circuit is shown in the figure:

The so-called six-step commutation method is to energize in the following order: AB->AC->BC->BA->CA->CB. Of course, other energization sequences can also be used, as long as the direction of change of the magnetic field can form a rotating magnetic field.

In general, PWM is also used for speed regulation. The simplest method is to modulate only the upper bridge arm MOS tube (Q1, Q3, Q5), and use GPIO control for the lower bridge arm (Q2, Q4, Q6). The advantage of this is that the control method is simple; the disadvantage is that when the upper bridge arm is cut off, it can only be continued through the body diode of the lower bridge arm MOS tube, and the body diode voltage drop is large, which will cause the lower bridge arm MOS tube to heat more seriously. The driving waveform using this driving method is shown in the figure:

The red box in the figure represents a cycle. It can be seen that only the upper bridge arm uses PWM for modulation.

A better method is to use complementary PWM signals for control, with the upper and lower tubes turned on alternately. The driving waveform of this method is shown in the figure:

The red box in the figure is a cycle. It can be seen that the upper and lower bridge arms use PWM signals for control at the same time. The waveform of the complementary PWM signal after expansion and amplification is shown in the figure:

When the upper bridge arm is turned on, the lower bridge arm is turned off, and when the upper bridge arm is turned off, the lower bridge arm is turned on.