Commutation, Demagnetization Delay And Zero Crossing Event; Figure 8: High And Low Frequency Timer Signals - ST STM32 User Manual

Implementation of six-step motor control
algorithm in STM32 Nucleo microcontroller
3.3.4

Commutation, demagnetization delay and zero crossing event

Since the BLDC is a synchronous motor, the drive main objective is to ensure the rotor
position synchronization with the stator magnetic field. It is possible to demonstrate that the
drive maximum efficiency is obtained by keeping the stator magnetic field with a 90-degree
spatial advance with respect to the rotor magnetic field, achieved by keeping the zero
crossing in the middle of each step (see
detection").
Since each motor has different inductance values, the current could reach zero with a delay
at each step commutation. This event called demagnetization determines the starting point
for zero crossing detection. The delay is a percentage of the step time (see
"Demagnetization
zero value in the floating phase after the demagnetization delay time.
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Figure 8: High and low frequency timer signals

time"). The BEMF signal can be measured when the current reaches the
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Figure 9: "BEMF signal and zero crossing
UM2124
Figure 10: