Motorola M68HC08 manual Freescale Semiconductor, Inc

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

BLDC Motor Control

Used Control Technique

•BLDC motor commutation service

•Back-EMF zero crossing moment capture service

•Calculation of commutation time

•Interactions between these commutation processes

From diagrams an overview of how the commutation works can be understood. After commuting the motor phases, there is a time interval (Per_Toff[n]) when the shape of back-EMF must stabilized (after the commutation the fly-back diodes are conducting the decaying phase current; therefore, sensing of the back-EMF is not possible). Then the new commutation time (T2[n]) is preset. The new commutation will be performed at this time if the back-EMF zero crossing is not captured. If the back-EMF zero crossing is captured before the preset commutation time expires, then the exact calculation of the commutation time (T2*[n]) is made, based on the captured zero crossing time (T_ZCros[n]). The new commutation is performed at this new time.

If for any reason the back-EMF feedback is lost within one commutation period, corrective actions are taken in order to return to the regular states.

The flowchart explaining the principle of BLDC commutation control with back-EMF zero crossing sensing is shown in Figure 3-16.

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	BLDC Motor Control	41
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