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Vectors of magnetic fields – Motorola M68HC08 User Manual

Page 47

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BLDC Motor Control

Used Control Technique

DRM028 — Rev 0

Designer Reference Manual

MOTOROLA

BLDC Motor Control

47

Figure 3-18. Vectors of Magnetic Fields

BORDER OF

STATOR POLE

STATOR MAGNETIC FIELD

ROTOR MAGNETIC

PHASE WINDING

ROTOR MOVEMENT

FIELD (CREATED BY PM)

DIRECTION OF

PHASE CURRENT

DURING ONE

COMMUTATION

ZERO CROSSING

EDGE INDICATOR

MOTOR IS RUNNING

MOTOR IS STARTING

ALIGNMENT STATE

STARTING (BACK-EMF ACQUISITION)

RUNNING

The rotor position is stabilized by
applying PWM signals to only two
motor phases

The two fast (faster then the rotor
can move) commutations are
applied to create an angular
difference of the stator magnetic
field and rotor magnetic field.

The back-EMF feedback is tested.
When the back-EMF zero crossing
is recognized the time of new
commutation is evaluated. Until at
least two successive back-EMF
zero crossings are received the
exact commutation time can not be
calculated. Therefore, the
commutation is done in advance in
order to assure that successive
back-EMF zero crossing events
would not be missed.

After several back-EMF zero
crossing events the exact
commutation time is calculated. The
commutation process is adjusted.
Motor is running with regular
back-EMF feedback.

AT STEADY-STATE CONDITION

WITH REGULAR BACK-EMF FEEDBACK

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Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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