beautypg.com

Bldc commutation time with zero crossing sensing – Motorola M68HC08 User Manual

Page 43

background image

BLDC Motor Control

Used Control Technique

DRM028 — Rev 0

Designer Reference Manual

MOTOROLA

BLDC Motor Control

43

Figure 3-17. BLDC Commutation Time with Zero Crossing Sensing

The following calculations are made to calculate the commutation time

(T2[n]

) during the Running state:

Service of commutation — The commutation time (T2[n]) is
predicted:

T2[n] = T_Cmt[n] + 2*Per_ZCrosFlt[n-1]

If 2*Per_ZCrosFlt>Per_Cmt_Max

then result is limited at Per_Cmt_Max

Service of received back-EMF zero crossing — The
commutation time (T2*[n]) is evaluated from the captured
back-EMF zero crossing time (T_ZCros[n]):

Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0

Per_ZCrosFlt[n] = (1/2*Per_ZCros[n]+1/2*Per_ZCros0)

HlfCmt[n] = 1/2*Per_ZCrosFlt[n]- Advance_angle =

= 1/2*Per_ZCrosFlt[n]- C_CMT_ADVANCE*Per_ZCrosFlt[n]=

Coef_HlfCmt*Per_ZCrosFlt[n]

2*Per_ZCrosFlt[n-1]

T_ZCros[n]

n-2

n-1

n

T_Cmt[n-2]

T_Cmt[n-1]

T_Cmt[n]

T_Cmt*[n+1]

COMMUTATION IS PRESET

T_Cmt**[n+1]

Per_HlfCmt[n]

Per_HlfCmt[n]

Per_ZCros[n]

Per_ZCros[n-1]

Per_ZCros[n-2]

Per_Toff[n]

Per_ZCros[n]

T_ZCros[n-1]

Per_ZCros0[n] =

Per_ZCros[n]

T2[n-3]

T2[n-2]

T2[n-1]

T2[n]

ZERO CROSSING

DETECTION SIGNAL

ZERO CROSSING

DETECTION SIGNAL

ZERO CROSSING

DETECTION SIGNAL

COMMUTATED AT PRESET TIME NO
BACK-BMF FEEDBACK WAS RECEIVED
CORRECTIVE CALCULATION 1.

BACK-EMF FEEDBACK
RECEIVED AND EVALUATED

COMMUTATED WHEN BACK-EMF
ZERO CROSSING IS MISSED
CORRECTION CALCULATION 2.

F

re

e

sc

a

le

S

e

m

ic

o

n

d

u

c

to

r,

I

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

n

c

.

..