Motorola M68HC08 manual Bldc Commutation Time with Zero Crossing Sensing

Freescale Semiconductor, Inc.

BLDC Motor Control

Used Control Technique

T_Cmt[n-2] T_Cmt[n-1] T_Cmt[n]

T2[n-3]	T2[n-2]	T2[n-1]	T2[n]
	n-2	n-1	n

Inc.

Per_ZCros[n-2]

2*Per_ZCrosFlt[n-1]

COMMUTATION IS PRESET

ZERO CROSSING					COMMUTATED AT PRESET TIME NO
DETECTION SIGNAL					BACK-BMF FEEDBACK WAS RECEIVED
			Per_ZCros[n]		CORRECTIVE CALCULATION 1.
					T_Cmt*[n+1]
	ZERO CROSSING
	DETECTION SIGNAL					BACK-EMF FEEDBACK
Per_ZCros0[n] =
Per_ZCros[n-1]		Per_ZCros[n]		Per_HlfCmt[n]		RECEIVED AND EVALUATED

Freescale Semiconductor,

T_ZCros[n-1]	T_ZCros[n]
Per_Toff[n]	T_Cmt**[n+1]

ZERO CROSSING			COMMUTATED WHEN BACK-EMF
			ZERO CROSSING IS MISSED
DETECTION SIGNAL			CORRECTION CALCULATION 2.
	Per_ZCros[n]	Per_HlfCmt[n]

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]
DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	BLDC Motor Control	43
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