Motorola M68HC08 manual Bldc Motor Back EMF and Magnetic Flux

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

BLDC Motor Control

Phase Magnetic
Flux Linkage
					Psi_A
					Psi_B
					Psi_C
		PH. A	PH. B	PH. C
Phase Back EMF			PH. A		Ui_A
				PH. B	Ui_B
Atop	Btop Ctop				Ui_C
				SPEED REVERSAL
				PH. C
Cbot		Abot	Bbot	“NATURAL” COMMUTATION POINT
				ACTING POWER SWITCH IN THE POWER STAGE
Phase-Phase					Ui_AB
					Ui_BC
Back EMF
			A–B		Ui_CA
				B–C
				C–A

Figure 3-3. BLDC Motor Back EMF and Magnetic Flux

The filled areas in the tops of the phase back-EMF voltage waveforms indicate the intervals where the particular phase power stage commutations occur. The power switches are cyclically commutated through the six steps; therefore, this technique is sometimes called six step commutation control. The crossing points of the phase back-EMF voltages represent the natural commutation points. In normal operation the commutation is performed here. Some control techniques advance the commutation by a defined angle in order to control the drive above the pulse-width modulator (PWM) voltage control.

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