AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 20

• Manufacturer Part Number: AN1914
• Description: 3-Phase BLDC Motor Control with Sensorless Back EMF Zero Crossing Detection Using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

Control Technique
5.4.1 Alignment
5.4.2 Running
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Be
when the rotor position is stabilized by applying PWM signals to only two motor phases (no
commutation). The Current Controller keeps the current within predefined limits. This state is
necessary in order to create a high start-up torque. When the preset time-out expires then this state is
finished.
The current PI controller works with constant execution (sampling) period determined by PWM
frequency: Current Controller period = 1/PWM frequency.
The BLDC motor rotor position with flux vectors during alignment is shown in
The commutation process is the series of states which assure that the Back-EMF zero crossing is
successfully captured, the new commutation time is calculated and, finally, the commutation is
performed. The following processes needs to be provided:
fore the motor starts, there is a short time (which depends on the motor’s electrical time constant)
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The Current Controller subroutine with PI regulator is called to control DC Bus current. It sets
the correct PWM ratio for the required current.
BLDC motor commutation service
Back-EMF Zero Crossing moment capture service
Computation of commutation times
Handler for interaction between these commutation processes
DSP56F80x MC PWM Module in Motor Control Applications
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 5-6. Alignment
Go to: www.freescale.com
Figure
5-6.