AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 19

• Manufacturer Part Number: AN1913D
• Description: 3-phase BLDC Motor Control with Sensorless Back-EMF ADC Zero Crossing Detection using DSP 56F80x
• Manufacturer: Freescale Semiconductor / Motorola

5.4.1 Alignment
Before the motor starts, there is a short time (which depends on the motor’s electrical time constant)
when the rotor position is aligned to a known position 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 and recognized the rotor position. When the preset
time-out expires, this state is finished.
The current is sampled and the Current Controller is calculated in every PWM cycle.
The BLDC motor rotor position (with flux vectors during alignment) is shown in
•
The Current Controller subroutine (with PI regulator) is called to control the DC-Bus current.
The subroutine sets the right PWM ratio for the required current.
BLDC control with BEMF Zero Crossing using ADC
Freescale Semiconductor, Inc.
Figure 5-5. Commutation Control States
For More Information On This Product,
(Back-EMF Acquisition)
commutations done?
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Minimal correct
Alignment time
Yes
Yes
Start motor
Alignment
expired?
Running
Starting
No
No
Figure
Control Technique
5-6.
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