AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 51

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

#define x_PER_CMTSTART
#define x_PER_TOFFSTART
Notes:
Notes:
Notes:
11.2.3 Minimal Zero Commutation of Starting (Back-EMF Acquisition) Stage
#define x_MIN_ZCROSOK_START
Notes:
11.2.4 Wrong Zero Crossing
#define x_MAX_ZCROSERR 0x04 /*Maximal Zero Crossing Errors (to stop commutations) */
Notes:
The unit of these constant is 1.777us. These constants are automatically calculated in newer SDK
software versions.
Then the first motor commutation period =
The Back-EMF Zero Crossing is not sensed during whole first period, because it is very small and
hence the Zero Crossing information is not reliable during this period.
Table 11-2
This constant x_MIN_ZCROSOK_START determines the minimal number of the Zero Crossing OK
commutation to finish the BLDC starting phase.
The constant
stops and starts the motor again, whenever
problematical Zero Crossing appears.
high load motor
high load motor
Slow motor/
Fast motor /
Motor size
mechanical
mechanical
It is recommended to set
Setting of this constant is an empirical process. It is difficult to use a precise formula, because
there are many factors involved which are difficult to obtain in the case of a real drive (motor
and load mechanical inertia, motor electromechanical constants, and sometimes also the motor
load). So they need to be set with a specific motor.
Slowing down the speed regulator (see
encountered using the above stated setting .
It is recommended to use the value 0x02 or 0x03 only. If this constant is set too high, the
motor control will not enter the Running stage fast enough.
During tuning of the software for other motors, this constant can be temporarily increased.
inertia
inertia
helps with setting of this constant
x_MAX_ZCROSERR
DSP56F80x MC PWM Module in Motor Control Applications
x_PER_CMTSTART_US
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>5000
<5000
[ s]
Table 11-2. Start-up Periods
0x0c00
0x1800
is used for control of commuting problems. The application software
x_PER_TOFFSTART_US = 2*x_PER_CMTSTART_US.
0x02
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x_PER_CMTSTART_US * 2
Section
x_PER_TOFFSTART_US
/* Start Commutation Period * [1.7777us] */
/* Start Zero Crossing
/* minimal Zero Crossing OK commutation
x_MAX_ZCROSERR
Toff Period * [1.7777us] */
to finish Bldc starting phase */
>10000
<10000
11.3.1) helps if a problem with start up is
Setting of SW parameters for other motor kits
[ s]
successive commutations with
First commutation
period
>10ms
<10ms
[s]
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