AN1905 ST Microelectronics, Inc., AN1905 Datasheet - Page 68

• Manufacturer Part Number: AN1905
• Description: St7mc Three-phase BLDC Motor Control Software Library
• Manufacturer: ST Microelectronics, Inc.

ST7MC THREE-PHASE BLDC MOTOR CONTROL SOFTWARE LIBRARY
integral action on the output will be increased). This is why this parameter has to be adjusted
prior to setting-up the integral coefficient of the PI regulator.
In theory, the higher the sampling rate, the better the regulation. In practice, you must keep in
mind that:
– the related CPU load will grow accordingly.
– In the stand alone library (sensor/sensorless), the speed information is based on a 6-step
– at high speed, in most cases, system inertia is such that the system response is slow: in
This parameter must be reported in the mtc.h file, in a specific define (50ms in the example
here below):
#define SAMPLING_TIME
■
This parameter K
sampling time value. The higher the K
response. Nevertheless, a value too high will lead to instability (see
sponse vs K
Figure 48. Speed correction versus K
Here is an empirical method to tune the K
– With K
– At a given speed, with some load, there will be an error respect to the target speed (so called
– When the system becomes unstable (with oscillations), stop increasing K
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time. There’s absolutely no need to have a sampling time lower than this duration (for exam-
ple, electrical frequency at max speed = 100 Hz -> T
these conditions there is no need to have a high sampling rate.
static error); by slowly increasing the K
Tuning the Proportional coefficient Kp
during the K
i
=0 and K
K
i
=0
p
value).
p
set-up
p
p
=0, start the motor; this is corresponding to open loop drive.
provides the instantaneous error correction and is independent from the
Static error
for K
50
p
=0
Speed
0
// 50ms
Target
p
, the lower the speed error and the better the dynamic
p
p
p
value (with K
value, the error will decrease.
coefficient:
K
p
=2
6_steps =
K
i
=0)
p
=5
10ms).
K
p
=10
Figure 48
p
(this is K
Time
for speed re-
K
p
=20
K
p
p limit
=0
).