User Guide
Table Of Contents
- 1.1 SETTING SOFTWARE PARAMETERS
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AN1292 Tuning Guide
2010 Microchip Technology Inc. DS70640A-page 11
• Inductance Variation
For the inductance variation (LsOver2Ls0) lookup table, the first value in the
table should always be one-half since the base speed inductance is divided by
its own doubled value. These values should work for most motors.
userparms.h
b) Runtime Parameters Adjustment
If the results of running the software in these conditions will stall the motor at a
speed higher than nominal, it is due to the fact that the lookup tables were filled
with estimated values, which at some point do not match the real non-linearities.
Once the motor stalls, immediately halt the program execution, capturing the
value of the index (FdWeakParm.qIndex) in the debugger watch window. The
index indicates the point where the values of IDREF (see the IDREF table in Step
5a), in ascending order, were not effective and should be updated. In order to
further improve the performance, the value indicated by the current index in the
lookup table should be replaced by the value indicated by the next index
(FdWeakParm.qIndex + 1) and the motor's behavior should be checked again.
The achievable speed should increase and repeating this process for several
times the maximum speed for the nominal current reference imposed on the
d-axis will be reached.
If the maximum speed obtained for the nominal current is lower than the targeted
one, the absolute value of the d-axis current reference should be increased
above the nominal value. As an example, if 5500 RPM cannot be reached,
change IDREF_SPEED17 current from -1.53 to -1.60 and try again. The d-current
reference increase should be started from the value denoted by the index where
the motor stalled. The index value should correspond to the actual speed of the
motor, measured at the shaft using a tachometer, keeping in mind that the lookup
index is calculated using the reference speed, not the actual speed.
Once the d-current increase stops increasing the speed (increasing the current
too much will generally stall the motor), the index corresponding to the stall will
indicate where the value for inductance should be adjusted (increasing or
decreasing its value). The inductance variation lookup table is the last to be
updated.