User Guide

AN1292 Tuning Guide
 2010 Microchip Technology Inc. DS70640A-page 3
e) Nominal and Maximum Speed
Nominal speed is a parameter provided by the manufacturer and represents the
speed achievable with the nominal current and voltage provided on the motor’s
plate.
Maximum speed is a parameter provided by the manufacturer and depends
mostly on the mechanical parameters of the motor. It may be observed that the
maximum speed is higher than the nominal speed, and the region in between
being covered in constant power mode, where the field weakening technique is
implied.
f) Predivision Factors
Predivision column corresponds to a scaling constant used for bringing the
resulting calculation of normalized values into the numerical representation
range, [-32768, 32767]. The Predivision scaling should not only bring the
constants into the range but also, in case of the inverse voltage constant (Kfi), to
divide its initial calculated value so that when it is multiplied afterwards due to
field weakening technique, it does not overflow the numerical representation
range.
The Predivision factors can be found in the software code in the form of division
operation term (left shift).
For example, NORM_LSDTBASE Predivision scaling is 256 in the spreadsheet,
which reflects in the following line of code:
estim.c
As it may be observed, instead of shifting to the left with 15, because of previous
predivision with 2
8
, it is finally shifted with 7.
The same happens for NORM_RS, which is predivided by 2 to keep NORM_RS
within range, which prevents a numeric overflow. This results in the estim.c
corresponding code section to counter balance the initial predivision by a shift of
14 instead of 15:
estim.c
In the case of NORM_INVKFIBASE, the Predivision is 2 and the reverse
multiplication is done on the following line of code:
estim.c