User's Manual

PMAC2 User Manual
Setting Up PMAC2 Commutation (Direct PWM or Sine Wave) 47
M171=I171*3/12 ; Set phase angle to 90 deg
P170=1 ; Phasing OK flag
ENDIF
IF (M128&7=3) ; Hall Effect State 6 (60 to 0 deg)?
M171=I171/12 ; Set phase angle to 30 deg
P170=1 ; Phasing OK flag
ENDIF
IF (M128&7=0 OR M128&7=7) ; Invalid states
P170=0 ; Phasing not OK
ENDIF
IF (P170=1) ; Phasing OK?
CMD#1J/ ; Enable motor
ELSE
CMD#1K ; Not OK; disable motor
ENDIF
DISABLE PLC 1 ; So program will not repeat
CLOSE
Note:
Ix75 is not used for the phase position offset in this method. It can be used to store
the final correction based off fine phasing.
The test showed that the hall-effect sensors were in the standard direction, not
reversed, so bit 22 is left at zero. With bit 23 (a value of 8 in the first hex digit) set
to 1 to specify hall effect sensing, the first two hex digits of Ix81 become $B5. If
Flag register 1 at address $C000 were used for the hall-effect inputs, Ix81 would
be set to $B5C000.
The description of Ix81 in the Software Reference shows the common values of
offsets used, for all the cases where the zero point in the hall-effect cycle is at a 0
o
,
60
o
, 120
o
, 180
o
, -120
o
, or -60
o
point – where manufacturers generally align the
sensors.
Power-On Phasing Search
Warning:
An unreliable phasing search method can lead to a runaway condition. Test the
phasing search method carefully to make sure it works properly under all
conceivable conditions. Make sure the Ix11 fatal following error limit is active
and as tight as possible so the motor will be killed quickly in the event of a serious
phasing search error.
If a non-absolute sensor is used for commutation, PMAC2 must perform a search move for the proper
phasing reference every time it powers up (with an absolute sensor, this only needs to be done once in the
development of the system). There are several ways to do this phasing search. PMAC2 has two automatic
methods executed by firmware; other methods or enhancements of these methods can be executed with
PLC programs.
A power-on phasing search permits commutation of permanent-magnet brushless motors without the need
for a more expensive and possibly less accurate absolute sensor. However, a phasing search may not be
dependable in some applications; in these cases an absolute sensor will be required.
The estimate from a power-on phasing search should be within +1-2
o
e of the true zero position, so many
people will just use the phasing established here throughout the application. It is also possible to adjust
the estimate when settled at the index pulse, using the results of the fine phasing test described above.