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Programming Examples (cont'd)
True Torque Control Programming
The drive can be programmed to utilize True Torque Control (TTC), the benefits of which are slip
compensation and high torque at low speed. In volts per hertz control (or across the line ), a typical AC
induction motor will lose 3-5% of its RPM as it goes from no load to full load; when operated in TTC mode,
a motor will slow a maximum of 0.5% of base RPM as it is loaded. Motors operated on volts per hertz
drives cannot develop their rated torque when operated at low frequencies; the same motor operated in
TTC mode can typically develop 200% of its rated torque at one Hz.
The drive divides the motor current it is providing into two components that are ninety degrees out of
phase: the excitation current and the torque current. Excitation current is the part of the total current that
develops the magnetic field in the motor's core. The torque current is the current that does the useful
work. According to the Pythagorean theorem, (total current)
2
= (torque current)
2
+ (excitation current)
2
.
The drive calculates and controls these currents based on motor models to optimize motor performance.
If a Toshiba/Houston motor is used, the drive will use an on-board motor model. If a generic motor is
used, the drive can be programmed to auto-tune. During auto tuning, the drive derives a motor model by
applying a voltage to the motor and analyzing the resulting decay.
These parameters must be adjusted to use TTC with a TOSHIBA/HOUSTON motor.
Group Parameter Value
UTILITY PARAMETERS BLIND FUNCTION SELECTION 1
UTILITY PARAMETERS MOTOR PARAMETERS BLIND 1
FUNDAMENTAL PARAMETERS #1 VOLTS PER HERTZ PATTERN 5
MOTOR PARAMETERS NUMBER OF MOTOR POLES *
MOTOR PARAMETERS MOTOR RATED CAPACITY *
MOTOR PARAMETERS MOTOR TYPE **
MOTOR PARAMETERS LOAD MOMENT OF INERTIA ***
The following parameters must be adjusted to use TTC for a GENERIC motor.
Group Parameter Value
UTILITY PARAMETERS BLIND FUNCTION SELECTION 1
UTILITY PARAMETERS MOTOR PARAMETERS BLIND 1
FUNDAMENTAL PARAMETERS #1 VOLTS PER HERTZ PATTERN 5
MOTOR PARAMETERS NUMBER OF MOTOR POLES *
MOTOR PARAMETERS MOTOR RATED CAPACITY *
MOTOR PARAMETERS MOTOR TYPE 2
MOTOR PARAMETERS MOTOR RATED VOLTAGE *
MOTOR PARAMETERS MOTOR RATED FREQUENCY *
MOTOR PARAMETERS MOTOR RATED RPM *
MOTOR PARAMETERS AUTO-TUNING ENABLE 1****
MOTOR PARAMETERS LOAD MOMENT OF INERTIA ***
* Enter appropriate value from motor's nameplate. KW = 0.746 X HP.
** Enter "0" for an EQPIII or "1" for a high efficiency motor.
*** If the drive displays AUTO TUNE ERROR, try a different inertia setting.
**** The drive will auto tune the next time a run is initiated. This parameter is then reset to "0" by the drive`.