Schematic

Closed Loop Torque Mode
146 Advanced Digital Motor Controller User Manual V1.8 August 28, 2017
Torque Mode Selection, Configuration and Operation
Use the PC utility and the menu “Operating Mode” to select Torque Mode. The controller will
now use user commands from RS232, USB, Analog or Pulse to command the motor current.
Commands are ranging from -1000 to +1000. The command is then scaled using the
amps limit configuration value.
For example, if the amps limit is set to 100A, a user command of 500 will cause the con-
troller to energize the motor until 50A are measured. If the motor is little loaded and the
desired current cannot be reached, the motor will run at full speed.
Torque Mode Tuning
In Torque Mode, the measured Motor Amps become the feedback in the closed loop sys-
tem. The PID then operates the same way as in the other Closed Loop modes described
in this manual (See “PID tuning in Position Mode” on page 128).
In most applications requiring torque mode, the loop response does not need to be very
quick and good results can be achieved with a wide range of PID gains. The P and I gains
are the primary component of the loop in this mode. Perform a first test using P=0, I=1
and D=0, and then adjust the I and P gain as needed until satisfactory results are reached.
In brushless controllers operating in sinusoidal mode, torque mode uses the PID that is
regulating the Field Oriented Control. The gains must be therefore set in the FOC menus.
See also the KIF and KPF configuration commands in the Commands Reference section.
Configuring the Loop Error Detection
In Torque Mode, it is very likely that the controller will encounter situation where the mo-
tor is not sufficiently loaded in order to reach the desired amps. In this case, controller
output will quickly rise to 100% while a significant Loop Error (i.e. desired amps - mea-
sured amps) is present. In the default configuration, the controller will shut down the
power if a large loop error is present for more than a preset amount of time. This safety
feature should be disabled in most systems using Torque Mode.
Torque Mode Limitations
The torque mode uses the Motor Amps and not the Battery Amps. See “Battery Current
vs. Motor Current”on page 30. In most Roboteq controllers, Battery Amps is measured
and Motor Amps is estimated. The estimation is fairly accurate at power level of 20% and
higher. Its accuracy drops below 20% of PWM output and no motor current is measured
at all when the power output level is 0%, even though current may be flowing in the
motor, as it would be the case if the motor is pushed. The torque mode will therefore not
operate with good precision at low power output levels.
Furthermore the resolution of the amps capture is limited to around 0.5% of the full range.
On high current controller models, for example, amps are measured with 500mA incre-
ments. If the amps limit is set to 100A, this means the torque will be adjustable with a 0.5%
resolution. If on the same large controller the amps limit is changed to 10A, the torque will
be adjustable with the same 500mA granularity which will result in 5% resolution. For best