35
Functional Description
4
Motor with SC speed controller
4.3
Overtemperature cut-off
The motor is deactivated if the temperature of the electronics exceeds the limit value of 100 °C.
The following condition must be fulfilled to reactivate the motor:
Temperature below the preset limit value
Adjustment of the controller parameters
The controller parameters are already preset for common applications. However, the controller para-
meters can be optimised to optimally adjust the controller to the respective application.
The digital controller operates with a sampling rate of approx. 500 µs.
Example of controller setting:
1. Set the initial configuration.
2. Increase controller gain (proportional component V).
3. Input speed jump from 1/3 of the maximum speed to 2/3.
4. Speed jump from 2/3 to 1/3 and observe behaviour.
5. Repeat steps 2 to 4, until the controller becomes unstable. Then reduce controller amplification
until stability is reliably ensured.
6. Repeat steps 2 to 5 with proportional integral-action component (VI)
Effect of pulse width modulation (PWM)
The power output stage of the integrated speed controller operates with so-called pulse width mo-
dulation (PWM). At a fixed frequency (the PWM frequency) the pulse duty factor is set between the
on time and the off time depending on the controller output value.
The advantage of this procedure is that the losses in the drive electronics are very low. In contrast,
the losses in a linear output stage can be very large and it becomes hot.
When the PWM is used the motor's inductance is used as a filter for the current. Therefore, the PWM
frequency should be high enough to adequately filter the current.
NOTE
Pulse duty factor
The PWM frequency of the speed controller is optimally matched to the connected motor. Never-
theless, it must be noted that with a low PWM pulse duty factor and larger motor load caused by
short-term high current flow in the motor, substantially higher losses can occur than with a large
pulse duty factor.
As large a pulse duty factor as possible should set in at the operating point. The required control
f
reserve must also be noted and observed!
To achieve this, if necessary, the motor operating voltage can be reduced.
f
NOTE
Efficiency
Please note that a reduction in efficiency at the motor also reduces the maximum allowable current
and therefore the maximum continuous torque.
