DG-IRMCK203 Datasheet, PDF (27/67 Pages) International Rectifier – Application Developer’s Guide

IRMCK203 Application Developer’s Guide
Figure 14. Start-up Diagnostic Function
Users can observe motor shaft movement during the Start-up diagnostic to determine an optimal value of KTorque.
As mentioned earlier, when the Start-up diagnostic is initiated, the drive will enter parking mode for 4 seconds;
thereafter open-loop start up will be initiated. There will be shaft movement due to parking of the motor during the
initial 4 seconds. It is important to observe the shaft movement only in the open-loop startup period. An optimal
KTorque value will generate higher starting torque and hence increased motor shaft rotation during open-loop
duration.
If measurement instrumentation (oscilloscope and voltage probe) is available, it can be used to observe the motor back
EMF to determine the optimal KTorque value. The motor back emf is proportional to motor speed. By observing
the motor line-line voltage at the end of the open-loop period (indicated by a momentary high pulse on D/A converter
channel 4), it is possible to determine an optimum value of KTorque.
Figure 15 and Figure 16 illustrate two example runs of the start-up diagnostic with two different values of KTorque
being used. As can be seen in these figures, after open-loop terminates, the speed of the motor coasts down. It is
apparent that the KTorque value used in Figure 16 provides higher voltage and frequency; hence the motor speed is
also higher.
DAC 4
output
Motor Line
Voltage
Open-Loop
Mode
Figure 15.
Coast Stopping
Open-loop start (KTorque = 400)
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