Induction Motor Soft-Starter

Initial posting September 19, 2019

Model updated February 20, 2022

In this example, a soft starter model for induction machine is implemented. The sequence of simulation is described as follows:

  1. The breaker (BRK_source) connects the source at a given time (0.2s).
  2. The command signal (start) enables the soft-starter to operate.
  3. The soft-starter measures the motor speed (Wm) and uses a PI controller to generates Alpha angle for the Thyristors.
  4. The voltage and current across the Motor starts to increase gradually as the soft-starter operates.
  5. The switch Enable/Disable the soft-starter can be used manually to turn off the soft-starter after the speed reaches to 1 pu. This can be adjusted to be automatic.

The firing angle of the soft-starter is defined by the PI controller. The proportional and integral gains of the PI controller can be adjusted to obtain the required slope of current raise during start up.

This is a simple implementation and the actual implementation in practical systems may have more controls and logic associated. These, if known, can be implemented using control blocks available in the PSCAD master library.