This model implements an induction machine using the SSN methodology that is stable without any parasitic load or snubber.
SPS uses a current injection with delay technique to simulate machines such as the induction machine. This can cause numerical instability when the machine runs in light load conditions. Typically, an SPS user will have to connect a parasitic load or snubber at the machine terminal to keep stability in all conditions.
Using SSN, it is possible to make an induction machine that is stable with negligible or no load at all. The model uses the same classic induction machine equations as SPS and EMTP, using a fixed DQ reference.
Note: This model uses a simplified SSN User Custom Code method, without S-function builder, to implement the SSN equations of the induction machine.
The model compares the new SSN-IM machine model with standard SPS (on the right part of the model).
Simulation results match until the 1 MW snubber is disconnected from the induction machine, at which time the SPS model becomes unstable. By comparison, the SSN-IM remains stable all the time.