How to choose switch model (Pejovic and Quasi-supra)

In eHS Gen 5 (State Space Analysis Method), switches can be model in two differents ways:

• Pejovic model;

• Quasi-supra model.

The selection between those two models depends on the characteristics of the circuit. Here are some guidelines on how to choose between them:

Pejovic model

The Pejovic model usually presents a more stable behavior, being recommended when the model has a high stiffness. It is recommended for modelling power electronic devices, as IGBT or diodes. However, this model may produce inaccurate results, for example, oscillating voltages and leakage current during blocking or excessive losses when operating at higher frequencies.

It is good option when configuring the model for the first time, since its more stable behavior will give a first approach towards the expected results; if such results are not suitable, they could be replaced by quasi-supra switches in order to achieve best accuracy.

Pejovic switches behavior depends entirely on the voltage and current on its terminals (contrary to quasi-supra switches, whose behavior depends on all inputs of the sub-circuit it belongs). Therefore, when a model contains many switches placed together, it could be better to choose Pejovic switches in order to avoid a cross-interaction among them that would end up producing divergent results.

Quasi-supra model

Quasi-supra model usually yields better and more accurate results, however the system has a more instable behavior, not infrequently resulting in divergent results. It is recommended for relay devices or fault simulations, as breaker or ideal switches.

This model is also recommended as an alternative when the Pejovic model does not give good results, as for example when there are excessive losses during conduction or high leakage currents during blocking.