convert switched shunts to p.u.

[ccoffrin]

In the PSSE reader switch shunt b values should be converted to p.u. to be consistent with fixed shunts.

[ccoffrin]

This needs to be delayed until discrete valued shunts are explicitly supported in the data model.

[jd-lara]

@ccoffrin for completeness on the handling of switched shunts, I would also say that there is a small difference in results between Matpower/PSSe/PowerModels with the switch shunts as follows:

1. PSSe treats the Switch shunts like a Dispatchable generator that only dispatches Q (discrete or linear depending on the "control mode"). As a note, the resulting dispatch isn't stored in the raw file.
2. Matpower reads Switch shunts and converts them into fixed Reactive power injections at the node. This creates a difference between Ybus when switch shunts are present.
3. PowerModels converts them into fixed shunts and adds them as impedances into the Ybus.

[ccoffrin]

Thanks for the heads up @jd-lara! I am not super excited by either of the conventions of PSSE and Matpower as you describe them. It seems strait-forward to me to model them as changeable impedances, which I believe is a more accurate model of what the hardware does.

@rdzman, could you give us some insight into Matpower's convention for treating switched shunts that occur in PSSE files?

[jd-lara]

Thanks for the heads up @jd-lara! I am not super excited by either of the conventions of PSSE and Matpower as you describe them. It seems strait-forward to me to model them as changeable impedances, which I believe is a more accurate model of what the hardware does.

@rdzman, could you give us some insight into Matpower's convention for treating switched shunts that occur in PSSE files?

Yeah, it been a bit of a headache to match and validate results recently on this... :\

[rdzman]

When reading a PSS/E RAW file, MATPOWER also converts the switched shunt to a fixed shunt impedance. So they end up as impedances in Ybus, just as with PowerModels.

[ccoffrin]

Thanks for the clarification @rdzman, I'll stick to that convention then.

[jd-lara]

Thanks for the heads up @jd-lara! I am not super excited by either of the conventions of PSSE and Matpower as you describe them. It seems strait-forward to me to model them as changeable impedances, which I believe is a more accurate model of what the hardware does.

@rdzman, could you give us some insight into Matpower's convention for treating switched shunts that occur in PSSE files?

@ccoffrin in fact I misinterpreted the way matpower uses the shunts and the column in the data model is for an impedance at V=1.0 and not a power value.