by Ric Austria

If only for this one new feature, the trip to attend the meeting (held April 28-29 in sunny Orlando, Florida) was worth it. The new feature is …
PSLF now allows “continuous” tap solutions for phase angle regulators, or PARs. Why does this matter? It matters a lot to those who work in the U.S. Eastern Interconnection (EIC) where most utilities use the competing software package, PSS/E.

Power flow models for the EIC use the default “continuous” solution setting for PARs in PSS/E. PSLF has, prior to the latest release, only provided for discrete and fixed solutions for PARs. (The rationale for this, mentioned at the meeting, was that in reality there are no continuous taps for PARs, only discrete taps.) Hence, for many years, those who needed to convert from PSS/E to PSLF data applied post-solution “fixes” to match the PAR taps, going from “continuous” mode in PSS/E to “discrete” mode in PSLF. But not anymore! Of course, tests of the implementation in PSLF are still pending. However, no question, this minor adaptation goes a long way towards improving compatibility between PSS/E and PSLF.

While we’re on this subject, two other features we asked of GE to implement that will greatly improve compatibility are:

  1. Increase the number of significant figures for voltage magnitude and phase angle when writing out raw power flow data. This would minimize mismatches when importing a solved power flow case using raw data. (Alternatively, a feature to import binary solved files would be better but may require more coordination between the developers of PSS/E and PSLF than presently exists.)
  2. Make the switched shunt hold setpoint available to PSLF’s user programming language (known as “epcl”). This is an undocumented and not-so-well-known parameter that determines when to stop switching shunts. The parameter, let’s call it SWSH, is generally larger than, and is typically some multiple of, the mismatch tolerance for the power flow solution. It comes into play when switched shunts oscillate from iteration to iteration. SWSH acts a secondary tolerance parameter that once met, stops further switching of shunts. Commercial software use it to improve their algorithm’s convergence characteristic when oscillating switched shunts are present. This feature is important to ensure that PSS/E and PSLF provide the same final switched shunt combination, and voltage solution.

Overall, kudos to the PSLF development team for applying upgrades to the software that make practical engineering sense. It is also encouraging to see the active involvement of planning and operations engineers providing input to the development process based on practical applications experience.

Other Discussions of Note

Solar PV Models – presented by Abe Ellis of Sandia National Lab. GE now has 2 model sets for PV inverters: ewtgfc-gewtge and pv1g-pv1e (new). Power flow modeling is similar to the wind farms (see “WECC” guidelines). For distributed PV (connected to distribution system), solar PV is modeled as part of the composite load model, rather than modeled explicitly. Harmonics – PV manufacturers have to qualify to IEEE 519 applicable to individual turbines, but for the whole plant there could still be an issue with harmonics. Solution at present is to add monitors when plant is completed and ask for post-implementation solution if violations are measured.

WECC Updates – presented by Enoch Davies of WECC. GENSAL model is being phased out due to insufficient modeling of saturation to be replaced by 2 new models. Guidelines are now available for modeling of wind (power flow and dynamics) and solar (power flow only for now) on the WECC website. WECC does not allow “blackbox”models (Hurrah for this!) with the only user-written models being for HVDC lines and converters. WECC staff conducts conversion of models from PSLF to PSSE. Tedious process. May take half day for power flow and 2-3 days for dynamics. Finally, WECC is pursuing an initiative for developing/updating load (composite) models.

PSLF feature updates – Generator voltage regulation can be specified by power factor in addition to reactive limits. Three new static var dynamic models. New stand-alone under/over voltage and frequency relay model for tripping generators. New electronic load model. New guidelines for HVDC modeling.

CIM (Common Information Model) – This is the dream of having a common data format for all power flow and stability software. At this time, most of the action is taking place in Europe where perhaps 8-10 vendor formats need to be ‘commonized’. PSLF will have capability to read/write CIM in a near-future version.

There was a lot more, but between Disney and Universal Studios who can be comprehensive? Anyway, good conference, good meeting, lots of nice planning/operations folks coming together.