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Robust Solver Convergence Behavior

asked 2025-01-06 08:41:23 -0600

nmsg gravatar image

updated 2025-01-07 09:39:21 -0600

Hello everyone,

While testing the robust solver for contingency analysis, I observed two behaviors which I cannot explain.

1. Non-Convergence with max Mismatch < 5 MVA

In some instances, the robust solver prints that it is unsuccessful even though the final mismatch is below 5 MVA. My tolerance is set to 1 MVA, but one of the measures that the robust solver usually takes is to increase the tolerance to 5 MVA and hence these models should converge.

2. Convergence with max Mismatch > 5 MVA

Oppositely, in some instances, the robust solver prints that it is successful even though the final mismatch is above 5.

Edit: Case 2 is explained by the creation of small islands and can be solved by turning them off.

Does someone have an explanation for this?

Thank you in advance!

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answered 2025-01-06 08:42:40 -0600

nmsg gravatar image

updated 2025-01-07 09:40:06 -0600

Here is an example of what is printed while the robust solver runs.

Example for case 1:

Processing contingency "SING OPN LIN 75 558-1529(1)" (#75 of 862):

OPEN LINE FROM BUS 558 NAME1 380.00] TO BUS 1529 [NAME2 380.00] CKT 1

Successful solution not achieved: Iteration limit exceeded

Largest mismatch is 113.04 MW or Mvar at bus 160396 [NAME3 330.00]

Total mismatch is 432.00 MVA

Storing the original solution state and options...

Attempting to solve with original settings...

Attempting to solve with various solution methods...

Attempting to solve with Data Check...

Attempting to solve with Var limit option change...

Attempting to solve with Constant Y load when load bus voltage is below PQBRAK...

Attempting to solve with low acceleration and high iterations...

Maximum mismatch changed from 90.86 MVA to 58.69 MVA at bus 160396.

Attempting to solve with more options...

Maximum mismatch changed from 58.69 MVA to 2.53 MVA at bus 160504.

Attempting to solve with Locking small generators...

Attempting to solve with locking 1391 generators with var band smaller than 4.00...

Solution failed. Restoring case and settings to ORIGINAL state.

Robust power flow solution UNSUCCESSFUL.

Testing RAS conditions after application of contingency [SING OPN LIN 75 558-1529(1)]

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Asked: 2025-01-06 08:41:23 -0600

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Last updated: yesterday