Cause of IterationDiverge error

[BartSchuurmans]

Hi PGM team,

We use PGM for power flow calculation with the following setup:

pgm = PowerGridModel(self._topology)

return pgm.calculate_power_flow(
    update_data=update_data,
    calculation_method=CalculationMethod.newton_raphson,
    threading=0,
    tap_changing_strategy=TapChangingStrategy.disabled,
)

update_data contains 1 year of data in 15 minute increments, and is the output of our simulation model. For some random iterations of our simulation, the PGM call gives the following error for a few of the timesteps in the batch:

ERROR:lv_flex_control.core.loadflow.pgm:A PowerGridBatchError occurred, see details below: There are errors in the batch calculation.
Try validate_input_data() or validate_batch_data() to validate your data.
ERROR:lv_flex_control.core.loadflow.pgm: failed scenarios: [2181 2182 2183 2184 2185 2186 2188 2189 2190 2191 2192 2193 2194 2195
2196 2197 2198 2199 2200 2201 2202 2203 2204]
ERROR:lv_flex_control.core.loadflow.pgm: succeeded scenarios: [    0     1     2 ... 35037 35038 35039]
ERROR:lv_flex_control.core.loadflow.pgm: error messages: ['Iteration failed to converge after 20 iterations! Max deviation: 2.79685, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.351751, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.312154, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.175115, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 19.0043, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.0785031, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 1.52355, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 15.5638, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.493483, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 1.03546, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 5.06317, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 4.0639, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 6.18306, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 1.83333, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 46.2831, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 37.0158, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 4.1603, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 1.60537, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.462272, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 27.3413, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.420215, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 3.04146, error tolerance: 1e-08.\n', 'Iteration failed to converge after 20 iterations! Max deviation: 0.0667944, error tolerance: 1e-08.\n']
ERROR:lv_flex_control.core.loadflow.pgm: errors: [IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 2.79685, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.351751, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.312154, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.175115, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 19.0043, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.0785031, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 1.52355, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 15.5638, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.493483, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 1.03546, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 5.06317, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 4.0639, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 6.18306, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 1.83333, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 46.2831, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 37.0158, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 4.1603, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 1.60537, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.462272, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 27.3413, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.420215, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 3.04146, error tolerance: 1e-08.\n'), IterationDiverge('Iteration failed to converge after 20 iterations! Max deviation: 0.0667944, error tolerance: 1e-08.\n')]

I have confirmed that this error is deterministic for this specific simulation. I have also tried increasing the max_iterations parameter to calculate_power_flow, but this increases the max deviation, so it is truly divergent.

validate_input_data() and validate_batch_data() both indicate that there are no errors.

What can be the cause of having divergence here? Is there an error in our grid topology and/or input data?

[nitbharambe]

Hi @BartSchuurmans ,
Nice job on the preliminary investigation of identifying that this is indeed deterministic.
The reason for diverge can be among many things and you need to go through each failing scenario individually.

A peculiar thing here is these are only continuous 10 scenarios from 2182 - 2204 which fail. Very likely indicating bad data. All the rest pass which would indicate grid parameters given in input_data are good. Check the update_data corresponding to the failing scenarios for any unrealistic values. eg if a p_specified got a value of 1000kW instead of 1000W because of bad data or something similar.