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STEPSS

Solver Settings

Solver settings control the behavior of the RAMSES simulation engine. They are specified as records starting with $ in the data files.

Sampling and Output

Section titled “Sampling and Output”

Plot Step

Section titled “Plot Step”

Sampling time for observed variables:

$PLOT_STEP time(s) ;

Display Profiling

Section titled “Display Profiling”

Display profiling results after simulation:

$DISP_PROF T/F ;

Run-Time Refresh Rate

Section titled “Run-Time Refresh Rate”

Refresh interval for runtime observable plots (requires Gnuplot):

$GP_REFRESH_RATE time_interval(s) ;

Gnuplot Invocation

Section titled “Gnuplot Invocation”

Enable or disable launching Gnuplot for runtime observables. When set to F, the runtime observable data are still written to file but Gnuplot is never called; useful for batch/headless runs:

$CALL_GP T/F ;

Default: T.

Gnuplot Output Mode

Section titled “Gnuplot Output Mode”

Select whether runtime observables are displayed in an interactive terminal window or written to PNG image files:

$GP_MODE term/png ;

Default: term.

Observable Buffer Size

Section titled “Observable Buffer Size”

Internal memory reserved for storing observables during simulation:

$OBS_BUFFER_SIZE size(GB) ;

Default: 8 GB. Set this to less than half of your available RAM for large simulations.

Sparse Solver

Section titled “Sparse Solver”

Selects the sparse linear solver used for Jacobian factorization:

$SPARSE_SOLVER name ;
  • KLU: SuiteSparse KLU solver (default)
  • ma41: HSL MA41 solver

System Parameters

Section titled “System Parameters”

Base Power

Section titled “Base Power”

Sets the global base power of the system:

$S_BASE BASE(MVA) ;

Nominal Frequency

Section titled “Nominal Frequency”
FNOM Frequency(Hz) ;

Reference Frame

Section titled “Reference Frame”
$OMEGA_REF SYN/COI ;
  • SYN: Synchronous reference frame (suitable for short-term simulations)
  • COI: Center of inertia reference (suitable for long-term simulations)

See Reference Frames for details.

Numerical Parameters

Section titled “Numerical Parameters”

Newton Tolerance

Section titled “Newton Tolerance”
$NEWTON_TOLER NETWORK_TOLERANCE INJ_RELATIVE_TOLERANCE INJ_ABSOLUTE_TOLERANCE ;

Default values: 1e-03, 5e-04, 5e-04.

Finite Difference Values

Section titled “Finite Difference Values”

Values used to compute Jacobian matrices of injectors numerically:

$FIN_DIFFER proportional_value absolute_value ;

Full Jacobian Update

Section titled “Full Jacobian Update”

Disable partial Jacobian updates (force full update at every step):

$FULL_UPDATE T/F ;

Skip Converged Blocks

Section titled “Skip Converged Blocks”

Activate/deactivate skipping of converged injectors in Newton iterations:

$SKIP_CONV T/F ;

Maximum Fault Value

Section titled “Maximum Fault Value”
$MAX_FAULT value ;

Minimum Branch Impedance

Section titled “Minimum Branch Impedance”

Branches whose series impedance magnitude is below this threshold have their resistance/reactance floored to it, to avoid a singular network admittance matrix:

$ZMIN value(pu) ;

Default: 1e-05.

Advanced Solver Options

Section titled “Advanced Solver Options”

Solution Scheme

Section titled “Solution Scheme”
$SCHEME DE/IN ;
  • DE: Decomposed scheme
  • IN: Integrated scheme

Latency Settings

Section titled “Latency Settings”
$LATENCY OBS_TIME_WINDOW(s) EARLY_STOP(T/F) ;

Subnetwork Latency

Section titled “Subnetwork Latency”

Apply the latency technique at the subnetwork level: subnetworks whose currents change less than the latency tolerance are not recomputed at each step. Only active when subnetworks exist:

$LAT_SUBNETS T/F ;

Default: F.

Load Restoration Time Constant

Section titled “Load Restoration Time Constant”
$T_LOAD_REST time(s) ;

Network Frequency Update

Section titled “Network Frequency Update”

Update network elements (admittances) with frequency:

Network frequency update model 
$NET_FREQ_UPD T/F ;

Parallel Computing

Section titled “Parallel Computing”

Number of Threads

Section titled “Number of Threads”
$NB_THREADS Number ;

Thread Distribution Strategy

Section titled “Thread Distribution Strategy”
$OMP STA/DYN/GUI chunk ;
OptionDescription
STAStatic assignment (better for NUMA architectures)
DYNDynamic assignment (better for UMA architectures)
GUIGuided assignment

chunk is the number of consecutive injectors assigned to each thread.

Miscellaneous

Section titled “Miscellaneous”

User Model Library

Section titled “User Model Library”

Load a compiled user-model library (MDL file) at startup, making its models available to the simulation (Windows/Intel builds only):

$BASE_MDL filename ;

License

Section titled “License”

Provide the licensee e-mail and the 64-character license key. A valid key unlocks the full version, removing the free-tier limit of 1000 buses:

$LICENSE email license_key ;

Typical Configuration

Section titled “Typical Configuration”
# System base
$S_BASE 100. ;
FNOM 50. ;


# Reference frame (COI for long-term)
$OMEGA_REF COI ;


# Solution scheme
$SCHEME IN ;


# Solver tolerances
$NEWTON_TOLER 1e-03 5e-04 5e-04 ;


# Plotting
$PLOT_STEP 0.01 ;


# Parallel computing
$NB_THREADS 2 ;
$OMP DYN 50 ;


# Acceleration features
$SKIP_CONV T ;
$FULL_UPDATE F ;

Next Steps

Section titled “Next Steps”