Software for

The STEPSS software is made up of three modules:

  • PFC (for Power Flow Computation) performs a power flow computation in order to determine the initial operating point of a dynamic simulation
  • RAMSES (for RApid Multiprocessor Simulation of Electric power Systems) simulates the dynamic evolution of the power system in response to disturbances/actions specified by the user
  • CODEGEN (for CODE GENerator) translates a model described by the user in a text file into its equivalent in FORTRAN 2003 language. The latter has to be compiled and linked to a user-defined executable version RAMSES.


  • differential/algebraic equations solver developed at the Univ. of Liège by P. Aristidou and T. Van Cutsem
  • simulation under the phasor approximation
  • significant speed-up obtained from decomposition (Schur-complement) and localization techniques
  • parallel processing on standard multicore computers.


  • receives user-defined models written in a simple homemade language
  • translates them into FORTRAN 2003 code, to be compiled and linked to the rest of RAMSES
  • 4 types of models : excitation control of sync. mach. / torque control of sync. mach. / injectors / two-ports
  • models freely shared by users -> open-source simulation software.

Each of the three modules can be used separately. For instance:

  • PFC alone: a power flow computation is run to inspect the power system state and/or save the corresponding power flow solution for use by RAMSES
  • PFC alone: a sequence of power flow computations is performed until obtaining the desired power system state. The corresponding power flow solution is saved for use by RAMSES
  • RAMSES alone: with the initial power flow solution produced by PFC or by the user, several dynamic simulations are run starting from that initial state, i.e. without invoking PFC each time
  • CODEGEN alone: a model is built and saved for future incorporation in a user-defined version of RAMSES.

         STEPSS can be used free of charge for non-commercial/non-profit purposes, in a version limited to 1000 buses and 2 cores.
         Please read the detailed license terms in the documentation

         Please check the Installation section in the documentation for accessing the software

         Please refer to the documentation       Still under construction !
         Click on "Help - User guide" in the program interface

Example 1: simple 5-bus system

An academic system aimed at illustrating various notions of dynamics, control and stability wtih synchronous machines

  • Detailed description of the system : in this PDF file
  • input files : in this zip file
  • configuration file to load in RAMSES when starting : sim.cfg (included in zip file)

Example 2: the IEEE Nordic test system

A test system set up and documented by the Task Force on "Test Systems for Voltage Stability and Security Analysis" of the IEEE PES Power System Dynamic Perfomance Committee.

  • detailed models, data and simulation results are given in the technical report which can be downloaded from the IEEE PES Resource Center, No PES-TR 19. See also or
  • input files : in this zip file. It contains a variants.pdf file explaining the various combinations of input files
  • configuration file to load in RAMSES when starting : sim_nothing.cfg, sim_trip.cfg or sim_short_trip.cfg (included in zip file).