Release Notes

The APIs before v3.0.0 are in beta and may change without prior notice.

v1.5 Notes

v1.5.8 (2021-12-xx)

  • Full initialization debug message will be printed only when -v 10 and run --init are both used.
  • Improved warning of out-of-limit initialization. Variables initialized at limits will be shown only at the debug level.
  • Initialization improvements for models REGCA1 and REECA1.
  • Added model HYGOV.
  • Changed the default vout of offline exciters to zeros. All vout equations need to be multipled by ue.

v1.5.7 (2021-12-11)

This minor release highlights the improved debugging of initialization.

Highly verbose initialization output can be enabled when the verbose level is 10 or less. For example,

andes -v 10 run test.xlsx -r tds --init

will set the verbose level to 10 and run test.xlsx in the current folder, proceed to time-domain simulation but only initialize the models. Outputs will be printed to the shell where the command is executed.

To save the output to a file, use the following in a UNIX shell:

andes -v 10 run test.xlsx -r tds --init > info.txt 2>&1

where the first > pipes the output to a file named info.txt, and 2>&1 appends stderr (2) to stdout (1).

The other main improvement is allowing automatic limit adjustment during initialization. Due to parameter errors, some variables will be initialized to values outside the given limits. Most commercial software does not attempt to fix the parameter but rather adjust the limit in run time.

The same approach is followed in ANDES by automatically adjusting the upper limit, if exceeded, to variable initial values. The lower limit, however, is kept unadjusted by default.

Discrete components now take an argument named allow_adjust so that the model developer can specify if its limits can be adjusted or must be kept as is. Each model is allowed to specify three config flags to customize runtime behaviors: allow_adjust, adjust_lower, and adjust_uppwer. By default, allow_adjust=True, adjust_upper=True, and adjust_lower=False. One can modify the config file to enable or disable the limit adjustments for specific models.

Other fixes include:

  • Bug fixes for GAST parameter AT.
  • Bug fixes for IEEET3, GAST, ESAC1A and ESST1A when device is off to avoid matrix singularity.

v1.5.6 (2021-11-25)

  • Allow specifying config options through command-line arguments --config-option.
  • Added a voltage and frequency playback model PLBVFU1.
  • Bug fixes to an SEXS equation.

v1.5.5 (2021-11-13)

  • Added a Timeseries model for reading timeseries data from xlsx.
  • Converted several models into Python packages.
  • Bug fixes to TGOV1 equations (#226)

v1.5.4 (2021-11-02)

  • Fixed a bug in generated select functions that omitted the coefficients of __ones.

v1.5.3 (2021-10-31)

  • Revered special arguments for the generated select function.
  • Stabilized the argument list of pycode. If the pycode is identical to existing ones, the existing file will not be overwritten. As a result, compiled code is fully cached.
  • Partially seperated time-domain integration method into

v1.5.2 (2021-10-27)

  • Removed CVXOPT dependency.
  • Removed __zeros and __ones as they are no longer needed.
  • Added andes prep -c to precompile the generated code.
  • Added utility functions for saving and loading system snapshots. See andes/utils/
  • Compiled numba code is always cached.
  • Bug fixes.

v1.5.1 (2021-10-23)

  • Restored compatibility with SymPy 1.6.
  • Added a group for voltage compensators.
  • New models: IEEEVC and GAST.

v1.5.0 (2021-10-13)

  • Support numba just-in-time compilation of all equation and Jacobian calls.

This option accelerates simulations by up to 30%. The acceleration is visible in medium-scale systems with multiple models. Such systems involve heavy function calls but a rather moderate load for linear equation solvers. The speed up is less significant in large-scale systems where solving equations is the major time consumer.

Numba is required and can be installed with pip install numba or conda install numba.

To turn on numba for ANDES, in the ANDES configuration under [System], set numba = 1 and numba_cache = 1.

The just-in-time compilation will compile the code upon the first execution based on the input types. When compilation is triggered, ANDES may appear frozen due to the compilation lag. The option numba_cache = 1 will cache compiled machine code, so that the lag only occurs once until the next andes prep.

  • Allow BackRef to populate to models through Group.

When model A stores an IdxParam pointing to a group, if BackRef with the name A are declared in both the group and the model, both BackRef will retrieve the backward references from model A.

  • Allow BaseVar to accept partial initializations.

If BaseVar.v_str_add = True, the value of v_str will be added in place to variable value. An example is that voltage compensator sets part of the input voltage, and exciter reads the bus voltage. Exciter has v.v_str_add = True so that when compensators exist, the input voltage will be bus voltage (vbus) plus (Eterm - vbus). If no compensator exists, exciter will use bus voltages and function as expected.

  • Added reserved variable names __ones and __zeros for ones and zeros with length equal to the device number.

__ones and __zeros are useful for vectorizing choicelist in Piecewise functions.

v1.4 Notes

v1.4.4 (2021-10-05)

  • Bug fixes for refreshing generated code.

v1.4.3 (2021-09-25)

This release features parallel processing that cuts the time for andes prepare by more than half.

  • andes prepare supports multiprocessing and uses it by default.
  • Added aliases andes st and andes prep for andes selftest and andes prepare.
  • andes.config_logger supports setting new stream_level and file_level.

New exciter models are contributed by Jinning Wang.

  • Added AC8B, IEEET3 and ESAC1A.

Other changes include disallowing numba's nopython mode.

v1.4.2 (2021-09-12)

  • Bug fixes
  • Dropped support for cvxoptklu.

v1.4.1 (2021-09-12)

  • Bug fixes.
  • Overhaul of the prepare and undill methods.
  • andes prepare can be called for specific models through -m, which takes one or many model names as arguments.

v1.4.0 (2021-09-08)

This release highlights the distributed energy resource protection model.

  • Added DGPRCT1 model to provide DG models with voltage- and frequency-based protection following IEEE 1547-2018.
  • REECA1E supports frequency droop on power.
  • Throws TypeError if type mismatches when using ExtAlgeb and ExtState.

v1.3 Notes

v1.3.12 (2021-08-22)

Plot enhancements:

  • plot() takes an argument mark for masking y-axis data based on the left and right range parameters.
  • TDS.plt provides a panoview method for plotting an panoramic view for selected variables and devices of a model.


  • Added WIP EV models and protection models.

Test case: - Added CURENT EI test system. - Added a number of IEEE 14 bus test systems for specific models.

v1.3.11 (2021-07-27)

  • Added REECA1E model with inertia emulation.
  • Fixed an issue where the vtype of services was ignored.
  • Changed default DPI for plotting to 100.

v1.3.10 (2021-06-08)

  • Bug fixes for controllers when generators are off.

v1.3.9 (2021-06-02)

  • Bug fixes in exciters when generators are offline.
  • Added safe_div function for initialization equations.

v1.3.8 (2021-06-02)

  • Added REGCVSG model for voltage-source controlled renewables.
  • Turbine governors are now aware of the generator connection status.

v1.3.7 (2021-05-03)

  • Allow manually specifying variables needing initialization preceding a variable. Specify a list of variable names through BaseVar.deps.

v1.3.6 (2021-04-23)

  • Patched ESD1 model. Converted into a package.
  • Bug fixes.

v1.3.5 (2021-03-20)

  • Fixed a bug in connectivity check when bus 0 is islanded.
  • Updated notebook examples.
  • Updated tutorials.

v1.3.4 (2021-03-13)

  • Fixed a bug for the generated renewable energy code.

v1.3.2 (2021-03-08)

  • Relaxed the version requirements for NumPy and SymPy.

v1.3.1 (2021-03-07)

  • Writes all generated Python code to ~/.andes/pycode by default.
  • Uses generated Python code by default instead of calls.pkl.
  • Works with NumPy 1.20; works on Apple Silicon (use miniforge) to install native Python and NumPy for Apple Silicon.
  • Generalized model initialization: automatically determines the initialization sequence and solve equations iteratively when necessary.
  • In System.config, save_pycode and use_pycode are now deprecated.

v1.3.0 (2021-02-20)

  • Allow State variable set check_init=False to skip initialization test. One use case is for integrators with non-zero inputs (such as state-of-charge integration).
  • Solves power flow for systems with multiple areas, each with one Slack generator.
  • Added Jumper for connecting two buses with zero impedance.
  • REGCA1 and synchronous generators can take power ratio parameters gammap and gammaq.
  • New models: IEESGO and IEEET1, EXAC4.
  • Refactored exciters, turbine governors, and renewable models into modules.

v1.2 Notes

v1.2.9 (2021-01-16)

  • Added system connectivity check for islanded buses.
  • Depend on openpyxl for reading excel files since xlrd dropped support for any format but xlsx since v2.0.0.

v1.2.7 (2020-12-08)

  • Time-domain integration now evaluates anti-windup limiter before algebraic residuals. It assures that algebraic residuals are calculated with the new state values if pegged at limits.
  • Fixed the conditions for Iq ramping in REGC; removed Iqmax and Iqmin.
  • Added a new plot function plotn to allow multiple subplots in one figure.
  • TDS.config.g_scale is now now used as a factor for scaling algebraic equations for better convergence. Setting it to 1.0 functions the same as before.

v1.2.6 (2020-12-01)

  • Added TGOV1N model which sums pref and paux after the 1/droop block.
  • Added ZIP and FLoad for dynamic analysis. Need to be initialized after power flow.
  • Added DAETimeSeries.get_data() method.
  • Added IEEE 14-bus test cases with solar PV (ieee14_solar.xlsx) and Generic Type 3 wind (ieee14_wt3.xlsx).

v1.2.5 (2020-11-19)

  • Added Summary model to allow arbitrary information for a test case. Works in xlsx and json formats.
  • PV reactive power limit works. Automatically determines the number of PVs to convert if npv2pq=0.
  • Limiter and AntiWindup limiter can use sign_upper=-1 and sign_lower=-1 to negate the provided limits.
  • Improved error messages for inconsistent data.
  • DAETimeSeries functions refactored.

v1.2.4 (2020-11-13)

  • Added switched shunt class ShuntSw.
  • BaseParam takes inconvert and oconvert for converting parameter elements from and to files.

v1.2.3 (2020-11-02)

  • Support variable sys_mva (system base mva) in equation strings.
  • Default support for KVXOPT through pip installation.

v1.2.2 (2020-11-01)

New Models:

  • PVD1 model, WECC distributed PV model. Supports multiple PVD1 devices on the same bus.
  • Added ACEc model, ACE calculation with continuous freq.

Changes and fixes:

  • Renamed TDS._itm_step to TDS.itm_step as a public API.
  • Allow variable sys_f (system frequency) in equation strings.
  • Fixed ACE equation. measurement.
  • Support kvxopt as a drop-in replacement for cvxopt to bring KLU to Windows (and other platforms).
  • Added kvxopt as a dependency for PyPI installation.

v1.2.1 (2020-10-11)

  • Renamed models.non_jit to models.file_classes.
  • Removed models/ as models have to be loaded and instantiated anyway before undill.
  • Skip generating empty equation calls.

v1.2.0 (2020-10-10)

This version contains major refactor for speed improvement.

  • Refactored Jacobian calls generation so that for each model, one call is generated for each Jacobian type.
  • Refactored Service equation generation so that the exact arguments are passed.

Also contains an experimental Python code dump function.

  • Controlled in System.config, one can turn on save_pycode to dump equation and Jacobian calls to ~/.andes/pycode. Requires one call to andes prepare.
  • The Python code dump can be reformatted with yapf through the config option yapf_pycode. Requires separate installation.
  • The dumped Python code can be used for subsequent simulations through the config option use_pycode.

v1.1 Notes

v1.1.5 (2020-10-08)

  • Allow plotting to existing axes with the same plot API.
  • Added TGOV1DB model (TGOV1 with an input dead-band).
  • Added an experimental numba support.
  • Patched LazyImport for a snappier command-line interface.
  • andes selftest -q now skips code generation.

v1.1.4 (2020-09-22)

  • Support BackRef for groups.
  • Added CLI --pool to use multiprocess.Pool for multiple cases. When combined with --shell, --pool returns System Objects in the list system.
  • Fixed bugs and improved manual.

v1.1.3 (2020-09-05)

  • Improved documentation.
  • Minor bug fixes.

v1.1.2 (2020-09-03)

  • Patched time-domain for continuing simulation.

v1.1.1 (2020-09-02)

  • Added back quasi-real-time speed control through --qrt and --kqrt KQRT.
  • Patched the time-domain routine for the final step.

v1.1.0 (2020-09-01)

  • Defaulted BaseVar.diag_eps to System.Config.diag_eps.
  • Added option TDS.config.g_scale to allow for scaling the algebraic mismatch with step size.
  • Added induction motor models Motor3 and Motor5 (PSAT models).
  • Allow a PFlow-TDS model to skip TDS initialization by setting ModelFlags.tds_init to False.
  • Added Motor models Motor3 and Motor5.
  • Imported get_case and list_cases to the root package level.
  • Added test cases (Kundur's system) with wind.

Added Generic Type 3 wind turbine component models:

  • Drive-train models WTDTA1 (dual-mass model) and WTDS (single-mass model).
  • Aerodynamic model WTARA1.
  • Pitch controller model WTPTA1.
  • Torque (a.k.a. Pref) model WTTQA1.

v1.0 Notes

v1.0.8 (2020-07-29)

New features and models:

  • Added renewable energy models REECA1 and REPCA1.
  • Added service EventFlag which automatically calls events if its input changes.
  • Added service ExtendedEvent which flags an extended event for a given time.
  • Added service ApplyFunc to apply a numeric function. For the most cases where one would need ApplyFunc, consider using ConstService first.
  • Allow selftest -q for quick selftest by skipping codegen.
  • Improved time stepping logic and convergence tests.
  • Updated examples.

Default behavior changes include:

  • andes prepare now takes three mutually exclusive arguments, full, quick and incremental. The command-line now defaults to the quick mode. andes.prepare() still uses the full mode.
  • Model.s_update now evaluates the generated and the user-provided calls in sequence for each service in order.
  • Renamed model REGCAU1 to REGCA1.

v1.0.7 (2020-07-18)

  • Use in-place assignment when updating Jacobian values in Triplets.
  • Patched a major but simple bug where the Jacobian refactorization flag is set to the wrong place.
  • New models: PMU, REGCAU1 (tests pending).
  • New blocks: DeadBand1, PIFreeze, PITrackAW, PITrackAWFreeze (tests pending), and LagFreeze (tests pending).
  • andes plot supports dashed horizontal and vertical lines through hline1, hline2, vline1 and vline2.
  • Discrete: renamed DeadBand to DeadBandRT (deadband with return).
  • Service: renamed FlagNotNone to FlagValue with an option to flip the flags.
  • Other tweaks.

v1.0.6 (2020-07-08)

  • Patched step size adjustment algorithm.
  • Added Area Control Error (ACE) model.

v1.0.5 (2020-07-02)

  • Minor bug fixes for service initialization.
  • Added a wrapper to call TDS.fg_update to allow passing variables from caller.
  • Added pre-event time to the switch_times.

v1.0.4 (2020-06-26)

  • Implemented compressed NumPy format (npz) for time-domain simulation output data file.
  • Implemented optional attribute vtype for specifying data type for Service.
  • Patched COI speed initialization.
  • Patched PSS/E parser for two-winding transformer winding and impedance modes.

v1.0.3 (2020-06-02)

  • Patches PQ model equations where the "or" logic "|" is ignored in equation strings. To adjust PQ load in time domain simulation, refer to the note in
  • Allow Model.alter to update service values.

v1.0.2 (2020-06-01)

  • Patches the conda-forge script to use SymPy < 1.6. After SymPy version 1.5.1, comparison operations cannot be sympified. Pip installations are not affected.

v1.0.1 (2020-05-27)

  • Generate one lambda function for each of f and g, instead of generating one for each single f/g equation. Requires to run andes prepare after updating.

v1.0.0 (2020-05-25)

This release is going to be tagged as v0.9.5 and later tagged as v1.0.0.

  • Added verification results using IEEE 14-bus, NPCC, and WECC systems under folder examples.
  • Patches GENROU and EXDC2 models.
  • Updated test cases for WECC, NPCC IEEE 14-bus.
  • Documentation improvements.
  • Various tweaks.


v0.9.4 (2020-05-20)

  • Added exciter models EXST1, ESST3A, ESDC2A, SEXS, and IEEEX1, turbine governor model IEEEG1 (dual-machine support), and stabilizer model ST2CUT.
  • Added blocks HVGate and LVGate with a work-around for sympy.maximum/ minimum.
  • Added services PostInitService (for storing initialized values), and VarService (variable services that get updated) after limiters and before equations).
  • Added service InitChecker for checking initialization values against typical values. Warnings will be issued when out of bound or equality/ inequality conditions are not met.
  • Allow internal variables to be associated with a discrete component which will be updated before initialization (through BaseVar.discrete).
  • Allow turbine governors to specify an optional Tn (turbine rating). If not provided, turbine rating will fall back to Sn (generator rating).
  • Renamed OptionalSelect to DataSelect; Added NumSelect, the array-based version of DataSelect.
  • Allow to regenerate code for updated models through andes prepare -qi.
  • Various patches to allow zeroing out time constants in transfer functions.

v0.9.3 (2020-05-05)

This version contains bug fixes and performance tweaks.

  • Fixed an AntiWindup issue that causes variables to stuck at limits.
  • Allow to resume from a stopped simulation and run to the new end time in
  • Improved TDS data dump speed by not constructing DataFrame by default.
  • Added tests for kundur_full.xlsx and kundur_aw.xlsx to ensure results are the same as known values.
  • Other bug fixes.

v0.9.1 (2020-05-02)

This version accelerates computations by about 35%.

  • Models with flag collate=False, which is the new default, will slice DAE arrays for all internal vars to reduce copying back and forth.
  • The change above greatly reduced computation time. For kundur_ieeest.xlsx, simulation time is down from 2.50 sec to 1.64 sec.
  • The side-effects include a change in variable ordering in output lst file. It also eliminated the feasibility of evaluating model equations in parallel, which has not been implemented and does not seem promising in Python.
  • Separated symbolic processor and documentation generator from Model into SymProcessor and Documenter classes.
  • andes prepare now shows progress in the console.
  • Store exit code in System.exit_code and returns to system when called from CLI.
  • Refactored the solver interface.
  • Patched Config.check for routines.
  • SciPy Newton-Krylov power flow solver is no longer supported.
  • Patched a bug in v0.9.0 related to dae.Tf.

v0.8.8 (2020-04-28)

This update contains a quick but significant fix to boost the simulation speed by avoiding calls to empty user-defined numerical calls.

  • In Model.flags and Block.flags, added f_num, g_num and j_num to indicate if user-defined numerical calls exist.
  • In Model.f_update, Model.g_update and Model.j_update, check the above flags to avoid unnecessary calls to empty numeric functions.
  • For the kundur_ieeest.xlsx case, simulation time was reduced from 3.5s to 2.7s.

v0.8.7 (2020-04-28)

  • Changed RefParam to a service type called BackRef.
  • Added DeviceFinder, a service type to find device idx when not provided. DeviceFinder will also automatically add devices if not found.
  • Added OptionalSelect, a service type to select optional parameters if provided and select fallback ones otherwise.
  • Added discrete types Derivative, Delay, and Average,
  • Implemented full IEEEST stabilizer.
  • Implemented COI for generator speed and angle measurement.

v0.8.6 (2020-04-21)

This release contains important documentation fixes and two new blocks.

  • Fixed documentations in andes doc to address a misplacement of symbols and equations.
  • Converted all blocks to the division-free formulation (with dae.zf renamed to dae.Tf).
  • Fixed equation errors in the block documentation.
  • Implemented two new blocks: Lag2ndOrd and LeadLag2ndOrd.
  • Added a prototype for IEEEST stabilizer with some fixes needed.

v0.8.5 (2020-04-17)

  • Converted the differential equations to the form of T \dot{x} = f(x, y), where T is supplied to t_const of State/ExtState.
  • Added the support for Config fields in documentation (in andes doc and on readthedocs).
  • Added Config consistency checking.
  • Converted Model.idx from a list to DataParam.
  • Renamed the API of routines (summary, init, run, report).
  • Automatically generated indices now start at 1 (i.e., "GENCLS_1" is the first GENCLS device).
  • Added test cases for WECC system. The model with classical generators is verified against TSAT.
  • Minor features: andes -v 1 for debug output with levels and line numbers.

v0.8.4 (2020-04-07)

  • Added support for JSON case files. Convert existing case file to JSON with --convert json.
  • Added support for PSS/E dyr files, loadable with -addfile ADDFILE.
  • Added andes plot --xargs for searching variable name and plotting. See example 6.
  • Various bug fixes: Fault power injection fix;

v0.8.3 (2020-03-25)

  • Improved storage for Jacobian triplets (see andes.core.triplet.JacTriplet).
  • On-the-fly parameter alteration for power flow calculations (Model.alter method).
  • Exported frequently used functions to the root package (andes.config_logger,, andes.prepare and andes.load).
  • Return a list of System objects when multiprocessing in an interactive environment.
  • Exported classes to andes.core.
  • Various bug fixes and documentation improvements.

v0.8.0 (2020-02-12)

  • First release of the hybrid symbolic-numeric framework in ANDES.
  • A new framework is used to describe DAE models, generate equation documentation, and generate code for numerical simulation.
  • Models are written in the new framework. Supported models include GENCLS, GENROU, EXDC2, TGOV1, TG2
  • PSS/E raw parser, MATPOWER parser, and ANDES xlsx parser.
  • Newton-Raphson power flow, trapezoidal rule for numerical integration, and full eigenvalue analysis.

v0.6.9 (2020-02-12)

  • Version 0.6.9 is the last version for the numeric-only modeling framework.
  • This version will not be updated any more. But, models, routines and functions will be ported to the new version.