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Use as Pandapower Solver

Advanced usage

0.6.0

As of version 0.6.0 lightsim2grid implements the new API of "newtonpf" required by pandapower. This means that it is asked specifically to provide ref a vector of integer identifying the slack buses (implements a distributed slack)

LightSim2grid can be used as a specific implementation of the pandapower "newtonpf" function.

Suppose you somehow get:

  • Ybus the admittance matrix of your powersystem, for example given by pandapower (will be converted to a scipy sparse.csc_matrix )
  • V0 the (complex) voltage vector at each bus, for example given by pandapower
  • Sbus the (complex) power absorb at each bus, for example as given by pandapower
  • ref Ids of the slack buses (added in version 0.5.6 to match recent pandapower changes)
  • pv list of PV buses
  • pq list of PQ buses
  • ppci a ppc internal pandapower test case (or dictionary, is used to retrieve the coefficients associated to each slack bus)
  • options list of pandapower "options" (or dictionary with keys max_iteration and tolerance_mva)

You can define replace the newtonpf function of pandapower.pandapower.newtonpf function with the following piece of code:

from lightsim2grid.newtonpf import newtonpf

# when pandapower version <= 2.7.0
# V, converged, iterations, J, Vm_it, Va_it = newtonpf(Ybus, Sbus, V0, pv, pq, ppci, options)

# when pandapower version > 2.7.0
V, converged, iterations, J, Vm_it, Va_it = newtonpf(Ybus, Sbus, V0, ref, pv, pq, ppci, options)

This function uses the KLU algorithm (or the solver provided in Eigen if KLU has not been instealld) and a c++ implementation of a Newton solver for speed.

Note

The oldest newtonpf function compatible with older version of pandapower (eg <=2.6.0) can still be accessed with from lightsim2grid.newtonpf import newtonpf_old

Even more advanced usage

You can customize even more the solvers that you want to use.

Lightsim2grid comes with 11 available solvers that can solver either AC or DC powerflows. We can cluster them into 3 categories.

If you want to stay "relatively high level", once you have a grid model, you can change the solver using the "enum" of the solvers you want to use as showed bellow:

from lightsim2grid.solver import SolverType
# init the grid model
from lightsim2grid.gridmodel import init
pp_net = ...  # any pandapower grid
lightsim_grid_model = init(pp_net)  # some warnings might be issued as well as some warnings

# change the solver used for the powerflow
lightsim_grid_model.change_solver(SolverType.KLUSolver)  # change the NR solver that uses KLU
# you can replace `SolverType.KLUSolver` by any of the 11 available solvers described bellow, 
# for example (and we will not write the 11...) `SolverType.KLUSolverSingleSlack`, `SolverType.SparseLUSolver` 
# or even `SolverType.NICSLUSolver`

All solvers can be accessed with the same API (if you want to use the raw python class, not recommended):

from lightsim2grid.solver import ASolverAvailable
Ybus = ...  # a csc sparse matrix (it's really important that it is a csc and not a csr !)
V0 = ...  # a complex vector (initial guess)
Sbus = ...  # a complex vector (power injected at each bus)
ref = ...  # a vector of integer giving the bus id of the slack buses
slack_weight = ...  # a vector of real number giving the weights associated to each slack bus
pv = ...  # a vector of integers giving the bus id of the PV bus
pq = ...  # a vector of integers giving the bus id of the PQ bus
max_it = ...  # a > 0 integer maximum number of iterations the solver is allowed to perform
tol = ...  # a > 0. real number giving the maximum KCL violation allowed for a all nodes

solver = ASolverAvailable()
converged = solver.solve(Ybus, V0, Sbus, ref, slack_weights, pv, pq, max_it, tol)

# to retrieve the voltages related information (in case converged is True)
solver.get_Va()  # voltage magnitude
solver.get_Vm()  # voltage angle
solver.get_V()  # complex voltage
# for compatible solvers
solver.get_J()  # see documentation of the `newton_pf` function for more information about the shape of J.

# some other usefull information
solver.get_nb_iter()  # return the number of iteration performed
solver.get_timers()  # some execution times for some function (TODO DOC)
sovler.get_error()  # the id of the error encountered  (TODO DOC)
sovler.converged()  # equal to the boolean `converged` above

Be carefull, there are some constraints on the data that are not necessarily checked, and might lead to hugly crash of the python virtual machine at execution time. So we encourage you to check that:

  • tol > 0.
  • maxt_it > 0
  • Ybus is a squared sparse matrix, in CSC format (see documentation of scipy sparse for more information) It is really important that this matrix is in CSC format
  • Sbus and V0 have the same size which corresponds to the size (number of rows or columns) of Ybus
  • for all node id in ref, slack_weight[node id] > 0.
  • sum(slack_weight) = 1. and all elements of slack_weight are > 0.
  • all the buses are on ref (for slack buses) or on pv (for PV buses) or on pq (for PQ buses) [informatically, this means that the ensemble [0, len(V0) - 1] is included in the union ref U pv U pq ]
  • all buses are only in one of ref, pv and pq [informatically an element of [0, len(V0) - 1] cannot be at the same time in pv and pq or in ref and pv or in ref and pq
  • there should be at least one element in ref (len(ref) > 0)

Warning

Just to emphasize that if any of the condition above is not met, this can result in crash of the python virtual machine without any exception thrown (segfault).

This is why we do not recommend to use these solvers directly !

AC solvers using Newton Raphson

There are 6 solvers in this categorie. They can in turn, be split into two main sub categories. The first one allows for a distributed slack bus (but can be a bit slower) as the other one does not allow for such (in case of multiple slack bus, only the first one is used as a real slack bus, the other ones are converted silently to PV buses)

The list is:

  • KLUSolver *: implementation of the Newton Raphson algorithm supporting the distributed slack bus, where the fast KLU implementation is used to iteratively update the jacobian matrix J.
  • NICSLUSolver *: implementation of the Newton Raphson algorithm supporting the distributed slack bus, where the fast NICSLU implementation is used to iteratively update the jacobian matrix J.
  • `SparseLUSolver`: implementation of the Newton Raphson algorithm supporting the distributed slack bus, where the Eigen default implementation is used to iteratively update the jacobian matrix J (instead of the faster KLU or NICSLU)
  • KLUSolverSingleSlack *: implementation of the Newton Raphson algorithm only supporting single slack bus [ignores slack_weight, assign all elements of ref into pv except the first one], where the fast KLU implementation is used to iteratively update the jacobian matrix J
  • NICSLUSolverSingleSlack *: implementation of the Newton Raphson algorithm only supporting single slack bus [ignores slack_weight, assign all elements of ref into pv except the first one], where the fast NICSLU implementation is used to iteratively update the jacobian matrix J.
  • `SparseLUSolverSingleSlack`: implementation of the Newton Raphson algorithm only supporting single slack bus [ignores slack_weight, assign all elements of ref into pv except the first one], where the Eigen default implementation is used to iteratively update the jacobian matrix J (instead of the faster KLU or NICSLU)

You can use them as:

from lightsim2grid.solver import KLUSolver  # or any of the names above

# retrieve some Ybus, V0, etc. as above
solver = KLUSolver()
converged = solver.solve(Ybus, V0, Sbus, ref, slack_weights, pv, pq, max_it, tol)
# process the results as above

Note

* these 4 solvers might not be available on all platforms (KLU is available if installed from pypi, but not necessarily when installed from source). The solvers based on NICSLU also requires an installation from source.

AC solvers using Gauss Seidel method

There are 2 solvers in this categorie. Neither of them supports distributed slack bus [they both ignore slack_weight and assign all elements of ref into pv except the first one]. If a grid with more more than 1 slack bus is provided, only the first one will be used as a slack bus, the others will be considered as "PV" nodes.

These solvers use the Gauss Seidel method to compute powerflows. This method will iteratively update the component of a bus based on the mismatch of the KCL. The "Gauss Seidel Synch" method is a custom implementation of this method that updates every components at once intead of updating them one by one for each iterations.

The two solvers there are GaussSeidelSolver and GaussSeidelSynchSolver. Unless for some particular use case, we do not recommend to use them as they often are slower than the Newton Raphson based solvers above.

DC solvers

This is another type of solvers available in lightsim2grid, they use a DC modeling of the powergrid equation and are often really fast compared to full AC powerflow.

The DC equations comes from the linearization of the AC equation, and solving a DC powerflow is basically equivalent to inverting a sparse matrix (or said differently solving for an equation of the sort Ybus * Theta = Sbus - strictly speaking it's not exactly this equation as we need a slack bus, for various reasons out of the scope of this documentation). In the current implementation it does not uses slack_weight and does not model distributed slack.

There are 3 solvers of this type that are different in the way they solve `Ybus * Theta = Sbus`:

  • DCSolver uses the default Eigen sparse LU implementation
  • KLUDCSolver uses the fast KLU solver
  • NICSLUDCSolver uses the fast NICSLU solver
from lightsim2grid.solver import DCSolver  # or any of the names above

# retrieve some Ybus, V0, etc. as above
dc_solver = DCSolver()
converged = dc_solver.solve(Ybus, V0, Sbus, ref, slack_weights, pv, pq, max_it, tol)
# process the results as above

Detailed documentation

lightsim2grid.newtonpf

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