"""
Module for power flow calculation.
"""
import logging
from collections import OrderedDict
from andes.utils.misc import elapsed
from andes.routines.base import BaseRoutine
from andes.variables.report import Report
from andes.shared import np, matrix, sparse, newton_krylov
logger = logging.getLogger(__name__)
[docs]class PFlow(BaseRoutine):
"""
Power flow calculation routine.
"""
[docs] def __init__(self, system=None, config=None):
super().__init__(system, config)
self.config.add(OrderedDict((('tol', 1e-6),
('max_iter', 25),
('method', 'NR'),
('check_conn', 1),
('n_factorize', 4),
('report', 1),
('degree', 0),
('init_tds', 0),
)))
self.config.add_extra("_help",
tol="convergence tolerance",
max_iter="max. number of iterations",
method="calculation method",
check_conn='check connectivity before power flow',
n_factorize="first N iterations to factorize Jacobian in dishonest method",
report="write output report",
degree='use degree in report',
init_tds="initialize TDS after PFlow",
)
self.config.add_extra("_alt",
tol="float",
method=("NR", "dishonest", "NK"),
check_conn=(0, 1),
max_iter=">=10",
n_factorize=">0",
report=(0, 1),
degree=(0, 1),
init_tds=(0, 1),
)
self.converged = False
self.inc = None
self.A = None
self.niter = 0
self.mis = [1]
self.models = OrderedDict()
self.x_sol = None
self.y_sol = None
[docs] def init(self):
"""
Initialize variables for power flow.
"""
system = self.system
t0, _ = elapsed()
self.models = system.find_models('pflow')
self.converged = False
self.res = matrix(0, (system.dae.n + system.dae.m, 1), 'd')
self.A = None
self.niter = 0
self.mis = [1]
self.exec_time = 0.0
self.x_sol = None
self.y_sol = None
self.system.set_var_arrays(self.models, inplace=True, alloc=False)
self.system.init(self.models, routine='pflow')
_, s1 = elapsed(t0)
logger.info('Power flow initialized in %s.', s1)
# force compile if numba is on - improves timing accuracy
if system.config.numba:
t0, _ = elapsed()
system.f_update(self.models)
system.g_update(self.models)
system.j_update(models=self.models)
_, s1 = elapsed(t0)
logger.info('Numba compilation for power flow finished in %s.', s1)
return system.dae.xy
[docs] def nr_step(self):
"""
Solve a single iteration step using the Newton-Raphson method.
Returns
-------
float
maximum absolute mismatch
"""
system = self.system
# ---------- Build numerical DAE----------
self.fg_update()
# ---------- update the Jacobian on conditions ----------
if self.config.method != 'dishonest' or (self.niter < self.config.n_factorize):
system.j_update(self.models)
self.solver.worker.new_A = True
# ---------- prepare and solve linear equations ----------
self.res[:system.dae.n] = -system.dae.f[:]
self.res[system.dae.n:] = -system.dae.g[:]
self.A = sparse([[system.dae.fx, system.dae.gx],
[system.dae.fy, system.dae.gy]])
if not self.config.linsolve:
self.inc = self.solver.solve(self.A, self.res)
else:
self.inc = self.solver.linsolve(self.A, self.res)
system.dae.x += np.ravel(self.inc[:system.dae.n])
system.dae.y += np.ravel(self.inc[system.dae.n:])
# find out variables associated with maximum mismatches
fmax = 0
if system.dae.n > 0:
fmax_idx = np.argmax(np.abs(system.dae.f))
fmax = system.dae.f[fmax_idx]
logger.debug("Max. diff mismatch %.10g on %s", fmax, system.dae.x_name[fmax_idx])
gmax_idx = np.argmax(np.abs(system.dae.g))
gmax = system.dae.g[gmax_idx]
logger.debug("Max. algeb mismatch %.10g on %s", gmax, system.dae.y_name[gmax_idx])
mis = max(abs(fmax), abs(gmax))
system.vars_to_models()
return mis
[docs] def nr_solve(self):
"""
Solve the power flow problem using itertive Newton's method.
"""
self.niter = 0
while True:
mis = self.nr_step()
logger.info('%d: |F(x)| = %.10g', self.niter, mis)
# store the increment
if self.niter == 0:
self.mis[0] = mis
else:
self.mis.append(mis)
# check for convergence
if mis < self.config.tol:
self.converged = True
break
if self.niter > self.config.max_iter:
break
if np.isnan(mis).any():
logger.error('NaN found in solution. Convergence is not likely')
break
if mis > 1e4 * self.mis[0]:
logger.error('Mismatch increased too fast. Convergence is not likely.')
break
self.niter += 1
return self.converged
[docs] def summary(self):
"""
Output a summary for the PFlow routine.
"""
# extract package name of the solver
sp_module = sparse.__module__
if '.' in sp_module:
sp_module = sp_module.split('.')[0]
out = list()
out.append('')
out.append('-> Power flow calculation')
out.append(f'{"Numba":>16s}: {"On" if self.system.config.numba else "Off"}')
out.append(f'{"Sparse solver":>16s}: {self.solver.sparselib.upper()}')
out.append(f'{"Solution method":>16s}: {self.config.method} method')
out_str = '\n'.join(out)
logger.info(out_str)
[docs] def run(self, **kwargs):
"""
Solve the power flow using the selected method.
Returns
-------
bool
convergence status
"""
system = self.system
if self.config.check_conn == 1:
self.system.connectivity()
self.summary()
self.init()
if system.dae.m == 0:
logger.error("Loaded case contains no power flow element.")
system.exit_code = 1
return False
method = self.config.method.lower()
t0, _ = elapsed()
# ---------- Call solution methods ----------
if method == 'nr':
self.nr_solve()
elif method == 'nk':
self.newton_krylov()
t1, s1 = elapsed(t0)
self.exec_time = t1 - t0
if not self.converged:
if abs(self.mis[-1] - self.mis[-2]) < self.config.tol:
max_idx = np.argmax(np.abs(system.dae.xy))
name = system.dae.xy_name[max_idx]
logger.error('Mismatch is not correctable possibly due to large load-generation imbalance.')
logger.error('Largest mismatch on equation associated with <%s>', name)
else:
logger.error('Power flow failed after %d iterations for "%s".', self.niter + 1, system.files.case)
else:
logger.info('Converged in %d iterations in %s.', self.niter + 1, s1)
# make a copy of power flow solutions
self.x_sol = system.dae.x.copy()
self.y_sol = system.dae.y.copy()
if self.config.init_tds:
system.TDS.init()
if self.config.report:
system.PFlow.report()
system.exit_code = 0 if self.converged else 1
return self.converged
[docs] def report(self):
"""
Write power flow report to a plain-text file.
Returns
-------
bool
True if report was written, False otherwise.
"""
if self.system.files.no_output is False:
r = Report(self.system)
r.write()
return True
return False
def _set_xy(self, xy):
"""
Helper function to set values for variables.
"""
system = self.system
system.dae.x[:] = xy[:system.dae.n]
system.dae.y[:] = xy[system.dae.n:]
system.vars_to_models()
def _fg_wrapper(self, xy):
"""
Wrapper for algebraic equations to be used with Newton-Krylov general solver
Parameters
----------
xy
Returns
-------
"""
self._set_xy(xy)
self.fg_update()
return self.system.dae.fg
[docs] def fg_update(self):
"""
Evaluate the limiters and residual equations.
"""
system = self.system
system.dae.clear_fg()
system.l_update_var(self.models, niter=self.niter, err=self.mis[-1])
system.s_update_var(self.models)
system.f_update(self.models)
system.g_update(self.models)
system.l_update_eq(self.models, niter=0)
system.fg_to_dae()
[docs] def newton_krylov(self, verbose=True):
"""
Full Newton-Krylov method from SciPy.
Warnings
--------
The result might be wrong if discrete are in use!
Parameters
----------
verbose
True if verbose.
Returns
-------
bool
Convergence status
"""
system = self.system
v0 = system.dae.xy
try:
ret = newton_krylov(self._fg_wrapper, v0, verbose=verbose)
self._set_xy(ret)
self.converged = True
except ValueError as e:
logger.error('Mismatch is not correctable. Equations may be unsolvable.')
logger.error(e)
self.converged = False
return self.converged