Custom termination event with discharge capacity

General
1

Hi,

I am doing a discharge event with a drive cycle current profile. Trying to terminate the event when the discharge capacity is closer to zero as voltage fluctuates. how to do that. thanks for your time.

regards

2

Capacity based termination works for charging but it gives me error for discharge, not sure why,

code snippet,

import pybamm
model = pybamm.lithium_ion.SPM()
parameter_values = pybamm.ParameterValues(“OKane2022”)

model.variables[“d_capacity [A.h]”] = model.variables[‘Discharge capacity [A.h]’]

def instantaneous_capacity(variables):
return variables[“d_capacity [A.h]”] - 3.0

capacity_termination = pybamm.step.CustomTermination(
name=“instantaneous capacity [A.h]”, event_function=instantaneous_capacity
)
terminations = [capacity_termination, “3 V”]

exp_dc = pybamm.Experiment(
[
(
pybamm.step.current(5.0, termination=terminations),
)
]
)

sim = pybamm.Simulation(model, parameter_values=parameter_values, experiment=exp_dc)
sol = sim.solve()

error message
--------------------------------------------------------------------------- SolverError Traceback (most recent call last) Cell In[352], line 3 1 sim = pybamm.Simulation(model, parameter_values=parameter_values, experiment=exp_dc) 2 # ----> 3 sol = sim.solve() File ~/.pyenv/versions/3.12.2/envs/cellmodelling/lib/python3.12/site-packages/pybamm/simulation.py:807, in Simulation.solve(self, t_eval, solver, save_at_cycles, calc_esoh, starting_solution, initial_soc, callbacks, showprogress, inputs, **kwargs) 805 if all(isinstance(step, pybamm.EmptySolution) for step in steps): 806 if len(steps) == 1: → 807 raise pybamm.SolverError( 808 f"Step ‘{step_str}’ is infeasible " 809 "due to exceeded bounds at initial conditions. " 810 "If this step is part of a longer cycle, " 811 "round brackets should be used to indicate this, " 812 “e.g.:\n pybamm.Experiment([(\n” 813 “\tDischarge at C/5 for 10 hours or until 3.3 V,\n” 814 “\tCharge at 1 A until 4.1 V,\n” 815 “\tHold at 4.1 V until 10 mA\n” 816 “])” 817 ) 818 else: 819 this_cycle = self.experiment.cycles[cycle_num - 1] SolverError: Step ‘Step(5.0, duration=86400, termination=[<pybamm.experiment.step.step_termination.CustomTermination object at 0x30e5c4c80>, <pybamm.experiment.step.step_termination.VoltageTermination object at 0x30e5c6840>], direction=Discharge)’ is infeasible due to exceeded bounds at initial conditions. If this step is part of a longer cycle, round brackets should be used to indicate this, e.g.: pybamm.Experiment([( Discharge at C/5 for 10 hours or until 3.3 V, Charge at 1 A until 4.1 V, Hold at 4.1 V until 10 mA ])

3

Discharge capacity starts at 0 then increases as you discharge, so the custom termination event is negative at the initial condition which is why you are getting the error. “3 - capacity” should work instead

1 Like
4

hi @valentinsulzer ,

thanks a lot for the kind reply. it works now.

model.variables[“d_capacity [A.h]”] = model.variables[‘Discharge capacity [A.h]’]

def instantaneous_capacity(variables):
return -0.25 - variables[“d_capacity [A.h]”]
#

The CustomTermination class takes a name and function

capacity_termination = pybamm.step.CustomTermination(
name=“instantaneous capacity [A.h]”, event_function=instantaneous_capacity
)

terminations = [capacity_termination, “3.0 V”]