Regarding the current drive cycle.

[manjunathnilugal]

Discussed in #2742

^{Originally posted by manjunathnilugal March 5, 2023}
Hello everyone,
I am trying to run a current drive cycle, at some current values the voltage reaches maximum cut-off voltage 4.15 V. In that case I want to change the current value to "0 A" and maintain constant voltage until next discharge current value.
I am attaching the code which I am trying to execute.

import pybamm
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

model = pybamm.lithium_ion.SPM()
V = model.variables["Terminal voltage [V]"]

dt = 3600
time = 0
end_time = 11*3600

geometry = model.default_geometry
param = pybamm.ParameterValues("Chen2020")
#model.events.append(pybamm.Event('V', V - 4.1))

Vmin = 2.5
Vmax = 4.15

param['Lower voltage cut-off [V]'] = Vmin
param['Upper voltage cut-off [V]'] = Vmax

param['Current function [A]'] = "[input]"

param.process_model(model)
param.process_geometry(geometry)

# set mesh
mesh = pybamm.Mesh(geometry, model.default_submesh_types, model.default_var_pts)

# discretise model
disc = pybamm.Discretisation(mesh, model.default_spatial_methods)
disc.process_model(model)

I = np.array([2, 1, -2, -1, -3, -1, -2, 3, 2, 5, 4])
    
step_solver = pybamm.CasadiSolver()
step_solution = None

for i,I in enumerate(I):
    Vt = np.array([0])
    
    if  Vt[-1] >= 4.2:
        inputs = {'Current function [A]': 0.001}
    else:
        inputs = {'Current function [A]': I}
    
    step_solution = step_solver.step(step_solution, model, dt=dt, inputs=inputs, npts=100)
    V = step_solution["Terminal voltage [V]"].entries
    Vt = np.concatenate((Vt,V))
    It = step_solution["Current [A]"].entries

step_solution.plot()

I am not able to iterate the current values in the step solution, the simulation exits after the cut-off voltage is reached. Is there any method to keep the track of the voltage variation in middle of simulation ?

Instead of creating a interpolant function for current, I want to pass current individually after checking the final voltage value after each iteration.

if final voltage value is >= 4.2V:
      Current is 0.001 A
else:
      Current is [i] A

Is it possible to do using pybamm.

[brosaplanella]

I would suggest using experiments for that (see this example). Note, however, that you can't set both the current and voltage. That is, if you set the voltage to 4.15 V, the current will be whatever value that ensures that voltage.

[Mrzhang-hub]

Thanks for your help and problem has been solved according to this post. But the solving speed is too slow via pybamm.experiment() compared to sim.step(). Have you met the same problem?

[manjunathnilugal]

yes, problem solving is very slow (time and ram consuming)
I have raised another discussion, in order to reduce the computation timing.
[https://github.com//discussions/2687],

[Mrzhang-hub]

Amazing, I will keep track of that. Thanks again!

[manjunathnilugal]

@Mrzhang-hub if you find better way to simulate faster, please post here.

[Mrzhang-hub]

I get the same error and could not solve this for now.
AttributeError: 'Solution' object has no attribute 'steps'