[Bug]: Pack simulation with ECM model and capacity as input parameter crashes

[matthias-wueest]

liionpack Version

0.4.1.dev2

Python Version

3.11.11

Describe the bug

I would like to simulate a pack that consists of cells with different capacities.
I'm using the ECM Thévenin model.
As I understood from the provided examples, cell-specific parameters can be set via input parameters.
However, as soon as I define "Cell capacity [A.h]" as an input parameter, the simulation crashes.

Questions:

• Is this a known problem?
• Is there a known solution?
• What are your recommendations?

Steps to Reproduce

---

Variant 1: works for me (capacity defined as general parameter)

import liionpack as lp
import pybamm
import numpy as np
import matplotlib.pyplot as plt

I_mag = 5.0
OCV_init = 4.0  # used for intial guess
Ri_init = 1e-6 # used for intial guess
R_busbar = 1e-6
R_connection = 1e-6 
Np = 1
Ns = 4
Nbatt = Np * Ns
netlist = lp.setup_circuit(
    Np=Np, Ns=Ns, Rb=R_busbar, Rc=R_connection, Ri=Ri_init, V=OCV_init, I=I_mag
)


def ecm_model(parameter_values = None):

    # Create the pybamm model
    model = pybamm.equivalent_circuit.Thevenin(options = {"number of rc elements":0, "calculate discharge energy":"true"}) 
    
    # Add events to the model
    model = lp.add_events_to_model(model)

    # Set up parameter value
    if parameter_values is None:
        parameter_values = pybamm.ParameterValues("ECM_Example")

    # Change parameter to be an input controlled by the external circuit
    #parameter_values.update({"Cell capacity [A.h]": "[input]"})

    # Set up solver and simulation
    solver = pybamm.CasadiSolver(mode="safe")

    sim = pybamm.Simulation(
        model=model,
        parameter_values=parameter_values,
        solver=solver,
    )

    return sim


# Define parameters
parameter_values = pybamm.ParameterValues("ECM_Example") 

inputs={
    "Cell capacity [A.h]": (100*np.ones(Np * Ns)),
   }

# Define experiment
I_pack = "100 A"
experiment = pybamm.Experiment(
    [
        f"Charge at {I_pack} for 30 minutes",
        "Rest for 15 minutes",
        F"Discharge at {I_pack} for 30 minutes",
        "Rest for 15 minutes",
    ],
    period= "10 seconds",
)

# Simulate pack
output = lp.solve(
    netlist=netlist,
    sim_func=ecm_model,
    parameter_values=parameter_values,
    experiment=experiment,
    #inputs=inputs,
)

# Plot output
lp.plot_output(output)

Note: In liionpack.solvers.py, I had to make the following small modification to make the ECM within Liiionpack work:

Original:
self.variable_names = [
"Terminal voltage [V]",
"Surface open-circuit voltage [V]",
]

Modified:
self.variable_names = [
"Battery voltage [V]",
"Open-circuit voltage [V]",
]

---

Variant 2: does not work for me (capacity defined as input parameter)

import liionpack as lp
import pybamm
import numpy as np
import matplotlib.pyplot as plt


I_mag = 5.0
OCV_init = 4.0  # used for intial guess
Ri_init = 1e-6 # used for intial guess
R_busbar = 1e-6
R_connection = 1e-6 
Np = 1
Ns = 4
Nbatt = Np * Ns
netlist = lp.setup_circuit(
    Np=Np, Ns=Ns, Rb=R_busbar, Rc=R_connection, Ri=Ri_init, V=OCV_init, I=I_mag
)


def ecm_model(parameter_values = None):

    # Create the pybamm model
    model = pybamm.equivalent_circuit.Thevenin(options = {"number of rc elements":0, "calculate discharge energy":"true"}) 
    
    # Add events to the model
    model = lp.add_events_to_model(model)

    # Set up parameter value
    if parameter_values is None:
        parameter_values = pybamm.ParameterValues("ECM_Example")

    # Change parameter to be an input controlled by the external circuit
    parameter_values.update({"Cell capacity [A.h]": "[input]"})

    # Set up solver and simulation
    solver = pybamm.CasadiSolver(mode="safe")

    sim = pybamm.Simulation(
        model=model,
        parameter_values=parameter_values,
        solver=solver,
    )

    return sim


# Define parameters
parameter_values = pybamm.ParameterValues("ECM_Example") 

inputs={
    "Cell capacity [A.h]": (100*np.ones(Np * Ns)),
   }

# Define experiment
I_pack = "100 A"
experiment = pybamm.Experiment(
    [
        f"Charge at {I_pack} for 30 minutes",
        "Rest for 15 minutes",
        F"Discharge at {I_pack} for 30 minutes",
        "Rest for 15 minutes",
    ],
    period= "10 seconds",
)

# Simulate pack
output = lp.solve(
    netlist=netlist,
    sim_func=ecm_model,
    parameter_values=parameter_values,
    experiment=experiment,
    inputs=inputs,
)

# Plot output
lp.plot_output(output)

Expected behaviour

No response

Relevant log output

Additional context

No response