Circuit Model Reference


Provided by	[physics continuum] > Models > Optional Models
Example Node Path	Continua > [solid physics continuum] > Models > Circuit Model
Requires	Physics Models: Space: any Time: Implicit Unsteady Material: Solid or Multi-Part Solid Optional Models: one of Battery, Electromagnetism
Activates	Solvers	See Circuit Solver.
	Other nodes	Circuits See Circuit Properties.
	Reports	Circuit Element Current, Circuit Element Current Derivative, Circuit Element Voltage See Circuit Element Reports.
	Field Functions	Current [circuit name] [circuit element] See Circuit Element Field Functions.

Circuit Properties

Circuits are stored under the Circuits node. Each Circuits > [circuit] node stores the circuit elements and connections that define the circuit and has the following properties:

Verbosity: Sets the level of output information that is displayed for this circuit while the solver is running.
Electrical Substeps: Specifies the number of substeps that the circuit solver runs for each simulation time-step (as specified for the Implicit Unsteady solver). This option is typically used when a circuit requires a time-accurate solution, but the solution for the battery or electromagnetic simulation does not require small time-steps. Increasing the number of substeps helps to reduce the dissipation of energy in the circuit. If the circuit solver takes significant time during substepping, a stop button () appears at the bottom of the simulation window, next to the circuit solver progress bar. To stop the solver, click .
Relative Tolerance: Specifies a convergence parameter for the circuit solver. You are advised not to change this parameter.
Grounds: Lists the circuit elements that have a grounded terminal. Read-only.
Number of allowed groundings: Specifies the maximum total number of grounded terminals in the circuit.

For information on elements and connections, see Circuit Elements Reference and Circuit Connections Reference.

Circuit Solver

The circuit solver is used in battery and electromagnetic simulations. The circuit solver operates with the electrical solver to compute the electrical solution for the circuit. In battery simulations, the circuit solver calculates the global battery voltage, and current in the case of a power load, based on the voltage of each battery cell.

The main computational cost of the circuit solver is in repeated calls to the electrical solver to obtain the battery cell voltage as the circuit solver iterates to a converged solution at each time-step. The number of ecells within a battery cell directly impacts the time that is required to reach each battery cell solution. Furthermore, the iterative solution of the electrical circuit for each battery cell can be fast when the current load is changing slowly. However, if the specified load is a power load for which both the voltage and current must be determined, or a rapidly varying current load, the circuit solver takes more iterative steps to reach a converged solution. For a power load, the specified load must not exceed the capacity of the battery circuit. If the load exceeds the capacity, no electrical solution exists and the electrical solver can fail to converge.

At each electrical time-step, the circuit solver determines the electrical solution. The circuit solver updates the load, iteratively finds the final current and voltage for each battery cell that satisfies the specified circuit load, and computes heat generation for circuit connectors.

To calculate voltage and current values, the circuit solver calls the battery cell model for each battery cell in the circuit. You cannot specify the battery cell model time-step. The initial time-step that is used in the battery cell model is the same as the time-step that is used in the circuit solver. However, when necessary, Simcenter STAR-CCM+ automatically adjusts the battery cell model time-step to stabilize the circuit solver and obtain a solution. To determine a solution, the battery cell model calls the unit cell battery model. You can specify the maximum time-step that the unit cell model can use.

The local temperatures that are input values to each ecell are mapped from the thermal solution. To start the simulation, the local temperatures are taken from the default initial state. The electrical solver uses Simcenter Battery Design Studio solvers that have been integrated into Simcenter STAR-CCM+ to incorporate the user-determined unit cell model. The electrical solver receives a current value from the circuit solver and computes the voltage and the internal heat generation of each ecell, and computes the output voltage for each battery cell for the circuit solver.

After each circuit solver time-step, the heat generation from each ecell is mapped to the thermal grid and used as input for the thermal solver. The circuit solver uses an adaptive time stepping scheme such that there is an electrical solution for each thermal solution time-step. The circuit solver and the thermal solver normally use the same time-step size, but the time-step sizes can be different.

If the electrical load is specified using a program file that is created in Simcenter Battery Design Studio, the electrical solver can take multiple substeps for each thermal time-step and is able to evaluate the load at intermediate thermal time values. If the electrical load is specified using a table, the load values are linearly interpolated so that only one load value is evaluated for each thermal time-step. It is possible to take substeps within each thermal time-step using a table load but the load value changes at the thermal time-step only. Similarly, using a scalar load option, the electrical solver evaluates the load at each thermal time-step.

The Solvers > Circuit node lets you activate or deactivate the circuit solver.

Circuit Element Reports

For any circuit element, you can define reports for the following quantities:

Circuit Element Current
Circuit Element Current Derivative (with respect to time)
Circuit Element Voltage

The report properties specify:

Circuit Element: The circuit element to which the report applies.
Terminals: The element terminal at which the quantity is calculated. For multicontact circuit elements, you can select any contact of the element. For all other types of circuit elements, Simcenter STAR-CCM+ reports the value at the negative terminal.
Units: The units to use for the quantity values.
Voltage Drop: Applies to Circuit Element Voltage reports only. When Activated, the voltage is measured with respect to the other terminal. When Deactivated, the voltage is measured with respect to ground.

Circuit Element Field Functions

Current [circuit name] [circuit element]: For each circuit element, the corresponding field function is created. Represents the electric current through the circuit element.