EquivCircuit.TTCexpoly — Two time-constant expoly-based equivalent-circuit model of a battery
Basic Thermal Parameters
The EquivCircuit.TTCexpoly component is an equivalent-circuit model of a generic battery. The open-circuit voltage depends on the state-of-charge (SoC) based on a polynomial with an exponential term. The transient response is modeled by a pair of SoC-dependent resistor-capacitor networks; see the following figure.
The gradual decay, with use, of a cell's capacity and increase of its resistance is modeled by enabling the include degradation effects boolean parameter. Enabling this feature adds a state-of-health (soh) output to the model. This signal is 1 when the cell has no decay and 0 when is completely decayed.
The soh output is given by
s is thickness of the solid-electrolyte interface (SEI),
Rs is radius of the particles of active material in the SEI.
The decay of the capacity is
C is the effective capacity, and
Cmax is the specified capacity equal to either the parameter CA or the input Cin.
The additional series resistance added to a cell is
with κ a parameter of the model.
The following equations govern the increase in the thickness of the SEI layer (s).
Select the thermal model of the battery from the heat model drop-down list. The available models are: isothermal, external port, and convection.
The isothermal model sets the cell temperature to a constant parameter, Tiso.
The external port model adds a thermal port to the battery model. The temperature of the heat port is the cell temperature. The parameters mcell and cp become available and are used in the heat equation
where Pcell is the heat generated in each cell, including chemical reactions and ohmic resistive losses, Qcell is the heat flow out of each cell, and Qflow is the heat flow out of the external port.
The convection model assumes the heat dissipation from each cell is due to uniform convection from the surface to an ambient temperature. The parameters mcell, cp, Acell, h, and Tamb become available, as does an output signal port that gives the cell temperature in Kelvin. The heat equation is the same as the heat equation for the external port, with Qcell given by
The capacity of the battery can either be a fixed value, CA, or be controlled via an input signal, Cin, if the use capacity input box is checked.
State of Charge
A signal output, soc, gives the state-of-charge of the battery, with 0 being fully discharged and 1 being fully charged.
The parameter SOCmin sets the minimum allowable state-of-charge; if the battery is discharged past this level, the simulation is either terminated and an error message is raised, or, if the allow overdischarge parameter is true, a warning is generated. A similar effect occurs if the battery is fully charged so that the state of charge reaches one; the simulation is terminated unless allow overcharge is true.
The parameter SOC0 assigns the initial state-of charge of the battery.
State of charge [0..1]
Sets capacity of cell, in ampere hours; available when use capacity input is true
Internal temperature of battery
Current into battery
Voltage across battery
Number of cells, connected in series
Capacity of cell; available when use capacity input is false
Initial state-of-charge [0..1]
Minimum allowable state-of-charge
Fixed cell resistance, if use cell resistance input is false
True allows simulation to continue with 1<SoC
True allows simulation to continue with SoC<SoCmin
Constant cell temperature; used with isothermal heat model
Specific heat capacity of cell
Mass of one cell
Surface coefficient of heat transfer; used with convection heat model
Surface area of one cell; used with convection heat model
Ambient temperature; used with convection heat model
expoly array for open-circuit voltage
expoly array for series resistance
expoly array for short time-constant resistance
expoly array for short time-constant duration
expoly array for long time-constant resistance
expoly array for long time-constant duration
An exponential-polynomial (expoly) is a polynomial with an exponential term included. Its coefficients are given by a one-dimensional array, k, such that ⅇxpoly⁡k,soc=k1⁢ⅇxp⁡k2⁢soc+k3+k4⁢soc+k5⁢soc2+⋯.
 Chen, M. and Rincón-Mora, G.A., Accurate electrical battery model capable of predicting runtime and I-V performance, IEEE Transactions of Energy Conversion, Vol. 21, No. 2, 2006.
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