Implement generic supercapacitor model
The Supercapacitor block implements a generic model parameterized to represent most popular types of supercapacitors. The block implements the following Stern equation and Tafel equation:
|A||Interfacial area between electrodes and electrolyte (m2)|
|c||Molar concentration (mol m −3) equal to c = 0.86/(8NAr3)|
|i||Current density (Am−2)|
|if||Leakage current (A)|
|i0||Exchange current density i0 = if/A (Am−2)|
|N||Number of layers of electrodes|
|Np||Number of parallel supercapacitors|
|Ns||Number of series supercapacitors|
|Q||Electric charge (C)|
|R||Ideal gas constant|
|r||Molecular radius equal x2|
|x2||Helmholtz layer length (m)|
|α||Charge transfer coefficient, Tafel equation (0<alpha<1)|
|ε||Permittivity of material|
|ε0||Permittivity of free space|
Specify the nominal capacitance of the supercapacitor, in farad.
Specify the internal resistance of the supercapacitor, in ohms.
Specify the rated voltage of the supercapacitor, in volts. Typical rated voltage is equal to 2.7 V.
Specify the surge voltage or maximum voltage of the supercapacitor. Surge voltage corresponds to the supercapacitor voltage when internal electrolyte becomes gas.
Specify the number of series capacitors to be represented.
Specify the number of parallel capacitors to be represented.
Specify the initial voltage of the supercapacitor, in volts.
Specify the leakage current of the supercapacitor, in amperes.
Specify the operating temperature of the supercapacitor. The nominal temperature is 25° C.
When this check box is selected, loads predetermined parameters of the Stern model into the mask of the block. These parameter values have been determined from experimental tests, and they can be used as default values to represent a common supercapacitor. Experimental validation of the model has shown a maximum error of 4.57% for self discharge and maximum error of 1.2% for charge and discharge when using the predetermined parameters.
When this check box is selected, the Number of layer, Molecular radius (m), Overpotential (V), Charge transfer coefficient alpha parameters appear dimmed.
Specify the number of layers related to the Stern model.
Specify the molecular radius related to the Stern model, in meters.
Specify the over-potential related to Tafel equation, in volts.
Specify the charge transfer coefficient related to Tafel equation as a value between 0 and 1.
When this check box is selected, the block plots a figure containing three graphs. The first graph represents capacitance as a function of time, the second graph represents voltage as a function of time, and the third represents current as a function of time.
Specify the charge current, in ampheres, used in the plot Capacitor vs Time and shown in the third graph.
Specify the maximum time value of the plot, in seconds.
Outputs a vector containing measurement signals. You can demultiplex these signals using the Bus Selector block.
|1||The supercapacitor current||A||Current|
|2||The supercapacitor voltage||V||Voltage|
|3||The state of charge (SOC), between 0 and 100||%||SOC|
The SOC for a fully charged supercapacitor is 100% and for an empty supercapacitor is 0%. The SOC is calculated as:
Internal resistance and capacitance are assumed constant during the charge and the discharge cycles.
The model does not take into account temperature effect.
No aging effect is taken into account.
Charge redistribution is the same for all values of voltage.
The block does not model cell balancing.
Current through the supercapacitor is assumed to be continuous.
The parallel_battery_SC_boost_converterparallel_battery_SC_boost_converter example shows a simple hybridization of a supercapacitor with a battery. The supercapacitor is connected to a buck/boost converter and the battery is connected to a boost converter. The DC bus voltage is equal to 42V. The converters are doing power management. The battery power is limited by a rate limiter block, therefore the transient power is supplied to the DC bus by the supercapacitor.