Rechargeable Battery

You can download the final simulation file here

In this tutorial we explain how to use the rechargeable battery model. There are two battery models, a Lead-Acid and a general rechargeable battery model.

Some battery model parameters can be obtained from manufacturer datasheets, while others need to be obtained by measurement. This tutorial describes how to obtain these parameters.
Although the number of parameters for the battery models is low, behind the mask is a detailed battery model. The Lead-Acid model even includes the transient response when charging or discharging the battery.

The parameters required by the Lead Acid model are:

• Ah (battery capacity: ampere-hour) = 40 (maximum charge of the battery)
• Rinternal = 10m ohm (total series resistance of this battery module)
• Initial_SoC = 80% (initial state of charge of this battery) (100 stands for a fully loaded battery or any other value between 0 and 100 for a partially discharged battery)
• U[volt] = 12 (nominal voltage)
• Tau = 20 seconds (Time constant related to the mass transport inside the battery. Mostly in the order of several tens of seconds to minutes.)

The battery model is more simple as there is another Li-Ion model that should be used when more details inside the model are required and the performance of the battery has to be fit to manufacturer data.
The parameters required by the battery model are:

• Rinternal = 10m ohm (total series resistance of this battery module)
• U[volt] = 200 (nominal voltage)
• Initial_SoC = 100% (initial state of charge of this battery) (100 stands for a fully loaded battery or any other value between 0 and 100 for a partially discharged battery)
• kWh (battery capacity: kilowatt-hour) = 25 (maximum charge of the battery)

Note the difference in the parameter for the capacity, being in \(Ah\) for the Lead Acid and in \(kWh\) for the general battery model.

The values for\(V_{oc}\), can be directly read from manufacturer datasheet. Other parameters can be obtained from the the battery discharge curve. From a discharge curve, you can read the paired values of \(V_{oc}\) and \(SoC\). In the Lead Acid model, the voltage is the nominal 12volt. In the Battery model, the default value is around 200 volt. In both models, you can set another voltage level. If you want to model the \(V_{oc}=f(SoC)\), you have to use the Li-Ion model.

The simulation below shows the charging of a Lead Acid battery. Scope1 shows the State of Charge \(SoC\) of the Lead Acid battery. The charging current is limited to 50 Ampere and the charging voltage is 14 volts. After 2900 seconds the Lead Acid battery is full and the open circuit voltage rises towards 14 volt, as can be seen in Scope2. Scope3 shows the Lead Acid battery voltage as function of the State of Charge \(SoC\) of the battery.

In electric vehicles, the auxiliary supplies are mainly powered from the Lead Acid battery, such as the car radio, small pumps and fans as well as other mainly low power drives. The Lead Acid battery is charged from the traction battery which has a larger energy density than the Lead Acid battery.
As visible in Scope4, the \(Soc\) of the traction battery nearly changes, while charging a regular Lead Acid battery.