Week 5 Battery characteristics using drive cycle

Simulate generic battery model charge discharge using UDDS data.

The following blocks are needed for modelling the battery.

1. Generic Battery Model

2. Signal Builder

3. Controlled current source

4. Bus Selector

5. Scope

6. Powergui

Steps for modelling:

The signal builder block is used to create the UDDS drive cycle data. The main drawback of this block is that it accepts data in the form of current profile. So the speed vs time data of the UDDS drive cycle data was converted to current vs time data. And the excel file containing the data is imported to the block.

The output of the signal builder is given to the current controlled source which is connected to the battery as a load. So the battery discharges according to this signal given by the signal builder which is the UDDS drive cycle data.

The Powergui block is necessary for simulation of any Simulink model containing SimPowerSystems™ blocks. It is used to store the equivalent Simulink circuit that represents the state-space equations of the model.

The output of the battery is given to the scope via bus selector. The bus selector outputs the battery signals (voltage, current, SOC) to the scope.

Since there are 1369 points in the current profile, we set the stop time as 1369 to get the entire discharge characteristics of the battery. The Lithium ion battery parameters are retained as default.

The simulation results are as follows:

Analysis:

• Initially the State of charge (SOC) of battery is 100%. That means the battery is fully charged. The rated voltage initially is 8.38 V (same as fully charged voltage in battery parameter) and the current is 0A.
• when the vehicle is started, battery discharges; as a result the voltage and the SOC decreases.
• After 1360sec the SOC of the battery is reduced to 96%; the voltage is reduced to 7.85V (where the nominal voltage of battery is 7.2V); the current is discharged similar to the UDDS drive cycle.

• During the time period as marked; we can see that the current is going to negative that means during this period the battery gets charged due to regenerative braking and soon after this period we can see that the current ihas become zero 0 that means no charging or discharging is taking place.. So similar changes can be observed in voltage and SOC graphs.

• In voltage graph; as the current goes negative, there is a peak transient in voltage graph that means the voltage of the battery is increasing due to charging and the same change is happening in SOC graph. As the current goes to 0; that means the vehicle has stopped and no charging or discharging of the battery is occuring. the voltage and SOC will be same as that of the previous ondition. So the battery voltage available from that instant is 8.3V and the state of charge of battery is 99.5% . and this process of the battery charging discharging continues in its entire period of drive cycle.