Week 8 Challenge

• In the Ultracapacitor (UC) model, we will be looking at the equations that define SOC, current and Open Circuit Voltage (OCV).
• These quantities are the important parameters that define the status of the UC while being used for driving.
• Using the basic working principle of UC, we will look at things that influence the OCV, SOC and capacitance.
• A simple OCV measurement effectively defines the State of Charge (SOC).
• The amount of charge is proportional to the current that can flow through the circuit.
• So OCV is sufficient to determine the basic status of the UC.

SIMULINK MODEL:

1. UC SOC Subsystem:

The SOC equation is modelled as

where η = Coulomb efficiency
I = Current
Q = Electric quantity

• The current flowing through the circuit when integrated gives the charge flown through the circuit.
• Taking a ratio of it over the total charge capacity gives SOC.
• Q depends on capacitance which is the charge storage capacity measured in Farads.

2. UC Charge Subsystem:

• The OCV is a measure of the electric field between plates.
• The capacitance & OCV is a measures of the electric field between plates.

The capacitance & Vmax give Q.

3. UC OCV Subsystem:

The integration of current over C gives OCV.

4. UC Current Subsystem:

The current consumed is calculated which is fed into a SOC calculation block.

where R = Lumped Resistance
Vmax = Maximum voltage
η = Efficiency during the charge-discharge cycle

5. UC Model:

In the UC model, calculations for current and SOC are done.

RESULT:

• Certain parameters should be considered for selecting the UC that would be part of the ESS.
• Maximum Charged Voltage should be decided based on DC-DC used.
• The minimum voltage should be decided based on bus voltage and DC-DC.
• The Power or Current required to be delivered by the UC to attain the vehicle characteristics.
• The voltage of a UC increases linearly when charged and currently drops.
• However, exceeding the voltage of UC beyond a limit can damage the UC.

• When discharging the voltage can drop quickly.
• If it gets too low, the DC-DC might not be able to boost it to the bus voltage level.
• The minimum voltage of UC should be kept in mind when the current is drawn.

The outputs of the UC Model are as follows:

For Constant PUC = 2000 W

For different PUCs

CONCLUSION:

The UC parameter file is loaded. The Ultracapacitor model is completed and simulated for t = 598 sec.