Week 8 Challenge
Week:8 (fuel cell)
Aim:
To load the UC parameter file. Complete the ultracapacitor model. Set simulation stop time to 598 sec.
Ultracapacitor:-
An Ultracapacitor also known as a supercapacitor or electrochemical capacitor is a device for storing electrical enegry which is growing radpidly in popularity The design and mechanism of operation is somewheer between and ordinary capacitor and a battery which open up some interesting and valuable applications.
Like a battery a single ultrcapacitor cell consists of a positive and negative electrode seperated by an electrolyte However ultracapacitor store energy electrostatically like e regualr capacitor not chemically like a battery there is a dielectric seperator dividing the electrolyte also like a capacitor
The small seperation between electrodes permitted by this structure lead to much higher energy density than a normal capacitor whilst a ultracapacitor stores less enegry than a eauivalenlty sized battery it can release it much quicker as the discharge is not depenedent on a chemical reaction taking place
Because no physical or chemical changes occur when charge is stored ultracapacitorn can also be used many times over without degradation
STEPS TO CONSTRCUT UC MODEL:-
There equation in UC model are defined first which gives us SOC Current and OCS
These are the 3 parameters which infulences UC
- OCV Defines the SOC of Ultracapacitor
- Max Voltage or voltage is directly proportional to the charge stored in the battery
- Amount if the charge is directly proportional to the current that can flow in the circuit.
Where:
- eta is the Coulomb efficiency.
- Q is the electric quantity or charge on UC.
- I is the current.
- Q depends on capacitance which is the charge storage capacity measured in measured in Farads.
The OCV is a measure of the electric field between plates.
- Capacitance and OCV gives 'Q'
- The integration of current over 'C' gives 'OCV'.
- In UC model calculation for current and SoC are done as said below:
- Firstly the current consumed is calculated which is fed into a SoC calcultaion block.
- The SoC is then calculated based on the amount of current drawn and pushed back into the UC.
Hence fomula for current is given as:
Where:
- R is the lumped resistance
- Vmax is the max. voltage
- eta is the efficiency during the charge-discharge cycle.
- PUC is the power demand which is to supplied by UC and it is the first input in this model which basically comes from Energy management systems.
As per the equation discussed above the model is constructed and its shown below
Simulink model:
- PCU is our input here which is nothing but the power demand for the uc. 20k watts is the value. In a complete fuel cell or eletric vehicle model it comes from the EMS (energy management system) block. This input goes inside the current calculation block. With the inside of current calculation block shown.
Implementation of current formula started above
- As you can we need SOC in current calculation, so SOC block does that and its implementation is shown in below:
If you see current and SOC calculation blocks are inter connected then both take each others quantity in there value calculation. The more the current is drawn the lower the SOC is going to get. Initial SOC has been set to 1 which basically means that we are going to draining the ultracapacitor
- A part from current the second input to the SOC block is charge Q. we know the formula to calculate Q hence we only need to implement that here:
- With the help of calculate current we can calculate the OCV. The formula was started above and its implementation is shown below:
- To find the voltage of the UC we need current and SOC as our input which helps us to find UC voltage. The formula for it is Simulink representation:
