Week 8 Challenge

Question:

Load the UC parameter file. Complete the Ultracapacitor model. Set simulation stop time to 598 sec.

The model output should give, current, SOC and Voltage as output.

Aim: To Construct a Simulink model for an Ultracapacitor

Objective:

1. Load the UC Parameter file.

2. set Simulation stop time to 598 sec.

3. The model output should give,

i. Current

ii. SOC

iii. Voltage , as a output.

Introduction:

Ultracapacitor: Ultracapacitor which is also known as a supercapacitor is an electrical device

that stores charge in large amounts. It is called ultra because it has a higher capacitance value

than regular capacitors. These capacitors have low voltage limits and they have become a better

choice over the common capacitors.This is because they offer higher power density, consume less

power, and are safe and easy to operate.

An ultracapacitor operates between the limit of an ordinary capacitor and a battery. Although, the

device has just begun to gain population in the industry. They are suitable for applications from

efficient large-scale energy storage to a very small portable devices. This is because of their energy

density, short charging cycle, and wide range of operating temperatures.

Specifications of Ultracapacitors:

The following are the specifications of ultracapacitors:

1. The device has a high capacitance of about 2 kF.

2. Supercapacitors bridge the gap between conventional capacitors and rechargeable batteries.

3. They are capable of storing large amounts of energy.

4. Supercapacitors can store electricity through either electrostatic charge absorption/desorption.

5. The charge time of the device is about 1-10 seconds.

Charecteristics:

Ultracapacitors have three main characteristics which include charge time, specific power, and cycle

life, and safety.

1. Charge Time

Unlike the ordinary capacitor, ultracapacitors have charge and discharge times. This means it is

possible to achieve high charge and discharge currents due to low internal resistance. This is having

an advantage over batteries because it usually takes several hours to reach a fully charged state.

Let take a cell phone battery as an example, it will take supercapacitors just two minutes to have

the same charge.

2. Specific Power

Ultracapacitors have a specific power 5 – 10 times greater than batteries. The specific power in both

a battery or supercapacitor is a measure used to compare different technologies in terms of

maximum power output divided by the total mass of the device. Let take for instance, Li-ion

batteries have a specific power of 1-3 kW/kg, it is around 10 kW/kg for supercapacitors. This is the

device is suitable for applications that require quick bursts of energy to be released from the storage

device.

3. Cycle Life and Safety

When compared with batteries, supercapacitors are much safer. This is because batteries are known

to explode due to excessive heating when circuited, whereas supercapacitors do not overheat due to

their low internal resistance. However, shorting a fully charged supercapacitor will result in electrical

arcing, and might damage the device. Well, it’s a turn up to batteries since they generate heat have

no business with the device.

Construction and properties of ultracapacitors:

Just like that of electrolytic capacitors, the construction of ultracapacitors is much related. They also

consist of two foil electrodes, an electrolyte, and a foil separator. The separator is sandwiched

between the electrodes and the foil is folded into a shape, usually rectangular or cylindrical. It is

then placed into housing, which is filled up with electrolytes and hermetically sealed. The

electrolytes used here are much different from that of ordinary electrolytic capacitors.

In ultracapacitors, porous materials are used as separators in order to store electric charge. it stores

irons in those pores at an atomic level. Activated charcoal is the most commonly used material in

modern ultracapacitors. Carbon cannot serve as a better insulator because it results in a maximum

operating voltage limited below 3 V. Also, activated charcoal is not a perfect material because the

charge carriers are comparable in size to the pores material and some of them cannot fit into the

smaller pores. This results in a reduced storage capacity.

However, one of the most interesting materials used in ultracapacitor research is graphene. It is a

substance that consists of pure carbon, arranged in a planer sheet only one atom thick. The energy

densities achieve using graphene in ultracapacitors are comparable to energy densities found in

batteries.

Advantages of ultracapacitor:

Below are the benefits of ultracapacitors in their various applications:

1. High specific power

2. Safety in Operation

3. Long Lifetime

4. Wide temperature range

5. Maintenance-free operation

6. Environmentally friendly

Disadvantages of ultracapacitor:

Despite the good benefits of an ultracapacitor, some limitations still occur. Below are the

disadvantages of supercapacitors in their various applications.

1. A relatively low specific energy

2. Linear discharge voltage. that is, if a battery rated at 2.7V, at 50% charge it would still output a

voltage close to 2.7V. on a supercapacitor, a 2.7V at 50% would output exactly half of its maximum

charge voltage which is 1.35V. in another word, the output voltage of this device will fall below the

minimum operating voltage of the device.

3. The cost of supercapacitors is relatively high. In fact, the cost per Wh of a supercapacitor is more

than 20times higher than that of Li-ion batteries.

Simulink Model:

Fig.1

Steps to Construct a model:

There are 3 factores which influences the UC;

1. OCV Defines the SOC of Ultracapacitor

2. Max Voltage or voltage is directly proportional to the charge stored in the battery

3. Amount if the charge is directly proportional to the current that can flow in the circuit.

To calculate SOC, we have to use formula shown as below:

Where,

eta is the Coulomb efficiency.

Q is the electric quantity or charge on UC.

I is the current.

To calculate the charge of UC, Formula is;

Where,

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 and Can be calculated using the formula;

Where, 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.

After opening the fig.1 we get the subsystem wich is shown below,

Fig.2

Fig.2 consist of 2 subsystem; 1st is for current and voltage and 2nd is for SOC.

After selecting current and voltage subsystem, it consist of 4 subsystem.

1. UC_Voltage

2. UC_Current

3. OCV

4. Charge on UC

Some blocks are indicating red colour which means that we have to specify value for this in

MATLAB command window/workspace.

This concluded the current and volatge subsystem.

2nd subsystem from fig.2 is the SOC

Blocks used:

1. Constant

2. Product

3. Add

4. Integrator

5. Inport

6. Outport

7. To workspace

8.Scope

9. Square

10. Square root

Here,

P_UC = 1 kw

C=50

Eff=0.9

R=0.25

SOC_Initial=1

V_Max=310

Simulation time=598 sec

On simulating above model For 598 sec, i.e. Fig.1 we get the following results;

Results:

1. UC_Voltage

2. UC_Current

3. UC_SOC

From the results it can observed that current and voltage behaviour is totally different .

we have applied 310V we are getting 304V at the end of 598 sec where as curren of demand is

increasing which can be seen from the plot. The increasing demand can be fulfilled by an

ultracapacitor. During this SOC is reduces to 98% from 100%.

Conclusion:

Ultracapacitors are specially designed capacitors with very high capacitance. They combine the

properties of capacitors and batteries into one device. This is how simulation of ultracapacitor is

achieved properly.

Link:

https://drive.google.com/file/d/11VXdvYYXaeRE6c51VFiKLZlpATSy0KJ2/view?usp=sharing

Kindly open attached simulink file with MATLAB?Simulink.