Regenerative Braking For Vehicles Engineering Essay

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The purpose of this project was to develop a PEM fuel cell hybrid system which functions as a regenerative braking system. Using fuel cell technology and the concepts of regenerative braking, this project aims to minimize energy loss and convert this energy into energy that can be used again. Fuel Cell technologies are expected to soon substitute the traditional power generators for residential applications. Using a PEM Fuel Cell, an ultra-capacitor, and a battery cell, this project made use of energy in such a way that power was utilized with greatest efficiency. As the vehicle moves up a slope from a stationary position, it uses the ultra-capacitor to thrust itself and then uses the motor to increase its speed. As the speed stabilizes, the battery is used to maintain a constant speed. The future of such fuel cell hybrid vehicles is something that is already happening in today's scientific pursuit but what this project aims to discover is how the combination of different power sources influences the efficiency of the electrically powered vehicle. For further study, more energy efficient fuel cell technology hybrid systems can be studied in order to provide a purer global environment.

Introduction

The concept of regenerative braking is not one that is unheard of in today's pursuit of science, technology, and automation. It has become a field that has already been ventured into and it is, therefore, very plausible to discover electric vehicles around us which work using a regenerative braking system. However, what this project aims to cover is slightly different. This project aims to test regenerative braking using a selective power sources and measure the efficiency. As hydrogen fuel cells are basically clean cells, they can be used to power most electric vehicles, therefore reducing the dependence on oil but, the reason this idea is not in widespread use is due to the fact that manufacturing fuel cells are "prohibitively expensive."

In this project, three different power sources were used. These include the ultra-capacitor, fuel cell, and the battery. As the ultra-capacitor and the fuel cell are regenerative power sources, they are suitable power sources for this experiment. A typical fuel cell combines hydrogen and oxygen to produce water and electricity. Electrolysis is what happens when the process is reversed. Ultra capacitors on the other hand store electrical energy by physically separating the negative and positive charges. Ultra capacitors tend to charge and discharge rather quickly and easily. Due to this particular characteristic of ultra capacitors, they cannot power a vehicle for long durations. It is when the vehicle needs to travel up a slope from a stationary position that the ultra capacitor comes into play. A battery, by contrast, chemically separates these charges. An ultra capacitor can be reused over and over again without a change in its performance levels. Using this property of an ultra capacitor, it was used to monitor the performance of the cycle at different speeds. As the vehicle requires a great amount of power to thrust forward, the ultra capacitor can be used to provide the power for that certain distance. While the ultra capacitor was used in the testing processes of the cycle, the battery was mainly used to regulate a smooth run. (Lampton, 2011)

Methods and Materials

As it is rather easy for each individual report to overlap in terms of content, each group member is focusing on a different set of topics in his/her report in the group.

2.1 The Process of Regeneration

Each time a car or any vehicle's breaks are exerted, some amount energy is wasted. According to the Law of Conservation of Energy, energy can never be wasted. It has to be converted to one form to the other. In the case of a vehicle slowing down, the kinetic energy produced by the vehicle must be transferred to another form. But, this energy ends up as heat and is effectively wasted.

Over the past few years, researchers in the field of power generation have devised different kinds of braking systems that could be used to summon up most of the car's kinetic energy and convert it to electricity so that this electricity can later on be used to recharge the car's batteries. This is what is termed as regenerative braking. This generated energy is stored in a storage battery and later used to power the motor whenever the vehicle is in its "electric mode."

Traditionally, brake pads are used to generate friction with the brake rotors in order to slow the vehicle. Due to this, additional friction is created between the "slowed wheels and the surface of the road." This is essentially how the car's kinetic energy turns into heat. By introducing regenerative braking, the system that drives the vehicle does the majority of the braking. As the driver steps on the brakes of any "electric or hybrid" vehicle, the brakes actually reverse the electric motor therefore slowing the vehicle's wheels. This electric motor also acts as an electric generator when it is reversed. Due to this particular characteristic, it produces electricity that is later fed into the vehicle's batteries. (Lampton, 2011)

In our project, three power sources were used namely the fuel cell, the battery and the ultra capacitor. These three sources were ordered from outside. As soon as the power cells arrived, our group got to working together on attaching the sources onto the bicycle. Along with these sources, we also required a speedometer and a GPS tracker in order to calculate the speed and to observe the route, respectively.

Speed(m/s)

Energy(J)

Voltage across the Capacitor(V)

Energy

Efficiency (%)

1.94

37.636

0.034

0.0335

0.08901052

2.22

49.284

0.059

0.1009

0.20473176

2.5

62.5

0.251

1.827

2.9232

2.78

77.284

0.285

2.3555

3.04784949

3.06

93.636

0.335

3.2545

3.47569311

3.33

110.889

0.356

3.6753

3.31439548

3.61

130.321

0.394

4.5018

3.45439338

3.89

151.321

0.443

5.6912

3.76101136

4.17

173.889

0.459

6.1097

3.51356325

4.44

197.136

0.555

8.9327

4.53123732

4.72

222.784

0.633

11.62

5.21581442

5

250

0.7

14.21

5.684

5.28

278.784

0.773

17.328

6.21556474

5.56

309.136

0.899

23.438

7.58177631

Figure 1: Table with the Calculated Experimental Values

Generally, regenerative braking systems tend to exponentially increase a system's fuel efficiency These systems are also vital in increasing the range of each vehicle. In pure electric cars, regenerative brakes are vital to increasing range and getting the most out of each charge.

The Motor as a Generator

Regenerative braking is tried on "hybrid gas/electric automobiles" to recollect a portion of the energy lost during braking. This summoned energy is later used to power the motor anytime the car is in electric mode. In the process of regenerative braking, motors function as generators and the output is transferred to the load and this in turn amplifies the braking effect.

2.3 The Limitations of Regenerative Braking

If regenerative braking is ideal for most vehicles, why is it that a majority of the vehicles seen on the road today prefer to use the traditional form of braking? The effect of Regenerative braking tends to drop at lower speeds. Along with the regenerative electric brake, the vehicle also requires the normal friction brake in case of a failure. Regenerative braking might not happen if any other electric part on the same supply is drawing power from battery or capacitors. Therefore, dynamic braking is used to soak up the excess energy. Dynamic braking is required to absorb the excess energy in order to allow a "satisfactory emergency braking performance." (Blanco,2011)

Results

In this experiment, my role consisted mainly of taking note of the calculations and measurements after the experiment was conducted. Apart from the initial

Kinetic energy can be calculated using the formula: . Once the brakes are applied, kinetic energy is converted to friction force where the result is equivalent to Force*Displacement. Once this friction force is created, it is stored in an ultra-capacitor whose voltage can be formulated by: 1/2CV.

Equating Kinetic energy to the Friction Force and

= 1/2CV + FS

In the experiment, using the electric bicycle, we measured the energy generated when the brakes were exerted from 20 km/hr to 0 km/hr. Along with energy, our group calculated the charging and discharging of the ultra capacitor as the brakes were applied.

Figure 2: A brief diagram of the circuit used in the electric bicycle consisting of two resistors, an ultra capacitor and a generator.

Figure 3

Using the graphs above, it is evident the voltage generated from braking is not sufficient to power up the motor of the vehicle.

Conclusion

The purpose of this experiment was to basically come up with PEM fuel cell hybrid system which functions as a regenerative braking system. With the switching of the power sources, the electric vehicle is tested for the minimal loss of energy. As the results show, the energy stored in the ultra capacitor is rather small and therefore the regenerative braking requires multiple charging in order to attain the power of 37V to power the electric vehicle. The future of such fuel cell hybrid vehicles is something that is already happening in today's scientific pursuit but what this project aims to discover is how the combination of different power sources influences the efficiency of the electrically powered vehicle. Further integration of antilock braking systems would pave way for the motor controller to take over the area of braking. With such possibilities in the field, it is surely an exciting area of science to work in.

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