Hybrid Technology-An Engineering Approach

(Israr Ahmed,Touseef Ahktar,Badar-ud-Duja Dar,Musawir Hussain)

Abstract

Hybrid technology means to combine two or more technologies into single system in order to utilize them with in the single system. In this way just using one system we can use any of our technology at a time according to our present situation. In this way we can have similar results as produced by the constituent technologies. Hybrid technology is emerging in the future and it will be on the peak in upcoming time especially in automobile industry. Not only in the automotive industry but also in the biology, electronics and electric power generation hybrid technology is making its mark.

The frequent use of electronic appliances increases the demand of power generation. On the other the renewable energy resources combined for power generation called hybrid power system. There are many hybrid technologies. In solar wind hybrid system, wind and solar energy from wind turbine and solar panel respectively are used for power generation. In wind diesel hybrid system, power is generated by wind turbine also with back up diesel generator. In wind fuel cell hybrid system, power is generated from wind energy and chemical energy of the battery. In the last technology, fuel cell- gas turbine, power is generated by chemical energy and gas turbine with the release of some waste heat. The waste heat is further used to power micro gas turbine for power generation. Hybrid technology in cars provides us many backups like saving environment from the pollution with better fuel economy and mileage. There is also another side of the picture that is expensiveness and maintenance of the hybrid vehicle but with the passage of the time, researchers are improving these defects.

Hybrid technology in cars has long fierce history behind it. It faced many ups and downs in its reputation and making its sense. From first hybrid vehicle “the Volt” to “Toyota Prius” it saw many tenures. Hybrid solar vehicles combine an Internal Combustion Engine and Photovoltaic Panels. On the other hand, Hybrid Electric Vehicles combine IC Engine and Electric Propulsion System. Then the components (like electric motor, generator and battery) of a hybrid electric vehicle, their purpose, the working of an HEV, and how it uses technologies like regenerative braking, electric motor drive/assist and automatic start/stop to increase the efficiency of the vehicle, is explained briefly. The control system in HEV, mainly Vehicle Management Unit is discussed along with its sub-components, namely Battery, Engine and Motor Management Systems. After that the types of HEV along with their structure and their working is explained. The types include Series, Parallel, Series-Parallel and Complex Hybrid Vehicles. At the end of this section, another type of HEV is discussed, called plug-in hybrid vehicle. This vehicle’s battery can also be charged from a standard electric power outlet.

Present researches on the hybrid technology in vehicles have many priorities like low cost compact high efficiency motors, cheaper and durable energy dense batteries, low cost power electronics, intelligent thermal management and control of overall energy management etc. These all priorities are because of climate change, CO2 emissions, diversity of energy supply and local air pollution. When we see present results of hybrid vehicle usage, they show us very positive aspects like decrease in the CO2 and NOx emissions, increase in our marketing, increase in mileage and fuel economy etc. These all aspects cannot be neglected and in the upcoming time hybrid vehicles will be all over us and this technology will be the backbone of automotive industry.

1. Introduction:

1.1. Hybrid technology:

Usually we use two or more technologies with in a system to increase the efficiency and performance of our system i.e. by taking advantages of different technologies and combining them with in a single system. We enhance the quality of our system. This is known as hybrid technology. Word “hybrid” means anything that is made by the combination of two different elements. In this way we can have anything with mixed characteristics of composing materials. When we produce any system or technology by mixing and combining two different technologies or system we can have a final system that can act as an effective, labor saving, cost effective and energy efficient structure.

Sometimes we require dual or multiple functions from our system. This multiple functioning makes our system more portable, reliable and adjustable. So rather using different technologies for individual and separate systems we design single system with multiple technologies using hybridization. In this way our system will be versatile saving us from using separate systems for different functioning.

A hybrid technology produces same power similar results as produced by constituent technologies, such as the vehicle powered by both an electric motor and an internal combustion engine as sources of power.

2. Applications of hybrid technologies:

Hybrid technology has vast number of applications in different fields science. We can use it in electrical power generation, biology, electronics, games and sports, vehicles etc.

2.1. Biology:

In biology we can breed hybrid plants intentionally by cross pollinating to different varieties of a plant such as hybrid grapes, sweet corn, lilies and lemon etc.

Figure 1: Hybridization in Biology

2.2. Electrical power generation:

In electrical power generation, we can use hybridization in designing of hybrid power source (two different power sources) or hybrid generation (electrical power system comprising two or more generators) and hybrid turbine etc. to make our system sophisticated.

Figure 2: Hybrid technology in electric power generation

2.3. Electronics:

In electronics we design hybrid computers, telephones circuit, mass spectrometer, integrated circuit, tablet, laptops etc.

Figure 3: hybrid technology in electronics

2.4. Vehicles:

Our main concern is the utilization and application of hybrid technology in vehicles. Hybrid vehicles may include hybrid electric vehicle, plug-in hybrid, hybrid bicycle and hybrid train etc.

Figure 4: hybrid technology in Vehicles

3. Hybrid technology in cars:

A hybrid car uses two or more distinct types of power sources, such as I.C (internal combustion) engine that not only drives the car but also charge the electric battery. Hybrid technology is the backbone of future automobiles industry. Unhybrid car that only draws power from internal combustion engine has many such problems that can be different to handle in function. The fossil fuels and other fuel resources are moving towards end line. So hybrid cars that also have other power sources than that of internal combustion engine can save fuel. Moreover, one of the biggest problem of world is pollution. This mission is increasing majorly due to I.C engine automobile. So using automobiles with hybrid technology will be decisive in preventing our environment from pollution and our earth from declining its natural fuel resources. So hybrid cars can be environmental friendly.

                  

Although hybrid cars can be expensive, difficult to handle with higher maintenance costs but we cannot neglect its financial benefits, less dependence on fossil fuels, regenerative brake system and higher resale value making it stepping stone of bright future because hybrid cars show us how to drive efficiently with excellent mileage and durability. We don’t have to worry about the batteries and environment accept less maintenance.

3.1. History:

Hybrid cars have long history of ups and downs behind it.

3.1.1. First hybrid car:

According to an authentic website named hybridcars.com there was a scientist named Dr. Ferdinand Porsche who built the first car with two power sources, first internal combustion engine and second electric motor. This car was constructed an 1898 with I.C engines that would drive the electric generator by which 4 electric motors would be driven.

Figure 5: First hybrid Car

3.1.2. The Volt:

After that a similar car to that of Dr. Porsche was modeled named “the Volt”. This car could be charged by using plug in electricity. When that electric power was completely consumed during driving, then electric power could be generated by the internal combustion engine that will turn on the generator.

3.1.3. Initial reputation of hybrid car:

Initially hybrid cars didn’t get any special attention. This is due to many reasons but it can be understood with an example. In 1905, H. Piper published a patent about this hybrid car that would draw power from both internal combustion engine and electric motor. According to that patent that car will be able to achieve the speed of 40 Kph. But after first two years only, internal combustion engines with petrol as a fuel was able to achieve that speed easily. So because it was thought that there is nothing special in that hybrid car. So it didn’t get any special attention.

3.1.4. Oil crisis in 1970’s:

After that angle of thinking changed when oil fuel demand increased for thirsty cars. Oil crisis increased and change the priorities altered. That’s why concerns started about saving the natural resources of fuel, oil and fossil fuels that was drastically declining and rising problem for future.

3.1.5. Climatic concerns in 1990’s:

The climate was changing rapidly due to emission from burning of fossil fuels. Moreover it was also that the global warming is dramatically increasing due to large CO₂ emissions. Thus that also drawn the attention towards the hybrid cars that will reduce the fossil fuel burning and as a result there will be less emission of the CO₂ that would prove beneficial and friendly for the environment.

3.1.6. Trend shifting to electric cars:

During 1990’s three big car makers of America shifted their focus towards diesel-electric hybrid car but they didn’t launch any production. Then the focus shifted completely towards electric cars. But their high cost and limited range limited their fame. Even the most advanced models were able to go about 100 miles before they needed to be plugged in. thus their production was stopped.

Figure 6: First Electric Car

3.1.7. Toyota’s Progress:

• In 1992, first Earth charter was released by Toyota in which it was divided to minimize the environmental impacts by automobiles. They planned to produce the cars with 50% better fuel economy.
• They decided to do massive research and development effort. They made ordinary improvements such as better and cheaper batteries, more powerful control electronics to co-ordinate the two power source system.

3.1.8. Toyota’s first break through:

After all, struggle of Toyota, they launched Prius in 1997 in Japan. Now Prius is most common hybrid car in other foreign countries. Although Honda has also launched some hybrid cars but Toyota’s production rate is far more than that of Honda.

Figure 7: Toyota’s first Prius

4. Related Theory

4.1. Hybrid technology in Power Generation:

Every device that we use in our day to day life such as mobile phones, computers washing machines and vacuum cleaners etc, requires electric power supply. Thus, the advancement in technology increase the electrical and electronic appliances usage which, in turn is increasing the power demand. Thus, to meet the load demand, different techniques are used for electric power generation. In the recent times, to avoid pollution and to conserve non-renewable energy resources like coal, petroleum, etc and renewable energy resources like solar, wind etc, care being preferred for power generation. The combination of renewable energy sources can also be used for generating power called as hybrid power system. So now we are going to study some of the hybrid technology for the electric power generation.

1.      Wind-solar (photovoltaic) hybrid system

2.      Wind-diesel hybrid system

3.      Wind-fuel cell hybrid system

4.      Fuel cell- gas turbine hybrid system

4.1.1. Wind-Solar Hybrid System:

Solar and wind hybrid power systems are designed using solar panels and small wind turbine generators for generating electricity. Generally, these solar wind hybrid polar power systems are capable to produce small power.

The typical power generation capacities of solar wind hybrid systems are in the range from 1 kW to 10 KW. Before discussing in brief about the solar and wind hybrid power system, we should know about the solar-power generation system and wind-power generation systems.

Figure 8: Wind Solar Hybrid System

4.1.1.1. Working of Solar-Wind Hybrid System:

                        To better understand the working of solar wind hybrid system, we must know the working of solar energy system and wind energy system. The block diagram of solar-wind hybrid system is shown in the figure in which the solar panels and wind turbines are used for power generation.

Figure 9: Solar Wind Hybrid Power System Block Diagram

4.1.1.2 Working of solar power system:

Solar power system can be defined as the system that uses solar energy for power generation with solar panels.

Solar energy is one of the major renewable energy resource that can be used for different applications, such as solar power generation, solar water heaters, solar calculators, solar chargers, solar pumps and so on. There are various advantages of solar energy usage in electric power generation including low pollution, cost effective power generation (neglecting installation cost), maintenance free power system, etc. solar power system consists of three major blocks namely solar panels, solar photovoltaic cells and battery for storing energy. The electrical energy (DC power) generated using solar panels can be stored in batteries or can be used for supplying DC loads or can be used for inverter to feed AC loads

Figure 10:working of solar power system

4.1.1.3. Working of wind power system:

Wind energy is also one the renewable energy resource that can be used for generating electrical energy with wind turbines coupled with generators. There are various advantages of wind energy, such as wind turbines power generation, for mechanical power with windmills, for pumping water using wind pumps and so on.

Figure 11:wind power system

Hence large wind turbines are made to rotate with the blowing wind and accordingly electricity can be generated.  The minimum wind speed required for connecting the generator to the power grid is called as cut in speed and maximum wind speed required for disconnecting the generator from the power grid is called as cut off speed. Generally, wind turbines work in the range of cut in and cut off speeds.

4.1.2. Wind-diesel hybrid system:

The given figure schematically shows how a wind turbine can be combined with diesel generators in a hybrid configuration. This combination enables the use of a renewable energy source in remote and isolated areas, where the grid structure is weak, insufficient or even not existing, and the cost of energy often constitutes a considerable part of the local economy

Figure 12: Wind Diesel Hybrid System

4.1.2.1. Working of wind-diesel hybrid system:

By connecting a wind turbine to a diesel generator back-up system, an uninterrupted power supply can be acquired, thus securing 100% supply. The diesel generator will take over production when the power generation from the wind turbines is temporarily insufficient to cover the grid demand. The wind turbines are virtually always connectable to the existing diesel generator sets. The new Wind-Diesel concept allows the size of the wind turbine generators to exceed the size of the diesel generators. The maximum fuel saving is achieved by declutching and stopping the diesel engine when the supply from the wind turbine generator exceeds the grid demand. The Wind-Diesel hybrid technology has the advantage of using standard control system, implemented with modern diesel generators that control the voltage and frequency, even when the diesel is not in operation. If the energy production from the wind turbines is higher than the grid demand, then the frequency is controlled by the use of a dump load which can utilize the excessive wind energy for a numerous other purposes.

4.1.3. Wind-Fuel cell hybrid system:

            A fuel cell is an electrochemical device that converts chemical energy directly into electrical energy. Like a battery, a fuel cell consists of a pair of electrodes and an electrolyte.

4.1.3.1. Working of Wind-Fuel cell hybrid system:

            The working of a wind Turbine-Fuel cell hybrid system is shown in the figure given below. The power produced by wind turbine is splits into two branches i.e direct and indirect branch.

            The wind turbine is directly delivered to the grid through the direct branch and the wind turbine energy is also delivering to the grid through the fuel cell by indirect branch. The indirect branch consists of an electrolyser, producing hydrogen stored in tanks, either in compressed or in liquid form which is then fed to the fuel cell to produce uninterrupted, constant power to the grid throughout the year. An internal loop provides the electrlolyser with electrical power at stand by levels from the fuel cell when the wind turbine is not in operation. This was deemed necessary to avoid on/off transient operation. The high pressure compressor or the liquefier are also powered either from wind turbine or from the fuel cell.

Figure 13: Wind Fuel Cell Hybrid

4.1.4. Fuel Cell-Gas Turbine hybrid power system:

            This hybrid power system consists of high temperature fuel cells and gas turbines. The size of these units run from about 250 KW to 5 MW.

4.1.4.1. Working of fuel cell- gas turbine hybrid system:

Different fuel cells can be used in this operation such as:

1. Proton exchange membrane (PEM)
2. Solid oxide fuel cell (SOFC)
3. Molten carbonate fuel cell (MCFC)
4. Phosphoric acid fuel cell (PAFC)

            But the most suitable are the SOFC or the MCFC fuel cell in combination with a gas turbine to increase overall thermal efficiency, with predicted efficiencies of 65% to 75%. Currently, efficiency of this hybrid systems is in the 60% range.

Fuel and air are fed into the fuel cell and the exhaust gases are starts to appear. There are many areas where the exhaust gases (waste heat) could be put in use in fuel cell installations.

1. Waste heat may be used for the hydrogen reforming process.
2. Waste heat can be used for steam or hot water generation in commercial and residential buildings.
3. Waste heat could be used in cooling system in buildings.
4. The waste heat from the fuel cell exhaust gases can be used to power a micro gas turbine to generate additional electricity.

The exhaust gases from the micro gas turbine is at about 200 ℃.

Fuel cell- gas turbine hybrid system are generally in the power range from several hundred KW up to 1 KW.

High temperature fuel cells are used in this system, as they operate well under the pressures and temperatures needed. In the case of SOFC, the pressurized environment improves the fuel cell efficiency. The turbine is able to recycle thermal and pressure energy that would normally be discarded.

Figure 14: Fuel Cell-Gas Turbine hybrid power system

4.2. Hybrid Technology in Vehicles

            Now that we have discussed the use of hybrid technology in turbines, we will move towards the use of hybrid technology in vehicles. Hybrid Vehicles are the vehicles that use more than one source of power to work. These sources of power can be different. So, the hybrid vehicles are classified in terms of the energy sources they are combining together. Two such types are discussed below.

4.2.1. Hybrid Solar Vehicle (HSV):

            A Hybrid Solar Vehicle is that vehicle which combines a system of IC (Internal Combustion) engine and Photovoltaic Panels. Solar Panels are installed on the roof of the vehicle. In most of the cases, solar panels are installed on the roof of a Hybrid Electric Vehicle (HEV). But, the small area of the solar panels results in low value of power it can generate. So, in most of the cases, the solar panels do not produce enough energy to boost the electric range of a hybrid vehicle significantly. Solar Panels are merely installed to power the air conditioning system of the car in most cases. Solar Panels are very expensive too. This results in a very limited use of HSVs. So, our main focus will be HEV.

4.2.2. Hybrid Electric Vehicle (HEV):

            A Hybrid Electric Vehicle is that vehicle which combines a system of IC (Internal Combustion) engine and Electric Propulsion System. In other words, it combines the mechanical drive train and electrical vehicle and form a hybrid vehicle drive train. The purpose of combining the two systems is to increase the overall efficiency of the vehicle. In order to understand the working of a hybrid electric vehicle, first of all we need to know the structure of this vehicle. After that it will be easier for us to understand the working.

4.2.2.1. Components of HEV:-

HEV contains all the basic components of a conventional gasoline vehicle. In addition to these, some other components are essential for it that are discussed below:

Electric Motor:

The Electric Motor in a hybrid electric vehicle is very complex. It draws the electrical energy from the battery and rotate the tires. Due to its advanced electronics, it is also able to act as a generator in some cases and convert the mechanical energy to electrical energy. This electrical energy is stored in the battery.

Generator:

In some cases, the electric motor also does the work of a generator. In other cases, a separate generator is installed in the hybrid energy vehicle. It converts mechanical energy into electrical energy, which is stored in the battery.

Battery:

A battery in a hybrid electric vehicle is different than a regular battery used in normal vehicles. In simple vehicles, the battery only helps in starting the engine. While, in case of hybrid electric vehicles, a battery can rotate the wheels completely through the electric motor, without the help of the engine.

Figure 15: Components of HEV

4.2.2.2. Working: -

A Hybrid Electric Vehicle is powered by a combination of Electric motors, generator and a conventional Internal Combustion Engine. Depending on the driving conditions of the vehicle, the wheels of the vehicle may be driven by either the IC engine or the electric motors individually. Or by both at the same time. Energy to drive the electric motors comes from a dedicated hybrid battery pack. The hybrid battery pack is mostly located towards the rear of the vehicle. This battery is charged by the generator. Generator is driven by the gas engine when it is running. In this way, a hybrid vehicles create their own electric power by the mechanical power, which would have been wasted otherwise.

4.2.2.3. Technologies in hybrid vehicle:

Hybrid Electric Vehicles use advance technologies to improve the overall fuel efficiency of the vehicle and provide better fuel economy. Some of the technologies are discussed below:

Regenerative Braking:-

Whenever the brakes of a hybrid vehicle are applied, the electric motors start acting as a generator (or if the vehicle has a separate generator, it starts working) and converts the mechanical energy of the wheels (rotational motion) in to electrical energy and recharge the hybrid battery pack. This also helps in slowing down the vehicle. This braking system is called regenerative braking and this helps in improving the overall efficiency of the vehicle.

Figure 16: Regenerative Braking System

Electric Motor Drive/Assist:-

The Electric Motor of a hybrid electric vehicle adds up its power, to the power generated by the IC engine, when more power is required. For example, when the vehicle is accelerating or climbing a hill, the electric motor assists the engine in speeding up the vehicle. Electric motors can also move the vehicles completely on their own, at low speeds. As, we know that an IC engine has a poor efficiency at low speeds. So, by moving the vehicle with the help of hybrid battery pack and electric motors alone, the efficiency of the vehicle is greatly improved.

Figure 17: Electric Motor Drive

Figure 18: Electric Motor Assist

Automatic Start/Stop:-

The system of the hybrid electric vehicle starts and stops the IC engine automatically. When the brakes of a hybrid electric vehicle are pressed, the engine is shut off. When the accelerator is pressed, the engine automatically starts. When the vehicle is moving at low speed, the engine is shut off. When the car gains speed, the engine starts automatically. Engine also shuts off when the hybrid electric vehicle is moving down a hill and starts automatically when it is moving up a hill. This automatic starting and stopping of the vehicle significantly improves the efficiency of a hybrid electric vehicle.

Figure 19: Automatic Start

Figure 20: Automatic Stop

Whether the whole power will come from either the motor, or the engine or they will work together to produce the power is decided by the control system in HEV. We will now discuss it in detail.

Control System in HEV:-

The control system in hybrid electric vehicle is an electric device that makes sure that the outcome of a system is the same as what is required of that system. Control system operates in real time to make sure that the outcome is the same as required. HEV control system monitors the safety issues of the hybrid electric vehicle, as a conventional control system monitors the safety issues of a normal vehicle. In addition to this, HEV control system determines that which energy source will drive the car, and the extent of the energy recovered when the brakes are applied.

The Control System of HEV consists of many sub systems. A number of components work together to perform the function of the Control System of HEV. The systems which are involved in the control system of a HEV are illustrated in figure 7, along with their functional connections.

Figure 21: General HEV Control Diagram

Vehicle Management Unit (VMU):-

The VMU is the brain of the vehicle. It collects (receives) and processes the data from other systems like Battery Management System (BMS), Engine Management System (EMS) and Motor Management System (MMS) and decides the most suitable response for each particular event. After making the decision, it communicates with the system responsible for the execution of the response.

The VMU performs the following tasks:

1. VMU detects any acceleration, deceleration and braking demands of the vehicle and regulates them.
2. During the gear shifting process, VMU synchronizes the system.
3. VMU is responsible for HEV strategy. I.e. it chooses between IC engine, Electric motor and a combination of the two, based on the inputs and data requirements of the system.

Battery Management System (BMS):-

Battery Management System is a system that prevents the battery from facing serious dangers and to increase a battery’s life. The major functions that a BMS performs are as follows:

1. BMS protects the battery against any kind of damage.
2. BMS works to increase the life of the battery.
3. BMS makes sure that the battery is in a state in which it can perform the functions that are required of it.
4. BMS estimates the capacity and ageing status of the battery cell.

The status of a battery is fully described by the following states:

State of Charge (SOC): It represents the remaining energy level that can perform useful work. It is a ratio of remaining and initial capacities of a battery. It is usually represented as a percentage.

State of Health (SOH): It represents the current condition of a battery. It is determined either by the remaining lifetime, or by the percentage degradation from initial lifetime of the battery.

State of Function (SOF): It determines that to what extent the battery can perform the vehicle functions. It is determined by both the values of SOC and SOH. It gives the relationship between required current and time, while considering the health issues of the battery.

Engine Management System (EMS):-

Engine Management System (EMS) manages the injection of fuel, ignition of fuel and other turbo issues of an IC engine. In an HEV too, the control of ICE is its main task. VMU is in contact with EMS continuously. Engine Management System reports the events to Vehicle Monitoring System. VMU communicates back the demands of the driver (such as braking and acceleration). In HEV, the VMU divides the driver’s demand of acceleration between ICE and Electric Motor and this is transparent to EMS.

Motor Management System (MMS):-

Motor Management System facilitates the control of electric motor, required by the Vehicle Management System. It also supervises the correct performance of it. The type of electric motor determines the type of control. Generally, the electric motor comprises of an electric motor and an alternating current.

4.2.3. Classification Of Hybrid Electric Vehicles:

            Now that we have discussed the working of a Hybrid Electric Vehicle, we move towards its classification in terms of the configuration. Following are the types of a Hybrid Electric Vehicle according to configuration:

4.2.3.1. Series Hybrid Vehicle:

In a Series Hybrid Vehicle, the engine does not directly power the vehicle and makes the wheels rotate. Rather, the engine provides the produced energy to the generator. The generator produces Electric Power. This electric power is then used by an electric motor to run. Excessive amount of electric power is stored in the battery pack. The electric motor transmits the power to the wheels and provides the traction power. The series structure is shown in figure 22 in the form of a schematic diagram.

Figure 22: Series Hybrid Structure

In series hybrid vehicle, the engine runs at its optimum conditions at all times. If the power required by the vehicle to move is less than the power produced at optimum conditions, then the extra power is used to charge the hybrid battery pack. In case, the vehicle is accelerating or climbing up a hill, the power required will become larger than the power produced at optimum conditions. So in this case, both the generator and the hybrid battery pack will provide electric power to the motor and it will transmit the power to the wheels and provide the traction power.

This system requires a control system to decide when the power needs to be drawn from the battery and when the battery is fully charged and make the best decisions for every scenario. For example, when the speed is slow and the battery is fully charged, it needs to turn of the engine and draw all the power from the battery.

4.2.3.2. Parallel Hybrid Vehicle:

In a parallel Hybrid Vehicle, the engine can directly power the vehicle and its wheels. Electric motor can also drive the wheel by taking electric power from the hybrid battery. It has a single electric motor. This electric motor works as a generator when the battery needs to be charged. The IC engine provides the generator with mechanical energy and it converts it into electrical energy. The parallel structure is shown in figure 9 in the form of a schematic diagram.

Figure 23: Parallel Hybrid Structure

In this structure, when brakes are applied the motor (acting as a generator) can use the motion of the wheels to produce electric power and charge the battery, while helping the vehicle to slow down.

As the structure has only one motor, so in case of parallel hybrid structure, the battery cannot be charged while simultaneously rotating the wheels by driving the electric motor. This results in a waste of energy produced by the IC engine. For example, when a car is moving at a slow pace and it accelerates slightly. Now, the power required to move the vehicles is slightly greater than the maximum power produced by the battery. So, the engine starts working. Now, the vehicle needs slightly more power and it is getting it, but the engine is working at its optimum conditions and producing a lot more power than the required amount. As in parallel hybrid vehicles, the battery cannot be charged while providing the traction power, so this energy is wasted. This is the biggest downfall of a Parallel Hybrid Vehicle.

4.2.3.3. Series-Parallel Hybrid Vehicle:

A series-parallel hybrid system combines the two systems (series hybrid system and parallel hybrid system) to combine the benefits of the two systems. It has a motor and a separate generator that enables it to charge the battery, while the battery is supplying electric power to the motor. Its structure is shown in figure 10 in the form of a schematic diagram.

Figure 24: Series-Parallel Hybrid Structure

In this type of hybrid vehicle, the traction power can be provided by either the IC engine, or the electric motor (through hybrid battery), or both of them at the same time. In case the battery is supplying the electric power to the motor and the IC engine is also working and producing more energy than the energy required by the vehicle. Then due to an additional generator, the vehicle will be able to recharge the battery with the extra energy from the engine while the battery is running the electric motor.

4.2.3.4. Complex Hybrid Vehicle:

A Complex Hybrid Vehicle has just one difference, that it has two separate mechanical links. One for the front wheels and one for the rear wheels. The front wheels are powered by both of the IC engine and the battery (through a motor). While, the rear wheels are powered by only the electric system. It is shown in the figure below:

Figure 25: Complex Hybrid Vehicle

The use of two separate mechanical links results in obtaining a flexible mounting (reduces the transmission of vibrations) and a light transmission system. Most of the hybrid vehicles these days are complex hybrid vehicles.

We will now discuss one more modified version of hybrid electric vehicles, called Plug-in Hybrid Vehicle.

4.2.3.5. Plug-in Hybrid Vehicle:

A plug-in hybrid vehicle is a vehicle that has a larger battery than the usual hybrid electric vehicles. Its battery can be charged either by the IC engine of the vehicle or by plugging into a standard electric power outlet (110V/220V). This allows the vehicle to travel more miles before the IC engine needs to start. As a result, its efficiency increases. It has all the specifications of any of the hybrid electric vehicles. It can be classified as:

Series Plug-in Hybrid Vehicle:

In this vehicle, only the electric motor provides the traction power. The vehicle propels only on the electric power. When the battery needs to be recharged, the IC engine generates electricity to power the electric motor.

Parallel or Blended Plug-in Hybrid Vehicle:

In this vehicle, both the engine and electric motor propel the vehicle under most of the driving conditions. At low speeds, only electric power is responsible for moving the vehicle.

5. Research Paper Reviews

5.1. Research Paper 01:

Paper Summary

Hybrid Vehicle: A Study on Technology Article

            The article starts with a brief history of hybrid technology and discusses various hybrid technologies (Hybrid Electric Vehicle, Hybrid Solar Vehicle and Plug in Hybrid Electric Vehicle), their working and shortcomings, efficiency of Hybrid Cars, case-studies on commercial hybrid vehicles. Article concludes on the advantages and disadvantages of hybrid cars.

With technology advancements in recent years, there has been tremendous increase in the usage of fossil fuels causing problems like climate changes, global warming, shortage of crude oil, etc.  Due to which, tech giants have started doing research for making Hybrid Technology usable into the daily life.

From all Hybrid Car technologies mentioned above, the Hybrid Electric Vehicle is considered as the most industrially matured technology and has efficiency more than cars running on petrol / diesel / CNG while Hybrid Solar Vehicle has low efficiency than vehicle running on petrol / diesel / CNG.

Hybrid vehicles use regenerative braking for breaking of car as well as to produce energy using generator which is then stores into batteries for later use. There are various types of hybrid vehicles one of them is Hybrid Electric Vehicle.

In Hybrid Electric Vehicle , the power of conventional internal combustion engine is combined with the electric propulsion system to get the maximum efficiency drive.

Moreover, it has been proposed in the article that the use of Ultra Capacitors is more effective to store and provide electrical energy than batteries.

Hybrid Electric Vehicles can be Series Hybrid, Parallel Hybrid, Series-Parallel Hybrid, or Complex Hybrid.

In Series Hybrid, vehicle driving power is provided by the electric motor, while Internal combustion engine drives the generator. The power produced from generator is then used to drives electric motor and charge batteries.

In Parallel Hybrid, vehicle drive can be provided by internal combustion engine as well as electric motor. Both internal combustion engine and electric motor are connected through transmission. When internal combustion engine drives the vehicle, then some torque is given to the electric motor which act as generator and charge the batteries. So in case when internal combustion engine is not driving the vehicle, batteries run the electric motor which in turn drives the wheels. Parallel hybrids depends more on regenerative braking and the internal combustion engine can also act as a generator for supplemental recharging. This makes them more efficient in daily urban 'stop-and-go' scenario. They use a smaller battery pack than other hybrids.

In Series-Parallel Hybrid also called Power-split Hybrid, advantages of both series hybrid and parallel hybrid are used. ICE has direct connection to generator (as in series) as well as Electrical Motor (as in parallel).

In Complex Hybrid, front wheels of the vehicle are derived by hybrid propulsion and the rare wheels are derived by pure electric propulsion.

 Hybrid electric vehicles can also be classified as Micro (2.5 kW), Mild (10-20 kW) and Full (30-50 kW) based upon their capacity.

Other type of hybrid vehicle is Hybrid Solar Vehicles, this hybrid technology is an integration of vehicles and photovoltaic  panels. In these hybrid vehicles, photovoltaic panels are mounted on the top of roof of the vehicle. This hybrid vehicle can also be of four types such as Series Hybrid, Parallel Hybrid, Series-Parallel Hybrid and Complex Hybrid. But Series Hybrid is the most efficient of them all and is also a major focus for on going research.

 Next type of Hybrid vehicles is Plug-in Hybrid Electric Vehicle.

In Plug-in Hybrid Electric Vehicle, batteries are larger and they can be charged either by gasoline engine or from a standard 110 volt / 230 volt electrical outlet by plugging in for few hours. Plug-in Hybrid Vehicles can be classified into Series Plug-in Hybrids and Parallel or Blended Plug-in Hybrids.

In Series Plug-In Hybrids also called Extended Range Electric Vehicles (EREVs), vehicle drive is only due Electric motor while the integrated Internal Combustion Engine is only used to drive the generator.

In Parallel or Blended Plug-In Hybrids, vehicle drive is due to both Engine as well as Electric motor. At low speeds only motor drives the wheels.

Then Article proposes Case-Study of Toyota Prius Series and Astrolab.

1. Toyota Prius Series

A.1. First Generation: Toyota Hybrid System

Toyota released two vehicle models NHW10 and the NHW11. In these Toyota Hybrid System was introduced. The batteries are always charged between 40%-60% for maximum battery life and efficiency. Double  Overhead Camshaft (DOHC) was introduced which allows engine to have four valves per cylinder instead of typical two valves. Four valves allows more air mixture to come in and make easier to pump the exhaust out of the cylinder, which in turn increases the performance of the engine.

Toyota Hybrid System constitutes of a petrol Engine, two motor generators (MG1 and MG2), a Power Control Unit (PCU), and a Battery. Low speed drive is entirely Electric (MG2) but as speed increase Engine kicks in and vehicle runs on both engine and motor. Engine also drives the generator (MG1) which charges the batteries. Power splitting is controlled by PCU. Batteries also gets charging as braking is initiated.

A.1. Second Generation: Hybrid Synergy Drive

Hybrid Synergy Drive introduces DC to DC converter which boosts the potential of battery to 500V or more. This allows the use of smaller battery packs and more powerful motors.

Hybrid Synergy Drive also introduces all electric air conditioner which eliminates the need of engine running continuously for air conditioning.

Hybrid Synergy Drive also introduces improvements to generator (MG2) by linking the front wheels which increases power density of the motor.

A.3. Third Generation: Hybrid Synergy Drive

The new Prius 3 has re-engineered Hybrid Synergy Drive system. It has less weight and also boosts the fuel economy (by 14%). It introduces more powerful engine with cooled exhuast gas recirculation, more powerful motor (by 20%), increase in Ni-MH battery capacity with reduced size, and new PCU is 36% lighter.

A.4. Toyota Prius Solar

Solar Electric Vehicles recently developed a prototype of Solar Prius. The PV panel has 16% efficiency. It has been estimated that the PV Prius can have a range based on solar power alone between 5 and 8 miles per day, and that it can consume between 17% and 29% less gasoline than the standard Prius.

A.5. Toyota Prius Plug-In Hybrid

This Prius version came out in 2012 which has 4.4 kWh Li-ion battery which allowed range of 23 km on all electric propulsion. The lithium-ion battery pack can be charged in 180 minutes at 120 volts or in 90 minutes at 240 volts.  According to Toyota the Prius plug-in is expected to release only 49g CO2 -emissions. Its mileage is same as the third generation Prius except for the fact that it has an all electric efficiency of 2.5L/100km. The main advantage is that the battery can be charges at any outlet.

2. Astrolab - Ventruri Automobiles

This is world’s first Electro-Solar Hybrid vehicle which allows charging of batteries either by solar supply or from the electricity outlet. It is capable of running on very little energy (16 kW motor). It has top speed of 120 km/hr and range of 110 kilometers which makes it viable choice for extensive trips on everything basis. This is the first vehicle to consume no fossil fuel.  The Astrolab has opened up a new era for automobile architecture: light and high profiled, it offers the rays of the Sun for 3.6 m² of the photovoltaic cells (for an overall vehicle length of fewer than 4 meters).

In Advantages and Disadvantages, Article implies that Electric motors use no energy when vehicle is stationary and they does not produce any exhaust. But Gas motors (Gasoline Engines) do waste some energy when idle but they provide high speeds and more power for a given motor weight and they also produce emissions when running. One benefit of gas motor is that it also charges the batteries when running. A hybrid never needs to be plugged into an outlet, it can itself charge batteries.

Hybrid technology is complex and expensive to build. Moreover, for customers it expects more repairing time in shops and large bills. When we compare the economy statistics of a hybrid vehicle with other gasoline powered vehicles, they can not convince customers to go for hybrid. Drivers report that real mileage of hybrid is actually 10% less than claimed.
Hybrid Vehicle offer more than just great fuel economy but they also offer many green advantages as well. They are highly recommended for regions where pollution is at its worst because they produce much less emissions.  Noise and environmental pollution is reduced considerably.

5.2. Research Paper 02:

Paper Summary

Hybrid Bike with Solar Charging (Petrol Cum Electric) Article

             The Article starts with a brief introduction to Hybrid Technology and its significance then thoroughly discusses various components of Battery Electric Vehicle (Battery, Power System, and Motor). After that Article propose some calculations regarding distance traveled, time for charge and discharge etc. and then conclusions are drawn from that.

In recent year, the consumption of combustible matter has increased exponentially and it is estimated that soon we will get short of fuel and fuel prices will get sky high. And therefore, there is the need of an alternative. Technologies are growing very rapidly. The concept of Electric vehicles has been around since 1890’s but at that time, abundance of fossil fuels made the gasoline engine more affordable and cheaper. But in today’s world, the fuel reservoirs are depleting, fuel costs are getting higher and higher and our environment is also at risk. So now Electric vehicles are becoming center of attention for the World. Electric Vehicles are very environment friendly, they run on batteries which could be charged on outlets. Future concerns suggest Electric vehicles a viable mean of transportation.

Three main components are primarily needed for Electric Vehicle which are Battery, Power System and Transmission System.

Today’s Electric vehicle are powered by a pack of batteries. Battery is self-contained electro chemical reactors, where electrochemical reaction takes place and electricity is produced. And during recharging the used reactants are brought back to their original state ready for another reaction. More efficient, powerful and long-lasting batteries are required to take electric vehicle to next level. Some latest batteries technologies include Lead-Acid Battery, Nckel-Cadmium batteries and Lithium Ion Batteries.

Out of the mentioned, commonly used and economical battery is Lead Acid battery. These batteries have the minimal purchase and operating costs. These gives the highest voltage discharge. These have the best reversible reaction which cause very little change on plates and these can operate safely on range of temperatures like 18 to 43 degree calcius.

Construction wise, battery consists of a plastic container which is acid proof and has great mechanical strength. Inside the main container, there are small compartments (cells ) which act as a source of 2 voltage.  To get 12 volts Lead Acid battery, 6 cells are arranged in series.

Inside each cell, there are there are two electrodes (of lead dioxide and other of spongy lead) which are dipped in electrolyte (Suphuric Acid). While working, Acid reacts with the plates to convert chemical energy into the electrical energy. And opposite occurs while charging. Vent holes are present in the plug to allow for the gases to escape while charging circuit.

The next good replacement for the Lead Acid Battery is Nickel-Metal Hybride Battery. Nickel metal provides double the specific energy then corresponding Lead acid battery. Looking ahead, we see Lithium based traction batteries which are currently under experimental stages.

Then comes the Power System which has basically two main components; motor which provides the traction power and controller unit which controls the use of this power. On contrast, the power system of a gasoline based vehicles have various components such as oil pump and water pump cooling system, engine carburetor, exhaust system, etc.

Electric motors are the main traction unit for an electric vehicle. Both Direct current (DC) motors and Alternating current (AC) motors are used. DC electric motors have three main components such as Coils, Armature, and Commutating device. And in AC electric motors, everything is the same just there is no need for commutating device because there is continuous reversal current. Usually more than one electric traction motors are used in vehicles for propulsion. Electric vehicles include electric cars, electric trains, electric lorries, electric aero planes, electric boats, electric motorcycles and scooters and electric spacecraft.

Recently, petroleum based transportation infrastructure has lead to several problems like environment impact and increase in oil prices. This has renewed interest in Electric powered vehicles which has zero impact on environment and also we have various way to generate electricity to feed these electric powered vehicles.

It was concluded in the article that a given Vehicle is giving 32 km/liter of mileage on gasoline but as an electric motor was added to front wheels, its performance is expected to increase by 60% ideally, 48% under bike load, 35% under 50kg load and under 100kg load by 27%. As speed increase beyond certain limit, then motor becomes generator and charges the batteries. So at low speeds it operate on motor hence saving the gasoline It is very effective in city riding where we always get slow pace traffic and a lot of traffic signals.
As we all aware that Gasoline is a non-renewable source of energy and is going to deplete on day but by lowering its consumption we can increase the life of its sustenance.

5.3. Recent Work in Hybrid and Electric Technology

At current state, Hybrid Technology is complex and expensive than Conventional gasoline technology but is not as effective in terms of power output. So currently Big Automobile manufacturers are busy in making it more effective and affordable for a street person.

• Traction power of an Electric or most part in Hybrid, comes from Electric motor. So having a powerful and efficient motor means more powerful drive. Getting a powerful and efficient motor is expensive so currently manufacturers are trying to make Low Cost Compact High Efficiency Motors which are inexpensive, have high efficiency and provide more power.
• Battery is a main component of Hybrid Power System. It stores the electric energy and supplies it on demand. To make hybrid effective we need long lasting bigger batteries and batteries are usually expensive. So currently manufacturers are trying to make Low Cost, Durable, Energy-dence Batteries which are inexpensive, have high efficiency and provide more power.
•  Electronic Components used in Hybrids are expensive so currently manufacturers are trying to establish new techniques to manufacture these components at minimal cost.
• Ultra capacitors (a.k.a. Super Capacitors), particularly as utilized at the present time in electric and hybrid vehicles. By comparison with batteries,  ultra capacitors  offer  the  advantages  of  very  short charge/discharge time, virtually unlimited cycle life, zero maintenance requirements, and operability over a very wide range of temperatures. Ultra capacitors, however, still lag behind batteries in the aspect of energy density. Current research efforts to close that so-called “energy gap”,  which will allow ultra capacitors to be competitive with batteries, are described. The chapter also lists the key commercial and academic players in the area of ultra capacitor development, and describes trends and future expectations for the technology. 

6. Result and discussion:

                  As it has been already discussed that hybrid car be environment friendly, fuel saving with high purchasing and maintenance cost. In future there will be hybrid cars around us or we can say that our upcoming time will be hybrid. We are going to discuss all these facts through statistical data.

6.1. Hybrid car Emissions:

                  When any fuel burns we have CO₂,CO, NO_x and SO_x emissions. These oxides don’t support the clean environment and cause different environment disturbing phenomenon like acid rain, greenhouse effect and global warming etc. Here we will discuss that what will be the effect of hybrid car usage on these emissions through statistical data i.e. graphical and tabular data.

6.1.1. Annual CO₂ Emissions:

                  When any fossil fuel burns there will be always CO₂ emission. This gas can be very dangerous for environment for environment. It causes global warming, greenhouse effect and ozone depletion etc. its emission can be reduced pretty much by using hybrid vehicles. Because a hybrid car consumes less fuel because of batteries that act as second power source. Here is the statistical data for different types of vehicles for CO₂ emission.

6.1.2. Carbon dioxide Emission for Different Hybrid Cars:

                  There are different companies manufacturing hybrid cars. They are trying their best to make such cars that cannot affect environment. They are organizing researches to do their best. Here is the data showing us the fruit of their struggle in reduction of emission.

                  It is point to be noted that in this data Tesla Roadster has extraordinary less emission than that of other hybrid cars. But Tesla Roadster is not a hybrid one. It is an electric car.

6.1.3. CO₂  Emission w.r.t velocity:

Graph shows that CO₂emission (g/Km) with respect to velocity for gasoline, diesel, LPG and hybrid vehicles.

6.1.4. Reduction in NO_x

The oxides of nitrogen in the atmosphere form HNO₂, HNO₃ by reacting with water and we have acid rain affecting our buildings and crops. Their reduction is necessary. Here we have some statistical data for different vehicles again NO_x reduction estimation in 2020. 

6.1.5. Toyota Prius VS Plug in Prius VS US Fleet average:

We have tabular data of mile per gallon, CO₂ emission (lb./mile), gallons of gasoline saved per year and finally cost saved in dollars per year. It can be seen that plug – in Toyota Prius has extraordinary good results in this regard. It is shown in following figure. 

6.1.6. Environmental Score Card:

Here we have hybrid score card for top 10 hybrid cars.in given table we have mile per gallon, greenhouse gas emission, Air pollution score and finally environmental improvement score card for these ten non – luxury hybrid cars.

6.1.7. Toyota’s Emission 2014 VS 2015:

                  In 2014 Toyota’s CO2 emission was 112.5 (g/Km). And by struggling this company brought this emission to 107.5 (g/Km) in 2015. We cannot reduce this amount abruptly. This will be a gradual process. 

6.2. Fuel efficiency:

For any vehicle one of the most important factors that anyone should be aware is its fuel efficiency. Fuel efficiency is measured by noting that how much distance is covered by car in one gallon of fuel. It is also known as mileage of the car. If mileage is large then its mean that this car has large fuel efficiency and cover greater distance in one gallon of gasoline or other fuel. Here we have comparison of Toyota Prius (full hybrid), Ford Fusion (full hybrid), Ford Fusion and Mazda 6. Here we have two types of mileage i.e. highway mileage and city mileage per gallon. 

6.2.1. Hybrid car mileage VS ordinary car mileage:

As it has been already discussed that the mileage is the journey travelled by the car per unit gallon of the fuel. As hybrid car not only draw power from internal combustion engine but also from another source. This is a result our car will consume less fuel and consequently our mileage will increase. The comparison of hybrid car with ordinary car mileage. Dotted line shown the hybrid car mileage trend.

In another trend of gasoline against hybrid car is shown for different quarters of year from 2011 to 2014. It is point to be noted that this trend is not of mileage rather it is of total no. of miles that any car can travel in its life and it is quarter for gasoline because maintenance of hybrid car is somewhat difficult.

6.2.2. Fuel Economy VS Vehicle Price:

                  As we want to increase the fuel economy of the car, as a result its price also increases. For different fuels this trend is shown in following graphical data from year 2010 to 2025.

6.3. Hybrid Marketing:

                  As all the advantages of hybrid cars are in front of us. Now it will not be a surprise to us that why hybrid car sailing is rising continuously. These sailings have major position in vehicle marketing and making their mark. This can also be seen from given figure below.

6.3.1. Hybrid Vehicle Stock:

                  Different countries now giving their attention to hybrid vehicles and expanding their stock of hybrid vehicles because they know their importance in keeping environment safe and efficiency high. For different countries this stock is given as.

6.3.2. US Vehicle Market:

                  In following distribution sheet the total vehicle sales of US is shown. Vertical bars shown the marketing through hybrid vehicle sales. It can be seen that major vehicle marketing of US is through hybrid sales.

6.3.3. Breakthrough of Toyota:

                  Toyota cannot be neglected in terms of its vehicle marketing and especially due to its hybrid sales. Here is a proof of this aspect that Toyota has major sharing in global hybrid marketing.

When we talk about hybrid vehicles of Toyota, the first grateful thing that comes in our mind is Prius like Toyota’s hybrid share all over the globe, the shares of Prius are major part of Toyota sailing especially in 2009 it was on fire.

6.4. Hybrid Car Battery Cost:

                  One of the main reasons that the hybrid car is costly is because its batteries are very expensive. This is a major problem and the world’s best vehicle companies are trying their best to user batteries as cheapest as possible. Their effort has shown some fruit as given below.

7. Conclusion:

                  The important of hybrid vehicles and hybrid technology cannot be unseen. Our future will by hybrid. Hybrid cars probably will take place of gasoline engine cars. Besides this is also our need. Because our fossil fuels are depletioning very rapidly. If we don’t take crucial steps, then might be we are going to deprive of these natural resources because of their tremendous consumption. Hybrid car will prove one of these steps that we need to take. Hybrid vehicles uses less fuel oil thus if increase hybrid vehicle production that fuel that we will save from vehicles, we may use it for some other purposes.

                  Mileage of a vehicle is measure of its efficiency. It is the miles travelled by any vehicle per gallon fuel. Hybrid cars Have better fuel efficiency because it consumes the power of battery also decreasing the fuel consumption. Thus covers more distance for a gallon fuel.

                  More important than anything is our environment. If our environment is healthy and clean, we will be healthy and far from diseases. In present time we inhale smoke more than oxygen. Thus if we introduce hybrid vehicles then there will be less consumption of fuel. As a result less emission of  CO₂, NO_x, SO_x and other oxides. These cause acid rain, global warming and greenhouse effect that make our environment to vomit. Thus hybrid cars are environment friendly and we are nothing without our environment.

                  No doubt that there are also some disadvantages of hybrid cars like its cost and maintenance difficulty and expensiveness. Hybrid vehicles are expensive because of its complex structure of co – ordination of two different sources. Moreover, its batteries are also costly but there are continuous attempts to make hybrid structure with less cost. It is also being attempted to operate these vehicles with cheaper batteries and all these attempts are not in vain rather we getting some positive results.

                  We know that these disadvantages cannot be neglected but we can also not neglect its benefits. Where there is light, there is a darkness. But it is up to us to convert that darkness into light. Hybrid technology will be the key to bright future because its positive aspects are more than negative. 

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Date Modified:7 July 2018
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