Electric Vehicle (EV) Technology
Brief History:
Electric vehicles (EV) are those that use electric motors instead of gasoline motors. They are good in protecting the environment.
Anyos Jedlik created electric motor in 1828. He made a small model car which could move on its own through the small electric motor. However, between 1832 and 1839, a large electric motor created by Scottish inventor Robert Anderson which was used to drive a carriage.
This invention sparked imaginations of others. In 1835, two small-scale EVs were created, one in Holland and one in the United States by Thomas Davenport. The first electric car was created by Davenport; however, these batteries were non-rechargeable and were not able to give the car much range.
Components of EV
Battery Charger/ Onboard charger
Battery Management System
Battery
It powers the electric motor. Its capacity is defined in Ah. The design of battery includes complex calculations which determines various battery parameters.
Power Converter
The electrical energy stored in battery is fixed DC which should be converted to variable DC or variable AC which depends on the type of electric motor used for power.
Electric Motor
The motor is turned by AC current to drive the car.
Clutch
The engine must be decoupled from wheels to shift from low speed to high speed gears or vice versa. The clutch performs this.
Transmission
The gear box is called the transmission which allows transfer of power from engine to wheels.
Drive train
The combination of Electric motor, Clutch, Gearbox is referred as drive train.
Benefits of EV
Battery EV
Hybrid EV
Hybrid are powered by gasoline and electricity. The electric energy that is generated by the car’s own braking system is used to recharge the battery. This is called as regenerative braking. This is a process where the electric motor helps to slow the vehicle and uses some of the energy normally converted to heat by the brakes.
HEVs start off by using the electric motor, then gasoline engine cuts in as load or speed rises. These two motors are controlled by an internal computer, which confirms best economy for driving conditions.
Some of the examples include Toyota Prius Hybrid, Honda Civic Hybrid and Toyota Camry Hybrid.
Plug-in Hybrid EV
They combine both gasoline or diesel engine with an electric motor and large rechargeable battery.
It allows them to drive to extended distances using electricity.
Once the battery is emptied the conventional engine turns on and the vehicle operates as conventional non-plug in hybrid.
Since they run on electricity from grid it produces significant less global warming pollution than the gas counterparts. They do not emit any tailpipe pollution.
Fuel cell EV
FCEVs use a propulsion system where energy is stored as hydrogen and converted to electricity by the fuel cell.
These vehicles produce no harmful tailpipe emissions
The benefits are energy security and economy strengthening.
FCEVs are fuelled with pure hydrogen gas stored in a tank on the vehicle. FCEVs are equipped with other advanced technologies to increase efficiency, such as regenerative braking systems, which capture the energy lost during braking and store it in a battery.
Comparison
A hybrid has two powertrains, one gasoline and one electric, which work together for maximum efficiency. In some situations, the engine can shut off entirely, relying solely on the battery.
The battery is charged by capturing energy from the braking system or directly from the gas motor.
Plug-In Hybrid (PHEV)
A plug-in hybrid, sometimes called a PHEV, is a step towards full electrification. PHEVs can go between 12 and 97 miles on electricity alone. Once the battery is drained, PHEVs operate like conventional hybrids and switch between gas and electric operation seamlessly.
Fuel EV
FCEVs use a propulsion system where energy is stored as hydrogen and converted to electricity by the fuel cell. These vehicles produce no harmful tailpipe emissions
Some of the challenges faced by EV technology are:
Charging Infrastructure
India is said to have around 650 charging stations, but the issue lies in the lack of private parking spaces which forms the hindrance for EV adoption. Also lack of affordable renewable energy where the charging EV is putting a toll on the stresses coal powered electricity grid.
Price of Electric Vehicles
The mass segment of EVs is likely to cost two-and-half times more than the same vehicle type powered by a conventional petrol/diesel-run engine. The average cost of electric cars in India is around INR 13 Lakh, which is much higher than the average INR 5 Lakh for economical cars run on traditional fuel.
Range anxiety is what makes consumers suffer from knowing that the electric vehicle might not have sufficient range to take them to their destination. This is linked to the lack of charging infrastructure in the country where conventional vehicles can be refuelled at petrol stations, such regularised infrastructure which is not yet available for EVs.
FAME Policy Flip-Flops
The Indian government is doing all it can to push EVs, the Faster Adoption and Manufacture Of (Hybrid) And Electric Vehicles (FAME) policy has been criticised by the industry in the past. The government had initially focussed on vehicle standardisation with FAME, which has side-lined for the emphasis on manufacturing.
EV consists of three major subsystems which are
(i)Electric propulsion
(ii) Energy source
(iii) Auxillary
The electric propulsion subsytem consists of electronic controller, power converter, electric motor, mechanical transmission, and driving wheels.
The energy source subsytem involves the energy source , energy management unit and energy refuelling unit.
The auxillary subsystem comprises of power steering unit , temperature control unit and auxillary power supply. The mechanical link is represented by double line and electrical link by thich line while the control link is represented by thin line.
The row on each lne denotes the direction of electrical power flow or control information communication. Based on control inputs from brake and accelator pedals the elctronic controller provides proper control signals to switch on or off the power devices of the power converter which functions to regulate power flow between the electric motor and energy source.
The backward power flows is due to regenerative braking of EV and this regenrative enrgy can be stored provided the energy source is receiptive. The energy management unit cooperates with the electronic controller to control regenerative btaking and energy recovery. It also works with energy refuelling to control refuelling and monitor usaboility of energy source.
The auxillary power supply provides the necessary power with different voltage levels for EV auxillaries especially temperature control and power steering units .
EV configurations
The different configurations are:
(1) Series hybrid
(2) Parallel hybrid
(3) Series-parallel hybrid
(4) Complex hybrid
Series Hybrid:
This configuration is the simplest one to make an HEV. Only the motor is connected to the wheels here, the engine is used to run a generator which provides the electrical power. It can be put as an EV that is assisted by an ICE generator. Series hybrid drive train is shown in Figure.
Drive train of series hybrid system.
The engine is used to generate electricity only and supply to the motor through a rectifier. Power from the battery goes to the motor through a DC-DC converter
Parallel Hybrid
This configuration connects both the ICE and the motor in parallel to the wheels. Either one of them or both take part in delivering the power. It can be considered as an IC engine vehicle with electric assistance.
The energy storages in such a vehicle can be charged by the electric motor by means of regenerative braking or by the ICE when it produces more than the power required to drive the wheels.
Parallel hybrid drive train is shown in figure.
Drive train of parallel hybrid system.
The engine and the motor both can run the can through the mechanical coupling
Series-Parallel Hybrid
To combine the series and the parallel configuration, this system acquires an additional mechanical link compared to the series type, or an extra generator when compared to the parallel type. Complications in drive train are caused to some extent by the presence of a planetary gear unit. The Figure shows a planetary gear arrangement:
The sun gear is connected to the generator,
The output shaft of the motor is connected to the ring gear,
The ICE is coupled to the planetary carrier, and the pinion gears keep the whole system connected.
An alternative to this system which is less complex is to use a transmotor, which is a floating-stator electric machine. In this system the engine is attached to the stator, and the rotor stays connected to the drive train wheel through the gears.
The motor speed is the relative speed between the rotor and the stator and controlling it adjusts the engine speed for any particular vehicle speed. Series-parallel hybrid drive train with planetary gear system is shown in Figure.
Figure shows the system with a transmotor
The complex hybrid is similar to the series-parallel hybrid since the generator and electric motor is both electric machines. However, the key difference is due to the bi-directional power flow of the electric motor in complex hybrid and the unidirectional power flow of the generator in the series-parallel hybrid.
The four subsystems that are part of the VSCM are the Vehicle Mode Control Process (VMCP), the Battery Mode Control Process (BMCP), the Energy Management Control Process (EMCP), and the Regenerative Braking Control Process (RBCP).
VMCP decides when to power up the vehicle by monitoring the position of the key in the ignition. When the truck is being activated (the key is turned "on") the VMCP communicates with the BCM to close the contactors and energize the high voltage system.
The BCM responds to the VCMP upon completion of the tasks and the VMCP then contacts the TIM. Once the TIM has been activated the high voltage system of the UT Future Truck is operational. At this point the VMCP can tell the electric motor to start the internal combustion engine.
Battery Mode Control Process - Another subsystem within the VSCM is the BMCP. The BMCP calculates the battery pack power limits and passes the information to the EMCP. The BMCP determines if the battery pack requires charging and what amount of power is required from the engine to maintain an appropriate state of charge in the battery pack. The power required to maintain the charge, Psoc, depends solely upon the state of charge of the battery pack, as seen in Figure
Energy Mode Control Process - The EMCP is the subsystem within the VSCM that is most critical to the successful operation of the Explorer's hybrid system. The EMCP coordinates the motor and engine to meet driver demanded power while simultaneously meeting the constraints imposed by other systems in the vehicle and maintaining the battery pack's state of charge.
Regenerative Braking Control Process - The final subsystem in the VSCM is the RBCP. The RBCP determines the braking intent of the driver by monitoring a brake line pressure sensor and, when appropriate, implements regenerative braking through the motor to charge the battery pack. This subsystem also monitors vehicle speed via a sensor attached to the truck's drives haft and reduces regenerative braking at low vehicle speeds.
The functional block diagrams of the various HEV configurations is shown. From Figure it can be observed that the key feature of:
series hybrid is to couple the ICE with the generator to produce electricity for pure electric propulsion.
parallel hybrid is to couple both the ICE and electric motor with the transmission via the same drive shaft to propel the vehicle.
Series hybrid Series -Parallel hybrid
Parallel Hybrid Complex hybrid
Series Hybrid:
In series hybrid system the mechanical output is first converted into electricity using generator. The converted electricity either charges the battery or can bypass the battery to propel the wheels through the motor and mechanical transmission.
The advantages of series hybrid drivetrains are:
Mechanical decoupling between the ICE and driven wheels allows IC engine to operating at its very narrow optimal region as shown in Figure.
Nearly the ideal torque-speed characteristics of electric motor make multi-gear transmission unnecessary.
However, a series hybrid drivetrain has the following disadvantages:
The energy is converted twice (mechanical to electrical and then to mechanical) and this reduces the overall efficiency.
Two electric machines are required and a big traction motor is required because it is the only torque source of the driven wheels.
The series hybrid drivetrain is used in heavy commercial vehicles, military vehicles and buses. The reason is that large vehicles have enough space for the bulky engine/generator system.
Configuration of Series Hybrid Vehicle
Parallel Hybrid System:
The parallel HEV allows both ICE and electric motor (EM) to deliver power to drive the wheels. Since both ICE and EM are coupled to the drive shaft of the wheels via two clutches, the propulsion power may be supplied by ICE alone, by EM only or by both ICE and EM.
The EM can also be used as a generator to charge the battery by regenerative braking or absorbing power from the ICE when its output is greater than that required to drive the wheels.
The advantages of the parallel hybrid drivetrain are:
Both engine and electric motor directly supply torques to the driven wheels and no energy form conversion occurs, hence energy loss is less
Compactness due to no need of the generator and smaller traction motor.
The drawbacks of parallel hybrid drivetrains are:
Mechanical coupling between the engines and the driven wheels, thus the engine operating points cannot be fixed in a narrow speed region.
The mechanical configuration and the control strategy are complex compared to series hybrid drivetrain. Due to its compact characteristics, small vehicles use parallel configuration. Most passenger cars employ this configuration.
In the series-parallel hybrid, the configuration incorporates the features of both the series and parallel HEVs. However, this configuration needs an additional electric machine and a planetary gear unit making the control complex.
Complex Hybrid System
The complex hybrid system involves a complex configuration which cannot be classified into the above three kinds. The complex hybrid is similar to the series-parallel hybrid since the generator and electric motor is both electric machines. However, the key difference is due to the bi-directional power flow of the electric motor in complex hybrid and the unidirectional power flow of the generator in the series-parallel hybrid. The major disadvantage of complex hybrid is higher complexity.
Power grids are facing a new and important challenge that is the oncoming mass penetration of plug-in Electrical Vehicles (EVs). However, the architectures of transmission and distribution grids are still focused on traditional design and operational rules.
Therefore it is necessary to predict adequate solutions for the problems which are going to rise to the electrical and production grids as well as the effect on their commercial operation as a result of the gradual integration of EVs into the network.
For example, the major congestion problems may appear in already heavily loaded grids as well as voltage profile problems mainly in radial networks, particularly if the peak load periods coincide with EV charging periods.
Vehicle to grid technology
The basic concept of vehicle-to-grid power is that EDVs provide power to the grid while they are parked.
To schedule dispatch of power, a grid operator needs to rely that enough vehicles are parked and potentially plugged in at any minute during the day.
The electricity from V2G is not cheap when compared to bulk electricity from large power plants.
The energy output may be quite small, making the cost to produce each kWh of little consequence for the overall economics.
The more important factors are:
References
1.Electric Vehicle Technology Explained Book by James Larminie
2.Modern Electric, Hybrid Electric, and Fuel Cell Vehicles: Fundamentals, Theory, and Design
3.Electric and Hybrid Vehicles: Design Fundamentals, Second Edition Textbook by Husain Iqbal
