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ELECTRIC and HYBRID VEHICLES
ELECTRIC and HYBRID VEHICLESK C Karthik2nd sem, M.Tech(A.E)
Need Electric and Hybrid vehiclesOver dependence on petrol/dieselRising petrol/diesel pricesPollution and the resultant global warmingNoise in conventional vehiclesNeed for alternate power sourcesNeed for Eco friendly vehicles EV, HEV - The solution?
Electric vehiclesAn Electric vehicle is an automobile that is propelled by one or more electric motors, using electrical energy stored in energy storage device.
The primary components are motor, controller, power source, and transmission.
Block diagram
An Electric vehicle system
AdvantagesNo Gas Required
No Emissions
Cost Effective
Low Maintenance
Pay back period
Low noise
DisadvantagesHigh Initial Cost- Many times that of conventional vehicles
Short Driving Range- Range anxiety
Recharging takes much longer time than refueling gasoline-lack of charging infrastructure
Battery pack takes space and weight of the vehicle which otherwise is available to the people
Concept of hybridizationMultiple sources of powerMaking ICE work in most efficient rangeSizing of motor and ICE lower compared to conventional vehicles and EV
Hybrid VehiclesThe term hybrid vehicles in general usage refer to vehicles with two or three different type of sources delivering power to the wheels for propulsion.
The most common hybrid vehicles have an IC engine and one or more electric machines for vehicle propulsion.
The IC engine can be used to generate electric energy on board to power the machines.
ClassificationBased on the path of energy flowMechanical power transmission path (MPTP)Electrical power transmission path (EPTP)Combination of MPTP and EPTP
Based on architectureSeriesParallelSeries-Parallel
ClassificationBased on degree of hybridizationMildPowerEnergy
Charge depleting
Charge sustaining
Mechanical power transmission path (MPTP)The primary powertrain components in a conventional ICE vehicle are engine and transmission. The energy flow in a vehicle starts from source of energy and ends at wheels with the delivery of propulsion power known as power transmission.
Power transmission path in conventional IC engine
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Electrical power transmission path (EPTP)In electric vehicle power transmission is almost electrical except for coupling devices between electric propulsion motor and wheels. The coupling device can simply be a gear to match electric machine speeds to vehicle speeds.
Power transmission path in an electric vehicle
Combination of MPTP and EPTPThe propulsion power is transmitted to wheels through either MPTP or EPTP or combination of both.
The MPTP is associated with an IC engine and transmission, whereas EPTP consists of energy storage system, a generator, propulsion motor and transmission.
Block diagram
A hybrid electric vehicle powertrain
Series HEVA series hybrid is one in which only one energy converter can provide propulsion power.
Only electric motor provides all propulsion power to wheels.
A downsized IC engine drives a generator, which supplements batteries and can charge them when it fall below certain charge level.
The drawback is size of traction motor, which as to be rated for max. power requirement of vehicle.
Block diagram
Series HEV powertrain
AdvantagesFlexibility of location of engine-generator set
Simplicity of Drive train
Suitable for short trips with stop and go traffic
DisadvantagesIt needs IC engine, generator and motor
Motor must be designed for maximum sustained power that vehicle require such as climbing a high gradient
All drivetrain components need to be sized for maximum power for long distance, high speed driving
Parallel HEVA parallel hybrid is one in which more than one energy conversion device can deliver propulsion power to the wheels.
The IC engine and electric motor are configured in parallel with a mechanical coupling.
The power requirements of electric motor is lower than that of series HEV.
Block diagramParallel HEV powertrain
AdvantagesIt needs only IC engine and motor/generator
A smaller engine and motor can be used to get same performance, until batteries are depleted
DisadvantagesThe control complexity increases, since power flow has to be regulated and blended from two parallel sources
The power blending from IC engine and motor needs a complex mechanical device
Series-Parallel HEVIt combines the benefits of series and parallel architecture with charge sustaining capability.
The power-split device divides the output from the engine into mechanical and electrical transmission paths.
Even IC engine is also used to charge the battery.
They are capable of providing continuous high output power compared to series or parallel powertrain.
Block diagram
Series Parallel combination HEV
Drive Modes of Operation
Torque characteristics
Electric motor and IC engine torque characteristics
Torque characteristicsThe torque characteristic of a motor is shown along with torque characteristics of IC engine.
For electric motor, a high torque is available at starting, which is the rated torque of motor.
The peak or rated power from a motor is obtained at base speed (w b) when motor characteristics enter the constant power region from constant torque region once voltage limit of power supply is reached.
The motor rated speed (w rated) is at end of the constant power region. The IC engine peak power and torque occur at the same speed.
Modes of operation-TOYOTA Prius
Commercial vehiclesToyota PriusToyota HighlanderFord EscapeMercury MarinerHonda InsightHonda Civic HEVHonda Accord HEV
ChallengesTime of battery changing is long
Batteries are heavy (100kg extra weight consumes 2L/100km more)
Batteries are expensive
Low performance in hot or cold temperatures also may damage the battery
Very sensitive to overcharge/undercharge(Battery life reduces dramatically)
Contain toxic heavy metals, disposal issue
Advantages of a Hybrid CarEnvironment friendly
Financial benefits
Less dependence on fossil fuels
Regenerative braking system
Built from lighter materials
Disadvantages of a Hybrid carLess power
Expensive
Poor handling
Higher maintenance cost
ConclusionUsing the concept of Hybridization of cars results in better efficiency and also saves a lot of fuel in todays fuel deficit world.
A hybrid gives a solution to all the problems to some extent.
One can surely conclude that this concept will follow with even better efficiency & conservation rate