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

11

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