Plug-in Electric Hybrid Vehicles

Size / Range

Technology

A plug-in hybrid electric vehicle (PHEV) is a hybrid vehicle with batteries that can be recharged by connecting a plug to an electric power source. It shares the characteristics of both conventional hybrid electric vehicles and battery electric vehicles, having an internal combustion engine and batteries for power. Most PHEVs on the road today are passenger cars, but there are also PHEV versions of commercial passenger vans, utility trucks, school buses, motorcycles, scooters, and military vehicles. PHEVs are sometimes called grid-connected hybrids, gas-optional hybrids, or GO-HEVs.

Hybrids Plus plug-in hybrid Toyota Prius conversion with PHEV-30 (30 mile or 48 km all-electric range) battery packs

PHEVs are based on the same three basic power train architectures as conventional hybrids.

Series hybrids use an internal combustion engine (ICE) to turn a generator, which in turn supplies current to an electric motor, which then rotates the vehicle’s drive wheels. A battery or capacitor pack, or a combination of the two, can be used to store excess charge.

Parallel hybrids, such as Honda's Insight, Civic, and Accord hybrids, can simultaneously transmit power to their drive wheels from two distinct sources.

Series-parallel hybrids have the flexibility to operate in either series or parallel mode. Hybrid power trains currently used by Ford, Lexus, Nissan, and Toyota, which some refer to as “series-parallel with power-split,” can operate in both series and parallel mode at the same time. As of 2007, most plug-in hybrid conversions of conventional hybrids utilize this architecture.

The Chevrolet Volt concept car is a series plug-in hybrid, meaning that its mechanical engine power is exclusively converted to electricity, not used directly.Modes of operation - A plug-in hybrid may be capable of charge-depleting and charge-sustaining modes. Combinations of these two modes are termed blended mode or mixed-mode. These vehicles can be designed to drive for an extended range in all-electric mode, either at low speeds only or at all speeds. These modes manage the vehicle's battery discharge strategy, and their use has a direct effect on the size and type of battery required:

Charge-depleting mode allows a fully charged PHEV to operate exclusively (or depending on the vehicle, almost exclusively, except during hard acceleration) on electric power until its battery state of charge is depleted to a predetermined level, at which time the vehicle's internal combustion engine or fuel cell will be engaged.

Charge-sustaining mode is used by production hybrid vehicles (HEVs) , and combines the operation of the vehicle's two power sources in such a manner that the vehicle is operating as efficiently as possible without allowing the battery state of charge to move outside a predetermined narrow band.


The redesigned Renault Kangoo Elect'road operates in blended mode, using engine and battery power simultaneously.

 

Blended mode is a type of charge-depleting mode normally employed by vehicles which do not have enough electric power to sustain high speeds without the help of the internal combustion portion of the power train. A blended control strategy typically increases the distance from stored grid electricity compared to a charge-depleting strategy. The Renault Kangoo and some Toyota Prius conversions are examples of vehicles that use this mode of operation.

Mixed mode describes a trip in which combinations of the above modes are utilized. For example, a PHEV-20 Prius conversion may begin a trip with 5 miles (8 km) of low speed charge-depleting, then get onto a freeway and operate in blended mode for 20 miles (32 km), using 10 miles (16 km) worth of all-electric range at twice the fuel economy.

Types

Single wheeled vehicles - The large Chinese wheelbarrows depicted with sails and masts.

Two-wheeled and cycle-type vehicles - Mopeds and electric bicycles are a simple form of a hybrid, as power is delivered both via an internal combustion engine or electric motor and the rider's muscles. Early prototypes of motorcycles in the late 1800's used the same principles.

In a parallel hybrid bicycle human and motor power are mechanically coupled at the pedal drive train or at the rear or the front wheel, e.g. using a hub motor, a roller pressing onto a tire, or a connection to a wheel using a transmission element.

  • In a series hybrid bicycle (SH) the user powers a generator using the pedals. This is converted into electricity and can be fed directly to the motor giving a chainless bicycle but also to charge a battery.

  • Heavy vehicles - Hybrid power trains are used for diesel-electric or turbo-electric railway locomotives, buses, heavy goods vehicles, mobile hydraulic machinery, and ships.

Three basic types of Hybrids

Mild – Uses the electric motor and battery as an assist to the internal combustion engine. A classification of hybrid vehicle that relies on the internal combustion engine to provide constant power for moving the vehicle. In this arrangement the electric drive motor acts to assist the engine when extra power is needed, but is incapable of propelling the vehicle alone.

Examples: Some of the early model Honda Civic hybrids were mild hybrids.

Full – The two propulsion systems (electric motor and internal combustion engine) can work independently or in conjunction with each other. A hybrid vehicle classification in which the arrangement of the electric drive motor, the internal combustion engine and battery system allow the hybrid vehicle to be powered solely by the electric motor under certain operating conditions—generally low speed maneuvering and light cruising. When additional power is needed, the engine kicks in and both power plants work together to propel the vehicle.

Examples: The Toyota Prius is a full hybrid.

Plug-in – The internal combustion engine acts only as a back-up to the main rechargeable motor and battery system. A plug-in hybrid is a regular hybrid vehicle that has a large high-capacity battery bank that can be re-charged by plugging in to normal household current as well as using the on-board charging capabilities of normal hybrids. While standard hybrids require a combination of regenerative braking and energy from the engine to recharge the batteries and propel the vehicle, plug-ins can essentially operate as electric vehicles with an internal combustion engine backup.

Also Known As: PHEVs (Plug-in Hybrid Electric Vehicles)

Applications

Performance and Efficiency

Plug-in hybrid electric vehicles share many component and powertrain architecture commonalities with power assist hybrid electric vehicles-but with the ability to recharge a larger energy storage system from off-board electrical power. The PHEV has unique battery requirements that often require a compromise between the high energy battery systems required by battery electric vehicles (BEV) and the high power energy storage systems used in power assist hybrid electric vehicles (HEVs). The duty cycle is generally a combination of deep and shallow discharge behavior found respectively in BEVs and HEVs and is dependent on both vehicle requirements and the energy management strategy of the hybrid powertrain.

Advantages and Disadvantages

Advantages

Disadvantages

Claimed fuel economy for PHEVs depends on the amount of driving between recharges. Disadvantages of plug-in hybrids include the additional cost, weight, and size of a larger battery pack.
No gasoline is used the MPG equivalent depends only on the efficiency of the electric sys Eletrical outlets ouside garages
The furthest all-electric range in a PHEV planned for mass production is the PHEV-60 BYD F6e. Emissions shifted to electric plants.
They have potential to be even more efficient than conventional hybrids because a more limited use of the PHEV's internal combustion engine may allow the engine to be used at closer to its maximum efficiency.  
PHEV adoption is a predicted reduction in carbon emissions.  
PHEVs can be viewed as an element in the "Pacala and Socolow wedges" approach which shows a way to stabilize CO emissions using a portfolio of existing techniques, including efficient vehicles.  
Vehicle-to-grid electricity, PHEVs and fully electric cars may allow for more efficient use of existing electric production capacity, much of which sits idle as operating reserve most of the time.  
Their potential ability to load balance or help the grid during peak loads.  
By using excess battery capacity to send power back into the grid and then recharge during off peak times using cheaper power  

Economic Performance

Quantifying the fuel savings of a plug-in requires proper characterization of plug-in design. Performance and cost requirements will likely dictate that the internal combustion engine engage regularly in a plug-in, even during trips far shorter than the nominal electric-only range of the vehicle. Assuming average driving patterns, a plug-in with an electric-only range of 20 miles could be expected to reduce fuel use by about one-third relative to a current hybrid. These potential savings are highly significant, but are less than the savings commonly proffered for plug-ins in the popular media. A plug-in with a 60-mile range could cut gasoline consumption by about two-thirds, though battery cost would be nearly three times that of the 20-mile plug-in.

The specific costs that the energy storage technology would need to achieve for the fuel cost savings over 5 years to offset the initial incremental cost. The chart includes both a present fuel cost ($2.15/gallon gasoline and 9 ¢/kWh electricity case) and a future fuel cost scenario ($4.30/gallon and 9 ¢/kWh). At today’s fuel costs, to be cost neutral, PHEV20 batteries would need to be at the projected long-term cost goals (labeled as Projected Battery Costs However, in the future fuel price scenario, both PHEV20 and PHEV40 energy storage systems only need to reach the $750 to $500/kWh range to be cost neutral respectively.

Battery Cost Requirements for Fuel Savings to Offset Incremental Cost within 5 Years

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