Plug-In Hybrid Defined

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Like a conventional hybrid, a plug-in hybrid or PHEV uses two different power systems.

PHEVs differ from their conventional cousins, however, because they have high-capacity battery packs. They are charged when you plug them into a household socket or a home or commercial charging station. Thus the “plug-in” part of their name.

The ability to charge the PHEV’s pack before driving away means you can get a substantial amount of all-electric range before the “plug” charge is depleted. When that happens, the car reverts to standard gas-electric hybrid mode. The internal combustion engine – ICE – and regenerative braking put some juice back in the battery as you drive.

The larger capacity of the PHEV’s battery also means that it can travel at higher speeds in all-electric mode.

Range varies with battery size. Today’s PHEVs vary in range from a low of 11 miles to a high of 72 miles on battery power (per EPA ratings). The ability to travel so far on electricity alone and then to operate as a regular hybrid gives PHEVS much better fuel efficiency than conventional hybrid models. Their ability to use a gasoline engine for propulsion gives them greater range than battery-electric cars, or BEVs.

There there are 14 PHEV models on the market today and the number grows each year.

Plug-in hybrids come with several powertrain types.

The most common is the series-parallel PHEV, in which the central power management system apportions power to the electric and gasoline powertrains. The “brain” picks the best ratios  for optimum fuel efficiency and power delivery at all times. Series-parallel PHEVs can run in all-electric mode, in ICE mode or in varying combinations of gas and electric power.

One model, the BMW i3 REx (it stands for range extender) uses a series hybrid system. Power to the wheels comes only from the electric motor system. The gas engine, a modified two-cylinder BMW motor scooter engine, isn’t connected to the wheels. It works only as a generator to produce electricity when the battery’s plug-in charge is depleted.  EPA-estimated range for an i3REx on a fully-charged battery and a tank of gas for the generator (only 2 gallons) is 150 miles. That includes 72 miles on the initial plug-in charge. While it is technically a plug-in hybrid, some prefer to call this type of drive system a range-extended EV.


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