100 Questions about Electric Vehicles

By David Herron

What is the difference between Plug-in Hybrid, Hybrid, or All-Electric battery-electric vehicles?

What is an Electric Vehicle? What will it take for automakers to build affordable 250 mile range electric cars?
There are two kinds of plug-in electric vehicles, the plug-in hybrid and the all-electric or battery-electric vehicle. Regular hybrid vehicles, while having electric components in the drive train, are not plug-in electric vehicles. The difference between them is primarily in how far you are willing to go to divorce yourself from gasoline. The plug-in hybrid (or PHEV) still relies on gasoline, and uses gasoline to implement long range driving, while the all-electric vehicle uses no gasoline, and therefore relies on fast charging for long range.

Let's take a look at the components in more depth.

Components of the All-Electric Vehicle (BEV). Source: David Herron

On a BEV (all-electric vehicle or battery electric vehicle), there is a charging port for recharging the car. Having a charging port is what makes a BEV an electric vehicle, because it can recharge the pack from the electricity grid.

The on-board charger converts the AC voltage from the grid to a DC voltage to recharge the battery pack, and also manages the charging process. Typically the traction-battery (battery pack) is at about 400 volts, and to recharge the battery the on-board charger must "step up" the voltage to match the battery pack voltage. Another component is the battery management system which ensures the cells are properly balanced. The BMS also monitors the cells to detect any that are weak.

Because electric vehicle motors almost universally run on AC, to get the car going requires an inverter to convert DC voltage from the battery to AC voltage for the electric motor.

The entire energy required to power a BEV comes from recharging the battery pack.

Components of the Plug-in Hybrid Electric Vehicle (PHEV). Source: David Herron

A PHEV (Plug-in Hybrid Electric Vehicle) is slightly different than the BEV. PHEV's contain the same set of components as are in a BEV, namely the charger, battery pack, and inverter. What PHEV's add is a second drive train powered by gasoline, which includes a gas tank and gasoline engine.

The electric side of the PHEV operates the same as the BEV -- The on-board charger is used for recharging the battery pack, and the battery pack drives an electric motor which drives the wheels.

The gasoline side of the PHEV operates as a gas car (FFV or fossil-fuel-vehicle) -- there is a gasoline tank, which fuels the gasoline engine. The gasoline engine serves two purposes, recharging the battery pack and driving the wheels.

It's a little more complex than that because there are PHEV two variants

  • Series-Hybrid Electric Vehicle: In this arrangement, the gas engine has no direct connection to the wheels and instead solely recharges the battery pack. It is the battery pack and electric motor that provides full capability of motion.
  • Parallel-Hybrid Electrc Vehicle): In this arrangement, both the electric motor and the gas engine carn drive the wheels. The gas engine can both recharge the battery pack and drive the wheels.
Components of a regular Hybrid vehicle. Source: David Herron

Hybrid vehicles have both a gasoline engine and electric motor, with a small battery pack and other electric drive train components to drive the motor. Where a hybrid differs from a plug-in hybrid or battery electric vehicle is that every unit of energy driving the vehicle is derived from the gasoline.

You simply cannot plug-in to charge the battery pack from the electric grid.

Therefore in terms of how far one is willing to go to divorce themselves from gasoline, driving a hybrid vehicle means one is completely unwilling to do so.

The electric side of a hybrid vehicle is fairly transparent to the driver. Some information is shown on infotainment screens about the drive train status, whether the battery is charging from the gasoline engine, etc. But beyond that the driver just drives, and refills their gasoline tank at gas stations, and has zero opportunity for an alternate energy source.

Plug-in Hybrid EV Modes of operation

Plug-in hybrid's primarily operate either in charge-depleting or charge-sustaining modes. Combinations of these modes are called blended mode or mixed-mode. Typically a PHEV will operate in electric mode, a.k.a. charge-depleting, until the state of charge reaches a threshold at which time it will switch to a mixed mode or charge sustaining mode. These modes manage the vehicle's battery discharge strategy, and their use has a direct effect on the size and type of battery required:

In Charge-depleting mode a PHEV or BEV operates exclusively (or almost exclusively) on electric power until its battery state of charge is depleted to a predetermined level. At that level the vehicle's internal combustion engine or fuel cell will start running.

In Charge-Sustaining mode an HEV or PHEV operates using the fossil fuel engine to maintain the battery pack at a fairly high state of charge. For a PHEV this means the vehicle operates as if it is an HEV (Hybrid electric vehicle).

In mixed mode or blended mode the vehicle operates in a combination of multiple modes. The control system will automatically switch between charge depleting and charge sustaining mode depending on conditions. In some PHEV's the electric motor is weak, and the car will use its fossil fuel engine when traveling at high speeds.

PHEV all-electric range

Many PHEV owners try to drive purely on electricity on the majority of days. Since most folks drive less than 40 miles per day, a 40-mile range PHEV has enough electric range to satisfy the vast majority of driving.

The range a PHEV can drive purely on electricity is its electric range. Many describe this as PHEV-20, PHEV-40, PHEV-80, and so on. The number there indicates the miles of range on electricity.

Therefore a PHEV-40 like the Chevy Volt can let one drive on electricity for the majority of ones driving needs. Indeed many Volt owners say they hardly ever buy gasoline.

History

In a large way the PHEV is responsible for the revival of the electric car. There are various factors behind this so it is difficult to pinpoint one cause, but the PHEV played a big role.

Specifically: Beginning in the late 1990's both Honda and Toyota began selling Hybrid cars as a way to meet environmental cleanliness goals.

During the 1990's and up til about 2004, California had its ZEV Mandate which forced automobile manufacturers to produce all-electric vehicles. Famously, CARB (the California Air Resources Board) voted to change the rules and gut the requirement to produce ZERO EMISSION VEHICLES (ZEV's). They replaced the ZEV requirement with a points system, and gave fuel-cell-electric-vehicles a big advantage in that system. The auto manufacturers canceled their battery electric (BEV) programs.

Since CARB also allowed the auto manufacturers to earn credits by selling Hybrid vehicles, many came on the market. The first two were the Toyota Prius and the Honda Insight, and of the two the Prius would play a more significant role.

Namely -- a set of DIY folks developed a method to convert a Prius into a Plug-in Hybrid. Primarily this work was performed under the CalCars banner. CalCars published the procedure for the Plug-in Hybrid Prius conversion on their website. From there hundreds of people either did Plug-in Prius conversions on their own, or bought kits from companies who commercialized the process.

CalCars then started taking their so-called Prius+ cars to every political event they could. This kept the possibility of a plug-in vehicle in the eyes of policy-makers.

During the 2000's the automakers did develop plug-in hybrid models of their own. Primarily these were concept vehicles rather than commercial.

By 2010, GM began selling the Chevy Volt. Despite GM's best effort to teach us the phrase "extended range electric vehicle" the Volt is a Plug-in Hybrid. The Volt has been fairly popular, and Volt owners tend to love the concept.

Toyota developed the Plug-in Prius, their own take on a Prius which could plug in. Mitsubishi developed the Outlander PHEV, an SUV with a PHEV drive train. Honda developed the Honda Accord PHEV. Ford developed a couple PHEV's under the Energi moniker. BMW developed both the BMW i8 sports car available solely as a PHEV, and the BMW i3 REX which is a PHEV version of the i3. And there are others.

Pragmatism -- Extending the range

All vehicles have a range limit based on the energy stored on board. There is nothing magical about a gasoline vehicle that nobody ever gets stuck without fuel. Gas vehicle owners do run out of gasoline, which is why the wise driver always has a gas can in the trunk just in case. It's not wise to keep gasoline in the gas can, but to have it there in case you run out.

Both gas vehicle owners and electric vehicle owners can get stuck on the side of the road without power.

The significant difference between FFV and BEV owners is the recharge time. FFV's (fossil fuel vehicles) can be refueled in a few minutes, where as BEV's take awhile. That can be anywhere from an hour to 4 hours.

Therefore if your real needs include frequent long range trips a PHEV is a more pragmatic choice. That is, until fast charging for electric vehicles is good enough and ubiquitous enough.

What is the difference between Plug-in Hybrid, Hybrid, or All-Electric battery-electric vehicles?

What is an Electric Vehicle? What will it take for automakers to build affordable 250 mile range electric cars?
(disqus.com) comments powered by Disqus