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BEV, PHEV or HEV: Their Differences and The Impact on Vehicle Architecture

Vehicles in the modern era are expected to be environmentally friendly. This includes preventing environmental pollution and global warming, as well as diversifying energy sources from petroleum in recent years. More and more cars with an electric motor are appearing on the car market all around the world. From fully electric, to plug-in hybrids, and hybrid electric vehicles (1). The goals of this article are to first make you, the reader, more familiar with several types of electric vehicles, and then to help you to recognize how these vehicles differences affect their architecture.


BEV stands for 'Battery Electric Vehicle'. This means that this electric car does not require a fuel engine. It is therefore fully electric, with a large battery pack. A BEV is considered emission-free (1). Users can charge the battery via an external outlet. BEVs currently exist in many forms, including cars, buses, motorbikes, scooters, and even boats. The highest selling BEVs globally include the Tesla Model 3 and Model Y, the SAIC-GM-Wuling Hongguang Mini, the Nissan Note, the VW ID.3, and the Renault Zoe (2).


You can also 'plug in' with a PHEV or ‘Plug in Hybrid Electric Vehicle’. The electric motor of such a plug-in hybrid supports a fuel engine that can be diesel or petrol. Especially in the city, such a PHEV has great advantages, because you can drive short distances and then recharge the battery while braking. Usually, you can drive up to 60 kilometers fully electrically with a plug-in hybrid. You charge the battery of a PHEV in the same way as with a fully electric car, i.e. by means of a charging cord. Examples of PHEVs include variants of the Toyota Corolla and RAV4, the Volvo XC40 and the BMW 3-Series. (2)


The electric motor and combustion engine in an HEV work together smartly to reduce fuel consumption (1). HEVs are the most common type of hybrid, and they have been around the longest too. HEVs have two power drives: a fuel-based engine and an electric motor with a larger battery. When the car starts, it first rolls under electric power. Then, as soon as the vehicle achieves speed, the gas engine starts. An onboard computer system determines when electricity or gas should be used. Through a process known as “regenerative braking,” the car’s electric battery gets a little recharge every time the driver touches the brakes. The Toyota Prius is the most well-known HEV (2).

Now, it is a good opportunity to gain some information about how these aforementioned differences affect the architecture. Several architectural differences are involved in moving from one of these types of EV to the next. The most obvious is battery capacity, which is measured in kilowatt hours (kWh). Since the electric motor in a mild hybrid electric vehicle (MHEV) is only assisting a gas engine, it might have a battery that is 1 kWh or less. An HEV’s battery has to deliver enough power to run the vehicle for brief periods, so it might be as large as 8 kWh, while a PHEV could have a battery as large as 15 kWh to drive further on electric power alone. The battery in a full BEV has to power everything in the vehicle, all the time, so typical BEV capacities range from about 40 kWh to 80 kWh, although some are now emerging with batteries as large as 200 kWh (2).

The biggest architectural change comes when moving from an HEV to a PHEV. That is the point where outside power — from the grid, possibly from an outlet at the vehicle owner’s house — now enters the vehicle. Receiving alternating current (AC) power from the outlet means the vehicle has to have an inlet, leading to an onboard charger that converts the power to direct current (DC) to charge the battery. As the battery powers devices in the vehicle, the power stays DC, but requires an inverter to change to AC to power the electric motors. The PHEV always has a gas engine to fall back on and has a smaller battery, so conventional charging will likely be sufficient to charge it in a short amount of time. PHEVs can typically charge in a couple of hours with a Mode 2 charging cord – that is, one that can plug into a standard household outlet (2).

Schematic of different types of Electric Vehicles (EVs) and their sources and consumption of energy and emission from tailpipe and energy generation.

For BEVs, this method may take more than a day to fully charge their higher-capacity batteries, so many BEV owners opt to install a wall-mounted EV charger in their home and/or use public charging stations, including fast-charging stations that can potentially charge the BEV in less than one hour. Consequently, when moving from a PHEV to a BEV, this change in charging speed becomes a consideration that drives architectural decisions. While BEVs remove all ICE components, which reduces complexity, the requirement for faster charging means adding DC charging capabilities. (2)

High-speed charging means higher power. While internal combustion engine (ICE) vehicles use 12-volt batteries, BEV batteries often deliver 350 volts, with some original equipment manufacturers (OEMs) even going as high as 800 volts. Higher power requires larger and more robust cables and connectors to allow for faster charging. The voltage has to be stepped down for different components — especially electronics that run on 12V or less — but overall this is an efficient approach that saves energy. OEMs are discovering that even mild hybrids can achieve efficiencies by using 48V for higher-power components such as air conditioners or active-suspension systems, and then stepping down voltage for electronics. The use of 48V also makes it ideal for turning the engine on and off when starting and stopping (2).

In summary, all of these aforementioned vehicle components like the batteries, converters, inverters, wires, and connectors add weight and complexity to the vehicle; but the experts have been taking some measurement to reduce the complexity with a thoughtful approach in designing the several types of electric vehicles.





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