An EV powertrain includes a battery pack, motor drive controller and power electronics, traction motor, and more. But that description only applies to battery electric vehicles (BEVs). For mild and strong hybrid vehicles (HEVs) and plug-in hybrid vehicles (PHEVs), the powertrain also includes an internal combustion engine (ICE) and transmission. This FAQ looks at the differences between the drivetrains in BEVs and various HEV architectures.
The architecture of a BEV consists of three sections, the energy source, power conversion, and drive system, or electro-mechanical actuator, all connected to the central vehicle controller (Figure 1). Each of the three sections includes multiple sub-systems. The energy source includes the battery pack, battery management system, onboard charger (OBC), and thermal management system. The power conversion section includes the main traction drive inverter and bidirectional dc/dc converter, and the electro-mechanical actuator includes the traction motor and mechanical transmission.
A BEV has two operating modes, drive and regenerative braking. Driving is straightforward, and the vehicle controller controls the traction inverter to drive the motor. Regenerative braking is more complex. In regenerative braking, the motor operates as a generator and feeds energy back into the traction inverter. From there it’s stored for the next drive cycle. Regenerative braking is good for supplementing the driving range of the vehicle, but it’s insufficient to completely stop the vehicle’s motion. Regenerative and friction braking must be used in tandem, and they must be controlled simultaneously to produce the required total braking.
While a BEV uses only an electric motor powered by the battery pack, various HEVs use both an electric motor and an ICE. In a HEV, gasoline or diesel is the fuel source; a PHEV uses a combination of gasoline or diesel and the electric grid as the fuel source; in a BEV, the electric grid is the only power source (Figure 2).
The relative sizes of the electric motor and ICE determine whether the vehicle is a mild or strong hybrid. Strong, or parallel, HEVs are like BEVs since the battery pack powers the traction motor directly (the traction motor is ‘strong’). The ICE is used as a generator to charge the high-voltage battery pack and extend the driving range. It does not use electricity from the grid. The size of the drive motors in BEVs and strong HEVs is usually from 60 kW to more than 180 kW.
In a mild, or series, HEV the ICE provides the primary motive power. The traction motor is weak or ‘mild’ and is only used to start the vehicle moving from a full stop or to assist the relatively small ICE during acceleration. Mild HEVs typically have a 48 Vdc battery pack with limited energy storage capacity and a low-power traction motor.
In the PHEV, the OBC is used to charge the battery. PHEVs have a high-voltage battery pack capable of powering the traction motor for up to 50 miles before switching the ICE on.
The basic elements of an EV drive train are the energy source, power conversion, and drive system. Different types of EVs like BEVs, HEVs, and PHEVs are differentiated by their primary energy source including gasoline and/or electric grid power, and their primary motive power source including electric traction motors and ICEs.
- Electric Powertrain and HEV/EV Ecosystem, Keysight Technologies
- Electric vehicle (EV) drivetrain system, Infineon
- Fault Diagnosis Methods and Fault Tolerant Control Strategies for Electric Vehicle Powertrains. MDPI energies
- Hybrid Electric Vehicles, U.S. Department of Energy
- What are the different types of Electric Vehicle?, charge wizard
You may also like:
Filed Under: Battery Pack, Battery Power - EV Engineering, BEV, FAQ, Featured, HEV