An electric vehicle (EV) powertrain includes a battery pack, a motor-drive controller with power electronics, a 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 article compares the differences between the drivetrains in BEVs and discusses various HEV architectures.
The architecture of a BEV consists of three sections: the energy source, power conversion, and the drive system or the electro-mechanical actuator. They’re all connected to the central vehicle controller (Figure 1). Each section includes multiple subsystems
The energy source includes the battery pack, battery management system, onboard charger (OBC), and thermal management system. The power conversion section consists of the main traction drive inverter and bidirectional dc/dc converter, and the electro-mechanical actuator includes the traction motor and mechanical transmission.
Figure 1. The basic architecture of an EV drivetrain consists of an energy source, a power conversion section, and a drive motor (Image: MDPI energies).
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 vehicle’s driving range, but it’s insufficient to completely stop the vehicle’s motion. Regenerative and friction braking must be used in tandem and controlled simultaneously to produce the required total braking.
Variations
While a BEV uses only an electric motor powered by the battery pack, various HEVs use 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).
Figure 2. HEV, PHEV, and BEV drivetrains include various combinations of battery and gasoline or diesel as the fuel. (Image: charge wizard).
The relative sizes of the electric motor and ICE determine whether the vehicle is a mild or strong hybrid. Strong, or parallel, HEVs are similar to BEVs, as 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.
The OBC charges the battery in a PHEV. The high-voltage battery pack can power the traction motor for up to 50 miles before switching the ICE on.
Summary
The basic elements of an EV drivetrain are the energy source, power conversion, and drive system. Different types of EVs — such as BEVs, HEVs, and PHEVs — are differentiated by their primary energy source. This includes gasoline and/or electric grid power, as well as their primary motive power sources: electric traction motors and internal combustion engines (ICEs).
References
- 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
Filed Under: Battery Pack, Battery Power - EV Engineering, FAQs, Featured