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What are the key components and considerations involved in power management for EVs?

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Electric vehicles (EVs) have several components that deal exclusively with power management. The components include:

  • A battery pack
  • A battery management system (BMS)
  • Power electronics
  • Electric motors
  • A regenerative braking system
  • An onboard charger

This FAQ will briefly introduce these components and the considerations to look for.

Figure 1 shows a schematic diagram of a hybrid EV (HEV) where the different parts are highlighted. A glance at the picture is enough to conclude that even in an HEV, EE parts dominate. Even more specific is the significant contribution of power management components.

Figure 1. The key components of an HEV, particularly related to power management. (Image: Electrical Engineering Portal)

Let’s briefly discuss each component as follows.

Battery pack

A battery pack in an EV stores and supplies electrical energy to power the vehicle’s electric motor. It consists of multiple battery cells arranged in series and parallel configurations to achieve the required voltage and capacity. These cells are grouped into modules and assembled into the final battery pack, as shown in Figure 2.

Figure 2. The arrangement of battery cells into a module, pack, and ultimately, an electric vehicle. (Image: University of Toronto)

High energy density is an essential feature of an EV battery pack that extends the vehicle’s range. Lithium-ion batteries are commonly used due to their high energy density and efficiency. Safety, lifespan, and cost are other considerations when choosing an EV battery pack. However, lithium-ion continues to improve in all these parameters.

Battery management system

A BMS in an EV complements the battery pack, monitoring, managing, and protecting it. It continuously tracks individual cells’ voltage, current, and temperature, as well as the entire pack. Figure 3 illustrates how the battery pack and BMS of an EV are connected.

Figure 3. The many functions of a BMS with respect to the battery pack. (Image: SRMTech)

By controlling charging and discharging processes, the BMS prevents overcharging, overheating, and short circuits. It regulates battery temperature through cooling or heating systems. It also interfaces with other vehicle systems and provides battery information to the driver.

Power electronics

Power electronics in EVs are systems that control and convert electrical energy between the battery, motor, and other components. Three components in EVs are part of the power electronics: traction inverter, dc-dc converter, and onboard charger. From time to time, power electronics continue to expand their share in the power management of EVs.

Some converters also perform bidirectional conversion, as shown in Figure 4, where the EV battery is connected to a bidirectional dc-dc converter.

Figure 4. The different ways in which power electronics are employed in EVs. (Image: MDPI)

The traction inverter converts the dc power from the battery to ac power for the motor, while a dc-dc converter steps up and down voltages wherever necessary. The onboard charger converts ac power from the grid to dc for battery charging. 

Power electronics in EVs require many considerations. Efficiency is one key area where the EV driving range is extended by extracting maximum power from the system. Power density allows you to pack more power output into compact and lightweight designs.

As efficiency and power density increase, thermal management takes priority because the EV system generates more heat. Engineers and marketers also consider reliability and cost. Recent semiconductor advancements have also seen the use of SiC and GaN as wide bandgap semiconductors for improved efficiency and power density.

Electric motor

An electric motor in an EV is a device that converts electrical energy from the battery into mechanical energy to drive the vehicle’s wheels. Unlike internal combustion engines, electric motors provide instant torque, resulting in rapid acceleration and smooth operation.

Many types of motors are used in EVs. Let’s consider three of the most commonly used (Figure 5). The permanent magnet synchronous motor (PMSM) is known for its high efficiency and torque density but relies on rare earth materials. 

Ac induction motors are another choice that manufacturers like Tesla use. These motors are reliable and less dependent on rare earth materials. Brushless dc motors (BLDC) are also used in EVs, offering high efficiency and reliability with reduced maintenance needs.

Figure 5. Images of the most commonly used motors in EVs: BLDC, PMSM, and induction motors. (Image: The Engineers Post – YouTube)

Regenerative braking system

A regenerative braking system in an EV captures kinetic energy during braking and converts it into electrical energy, which is then stored in the vehicle’s battery. Figure 6 illustrates this process, with the battery charging and discharging depending on whether the accelerator pedal or brake is applied. 

The regenerative braking process significantly enhances overall energy efficiency by slowing the vehicle and reusing energy that would otherwise be lost as heat in conventional braking systems. The system can recapture up to 70% of the kinetic energy depending on the vehicle model and driving conditions. This recovered energy extends the vehicle’s range and reduces the frequency of recharging.

Figure 6. The regenerative braking mechanism in EVs. (Image: LinkedIn)

Regenerative braking systems are often combined with conventional friction brakes to ensure effective braking at all speeds and conditions. This hybrid approach ensures safety and reliability.

Regenerative braking can alter the driving feel, often allowing for “one-pedal driving,” where lifting off the accelerator slows the vehicle. Drivers may need time to adapt to this system.

Onboard charger

The onboard charger can also be categorized into power electronics, but we cover them here separately because it is a dedicated part of an EV.

An onboard charger converts ac from external power sources, such as residential outlets or public charging stations, into dc to charge the vehicle’s battery. Figure 7 represents onboard charges during Levels 1, 2, and 3 of EV charging.

Figure 7. The use of an EV onboard charger (OBC) in level 1/2/3. (Image: everything PE)

Power conversion efficiency has been a research topic for engineers who are continuously trying to lower the losses in the onboard charger. Charging speed is also a critical parameter that enables the fast charging of EVs. Another consideration in the onboard charger is the ability to charge bidirectionally. Although this technology is still in R&D and has been implemented on pilot projects, it will have a wide scope in the near future.

Summary

EVs are designed to run entirely on power, and therefore, there are several components and considerations. If you look closely, the battery pack, electric motor, and onboard charger are present in different corners of the EV. The power electronics bind them together. 

R&D work on each of these components is ongoing globally. Battery packs focus on battery chemistry and thermal management. Power electronics and electric motors are focusing more on efficient energy conversion. Regenerative braking is not a new concept, but it has slowly and steadily been taken seriously in the R&D wing of manufacturing companies.

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