As electric vehicle (EV) technology continues to evolve, several trends are shaping the future of vehicle design. Here, we’ll explore the key classifications of EVs, the trends shaping their developmental trajectory, and the implications for component design, specifically as it relates to capacitors. These components serve critical energy storage and discharge functions in EVs.
Comparing EV classifications
EV designs fall into four main classifications, each with unique technologies and design approaches for elements like powertrain architecture and charging requirements. Recognizing the similarities and differences between the most common types of EVs develops a foundation for understanding how and where industry trends are evolving.
Fully hybrid electric
Fully hybrid electric vehicles (full HEVs or strong HEVs) leverage an internal combustion engine (ICE) and an electric motor to power motion. The electric motor runs on a small, high-voltage battery (70 to 170 kW) charged via regenerative braking. The ICE offers power in the face of low battery, high speed, or acceleration.
These vehicles cannot be charged from the grid. While their range is similar to a conventional gas-powered car, the relatively low energy capacity of the battery (2 to 5 kWh) supports only a limited driving range in electric mode.
Plug-in hybrid electric
A plug-in hybrid electric vehicle (PHEV) includes an ICE and an electric motor, similar to an HEV. However, unlike an HEV, the battery in a PHEV can be charged on the electrical grid, which requires an onboard charger (OBC) and a charging plug. The battery capacity of a PHEV is typically larger than that of a full HEV, often around 15 kWh. If equipped with a bidirectional charger, as seen in some fuel cell electric vehicles (FCEVs), a PHEV can serve as a source of electricity for vehicle-to-grid (V2G) and vehicle-to-home (V2H) applications.
Battery electric
A battery electric vehicle (BEV), or full electric vehicle, is powered exclusively by an electric motor without an ICE. BEVs feature high-power, high-energy capacity batteries, typically ranging from 30 to 100 kWh, which can be charged from the electrical grid. Like PHEVs, if equipped with a bidirectional charger, BEVs can be used as a source of electricity for V2G and V2H applications.
Fuel-cell EVs
Like BEVs, fuel-cell electric vehicles (FCEVs) — sometimes called FCVs or hydrogen-powered cars — are powered by an electric motor alone. In this case, electricity is generated from hydrogen via a fuel-cell stack. FCEVs contain a battery or supercapacitor stack to manage functions like braking energy recovery. The battery is typically high voltage but low capacity (i.e., a few KWhs).
When designed with a larger battery (10 kWh), FCEVs can be charged on the grid, similar to PHEVs. When electricity is generated via renewable sources like photovoltaics or wind, this feature allows for cleaner driving because it reduces dependence on hydrogen fuel. Like PHEVs and BEVs, FCEVs can serve as a source of electricity for V2G and V2H applications with a bidirectional charger.
Trends in EV design and charging
Several trends continue to shape engineering design across the EV space, particularly in terms of charging and power management. High-power DC charging is expanding, focusing on faster, more efficient charging systems. Bidirectional charging is gaining popularity, offering V2G and V2H capabilities.
High-voltage architecture is becoming the norm, promoting higher efficiency. Lastly, for the purposes of this article, the integration of electric drive train components and the growing use of wide-bandgap semiconductors are further optimizing performance and reducing system complexity in EVs.
High-power dc charging
Dc chargers leverage a high-power ac/dc converter to shift ac grid voltage into an appropriate dc voltage for EV batteries (e.g., 150, 400, 800 V). With different batteries featuring different voltage levels, there’s an incentive to increase the maximum charger voltage from 500 to 1000 V.
More and more dc chargers are being deployed at high power levels, ranging from 22 to 350 kW. These systems can accommodate high-voltage battery systems and boost the charger’s voltage enough to enable fast charging.
The goal of adopting 1000-V chargers is to simplify life for EV owners. With these in place, they won’t need to hunt for a station that accommodates a specific vehicle battery voltage. On the components level, the push for smaller charger footprints, better thermal management, and higher breakdown voltages are driving the inclusion of silicon carbide (SiC) MOSFET devices in charging technology.
Bidirectional charging
Bidirectional charging in EVs is gaining traction because it’s a huge perk to charge a vehicle and discharge electricity back into the grid or your home. This capability, known as V2G or V2H, offers a backup power source during grid outages or high-demand periods. When it comes to electronics, bidirectional chargers require complex design specifications to account for durability for higher power conversion cycles (and more of them), managing compatibility with varying grid standards and specialized component selection to manage electrical noise and ensure efficiency.
High-voltage architecture
The trend toward high-voltage EV charging architecture involves shifting from 400 to 800-V battery systems to enable greater power density and faster charging. This shift helps address consumer range anxiety and concerns around charge time. Higher voltage allows lower currents to deliver the same amount of power, which reduces heat generation and leads to more efficient energy transmission via smaller, lighter wires.
To operate at higher voltages, manufacturers must carefully select components. Capacitors, for example, must be highly reliable and designed to handle these elevated voltages while ensuring safe and efficient energy conversion.
Integrating electric drivetrain building blocks
There are opportunities for efficiency and cost savings when combining EV subsystems into multi-function modules. For example, it’s becoming more common to see bidirectional charging, all-in-one power systems, and OBC, shown in Figure 1, combined with dc-dc converter units.
These integrations improve power density, reduce weight, and enable better thermal management. Key technologies, such as multilayer ceramic capacitors (MLCCs) and SiC devices, support this trend by enhancing energy efficiency and reducing losses in components like inverters and chargers. This allows for more compact, efficient, and high-performance EV systems.
Figure 1. This diagram illustrates the placement and functions of various capacitors in an EV’s onboard charger.
Availability of wide bandgap support
The emergence of wide-bandgap (WBG) semiconductors featuring SiC and GaN is growing in EV design because of the need to balance operating at higher voltages and maintaining power system efficiency. Power electronics supported by WBG enable fast switching and lower power loss, even at higher switching frequencies. This combination accommodates the development of high-power density, high-efficiency power converters. It also helps that they’re more plentiful and less costly to purchase nowadays.
SiC is common in higher-power systems like 800-V inverters, where higher switching frequencies enhance performance while reducing size and weight. GaN is emerging in lower-power systems like dc-dc converters, shown in Figure 2.
Figure 2. This diagram illustrates the placement and functions of various capacitors used in dc-dc charging.
Adapting to high-voltage, high-frequency demands
As EV innovation continues, the need for capacitors that can handle higher voltages and faster switching frequencies has become critical to ensure efficient and reliable performance in power converters. Regardless of the type of power converter, capacitors serve a handful of essential functions:
Filter
Filter capacitors are a type of component commonly used as input and output capacitors. On the ac side of a system, these capacitors typically provide electromagnetic interference (EMI) filtering. On the dc side, they smooth the ripple components of the ac and filter out noise.
DC link
Dc link capacitors serve as an intermediary between an input source and an output load with mismatched specifications (such as instantaneous power, voltages, and frequencies). They help offset the effects of inductance in inverters, motor controllers, and battery systems in EVs. Dc link capacitors also serve as filters that protect subsystems from voltage spikes, surges, and EMI.
Snubber
Snubber capacitors address the negative impacts of switching in switching power supplies. For example, insulated-gate bipolar transistors (IGBTs) are used for fast and efficient switching in EV inverters. These inverters, shown in Figure 3, convert dc battery power to ac power, which drives the traction motor, and convert ac power back to dc power when the vehicle is breaking. The power module will require snubber capacitors to protect the semiconductors by absorbing noise.
Figure 3. This diagram illustrates the placement and functions of various capacitors in an EV’s traction inverter system.
Resonant
Resonant converters, designed to increase efficiency, are switching-based converters that incorporate a resonant tank for controlling input-to-output power flow in high-voltage applications. They function to smooth waveforms, improve power factor, and reduce switching losses caused by MOSFETs and IGBTs.
The shift toward WBG semiconductors and higher voltage systems in EVs is driving significant changes in electronic component design, and capacitors are no exception. Capacitors now need to handle higher switching frequencies, which demand smaller capacitance values, low equivalent series resistance (ESR), and low equivalent series inductance (ESL) to minimize losses while accommodating higher currents.
The higher operating voltages mentioned throughout this piece also require capacitors with enhanced reliability at those elevated voltage levels. Selecting the ideal capacitors depends on the power converter topology used and the design constraints (including the size, temperature, environmental) facing the engineering team.
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