Road transport accounts for nearly one-fifth of global CO2 emissions, and that makes e-mobility, which commonly refers to the use of electric vehicles for transportation purposes, a critical technology landscape. With range anxiety taking the centerstage in e-mobility, engineers have turned their attention toward the major building blocks in EV charging infrastructure: on-board chargers (OBCs), DC/DC converters, and fast DC chargers.
For a start, e-mobility has been confronting charging as one of the major challenges, along with energy storage and cost. First-generation EVs had the slowest form of charging, with 3.7 kW of power, requiring a minimum of eight hours for charging a 25-kWh battery pack. However, with technological advancements, the power rating has been upgraded to 6.6–22 kW to enable fast AC charging.
Another notable shift in the EV charging infrastructure relates to battery voltage increases from 400-V to 800-V levels, driven by Porsche, Hyundai, and other carmakers. As a result, the charger voltage increases from 500 V to 1,000 V, and chargers are starting to use power components rated at 1,200 V.
In the rapidly emerging EV and hybrid vehicle designs, the above shifts will have a significant impact on the selection of components such as IGBTs, high-voltage gate drivers, superjunction rectifiers, high-voltage MOSFETs, and high-voltage DC/DC converters.
This article will provide a sneak peek into current and future EV charging infrastructure needs from the standpoint of power semiconductors, microcontrollers, and driver components.
On-board charger
An OBC handles charging when an EV connects to a charging station through an appropriate cable. It provides the critical function of charging the high-voltage DC battery packs in EVs from an infrastructure power grid. It’s a converter device similar to traction inverters but does the opposite, converting the AC power from the wall into DC power to suit the battery.
The OBC converts the AC supply voltage from the grid to the DC voltage level required by EV battery packs. (Source: Wolfspeed)
An OBC design comprises two main blocks: an active front end (AFE) for AC/DC conversion and a DC/DC converter. The AFE gets single-phase or three-phase power from the grid and outputs it to DC intermediate voltages, converted to the voltage required for fast-charging the EV batteries.
The recharge time, the time it takes for an EV to fill up, depends largely on the OBC’s power rating. Not surprisingly, therefore, OBCs have become a crucial design battleground in deciding the charging time based on the specifications offered by OEMs. Here, a new generation of power semiconductors enables significantly faster charging than before.
Then there are bidirectional OBCs that can help replenish the grid when necessary. A bidirectional OBC, which moves power back and forth efficiently with minimal loss, can balance high density with high efficiency and provide a wide output voltage range in both charging and discharging modes.
Bidirectional charging is precisely what the name implies: electricity flowing both ways. (Source: Wallbox)
From AC charging to DC fast charging
Most charging stations currently use AC power due to low technical barriers, low cost, and strong adaptability, especially in residential, office, and commercial places. However, as the charging technology matures, efficient DC charging points are gradually becoming popular on highways and at public charging stations, where EV drivers don’t have much time to recharge.
DC charging solutions are even making their way into home charging, offering new possibilities for users, as they allow fast charging as well as bidirectional charging. These chargers bypass the OBC installed on the EVs and directly provide a fast DC charge to the battery.
For DC fast charging, while the standard was once 150 kW, we are now witnessing capacities of 350 kW and beyond. These improvements are likely to continue to boost DC fast-charging stations’ capacity. Consequently, EVs will charge faster, which in turn will help ensure that chargers are not the bottleneck for getting more EVs on the road. Moreover, as DC fast chargers allow higher power levels, charging stations can deploy numerous charge points so that multiple vehicles can be charged simultaneously.
In DC fast-charger designs, minimizing charging time while optimizing system efficiency is a major focus, and that makes voltage range and load requirements key design considerations in component selection. In other words, power density and system efficiency are vital for both power components and modules used in DC fast chargers.
Take the case of WolfPACK, Wolfspeed’s power module built around 1,200-V silicon carbide (SiC) MOSFETs. While serving EV fast-charging applications, it aims to maximize power density and efficiency as well as shrink product form factor and reduce design complexity.
SiC devices are the heart and soul of the WolfPACK power module. (Source: Wolfspeed)
Furthermore, while every switch needs a driver and every driver needs to be controlled, microcontrollers play an important role in the temperature and voltage monitoring of EV charging designs. These MCUs work alongside gate drivers and power devices to boost charging efficiency.
Super-fast EV charging
It’s apparent that EV charging stations are now an essential part of the e-mobility infrastructure. While the momentum is clearly on the SiC side, EV charging designers can still use 650-V silicon MOSFETs for the main DC/DC stage rather than the costly 1,200-V SiC devices for many EV charging applications. It’s also important to note that IGBTs, such as IKW75N65EH5XKSA1 from Infineon, are still in play, predominantly due to their cost advantage.
However, 1,200-V SiC MOSFETs like Infineon’s FF8MR12W2M1B11BOMA1 are optimized for EV charging designs. Add the SiC-based Schottky diodes such as IDWD20G120C5XKSA1 to the mix, and you have SiC written all over the EV charging infrastructure design roadmap.
Likewise, Wolfspeed’s SiC MOSFETs and Schottky diodes — for instance, C2M0160120D and E3D20065D, respectively — have been designed and optimized for high-voltage applications like EV charging and DC/DC converters. These power semiconductors accommodate the shift from Tesla’s 400-V Supercharger network to 800-V DC fast-charging implementation in Porsche’s Taycan, Kia EV6, and General Motors’ Hummer EVs. Luxury EV maker Lucid has even gone beyond that level with its 900-V architecture.
That boost in battery voltage has clearly tilted the balance in favor of SiC components. It also shows why the EV charging infrastructure, especially the DC charger technology, is evolving rapidly.
The biggest e-mobility stumbling block, driver anxiety, is intrinsically tied to the EV charging infrastructure. Therefore, design innovations in this area — super-fast EV charging translating into shorter charge time — will inevitably lead to more EV sales and adoption. Components and design building blocks are there anyway.