Page 6 - PEN eBook May 2022

COVER STORY – DESIGN Cover Story – Design

In the quest for more power-dense and more efficient OBCs, designers are looking to advanced
technology to make the next step in innovation by moving from current silicon-based solutions
to power-semiconductor technologies that use wide-bandgap (WBG) materials, such as silicon

carbide (SiC) and gallium nitride (GaN). Compared with traditional topologies based on silicon
devices, once the improved figures of merit (FoMs) of WBG devices are well-understood, innovative
ideas could help designers develop new topologies at higher switching frequencies with modulation
schemes that were not possible or were too complex to be implemented before. In addition, an
effective thermal design (i.e., innovative packaging that includes new cooling concepts) opens up
the horizon for upcoming OBC designs in terms of power density and efficiency.

This article identifies trends in OBC designs, compares the FoMs among semiconductor technologies,
and introduces new surface-mount device (SMD) packaging. The comprehensive solutions bring

innovation in different topologies, offer more efficiency and power density, and enable bidirectionality
that integrates EVs into the smart grid.

Wide-Bandgap OBC TRENDS

The role of an OBC is to convert AC power from the power grid into a DC voltage that can be used
Transistors in to charge the traction battery. Because the OBC can perform this function only while the vehicle
is stopped and the DC/DC only while the vehicle is moving, this concept adds extra weight that

On-Board Chargers for must be carried around but also be cooled. Thus, the size and weight of the OBC plus the DC/DC
must be minimized to reduce its effect on the driving range as well as the volume occupied in the
e-Powertrain compartment while still allowing for rapid and efficient charging.
Electric Vehicles Similarly, under the influence of future power-grid regulations, which are moving toward smart

grids, and the possibility of having an emergency power supply for blackouts or natural disasters,
Important aspects and solutions OBCs are also impacted by the fact that they need to allow a bidirectional power flow.

for more power-dense and efficient These aspects are closely linked and interrelated when identifying the five key challenges for OBC

on-board charger designs designers:

By Rafael A. Garcia Mora, system application engineer for OBC applications at 1. Power classes are continuously increasing to accelerate the charging times. Current plug-in
Infineon Technologies hybrid vehicles and BEVs have OBCs in the range of a 3.6- to 7.2-kW power class. Current OBC
designs at original design manufacturers for the next generation of EVs in the next three to five
years are moving up to the range of a 7.2- to 11-kW power class. In the case of luxury cars or
Development and innovation in the automotive industry continue at a rapid pace in almost all high-profile cars with 800-V batteries, OBCs can be designed for up to 22 kW.

aspects of vehicle design, including the chassis, the powertrain, infotainment, connectivity, and
driving-assistance systems. A topic that challenges the fast and wide adoption of battery electric 2. The increase in power density is significant, as it implies a reduction in size and weight,
vehicles (BEVs), due to increased driver concerns and stress, is the time taken to recharge these contributing to an extended EV driving range. Enhancing efficiency not only reduces the heat
vehicles — especially on long highway journeys. The design of the on-board charger (OBC) is an buildup within the OBC (which reduces size and increases power density due to reduced thermal
area that is coming under more scrutiny than most. management), but it also allows more energy from a finite grid source to be delivered to charge

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