Global electric vehicle (EV) sales have rapidly increased in recent years, with the exponential growth curve taking shape. Decarbonization regulations and product development are pushing EVs forward, though still with two familiar hurdles not yet fully cleared—cost and range. Fortunately, the two tie together through efficiency; the more efficient the power conversion becomes, the more cost design teams can get out of vehicles and the further it can drive in a single charge.
Mass is one of the most direct influencers of electrical efficiency, as power spent dragging mass around is a loss that reduces the driving range. As a result, the state of new product development points engineers’ focus toward defining creative ways to reduce mass.
This article will outline how the development of 48V battery systems can reduce mass to improve electrical efficiency in EVs. In addition, it will describe how new components like ERUC23 coupled inductors deliver 75% volume reduction over single inductor counterparts and enhance efficiency to extend vehicle range,
The Move to 48V Automotive Systems
One trend in power conversion for automotive applications is the transition from 12V systems to 48V. This shift allows vehicle systems to deliver more consistent power with higher efficiency at higher loads, extending the time between battery charges. Additionally, 48V batteries are more energy-dense, delivering these advantages in a smaller space. The higher voltage also enables a lower current draw, improving efficiency while reducing wiring material content and complexity. These benefits have substantial advantages in the context of EVs, as each component’s efficiency correlates directly with the vehicle’s range and overall performance.
12V Systems Still Have a Place
Despite the clear efficiency benefits of 48V systems, existing 12V applications still require support. The lower-voltage legacy batteries enable rapid response to system changes, and most vehicle electronics still run on a 12V battery power source.
However, removing a heavy 12V battery from the system could improve vehicle range through decreased mass. One approach to making the 12V battery redundant is to use a hybrid DC/DC converter.
Power Conversion Basics
Power conversion in EV engines is a significant reason they are a more sustainable option than internal combustion engine (ICE) vehicles. While an ICE converts chemical energy (gasoline) to thermal and then to electrical, EVs skip the thermal conversion step and move directly from chemical (in the battery) to electrical. With approximately 30 percent of thermal efficiency lost to power conversion, removing this step increases electrical efficiency substantially.
Converting power between 48V and 12V systems also helps when optimizing system efficiency. Balancing power between existing voltage sources relies less on external sources like a secondary battery for energy storage or V2G, and it can boost system efficiency if engineers manage conversion losses. Attaining this balance involves various power conversion technologies that present their challenges.
Power Conversion Topologies
There are four primary power conversion topologies for in-vehicle systems with a hybrid design:
- Buck (high → low voltage step-down)
- Boost (low → high voltage step-up)
- Buck-boost (step up or down depending on duty cycle)
- Hybrid converter topology (steps 48V down to 12V)
What Is a Hybrid DC/DC Converter?
Hybrid DC/DC converters enable a 48V battery to act as the primary power source while stepping the voltage down to power the 12V components—without needing a 12V battery. This approach delivers efficiency gains by using a single power source and removing a high-mass, large-footprint component.
Hybrid Conversion Challenges
However, some challenges exist with the hybrid converter. While there are fewer components, the system has added circuitry complexity, partially counteracting cost improvements from removing a 12V battery. In addition, this voltage conversion introduces the risk of periodic DC voltage variation, known as ripple, which is an efficiency penalty. To realize the advantages of hybrid DC/DC converters, engineers must solve these design challenges in the small design envelope in an EV. Tight design spaces drive system components’ need for integration and combined functionality as there is not much space for external connections.
Addressing Hybrid Conversion Challenges with TDK ERUC23 SMT Flat Wire Coupled Inductor
TDK’s ERUC23 SMT Flat Wire Coupled Inductors offer a substantial design improvement to address hybrid conversion challenges directly (Figure 1). Expanding upon TDK’s flat wire ERU inductors, the ERUC23 integrates two windings into one component with the benefit of inductive coupling. This innovative construction incorporates low-loss ferrite core material, optimized coupled coil construction, flat wire winding, and self-leaded design. These features ensure high saturation current, improved efficiency due to reduced ripple current, low DC resistance, and compatibility with RoHS and AEC-Q200 standards, making them ideal for compact coupled inductors in various applications such as dual-phase Buck, Boost, and Buck-Boost converters, including the 48V to 12V hybrid converter.
ERUC23 Comparison to Single Inductors
Traditional inductors suffer efficiency loss during power conversion. The ERUC23 reduces the packaging space of its single inductor counterpart from nearly 24,000 mm3 to about 5,300 mm3, a reduction of just under 78%. Dimensions and product details are shown in Figure 2 below:
In addition, the ERUC23 reduces core loss, improving performance while enhancing power density. It also nearly doubles current output from 33A to 60A when used with an i7A series converter.
Another advantage the ERU23C enjoys over single inductors is ripple current reduction caused by DC voltage variation. Figure 3 below shows the coupled-to-non-coupled ripple current reduction ratio vs. the coupling factor. Lower reduction ratios signify a more uniform current. The coupling factor compares mutual inductance to leakage inductance (higher coupling factors provide less ripple).
Ripple is reduced when moving lower and to the right on this graph. The 50% duty cycle shows the best ripple current reduction. The ERUC23 exhibits a coupling factor just below 3, illustrating high ripple reduction performance.
ERUC23 for Hybrid DC/DC
The ERUC23 is ideal for hybrid DC/DC in EVs, as it reduces ripple and core loss in a smaller packaging envelope, thereby boosting electrical efficiency through reduced line loss. Its topology flexibility and applicability for dual-phase buck, boost, buck-boost, and hybrid DC-DC conversion applications minimizes voltage variation and eliminates heat loss-driven material fatigue, extending component lifetimes.
Conclusion
TDK’s ERUC23 SMT Flat Wire Coupled Inductors mark a significant advancement in automotive power conversion. These inductors meet the challenges of hybrid DC/DC converters head-on by addressing the critical issues of space, mass, and efficiency. The ERUC23 can help deliver more efficient, reliable, and performance-oriented electric vehicles. Adopting such innovative components is a significant step in overcoming modern EVs’ engineering, design, efficiency, and cost challenges, propelling them to an even higher share of the global automotive market.
