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Taking a Hybrid Energy Storage Approach for High-Power Automotive Features

Taking a Hybrid Energy Storage Approach for High-Power Automotive Features

| Stefan Werkstetter, Systems Applications Engineering Manager

Today's modern vehicle energy distribution networks have high requirements with regards to both voltage stability and power availability. Even though 48V systems are emerging slowly, the industry’s main focus is still on 12V applications. The ongoing electrification and addition of new features drives both common energy storages and system architectures to their limits. In the last few years, many different architectures were developed to address the typical problems of the increasing number of high-power loads. New features like electric active roll control, electric power steering or electric turbo chargers have very demanding power requirements and can be characterized by frequent, very short high-power discharge events.

One approach for dealing with these power requirements is to isolate the high-power consumer from the vehicle's main energy distribution network. This so-called island architecture ensures that the electrical stress is only present in the isolated sub-network and does not spread over the whole vehicle. Due to their increased cost and complexity, these architectures are typically seen in premium car platforms.

A common approach for small- to medium-sized car platforms is to optimize the vehicle's energy storage to meet power and energy requirements of new features.

A common approach for small- to medium-sized car platforms is to optimize the vehicle's energy storage to meet power and energy requirements of new features. Traditionally, lead-acid batteries are the first choice due to low cost, relatively high reliability and simple monitoring. If lead-acid batteries are exposed to rapid cycling applications like the ones mentioned above, they are subject to accelerated aging, so this technology is not the ideal solution for these demanding high-power applications.

To counter this effect, lead-acid batteries need to be oversized, which increases weight and volume demand—both not desired by automotive car makers. In the past few years, lithium-ion batteries have become more common in the automotive industry, having significantly increased power and energy density, compared to lead acid batteries. However, lithium-ion batteries still suffer poor low temperature performance, are more expensive and need more complex monitoring and control systems to avoid damage.

Maxwell's solution for small- to medium-sized car platforms is a hybrid energy storage based on a lead-acid battery and an ultracapacitor in parallel. This combines the high energy density of the lead-acid battery with the high power density of the ultracapacitor. Each device can focus on its own sweet spot—the battery provides the required energy with little fluctuation and the ultracapacitor takes care of high-power discharge and transient events.

The hybrid approach also opens the possibility to downsize the lead-acid battery, which can result in weight savings of up to 40 percent. Such a hybrid energy storage shows very good power and energy performance from -40°C to +65°C. Unlike batteries, ultracapacitors are designed to survive the whole vehicle life without need for maintenance or replacement. This results in a lower total cost of ownership of such a high performance hybrid energy storage, compared to lead-acid or lithium-ion batteries with equivalent power and energy density.

Hybrid energy storage designs are becoming more and more common in other market segments such as grid and industrial applications, which confirms the effectiveness of this approach.

READ NEXT - From Start-Stop to Autonomous Driving: Ultracapacitors Enabling Next-Generation Automotive Features (VIDEO)

Mike EverettStefan Werkstetter
Systems Applications Engineering Manager
About this author

Stefan Werkstetter is systems applications engineering manager at Maxwell Technologies and is a state-certified electrical engineer with a focus on computer science. He has several years of experience in electrical systems pre-development, evaluation and testing. Prior to joining Maxwell, he worked in the automotive industry for a German original equipment manufacturer and as a technician in telecommunication electronics. On his free time, he enjoys hiking, camping, gardening and spending time with his wife and two sons.

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