Electric vehicles face a significant challenge in their development due to the limitations of battery technology. While battery power is expected to increase with technological advancements, the focus will soon shift from energy capacity to cost, reliability, and safety. To address these issues, Rudolf and Zwickau University of Applied Sciences have developed an innovative hybrid energy storage system (HESS) that combines lithium-ion batteries with double-layer capacitors (EDLCs). This system uses a unique topology to integrate low-impedance EDLCs with higher-impedance batteries, enabling efficient power management and improved performance.
The design employs ultra-fast power MOS switches for full digital control, allowing for adaptive matching and optimized energy distribution. This system not only doubles the lifespan of lithium-ion batteries but also enhances reliability and reduces development costs, making it ideal for light electric vehicles (LEVs). The combination of batteries and supercapacitors ensures that the battery operates within its optimal range, minimizing stress and extending its life. Additionally, the system maintains stable temperatures, further improving longevity.
Through practical implementation, researchers confirmed that existing battery systems can effectively work with supercapacitors. The battery handles continuous energy supply, while the supercapacitor manages short-term peak currents and voltages. This collaboration ensures the battery remains within its rated current limits, avoiding overloads and damage. As a result, the system can be charged quickly without harming the battery, and it retains charge even after long periods of inactivity.
Supercapacitors are known for their robustness, long service life, and ability to operate across a wide temperature range. They store energy in a Helmholtz layer, which allows them to deliver large amounts of energy in seconds. With a 10-year lifespan and up to 500,000 charge cycles, they outperform traditional batteries in terms of durability. Their discharge characteristics are also superior, with a higher depth of discharge compared to lithium batteries.
To integrate the best features of both technologies, a hybrid buck/boost converter is used to balance charging and current characteristics. Various topologies exist, including parallel circuits and bidirectional transformers, but many are complex and costly. In response, the R&D team opted for a unidirectional DC-DC converter, simplifying the design and reducing costs.
This approach enables dynamic coupling of the supercapacitor to the inverter, allowing it to handle peak currents efficiently. Voltage ratios are adjusted to optimize energy utilization, ensuring maximum efficiency. The system is designed with a microcontroller that controls power MOSFETs, offering flexible parameter settings and real-time adjustments.
In applications like professional power tools, this system improves battery life and performance. The demonstration device, such as a battery-powered screwdriver, showcases the system’s capabilities, including adjustable current limits and predictable battery health monitoring.
The control algorithm was developed using model-based design, enabling accurate simulation and automated code generation. A high-performance microcontroller manages signals and generates PWM timing for power components, ensuring precise control and efficient operation.
Overall, this hybrid system represents a significant advancement in energy storage for electric vehicles, offering enhanced reliability, extended battery life, and improved performance. It paves the way for more sustainable and efficient electric mobility solutions.
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