Double-Layer Ring Equalizer Boosts EV Battery Efficiency
In the fast-evolving world of electric mobility, battery management systems (BMS) continue to play a pivotal role in defining the performance, safety, and longevity of electric vehicles (EVs). As demand for longer driving ranges and faster charging grows, so does the need for smarter, more efficient battery technologies. Among the most critical challenges in lithium-ion battery packs is the issue of cell imbalance, which can lead to reduced capacity, shortened lifespan, and even safety hazards. A recent breakthrough from researchers at Yancheng Institute of Technology offers a promising solution: a double-layer ring equalizer that significantly enhances both the speed and efficiency of battery balancing.
The research, led by Han Xinsheng, a master’s student, along with Professor Kan Jiarong, Ling Huiying, Wang Peng, and Cheng Qian, introduces a novel hybrid topology that combines the strengths of Buck-Boost converters and switched-capacitor circuits in a dual-tiered architecture. Published in Electronic Science and Technology, this innovation marks a substantial leap forward in active battery equalization technology. The study not only presents a new circuit design but also introduces a graph-theoretic analytical framework to evaluate its performance—setting a new standard for how future BMS architectures might be assessed.
Lithium-ion batteries have become the cornerstone of modern electric transportation due to their high energy density, long cycle life, and stable charge retention. However, when individual cells are connected in series to form a battery pack, inherent variations in capacity, aging characteristics, and thermal distribution can cause voltage imbalances during charging and discharging cycles. Without proper management, these discrepancies can escalate into overcharging or deep discharging of certain cells, leading to accelerated degradation and potential safety risks such as thermal runaway.
Traditional passive balancing methods dissipate excess energy through resistors, a simple but inefficient approach that wastes power as heat. In contrast, active balancing techniques transfer energy from higher-charged cells to lower-charged ones, preserving overall energy and improving system efficiency. Among active topologies, the Buck-Boost converter has gained popularity for its ability to step up or step down voltage and enable bidirectional energy flow. However, conventional Buck-Boost-based equalizers suffer from long energy transfer paths when applied to large battery strings, resulting in reduced efficiency and slower balancing speeds—especially as the number of cells increases.
To address these limitations, the team at Yancheng Institute of Technology proposed a modular, hierarchical solution: the double-layer ring equalizer. This architecture divides the battery pack into smaller modules—each containing four cells—and implements two levels of balancing: intra-module (within each group) and inter-module (between groups). At the lower level, adjacent cells within a module are balanced using Buck-Boost circuits, while the first and last cells in each module use switched-capacitor circuits to close the loop, forming a “bottom ring.” At the upper level, adjacent modules are connected via Buck-Boost links, with the first and last modules linked by a switched-capacitor connection, creating a “top ring.” This dual-ring structure enables energy to flow both locally and globally, minimizing transfer distance and maximizing efficiency.
What sets this design apart is not just its physical layout but the rigorous analytical method used to validate it. The researchers employed graph theory—a mathematical framework typically used in network analysis—to model the energy transfer paths within the system. In this model, battery cells are represented as nodes, energy flows as directed edges, and balancing components (inductors and capacitors) as auxiliary points. By assigning weights based on efficiency and path length, the team was able to compute expected performance metrics such as average balancing speed and overall system efficiency.
This approach provides a systematic way to compare different topologies, moving beyond empirical testing to predictive modeling. It allows engineers to anticipate how changes in circuit design will affect real-world performance, enabling faster optimization and more informed decision-making in BMS development.
One of the key advantages of the double-layer architecture is its ability to shorten energy transfer paths. In traditional single-layer ring equalizers, moving energy from one end of a 12-cell string to the other may require passing through multiple intermediate stages, each introducing losses. In contrast, the dual-ring structure allows for more direct routes. For instance, if two cells in the same module are imbalanced, correction occurs quickly within the local ring. If cells in different modules are involved, the top ring facilitates inter-module transfer without requiring long cascaded paths.
Simulation results conducted on MATLAB/Simulink demonstrated that the double-layer system achieved full voltage balance across 12 cells in just 0.39 seconds—46% faster than a comparable single-layer system, which took 0.72 seconds under identical conditions. This improvement in speed is crucial for real-time applications where rapid response to imbalance is essential, such as during fast charging or regenerative braking.
Equally important is the gain in efficiency. Experimental testing on a four-cell prototype revealed that the double-layer equalizer achieved a system-level efficiency of 67.32%, compared to 40.54% for the single-layer counterpart—a remarkable 27.78% increase. This means less energy is lost as heat during balancing, translating to better thermal management, reduced stress on components, and ultimately, longer battery life.
The efficiency gains stem from several factors. First, the use of switched-capacitor circuits for end-to-end balancing reduces reliance on inductive elements, which are prone to conduction and switching losses. Capacitive transfer, while limited in power handling, is highly efficient for small-to-moderate energy shifts—exactly the kind needed for fine-tuning cell voltages. Second, the modular design limits the number of conversion stages any given unit of energy must pass through. Third, the hybrid topology leverages zero-voltage switching (ZVS) in the Buck-Boost circuits, further reducing switching losses and improving overall conversion efficiency.
Another benefit of the proposed system is its scalability. While the study focused on a 12-cell configuration divided into three four-cell modules, the concept can be extended to larger packs with more modules. The hierarchical nature of the design ensures that as the battery string grows, the relative complexity and efficiency degradation remain manageable. This makes it particularly suitable for EVs, where battery packs often consist of hundreds of cells arranged in series-parallel configurations.
From a control perspective, the double-layer ring equalizer offers flexibility. Each module can be monitored and managed independently, allowing for localized balancing decisions while still maintaining global coordination. This distributed intelligence aligns well with modern BMS trends that emphasize modularity, fault tolerance, and adaptive control strategies. Moreover, the symmetry of the ring structure simplifies control algorithms, as the same logic can be applied to each segment of the network.
The implications of this research extend beyond electric cars. The same principles could be applied to energy storage systems for renewable integration, uninterruptible power supplies, and aerospace applications—any domain where reliable, high-performance battery operation is critical. As the world transitions toward electrification, the ability to manage large battery arrays efficiently and safely becomes increasingly vital.
While the current prototype demonstrates clear advantages, there are still areas for refinement. For example, the use of discrete inductors and capacitors adds to the size and cost of the system. Future work could explore integrated magnetics or planar components to reduce footprint. Additionally, dynamic load balancing and adaptive duty cycle control could further optimize performance under varying operating conditions.
The team also acknowledges that real-world deployment will require robust fault detection and isolation mechanisms. In a ring topology, a single point of failure—such as a shorted switch or open inductor—could potentially disrupt the entire balancing network. Implementing redundancy or bypass paths would enhance reliability, especially in safety-critical applications like automotive systems.
Nonetheless, the foundational work presented here lays a strong groundwork for next-generation battery balancing solutions. By combining proven power electronics with advanced network analysis, the researchers have opened a new pathway for innovation in BMS design. Their work exemplifies how interdisciplinary thinking—merging electrical engineering, control theory, and applied mathematics—can yield practical, high-impact technologies.
The significance of this advancement lies not only in its technical merits but also in its potential to influence industry standards. As automakers and battery manufacturers seek to improve pack efficiency and reduce warranty claims related to battery degradation, solutions like the double-layer ring equalizer could become integral to future BMS architectures. With global EV sales projected to reach tens of millions annually in the coming decade, even small improvements in battery management can translate into massive energy savings and reduced environmental impact.
Moreover, enhanced balancing efficiency contributes to better state-of-charge estimation, a key function in BMS software. When cells are kept in closer voltage alignment, the accuracy of algorithms that predict remaining range improves, enhancing driver confidence and user experience. This synergy between hardware and software underscores the holistic nature of modern EV development.
The research also highlights the growing importance of academic contributions in driving technological progress. Institutions like Yancheng Institute of Technology are playing an increasingly vital role in advancing core technologies that support the green energy transition. Supported by funding from the National Natural Science Foundation of China and the Postgraduate Practice and Innovation Plan of Jiangsu, this project reflects a broader trend of government-backed research aimed at strengthening domestic innovation capacity in strategic sectors.
Looking ahead, the team plans to explore digital twin implementations of the equalizer, integrating real-time simulation with physical hardware for predictive maintenance and performance optimization. They are also investigating the use of wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) to further boost switching efficiency and reduce losses at higher frequencies.
In conclusion, the double-layer ring equalizer represents a significant step forward in active battery balancing technology. Its hybrid topology, modular design, and graph-based analysis offer a compelling combination of speed, efficiency, and scalability. By addressing the fundamental limitations of existing systems, it paves the way for smarter, more resilient battery management in electric vehicles and beyond.
As the automotive industry races toward a fully electrified future, innovations like this remind us that the journey is not just about bigger batteries or faster chargers—it’s also about how intelligently we manage the energy we already have. The work of Han Xinsheng, Kan Jiarong, Ling Huiying, Wang Peng, and Cheng Qian at Yancheng Institute of Technology stands as a testament to the power of engineering ingenuity in solving real-world challenges. Their contribution, published in Electronic Science and Technology, is likely to influence the next generation of battery systems, bringing us one step closer to sustainable, high-performance electric mobility.
Han Xinsheng, Kan Jiarong, Ling Huiying, Wang Peng, Cheng Qian, Yancheng Institute of Technology, Electronic Science and Technology, doi:10.16180/j.cnki.issn1007-7820.2024.04.003