Innovative Bilevel Equalizer for Enhancing Lithium-Ion Battery Performance

1. Innovative Bilevel Equalizer for Enhancing Lithium- Ion Battery Performance The rapid expansion of electric-powered vehicles, such as drones (UAVs), electric cars, scooters, and buses, shows no signs of slowing down. These vehicles rely heavily on lithium-ion batteries (LIBs), which require electronic equalizer circuits (EQUs) to balance cell voltages. However, existing equalizer solutions often present challenges in terms of cost and performance. To address these issues, SEMCO has introduced a new hybrid equalizer technology known as the Bilevel Equalizer (BEQ). In addition to consumer vehicles, electric-powered aerospace and military systems like drones also predominantly use lithium-ion batteries. These large battery packs, consisting of potentially hundreds of cells, require EQUs to balance voltages. Unfortunately, current EQUs are limited by cost and performance inefficiencies. Recent studies have highlighted SEMCO’s Bilevel Equalizer as a promising hybrid solution to overcome these challenges. This innovative design offers valuable insights into optimizing both the active and passive components of the equalization system. Most large LIBs today use passive equalizers (PEQs), which utilize transistors and resistors to balance cell voltages by discharging higher-voltage cells. While cost-effective and simple, PEQs generate heat, waste energy, and are ineffective during discharge. As a result, the overall battery capacity can be compromised by just one or two weak cells as the battery ages.

2. PEQs also face limitations in managing larger voltage imbalances due to their restricted equalization currents, typically below 200-300 mA. Although active equalizers (AEQs) can transfer charge between cells and avoid some of the issues of PEQs, they are rarely used due to higher costs and increased complexity. AEQs capable of handling larger current imbalances can become prohibitively expensive for large-scale applications.

3. Battery management system (BMS) designers often avoid using AEQs, preferring the simplicity and affordability of PEQs, despite their limitations. Once a company implements a BMS with a PEQ, inertia and long-term cost considerations can hinder the transition to more efficient systems like AEQs. Introducing the Bilevel Equalizer To bridge the gap between performance and cost, SEMCO has developed the Bilevel Equalizer (BEQ), a hybrid design that delivers near-AEQ performance with a moderate cost increase over PEQs. The BEQ balances voltages at two levels—both across sections of connected cells and within individual cells in each section. This structure is especially useful for large applications like aerospace, where the BEQ can be integrated into existing PEQ systems with minimal hardware modifications.

4. In the BEQ system, multiple AEQ units transfer charge between sections of connected cells, while PEQs handle equalization within those sections. For instance, a battery with 196 cells can be divided into 14 sections of 14 cells each. The BEQ approach requires only 13 AEQ units to balance the system, compared to the 196 AEQ units needed for cell-level balancing. This significantly reduces cost without sacrificing performance. Another cost advantage is the BEQ’s simplicity. Unlike traditional AEQs, the BEQ system does not require transformers, which are both costly and cumbersome. As a result, the BEQ can provide equalization currents in the range of 5 A or more, offering an economical solution for large battery packs. Conclusion While passive equalizers (PEQs) remain the most common due to their low cost, they are limited by energy losses and performance inefficiencies during battery discharge. Active equalizers (AEQs), though highly efficient, are rarely adopted due to their complexity and expense. SEMCO’s hybrid Bilevel Equalizer (BEQ) offers a middle ground, delivering enhanced performance at a lower cost. Its unique design makes it a cost-effective solution for large imbalances, providing a viable alternative to both PEQs and AEQs in high-demand applications.