The field of battery management systems (BMS) has seen significant patent activity, particularly in the areas of state-of-charge (SOC) estimation algorithms, cell balancing circuits, and safety monitoring. These electronic control methods are critical for optimizing battery performance, extending lifespan, and ensuring operational safety. This review systematically examines key patents in these domains, focusing on the underlying methodologies rather than hardware implementations.
State-of-charge estimation is a fundamental BMS function, with Kalman filters and Coulomb counting being the most widely patented techniques. Kalman filter-based SOC estimation has evolved from basic linear models to advanced nonlinear variants. Early patents focused on linear Kalman filters applied to lead-acid batteries, where the algorithm estimated SOC by modeling voltage-current relationships. Later innovations introduced extended Kalman filters (EKF) to handle the nonlinear behavior of lithium-ion batteries. These patents typically describe the use of battery equivalent circuit models with parameters that are continuously updated based on real-time measurements. Unscented Kalman filters (UKF) and particle filters subsequently emerged in patents to address the limitations of EKF in highly nonlinear operating conditions. These advanced filtering techniques demonstrate improved accuracy, particularly under dynamic load profiles and wide temperature ranges.
Coulomb counting remains a widely patented SOC estimation method due to its simplicity. Modern patents have focused on addressing its inherent drift problem through hybrid approaches. Several patents combine Coulomb counting with voltage-based correction algorithms, where the accumulated charge is periodically recalibrated using open-circuit voltage measurements. Others integrate temperature compensation factors to improve accuracy across different operating conditions. A notable trend in recent patents is the fusion of Coulomb counting with model-based approaches, creating redundant estimation systems that cross-validate SOC calculations.
Cell balancing circuits have generated substantial patent activity, with methods broadly categorized into passive and active balancing. Passive balancing patents typically describe resistor-based discharge systems where excess energy from higher-voltage cells is dissipated as heat. These designs often incorporate switching networks controlled by voltage threshold algorithms. More sophisticated patents introduce adaptive thresholding that adjusts balancing parameters based on battery age and temperature.
Active balancing patents present more complex energy transfer mechanisms between cells. Inductor-based balancing circuits appear frequently, with patents detailing various switching topologies for bidirectional energy transfer. Transformer-based systems are also well-represented, particularly for high-voltage battery packs where isolation is required. Recent patents show a shift towards capacitor-based charge shuttling techniques that offer higher efficiency. Many active balancing patents incorporate SOC information from estimation algorithms to enable capacity-based balancing rather than simple voltage matching.
Safety monitoring represents another heavily patented BMS function, with innovations focusing on early fault detection and prevention. Overvoltage protection algorithms are commonly patented, with many employing multi-stage response strategies. Initial stages may involve gradual current reduction, while severe overvoltage triggers immediate disconnection. Similarly, undervoltage protection patents describe state-dependent threshold adjustments to prevent damage from deep discharge.
Thermal runaway prevention has generated numerous patents, particularly for lithium-ion systems. Many describe hierarchical temperature monitoring approaches using multiple sensor inputs and predictive algorithms. Some patents employ thermal models to estimate internal cell temperatures based on surface measurements, while others use impedance-based techniques to detect early warning signs of thermal instability.
Short-circuit detection patents reveal two main approaches: current-based and impedance-based methods. Current-based patents typically describe fast-response algorithms that analyze current slew rates and absolute magnitudes. Impedance-based approaches focus on detecting anomalous changes in cell resistance, often using AC injection techniques. Advanced patents combine both methods with statistical analysis to reduce false positives.
Aging detection and state-of-health (SOH) estimation have seen growing patent activity. Many patents track capacity fade by comparing actual and theoretical charge throughput over cycles. Others monitor resistance growth through periodic impedance measurements. Some innovative approaches analyze the divergence between model-predicted and measured voltage responses to quantify degradation.
Communication protocols for BMS implementations are also well-represented in patents. CAN bus remains the dominant interface, with many patents describing optimized message scheduling algorithms to handle real-time BMS data. Wireless BMS patents have emerged more recently, focusing on robust transmission schemes for critical safety data.
The patent landscape shows clear trends toward increasing algorithm complexity and integration. Early patents tended to focus on single-function implementations, while recent filings describe comprehensive systems where SOC estimation, cell balancing, and safety monitoring are tightly coupled. There is also a noticeable shift from purely deterministic algorithms to hybrid approaches incorporating machine learning elements.
Region-specific patterns emerge in patent analysis, with Asian filings dominating in advanced SOC estimation techniques, while North American patents show stronger representation in safety monitoring systems. European patents are particularly active in cell balancing innovations, especially for automotive applications.
The evolution of BMS patents reflects the growing demands of diverse battery applications. Electric vehicle requirements have driven innovations in high-speed SOC estimation and dynamic balancing algorithms. Grid storage applications have influenced the development of long-term degradation monitoring techniques. Consumer electronics needs have spurred ultra-compact BMS solutions with minimal computational overhead.
Future patent directions are likely to focus on quantum-resistant encryption for BMS communications, federated learning approaches for SOC estimation, and physics-informed neural networks for safety prediction. The increasing importance of battery recycling may also drive patents for SOH estimation methods that support second-life applications.
This analysis demonstrates that BMS patent activity remains robust, with continuous improvements in accuracy, reliability, and functionality. The convergence of control theory, electrochemistry, and data science in recent patents suggests that BMS algorithms will continue to evolve in sophistication, enabling safer and more efficient battery systems across all applications.