Battery Pack Charging Control Using OCV-PID Voltage Compensation
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Solution Overview
Problem
Existing fast charging methods for battery packs fail to consider cell degeneration, leading to excessive cell voltage and accelerated degradation due to unpredictable voltage changes, which conventional current reduction methods cannot effectively mitigate.
Innovation Solution
A battery management system (BMS) derives a compensation charging rate through PID control based on error voltage between cell voltages and open circuit voltage (OCV), using a proportional, integral, and differential value to prevent cell voltage from exceeding the upper limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If battery packs are connected in series to increase output voltage, then power output is improved, but the risk of thermal runaway increases due to higher voltage
Solution Approach 1:
The battery pack is divided into multiple individual battery cells, each with its own voltage and state of charge. Instead of treating the pack as a single unit, the control system segments the pack into manageable cells that can be monitored and controlled independently, allowing high voltage operation while maintaining safety through individual cell management
Solution Approach 2:
The control system continuously monitors the state of charge and voltage of each individual battery cell and uses this feedback information to dynamically adjust the charging current. This feedback mechanism prevents any single cell from being overcharged, thereby reducing thermal runaway risk while maintaining high power output capability
2Productivity
If fast charging is performed to reduce charging time, then productivity is improved, but temperature increases causing safety issues
Solution Approach 1:
The charging current is made dynamic rather than constant. The control system continuously adjusts the charging current based on real-time temperature measurements and state of charge levels. When temperature rises during fast charging, the system automatically reduces the current to prevent overheating, enabling safe fast charging operation
Solution Approach 2:
The charging process uses periodic pulse charging rather than continuous constant current charging. This allows brief intervals for heat dissipation while maintaining high average charging power, effectively managing temperature during fast charging operations
3Loss of time
If individual battery cell voltages are not equalized during charging, then charging time is reduced, but reliability decreases due to overcharge risk
Solution Approach 1:
The control system applies different charging currents to different battery cells based on their individual state of charge levels. Instead of using a single uniform charging current for all cells, each cell receives customized current tailored to its specific voltage level, preventing overcharge while minimizing total charging time
Solution Approach 2:
The system charges battery cells at different rates simultaneously - cells with lower voltage receive higher current while cells near full charge receive reduced current. This partial action approach ensures all cells are charged appropriately without waiting for the slowest cell, reducing overall charging time while maintaining reliability
Data Source
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AI summary
A battery system may include: a battery pack including a plurality of battery cells; and a battery management system configured to derive a charging rate based on a charging target SOC (State of Charge) for the battery pack and the temperature of the battery pack, and compensate for the charging rate through PID control based on an error voltage between any one of the plurality of cell voltages and an open circuit voltage (OCV) corresponding to the charging target SOC to generate a compensation charging rate.