Battery Current Limit Calculation via Resistance Decomposition
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Solution Overview
Problem
Existing methods for calculating maximum charging/discharging currents for batteries, particularly in vehicle power supply devices, face challenges due to errors in remaining capacity detection and hysteresis variation, leading to potential battery overload and reduced lifespan.
Innovation Solution
A method that calculates resistance values based on average current and voltage, divides them into physical and chemical components, corrects these components using temperature and historical data, and estimates open-circuit voltages to predict maximum current values, creating a current-voltage curve for accurate current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the battery is discharged at a large amount of current when the remaining capacity is low, then the voltage of the batteries abruptly falls under hard acceleration, but remarkable battery property reduction occurs
Solution Approach 1:
The patent implements dynamic current limiting by continuously monitoring battery state (SOC, temperature) and adjusting the maximum allowable charging/discharging current in real-time. The control device dynamically determines current limits based on detected battery parameters, allowing high current when conditions permit and restricting current when conditions deteriorate, thus resolving the contradiction between power output and battery protection.
2Power
If the battery is charged at a large amount of current when the remaining capacity is high, then the voltage of the batteries abruptly increase under hard braking, but remarkable battery property reduction occurs
Solution Approach 1:
The control device dynamically adjusts charging current limits based on real-time battery state detection. When SOC is high and temperature conditions permit, higher charging currents are allowed during regenerative braking. When SOC approaches full charge or temperature exceeds thresholds, the system automatically reduces current limits, preventing voltage abrupt increases and battery property degradation while maximizing energy recovery.
3Device complexity
If a table-referencing method is used to calculate current limit values, then the calculation is simple, but it cannot respond to the hysteresis variation of batteries causing errors
Solution Approach 1:
The patent implements a feedback-based current limit calculation system that continuously detects battery state (SOC, temperature, voltage) and adjusts current limits accordingly. The control device uses detected battery parameters to dynamically determine appropriate current limits, creating a closed-loop system that responds to hysteresis variations and other battery state changes, thereby improving accuracy over static table-referencing methods.
4Measurement precision
If a model-using method is used to calculate current limit values, then the calculation considers battery state, but the remaining capacity detection is significantly affected by error of resistance caused by synchronization time lag
Solution Approach 1:
The patent applies preliminary correction actions to compensate for synchronization time lag effects. The control device detects battery parameters and applies correction values based on predetermined correction tables or models that account for the time lag between voltage and current detection. This preliminary correction prevents synchronization errors from affecting SOC calculation accuracy, allowing model-based current limit determination to proceed with high precision.
Data Source
AI summary
A method includes steps of dividing resistance R into a physical and chemical resistances Ro and Rp, obtaining corrected open-circuit voltages Vo corresponding to setting currents Ia to Ix, acquiring predicted reaching voltages Va to Vx corresponding to the setting currents Ia to Ix, and creating a current-voltage curve. The corrected open-circuit voltages Vo are obtained to predict available maximum currents I—target in a particular time t2. The predicted reaching voltages Va to Vx are acquired based on corrected physical and chemical resistances Ro and Rp, and the corrected open-circuit voltages Vo. The current-voltage curve is creased based on the setting currents Ia to Ix and the predicted reaching voltages Va to Vx to acquire upper and lower limit voltages Vmax and Vmin, and upper and lower limit currents Imax and Imin at a temperature whereby assigning these limit currents to available maximum currents I—target in charging and discharging operations, respectively.