Internal Resistance Calculation for Secondary Batteries Without Interruption
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Solution Overview
Problem
Existing methods for calculating internal resistance in secondary batteries, such as those in electric vehicles, fail to account for State Of Charge (SOC) and require temporary interruption of charging or discharging, leading to inaccurate measurements.
Innovation Solution
An internal resistance calculating device that measures both-end voltage values at predetermined thresholds and current values after changes in charge or discharge current, using capacitors to hold voltage values and a differential amplifier to calculate resistance without interrupting the battery's operation, ensuring measurements are taken with constant SOC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the charge or discharge is temporarily interrupted to calculate internal resistance, then the measurement can be performed, but the productivity is reduced due to operation interruption
Solution Approach 1:
The patent applies preliminary action by pre-holding voltage values in first and second voltage holding units (capacitors) at specific SOC points (30% and 70%) before the actual internal resistance calculation is needed. This allows the system to perform measurements without interrupting ongoing charge/discharge operations, as all necessary voltage data is already captured and stored for immediate use in the calculation formula.
2Device complexity
If SOC is not taken into account during internal resistance measurement, then the measurement process is simpler, but the measurement precision deteriorates due to SOC variation
Solution Approach 1:
The patent applies parameter changes by selecting specific SOC (State of Charge) values (30% and 70%) as predetermined parameters for voltage measurement. The internal resistance calculating unit uses these fixed SOC points to ensure consistent and accurate measurements. By changing the measurement approach to focus on specific SOC parameters rather than continuous monitoring, the system achieves high precision without excessive complexity.
3Measurement precision
If high-resolution AD converters are used to reduce noise in voltage measurements, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent introduces voltage holding units (capacitors C1 and C2) as intermediary elements that store voltage values at predetermined SOC points. These intermediaries hold the voltage information stable, allowing subsequent calculation without requiring high-resolution AD converters during the actual measurement process. The capacitors act as buffers that maintain voltage data, reducing the noise sensitivity and resolution requirements of the conversion process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate internal resistance calculations without interrupting charging or discharging, reduces noise requirements, and eliminates the need for high-resolution AD converters, providing precise measurements by maintaining constant SOC during calculations.
Implementation Method 1
each of the first voltage holding unit and the second voltage holding unit is constituted of a capacitor
Implementation Method 2
each of the first voltage holding unit and the second voltage holding unit is constituted of a capacitor
Implementation Method 3
a differential amplifier configured to calculate a difference between the first voltage value held in the first voltage holding unit and the second voltage value held in the second voltage holding unit
Data Source
AI summary
An internal resistance calculating device includes a charging unit charging a secondary battery, a voltage measuring unit measuring a both-end voltage value of the secondary battery, a capacitor holding a first voltage value predetermined by the both-end voltage value measured by the voltage measuring unit after charging is started, a capacitor holding, as a second voltage value, the both-end voltage value when charge current is changed for a predetermined current value or more within predetermined time after the both-end voltage value become the first voltage value, a current measuring unit measuring a first charge current value when the both-end voltage value become a threshold-value voltage and a second charge current value when the both-end voltage value become the second voltage value, and a μCOM calculating an internal resistance value of the secondary battery based on the first and second voltage values and the first and second charge current values.