Battery Pack Degradation Detection via Segmented Resistance Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing battery pack technologies fail to accurately detect the degradation level of lithium ion secondary batteries, particularly when the polarization resistance component increases, and require expensive high-speed A/D converters for measurement, which are not feasible in all applications.
Innovation Solution
A battery pack design that includes a control unit to measure closed circuit voltage and charging current, followed by open circuit voltages at different waiting times, calculating DC and polarization resistance components to accurately determine the degradation degree by subtracting the initial internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If DC resistance measurement method is used to detect battery degradation, then the measurement process is simple, but the degradation detection accuracy deteriorates when polarization resistance component increases
Solution Approach 1:
The patent segments the internal resistance measurement into two distinct components: DC resistance (measured immediately after current interruption) and polarization resistance (measured after a waiting period). By separating these measurements in time, the system can accurately detect both types of degradation without requiring complex simultaneous measurement equipment.
Solution Approach 2:
The patent applies preliminary action by measuring the DC resistance component immediately after current interruption before the polarization resistance has time to develop. This timing strategy captures the pure DC resistance value, and the subsequent waiting period allows polarization resistance to manifest separately for its own measurement.
2Speed
If high-speed A/D converter is used for resistance measurement, then the measurement speed is improved, but the device cost increases
Solution Approach 1:
The patent uses periodic action by implementing a time-delayed measurement sequence rather than continuous high-speed measurement. The system waits for specific time intervals (immediate measurement for DC resistance, then after a waiting period for polarization resistance) which allows standard A/D converters to capture the necessary data without requiring high-speed conversion capabilities.
Solution Approach 2:
The patent replaces expensive high-speed A/D converters with standard, lower-cost A/D converters by changing the measurement strategy from simultaneous high-speed sampling to sequential time-delayed sampling. This substitution maintains measurement accuracy while significantly reducing hardware costs.
3Device complexity
If single open circuit voltage measurement is used, then the measurement process is simple, but the degradation detection accuracy deteriorates
Solution Approach 1:
The patent segments the voltage measurement process into two distinct measurements: the first open circuit voltage measurement taken immediately after current interruption to capture DC resistance effects, and the second open circuit voltage measurement taken after a waiting period to capture polarization resistance effects. This segmentation enables accurate differentiation of degradation types.
Solution Approach 2:
The patent uses the waiting period as an intermediary element between the two voltage measurements. This time interval allows the battery's polarization resistance to manifest and change the voltage reading, serving as a mediator that enables the system to detect and differentiate between DC and polarization resistance components.
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 method allows for correct detection of battery degradation even when DC resistance components are similar, preventing incorrect full charge capacity calculations and potential power shutdowns, while being cost-effective and applicable in various usage scenarios.
Implementation Method 1
calculates a direct current (DC) resistance component from a charging current and a voltage difference between a closed circuit voltage and a first open circuit voltage
Data Source
AI summary
A battery pack includes: one or two or more secondary batteries; a charge control switch that turns on/off a charging current to the secondary battery; a discharge control switch that turns on/off a discharging current from the secondary battery; a current-detecting element for detecting the charging current and the discharging current; a voltage measuring part that measures the voltage of the secondary battery; a control unit that controls the charge control switch and the discharge control unit; and a storage unit that stores an initial internal resistance of the secondary battery. The control unit measures a closed circuit voltage and a charging current during charging, and a first closed circuit voltage after a first waiting time and a second closed circuit voltage after a second waiting time. The second waiting time is longer than the first waiting time.