Traction Battery SoH Estimation Using Normalized Internal Resistance
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Solution Overview
Problem
Conventional methods for determining the state of a traction battery in electric vehicles are energy-intensive, time-consuming, and require disassembly, making them inefficient and labor-intensive, while also being unsuitable for accurately assessing the serial internal resistance, which is crucial for evaluating the battery's health and power capability.
Innovation Solution
A method that normalizes the ohmic internal resistance of the traction battery using variables like temperature and battery type, allowing for quick and economical evaluation of the battery's state of health (SoH) without direct galvanic access, using a test load and mathematical functions or tables to establish the normalized internal resistance, enabling comparison across different conditions and battery types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods are used to determine battery state, then measurement accuracy is improved, but energy consumption increases and measurement time increases
Solution Approach 1:
The patent changes the measurement parameters from traditional full discharge tests to pulse load measurements with specific current amplitudes and durations. By using normalized internal resistance calculations that account for temperature and battery type, the method achieves accurate SoH determination with minimal energy consumption during the measurement process.
Solution Approach 2:
Instead of performing complete discharge cycles to assess battery health, the patent applies partial load pulses that are sufficient to elicit measurable voltage responses. This partial action provides enough information for accurate SoH calculation without depleting the battery, thereby reducing energy consumption while maintaining measurement precision.
2Measurement precision
If conventional methods are used to determine battery state, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent employs periodic pulse load applications instead of continuous discharge testing. Multiple short pulses are applied at different time points, and the internal resistance is calculated from the voltage responses. This periodic measurement approach reduces total measurement time while maintaining accuracy through multiple data points for validation.
Solution Approach 2:
The patent performs preliminary normalization by establishing reference internal resistance values for different battery types and temperature conditions before conducting measurements. This preliminary action allows for direct comparison and accurate SoH determination without requiring lengthy calibration procedures during each measurement, significantly reducing measurement time.
3Measurement precision
If direct galvanic access is used for measurement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses the battery's own voltage response as an intermediary to determine internal resistance. Instead of requiring direct galvanic access and complex measurement equipment, the method applies load pulses through existing vehicle electrical systems and measures voltage changes through standard terminals. The internal resistance is calculated from these indirect measurements, eliminating the need for complex direct measurement equipment.
4Reliability
If manufacturer-specific energy buffers are required, then measurement reliability is improved, but adaptability decreases
Solution Approach 1:
The patent develops a universal measurement method that works across different battery types (lead-acid, NiMH, Li-ion) by normalizing internal resistance values according to battery type and temperature. The same pulse load methodology and calculation algorithms can be applied to any traction battery, eliminating dependence on manufacturer-specific energy buffers and measurement procedures while maintaining reliability through type-specific normalization factors.
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
Enables rapid, accurate, and cost-effective determination of the traction battery's SoH with minimal energy load and equipment requirements, reducing error tolerance and eliminating dependence on manufacturer-specific energy buffers, allowing for independent assessment of battery health without disassembly.
Implementation Method 1
the traction battery is charged or discharged by means of a test load and, at at least one point in time, a respective output voltage and charging or discharging current value pair of the traction battery is acquired
Implementation Method 2
an ohmic internal resistance of the traction battery is established on the basis of the acquired output voltage and charging or discharging current value pair
Data Source
AI summary
A method for determining a state value of a traction battery of an electric vehicle characterises the ageing state, preferably an SoH value. The traction battery is charged or discharged by a test load and a respective output voltage and load current value pair is acquired. An ohmic internal resistance is established on the basis of the acquired value pair. The state value is established on the basis of the established ohmic internal resistance. At least one normalisation variable characterizing the traction battery is established. On the basis of the established ohmic internal resistance and the normalisation variable, a normalised internal resistance based on a reference value of the normalisation variable is established. The state value is established on the basis of the normalised internal resistance. A diagnostics device has an evaluation unit which is directly or indirectly couplable to the traction battery and carries out the method.