Vehicle Battery Pack Impedance Measurement Using DC/DC Injection
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Solution Overview
Problem
Existing battery systems for electric vehicles lack a reliable and efficient method for evaluating the performance and health of lithium-ion batteries, particularly in terms of impedance measurement, which is crucial for assessing aging, lithium plating formation, and electrolyte conductivity.
Innovation Solution
A battery system with an integrated current injection circuit and measuring circuit, utilizing a bi-directional DC/DC converter to generate current signals at various frequencies, allowing for impedance evaluation by analyzing the voltage-to-current ratio, and incorporating energy balancing mechanisms to manage power distribution across multiple battery packs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate evaluation unit with dedicated current injection circuit and measuring circuit is added to the battery system, then impedance measurement precision is improved, but device complexity increases
Solution Approach 1:
The DC/DC converter is designed to perform multiple functions: it serves as both the power conversion device for charging/discharging the battery and as the current injection circuit for impedance measurement. By making the DC/DC converter bi-directional and capable of operating in different modes (power transfer mode and measurement mode), the system eliminates the need for a separate dedicated current injection device, thus reducing device complexity while maintaining measurement precision
Solution Approach 2:
The evaluation unit merges the DC/DC converter, current injection circuit, and measuring circuit into an integrated system. The DC/DC converter's control unit is enhanced to function as both the control device for power management and as the evaluation device for impedance measurement, combining multiple functions into a single integrated unit that reduces overall system complexity
2Device complexity
If the DC/DC converter is used for both power supply and impedance measurement, then device complexity is reduced, but measurement precision may deteriorate
Solution Approach 1:
The DC/DC converter is designed with dynamic switching capability between different operational modes. The control unit can dynamically switch between power transfer mode (for charging/discharging) and measurement mode (for impedance evaluation). This dynamic operation allows the same hardware to be optimized for different functions at different times, maintaining measurement precision while reducing device complexity
Solution Approach 2:
The system employs periodic action by alternating between measurement cycles and power transfer cycles. During measurement cycles, the DC/DC converter operates in current injection mode with the measuring circuit active, and during power transfer cycles, it operates in charging/discharging mode. This periodic switching ensures that measurement operations are performed under optimal conditions while still utilizing the integrated DC/DC converter structure
3Quantity of substance
If multiple battery packs are connected in series or parallel, then energy storage capacity is improved, but difficulty in evaluating individual battery impedance increases
Solution Approach 1:
The evaluation system employs segmentation by independently evaluating each battery pack within the series or parallel configuration. The control unit sequentially connects the DC/DC converter to each battery pack through switching circuitry, allowing individual impedance measurement of each cell or module. This segmented approach enables precise monitoring of each battery's health status while maintaining the overall multi-pack configuration for enhanced energy storage capacity
Solution Approach 2:
The DC/DC converter acts as an intermediary device that can be selectively connected to different battery packs in the series or parallel configuration. Through controlled switching, the DC/DC converter mediates the connection between the measurement circuit and individual battery packs, enabling isolated impedance evaluation of each pack without disrupting the overall multi-pack arrangement. This intermediary function simplifies the measurement process while maintaining the ability to assess individual battery performance
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 accurate and continuous impedance measurement, enabling precise assessment of battery health and performance characteristics, including aging and electrolyte conductivity, thereby enhancing safety and reliability of electric vehicles.
Implementation Method 1
The first DC/DC converter of the current injection circuit, as an existing power converter of the battery system (100) for supplying power from the first battery pack to loads of the vehicle (10), is configured to generate a first current signal at a plurality of frequencies for evaluating the impedance
Implementation Method 2
The measuring circuit is configured to record and/or analyze the first current signal from the first DC/DC converter for evaluating the impedance of the first battery pack by means of a ratio of a voltage difference of the first battery pack to the current of the first current signal
Data Source
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AI summary
The disclosure relates to a battery system (100) for a vehicle (10), a vehicle comprising a battery system, a method for evaluating an impedance of a battery system and a computer program element. The battery system (100) comprises a first battery pack (110) and an evaluation unit for evaluating an impedance of the first battery pack (110). The evaluation unit comprises a current injection circuit, which has a first DC/DC converter (112) and is arranged in the battery system (100) and/or adjacent to the first battery pack (110), and a measuring circuit. The first DC/DC converter (112) is configured to generate a first current signal (111) at a plurality of frequencies, and the measuring circuit is configured to record and/or analyze the first current signal (111) from the first DC/DC converter (112) for evaluating the impedance of the first battery pack (110) by means of a ratio of a voltage difference of the first battery pack (110) to the current of the first current signal.