Battery Impedance Correction for Induced EMF Measurement Error
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Solution Overview
Problem
Existing impedance calculation methods for storage batteries are hindered by the accuracy reduction due to induced electromotive forces caused by magnetic flux, and the restricted conduction path arrangements in conventional four-terminal methods limit the applicability of these techniques.
Innovation Solution
An impedance calculation apparatus that applies an AC signal at a specific frequency to calculate an error in the impedance, separate error calculation and impedance calculation periods, and corrects the impedance based on this error to account for induced electromotive forces, using a control apparatus to manage switches and sensors for accurate impedance determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an AC signal is applied to the storage battery to calculate impedance, then the impedance can be determined for monitoring battery state, but induced electromotive forces cause accuracy reduction
Solution Approach 1:
The patent extracts and separates the error calculation from the main impedance calculation process. By identifying a specific frequency where the imaginary part of impedance is zero, the system can isolate and measure only the error component (induced electromotive force) without interference from reactive impedance, then subtract this error from the total impedance measurement to obtain accurate results.
Solution Approach 2:
The patent changes the frequency parameter of the AC signal to a specific value where the imaginary part of the storage battery impedance becomes zero. This parameter change allows the real part of the impedance to represent only the resistive component, enabling separate measurement and correction of error components caused by induced electromotive forces.
2Measurement precision
If conventional four-terminal method is used for impedance calculation, then impedance can be measured, but conduction path arrangements are restricted
Solution Approach 1:
The patent makes the impedance calculation system universal by enabling it to operate with various conduction path arrangements. By using frequency-based error separation and correction rather than relying on specific four-terminal configurations, the system can adapt to different circuit topologies including series-parallel hybrid configurations, making it applicable to diverse battery pack arrangements in hybrid and electric vehicles.
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
The apparatus accurately calculates impedance by correcting for induced electromotive forces, enhancing accuracy and applicability across various vehicle power systems, including hybrid and electric vehicles, by minimizing the influence of magnetic flux and inverter currents.
Implementation Method 1
an error calculation unit that applies an AC signal having a specified frequency at which at least either a real part component or an imaginary part component of an impedance of the storage battery is a specific value, to calculate an impedance error of the storage battery
Implementation Method 2
a correction unit that corrects, based on the impedance error, the impedance of the storage battery calculated by the impedance calculation unit
Data Source
AI summary
An impedance calculation apparatus applicable to a power source system provided with a storage battery, applying an AC signal to the storage battery to calculate an impedance of the storage battery, during a predetermined impedance calculation period, the impedance calculation apparatus includes: an error calculation unit that applies the AC signal having a specified frequency at which at least either a real part component or an imaginary part component of an impedance of the storage battery is a specific value, to calculate an impedance error of the storage battery, during an error calculation period different from the impedance calculation period; an impedance calculation unit that calculates an impedance of the storage battery during the impedance calculation period; and a correction unit that corrects, based on the impedance error, the impedance of the storage battery calculated by the impedance calculation unit.