Nickel Hydride Battery Memory Effect Estimation via Interval Integration
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Solution Overview
Problem
Existing battery systems face challenges in accurately estimating the memory quantity of nickel hydride batteries, which affects the accuracy of state-of-charge estimation due to dependencies on conditions such as open circuit voltage and temperature, and the need for improved integration of memory quantity over time.
Innovation Solution
A battery system with an electronic control unit that stores data on the relationship between elapsed time, open circuit voltage, and temperature to calculate and integrate memory quantity, using a power root scale to reduce data volume and computation load, allowing for accurate estimation of current memory quantity and reducing power consumption during stop periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the memory quantity is estimated using integration results to the present, then the calculation is simplified, but the accuracy in estimating the memory quantity deteriorates because the memory effect depends on usage conditions during the period
Solution Approach 1:
The patent segments the usage period into multiple intervals based on changes in usage conditions (charge/discharge states, temperature). For each interval, the memory quantity is calculated separately using the integrated value at the interval start and the integrated value at the interval end, rather than using a single integration result from the beginning. This segmentation allows the calculation to adapt to changing conditions while maintaining accuracy.
Solution Approach 2:
The patent implements a dynamic calculation approach where the memory quantity estimation adapts to changing usage conditions. By using the interval start integrated value and interval end integrated value to calculate memory quantity for each specific interval, the system dynamically adjusts the estimation based on actual usage patterns, temperature changes, and charge/discharge states rather than relying on a static integration from the beginning.
2Measurement precision
If data is stored for each condition of use classification, then the accuracy in estimating memory quantity is improved, but the data volume and computation load increase
Solution Approach 1:
The patent creates a universal calculation method that works across all condition classifications. Instead of storing separate complex models for each condition, the system uses a unified approach where the same calculation formula (using interval start and interval end integrated values) applies to all conditions. The electronic control unit classifies conditions and selects appropriate data, but the core calculation methodology remains universal and consistent.
3Measurement precision
If continuous calculation is performed to accurately track memory quantity changes, then estimation accuracy is improved, but power consumption increases during stop periods
Solution Approach 1:
The patent implements periodic calculation instead of continuous calculation. The memory quantity is calculated at specific intervals when usage conditions change or at predetermined time points, rather than continuously. During stop periods, the system stores the integrated value without active calculation, reducing power consumption while maintaining accuracy by resuming calculation when conditions change.
Data Source
AI summary
A battery system includes a nickel hydride battery and an electronic control unit. The electronic control unit is configured to store data indicating a corresponding relationship between an elapsed time from start of use of the nickel hydride battery and a memory quantity. The data are data determined in a classified manner individually for each of conditions of use that are defined in such a manner as to include an open circuit voltage and a temperature. The electronic control unit is configured to sequentially calculate, with reference to the data, the memory quantity within a time when classification of the conditions of use does not change. The memory quantity is a quantity indicating an amount of change in voltage resulting from a memory effect. The electronic control unit is configured to estimate a current memory quantity of the nickel hydride battery by integrating the calculated memory quantity.