Battery Charge State Initialization Under Short Relaxation Time
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Solution Overview
Problem
Existing methods for estimating the initial state of charge of a battery in hybrid and electric vehicles are imprecise, especially when the battery relaxation time is too short, as they do not account for battery polarization and relaxation time.
Innovation Solution
A method that includes an initialization phase for estimating the state of charge, which involves receiving a memorized state-of-charge value, calculating a state-of-charge value from the no-load voltage, calculating an error due to battery relaxation, and adjusting the estimate based on this error and the polarization direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the initialization method uses open-circuit voltage measurement when the battery wakes, then the state of charge estimate can be obtained quickly, but the measurement precision deteriorates when relaxation time is too short due to battery polarization
Solution Approach 1:
The system performs preliminary actions by storing the state of charge value just before the battery enters sleep mode in memory. This pre-stored value serves as a reference for correcting the open-circuit voltage measurement taken after wake-up, allowing the system to compensate for polarization effects without requiring long relaxation periods.
Solution Approach 2:
The system implements feedback by comparing the open-circuit voltage-derived state of charge with the previously stored state of charge value. The difference between these two values provides feedback information about polarization effects, which is then used to correct the initial state of charge estimate, improving measurement precision even with short relaxation times.
2Use of energy by moving object
If the battery enters sleep mode frequently to save energy, then the use of energy is reduced, but the reliability of state of charge initialization deteriorates because the battery does not have sufficient relaxation time
Solution Approach 1:
The system performs preliminary action by capturing and storing the state of charge value immediately before the battery enters sleep mode. This pre-captured value remains in memory regardless of how short the sleep duration is, ensuring that reliable reference data is available for correcting the post-wake-up open-circuit voltage measurement, thus maintaining initialization reliability even with frequent sleep cycles.
Solution Approach 2:
The stored previous state of charge value acts as an intermediary element that bridges the gap between frequent sleep modes and accurate state of charge initialization. This intermediary reference value allows the system to correct polarization effects without requiring the battery to undergo long relaxation periods, enabling frequent energy-saving sleep cycles while maintaining measurement reliability.
3Measurement precision
If the system waits for the battery to reach steady state before measurement, then the measurement precision is improved, but the loss of time increases due to required relaxation periods of several minutes to hours
Solution Approach 1:
The system performs preliminary action by storing the state of charge value before sleep mode in advance. This pre-stored reference value enables the system to correct the open-circuit voltage measurement taken after wake-up, eliminating the need to wait for long relaxation periods to reach steady state, thus significantly reducing the time loss while maintaining measurement precision.
Solution Approach 2:
Instead of waiting for the battery to reach steady state after wake-up (the conventional approach), the system inverts the logic by using a reference value captured before sleep mode to correct the post-wake-up measurement. This inversion allows the system to obtain accurate state of charge estimates without requiring the battery to undergo long relaxation periods, thus solving the time-loss problem.
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 provides a reliable estimate of the initial state of charge, even during short relaxation periods, by accounting for errors caused by incomplete relaxation and polarization direction, thereby optimizing battery performance and longevity.
Implementation Method 1
an electrochemical energy storage device, and more specifically an accumulator battery
Implementation Method 2
the charging and/or discharging periods of the battery are separated by periods of relaxation, during which no current is flowing through the battery. After a given relaxation time, the battery reaches a steady state.
Implementation Method 3
the no-load voltage (open-circuit voltage) can be measured at the terminals of the battery, and this corresponds to the steady-state electromotive force thereof
Data Source
AI summary
A method for estimating the charge state of a battery includes initializing the charge state, including estimating an initial charge state value. The initializing includes: receiving a stored charge state value for a sleep mode time of the battery, computing a charge state value from a measurement of the no-load voltage at the terminals of the battery at a wake-up time of the battery, and computing an error in the measurement of the no-load voltage due to the relaxation of the battery. The error is computed as a function of the current temperature of the battery and of a target relaxation duration modelled for each temperature. The initial value of the charge state is computed based on a comparison between the recorded and computed charge state values and as a function of the error.