Battery SOC Cutoff for Mixed-Cell Discharge Accuracy
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Solution Overview
Problem
Existing battery management systems struggle to accurately estimate the state of charge (SOC) of batteries containing multiple types of cells with different positive electrode materials, leading to inaccuracies in remaining dischargeable capacity, which can cause electric apparatuses to shut down prematurely.
Innovation Solution
A state-of-charge cut-off control method that calculates the current remaining dischargeable capacity of a battery cell using a specific equation, taking into account its nominal capacity, available capacity, state of health, and net discharge capacity, and sets the SOC to 0 when the battery releases its nominal capacity, ensuring the remaining dischargeable capacity is greater than 0, thereby reducing the risk of premature shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SOC estimation methods (OCV method or Ampere-hour integral method) are used for batteries with multiple cell types, then the estimation process is simple, but the SOC estimation accuracy deteriorates significantly
Solution Approach 1:
The patent segments the battery pack into individual battery cells and tracks each cell's capacity separately. By monitoring the capacity of each cell independently and identifying the minimum capacity cell, the system accurately determines the actual SOC of the entire battery pack, resolving the inaccuracy caused by treating all cells as having uniform capacity.
Solution Approach 2:
The patent changes the parameter used for SOC estimation from a uniform battery-level capacity to cell-level capacity parameters. It introduces the concept of net discharge capacity and tracks capacity changes for each cell type, using these dynamic parameters to calculate accurate SOC even in batteries with heterogeneous cell types.
2Reliability
If SOC estimation is based on uniform capacity assumptions, then the calculation is straightforward, but the remaining dischargeable capacity becomes inaccurate leading to premature shutdown
Solution Approach 1:
The patent performs preliminary capacity calibration for each battery cell during manufacturing or initial use. It establishes the nominal capacity and available capacity for each cell type in advance, and uses these pre-determined parameters as the basis for ongoing SOC calculations, ensuring accuracy without requiring complex real-time measurements.
Solution Approach 2:
The patent implements continuous monitoring of each cell's discharge capacity and compares it against the nominal capacity to dynamically update the SOC estimation. This feedback mechanism ensures that the remaining dischargeable capacity calculation remains accurate even as cells age and their capacities change, preventing premature shutdown.
3Quantity of substance
If the battery uses cells with different available capacities, then the battery can utilize more total capacity, but the SOC estimation error increases when using individual cell parameters
Solution Approach 1:
The patent applies partial action by considering only the minimum capacity cell when calculating overall battery SOC, rather than attempting to optimize for each cell individually. This approach ensures that the battery pack SOC estimation is conservative and accurate, preventing overestimation that would lead to premature shutdown, while still allowing the full capacity of each cell to be utilized during discharge.
Data Source
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AI summary
Embodiments of this application relate to the technical field of batteries, and in particular, to a state-of-charge cut-off method, apparatus and control system, and a storage medium. The method includes: obtaining, in a discharging process of a battery, a net discharge capacity of a first battery cell from being fully charged to current time; obtaining an available capacity of the first battery cell and a state of health SOH of the first battery cell; obtaining a current remaining dischargeable capacity of the first battery cell, based on a nominal capacity of the battery, the net discharge capacity of the first battery cell, the available capacity of the first battery cell, and the SOH of the first battery cell; and setting a state of charge SOC of the first battery cell to 0 when a sum of the current remaining dischargeable capacity of the first battery cell and the net discharge capacity of the first battery cell is greater than or equal to the nominal capacity of the battery and the net discharge capacity of the first battery cell is equal to the nominal capacity of the battery. The method according to the embodiments of this application can accurately estimate a state of charge SOC of a battery including at least two different types of battery cells, reducing a probability that an electric apparatus shuts down before the SOC becomes 0.