Battery SOC Estimation Using Discharge Threshold Correction
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of secondary batteries, such as nickel-metalhydride and lithium ion batteries, face accuracy issues due to the memory effect, which affects the correlation between open circuit voltage (OCV) and SOC, leading to inaccurate SOC estimation even with correction techniques based on temperature and charge/discharge current.
Innovation Solution
An apparatus that includes a storage unit for correlation information between OCV and SOC, a total-amount-of-electric-discharge detection unit, and a correction unit that adjusts the correlation information based on a predetermined threshold value, replacing or mixing initial and saturated state correlation information to enhance estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correction value is computed from temperature and charge/discharge current, then correction is applied to OCV-SOC map, but accurate correction performance is not necessarily assured
Solution Approach 1:
The patent changes the correction parameter from temperature and current to total amount of electric discharge. By detecting the cumulative discharge amount and comparing it with threshold values, the system selects or mixes correlation information appropriate to the battery's usage state, achieving reliable correction performance that accurately reflects the memory effect progression.
Solution Approach 2:
The system continuously monitors the total amount of electric discharge and uses this feedback to dynamically adjust the correlation information selection. This closed-loop approach ensures that the correction always reflects the current state of the memory effect, improving both accuracy and reliability of SOC estimation.
2Measurement precision
If correction is made using temperature and charge/discharge current, then some accuracy improvement is achieved, but the complexity of correction calculation increases
Solution Approach 1:
The patent extracts the essential factor for memory effect correction - the total amount of electric discharge - from the complex set of parameters including temperature and current. By focusing only on the cumulative discharge amount, the system simplifies the correction calculation while maintaining accuracy, eliminating the need for complex multi-parameter calculations.
3Measurement precision
If OCV-SOC correlation is used in initial state, then accurate SOC estimation is achieved, but accuracy deteriorates when memory effect occurs
Solution Approach 1:
The patent makes the OCV-SOC correlation dynamic by selecting or mixing different correlation information based on the total discharge amount. Instead of using a fixed initial-state correlation, the system adapts the correlation to the current state of the battery, maintaining accuracy even as the memory effect develops and the battery transitions from initial to saturated state.
Data Source
AI summary
An apparatus for estimating a state of charge (SOC) of a secondary battery. A control section of a battery controller (ECU) computes a total amount of electric discharge of a secondary battery and compares the total amount of electric discharge with a predetermined threshold value. The threshold value is set so as to fall within a range of; for instance, 400 Ah to 1600 Ah. When the total amount of electric discharge is equal to or greater than the predetermined threshold value, an open-circuit-voltage (OCV)-SOC map is replaced with a map achieved in a state where a memory effect is saturated. When the total amount of electric discharge is smaller than the predetermined threshold value, a correction is made to the map so as to achieve a map that is a mixture consisting of the OCV-SOC map achieved in an initial state and the OCV-SOC map achieved in the saturated state at a predetermined ratio. The SOC is estimated by use of the corrected map.