Battery Monitoring via Low-Current OCV and Impedance Estimation
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Solution Overview
Problem
It is challenging to accurately measure the state of charge (SOC) and state of health (SOH) of secondary cells, particularly in applications like automated guided vehicles and drones where cells are constantly being charged and discharged, making it difficult to grasp the SOC and SOH accurately.
Innovation Solution
A battery monitoring device that includes a measurement unit to measure voltage and current, and a calculation unit to estimate SOC and SOH by identifying a low current interval, calculating impedance, and referencing relationship data to determine the SOC and SOH, even in continuously charging and discharging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC impedance measurement technique is used to measure internal resistance for diagnosing degradation state, then measurement precision is improved, but it becomes difficult to measure in constantly operating applications where cells are continuously charged and discharged
Solution Approach 1:
The system pre-stores the relationship between SOC and OCV, and the relationship between impedance and SOH in memory before operation. This preliminary preparation allows the system to perform accurate measurements during continuous operation without requiring external measurement equipment or stopping the cells, resolving the contradiction between measurement precision and ease of operation during continuous charging/discharging.
2Ease of operation
If direct current resistance measurement technique is used to measure internal resistance, then ease of operation is improved, but measurement precision deteriorates in continuously operating conditions
Solution Approach 1:
The system uses OCV as an intermediary parameter to estimate SOC, and uses impedance as an intermediary parameter to estimate SOH. By measuring voltage during continuous operation and using these intermediary parameters with pre-stored relationship data, the system achieves both ease of operation during continuous charging/discharging and high measurement precision for SOC and SOH estimation.
3Productivity
If voltage measurement is performed during transient current response to calculate impedance, then productivity is improved by enabling continuous monitoring, but measurement precision may be affected by current fluctuations
Solution Approach 1:
The system dynamically adapts to transient current conditions by using real-time voltage measurements during actual charging/discharging operations. Instead of requiring static measurement conditions, the system calculates impedance dynamically using the relationship between voltage, current, and the pre-stored SOC-OCV and impedance-SOH relationships, enabling continuous monitoring while maintaining measurement precision through adaptive calculation methods.
Data Source
AI summary
A battery monitoring device includes a measurement unit and a calculation unit. The measurement unit includes a voltage measurement unit and a current measurement unit. The calculation unit includes: storage that holds first relationship data indicating a relationship between SOC and OCV and second relationship data indicating a relationship between impedance and SOH; an impedance calculation unit that identifies a low current interval, sets a voltage obtained during the low current interval as a provisional OCV, and calculates an impedance of secondary cells from a voltage value and a current value in a transient current response; an SOH estimate unit that estimates an SOH by referencing the second relationship data using the impedance; and an SOC estimate unit that estimates an SOC by referencing the first relationship data based on the provisional OCV.