Battery SOH Sensing Circuit Using Two-Stage Capacitor Charging
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Solution Overview
Problem
Conventional battery management systems lack effective methods to monitor the state of health (SOH) of batteries by accurately measuring battery voltage and internal resistance over time to identify degradation.
Innovation Solution
A system and method that involves a sensing circuit with resistors and capacitors to measure battery voltage and internal resistance, using a voltage divider circuit and an analog-to-digital converter (ADC) to compare these values against historical measurements to detect battery degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional battery management systems use simple sensing units to measure temperature and battery current, then the device complexity is reduced, but the measurement precision of battery voltage and internal resistance is insufficient to accurately identify degradation
Solution Approach 1:
The sensing circuit is segmented into multiple functional stages: a first charging stage using a first resistor to charge a capacitor to a first voltage level, and a second charging stage using a second resistor to charge the capacitor to a second voltage level. This segmentation allows the circuit to measure both voltage and internal resistance separately through controlled charging phases, improving measurement precision without requiring a completely complex circuit design.
Solution Approach 2:
The capacitor is pre-charged to a first voltage level in the first charging stage before proceeding to the second charging stage. This preliminary action establishes a known initial state that enables accurate measurement of the battery's internal resistance during the second charging stage, as the capacitor's charge state is controlled and predictable before the actual measurement occurs.
2Reliability
If the sensing circuit directly measures battery voltage without controlled charging stages, then the measurement process is simplified, but the ability to accurately compare against historical values to identify degradation is compromised
Solution Approach 1:
The sensing circuit operates in periodic charging stages, alternating between a first charging stage with a first resistor and a second charging stage with a second resistor. This periodic action allows the system to systematically vary the charging conditions and measure the battery's response at different stages, enabling reliable identification of degradation by comparing the measured values against historical data while maintaining controlled measurement conditions.
Solution Approach 2:
The system measures the capacitor's voltage at different charging stages and uses this feedback information to determine the battery's internal resistance and voltage characteristics. By comparing the measured values during the charging stages against historical values stored in memory, the system can identify degradation and provide accurate SOH assessment, with the feedback loop enabling continuous monitoring and comparison.
3Measurement precision
If the system uses a single resistor for charging the capacitor, then the circuit complexity is reduced, but the measurement precision for distinguishing between voltage changes and internal resistance changes is insufficient
Solution Approach 1:
The circuit uses different resistors with different resistance values in different charging stages: a first resistor with a first resistance value in the first charging stage, and a second resistor with a second resistance value in the second charging stage. This local quality differentiation allows the system to optimize the charging characteristics for each measurement purpose, enabling precise distinction between voltage changes and internal resistance changes by observing the capacitor's charging behavior under different resistance conditions.
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
Accurately identifies battery degradation by comparing measured delta voltage values to historical references, enabling precise monitoring of battery health and performance.
Implementation Method 1
a capacitor selectively electrically connectable between the first and second resistors via the first and second switches, respectively
Implementation Method 2
a voltage divider circuit configured to reduce voltage of the capacitor prior to reaching the voltage node
Implementation Method 3
an analog-to-digital converter (ADC) electrically connected to the voltage node
Data Source
AI summary
A system and method monitor a state of health (SOH) of a battery. The battery has a voltage (Vb) and an internal series resistance (Rb). The system includes a capacitor and employs a high ohmic load during a capacitor pre-charging stage to control current inrush, with the pre-charging stage being used to measure the battery voltage. The system also employs a low ohmic load during a second stage that completes charging of the capacitor, with the second stage being used to estimate any change in the internal resistance. Switches interchange the two ohmic loads. A measured delta Vs is compared to a delta Vs stored in memory that defines a historical voltage value of a healthy battery. A change in Vb and/or Rb is identified, thus identifying a SOH of the battery as degraded when there is a difference between the measured delta Vs and the stored delta Vs.