Model-Based Battery Fuel Gauge Eliminates Sense Resistor
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Solution Overview
Problem
Existing battery fuel gauges require a current sense resistor, leading to voltage loss and power dissipation, and struggle with accuracy when batteries are repeatedly partially charged and discharged, as they operate as integrators prone to integration errors and do not account for variable loads.
Innovation Solution
A battery fuel gauge that models the battery's state of charge by tracking open circuit voltage independently of the load, using an RC circuit approximation to estimate the state of charge without a current sense resistor, allowing for digital or analog implementations that consume minimal power and provide accurate readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sense resistor is used to monitor battery current, then the state of charge can be tracked, but voltage loss and power dissipation occur
Solution Approach 1:
The patent removes the current sense resistor from the battery circuit entirely. Instead of monitoring current through a resistor, the fuel gauge directly measures battery voltage and uses a model-based approach to estimate state of charge, eliminating the energy loss associated with the sense resistor while maintaining measurement capability
Solution Approach 2:
The patent replaces the physical current sensing mechanism (resistor-based electrical measurement) with a model-based estimation system that uses voltage measurements and algorithmic computation to determine state of charge, substituting direct electrical measurement with a computational approach
2Measurement precision
If integration-based fuel gauges are used to track charge, then state of charge can be monitored, but integration errors accumulate over time
Solution Approach 1:
The patent incorporates a model-based estimation system that continuously compares measured voltage against expected voltage based on the battery model and adjusts the state of charge estimate accordingly. This feedback mechanism prevents error accumulation by constantly validating measurements against the physical model, ensuring reliability even during partial charge/discharge cycles
Solution Approach 2:
The patent changes the fundamental measurement parameter from current integration to voltage-based model estimation. By measuring voltage and using a battery model to infer state of charge rather than integrating current over time, the system avoids the accumulation of integration errors that plague traditional approaches
3Device complexity
If terminal voltage monitoring is used to detect low battery, then simplicity is achieved, but ongoing state of charge indication is lost due to variable loads
Solution Approach 1:
The patent creates a system that uses the same voltage measurement infrastructure to achieve multiple functions: both simple low-battery detection and continuous accurate state of charge indication. The model-based approach allows the system to compensate for variable loads and provide ongoing accurate state of charge information while maintaining simplicity
Solution Approach 2:
The patent introduces a battery model as an intermediary between the voltage measurement and the state of charge determination. This model acts as a mediator that translates simple voltage measurements into accurate state of charge information while accounting for variable loads, bridging the gap between simplicity and precision
Data Source
AI summary
Model-based battery fuel gauges that connect across a rechargeable battery and track the per-cent state of charge of the battery. The model based fuel gauges provide a measure of the open terminal voltage of a battery, even when the battery is powering a load, to provide the state of charge information. Analog and digital implementations of the battery model fuel gauges may be used, and incorporated into a battery powered device in various ways, including constantly powered implementations and implementations that are turned on and off with the battery powered device. Various exemplary embodiments are disclosed.