Battery Capacity Tracking via Partial Discharge and Voltage Measurement
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Solution Overview
Problem
Existing techniques for tracking battery capacity in portable devices that remain plugged in for extended periods are inaccurate, as they rely on users exercising the battery through different states of charge, leading to erroneous estimates of remaining battery life.
Innovation Solution
A system that performs open-circuit voltage measurements at different states of charge and calculates capacity fade by draining a small charge from the battery while plugged in, using integrated current measurements to estimate capacity changes over time, which are then applied to a more accurate previously measured capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery remains plugged in for extended periods, then the device maintains high state of charge, but the battery capacity fades inaccurately without exercise
Solution Approach 1:
The system performs a small partial discharge (less than 5% of total capacity) from the battery while it remains plugged in, rather than requiring a full discharge cycle. This partial action is sufficient to create measurable voltage differences for capacity estimation without disrupting the user's plugged-in usage pattern or requiring the device to be unplugged.
Solution Approach 2:
The system performs open-circuit voltage measurements at different states of charge (including a preliminary measurement at the first state of charge before discharge, and a second measurement after discharge) to establish baseline data for capacity fade calculation. This preliminary measurement approach allows the system to track capacity changes proactively before significant fade occurs.
2Measurement precision
If conventional capacity tracking methods are used while plugged in, then the system maintains simplicity, but the battery life estimation becomes erroneous
Solution Approach 1:
The capacity tracking process is segmented into distinct phases: (1) first open-circuit voltage measurement at first state of charge, (2) controlled discharge phase with current integration, (3) second open-circuit voltage measurement at second state of charge, and (4) capacity calculation phase. This segmentation allows each phase to be optimized independently while maintaining overall system manageability.
Solution Approach 2:
The system uses open-circuit voltage measurements as an intermediary indicator to infer battery capacity state. Instead of directly measuring capacity (which would require full discharge cycles), the voltage measurements serve as a proxy that correlates with capacity, enabling indirect but accurate tracking without complex direct capacity measurement hardware.
3Measurement precision
If the battery is discharged significantly to measure capacity, then measurement accuracy improves, but user convenience and state of charge maintenance deteriorate
Solution Approach 1:
The system discharges only a small portion (less than 5% of total capacity) of the battery for measurement purposes, which is far less than traditional methods requiring significant discharge. This partial discharge is sufficient to create measurable voltage changes while minimizing recharge time and maintaining user convenience.
Solution Approach 2:
The system changes the measurement parameter from requiring large state of charge transitions to utilizing small voltage differences measured through open-circuit voltage sampling at slightly different charge levels. This parameter change enables accurate capacity tracking with minimal discharge, reducing the recharge time penalty.
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
This method provides an accurate estimate of battery capacity fade, even when the device is left plugged in, by increasing the frequency of top-of-charge measurements and projecting the capacity forward, ensuring user expectations of high state-of-charge maintenance are met.
Implementation Method 1
The system performs a first open-circuit voltage measurement on the battery once the battery is rested at a first state of charge. Next, the system performs a second open-circuit voltage measurement on the battery once the battery has rested at the second state of charge.
Implementation Method 2
the system causes the battery to transition to a second state of charge while the portable electronic device remains plugged in to the power adapter by discharging a small charge from the battery measured by integrating the measured current through the battery
Data Source
AI summary
A system for tracking the capacity of a battery in a portable electronic device is described. While the portable electronic device remains plugged in to a power adapter, the system estimates the capacity of the battery by performing the following operations. The system measures a first open-circuit voltage for the battery while the battery rests at a first state of charge. Next, the system causes the battery to transition to a second state of charge. While the battery transitions to the second state of charge, the system integrates a current through the battery to determine a net change in charge for the battery. Next, the system measures a second open-circuit voltage for the battery while the battery rests at the second state of charge. Finally, the system estimates a capacity for the battery based on the first open-circuit voltage, the second open-circuit voltage and the net change in charge. This capacity measurement is repeated and the multiple results are fit to a line. The slope of fitted line is then used to estimate how the true battery capacity has faded since last measured using traditional methods that require the battery to be rested at a low state of charge.