Sodium-Sulfur Battery End-of-Discharge Voltage Correction
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Solution Overview
Problem
Conventional methods for correcting end-of-discharge voltage in sodium-sulfur batteries fail to accurately account for internal resistance, leading to inadequate correction of the end-of-discharge voltage.
Innovation Solution
A device and method that derive the discharge depth and equivalent cycle count of sodium-sulfur battery cells, adjust the ohmic resistance based on these parameters, and consider the healthy parallel number to accurately calculate the end-of-discharge voltage by subtracting the product of discharge current and internal resistance from the open voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional correction methods using simple cycle count and healthy parallel number are used, then the correction process is simple, but the internal resistance correction accuracy deteriorates
Solution Approach 1:
The patent transforms the simple cycle count into an equivalent cycle count by changing the parameter through weighting based on discharge depth. This allows the system to maintain measurement simplicity while improving accuracy by considering that deeper discharges cause more degradation than shallow ones.
Solution Approach 2:
The patent introduces dynamic adjustment of the healthy parallel number based on observed voltage differences between parallel units. Instead of using a static value, the system continuously adapts the healthy parallel number to reflect actual battery conditions, improving correction accuracy without requiring complex hardware changes.
2Device complexity
If the healthy parallel number is not dynamically adjusted, then the calculation process is simple, but the end-of-discharge voltage correction accuracy deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the voltage difference between parallel-connected battery units is continuously monitored. This feedback is used to dynamically adjust the healthy parallel number, ensuring that the correction algorithm adapts to actual battery conditions and maintains high accuracy.
Solution Approach 2:
The patent performs preliminary correction calculations using an initial healthy parallel number, then refines this correction by applying additional adjustments based on observed voltage differences. This two-stage approach ensures accurate correction while keeping the calculation process manageable.
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 approach accurately corrects the ohmic resistance and subsequently the end-of-discharge voltage, preventing false detection and ensuring reliable battery operation.
Implementation Method 1
subtracting, from an end-of-discharge open voltage, the product of a discharge current of the first parallel-connected unit and the estimated value of the ohmic resistance of the first parallel-connected unit
Data Source
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AI summary
Provided are an end-of-discharge voltage correction device and an end-of-discharge voltage correction method for appropriately correcting an end-of-discharge voltage. An end-of-discharge voltage correction section subtracts, from an end-of-discharge open voltage VLOC, the product I×RO of a discharge current I of a block and an ohmic resistance RO of the block and the product lTD×RP of a discharge current ITD obtained by performing a time delay process on the discharge current I of the block and a polarization resistance RP of the block. Then, a resulting value is set as an end-of-discharge voltage VL. The ohmic resistance RO is increased as an equivalent cycle count CY increases, and is increased as a healthy parallel number NPH decreases. An increment ΔCY of the equivalent cycle count CY in each charge/discharge cycle becomes greater as a discharge depth DD increases. The healthy parallel number NPH is derived by multiplying a healthy parallel number NPHR of a reference block by the ratio of a capacity CPR of the reference block to a capacity CPS of a target block.