Supercapacitor Series Circuit for Linear Traction Battery SOC Monitoring
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for monitoring the State of Charge (SOC) of traction batteries, such as current integration and voltage-based approaches, face challenges with precision due to the non-linearity and hysteresis in lithium-ion battery SOC vs. voltage curves, especially in the intermediate range, and require high-accuracy current sensors, which add complexity and cost.
Innovation Solution
Incorporating a supercapacitor in series with the traction battery cells to sense voltage, which exhibits linear and reversible changes with charge, allowing for accurate SOC monitoring by determining battery capacity using the sensed voltage across the capacitive circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current integration or voltage-based methods are used to monitor SOC, then SOC monitoring is achieved, but measurement precision deteriorates due to non-linearity and hysteresis in lithium-ion battery SOC vs. voltage curves
Solution Approach 1:
A supercapacitor is introduced as an intermediary component connected in series with the lithium-ion battery. The supercapacitor's voltage exhibits linear and reversible changes with charge, serving as a mediator that translates the non-linear battery SOC into a linearly proportional voltage signal that can be accurately measured and used for precise SOC monitoring.
Solution Approach 2:
The invention changes the measurement parameter from directly measuring battery voltage (which has non-linear SOC relationship) to measuring supercapacitor voltage (which has linear SOC relationship). By utilizing the supercapacitor's linear voltage-charge characteristic, the system transforms the non-linear measurement problem into a linear one, significantly improving measurement precision across the entire SOC range.
2Measurement precision
If high-accuracy current sensors are used to improve SOC monitoring precision, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
Instead of using complex current sensors to directly measure and integrate current for SOC calculation, the invention uses a supercapacitor as an intermediary that naturally integrates current over time through its voltage response. The supercapacitor's voltage automatically reflects the cumulative charge, eliminating the need for complex current sensing and integration circuitry.
Solution Approach 2:
The invention replaces the mechanical/electrical system of current sensors and integration circuits with a passive electrochemical system (supercapacitor). The supercapacitor physically performs the integration function through its charge-discharge characteristics, substituting complex active electronics with a simple passive component that provides the same functional outcome.
3Measurement precision
If high-accuracy current sensors are used to improve SOC monitoring precision, then measurement precision improves, but cost increases
Solution Approach 1:
The invention replaces expensive, high-precision current sensors with a relatively inexpensive supercapacitor. While the supercapacitor has a shorter lifespan than the battery, it serves its monitoring function effectively for the required period, providing a cost-effective solution that achieves high measurement precision without the burden of expensive sensing components.
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 precise SOC monitoring across a wide range (20% to 80%) without the need for high-resolution voltage measurements, improving accuracy and reducing costs by using a low-cost supercapacitor that contributes minimally to the battery's voltage and charge characteristics.
Implementation Method 1
A method for state of charge monitoring may include sensing voltage on a capacitive circuit with a supercapacitor connected in series with a traction battery to produce a sensed voltage
Data Source
AI summary
A capacitive circuit with a supercapacitor is connected in series with a traction battery to provide a current sensor to produce a sensed signal that is linear across the operating range of the traction battery. The linear response of the capacitive circuit is an improvement over merely measuring the voltage across the battery, which is not linear over some ranges, e.g., 20% to 80% state of charge.