Battery SOC Estimation Using Equivalent Circuit Model
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In wireless transit systems, accurate State of Charge (SOC) estimation of batteries is challenging due to temperature variations, leading to potential overcharging or overdischarging, which can cause battery deterioration, and existing methods are complex or prone to errors.
Innovation Solution
A battery SOC estimation program that calculates SOC using an equivalent circuit model with three components: a resistance influenced by instantaneous current, a capacitance and resistance for slow responses, and open circuit voltage, allowing for online estimation and control of charging to prevent overcharging and overdischarging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If battery SOC is estimated by current integration method, then SOC can be estimated over time, but measurement error accumulates and estimation accuracy decreases as integration time increases
Solution Approach 1:
The patent implements feedback by continuously monitoring terminal voltage and current, and using these measurements to dynamically update the SOC estimation through the equivalent circuit model. The system feeds back the estimated SOC and internal resistance values to adjust charging control in real-time, preventing error accumulation by constantly validating against actual measurements.
Solution Approach 2:
The patent replaces the pure current integration method with an electrical model-based approach using an equivalent circuit model. This substitution introduces voltage measurements and mathematical modeling to replace the simple integration process, thereby eliminating error accumulation while maintaining long-term estimation capability.
2Measurement precision
If battery temperature is controlled to maintain desirable SOC, then SOC control accuracy is improved and overcharging is prevented, but device structure becomes complicated
Solution Approach 1:
The patent introduces an equivalent circuit model as an intermediary between voltage/current measurements and SOC estimation. This mathematical model acts as a mediator that translates electrical measurements into accurate SOC values without requiring direct temperature control hardware, thereby maintaining accuracy while avoiding structural complexity.
Solution Approach 2:
The patent substitutes physical temperature control devices with a mathematical modeling approach. By using the equivalent circuit model that accounts for temperature effects on internal resistance, the system achieves temperature-compensated SOC estimation without requiring physical temperature sensors or active temperature control mechanisms.
3Productivity
If charging current is increased for fast charging, then charging speed is improved, but risk of overcharging and battery deterioration increases
Solution Approach 1:
The patent implements real-time feedback control by continuously monitoring terminal voltage, current, and estimated SOC. The system uses this feedback to dynamically adjust charging current, allowing high current when SOC is low for fast charging, and automatically reducing current as SOC approaches the target level, thereby enabling fast charging while preventing overcharging and battery deterioration.
Solution Approach 2:
The patent applies dynamic charging control where the charging current is not fixed but varies continuously based on real-time SOC estimation. The system transitions from high current charging to lower current as SOC increases, creating a dynamic charging profile that optimizes both charging speed and battery safety throughout the charging process.
Data Source
AI summary
Occurrence of overcharging and over discharging of batteries mounted on vehicles that travel on tracks in a wireless transit system is prevented by estimating a state of charge (SOC) of the batteries with accuracy. An equivalent circuit of the battery is composed of three circuit elements connected in series, including (i) a first component resistance R1 (ii) a component circuit which includes a capacitance C and a second component resistance R2 connected in parallel and (iii) an open circuit voltage of the battery. The open circuit voltage of the equivalent circuit is calculated using R1 calculated from measurements of current and voltage of the battery, as well as values k=R2/R1 and τ=C×R2. The SOC if the battery is calculated from the open circuit voltage.