Battery SOC Estimation via Equivalent Constant Current Model
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Solution Overview
Problem
Battery management systems in electric and hybrid vehicles face challenges in accurately calculating the state of charge (SOC) and predicted voltage of battery cells due to variations in current, temperature, and overpotential over the battery's lifetime, leading to decreased performance.
Innovation Solution
A system and method that includes a state of charge (SOC) calculation module and an overpotential calculation module, which uses measured current, lagged currents, and weighting factors to calculate an equivalent constant current, and subsequently determines the overpotential and predicted voltage of the battery cell, incorporating temperature and SOC as variables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional battery management systems use simple current measurement for SOC calculation, then the system complexity is low, but the measurement precision of SOC and predicted voltage deteriorates due to variations in current, temperature, and overpotential
Solution Approach 1:
The patent segments the current measurement into multiple components: instantaneous current, lagged current (filtered), and equivalent constant current. Each component is calculated separately using different time constants and weighting factors to capture different aspects of battery behavior, improving SOC estimation accuracy while managing complexity through modular calculation steps
Solution Approach 2:
The system performs preliminary calculations of lagged current using low-pass filters with predetermined time constants before computing the final equivalent constant current. This preliminary processing of current data allows the system to account for transient dynamics in advance, improving measurement precision without adding complexity during the main SOC calculation
2Measurement precision
If the system accounts for transient and steady-state dynamics through multiple current components, then the measurement precision improves, but the calculation time and processing complexity increase
Solution Approach 1:
The patent implements a dynamic current model that adapts between transient and steady-state conditions. The system dynamically adjusts the weighting factors applied to instantaneous versus lagged current components based on the battery's operational state, allowing accurate overpotential calculation during both transient charging/discharging and steady-state conditions without requiring separate calculation paths
Solution Approach 2:
The system changes the effective time constant parameter dynamically by adjusting weighting factors between instantaneous current (weighting factor approaching 1) and lagged current (weighting factor approaching the time constant ratio). This parameter adjustment allows the same calculation framework to handle both fast transient responses and slower steady-state behavior, reducing overall calculation time
Data Source
AI summary
A system includes a state of charge (SOC) calculation module configured to calculate an SOC of a battery cell based on a measured current of the battery cell and an overpotential calculation module configured to receive the measured current and output lagged currents based on the measured current and respective time constants, output a weighted measured current and weighted lagged currents based on a plurality of weighting factors, wherein a sum of the plurality of weighting factors is 1, calculate an equivalent constant current corresponding to the measured current based on the weighted measured current and the weighted lag currents, and calculate an overpotential of the battery cell based on the equivalent constant current. The system is configured to output a predicted voltage of the battery cell based on the calculated SOC and the calculated overpotential of the battery cell.