Electric Vehicle Battery SOC Estimation via Polarization Resolution
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of electric power storage devices in electric vehicles are prone to precision errors due to disturbances from vehicle travel and environmental variations, particularly affecting voltage calculations and internal resistance corrections.
Innovation Solution
The method involves allowing electric power storage devices to communicate and calculate their voltage-current characteristics during stable charging conditions, enabling accurate open-circuit voltage (OCV) calculation and subsequent precise SOC estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If SOC is calculated repeatedly during vehicle travel using existing methods, then continuous SOC monitoring is achieved, but measurement precision deteriorates due to disturbance from vehicle travel and environmental variations
Solution Approach 1:
The patent performs preliminary charging/discharging operations before SOC calculation to resolve polarization effects. By pre-charging or pre-discharging the battery to a stable state, the system eliminates polarization voltage interference that would otherwise degrade measurement precision during vehicle travel.
Solution Approach 2:
The patent introduces an intermediary stabilization process between charging/discharging operations and SOC measurement. This intermediary step allows the system to transition from a disturbed state (during travel) to a stable state suitable for accurate measurement, effectively mediating between continuous operation and precise measurement requirements.
2Speed
If battery voltage is measured during vehicle travel, then real-time monitoring is achieved, but manufacturing precision deteriorates due to polarization voltage affecting OCV calculation
Solution Approach 1:
The patent implements periodic charging/discharging cycles at specific intervals during vehicle operation. These periodic operations are timed to resolve polarization effects before critical SOC measurements are taken, maintaining both real-time monitoring capability and measurement accuracy through rhythmically repeated stabilization cycles.
Solution Approach 2:
The patent changes the operational parameters of the battery system by intentionally varying charging/discharging current levels and durations. By adjusting these parameters periodically, the system modifies the battery's electrical state to eliminate polarization effects, thereby improving OCV calculation precision without sacrificing real-time monitoring speed.
3Temperature
If internal resistance correction is performed based on temperature during vehicle travel, then temperature compensation is achieved, but reliability deteriorates due to significant environmental variations
Solution Approach 1:
The patent implements a feedback mechanism where temperature measurements during vehicle travel are continuously monitored and used to adjust charging/discharging operations. The system feeds back temperature information to modify operational parameters, creating a closed-loop control that compensates for environmental variations and maintains reliable SOC estimation despite temperature changes.
Data Source
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AI summary
When charging each electric power storage device from a power supply external to a vehicle is requested (YES in S10), then before each electric power storage device is charged the electric power storage devices charge/discharge therebetween (S20). A battery ECU calculates a voltage-current characteristic of each electric power storage device, as based on each electric power storage device's voltage and current collected when the electric power storage devices charge/discharge therebetween (S30). Each electric power storage device's OCV is calculated as based on the calculated voltage-current characteristic (S40), and each electric power storage device's SOC is estimated from the calculated OCV (S50).