Electric Motor Vehicle Battery Polarization Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Continuous discharging of secondary batteries leads to uneven concentration of charge carriers, causing polarization, which decreases the open circuit voltage (OCV) and limits battery output, increasing the chances of reaching a lower limit voltage.
Innovation Solution
A control method that calculates a first OCV assuming no polarization and a second OCV including voltage changes due to polarization, augmenting the electricity input limit value when the voltage difference is large to reduce polarization and prevent battery output limitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous discharging is performed to meet power demands, then productivity is improved, but polarization occurs causing voltage to decrease and reach lower limit voltage, limiting battery output
Solution Approach 1:
The control device performs preliminary action by calculating the voltage difference between first OCV (without polarization) and second OCV (with polarization) before discharging reaches the lower limit voltage. When the voltage difference exceeds a threshold indicating significant polarization, the device preemptively limits the discharging current to prevent voltage from reaching the lower limit, thus avoiding output limitation while maintaining productivity.
Solution Approach 2:
The control device implements feedback by continuously monitoring the voltage difference between first OCV and second OCV during discharging. This feedback mechanism detects polarization levels in real-time and adjusts the discharging current accordingly, maintaining battery output stability while maximizing discharging capacity.
2Power
If polarization is allowed to occur during discharging, then short-term power output is maintained, but voltage decreases making the battery more susceptible to reaching lower limit voltage and output limitation
Solution Approach 1:
The control device calculates the voltage difference between first OCV and second OCV in advance during discharging operations. When this difference exceeds a predetermined threshold indicating significant polarization, the device preemptively limits the discharging current to maintain voltage margin, preventing the battery voltage from reaching the lower limit and avoiding output limitation.
Solution Approach 2:
The control device continuously monitors the voltage difference between first OCV (calculated from SOC assuming no polarization) and second OCV (actual measured voltage including polarization effects). This real-time feedback enables dynamic adjustment of discharging current to maintain adequate voltage margin while preserving instantaneous power output capability.
3Reliability
If the electricity input limit value is kept low to protect the battery, then battery reliability is improved, but charging opportunities are reduced and polarization disappears slowly
Solution Approach 1:
The control device dynamically adjusts the electricity input limit value based on real-time polarization conditions. When the voltage difference between first OCV and second OCV is small (indicating low polarization), the device increases the input limit to maximize charging speed. When the voltage difference exceeds a threshold (indicating high polarization), the device reduces the input limit to protect the battery. This dynamic adjustment optimizes both battery protection and charging efficiency.
Solution Approach 2:
The control device changes the electricity input limit parameter based on the calculated voltage difference between first OCV and second OCV. By adjusting this parameter dynamically according to polarization levels, the system achieves both battery protection and rapid charging when conditions permit, resolving the contradiction between reliability and productivity.
Data Source
AI summary
Provided is an electric motor vehicle including a secondary battery, an electric motor, and a control device that controls an input to and an output from the secondary battery. Using an SOC of the secondary battery, the control device calculates a first OCV that is an OCV based on an assumption of absence of a change in voltage due to polarization. Using a voltage and a current of the secondary battery, the control device calculates a second OCV that is an OCV including a change in voltage due to polarization. When a voltage difference between the first OCV and the second OCV resulting from discharging of the secondary battery is large, the control device augments a limit value of electricity input into the secondary battery to be higher than a limit value when the voltage difference is small.