Battery Capacity Estimation via Open Circuit Voltage
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Solution Overview
Problem
Existing methods for determining the energy capacity of electrochemical batteries often require controlled current or deep discharge, which can be damaging and impractical for vehicles, especially hybrid and conventional automotive systems.
Innovation Solution
A method involving measuring initial and final open circuit voltages after resting the battery to establish equilibrium, followed by a controlled energy change and subsequent voltage measurement to calculate the available energy capacity without deep discharge or controlled current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If deep discharge cycling is used to determine battery capacity, then capacity measurement can be performed, but battery damage occurs and battery related functions are lost
Solution Approach 1:
The patent applies partial action by performing only a small controlled charge (e.g., 1-5% of battery capacity) instead of complete deep discharge cycles. This partial charging approach provides sufficient data for capacity estimation while avoiding the harmful effects of deep discharge that cause battery damage and loss of functions.
Solution Approach 2:
The method performs preliminary small charge steps before any significant discharge occurs. By first applying minor charge increments and measuring voltage responses, the system gathers necessary data for capacity calculation without subjecting the battery to damaging deep discharge conditions.
2Measurement precision
If controlled current charging is used to determine battery capacity, then capacity can be measured, but current control capability is required which is lacking in conventional vehicles
Solution Approach 1:
The method enables the battery system to self-diagnose its capacity using only standard voltage measurements that any vehicle can perform. By analyzing the natural voltage response to small charge inputs without requiring controlled current profiles, the system eliminates the need for complex current control hardware while achieving accurate capacity estimation.
Solution Approach 2:
The patent replaces the mechanical/electrical current control system with a purely electrical voltage measurement approach. Instead of using controlled current charging which requires complex control circuitry, the method uses simple voltage sampling during natural charging or discharge to infer capacity, substituting a complex control system with simpler measurement-based analysis.
3Measurement precision
If the battery is rested before voltage measurement to obtain diffusion equilibrium, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent applies partial action by using small incremental charge steps (1-5% of capacity) rather than requiring complete charge-discharge cycles. This approach achieves sufficient diffusion equilibrium for accurate measurement while dramatically reducing the time required compared to traditional methods that require full cycling or extended resting periods.
Solution Approach 2:
The method uses periodic small charge pulses followed by brief rest periods for voltage measurement. By repeating this cycle of small charge input and measurement multiple times, the system accumulates sufficient data for accurate capacity estimation while keeping each individual rest period short, thus reducing total measurement time.
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 accurately determines battery capacity with minimal risk of damage, as demonstrated by tests showing calculated capacities within a reasonable percentage error of actual discharge values, providing a reliable state of health assessment for batteries.
Implementation Method 1
resting the battery before each of the measuring the steps for the first open circuit voltage and the second open circuit voltage to obtain a diffusion equilibrium state in the battery
Data Source
Figure 1~2
AI summary
A method of determining the available energy of a battery provides for measuring first and second open circuit voltage of the battery with a change of energy level occurring therebetween. The two open circuit voltages are correlated to a state of charge level and the measured amount of change of energy is divided by the change of the state of charge.