NiMH Battery Charging End Criteria Using Voltage and Temperature Gradients
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Solution Overview
Problem
Calculating the state of charge for NiMH batteries in driverless transport vehicles is prone to errors due to the poor correlation between applied voltage and state of charge, leading to discrepancies between calculated and actual charge levels, necessitating a robust and reliable method for accurate battery charging.
Innovation Solution
A method involving the measurement of charging current, battery voltage, and temperature gradients during a charging process, with multiple end criteria based on these gradients to determine when the battery is fully charged, including phases with constant voltage and current, and terminating the process when specific criteria are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the state of charge is calculated using an ampere-hour meter by integrating the current flowing through the battery, then the state of charge can be determined, but errors accumulate in the long term leading to discrepancies between calculated and actual state of charge
Solution Approach 1:
The patent applies feedback by continuously monitoring multiple parameters (voltage, current, temperature) and using them to correct the state of charge calculation. The ampere-hour meter calculation is continuously adjusted based on real-time voltage and temperature measurements, creating a closed-loop system that prevents error accumulation and maintains long-term reliability.
Solution Approach 2:
The patent changes from relying solely on current integration to monitoring multiple parameters simultaneously (voltage, current, temperature). By incorporating voltage gradient and temperature gradient as additional parameters, the system compensates for the limitations of ampere-hour metering and improves both measurement precision and long-term reliability.
2Productivity
If the charging process is terminated based on a single end criterion, then the charging can be stopped quickly, but premature termination may occur leading to incomplete charging
Solution Approach 1:
The patent applies preliminary action by establishing multiple end criteria before the charging process begins. These criteria (voltage gradient threshold, temperature gradient threshold, absolute temperature threshold) are pre-defined based on battery characteristics, allowing the system to accurately determine charging completion without premature termination while maintaining efficient charging speed.
Solution Approach 2:
The patent uses multiple end criteria rather than a single criterion, which represents an excessive approach to ensure accurate charging completion. By requiring satisfaction of multiple criteria simultaneously, the system prevents premature termination while maintaining high productivity through optimized charging current control.
Data Source
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AI summary
The invention relates to a method for operating a battery, in particular in a driverless transport vehicle, the battery being charged starting from a starting time (T0); during the charging process at a number of measurement times a charging current (IL) flowing through the battery, a battery voltage (UB) applied to the battery and a battery temperature (TB) prevailing in the battery are measured; whereby an amount of charge (ΔQ) introduced into the battery from the charging current (IL) is calculated; a voltage gradient (GU) is calculated from the battery voltage (UB) and the amount of charge (ΔQ); a first end criterion is determined from a curve of the voltage gradient (GU); a temperature gradient (GT) is calculated from the battery temperature (TB) and the amount of charge (ΔQ); a second end criterion is determined from a curve of the temperature gradient (GT); a temperature increase (AT) is calculated from a curve of the battery temperature (TB); a third end criterion is determined if the temperature increase (AT) exceeds a threshold value; and the charging process is ended after at least one of the end criteria is present.