NiMH Battery Charging End Detection Using Voltage and Temperature Gradients
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Solution Overview
Problem
Calculating the current charge status of NiMH batteries in driverless transport vehicles is prone to errors due to poor correlation between voltage applied and charge status, leading to deviations between calculated and actual charge levels, making it difficult to determine when the battery is fully charged.
Innovation Solution
A method that measures charging current, battery voltage, and temperature at multiple times during a charging process, calculates voltage and temperature gradients, and uses end criteria based on these gradients to determine when the battery is fully charged, ensuring accurate and reliable charging termination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ampere-hour meter is used to calculate charge status by integrating current, then charge status can be calculated, but deviations between calculated and actual charge status occur over time
Solution Approach 1:
The patent uses multiple feedback mechanisms including voltage gradient feedback (comparing measured voltage gradients against expected gradients for full charge), temperature gradient feedback (monitoring temperature changes during charging), and ampere-hour meter feedback (integrating charging current). These feedback loops continuously adjust the charge status calculation and provide cross-validation to maintain accuracy over time.
Solution Approach 2:
The patent monitors changes in multiple parameters (voltage, temperature, current) and their gradients over time. By analyzing the rate of change of these parameters rather than static values, the system can detect the full charge state more accurately. The voltage gradient (dV/dt) and temperature gradient (dT/dt) serve as dynamic indicators that change as the battery approaches full charge.
2Productivity
If charging process is terminated based on single end criterion, then charging can be ended quickly, but premature termination may occur before battery is fully charged
Solution Approach 1:
The patent applies multiple end criteria beyond what a single criterion would provide. Instead of relying on one threshold, it uses a combination of voltage gradient threshold, temperature gradient threshold, and ampere-hour meter thresholds. This excessive action ensures that even if one criterion is met prematurely, the other criteria will prevent incorrect termination.
Solution Approach 2:
The system performs preliminary monitoring and evaluation of multiple parameters throughout the charging process. Before making the final termination decision, it has already collected and analyzed voltage, temperature, and current data across multiple time points, allowing it to predict the charge status and make an informed termination decision rather than relying on a single moment's data.
Data Source
AI summary
In a method for operating a battery, e.g., in a driverless transport vehicle, the battery is charged in a charging process starting from a start time; during the charging process at a number of measurement times a charging current flowing through the battery, a battery voltage applied to the battery and a battery temperature prevailing in the battery are measured; an amount of charge introduced into the battery is calculated from the charging current; a voltage gradient is calculated from the battery voltage and the amount of charge; a first end criterion is determined from a curve of the voltage gradient; a temperature gradient is calculated from the battery temperature and the amount of charge; a second end criterion is determined from a curve of the temperature gradient; a temperature increase is calculated from a curve of the battery temperature; a third end criterion is determined if the temperature increase exceeds a threshold value; and the charging process is ended after at least one of the end criteria is present.