Battery Voltage Measurement Compensation in Multi-ADC BMS
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Solution Overview
Problem
Battery Management Systems (BMS) face challenges in accurately measuring battery voltages due to voltage drops across external resistances, leading to measurement errors, especially when batteries are bypassed or shorted, which affects the accuracy and safety of battery charging and discharging processes.
Innovation Solution
A digital processor is used to calculate and compensate for error voltages by converting analogue voltage differences into digital signals, applying formulas to adjust the measured-voltage output signals, and performing calibration routines to determine gain-correction and offset-correction voltages, thereby reducing measurement errors and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external resistances are used in battery connection terminals, then current protection and signal conditioning are improved, but voltage measurement accuracy deteriorates due to voltage drops across the resistances
Solution Approach 1:
The system performs preliminary actions by measuring the voltages across the external resistances (V1, V2, V3) before calculating the battery voltages. These preliminary measurements are then used to compute compensation values that are applied to correct the final voltage readings, thereby eliminating the measurement error caused by the voltage drops across the protection resistances.
Solution Approach 2:
The system implements feedback by continuously monitoring the voltage drops across the external resistances and using this information to adjust and compensate the measured battery voltages. The compensation mechanism uses the measured resistance voltages to calculate and subtract the erroneous voltage drops from the total measured voltages, ensuring accurate battery voltage readings despite the presence of protection resistances.
2Measurement precision
If analog compensation circuits are used, then voltage measurement accuracy is improved, but current consumption and die size increase
Solution Approach 1:
The system replaces the mechanical/analog compensation circuitry with digital signal processing. Instead of using physical analog components to compensate for voltage drops, the system uses digital calculations based on measured resistance voltages to compute and apply compensation factors to the battery voltage measurements. This digital approach achieves the same compensation effect while consuming less current and occupying smaller die area.
3Measurement precision
If multiple ADCs are used for each battery terminal, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system implements multi-functionality by using a single ADC to perform multiple measurement tasks. The same ADC is sequentially used to measure both the battery voltages and the resistance voltages, thereby eliminating the need for separate ADCs for each measurement function. This approach reduces device complexity and cost while maintaining the capability to accurately measure both battery and resistance voltages through time-multiplexed operation.
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
The solution achieves sub-500µV accuracy in battery voltage measurements, enhancing the reliability and safety of battery management systems by minimizing measurement errors and allowing for scalable implementation across different technologies.
Implementation Method 1
each ADC is configured to convert the difference between the analogue voltages at its first and the second ADC input terminals to a digital signal
Data Source
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AI summary
A battery management system comprising: a sequence of four or more battery connection terminals for connecting to a series of batteries; a resistance associated with each battery connection terminal; and a sequence of three or more ADCs. Each ADC is associated with a pair of the battery connection terminals and is configured to convert the difference between the analogue voltages at its first and the second ADC input terminals to a digital signal, and to provide that digital signal at its ADC output terminal. The battery management system also includes a digital processor that is configured to, for each ADC in the sequence: calculate an error voltage for the ADC based on: i) the digital signal for the preceding ADC in the sequence if there is one; and ii) the digital signal for the next ADC in the sequence if there is one; and provide a measured-voltage output signal by subtracting the error voltage from the digital signal for the ADC.