Resistor Ladder Cell-Voltage Balancing Without High-Resolution ADCs
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Solution Overview
Problem
Current methods for balancing voltage in multicell batteries are costly and inefficient, often relying on high-resolution analog to digital converters (ADCs) that are expensive and prone to inaccuracies, which can lead to catastrophic failures, reduced battery capacity, and increased costs in applications like portable computer battery packs.
Innovation Solution
A system using a resistor ladder with voltage-controlled oscillators (VCOs) and digital level shifters to measure and balance battery cell voltages, allowing for accurate voltage balancing without the need for high-resolution ADCs, and incorporating a logic circuit for calibration and error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-resolution ADCs are used to measure battery cell voltages, then measurement precision is improved, but device cost and complexity increase significantly
Solution Approach 1:
The patent introduces a resistor ladder network as an intermediary component between the battery cells and the ADC. This resistor ladder divides the voltage range into manageable segments, allowing a lower-resolution ADC to achieve effective high-resolution measurements through the intermediary's voltage division functionality.
Solution Approach 2:
The voltage measurement range is segmented into multiple discrete levels using the resistor ladder network. Instead of requiring a single high-resolution ADC to measure the entire voltage range in one step, the system segments the measurement into multiple coarse steps that, when combined, achieve fine resolution equivalent to high-resolution ADCs.
2Measurement precision
If high-resolution ADCs are used to measure battery cell voltages, then measurement precision is improved, but the system becomes more prone to inaccuracies and failures
Solution Approach 1:
The resistor ladder network provides a buffered, stabilized voltage signal to the ADC, cushioning against voltage fluctuations and noise that could cause measurement inaccuracies. This intermediary structure protects the sensitive ADC from direct exposure to unstable battery voltage conditions.
Solution Approach 2:
The resistor ladder acts as a buffer intermediary between the battery cells and ADC, isolating the ADC from direct voltage variations and reducing the impact of noise, interference, and voltage spikes that could cause measurement errors or component failure.
3Device complexity
If passive discharge is used to balance high-voltage cells, then device complexity is reduced, but energy loss increases
Solution Approach 1:
The system continuously monitors battery cell voltages through the resistor ladder-ADC measurement system and provides feedback control for active balancing. When imbalance is detected, the control circuit actively redirects charge current to equalize cell voltages, preventing the need for energy-wasting passive discharge while maintaining system complexity at an acceptable level.
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 solution provides accurate and cost-effective voltage balancing, reducing the risk of battery failure and increasing the efficiency of battery management systems by using less expensive and more reliable components, while maintaining high accuracy in voltage measurement and balancing.
Implementation Method 1
voltage-controlled oscillators (VCOs) and digital level shifters to measure and balance battery cell voltages
Data Source
AI summary
A resistor ladder comprising identical resistors is disposed electrically in parallel with a multicell battery to calibrate voltage-controlled oscillators (VOCs) or analog-to-digital convertors (ADCs) for voltage balancing the battery cells in the multicell battery. Switches in a first state provide the voltage across each resistor as inputs to the VCOs or ADCs. The number of oscillations of the output signal of each VCO or ADC over a predetermined time period are compared to determine an offset error. Switches in a second state provide the voltage across each battery cell as inputs to the VCOs or ADCs. The battery cells with a higher relative voltage can be discharged until they are balanced. Some aspects describe temperature-adjusted and interpolated determinations of electrical quantities in the cells such as voltage and/or current.