Battery Cell Balancing Resistor and Low Pass Filter
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Solution Overview
Problem
In electric and hybrid vehicles, the noisy operating environment makes it difficult to accurately measure and balance the voltage across battery cells, leading to potential catastrophic failures due to incomplete charge and discharge cycles and undetected electrical faults in the balancing circuit.
Innovation Solution
A battery cell balancing and measuring apparatus using low pass RC filters and switches to accurately measure cell voltages and provide a discharge path, with resistors serving dual roles in both filtering and discharging, allowing for independent cell discharge and fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage measurement is performed in noisy operating environments, then cell balancing can be achieved, but measurement accuracy deteriorates due to electrical noise
Solution Approach 1:
The patent applies preliminary action by performing voltage measurement only after completely discharging the balancing capacitor through the discharge switch and resistor before measuring. This ensures the capacitor does not interfere with the voltage measurement, eliminating measurement errors caused by residual charge while maintaining reliable cell balancing in noisy environments.
Solution Approach 2:
The patent introduces an intermediary measurement process where the discharge switch and resistor serve as mediators to completely discharge the capacitor before voltage measurement. This intermediary action isolates the measurement process from the noisy operating environment by ensuring the capacitor is in a known neutral state, thereby improving measurement precision while maintaining balancing reliability.
2Reliability
If discharge resistor is used for cell balancing, then cells can be discharged to match voltage, but electrical faults such as disconnected or burned out resistors may go undetected
Solution Approach 1:
The patent implements feedback by measuring the voltage across the discharge resistor through the discharge switch after capacitor discharge. This measurement provides feedback on the operational status of the discharge path components, enabling detection of faults such as disconnected or burned out resistors while maintaining the cell balancing function.
Solution Approach 2:
The patent applies self-service by using the existing discharge resistor and switch components to perform dual functions: cell balancing discharge and fault detection. The same discharge path that balances cells also enables fault detection through voltage measurement, eliminating the need for separate detection components and enabling the system to monitor its own health.
3Measurement precision
If capacitor is used for voltage measurement, then filtering can be provided, but the capacitor may retain charge and interfere with accurate measurement
Solution Approach 1:
The patent applies preliminary action by completely discharging the capacitor through the discharge switch and resistor before performing voltage measurement. This preliminary discharge action removes the interfering charge from the capacitor, ensuring accurate measurement while maintaining the filtering benefits during normal operation.
Solution Approach 2:
The patent implements periodic action by alternately switching between capacitor charging (for filtering during measurement) and discharging (for preparation before measurement). This periodic switching between states allows the capacitor to provide filtering when needed while being completely discharged before actual voltage measurement, resolving the conflict between filtering and measurement accuracy.
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 apparatus effectively filters out electrical noise, enabling accurate voltage measurement and independent cell discharge, while also facilitating fault detection, thus preventing catastrophic failures and ensuring optimal battery balance.
Implementation Method 1
Each resistor of the plurality of resistors provides a low pass filter path for the respective battery cell via the capacitor
Implementation Method 2
Each terminal pair having a capacitor and a switch coupled in parallel with each other, the capacitor and the switch coupled across respective terminal pair
Data Source
AI summary
A battery cell balancing and measuring apparatus is provided. The apparatus includes a plurality of terminals having a portion of the terminals grouped as terminal pairs, each terminal of the plurality of terminals operable to couple to a node in a battery stack. Each terminal pair having a capacitor and a switch coupled in parallel with each other, the capacitor and the switch coupled across respective terminal pair. The apparatus includes a plurality of resistors, each resistor of the plurality of resistors coupled to a terminal of the plurality of terminals. Each resistor of the plurality of resistors provides a discharge path for a respective battery cell coupled to a terminal pair via the switch and wherein each resistor of the plurality of resistors provides a low pass filter path for the respective battery cell via the capacitor.