Calibrating Passive Balancing Load Resistors in Battery Systems
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Solution Overview
Problem
Existing methods for determining the balancing charge in passive battery balancing systems are inaccurate due to tolerance in load resistors, making precise charge determination challenging without high-precision equipment or re-measurement of resistance values.
Innovation Solution
A method to calibrate the load resistor values in passive balancing systems by measuring the voltage profile and discharge time, allowing for precise determination of the charge transferred during balancing, which can be done in the field without specialized equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive balancing is used with standard load resistors, then cost is reduced, but measurement precision of balancing charge deteriorates due to resistor tolerance
Solution Approach 1:
The patent applies preliminary action by performing a calibration measurement before actual balancing operations. A known test charge is supplied to the cell, and the resulting voltage change is measured to calculate the actual resistance value of the load resistor. This pre-determined resistance value is then stored and used for accurate balancing charge calculations during normal operation, eliminating the need for expensive high-precision resistors.
2Measurement precision
If high-precision load resistors or re-measurement of resistance values is used, then measurement precision of balancing charge is improved, but cost increases
Solution Approach 1:
The system performs self-calibration by using its own components (voltage sensor, current sensor, and cell) to determine the actual resistance value of the load resistor. A test charge is supplied through the load resistor, and the resulting voltage and current measurements allow the system to calculate and store the precise resistance value without requiring external calibration equipment or high-precision resistors.
3Measurement precision
If laboratory-grade equipment is used for calibration, then measurement precision is improved, but device complexity and ease of operation worsen due to specialized equipment requirements
Solution Approach 1:
The calibration system uses the battery management system's existing sensors and circuitry to perform self-calibration. The voltage sensor and current sensor already present in the balancing circuit are utilized to measure the voltage change and current flow during a test charge operation, eliminating the need for external laboratory-grade measurement equipment.
Solution Approach 2:
The calibration procedure leverages the multi-functionality of the battery management system components. The same voltage sensor used for monitoring cell voltage during operation is used for calibration measurements, and the same current sensor used for balancing control is used for determining load resistor characteristics. This universal use of components simplifies the overall system and reduces calibration complexity.
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
Enables accurate determination of the balancing charge, facilitating better diagnosis of internal issues like soft short circuits and extending the battery system's service life without the need for laboratory-grade equipment or frequent workshops.
Implementation Method 1
discharge circuit having a load resistor Ri... actuation of the discharge circuit of the cell unit i for a discharge time ti... determination of Ri
Data Source
AI summary
A method is provided for calibrating a passive balancing system in a battery system which has a plurality of lithium ion cells and a battery management system, in which cell units consisting of individual cells or parallel-connected groups of a plurality of cells are each provided with a discharge circuit having a load resistance Ri representing the calibration parameter, and the cell units are serially connected in series. The battery management system is designed to measure the voltage Ui of each cell unit and to actuate the discharge circuit at a selectable time in order to discharge the cell unit in a controlled manner via the load resistance Ri. The method includes actuating the discharge circuit of the cell unit for a discharge time ti in order to remove a charge Qi, and determining ti, Qi and the voltage characteristic over time Ui(t); and determining Ri.