Battery Cell Voltage Correction During Equalization
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Solution Overview
Problem
Conventional methods for equalizing lithium-ion battery cells in series fail to accurately detect cell voltage due to variations in load and wiring resistance, leading to incomplete voltage correction during the equalization process.
Innovation Solution
A management device that measures wiring resistance and corrects cell voltage measurements by calculating voltage drops based on the measured current and stored resistance values, ensuring accurate voltage detection and correction regardless of discharge switch states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the discharge circuit is connected between two adjacent wirings for voltage measurement, then the equalizing process can be performed, but the cell voltage measurement accuracy deteriorates due to voltage drop from wiring resistance
Solution Approach 1:
The patent measures the wiring resistance in advance before the equalizing process begins. By obtaining the resistance value beforehand, the system can later calculate and compensate for the voltage drop during equalization, thereby maintaining measurement accuracy while enabling the equalizing process to proceed.
Solution Approach 2:
The patent implements a feedback mechanism where the measured wiring resistance is used to calculate the voltage drop during equalization. This calculated voltage drop is then fed back to correct the cell voltage measurement, forming a closed-loop system that compensates for the measurement error introduced by the discharge circuit connection.
2Area of stationary object
If the wiring length is increased to connect all cells, then the voltage measurement coverage is improved, but the voltage drop due to wiring resistance increases
Solution Approach 1:
The system performs preliminary measurement of the wiring resistance during the initial state before equalization begins. This advance measurement captures the total resistance of the wiring path, which is then used to compensate for voltage drops during subsequent equalization operations, allowing long wiring to be used without sacrificing accuracy.
Solution Approach 2:
The patent converts the harmful effect of wiring resistance (which causes voltage drop) into a usable parameter. By measuring the resistance in advance and using it to calculate compensation values, the system transforms the resistance from a source of error into a correction factor that improves measurement accuracy.
3Productivity
If the equalization current is increased to speed up the equalizing process, then the productivity is improved, but the voltage drop due to wiring resistance increases
Solution Approach 1:
The system uses feedback by continuously monitoring the equalization current and using the pre-measured wiring resistance to calculate the instantaneous voltage drop. This calculated drop is then used to correct the cell voltage measurement in real-time, allowing high current equalization to proceed without compromising measurement accuracy.
Solution Approach 2:
The patent changes the parameter being measured from the raw voltage reading to a corrected voltage value that accounts for the voltage drop. By applying the correction based on current and resistance parameters, the system maintains accurate cell voltage measurement even when operating at high equalization currents for faster processing.
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 enables high-accuracy detection and correction of cell voltages during the equalization process, accounting for variations in load and wiring resistance, thereby improving the overall accuracy of the voltage measurement and balancing process.
Implementation Method 1
the voltage measurement circuit measures the voltage between two adjacent wirings to measure the voltage of each cell
Implementation Method 2
the voltage of the cell during equalizing discharge appears to be reduced by an amount of voltage drop due to a wiring resistance from the voltage measurement circuit
Data Source
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AI summary
In order to detect a cell voltage with high accuracy during an equalizing process among a plurality of cells, during execution of the equalizing process among the plurality of cells (V1 to V3), controller (40) measures a value of a current flowing to a negative electrode of an nth cell through an nth discharge resistor, calculates an (n-1)th voltage drop value due to a wiring resistance value of an (n-1)th wiring and an nth voltage drop value due to a wiring resistance value of an nth wiring based on the measured current value, and the wiring resistance value of the (n-1)th wiring connected to a positive electrode of the nth cell and a wiring resistance value of the nth wiring connected to the negative electrode of the nth cell, the wiring resistance value of the (n-1)th wiring and the wiring resistance value of the nth wiring being measured in advance, and, based on the (n-1)th voltage drop value and the nth voltage drop value, corrects the voltage value of the nth cell, a voltage value of an (n-1)th cell, and a voltage value of an (n+1)th cell measured by voltage measurement circuit (32).