Battery Cell Discharge Resistance Control for State of Charge Equalization

Solution Overview

Problem

Battery units in electric, hybrid, and plug-in hybrid vehicles face challenges in equalizing the state of charge across series-connected cells due to manufacturing tolerances and aging, leading to inefficiencies and potential defects, which existing methods do not adequately address.

Innovation Solution

A method that determines and adjusts the discharge resistance value during each discharge process, using a battery control unit to calculate and store the optimal resistance value, allowing for precise state of charge equalization and defect detection, while compensating for manufacturing and aging-induced variance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a discharge resistance is connected in parallel to equalize load states of battery cells, then the state of charge equalization is achieved, but the manufacturing tolerances and aging cause variance in resistance values leading to imprecise equalization

Engineering Contradiction:

Improvedischarge resistance value consistencyVSAvoidstate of charge equalization accuracy

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The system performs a preliminary determination of the actual discharge resistance value before using it for equalization. The control unit determines the resistance value by measuring voltage and current during an initial discharge process, then stores this determined value for subsequent equalization operations, ensuring accurate equalization despite manufacturing variations

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements feedback by continuously monitoring the discharge process parameters (voltage, current, time) and using this information to calculate and store the actual discharge resistance value. This feedback loop allows the system to compensate for resistance value variations and maintain precise equalization control

Inventive Principle:

Principle #23Feedback

2Reliability

If multiple discharge processes are performed to equalize battery cells, then state of charge equalization is achieved, but the number of discharge processes increases leading to extended time and reduced productivity

Engineering Contradiction:

Improvestate of charge equalization accuracyVSAvoidequalization process efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs a preliminary determination of the actual discharge resistance value before using it for equalization. The control unit determines the resistance value by measuring voltage and current during an initial discharge process, then stores this determined value for subsequent equalization operations, ensuring accurate equalization despite manufacturing variations

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the operational parameters by using the determined resistance value to calculate and adjust the discharge time duration. By incorporating the actual resistance value into the time calculation, the system achieves precise equalization in fewer discharge cycles, improving productivity while maintaining accuracy

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If fixed discharge resistance values are used for equalization, then device complexity is reduced, but the ability to compensate for aging and manufacturing variance is lost

Engineering Contradiction:

Improvecontrol system simplicityVSAvoidcompensation for resistance value variance

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The system performs self-characterization by automatically determining its own discharge resistance value during operation. The control unit measures voltage and current, calculates the resistance value, and stores it for future use, enabling the system to adapt to its actual characteristics without external calibration or complex pre-programming

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The system implements feedback by continuously monitoring the discharge process parameters (voltage, current, time) and using this information to calculate and store the actual discharge resistance value. This feedback loop allows the system to compensate for resistance value variations and maintain precise equalization control

Inventive Principle:

Principle #23Feedback

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 method enables precise discharging, reduces the number of discharge processes, extends vehicle range, lowers recharging costs, and allows for real-time diagnosis of defects in the battery unit.

Implementation Method 1

a discharge process of at least one battery cell is performed via a connectable discharge resistance

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS10355504B2Method for operating a battery unit

Publication Date: 2019.07.16 ROBERT BOSCH GMBH

AI summary

The invention relates to a method for operating a battery unit comprising at least two series-connected battery cells, wherein a discharge process of at least one battery cell is carried out via a connectable discharge resistor in order to equalize states of charge of the battery cells. According to the invention, the value of the discharge resistance is ascertained during the discharge process of the at least one battery cell, and the previously ascertained value of the discharge resistance is taken into account during a subsequent discharge process of the battery cell.