Battery Cell Efficiency Equalization for Simultaneous End-of-Charge

Solution Overview

Problem

Existing methods for charging and discharging energy storage devices with battery cells connected in series are inefficient as they require auxiliary currents and do not allow all cells to reach their end-of-charge voltage simultaneously, leading to uneven cell aging and reduced service life.

Innovation Solution

Adjusting the efficiency of all battery cells to the worst efficiency within the cell block, ensuring all cells experience the same losses, allowing them to reach their end-of-charge voltage simultaneously by using switchable resistors or DC-DC converters to equalize cell voltages and capacities, thereby eliminating the need for auxiliary currents and extending the service life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional charging methods are used where charge equalization begins only when at least one battery cell reaches end-of-charge voltage, then battery cell safety is maintained, but charging time increases significantly

Engineering Contradiction:

Improvebattery cell safetyVSAvoidcharging time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by determining the efficiency of each battery cell before the charging process begins and pre-calculating the energy extraction requirements. This allows the system to start charging all cells simultaneously with optimized currents from the beginning, rather than waiting until one cell reaches end-of-charge voltage to begin equalization. The control device pre-processes efficiency data and prepares extraction schedules, enabling faster charging while maintaining safety.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of charging current by determining individual maximum charging currents based on each cell's efficiency and capacity. Instead of using a uniform charging approach, the system adjusts charging parameters (current magnitude and duration) for each cell based on its specific efficiency characteristics. This allows simultaneous charging of all cells at optimized rates, reducing total charging time while preventing overcharge conditions.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If passive balancing is used to convert excess energy into heat via resistors, then charge equalization is achieved, but energy is lost and charging efficiency decreases

Engineering Contradiction:

Improvecharge equalizationVSAvoidcharging efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent converts the previously harmful excess energy (which would be wasted as heat in passive balancing) into a beneficial resource. By determining cell efficiencies and calculating precise extraction requirements, the system extracts excess energy from high-efficiency cells and redirects it to charge low-efficiency cells. This transforms waste energy into useful charging capacity, improving overall system efficiency while maintaining charge equalization.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The control device acts as an intermediary that manages energy flow between battery cells. Instead of directly dissipating excess energy through resistors, the control device mediates by extracting energy from high-efficiency cells and redistributing it to low-efficiency cells. This intermediary function enables efficient energy transfer and equalization without thermal losses.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If active balancing is used to transfer energy between cells, then charging efficiency improves, but charge equalization still begins only when one cell reaches end-of-charge voltage

Engineering Contradiction:

Improvecharging efficiencyVSAvoidcharging time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by determining the efficiency of each battery cell before the charging process begins and pre-calculating the energy extraction requirements. This allows the system to start charging all cells simultaneously with optimized currents from the beginning, rather than waiting until one cell reaches end-of-charge voltage to begin equalization. The control device pre-processes efficiency data and prepares extraction schedules, enabling faster charging while maintaining safety.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of charging current by determining individual maximum charging currents based on each cell's efficiency and capacity. Instead of using a uniform charging approach, the system adjusts charging parameters (current magnitude and duration) for each cell based on its specific efficiency characteristics. This allows simultaneous charging of all cells at optimized rates, reducing total charging time while preventing overcharge conditions.

Inventive Principle:

Principle #35Parameter changes

4Productivity

If different charging currents are applied to different battery cells based on efficiency, then simultaneous end-of-charge is achieved, but device complexity increases

Engineering Contradiction:

Improvecharging speedVSAvoidcontrol complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent applies local quality by determining and applying individual charging parameters for each battery cell based on its specific efficiency characteristics. Each cell receives a customized charging current and extraction schedule tailored to its performance characteristics. This localized approach enables simultaneous end-of-charge achievement while managing complexity through systematic individual cell assessment and control.

Inventive Principle:

Principle #3Local quality

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 approach allows all battery cells to reach their end-of-charge voltage simultaneously, reducing charging and discharging time, preventing overcharging or deep discharging, and eliminating the need for active or passive balancing, thus extending the service life and maintaining even cell state of charge.

Implementation Method 1

using switchable resistors or DC-DC converters to equalize cell voltages and capacities

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

using switchable resistors or DC-DC converters to equalize cell voltages and capacities

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentEP4052321B1Method for charging and/or discharging a rechargeable energy store

Publication Date: 2023.08.16 BENNING CMS TECH GMBH

Figure 1

AI summary

What is proposed is a method for charging and/or discharging an energy store (1) with a current Io, wherein the energy store (1) has at least one cell block (2) having a number J of series-connected battery cells (3, 4, 5, 6, 7), at least some of the battery cells (3, 4, 5, 6, 7) of which may have different efficiencies ηN, where 1 ≤ N ≤ J, having the following method steps: - determining the battery cell (3, 4, 5, 6, 7) having the poorest efficiency ηmin, - assimilating the efficiency ηN of all of the other battery cells (3, 4, 5, 6, 7) to this poorest efficiency ηmin such that the following applies to the assimilated efficiency ηN' of the battery cells: ηN' = ηmin.