Parallel Charging Path Switching for Voltage Drop Element Overheating
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Solution Overview
Problem
Large lithium ion secondary batteries face failures due to current concentration in voltage drop elements during charging, which can lead to overheating and failure, especially when multiple voltage drop elements are connected in parallel.
Innovation Solution
A charge control apparatus with multiple charging paths connected in parallel, each equipped with a voltage drop element and a switch, controlled by a unit that switches the paths during charging to prevent current concentration and manage temperature, using back-to-back connected FETs with parasitic diodes to distribute current and lower charge voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple voltage drop elements are connected in parallel to reduce current through one element, then the power loss and failure risk in individual elements is reduced, but current concentration in one element due to characteristic variations and temperature characteristics causes failure
Solution Approach 1:
The charging path is divided into multiple segments (first charging path and second charging path) with separate voltage drop elements (first diode and second diode). The control unit independently controls switches in each segment to distribute charging current across multiple paths, preventing current concentration in a single voltage drop element and thereby improving reliability.
Solution Approach 2:
The system dynamically switches between different charging paths based on real-time conditions. The control unit monitors the state of voltage drop elements and actively switches the charging path to bypass elements that have degraded or failed, ensuring continuous operation and preventing failure through dynamic current redistribution.
2Device complexity
If a single charging path with voltage drop element is used, then the circuit is simple, but current concentration causes overheating and failure of the voltage drop element
Solution Approach 1:
Multiple charging paths are merged into a single charging system with a unified control unit. The first charging path and second charging path are combined such that they share common components (energy storage device, control unit) while having separate voltage drop elements and switches, reducing overall complexity compared to completely independent systems while improving reliability.
3Productivity
If charging continues through a degraded voltage drop element, then charging is maintained, but the element temperature increases causing failure
Solution Approach 1:
The control unit continuously monitors the state of voltage drop elements and uses this feedback to make real-time switching decisions. When a voltage drop element shows signs of degradation or excessive temperature, the control unit detects this condition and switches the charging path to a healthy element, maintaining charging continuity while preventing thermal failure through closed-loop control.
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 configuration effectively suppresses failures in voltage drop elements by distributing current and managing temperature, ensuring safe charging of energy storage devices by preventing overheating and maintaining charge voltage within safe limits.
Implementation Method 1
using back-to-back connected FETs with parasitic diodes to distribute current and lower charge voltage
Implementation Method 2
A large lithium ion secondary battery such as a vehicle engine starting battery has a large charge/discharge current and a large power loss on the energization path
Data Source
AI summary
This charging control device 50 controls charging of electricity storage elements B1-B4 and is provided with: a plurality of charging paths 61A, 61B leading to the electricity storage elements and connected in parallel with each other; voltage drop elements 64A, 64B and switches 65A, 65B which are connected in series on the charging paths; and a control unit 100. The control unit 100 controls the switches 65A, 65B and thereby switches a charging path not to be energized among the plurality of charging paths 61A, 61B during charging.