Split EV Battery SOC Balancing Before Series-Parallel Charging
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Solution Overview
Problem
Electric vehicles with high-voltage battery systems face compatibility issues with charging stations that support lower voltages, leading to potential inrush current, energy waste, and overheating due to unbalanced state of charge (SOC) between split battery sectors when connected in series or parallel.
Innovation Solution
Implementing galvanically isolated bidirectional DC/DC converters to balance the SOC between split battery sectors, allowing them to be connected in series for high-voltage chargers and in parallel for lower-voltage chargers, using a multistage onboard charger architecture with power factor correction and controlled by busbars and contactors to manage sector connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If battery sectors are connected in series for high-voltage charging, then charging compatibility is improved, but unbalanced SOC causes inrush current and overheating
Solution Approach 1:
The DC/DC converter performs preliminary SOC balancing between battery sectors before they are connected in series for high-voltage charging. This advance action ensures that voltage differences are equalized beforehand, preventing inrush current and overheating that would otherwise occur during charging operations.
Solution Approach 2:
The DC/DC converter acts as an intermediary device between battery sectors to transfer energy and balance SOC levels. This mediator enables safe series connection by ensuring voltage compatibility, thus allowing high-voltage charging without the harmful effects of unbalanced sectors.
2Adaptability or versatility
If battery sectors are connected in parallel for lower-voltage charging, then charging flexibility is improved, but unbalanced SOC causes energy waste
Solution Approach 1:
The DC/DC converter performs preliminary SOC balancing before parallel connection for lower-voltage charging. By equalizing voltage levels in advance, the system prevents energy waste that would occur during charging operations with unbalanced sectors.
3Loss of energy
If bidirectional DC/DC converters are implemented for SOC balancing, then energy transfer efficiency is improved, but device complexity increases
Solution Approach 1:
The bidirectional DC/DC converter is designed to perform multiple functions: SOC balancing between sectors, energy transfer during charging operations, and voltage level adaptation. This multi-functionality improves energy transfer efficiency while the integrated design helps manage system 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
Ensures efficient energy transfer and prevents overheating by maintaining balanced voltage/SOC between battery sectors, ensuring compatibility with both high and legacy voltage charging systems, reducing energy waste and inrush current.
Implementation Method 1
a first bidirectional DC/DC converter, the first bidirectional DC/DC converter being galvanically isolated and coupled to the first sector; and a second bidirectional DC/DC converter, the second bidirectional DC/DC converter being galvanically isolated and coupled to the second sector
Data Source
AI summary
An electric vehicle comprises: a battery system split into first and second sectors substantially equal to each other; a first bidirectional DC/DC converter, the first bidirectional DC/DC converter being galvanically isolated and coupled to the first sector; and a second bidirectional DC/DC converter, the second bidirectional DC/DC converter being galvanically isolated and coupled to the second sector; wherein the first and second bidirectional DC/DC converters balance respective states of charge of the first and second sectors before the first and second sectors are connected in parallel.