Distributed Converter Current Allocation for EV Battery Balance
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Solution Overview
Problem
Existing hybrid-electric and electric vehicle systems face inefficiencies in power distribution from high-voltage to low-voltage electrical buses, as they typically rely on a single power converter, which leads to suboptimal converter efficiency and potential battery cell imbalances due to unequal current distribution.
Innovation Solution
Implementing a system with multiple power converters electrically coupled to a traction battery, where a controller dynamically assigns current demand to ensure that only efficient converters operate above a threshold, while others remain at zero current, and redistributes based on battery cell state of charge and power capability to maintain balance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single power converter is used to transfer energy from high-voltage bus to low-voltage bus, then the system structure is simple, but the converter efficiency is suboptimal and battery cell imbalances occur
Solution Approach 1:
The single power converter is segmented into multiple parallel power converters, each capable of independent operation. This segmentation allows the system to distribute the total current demand across multiple converters, enabling each converter to operate at optimal current levels for maximum efficiency while maintaining the overall energy transfer function from high-voltage to low-voltage bus.
Solution Approach 2:
The system implements dynamic current distribution control where the controller continuously monitors and adjusts the current allocation to each power converter based on real-time efficiency metrics and battery cell states. This dynamic adjustment ensures that converters are actively engaged only when they can operate efficiently, adapting the system configuration to changing operational conditions.
2Stability of the object's composition
If current is distributed equally among all power converters, then the control is simple, but battery cell imbalances occur due to unequal current distribution
Solution Approach 1:
The controller implements feedback control by continuously monitoring the state of charge and health of individual battery cells, then using this information to dynamically adjust the current distribution among power converters. This closed-loop feedback mechanism ensures that current is directed through converters connected to cells that need charging or can accept current, preventing cell imbalances while maintaining sophisticated control.
Solution Approach 2:
The system applies local quality control by treating each battery cell and its associated power converter as a distinct unit with unique characteristics. Instead of uniform current distribution, the controller tailors the current allocation to the specific needs and capabilities of each cell-converter pair, optimizing both cell balance and overall system efficiency.
3Loss of energy
If power converters operate below threshold current, then more converters can be utilized, but converter efficiency falls below predetermined efficiency
Solution Approach 1:
The system maintains continuous useful action by ensuring that only power converters operating above the efficiency threshold current are actively engaged in energy transfer. The controller continuously monitors converter performance and dynamically adjusts the operational status of each converter, maintaining an optimal subset of active converters that collectively satisfy the total current demand while operating in their high-efficiency regions.
Data Source
AI summary
A vehicle includes a traction battery comprising a plurality of cells. The vehicle also includes a plurality of power converters each electrically coupled between a corresponding group of cells and an electrical bus. A controller is programmed to satisfy a current demand of the electrical bus by operating a subset of the power converters to each draw a current that exceeds a threshold corresponding to a power converter efficiency exceeding a predetermined efficiency. Power converters not assigned to the subset are operated at zero current.