Spare-Cell Battery Balancing for Weak Cell Capacity Limits
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Solution Overview
Problem
Existing battery management systems (BMS) for EVs limit battery pack capacity due to inefficient cell balancing methods, where the weakest cell determines the overall capacity, leading to reduced performance and driving distance, as they downgrade other cells to match the weakest cell's state of charge, resulting in energy wastage and potential damage.
Innovation Solution
A battery pack system with a balancing cell that can be selectively switched into connection with underperforming cells during charging and discharging, using a cell monitoring and switch control unit to manage parameters like voltage and time, allowing the balancing cell to supplement underperforming cells, thereby maintaining equal state of charge across all cells without wasting energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive balancing is used to equalize state of charge by dissipating energy as heat through resistors, then cell voltage equality is achieved, but energy is wasted and heat is generated which harms the underperforming cell
Solution Approach 1:
A balancing cell is introduced as an intermediary component between the underperforming cell and ground. Instead of directly dissipating energy from the underperforming cell through resistors, the balancing cell acts as a mediator that temporarily stores excess charge from the underperforming cell and later transfers it to other cells that need charging, thereby eliminating energy waste and harmful heat generation while maintaining cell voltage equality
Solution Approach 2:
The patent recovers the energy that would otherwise be discarded as heat in passive balancing. The balancing cell captures the excess charge from the underperforming cell during charging phases and subsequently transfers this recovered energy to other cells during discharge or balancing phases, transforming a lossy process into an energy-efficient cyclic transfer mechanism
2Device complexity
If the battery pack capacity is determined by the weakest cell, then cell balancing is simplified, but the total capacity of the pack is reduced
Solution Approach 1:
The patent implements dynamic cell balancing where the balancing cell is selectively connected to different cells based on their individual charge states. Instead of a static approach where all cells are treated equally, the system dynamically identifies underperforming cells and applies balancing only where needed, allowing the battery pack to operate at its true total capacity rather than being limited by the weakest cell
Solution Approach 2:
The balancing operation is applied locally to specific underperforming cells rather than uniformly to all cells. The balancing cell is selectively switched into connection with only those cells that require balancing, leaving other cells unaffected and operating at their full capacity potential, thereby preserving overall pack capacity while maintaining simplicity
3Reliability
If charge is diverted from the underperforming cell to ground to allow other cells to fully charge, then cell voltage equality is maintained, but the underperforming cell is further degraded
Solution Approach 1:
The balancing cell serves as a protective intermediary that prevents direct charge diversion to ground from the underperforming cell. By inserting the balancing cell into the charge path, it intercepts excess charge and redirects it for later use, thereby maintaining cell voltage equality while protecting the underperforming cell from further degradation and extending its operational lifespan
Solution Approach 2:
The balancing cell provides beforehand cushioning by being pre-positioned to receive and store excess charge from the underperforming cell before it can cause harmful effects. This preventive mechanism cushions the underperforming cell against overcharging and thermal degradation, allowing it to maintain voltage equality without suffering additional damage
Data Source
AI summary
A battery and battery balancing system comprising a battery pack comprising two or more cells connected in series and a separate balancing cell, which is not series connected in the battery pack. The balancing cell is configured to be selectively switched into connection with one or more cells of the battery pack. A charging input is configured to accept a charging current from a power source to charge the battery pack. Two or more balancing cell switches, responsive to switch control signals, configured to selectively connect the balancing cell to a cell in the battery pack. A cell monitoring and switch control unit configured to monitor cell parameters during charging and generate the switch control signals, such that upon the monitoring determining that a cell in the battery pack is an underperforming cell, switching the balancing cell into connection with the underperforming cell to supplement the underperforming cell.