Battery Brick SOC Balancing in Series-Parallel Power Modules
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Solution Overview
Problem
Existing battery management systems face challenges in achieving uniform state-of-charge (SOC) balancing across series and parallel connected battery power modules, leading to uneven health degradation and reduced overall system efficiency.
Innovation Solution
The proposed solution involves a battery management system (BMS) that modulates battery cell current by using a network of battery bricks and power modules. Each brick consists of multiple parallel battery power modules, and the bricks are connected in series. The BMS derives a balancing current for each module based on its current SOC and a desired SOC, ensuring hierarchical SOC balancing across the entire battery pack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional battery management systems use series and parallel connected battery cells to increase capacity and voltage, then the overall system capacity and voltage are improved, but non-uniform heat distribution and intrinsic cell mismatches cause unequal state-of-health degradation among cells
Solution Approach 1:
The battery pack is divided into multiple independent battery power modules (BPMs), where each module contains its own DC-DC converter and control circuitry. This segmentation allows individual control of each module's charging and discharging current, enabling the system to compensate for cell mismatches and achieve more uniform state-of-health across all cells while maintaining high capacity through parallel connections.
Solution Approach 2:
Each battery power module is equipped with local control capabilities through integrated DC-DC converters that can independently regulate current based on the specific state of health of its associated battery cells. This local quality approach allows tailored current distribution to address non-uniform heat distribution and cell mismatches, improving overall reliability while maintaining system capacity.
2Reliability
If battery packs employ balancing circuits to control cells' SOCs, then state-of-charge balancing is achieved, but system complexity and cost increase
Solution Approach 1:
The DC-DC converters in each battery power module serve multiple functions: they enable independent current control for state-of-charge balancing, provide overcharge protection, facilitate modular expansion, and allow for flexible system configuration. This multi-functionality achieves SOC balancing without requiring separate dedicated balancing circuits, thereby reducing overall system complexity.
Solution Approach 2:
Each battery power module is equipped with integrated control circuitry that autonomously monitors its own battery cell's state-of-charge and automatically adjusts its charging and discharging current accordingly. This self-service capability eliminates the need for complex centralized balancing circuits, as each module independently maintains its SOC within desired ranges through its own control mechanisms.
3Adaptability or versatility
If modular battery architecture with multiple bricks and power modules is used, then system modularity and paralleling capabilities are improved, but control system complexity increases
Solution Approach 1:
The battery system is segmented into hierarchical modules: battery bricks containing multiple battery power modules, with each BPM further divided into controllable units. This segmentation enables flexible system configuration and scaling while maintaining manageable control complexity through standardized interfaces and protocols at each hierarchical level.
Solution Approach 2:
The control system implements hierarchical feedback mechanisms where each battery power module monitors its own operational parameters and communicates with the central controller, which coordinates across all modules. This feedback structure enables the complex modular system to be controlled efficiently through distributed intelligence, reducing the burden on centralized control while maintaining system-wide coordination.
Data Source
AI summary
An apparatus includes a battery pack with N battery bricks, each with a DC output voltage. The output of each brick is connected in series providing a bus voltage. Each brick includes battery power modules (“BPMs”) connected in parallel and each connected to a battery cell. Each BPM charges/discharges the connected battery cell. Each brick has a battery brick controller that provides a control signal to each brick's BPMs. A control signal of a BPM is derived from a BPM error signal that includes a battery cell current of the battery cell of BPM subtracted from a summation of an average current signal, a local droop current and a balancing current. The balancing current is based on a current SOC of the battery cell connected to the BPM and a desired SOC for the battery cell connected to the BPM. A BMS derives the balancing current for the BPMs.