Self-Balancing Switching Control for Dual-Pack RESS Mode Transitions
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Solution Overview
Problem
In rechargeable energy storage systems (RESS) with dual battery packs, transitioning between series and parallel modes can lead to undesirable current spikes due to cell imbalances, which can negatively impact system performance.
Innovation Solution
The implementation of a controller-driven self-balancing switching control system that automatically balances the state of charge or pack voltage of the battery packs before mode transitions, using cell balancing circuits and semiconductor switches responsive to PWM signals, to prevent imbalances and ensure safe mode changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If series-to-parallel mode transition is executed without pre-balancing, then switching speed is improved, but current spikes occur due to cell imbalances
Solution Approach 1:
The system performs cell balancing operations before executing the series-to-parallel mode transition. The controller detects cell imbalances and activates balancing circuits to equalize cell voltages prior to switching, preventing current spikes during the transition while maintaining fast switching response.
Solution Approach 2:
The balancing circuits are activated in advance to counteract the potential harmful effect of current spikes. By pre-balancing the cell voltages before the mode transition, the system neutralizes the imbalance that would otherwise cause harmful current surges during switching.
2Reliability
If cell balancing operation is performed before mode transition, then RESS performance is improved, but transition time is increased
Solution Approach 1:
The system performs only the necessary balancing operations required to equalize cell voltages within acceptable thresholds before mode transition, rather than continuous full balancing. This partial action approach achieves sufficient balancing to prevent current spikes while minimizing the time added to the transition process.
Solution Approach 2:
Cell balancing is performed in advance during periods when mode transition is anticipated but not yet executed. The controller monitors cell imbalances and initiates balancing operations during idle periods or when the system is in a stable state, so that when the transition is finally commanded, the balancing is already complete or near-complete.
3Device complexity
If cell imbalances are not addressed, then system complexity is reduced, but harmful effects increase
Solution Approach 1:
The system incorporates automatic cell balancing functionality that operates autonomously based on controller detection of voltage imbalances. The balancing circuits are integrated into the existing RESS architecture, allowing the system to self-correct cell imbalances without requiring additional complex external equipment or manual intervention.
Solution Approach 2:
The controller continuously monitors cell voltages and provides feedback to determine when balancing operations are required. Based on the detected voltage differences between cells, the controller automatically activates or deactivates balancing circuits, creating a closed-loop system that maintains cell balance while minimizing unnecessary balancing operations that would increase complexity.
Data Source
AI summary
An electrical system includes a rechargeable energy storage system (RESS) and a controller. The RESS includes first and second battery packs connected to a voltage bus, each pack having a respective plurality of battery cells and a corresponding cell balancing circuit. The RESS further includes switches that selectively connect or disconnect the packs to or from each other to achieve series and parallel modes. The controller executes a method by detecting a requested series to parallel mode transition. Responsive to a threshold imbalance being present in a state of charge or pack voltage of the packs relative to each other, the controller balances the state of charge/voltage using open/closed state control of the cell balancing circuits, and possibly a switching block having PWM-controlled switches and a circuit element. The controller may execute the requested mode transition upon balancing.