Second-Life EV Battery Pack Grouping for Balanced ESS Operation
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Solution Overview
Problem
Existing energy storage systems (ESS) are costly, and repurposing electric vehicle (EV) batteries for stationary storage can significantly reduce these costs, but integrating multiple EV batteries with varying states of health (SOH) efficiently remains a challenge.
Innovation Solution
An integrated battery energy storage system (ESS) that aggregates EV battery packs in series/parallel arrangements, using a battery pack controller (BPC) and smart combiner to manage and balance the batteries, ensuring efficient operation and safety within an environmentally controlled enclosure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple EV batteries with varying states of health are integrated into an energy storage system, then the system can reduce ESS costs and maximize yields, but the complexity of managing and balancing batteries with different voltages and capacities increases
Solution Approach 1:
The system segments batteries into different series strings based on their voltage characteristics and state of health. Each string is managed semi-independently, allowing the system to handle varying battery conditions without requiring complete system reconfiguration. This segmentation reduces the complexity of managing heterogeneous batteries while maintaining overall system efficiency.
Solution Approach 2:
The system dynamically reconfigures battery connections between series and parallel arrangements based on real-time voltage measurements and operational requirements. The controller adjusts which batteries are connected in series versus parallel to optimize energy storage efficiency while accommodating batteries with different states of health, thereby managing complexity through adaptive rather than static configuration.
2Power
If EV batteries are connected in series to achieve higher voltages, then the system can deliver higher power output, but the variability in individual battery voltages makes it difficult to maintain balanced operation
Solution Approach 1:
Before connecting batteries in series, the system performs preliminary voltage measurements and assessments to identify suitable battery combinations. The controller pre-determines which batteries should be grouped together in series strings based on their voltage characteristics, ensuring that batteries with compatible voltage ranges are paired together. This preliminary action prevents voltage imbalance issues before they occur during operation.
Solution Approach 2:
The system changes operational parameters by dynamically switching between series and parallel connections based on real-time battery voltage measurements. When voltage imbalance is detected in series connections, the controller reconfigures the battery arrangement, potentially switching to parallel connections or reassigning batteries to different strings, thereby maintaining operational balance while preserving power output capability.
3Productivity
If EV batteries with different capacities are used to maximize system utilization, then the system can accommodate more batteries and reduce costs, but the charge/discharge cycles become unbalanced across individual packs
Solution Approach 1:
The system applies different operational characteristics to different battery packs based on their individual capacity and state of health. Rather than treating all batteries uniformly, the controller assigns batteries to specific roles (e.g., primary charge/discharge, auxiliary support) based on their local qualities. This allows the system to maximize utilization of all batteries while accommodating their different capacities, as each battery operates within its optimal performance envelope.
Solution Approach 2:
The system maintains continuous useful action by keeping all batteries engaged in charge/discharge cycles through dynamic reconfiguration. When some batteries reach their charge or discharge limits, the controller seamlessly transitions the load to other batteries in the system, ensuring that useful action continues without interruption. This continuous engagement maximizes system utilization while distributing wear across all batteries, extending their collective usable lifetime.
Data Source
AI summary
An energy storage system and method employing second-life electric vehicle batteries. The system includes a plurality of electric vehicle battery packs; and a processor configured to: couple the plurality of electric vehicle battery packs in a series/parallel arrangement, the series/parallel arrangement including a plurality of series strings of electric vehicle battery packs, each of the plurality of series strings of electric vehicle battery packs includes at least two of the plurality of electric vehicle battery packs coupled in series, and the plurality of series strings are connected in parallel; and wherein the coupling of the plurality of electric vehicle battery packs includes one or more of connecting electric vehicle battery packs with lower voltages in series, connecting electric vehicle battery packs with higher voltages in series, connecting electric vehicle battery packs with majority voltages in series, and connecting electric vehicle battery packs within a programmed voltage connection window in parallel.