Contactor Wear Reduction in Battery Pack Switching
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Solution Overview
Problem
The premature failure of contactors in energy storage systems due to mechanical and electrical wear, leading to increased replacement costs and reduced system lifespan, is a significant issue in vehicles powered by rechargeable energy storage systems.
Innovation Solution
A method is introduced that creates a window of opportunity for equalization between battery packs by preventing contactors from opening during current transfer, measuring current transfer to determine when to open or close contactors, thereby reducing voltage differences and electrical wear, and optimizing the reconnection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If contactors are frequently opened and closed to connect and disconnect battery packs, then the flexibility and control of power distribution is improved, but mechanical and electrical wear increases leading to contactor failure
Solution Approach 1:
The system performs equalization of battery pack voltages before disconnecting contactors by maintaining them in a closed state during a predefined equalization period. This preliminary action ensures voltage balance is achieved prior to disconnection, preventing voltage differences that would cause harmful discharge currents and wear during subsequent reconnections.
2Stability of the object's composition
If battery packs are disconnected to enable equalization, then voltage balance between packs is improved, but contactor wear increases due to frequent switching
Solution Approach 1:
The contactors are maintained in a continuous closed state during the equalization period, allowing voltage balance to be achieved without interruption. This continuous operation eliminates the opening/closing cycles that cause wear, while still enabling equalization through controlled current flow between battery packs.
Solution Approach 2:
The contactors serve dual functions: they act as switching devices for connecting/disconnecting battery packs from the traction voltage bus, and simultaneously serve as closed circuits that enable equalization current flow between packs. This multi-functionality allows the same component to achieve both power distribution control and voltage equalization without requiring separate equalization switches.
3Device complexity
If voltage differences between battery packs are not equalized, then system operation is simpler, but excessive discharge currents occur during reconnection causing premature failure
Solution Approach 1:
The system automatically performs voltage equalization as a preliminary step before disconnection by keeping contactors closed during an equalization period. This preliminary equalization action prevents large voltage differences from developing, thereby avoiding excessive discharge currents and contactor damage during subsequent reconnections, without requiring complex manual intervention.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach extends the lifespan of the switching arrangement and contactors, improves start-up times, and ensures quicker, more reliable reconnection of battery packs, reducing excessive wear and potential failures.
Implementation Method 1
the contactors being configured to connect and disconnect the battery packs relative a traction voltage bus by closing and opening, respectively
Data Source
Figure 1
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Figure 3A~3B
AI summary
The present invention relates to a method for operating a switching arrangement (115) of a rechargeable energy storage system, RESS (130), the RESS comprising a plurality of parallelly arranged battery packs (131, 132, 133) and the switching arrangement comprising an associated contactor (141, 142, 143) for each battery pack, the contactors being configured to connect and disconnect the battery packs relative a traction voltage bus (135) by closing and opening, respectively, the traction voltage bus being connected to at least one load (110). The method comprises: - providing a window of opportunity (S10) in which no request for powering the load by the battery packs, and no request for charging the battery packs, are allowed to be implemented, - in the window of opportunity, preventing the contactors to open (S30) enabling equalization due to current transfer between the battery packs, - measuring the current transfer (S20, S40) between the battery packs, and in response to the measured current transfer, preventing the contactors to open (S30) and/or opening the contactors (S50).