Battery Pack Contactor Switching to Reduce Arc Wear
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Solution Overview
Problem
Contactors in energy storage systems experience significant wear due to electric arcs during the disconnection process, leading to premature failure and high replacement costs, as the existing technologies do not effectively manage the residue energy and inductance that cause these arcs.
Innovation Solution
A switching arrangement is introduced that includes an electric arc reducing circuitry associated with one contactor, which is configured to be opened last during disconnection, using a snubber circuit to accumulate residue energy and inductance, thereby reducing or preventing the formation of electric arcs and minimizing contactor wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contactors are used to connect and disconnect battery packs from the load, then the energy storage system can be controlled to power the load, but the contactors experience significant wear due to electric arcs during disconnection
Solution Approach 1:
A discharge contactor is introduced as an intermediary component between the battery packs and the load. This discharge contactor provides a dedicated path for residual current and inductance to dissipate safely, preventing electric arcs at the main power contactors. The discharge contactor acts as a mediator that handles the harmful disconnection process, protecting the main contactors from wear.
Solution Approach 2:
The system performs preliminary actions by opening the discharge contactor before opening the main power contactors during disconnection. This preliminary action ensures that the residual energy and inductance are already managed through the discharge path before the main contactors interrupt the primary current flow, preventing electric arcs at the critical power contactors.
2Adaptability or versatility
If multiple battery packs are parallelly connected to meet higher power requirements, then the system can adapt to power demands, but the complexity of managing disconnection sequences increases
Solution Approach 1:
The discharge contactor serves multiple functions: it provides a discharge path for residual current, manages inductance from electric machines, and protects all parallel-connected battery packs simultaneously. This universal component simplifies the overall system by providing a single solution that works for all battery packs regardless of their number or configuration.
Solution Approach 2:
The discharge management functionality is merged into a single dedicated circuit with the discharge contactor, rather than requiring individual discharge mechanisms for each battery pack. This consolidation reduces the overall complexity of the switching arrangement while maintaining the ability to handle multiple parallel battery packs.
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
The solution effectively reduces contactor wear by managing residue energy and inductance, extending the lifespan of contactors and reducing replacement costs by minimizing the formation of electric arcs during the disconnection process.
Implementation Method 1
the electric breakdown voltage will typically be exceeded when a contactor is opened under load since the air gap initially is zero. The resistivity of the resulting electric arc is low meaning that the electric arc will be sustained for a short time before it is interrupted. When a contactor is closed, on the other side, the electric breakdown voltage is typically exceeded just before the contactor reaches a fully closed state, resulting in a small electric arc. However, the electric wear originated by inductance can be much more severe than the wear from exceeding the electric breakdown voltage.
Implementation Method 2
Electric wear may e.g. origin from electric arcs in the air gap of a non-closed contactor. Electric arcs typically appear when the voltage over the air gap exceeds the breakdown voltage of air (3 kV/mm) or when an inductive circuit is broken since an inductor opposes a change of the current through it.
Data Source
AI summary
A switching arrangement for reducing contactor wear of an energy storage system having a plurality of battery packs arranged in parallel for powering a load. The switching arrangement includes a contactor for each battery pack. The contactors connect and disconnect the battery packs relative to the load by closing and opening, respectively, an electric arc reducing circuitry associated to one of the contactors. The switching arrangement is configured to electrically disconnect the battery packs from the load by means of the contactors such that the contactor being associated with the electric arc reducing circuitry is opened last.