Sequential Battery Pack Relay Control to Limit Inrush Current
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Solution Overview
Problem
Electric working machines with multiple battery packs connected in parallel are prone to internal relay damage due to inrush current when activated, particularly when voltage differences exist among the battery packs.
Innovation Solution
The electric working machine is configured to connect battery packs sequentially, using external relays to manage the connection process, ensuring that internal relays of subsequent battery packs are brought into a closed state only after the first pack is connected, thereby mitigating inrush current effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple battery packs are connected in parallel with internal relays concurrently closed, then the electric working machine can be activated, but the internal relays are subjected to inrush current and may be damaged
Solution Approach 1:
The patent applies preliminary action by closing the internal relay of the first battery pack before closing the internal relays of subsequent battery packs. This sequential approach prepares the electrical system in advance, allowing the first battery pack to be connected and stabilized before additional packs are introduced, thereby preventing inrush current damage while maintaining activation efficiency
Solution Approach 2:
The patent segments the battery pack connection process into distinct stages: first battery pack connection with internal relay closure, followed by subsequent battery pack connections. This segmentation divides the simultaneous activation process into sequential steps, isolating the inrush current effect to controlled transitions and protecting internal relays from damage
2Device complexity
If internal relays of all battery packs are closed concurrently, then the connection process is simple, but voltage differences cause higher inrush current and increased failure possibility
Solution Approach 1:
The controller is configured to close the internal relay of the first battery pack preliminarily before closing internal relays of subsequent packs. This preliminary action establishes a reference voltage state, allowing subsequent connections to occur with reduced voltage differential and minimized inrush current, thereby improving reliability without requiring complex external control circuitry
Solution Approach 2:
The patent introduces an intermediary control mechanism where the controller manages the sequential closing of internal relays based on battery pack identification. This intermediary control coordinates the timing of relay closure, ensuring that voltage differences are managed and inrush current is minimized while maintaining system reliability
Data Source
AI summary
An electric working machine includes an electric device, electric circuitry, battery packs to be connected sequentially to the electric device via the electric circuitry to parallelly connected, the battery packs including internal relay(s) to open/close an internal circuit, and a controller. The electric circuitry includes external relays corresponding to respective battery packs. The controller is configured or programmed to perform a first latter process wherein, while a first battery pack to be connected first to the electric device is in electrical connection with the electric device, the controller brings the internal relay(s) of a second battery pack to be connected second or later to the electric device into a closed state, and a second latter process wherein the controller brings, into the closed state, the external relay corresponding to the second battery pack where the internal relay(s) is in the closed state.