AC Power Source Switching Device Relay Control
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Solution Overview
Problem
Conventional power source switching devices require detection of zero current on feeder wires to disconnect relays, complicating the switching process and preventing reduction in switching duration between AC power sources, which can lead to apparatus failures due to arc discharge.
Innovation Solution
Incorporating a third relay and a welding detection unit to switch AC power sources while preventing the second relay from switching back on until the first relay's welding is detected, allowing parallel control of relays to reduce switching duration and prevent arc discharge failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the relay is disconnected after the current flowing on the feeder wire becomes zero to suppress arc discharge, then the reliability is improved, but the switching duration between AC power sources cannot be reduced and the device complexity increases due to zero current detection requirement
Solution Approach 1:
The patent applies preliminary action by switching the third relay (selecting the second AC power source) before disconnecting the first relay, rather than waiting for zero current detection. The control unit switches the third relay to the second AC power source side first, then disconnects the first relay, eliminating the need for complex zero current detection while ensuring safe switching by maintaining power supply continuity through the second AC power source.
2Reliability
If the relay is disconnected after the current flowing on the feeder wire becomes zero to suppress arc discharge, then the reliability is improved, but the switching duration between AC power sources is extended
Solution Approach 1:
The patent applies preliminary action by switching the third relay (selecting the second AC power source) before disconnecting the first relay, rather than waiting for zero current detection. The control unit switches the third relay to the second AC power source side first, then disconnects the first relay, eliminating the need for complex zero current detection while ensuring safe switching by maintaining power supply continuity through the second AC power source.
Solution Approach 2:
The third relay acts as an intermediary that bridges the transition between the first and second AC power sources. By introducing this intermediate switching element, the system can overlap the switching operations, allowing the third relay to select the second AC power source while the first relay is still connected, thereby reducing the overall switching duration without causing arc discharge issues.
3Productivity
If a third relay is added to switch between AC power sources to reduce switching duration, then the productivity is improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the switching function into two separate relays: the first relay for disconnecting the first AC power source and the third relay for selecting the second AC power source. This segmentation allows the switching operations to be performed in parallel or overlapping manner, improving switching speed. The control unit independently controls each relay based on switching signals, enabling faster transitions despite the increased number of components.
Data Source
AI summary
A third relay switches between an output of a first AC power source fed via a first relay and an output of a second AC power source fed via a second relay, and supplies the output after the switching to a load. A welding detection unit detects welding of the first relay. In order to switch the output of the first AC power source to the output of the second AC power source and supply the output of the second AC power source to the load, a power source switching control unit switches the first relay from the closed state to the open state, switches the third relay so as to select and feed the output of the second AC power source, and then prohibits switching of the second relay from the open state to the closed state until a first-relay welding detection processing by the welding detection unit is completed.