Zero-Crossing Relay Synchronization via Central Timing Controller
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Solution Overview
Problem
Existing systems face challenges in synchronizing relay switching times with zero-crossing of AC voltage to prevent inrush currents, which can damage relays and equipment, leading to reduced life expectancy and increased replacement costs.
Innovation Solution
A timing controller connected to the AC electric mains determines the zero-crossing and transmits a reference time to relay controllers via a network, allowing them to synchronize switching times without direct connection to the mains, thus avoiding inrush currents and reducing equipment and certification costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relay switching is performed without zero-crossing synchronization, then switching operation is simple and responsive, but inrush current damages relay contacts and reduces equipment life expectancy
Solution Approach 1:
The system performs preliminary detection of the zero-crossing point of the AC voltage waveform before executing the relay switching operation. By identifying the zero-crossing moment in advance and scheduling the switching action to occur at this specific timing, the patent prevents inrush current from damaging relay contacts while maintaining relatively simple control logic through predetermined switching timing.
Solution Approach 2:
The system continuously monitors the AC voltage waveform to detect zero-crossing events and uses this feedback information to synchronize relay switching operations. By implementing a feedback mechanism that tracks the phase of the AC voltage and triggers switching only when the voltage crosses zero, the patent ensures reliable relay operation without excessive complexity in the control system.
2Reliability
If each relay controller is directly connected to AC mains for zero-crossing detection, then switching synchronization is achieved, but additional equipment, connections, and wiring are required
Solution Approach 1:
The patent introduces a central timing controller as an intermediary device that is directly connected to the AC mains for zero-crossing detection. This timing controller then communicates the zero-crossing timing information to multiple relay controllers through a network, eliminating the need for each relay controller to have its own direct AC mains connection. This intermediary approach maintains switching synchronization accuracy while significantly reducing system wiring complexity and equipment requirements.
Solution Approach 2:
The timing controller serves as a universal resource that provides zero-crossing detection services to multiple relay controllers simultaneously. By implementing a multi-functional timing controller that can serve the entire system rather than requiring dedicated detection circuits in each relay controller, the patent reduces overall system complexity while maintaining reliable switching synchronization across all relays.
3Productivity
If relay switching occurs at peak voltage, then switching response is immediate, but high voltage stress and inrush current fuse relay contacts
Solution Approach 1:
The patent changes the timing parameter of the switching operation from peak voltage moment to zero-crossing moment of the AC waveform. By selecting a different point in the AC voltage cycle (zero-crossing instead of peak), the system maintains switching responsiveness while eliminating the harmful inrush current and voltage stress that would otherwise fuse relay contacts. This parameter change optimizes both reliability and safety.
Solution Approach 2:
The patent converts the typically undesirable zero-crossing moment (where voltage is momentarily zero and might seem unsuitable for switching) into a beneficial switching opportunity. By recognizing that switching at zero-crossing eliminates inrush current and contact damage, the patent transforms what could be seen as a disadvantage (zero voltage moment) into a significant advantage for relay protection and extended equipment life.
Data Source
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AI summary
Methods, devices, and systems for synchronizing switching times of relays to a zero-crossing are described herein. One device includes a memory, and a processor configured to execute executable instructions stored in the memory to receive phase information of an alternating-current (AC) electric mains, determine, from the phase information, a zero-crossing of the phase of the AC electric mains, determine a reference time based on the zero-crossing for a number of relays corresponding to a number of relay controllers, and transmit the reference time to the number of relay controllers.