Relay Control Unit Zero-Crossing Switching Delay Adjustment
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Solution Overview
Problem
Mechanical relays used in home appliances experience degradation due to plasmatic arcs when switching at random times relative to AC mains power, causing electromagnetic noise and reliability issues, which can be mitigated by precise control of the switching times at zero crossings of the AC voltage.
Innovation Solution
A method to determine and adjust the control delay of a relay's switching time to align with the zero crossing of the AC voltage, using a control signal that adjusts the coil current's temporal course and derivatives to accurately detect and synchronize the connect/disconnect instants, thereby reducing arc generation and relay degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the relay is switched on or off at random time instants, then the switching operation is simple and fast, but plasmatic arcs form between the relay contacts causing degradation of relay mechanics and electromagnetic emission noise
Solution Approach 1:
The control unit determines the control delay time in advance by measuring the time difference between the control signal edge and the actual contact switching moment. This preliminary determination allows the system to pre-calculate the optimal control time instant that will result in zero-crossing switching, preventing plasmatic arcs before they occur.
Solution Approach 2:
The system measures the actual switching moment of the relay contacts and compares it with the intended control time instant. This feedback mechanism allows the control unit to accurately determine the control delay and adjust future control signals to achieve precise zero-crossing synchronization, eliminating arc-related degradation.
2Reliability
If the relay switching time is advanced to align with zero crossing, then plasmatic arcs are avoided and relay reliability is improved, but the control system complexity increases due to the need to determine control delay
Solution Approach 1:
The control unit automatically determines its own control delay parameter by performing a single measurement sequence: applying a test control signal, measuring the actual contact switching moment, and calculating the time difference. This self-calibration eliminates the need for external adjustment or complex configuration, reducing overall system complexity while achieving precise zero-crossing control.
Solution Approach 2:
The system transforms the complex problem of precise timing control into a simple parameter determination task. By changing the control delay time parameter based on the measured time difference, the system achieves accurate zero-crossing synchronization through a single adjustable parameter rather than complex control logic.
3Device complexity
If the control delay is not accurately determined, then the control system remains simple, but the relay contacts are damaged by plasmatic arcs and contact material is evaporated and scattered
Solution Approach 1:
The system replaces mechanical trial-and-error adjustment with electronic measurement and calculation. By using electronic timers and microprocessors to precisely measure the control delay and calculate the optimal control time instant, the system achieves accurate zero-crossing control without complex mechanical adjustment mechanisms, preventing contact material damage.
Solution Approach 2:
The control unit performs preliminary determination of the control delay parameter before normal operation begins. This advance calculation of the optimal control time instant ensures that all subsequent switching operations occur at zero-crossing points, preventing plasmatic arcs and contact material evaporation from the outset.
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 effectively reduces relay degradation and electromagnetic noise by precisely controlling the switching times, enhancing the reliability of home appliances by minimizing arc duration and frequency during switch-on and switch-off events.
Implementation Method 1
the coil current creating a magnetic field which attracts the movable anchor
Implementation Method 2
the zero crossing time instant of the AC voltage which is applied to the load ports of the relay
Data Source
Figure 1~2a
Figure 2b~3a
Figure 3b
AI summary
A method (800) for controlling a relay (1) is described, wherein the relay (1) comprises a movable anchor (3) and a coil (2) which is configured to exert a force onto the anchor (3) subject to a coil current (200) at a control port (4), in order to connect contacts (5) of the relay (1). The method (800) comprises applying (801), at a control time instant (331), a control signal to the control port (4) for initiating a switch-off event or a switch-on event of the relay (1); wherein the control time instant (331) depends on a previously determined control delay (340) of the relay (1). Furthermore, the method (800) comprises determining (802) a temporal course (202) of the coil current (200) subject to the control signal. In addition, the method (800) comprises detecting (803) a disconnect time instant (333), at which the contacts (5) of the relay (1) disconnect, or a connect time instant (312), at which the contacts (5) of the relay (1) connect, based on a derivative (321, 302) of the temporal course (202) of the coil current (200). The method (800) further comprises updating (804) the control delay (340) based on the detected disconnect time instant (333) or based on the detected connect time instant (312).