Adaptive Relay Coil Switching for Contact Life Extension

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Solution Overview

Problem

Traditional relay systems experience degradation when switching high-current loads, leading to issues like fused or pitted contacts, especially under large voltage potentials, and existing solutions fail to accurately verify or maintain correct switching times, particularly in 3-phase systems without feedback.

Innovation Solution

The method involves an initial calibration to adjust relay coil switching times relative to zero crossings of the power supply, using feedback signals to adaptively adjust switching times to ensure relay contacts close near zero-cross +/−1 ms for operation and open 1-2 ms before zero-cross for release, employing a modified line-straddling algorithm to maintain optimal switching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If relay switching is performed without precise timing control, then the relay can operate high-current loads, but the relay contacts experience degradation such as fusing or pitting

Engineering Contradiction:

Improverelay contact lifeVSAvoidcontact degradation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary calibration to determine the actual relay operate and release times, then uses these measured values to pre-calculate optimal switching times that occur +/−1 ms of zero-cross. This preliminary characterization of relay timing behavior enables subsequent switching operations to be timed precisely, preventing contact degradation from switching at high voltage potentials

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system measures the actual pulse width of the AC signal and uses this feedback to adaptively adjust the switching times. By continuously monitoring the relationship between zero-cross detection and actual relay contact closure/release, the system can maintain optimal switching timing even as conditions change, ensuring reliable operation and extended contact life

Inventive Principle:

Principle #23Feedback

2Measurement precision

If traditional zero-cross switching is used, then switching occurs at zero voltage, but existing solutions fail to accurately verify or maintain correct switching times

Engineering Contradiction:

Improveswitching time accuracyVSAvoidswitching time verification

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system replaces simple zero-cross detection with a digital signal processing approach that measures actual AC signal characteristics and calculates optimal switching times based on measured relay performance. This substitution of mechanical/timing-based switching with digitally-controlled switching based on actual measurements enables precise verification and maintenance of switching times

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Manufacturing precision

If relay switching timing is not adapted to actual AC signal characteristics, then the control system is simple, but switching accuracy deteriorates

Engineering Contradiction:

Improveswitching time precisionVSAvoidcalibration and control system

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The system performs self-calibration by automatically measuring its own relay operate and release times, then using these measured values to calculate optimal switching times. This self-characterization eliminates the need for external calibration equipment or complex setup procedures, achieving high switching precision while keeping the control system relatively simple

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The system dynamically adjusts switching time parameters based on measured AC signal characteristics and relay performance. By changing the switching time parameter from a fixed value to an adaptively-calculated value based on actual measurements, the system achieves high precision switching while the added complexity is limited to simple measurement and calculation operations

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9679728B2Methods, apparatus and articles of manufacture to regulate relay coil switching

Publication Date: 2017.06.13 WHIRLPOOL CORP

AI summary

Methods, apparatus, and articles of manufacture to regulate relay coil switching are disclosed. A disclosed example method of regulating switching times of a relay having a pair of contacts to selectively and electrically couple an analog alternating current (AC) power source and a load includes forming a digital pulse train representative of an AC signal at the load, determining a first value corresponding to a representative pulse width of the digital pulse train, providing a first relay switching signal to the relay at a first time relative to a zero crossing of the AC signal, selecting a second time for providing a second relay switching signal to the relay based the first value and a second value representative of the width of a first pulse of the digital pulse train associated with the first relay switching signal at the first time, and providing the second relay switching signal to the relay at the second time.