Relay Actuation Timing via Load Current Zero-Crossing Detection
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Solution Overview
Problem
Existing electrical systems that use relays to control power flow face inaccuracies in determining zero-crossing points for load current due to differences between voltage and current waveforms, and require additional components, increasing complexity and cost.
Innovation Solution
A relay control device that uses a current sense component, such as a transformer, resistor, or Hall effect sensor, to measure load current and synchronize a timer with the frequency of the input voltage, allowing precise control of relay actuation timing without separate voltage detection circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage detector is used to detect zero-crossing points, then relay actuation timing can be controlled, but measurement accuracy deteriorates due to waveform differences between voltage and current
Solution Approach 1:
A current transformer is introduced as an intermediary device to sense the load current and generate a proportional secondary current. This secondary current is then converted to a voltage signal that accurately represents the primary current waveform, including its zero-crossing points. This intermediary approach solves the problem of accurately detecting current zero-crossings without directly measuring the high-voltage current, thereby improving measurement accuracy while maintaining system reliability.
2Ease of operation
If separate voltage detection and current sensing circuitry are used, then relay actuation can be controlled, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into a single integrated circuit board. The current transformer, rectifier, filter capacitor, and microcontroller are all mounted on the same PCB, allowing the system to perform current sensing, signal conditioning, zero-crossing detection, and relay control in one unified device. This merging eliminates the need for separate voltage detection circuitry and reduces the overall system complexity while maintaining full relay control capability.
Solution Approach 2:
The current transformer and associated circuitry serve multiple functions: they sense the load current, generate a proportional signal for microcontroller processing, provide information for zero-crossing detection, and enable both leading and lagging power factor compensation. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby simplifying the overall device architecture.
3Measurement precision
If additional detection components are added, then measurement capability is improved, but manufacturing cost increases
Solution Approach 1:
The current transformer creates an accurate electrical copy of the primary current waveform in its secondary winding. This copied signal is a scaled-down version that faithfully reproduces the original current's magnitude variations and zero-crossing points. By working with this copied signal rather than the original high-voltage current, the system achieves precise measurement capability using lower-power, less expensive components, thereby reducing manufacturing costs.
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 solution reduces system complexity, improves accuracy in determining zero-crossing points, and eliminates the need for additional components, thereby enhancing the operational lifespan of relays and reducing costs.
Implementation Method 1
obtain measurements of a load current with a current sense transformer
Implementation Method 2
obtain measurements of a load current with a Hall effect sensor
Data Source
AI summary
In some aspects, a relay control device includes a processor and a timer. The processor is electrically connectable to a relay that controls current flow to a load device. The processor causes the relay to be actuated at a first point in time so that a current flows to the load device. The processor determines an actuation duration for the relay from a measurement of the load current that is obtained with a current sense component. The processor determines a frequency of an input voltage or current from the measured load current. The processor synchronizes the timer with this frequency and identifies a zero-crossing point for a second load current based on the synchronized timer. The processor subsequently causes the relay to be actuated at a time that is offset from the zero-crossing point by the actuation duration.