Laundry Appliance Voltage Phase Detection for TRIAC Heating Control
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Solution Overview
Problem
Conventional electric clothes dryers lack fine-grained control over temperature due to the use of electromechanical relays, leading to unnecessary power consumption and potential damage to clothes, and the variability in line voltage phase complicates the use of TRIACs for precise control.
Innovation Solution
A system and method that detects the line voltage phase by sampling AC voltage using an ADC and a controller, allowing for precise control of TRIACs to modulate power to the heating elements based on predetermined timing signatures, ensuring safe and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If electromechanical relays are used to control heating elements, then the appliance can operate with simple control logic, but fine-grained temperature control is prevented leading to unnecessary power consumption
Solution Approach 1:
The patent replaces electromechanical relays with electronic TRIACs controlled by phase-angle firing. The microcontroller generates PWM signals to control TRIAC gate timing, enabling precise modulation of heating element power. This substitution of mechanical relay control with electronic phase-control achieves fine-grained temperature regulation while reducing power consumption through optimized heating cycles.
2Ease of operation
If TRIACs are used for precise power control, then fine-grained temperature control is achieved, but variability in line voltage phase complicates the control system
Solution Approach 1:
The patent implements preliminary detection of line voltage phase characteristics before TRIAC control operations. The system samples AC voltage waveforms during initial power-up or idle periods to determine phase relationships and timing signatures. This preliminary characterization stored in lookup tables enables the microcontroller to pre-calculate optimal TRIAC firing angles, eliminating the need for complex real-time phase detection during heating cycles and simplifying the control logic.
Solution Approach 2:
The patent introduces an intermediary layer of pre-computed timing signatures and lookup tables between the variable line voltage input and the TRIAC control output. The system measures line voltage phase characteristics and maps them to predetermined timing profiles that account for different voltage sources (208V, 240V, three-phase). This intermediary mapping table absorbs the complexity of voltage variability, allowing the TRIAC control logic to operate with simple, pre-determined timing parameters regardless of actual line conditions.
3Measurement precision
If phase detection is implemented for TRIAC control, then precise power modulation is achieved, but the system requires additional voltage sampling and analysis capabilities
Solution Approach 1:
The patent implements phase detection with higher resolution than strictly necessary for basic operation. The system samples AC voltage at multiple points across the waveform and performs comprehensive timing signature analysis that exceeds minimum requirements. This excessive measurement precision provides robust phase characterization that accounts for voltage variations, noise, and timing jitter, ensuring accurate TRIAC control under all operating conditions while using standard ADC capabilities.
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
Enables fine-grained control over heating in electric clothes dryers, reducing power consumption, preventing damage to clothes, and extending the life of heating elements by accurately determining zero-crossings for TRIAC switching, thus optimizing energy use and operational safety.
Implementation Method 1
an analog to digital converter (ADC) configured to sample an AC voltage from a first power line
Implementation Method 2
at least one electric heating element configured to produce heat
Data Source
AI summary
A laundry machine comprising: a drum; a motor to rotate the drum; electric heating element(s) configured to produce heat; an airflow path from the heating element(s) to the drum; an analog to digital converter (ADC) configured to sample an AC voltage from a first power line of a group of power lines connected to the machine; and a controller configured to: (a) trigger the ADC to sample an AC voltage from the first power line, (b) determine a timing of occurrence of a peak value of the sampled AC voltage from the first power line, (c) compare the timing of occurrence of the peak value to predetermined timing signatures, (d) choose one of the timing signatures based on the comparison, and (e) control power to the electric heating element based on the chosen timing signature. Methods of operating a laundry washing machine are also provided.