Power Amplifier Thermal Stress Mitigation via RF Power Cycling

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Solution Overview

Problem

Power amplifier electronics components used in RF cooking ovens experience unexpected failures due to thermal stresses, despite operating in what seems to be less challenging conditions, with connecting wires being the primary source of failures and initial solutions like increasing wire size causing resonant frequencies and increased thermal stress.

Innovation Solution

Implementing a thermal stress mitigation technique through power cycling between high and low powers, using a learning procedure to control RF energy application, and employing a DC biasing current to minimize temperature changes, along with strategies like power envelope control and delayed power transitions to reduce thermal stress on power amplifier electronics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If power amplifier electronics operate at high power continuously, then cooking efficiency is improved, but thermal stress on components increases causing failures

Engineering Contradiction:

Improvecooking efficiencyVSAvoidcomponent reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system implements periodic power cycling between high and low power states during operation. The control electronics deliberately cycle the power amplifier through different power levels rather than maintaining continuous high power, which reduces thermal stress on components while still achieving effective cooking through alternating heating phases.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system applies beforehand cushioning by implementing thermal stress mitigation techniques before component failures can occur. The control electronics monitor and manage power delivery to prevent excessive thermal accumulation, and the patent specifically addresses preventing thermal stress damage before it causes component failure.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If wire size is increased to reduce thermal stress, then component reliability improves, but resonant frequencies are introduced causing increased thermal stress

Engineering Contradiction:

Improveconnecting wire reliabilityVSAvoidresonant frequency thermal stress

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The system changes operational parameters by implementing power cycling that avoids sustained operation at resonant frequencies. The control electronics modulate the power delivery parameters to prevent the connecting wires from experiencing thermal stress conditions that would excite resonant frequencies, thereby solving the problem without requiring larger wires.

Inventive Principle:

Principle #35Parameter changes

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

The solution effectively reduces thermal stresses on power amplifier electronics, preventing component damage and ensuring the longevity of oven components, while maintaining cooking performance and efficiency.

Implementation Method 1

an RF heating system configured to provide RF energy into the cooking chamber using solid state electronic components. The solid state electronic components include power amplifier electronics and control electronics configured to control operation of the power amplifier electronics.

Methodology Applied

Scientific EffectRF energy generation: Electromagnetic Induction

Implementation Method 2

The control electronics may be configured to employ a thermal stress mitigation technique to control thermal stresses on the power amplifier electronics associated with the power cycling.

Methodology Applied

Scientific EffectThermal stress control: Thermal Expansion

Implementation Method 3

employing a DC biasing current to minimize temperature changes

Methodology Applied

Scientific EffectDC biasing: Joule Heating

Data Source

PatentUS11490472B2Power control solution for reducing thermal stress on an intermittently operable chipset controlling RF application for cooking

Publication Date: 2022.11.01 ILLINOIS TOOL WORKS INC

AI summary

Control electronics may control power amplifier electronics associated with application of RF energy generated using solid state electronic components. The power amplifier electronics may be configured to control application of RF energy in an oven according to a cooking recipe at least in part based on a learning procedure that generates a power cycling between high and low powers when the learning procedure is executed. The control electronics may include processing circuitry configured to employ a thermal stress mitigation technique to control thermal stresses on the power amplifier electronics associated with the power cycling.