Induction Heating Controller Duty Cycle Modulation

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Solution Overview

Problem

Existing induction heating systems face challenges in controlling power delivery to an inductor without continuously changing the frequency, which can lead to issues like pan detection and resonance, potentially causing failure in induction heating components.

Innovation Solution

The method involves using pulse-width modulation (PWM) to vary the duty cycle of the power transistor drive signals, maintaining a constant frequency and adjusting the duty cycle to control power and measure electrical parameters, thereby monitoring the cooking vessel's temperature without frequency changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the power transistor drive frequency is changed to control power delivery and measure temperature, then power control and temperature monitoring are achieved, but frequency-related issues such as pan detection and resonance occur, potentially causing system failure

Engineering Contradiction:

Improvetemperature monitoringVSAvoidsystem reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent segments the control process into distinct heating intervals and measurement intervals. During measurement intervals, the system uses a first duty cycle value to measure electrical parameters correlated to temperature, while during heating intervals, it uses a second duty cycle value to deliver power. This temporal segmentation allows temperature monitoring without the harmful effects of frequency changes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system implements periodic switching between measurement and heating modes using pulse-width modulation (PWM). By periodically varying the duty cycle within a fixed frequency framework rather than changing frequency itself, the system achieves both power control and temperature measurement while avoiding resonance and pan detection issues.

Inventive Principle:

Principle #19Periodic action

2Power

If the power transistor drive frequency is changed to adjust cooking temperature, then power control is improved, but the complexity of frequency selection and the risk of resonance increase

Engineering Contradiction:

Improvepower controlVSAvoidfrequency selection complexity

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

Instead of changing the frequency parameter, the patent changes the duty cycle parameter while maintaining a fixed frequency. The controller adjusts the duty cycle of power transistor drive signals to control the average power delivered to the induction heating element, thereby achieving power control without the complexity of frequency selection and resonance avoidance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical approach of frequency tuning with an electronic duty cycle modulation approach. By using PWM to vary the duty cycle at a fixed frequency, the system achieves the same power control objective without the mechanical complexity of frequency selection and the associated resonance risks.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If multiple frequencies are used for power control and temperature measurement, then cooking performance is improved, but the risk of pan detection and resonance increases

Engineering Contradiction:

Improvecooking performanceVSAvoidpan detection and resonance

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The system dynamically adjusts the duty cycle value based on the operational phase (heating or measurement) while maintaining a fixed frequency. This dynamic duty cycle control within a static frequency framework enables improved cooking performance through precise power modulation and temperature monitoring without introducing the harmful effects of multiple frequencies.

Inventive Principle:

Principle #15Dynamics

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 minimizes the risk of frequency-related issues, ensures consistent power delivery, and effectively monitors the cooking vessel's temperature, enhancing cooking performance and system reliability.

Implementation Method 1

controlling the power delivered by a static power conversion unit to an inductor, particularly for an induction heating system used in cooking appliance

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

induction heating system used in cooking appliance

Methodology Applied

Scientific EffectInduction heating: Induction Heating

Implementation Method 3

the control of power and the measurement of the induction converter electrical parameter are accomplished with a pulse-width modulation (PWM) methodology by varying the duty cycle of the power transistor drive signals

Methodology Applied

Scientific EffectPulse-width modulation:

Data Source

PatentEP2175690B1A method for controlling a static power conversion unit and induction heating system for cooking appliances using such method

Publication Date: 2017.03.08 WHIRLPOOL CORP

AI summary

In a method for controlling a static power conversion unit to an inductor, particularly for an induction system used in cooking appliances, the value of an electrical parameter of the circuit is monitored at predetermined time intervals (Δt1) and at a predetermined duty cycle of the power transistor switching frequency, and on the basis of said monitored value, the duty cycle is modulated accordingly between said predetermined time intervals in order to keep the delivered power at a predetermined constant value.