Induction Heating Resonant Circuit Boiling Point Detection
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Solution Overview
Problem
Induction heating devices with multiple resonant circuits can produce annoying noises due to beat frequencies when varying heating powers, and existing methods for adjusting heating power, such as frequency modulation or pulse width modulation, result in high switch-on and switch-off currents and interference spectra, making it difficult to accurately determine the boiling point of liquids, especially when cooking foodstuffs like rice in water.
Innovation Solution
A method that involves determining a parameter value of the resonant circuit, such as the period duration of natural resonant oscillations, to adjust heating power setpoints periodically, allowing for reliable detection of the boiling point by varying the heating power and monitoring changes in the parameter value, which enables precise temperature control and automatic cooking functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If frequency modulation is used to adjust heating power, then heating power can be adjusted, but beat frequencies occur causing annoying noises
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) to periodically switch the excitation signal on and off. Instead of continuously varying frequency, the system maintains a constant excitation frequency and adjusts the duty cycle of periodic pulses to control heating power, thereby avoiding beat frequencies while achieving power adjustment.
Solution Approach 2:
The patent changes the parameter being modulated from frequency to pulse width (duty cycle). By keeping the excitation frequency constant and varying only the pulse width of the rectangular voltage, the system achieves heating power adjustment without creating the frequency differences that cause beat frequencies and annoying noises.
2Power
If pulse width modulation is used to adjust heating power, then heating power can be adjusted, but high switch-on and switch-off currents occur producing interference spectra
Solution Approach 1:
The patent applies dynamics by gradually changing the pulse width rather than making abrupt transitions. The control device dynamically adjusts the duty cycle in a controlled manner, which reduces the magnitude of switch-on and switch-off currents compared to sudden full-power switching, thereby minimizing interference spectra while maintaining effective heating power control.
3Temperature
If conventional heating methods are used, then heating can be applied, but accurate determination of boiling point is difficult especially with foodstuffs
Solution Approach 1:
The patent implements feedback by continuously monitoring the period duration of natural resonant oscillations of the resonant circuit, which changes with temperature. The control device uses this feedback information to track temperature changes and accurately determine the boiling point, even when foodstuffs are present and convection patterns are altered, providing precise temperature control and detection.
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 allows for reliable temperature-controlled cooking, particularly in determining the boiling point of liquids, reducing noise and interference, and enabling efficient cooking processes like preparing rice by varying heating power setpoints and monitoring temperature changes, ensuring accurate detection and automation of cooking phases.
Implementation Method 1
a magnetic alternating field, which induces eddy currents in a cooking vessel which is to be heated and which has a bottom made of ferromagnetic material, is produced by means of an induction heating coil and causes losses due to reversal of magnetization, as a result of which the cooking vessel is heated
Implementation Method 2
induces eddy currents in a cooking vessel which is to be heated
Implementation Method 3
causes losses due to reversal of magnetization
Implementation Method 4
The induction heating coil in conjunction with the cookware to be heated forms an inductive and a resistive part of the resonant circuit
Data Source
AI summary
A method and apparatus for preparing foodstuffs cooked in a liquid in a cooking vessel is provided. According to various aspects, an induction heating device includes a resonant circuit with an induction heating coil. A parameter value of the resonant circuit may be determined, depending on a temperature of a bottom of the vessel. During a heating-up phase, a high-frequency rectangular voltage may be applied to the resonant circuit to supply heating power to the bottom of the vessel. A heating power setpoint may be periodically varied and may be set to a first value during a first interval of a period, and set to a second, smaller value during a remaining interval. A determination of a change in the parameter value within the period may be made, and an evaluation of the change in order to determine the boiling point of the liquid and end the heating-up phase.