Induction Heating Resonant Circuit Noise Control
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Solution Overview
Problem
Induction heating devices with multiple resonant circuits produce interfering noise due to frequency beats when setting different heating powers, and existing methods for power control result in high switch-on and switch-off currents, leading to a broadband interference spectrum. Additionally, there is a need to determine the temperature of the cooking vessel base for precise heating control and automatic cooking functions.
Innovation Solution
A method that determines a parameter value of the resonant circuit, such as the period duration of its natural oscillation, dependent on the cooking vessel base temperature, using a radio-frequency square-wave voltage to supply heating power. The heating power setpoint is reduced after boiling point determination, and the parameter value is adjusted to a setpoint value for continued boiling, allowing for temperature-controlled heating and automatic power adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If frequency of excitation signal is varied to control heating power, then heating power is controlled effectively, but interfering noise is produced due to frequency beats between multiple resonant circuits
Solution Approach 1:
The patent applies pulse-width modulation (PWM) with periodic square-wave excitation signals at a constant frequency to control heating power. By varying the duty cycle (pulse width) rather than frequency, the method maintains constant excitation frequency across all resonant circuits, eliminating frequency beats and interfering noise while still achieving effective power control through periodic on-off cycling of the excitation signal
Solution Approach 2:
The patent changes the control parameter from frequency variation to pulse width (duty cycle) variation. By keeping the excitation frequency constant and only modifying the pulse width of the square-wave signal, the system achieves heating power control without producing frequency beats, thus resolving the noise issue while maintaining power adjustment capability
2Object-generated harmful factors
If pulse width of excitation signal is varied at constant frequency to avoid interference noise, then interfering noise is reduced, but high switch-on and switch-off currents are produced in semiconductor switches
Solution Approach 1:
The patent introduces a soft-start mechanism that gradually increases the pulse width from zero to the target duty cycle over a predetermined time period, rather than abruptly switching on at full power. This preliminary gradual activation prevents high inrush currents and switch-on transients in the semiconductor switches, while still using PWM for noise-free power control
Solution Approach 2:
The patent implements current limiting and gradual power ramp-up mechanisms that cushion the abrupt current spikes during switch-on and switch-off transitions. By controlling the rate of change of the excitation signal and implementing soft-start/soft-stop sequences, the system protects semiconductor switches from high transient currents while maintaining effective PWM-based power control
3Reliability
If heating power is continuously high to maintain boiling, then boiling is maintained, but energy is wasted and temperature control precision is reduced
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the heating state (boiling detection) and adjusts the pulse width of the excitation signal accordingly. When boiling is detected, the system reduces the duty cycle to maintain boiling at minimum energy consumption rather than applying continuous high power, thus achieving both reliable boiling maintenance and energy efficiency
Solution Approach 2:
The patent applies partial action by using pulse-width modulation to deliver heating power in controlled pulses rather than continuous full power. By adjusting the duty cycle to provide just enough heating energy to maintain boiling, the system avoids excessive energy consumption while still reliably maintaining the boiling state through periodic heating pulses
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 method enables efficient, noise-free heating with precise temperature control, reducing interference and maintaining optimal boiling stages by adjusting heating power based on the identified parameter values, ensuring consistent and efficient boiling processes.
Implementation Method 1
an alternating magnetic field is generated by means of an induction heating coil, the said alternating magnetic field inducing eddy currents in a cooking vessel which is to be heated and has a base which is composed of ferromagnetic material, and creating remagnetization losses, as a result of which the cooking vessel is heated
Implementation Method 2
inducing eddy currents in a cooking vessel
Implementation Method 3
creating remagnetization losses
Implementation Method 4
The induction heating coil is a constituent part of a resonant circuit which comprises the induction heating coil and one or more capacitors
Implementation Method 5
a low-frequency mains AC voltage with a mains frequency of, for example, 50 Hz or 60 Hz is first rectified and then converted into an excitation or drive signal with a higher frequency by means of semiconductor switches
Data Source
AI summary
A method for heating a liquid in a cooking vessel is provided. According to various aspects, an induction heating device includes a resonant circuit having an induction heating coil. A parameter value of the resonant circuit may be determined, depending on a temperature of the cooking vessel. A radio-frequency square-wave voltage may be applied at a predefined heating power setpoint value to the resonant circuit to supply heating power to the cooking vessel. The time profile of the parameter value may be evaluated for determining the boiling point of the liquid. After the boiling point has been determined, the heating power setpoint value may be reduced by a predefined amount over a predefined time period after which a current parameter value may be determined and stored. The parameter value may be adjusted to a setpoint value which is dependent on the stored parameter value.