Induction Heating Resonant Circuit Noise Suppression
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Solution Overview
Problem
Induction heating devices with multiple resonant circuits can produce annoying noises due to beat frequencies when different heating powers are set, and existing methods for adjusting heating power either result in high switch-on and switch-off currents or fail to accurately control temperature in cooking vessels.
Innovation Solution
A method that determines and stores a parameter value related to the natural-frequency resonant oscillation of the resonant circuit, dependent on the cooking vessel's temperature, and uses closed-loop regulation to control the heating power, allowing for precise energy supply based on user selection and cooking vessel type, thereby avoiding noise and ensuring accurate temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If frequency of excitation signal is varied to adjust heating power, then heating power emission is improved, but beat frequencies causing annoying noises occur in multiple resonant circuits
Solution Approach 1:
The patent applies pulse width modulation (PWM) to generate periodic excitation signals with variable duty cycles. By switching the excitation signal on and off periodically at the resonant frequency while varying the pulse width, the system adjusts heating power without changing frequency, thus avoiding beat frequencies and annoying noises in multiple resonant circuits.
Solution Approach 2:
The patent changes the parameter being modulated from frequency to pulse width (duty cycle). Instead of varying the excitation frequency to control power, the system maintains constant resonant frequency and adjusts the effective power by changing the pulse width of rectangular voltage signals, thereby eliminating beat frequency issues while achieving power control.
2Object-generated harmful factors
If pulse width modulation is used to adjust heating power at constant frequency, then beat frequencies are prevented, but high switch-on and switch-off currents occur in semiconductor switches
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitor banks before switching. The circuit includes capacitors connected in parallel with the induction heating coil that are charged to the DC link voltage before the switching transition. This pre-charging action reduces the inrush current during switch-on and limits the discharge current during switch-off, protecting semiconductor switches from high current spikes.
Solution Approach 2:
The patent provides beforehand cushioning by incorporating snubber circuits and pre-charged capacitor banks that cushion the high switch-on and switch-off currents. The capacitors act as energy buffers that are already charged and ready to supply or absorb energy during switching transitions, preventing dangerous current peaks in the semiconductor switches.
3Power
If effective value control by varying pulse width is used, then heating power is adjusted, but wide-bandwidth and energy-rich interference spectrum is produced
Solution Approach 1:
The patent introduces an intermediary resonant circuit between the semiconductor switches and the load. The resonant circuit, comprising the induction heating coil and capacitors, acts as a filter that confines the spectral content to a narrow bandwidth around the resonant frequency. This intermediary circuit transforms the wide-bandwidth switching signals into a narrow-bandwidth resonant oscillation, reducing electromagnetic interference.
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 effectively suppresses noise and allows for precise temperature control of cooking vessels by regulating the resonant circuit's parameter value, ensuring efficient energy supply and maintaining a stable temperature, even when different cooking vessels are used.
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 magnetisation, as a result of which the cooking vessel is heated
Implementation Method 2
a magnetic alternating field, which induces eddy currents in a cooking vessel which is to be heated
Implementation Method 3
a cooking vessel which is to be heated and which has a bottom made of ferromagnetic material
Implementation Method 4
causes losses due to reversal of magnetisation, as a result of which the cooking vessel is heated
Implementation Method 5
a parameter value of the resonant circuit is determined and stored. The parameter value may include a period duration of a natural-frequency resonant oscillation of the resonant circuit and may be dependent on a temperature of a bottom of the cooking vessel
Data Source
AI summary
A method for heating a cooking vessel utilizing an induction heating device is provided. According to various aspects, the induction heating device includes a resonant circuit with an induction heating coil. A specified amount of energy may be supplied to the cooking vessel with the induction heating device depending on a heating power level selected by a user and/or on a cooking vessel type selected by the user. A parameter value of the resonant circuit which is dependent on a temperature of the cooking vessel, in particular of the bottom of the cooking vessel, may be determined and stored. The parameter value may be regulated to a setpoint which is dependent on the stored parameter value.