Shared Inverter Pan Detection in Induction Cooktops Without Relay Wear
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Solution Overview
Problem
Existing induction cooktops with shared Half-Bridge inverters face challenges in pan detection due to the need for periodic activation of relays, leading to mechanical wear, electrical contact issues, and electromagnetic noise, as well as increased complexity and cost.
Innovation Solution
The induction cooktop employs a shared high frequency switching converter that performs periodic pan detection using resonant circuits, eliminating the need for auxiliary detection circuits and temporary relay activation, thereby reducing mechanical and electrical wear, and minimizing electromagnetic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sharing relays are periodically activated for pan detection, then pan detection functionality is achieved, but mechanical wear and electromagnetic noise increase
Solution Approach 1:
The patent replaces the mechanical relay switching system with an electronic control approach. The half-bridge inverter is controlled to operate in a high-frequency switching mode where the switches are modulated to enable pan detection through impedance sensing without requiring physical relay activation. This electronic substitution eliminates mechanical wear and reduces electromagnetic noise associated with relay switching.
Solution Approach 2:
The patent implements periodic pan detection by modulating the half-bridge inverter switches at a high frequency (e.g., 20-100 kHz). The switches are turned on and off periodically to excite the resonant circuit formed by the coil and capacitor, allowing impedance measurement for pan detection. This high-frequency periodic action enables continuous monitoring without the drawbacks of low-frequency relay switching.
2Reliability
If auxiliary detection circuits are added for pan detection, then pan detection capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the half-bridge inverter perform multiple functions: power delivery to the induction coil and pan detection. By controlling the switches in different modulation modes, the same circuit hardware enables both cooking operation and impedance-based pan detection. This eliminates the need for separate auxiliary detection circuits and reduces overall device complexity.
Solution Approach 2:
The patent merges the power delivery function and detection function into a single integrated circuit system. The half-bridge inverter, resonant capacitor, and control unit work together to provide both cooking power and pan detection capability. The detection is performed by sensing the impedance changes in the resonant circuit during normal operation, combining multiple functions into one unified system.
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 seamless pan detection across all induction heaters regardless of main switch states, reducing wear and tear, electromagnetic noise, and providing smoother power delivery with lower flicker emissions.
Implementation Method 1
a resonant capacitor assembly distinct from the converter switches and operable to form a resonant circuit with said induction heater
Implementation Method 2
a switching converter coupled to said resonant capacitor assembly and to said induction heater, said switching converter being shared by said induction heater and another induction heater
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An induction cooktop comprising: a first main switch (17) and a second main switch (18) configured to be operated by a control unit (15) to selectively connect a first induction heater (3) and a second induction heater (4), to a switching converter (16) for selectively energizing the first induction heater (3) and/or the second induction heater (4); wherein the control unit (15) is configured: to sense an electric parameter regarding the first induction heater (3) in a first resonant circuit (65), preferably a current through the first induction heater (3) or a voltage in a point of the first resonant circuit (65), when the first induction heater (3) is not fed from the switching converter (16) and a first auxiliary switch (30) closes the first resonant circuit (65) in such a way that the at least resonant capacitor assembly (60; 62) is connected to the first induction heater (3) by means of the first auxiliary switch (30) and a damped oscillation occurs between them; to sense an electric parameter regarding the second induction heater (4) in a second resonant circuit (65), preferably a current through the second induction heater (4) or a voltage in a point of the second resonant circuit (65), when the second induction heater (4) is not fed from the switching converter (16) and the second auxiliary switch (40) closes the second resonant circuit (66) in such a way that the at least resonant capacitor assembly (61; 62) is connected to the second induction heater (4) by means of the second auxiliary switch (40) and a damped oscillation occurs between them; to detect the presence of a pan on the cooktop (1) on the basis of the sensed electric parameter.