Electric Range Resonant Inverter Control for Soft Switching
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Solution Overview
Problem
In induction heating cookers, single-ended resonant inverters face issues with hard switching at low output frequencies due to increased resonance voltage, leading to heat generation and stress on switching elements, despite efforts to minimize switching loss and noise.
Innovation Solution
A power conversion device for electric ranges that adjusts the delay time of the switching control signal based on the difference between the resonance frequency and the switching timing reference signal, using a comparator to generate a switching timing reference signal and a control unit to determine the delay time, thereby preventing hard switching and ensuring soft switching operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If single-ended resonant inverter is used to reduce switching loss and noise, then switching loss and switching noise are reduced, but voltage across switch becomes large leading to hard switching at low output frequencies
Solution Approach 1:
The patent applies dynamics by making the delay time variable rather than fixed. The control unit adjusts the delay time based on the output frequency to maintain soft switching conditions across different operating points. This dynamic adjustment resolves the contradiction by adapting the switching timing to prevent hard switching while preserving the low switching loss benefits of resonant operation.
Solution Approach 2:
The patent changes the parameter of delay time based on frequency conditions. By modifying the delay time parameter according to the output frequency, the system maintains soft switching at low frequencies while preserving efficient operation at higher frequencies, thus resolving the contradiction between switching loss reduction and switching element stress.
2Reliability
If delay time is increased to prevent hard switching, then soft switching is maintained, but output holding time is reduced
Solution Approach 1:
The patent uses dynamic adjustment of delay time based on frequency feedback. The control unit monitors the output frequency and adjusts the delay time accordingly, increasing it only when necessary to prevent hard switching. This dynamic approach maintains soft switching reliability while minimizing the impact on output holding time by applying delay adjustments only when frequency conditions require them.
Solution Approach 2:
The patent implements feedback by having the control unit monitor the output frequency and adjust the delay time based on the frequency difference. This feedback mechanism ensures that delay time is increased only when the frequency difference indicates a risk of hard switching, thereby maintaining soft switching operation while preserving output holding time under normal operating conditions.
3Device complexity
If fixed delay time is used for switching control, then control is simple, but hard switching occurs at low output frequencies
Solution Approach 1:
The patent transitions from a static delay time to a dynamic, frequency-dependent delay time. The control unit calculates the frequency difference and adjusts the delay time accordingly, adding complexity only to the extent necessary to prevent hard switching. This dynamic approach maintains reliability while keeping the control circuit relatively simple by using straightforward frequency comparison and delay adjustment logic.
Solution Approach 2:
The patent changes the delay time parameter based on the frequency difference calculated by the control unit. This parameter change approach allows the system to maintain simple control architecture while improving reliability by adapting the delay time to frequency conditions, avoiding hard switching without requiring complex control circuits.
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 prevents hard switching even at low output frequencies, secures output holding time, and reduces stress on switching elements, enabling a linear output design by adjusting the delay time according to the frequency difference.
Implementation Method 1
a working coil which is disposed under the plate and inductively heats the object to be heated by applying the rectified voltage by switching of the switching element
Implementation Method 2
The resonance tank has a structure in which a container and a working coil are represented in series with an equivalent inductance Lr and an equivalent resistance Req, and a resonance capacitor Cr is connected in parallel thereto
Data Source
AI summary
Disclosed are a power conversion device for an electric range, and a control method thereof. The control method according to one embodiment of the present invention comprises: receiving a user's selection of the number of outputs through an interface unit, and determining the resonance frequency from the number of outputs and an object to be heated; comparing a rectified voltage and the voltage at both ends of a switching element, and generating a switching timing reference signal; and determining a delay time according to the difference between the resonance frequency and the frequency of the switching timing reference signal, and outputting a switching control signal that turns on after the delay time has passed since the falling edge of the switching timing reference signal.