Variable Dead Time Control for High-Frequency Inverter Thermal Loss
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Solution Overview
Problem
Conventional high frequency heating apparatuses for microwave ovens suffer from excessive thermal loss and noise generation in semiconductor switching elements, leading to energy wastage and reduced service life, especially at high switching frequencies.
Innovation Solution
A high frequency heating apparatus with a variable dead time preparation circuit that adjusts the dead time period based on switching frequency, preventing simultaneous turn-on of semiconductor switching elements and minimizing thermal loss and noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed dead time is used in the inverter circuit, then the circuit structure is simple, but thermal loss and noise increase at high switching frequencies
Solution Approach 1:
The patent applies dynamics by making the dead time variable rather than fixed. The dead time is dynamically adjusted based on the switching frequency - it is extended when switching frequency increases and reduced when switching frequency decreases. This dynamic adaptation prevents simultaneous turn-on of switching elements at high frequencies, thereby reducing thermal loss and noise while maintaining circuit functionality.
Solution Approach 2:
The patent changes the parameter of dead time from a constant value to a variable value that depends on switching frequency. By monitoring the switching frequency and adjusting the dead time parameter accordingly, the circuit optimizes its performance across different operating conditions, reducing thermal loss at high frequencies while maintaining simplicity at lower frequencies.
2Device complexity
If a fixed dead time is used in the inverter circuit, then the control system is simple, but noise generation increases at high switching frequencies
Solution Approach 1:
The control system dynamically adjusts the dead time based on detected switching frequency. When the switching frequency increases, the dead time is automatically extended to prevent simultaneous turn-on of switching elements, which would generate noise. This dynamic control adapts the system to varying operating conditions without requiring complex overhead.
Solution Approach 2:
The patent implements feedback by detecting the switching frequency and using this information to adjust the dead time. The control system continuously monitors the switching frequency and provides feedback to the dead time generation circuit, which then adjusts the dead time accordingly. This feedback mechanism effectively reduces noise generation at high switching frequencies while maintaining simple control architecture.
3Productivity
If switching frequency is increased to improve productivity, then cooking speed increases, but thermal loss in switching elements increases
Solution Approach 1:
The patent enables the dead time to dynamically adapt to the switching frequency. When productivity requirements demand higher switching frequencies, the dead time is automatically extended to prevent simultaneous turn-on of switching elements, thereby controlling thermal loss. This allows the system to operate at high frequencies for improved cooking speed while managing the thermal loss through adaptive dead time adjustment.
Solution Approach 2:
The system changes the dead time parameter in response to switching frequency changes. At higher switching frequencies required for faster cooking, the dead time parameter is increased to prevent overlapping conduction of switching elements, thus controlling thermal loss. This parameter adaptation allows high productivity operation without excessive energy loss.
4Productivity
If switching frequency is increased to improve productivity, then cooking speed increases, but service life of switching elements decreases
Solution Approach 1:
The patent makes the dead time dynamic to protect switching elements during high-frequency operation. When switching frequency increases to improve cooking speed, the extended dead time prevents simultaneous turn-on of switching elements, avoiding excessive current stress and thermal loading. This protective mechanism maintains the service life of switching elements even during high-productivity operation.
Solution Approach 2:
The patent applies beforehand cushioning by pre-extending the dead time before simultaneous turn-on can occur. When high switching frequency is detected, the dead time is increased in advance to create a protective buffer that prevents harmful overlapping conduction of switching elements. This prior cushioning protects the switching elements from stress that would reduce their service life.
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
The solution effectively reduces thermal loss and noise in semiconductor switching elements, conserving energy and extending the service life of these components by optimizing dead time according to switching frequency.
Implementation Method 1
a leakage transformer 2, a first capacitor 4, a second capacitor 5
Implementation Method 2
a magnetron 11... the magnetron to generate electromagnetic waves
Implementation Method 3
inductance L and capacitance C jointly form a resonance circuit, which generates resonant characteristics having the peak resonant frequency f0
Implementation Method 4
two switching elements consisting of an arm of the bridge... a first semiconductor switching element 6, a second semiconductor switching element 7
Data Source
AI summary
A resonance type high frequency heating apparatus comprising; a direct current power supply; a series connection circuit consisting of a pair of semiconductor switching elements connected in parallel to the direct current power supply; another series connection circuit having a primary coil of a leakage transformer and a capacitor connected to both ends of one of the pair of semiconductor switching elements; and a drive means for driving each of the pair of semiconductor switching elements; wherein a variable dead time preparation circuit is provided in the drive means, and the variable dead time preparation circuit enables dead time to remain constant at below a predetermined frequency and causes the dead time to increase sharply at a point above a predetermined frequency.