Magnetron Power Control via Switching Frequency Modulation
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Solution Overview
Problem
Conventional high-frequency heating devices face challenges in preventing excessive voltage application to the magnetron and secondary side rectifier circuit during startup, leading to unstable oscillation and potential component damage, especially due to the high sharpness of the resonance circuit.
Innovation Solution
A power control apparatus is introduced that includes an input current detection section, input voltage detection section, resonance voltage comparison section, and a magnetron oscillation detection section, which generate switching frequency control signals to stabilize the oscillation of the magnetron, preventing excessive voltage and reducing the time to stable oscillation by modulating the switching frequency based on resonance voltage and power control information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resonance circuit has high sharpness to improve voltage control precision, then voltage regulation accuracy is improved, but the time to reach stable oscillation increases and excessive voltage may damage components
Solution Approach 1:
The patent dynamically adjusts the switching frequency of the inverter based on the oscillation state of the magnetron. During startup, the frequency is adjusted to prevent excessive voltage. Once stable oscillation is detected, the frequency is optimized for efficient operation. This dynamic adjustment resolves the contradiction by adapting the system behavior to different operational phases.
Solution Approach 2:
The patent employs feedback mechanisms where the oscillation state of the magnetron is detected and used to control the switching frequency. The detection section monitors the magnetron's oscillation, and this information feeds back to the control section which adjusts the inverter's switching frequency accordingly, preventing excessive voltage during startup while maintaining efficiency during stable operation.
2Adaptability or versatility
If the switching frequency is lowered near resonance frequency to increase voltage boost ratio, then the width of usable phase range is improved, but excessive voltage may be applied to the magnetron and rectifier circuit
Solution Approach 1:
The patent applies preliminary action by detecting the magnetron's oscillation state before excessive voltage can occur. The detection section monitors startup conditions, and the control section preemptively adjusts the switching frequency to prevent voltage spikes before they can damage components, rather than reacting after damage occurs.
Solution Approach 2:
The system dynamically changes the switching frequency based on real-time detection of magnetron oscillation. During startup, the frequency is controlled to prevent excessive voltage. After stable oscillation is achieved, the frequency is adjusted to maximize the usable phase range and voltage boost ratio, thus resolving the contradiction between adaptability and reliability.
3Ease of manufacture
If a two-transistor bridge arm structure is used to reduce transistor withstand voltage requirements, then apparatus cost is reduced, but voltage control during startup becomes more challenging
Solution Approach 1:
The patent introduces a detection section and control section as intermediary components between the power source and the magnetron. These intermediaries monitor the oscillation state and adjust the switching frequency accordingly, enabling simple two-transistor bridge arms to achieve sophisticated voltage control without requiring expensive high-withstand-voltage transistors.
Solution Approach 2:
The patent changes the operating parameter (switching frequency) of the two-transistor bridge arm inverter based on magnetron oscillation detection. By dynamically adjusting the frequency parameter, the system compensates for the simpler transistor structure, achieving effective voltage control during startup and stable operation without increasing component cost.
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 prevents excessive voltage application to the magnetron and secondary side rectifier circuit, reducing the time to stable oscillation and eliminating the influence of high resonance circuit sharpness, thereby enhancing the reliability and efficiency of high-frequency dielectric heating.
Implementation Method 1
a resonance circuit which is connected to the series circuit and includes a primary winding of a leakage transformer and a condenser, the primary winding and the condenser being series-connected
Implementation Method 2
a rectifier circuit connected to a secondary winding of the leakage transformer and configured to supply high voltage to a magnetron
Implementation Method 3
at least one or more of a series circuit which has at least two semiconductor switching devices and to which the DC power source is input
Implementation Method 4
a DC power supply circuit configured to generate a DC power source produced by rectifying a voltage of an AC power source
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
In order to prevent an excessive voltage from being applied to a magnetron and a rectifier circuit on a secondary side of a leakage transformer and reduce a required time until the start of oscillation of the magnetron, a power control apparatus for high-frequency dielectric heating of the present invention is equipped with a magnetron oscillation detection section for setting magnetron oscillation detection information to be true after a predetermined time has elapsed since the start of the oscillation of the magnetron was detected; and has a configuration in which control is switched, depending on the magnetron oscillation detection information, between a voltage control in which an applied voltage to the magnetron is controlled and a power control in which the input current of an inverter power supply circuit is controlled, and in which the minimum frequency of a switching frequency is switched between a first frequency and a second frequency higher than the first frequency.