Microwave oven circuit, control method and control device of microwave oven circuit and microwave oven
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Solution Overview
Problem
Existing microwave oven circuits face challenges with high voltage damage to rectifier bridge stacks and IGBTs due to abnormal voltage spikes during startup, leading to increased maintenance rates.
Innovation Solution
A control method that detects the zero crossing point of the electric supply signal to power on the inverter circuit, delays the power signal input for a predetermined time, and adjusts the frequency to match the magnetron current, reducing reverse voltage across the rectifier bridge stack and preventing overvoltage damage to the IGBT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the microwave relay is turned on immediately without zero crossing detection, then the startup response is faster, but the voltage across the rectifier bridge stack becomes excessively high (up to 1000V) which damages the bridge stack
Solution Approach 1:
The control device detects the zero crossing point of the electric supply signal before turning on the microwave relay. This preliminary detection ensures that the relay is activated at the optimal moment in the AC cycle, preventing excessive voltage spikes across the rectifier bridge stack while maintaining fast startup response
2Speed
If the power signal is input immediately when the relay is turned on, then the power delivery is faster, but the reverse voltage damages the rectifier bridge stack and overvoltage damages the IGBT
Solution Approach 1:
The control device delays the input of the power signal until after the microwave relay has been turned on at the zero crossing point. This timing sequence ensures that the power signal is delivered promptly while avoiding the generation of harmful reverse voltage and overvoltage conditions
Solution Approach 2:
By controlling the timing of power signal input relative to relay activation, the system preemptively prevents the formation of excessive reverse voltage across the rectifier bridge stack and overvoltage at the IGBT, eliminating the harmful effects before they can occur
3Power
If the IGBT switching frequency is increased to improve power delivery, then the power output is higher, but the G pole voltage exceeds 25V which damages the IGBT
Solution Approach 1:
The control device prevents overvoltage damage to the IGBT by ensuring proper timing of the power signal input relative to the relay activation. This preemptive timing control keeps the G pole voltage within the safe 25V limit while maintaining effective power delivery to the magnetron
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 solution effectively reduces the voltage across the rectifier bridge stack and prevents damage to the IGBT, improving the reliability and extending the service life of these components by ensuring stable power initialization and operation.
Implementation Method 1
when the inverter circuit needs to be started, detecting a zero crossing point of an electric supply signal for supplying power to the microwave oven circuit
Implementation Method 2
the inverter drives a magnetron to generate microwaves according to the received signal
Implementation Method 3
after being rectified by a rectifier bridge stack 1'
Implementation Method 4
electric supply flows through a filter circuit 2' consisting of an inductor L1' and a capacitor C1'
Implementation Method 5
electric supply flows through a filter circuit 2' consisting of an inductor L1' and a capacitor C1'
Implementation Method 6
resonant network consisting of a resonant capacitor 3' and a high frequency step-up transformer 4'
Implementation Method 7
D2'
Data Source
Figure 1~3
Figure 4
Figure 5~6
AI summary
The present invention provides a microwave oven circuit, a control method and a control device of the microwave oven circuit, and a microwave oven. The microwave oven circuit includes a magnetron and an inverter circuit for driving the magnetron to work. The control method includes: when an inverter circuit (22) needs to be started, detecting a zero crossing point of an electric supply signal for supplying power to the microwave oven circuit, when an electric supply signal is detected to reach the zero crossing point, controlling the inverter circuit (22) to be powered on, and when a power-on time length of the inverter circuit (22) reaches a first predetermined time length. The control method further includes inputting a first power signal with a frequency lower than a target frequency to the inverter circuit (22), detecting the current in the magnetron (21), and when the current in the magnetron (21) reaches a predetermined current value, inputting a second power signal with a frequency equal to the target frequency to the inverter circuit (22).