JPS62140390A - Inverter source control for magnetron - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling an inverter power supply for a magnetron.

Conventional technology Inverter power supplies for magnetrons connect a resonant capacitor in parallel with the primary windings of the isolation transformers 2 and 7, connect a power switching element in series with the parallel resonant circuit, and apply a DC voltage. QN, Q of power switching element
A high-voltage, high-frequency voltage is generated by the FF and the parallel resonant circuit, stepped up by the isolation transformer, applied between the anode and cathode of the magnetron, and then stepped down and connected to the heater of the magnetron. When the inverter power supply and magnetron start operating, a surge current of 1.6 to 2 times the steady state flows through the power switching element due to a transient phenomenon, and the higher the high frequency output of the magnetron, the more
Since the current surge is also large, a soft start method has been adopted in which when the inverter power supply starts operating, it operates at a low power high frequency output for several seconds and then shifts to the set high frequency output.

However, if the set high-frequency output after soft start is very small and the magnetron is cold (for example, below the rated output μ), there is a problem that the magnetron will not oscillate. Ta.

In order to solve the second problem, the present invention steps up the high frequency voltage obtained by an inverter and applies it between the anode and cathode of the magnetron. At the start of operation of the magnetron inverter power supply that applies a high frequency voltage to the heater of the magnetron, the magnetron oscillates with a low power high frequency output for several seconds, then oscillates with a high power high frequency output for less than 1°, and then It is characterized by shifting the high frequency output to an arbitrary setting power from low power to high power.

In the working magnetron, current flows through the filament through the tertiary winding of the isolation transformer, and when the filament emits enough thermoelectrons to cause the magnetron to oscillate, high voltage is applied between the anode and cathode by the secondary winding, causing oscillation. begins. By the way, the high frequency filter consisting of a choke coil and feedthrough capacitor connected to the magnetron's heater circuit has the magnetron's oscillation frequency of 2460M[]Z
The impedance is negligible at commercial frequencies.

However, with respect to the high frequency of the inverter power source, inductance cannot be ignored not only in the coil of the high frequency filter but also in the wiring of the heater circuit, and the apparent resistance increases due to the skin effect. However, there is an inverse relationship between the high frequency output and the switching frequency, and the switching frequency is high during the soft start period. Therefore, the filament current is difficult to flow and heat? Ij.

The amount of offspring released is also limited. Therefore, after a soft start, once the frequency is lowered and the high frequency output is started, the second filament current is passed sufficiently to cause complete oscillation, and then the power is reduced.The filament is warmed up and a sufficient number of thermionic electrons are supplied, and the oscillation continues. It will be done.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In FIG. 2, the primary winding &! of an isolation transformer 6 consisting of primary, secondary, and tertiary windings. 6P is connected in parallel with a resonant coil 5 conductor 2, a power switching element 3 is connected in series with the primary winding 6P, a flywheel diode 4 is connected in parallel with the power switching element 3,
A primary circuit is constructed by connecting the DC power supply 1 to both ends of a circuit in which the primary winding 6P and the power switching element 3 are connected in series.

A magnetron 6 is connected in parallel to the secondary winding 5S, and the anode side is grounded to form a secondary circuit, and a tertiary winding 6t and the heater of the magnetron 6 are connected to form a tertiary circuit. be.

When the inverter power supply and the magnetron 6 start operating, a transient phenomenon causes a surge current 1.5 to 2 times higher than in steady operation to flow through the power switching element 3. Therefore, to prevent damage to the power switching element 3, the surge current is suppressed or power switching is performed. It is better to suppress the surge current from the viewpoint of car cost, which requires increasing the rating of the element 3. Since the surge current increases as the high-frequency output of the magnetron increases, a soft start method may be considered in which the inverter power supply operates at a low-power high-frequency output for several seconds at the start of operation, and then shifts to the high-frequency output set at 6 heno. By the way, in the magnetron 6, when a current flows through the filament through the tertiary winding 6t and sufficient thermoelectrons are emitted from the filament to cause the magnetron 6 to oscillate, the secondary winding 5S generates a high voltage between the cyanode and the cathode. It oscillates only when the magnetron 6's heater circuit is applied, but the inductance of the wiring as well as the choke coil of the high-frequency filter 7 connected to the heater circuit of the magnetron 6 becomes a non-negligible value for the switching frequency of the inverter. At the same time, the apparent resistance increases due to the skin effect.

Furthermore, as shown in Figure 3, there is an inversely proportional relationship between the high frequency output and the switching frequency.During the soft start period, the switching frequency is high, making it difficult for the filament current to flow and limiting the amount of thermionic emissions. Immediately after soft start, if you try to oscillate at a power even lower than the low power at soft start (less than the rated μ),
As the switching frequency becomes higher, the filament current becomes more and more current, and the amount of thermoelectrons emitted from the filament decreases, resulting in a state where no oscillation occurs.

Therefore, as shown in Figure 1, a few seconds (approximately 4
seconds) After oscillating with a low power high frequency output PL (approximately 200W), oscillate for a few seconds with the rated high frequency output PH to warm up the filament sufficiently, then apply a power PLL (100W or less) that is even lower than the low power at soft start. However, the magnetron continues to oscillate.

Therefore, first it oscillates with a high frequency output of low power PL (approximately 200W) for a few seconds, then oscillates with a high power h (rated output) for a few seconds, and then oscillates with the arbitrary high frequency output you set (for example, PM + PL I PLL, etc.). ) With this method, it is now possible to oscillate at extremely low power (approximately 60W) when the magnetron is cold, and any high-frequency output within the rating can be obtained regardless of the state of the magnetron. J: I'm going to growl. Note that the rated output operation for several seconds after soft start has no effect on the subsequent minimal power.

For example, when meat is thawed in a microwave oven, the heat passes through and the meat does not burn.

Effect of the invention As described above, according to the present invention, the following effects can be obtained.

■ Any set high frequency output within the rating can be obtained from the start even when the magnetron is cold.

■ It is possible to suppress the current surge (1.6 to 2 times the steady state) caused by the transient phenomenon when the inverter and magnetron start oscillating, so there is no need to select a current rating of the power switching element larger than necessary. By suppressing current surges caused by transient phenomena at the start of oscillation of inverters and magnetrons, it is possible to suppress the voltage peaks that occur in the secondary windings of isolation transformers. becomes easier and reduces costs.

[Brief explanation of drawings]

Fig. 1 is a time chart of the high frequency output at the start of inverter operation in one embodiment of the present invention, the figure on page 29 is an electric circuit diagram of the inverter power supply for the magnetron of the same embodiment, and Fig. 3 shows the switching frequency and high frequency output. It is a figure showing a relationship. 3...Power switching element, 6...
・Isolation transformer, 6P...Primary winding, 6S...
...Secondary winding, 6t...Tertiary winding, 6...
... Magnetron, 7. Group, high frequency filter. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Number of switching cycles: 5 cycles

Claims (1)

[Claims] When the inverter power supply for the magnetron starts operating, the high-frequency voltage obtained by the inverter is boosted and applied between the anode and cathode of the magnetron, and the stepped-down high-frequency voltage is applied to the heater of the magnetron. An inverter power supply control method for a magnetron, characterized in that after oscillating with an output, oscillating with a high power high frequency output for within 10 seconds, and then shifting the high frequency output to an arbitrary setting power from low power to high power.