High-frequency heating device

• US 20070195561A1
• Filed: 04/04/2005
• Published: 08/23/2007
• Est. Priority Date: 04/07/2004
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Moriya, Hideaki, Sakai, Shinichi, Suenaga, Haruo, Shirokawa, Nobuo, Matsukura, Toyotsugu, Morikawa, Hisashi
• Granted Patent: US 8,217,323 B2
• Time in Patent Office: Days
• US Class Current: 363/21.02
• CPC Class Codes: H05B 6/681 Circuits comprising an inverter, a boost transformer and a magnetron
• CPC Class Codes: H05B 6/685 the measurements being made at the low voltage side of the circuit
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

An object of the present invention is to provide an inverter circuit in which soft start can be implemented by a simple circuit added thereto. In high-frequency heating apparatus for driving a magnetron, a DC power supply is chopped by two semiconductor switching devices, and this is output as an AC current through a resonance circuit. The high-frequency heating apparatus includes a dead time generation circuit for turning off the semiconductor switching devices concurrently. In the high-frequency heating apparatus, a drive unit for driving the aforementioned semiconductor switching devices has a function of limiting the lowest frequency of a frequency with which the semiconductor switching devices are driven. The aforementioned lowest frequency is set to be high at the beginning of operation of the high-frequency heating apparatus, and the aforementioned lowest frequency is set to be lower gradually thereafter.

Claims

1. A high-frequency heating apparatus for driving a magnetron, comprising:

a DC power supply including an AC power supply, a rectifier circuit for rectifying a voltage of the AC power supply, and a smoothing capacitor for smoothing an output voltage of the rectifier circuit;

a series circuit including two semiconductor switching devices, the series circuit being connected in parallel to the AC power supply;

a resonance circuit connected to a primary winding of a leakage transformer and a capacitor, one end of the resonance circuit being connected to a middle point of the series circuit in an AC equivalent circuit while the other end of the resonance circuit is connected to one end of the AC power supply;

a drive unit for driving each of the semiconductor switching devices;

a rectifier unit connected to a secondary winding of the leakage transformer;

a magnetron connected to the rectifier unit; and

a dead time generation circuit for turning off the semiconductor switching devices concurrently,

wherein the drive unit has a function of limiting the lowest frequency of a frequency with which the semiconductor switching devices are driven, so that the lowest frequency is set to be high at the beginning of operation of the high-frequency heating apparatus, and the lowest frequency is set to be lower gradually thereafter.

4. The high-frequency heating apparatus according to claim 1, further comprising:

an error signal generation circuit for generating an error signal from a difference between an input current of the AC power supply and a reference current; and

a frequency-modulated signal generation circuit for correcting a rectified voltage/rectified current obtained by rectifying the AC power supply, based on an output (error signal) of the error signal generation circuit, an output of the frequency-modulated signal generation circuit being supplied to the dead time generation circuit;

wherein a lowest frequency limiting circuit is inserted between the frequency-modulated signal generation circuit and the dead time generation circuit, the lowest frequency limiting circuit supplies a limited frequency to the dead time generation circuit based on the output signal of the frequency-modulated signal generation circuit so that a set frequency of the lowest frequency limiting circuit is set to be higher than the output of the frequency-modulated signal generation circuit at the beginning of operation of the aforementioned high-frequency heating apparatus, and in accordance with time having passed since the beginning of operation, the limited frequency is lowered gradually, while with lowering of the limited frequency, a signal higher in switching frequency of the limited frequency and the output signal of the frequency-modulated signal generation circuit is selected as a signal to be supplied to the dead time generation circuit in accordance with time having passed, so that the selected signal is changed over gradually to the output signal of the frequency-modulated signal generation circuit.

5. The high-frequency heating apparatus according to claim 4, wherein the lowest frequency limiting circuit has a capacitor, the capacitor is charged during suspension of the high-frequency heating apparatus, and as soon as the high-frequency heating apparatus begins to operate, a voltage of the capacitor is supplied to the dead time generation circuit, and charges accumulated in the capacitor are discharged.

6. The high-frequency heating apparatus according to claim 4, wherein the dead time generation circuit generates a fixed or marginally increased dead time regardless of a switching frequency.

7. The high-frequency heating apparatus according to claim 1, wherein the dead time generation circuit generates a dead time increased in accordance with increase of a switching frequency.

8. The high-frequency heating apparatus according to claim 7, wherein the dead time generation circuit fixes or marginally increases the dead time at a switching frequency not higher than a predetermined frequency.

9. The high-frequency heating apparatus according to claim 7, wherein the dead time generation circuit suddenly increases the dead time at a switching frequency not lower than a predetermined frequency.

13. The high-frequency heating apparatus according to claim 1, wherein the dead time generation circuit generates a dead time based on positive and negative offset voltages each varying with a first inclination in proportion to increase of a switching frequency and varying with a second inclination when the switching frequency reaches a predetermined frequency or higher.

14. The high-frequency heating apparatus according to claim 1, wherein the dead time generation circuit includes a VCC power supply, a duty control power supply, a first current varying in proportion to a switching frequency, a second current beginning to flow at a predetermined frequency and varying in proportion to the switching frequency, a third current obtaining by and multiplying a combining current of the two currents by a predetermined coefficient, and a upper and lower potential generation unit for generating two upper and lower potentials obtained by adding positive and negative offset voltages proportional to the third current, to the duty control power supply respectively, and a dead time is generated based on the two upper and lower potentials.

2. A high-frequency heating apparatus for driving a magnetron, comprising:

a DC power supply including an AC power supply, a rectifier circuit for rectifying a voltage of the AC power supply, and a smoothing capacitor for smoothing an output voltage of the rectifier circuit;

two series circuits each including two semiconductor switching devices, each of the series circuits being connected in parallel to the AC power supply;

a resonance circuit connected to a primary winding of a leakage transformer and a capacitor, one end of the resonance circuit being connected to a middle point of one of the series circuits while the other end of the resonance circuit is connected to a middle point of the other series circuit;

a drive unit for driving each of the semiconductor switching devices;

a rectifier unit connected to a secondary winding of the leakage transformer;

a magnetron connected to the rectifier unit; and

a dead time generation circuit for turning off the semiconductor switching devices concurrently,

wherein the drive unit has a function of limiting the lowest frequency of a frequency with which the semiconductor switching devices are driven, so that the lowest frequency is set to be high at the beginning of operation of the high-frequency heating apparatus, and the lowest frequency is set to be lower gradually thereafter.

16. The high-frequency heating apparatus according to claim 2, further comprising:

an error signal generation circuit for generating an error signal from a difference between an input current of the AC power supply and a reference current; and

a frequency-modulated signal generation circuit for correcting a rectified voltage/rectified current obtained by rectifying the AC power supply, based on an output (error signal) of the error signal generation circuit, an output of the frequency-modulated signal generation circuit being supplied to the dead time generation circuit;

wherein a lowest frequency limiting circuit is inserted between the frequency-modulated signal generation circuit and the dead time generation circuit, the lowest frequency limiting circuit supplies a limited frequency to the dead time generation circuit based on the output signal of the frequency-modulated signal generation circuit so that a set frequency of the lowest frequency limiting circuit is set to be higher than the output of the frequency-modulated signal generation circuit at the beginning of operation of the aforementioned high-frequency heating apparatus, and in accordance with time having passed since the beginning of operation, the limited frequency is lowered gradually, while with lowering of the limited frequency, a signal higher in switching frequency of the limited frequency and the output signal of the frequency-modulated signal generation circuit is selected as a signal to be supplied to the dead time generation circuit in accordance with time having passed, so that the selected signal is changed over gradually to the output signal of the frequency-modulated signal generation circuit.

19. The high-frequency heating apparatus according to claim 2, wherein the dead time generation circuit generates a dead time increased in accordance with increase of a switching frequency.

22. The high-frequency heating apparatus according to claim 2, wherein the dead time generation circuit generates a dead time based on positive and negative offset voltages each varying with a first inclination in proportion to increase of a switching frequency and varying with a second inclination when the switching frequency reaches a predetermined frequency or higher.

23. The high-frequency heating apparatus according to claim 2, wherein the dead time generation circuit includes a VCC power supply, a duty control power supply, a first current varying in proportion to a switching frequency, a second current beginning to flow at a predetermined frequency and varying in proportion to the switching frequency, a third current obtaining by and multiplying a combining current of the two currents by a predetermined coefficient, and a upper and lower potential generation unit for generating two upper and lower potentials obtained by adding positive and negative offset voltages proportional to the third current, to the duty control power supply respectively, and a dead time is generated based on the two upper and lower potentials.

28. The high-frequency heating apparatus according to claim 23, wherein the dead time generation circuit fixes or marginally increases the dead time at a switching frequency not higher than a predetermined frequency.

29. The high-frequency heating apparatus according to claim 23, wherein the dead time generation circuit suddenly increases the dead time at a switching frequency not lower than a predetermined frequency.

3. A high-frequency heating apparatus for driving a magnetron, comprising:

a DC power supply including an AC power supply, a rectifier circuit for rectifying a voltage of the AC power supply, and a smoothing capacitor for smoothing an output voltage of the rectifier circuit;

a series circuit including two semiconductor switching devices, the series circuit being connected in parallel to the AC power supply;

a resonance circuit connected to a primary winding of a leakage transformer and a capacitor, the resonance circuit being connected in parallel to one of the semiconductor switching devices;

a drive unit for driving each of the semiconductor switching devices;

a rectifier unit connected to a secondary winding of the leakage transformer;

a magnetron connected to the rectifier unit; and

a dead time generation circuit for turning off the semiconductor switching devices concurrently,

wherein the drive unit has a function of limiting the lowest frequency of a frequency with which the semiconductor switching devices are driven, so that the lowest frequency is set to be high at the beginning of operation of the high-frequency heating apparatus, and the lowest frequency is set to be lower gradually thereafter.

24. The high-frequency heating apparatus according to claim 3, further comprising:

an error signal generation circuit for generating an error signal from a difference between an input current of the AC power supply and a reference current; and

a frequency-modulated signal generation circuit for correcting a rectified voltage/rectified current obtained by rectifying the AC power supply, based on an output (error signal) of the error signal generation circuit, an output of the frequency-modulated signal generation circuit being supplied to the dead time generation circuit;

wherein a lowest frequency limiting circuit is inserted between the frequency-modulated signal generation circuit and the dead time generation circuit, the lowest frequency limiting circuit supplies a limited frequency to the dead time generation circuit based on the output signal of the frequency-modulated signal generation circuit so that a set frequency of the lowest frequency limiting circuit is set to be higher than the output of the frequency-modulated signal generation circuit at the beginning of operation of the aforementioned high-frequency heating apparatus, and in accordance with time having passed since the beginning of operation, the limited frequency is lowered gradually, while with lowering of the limited frequency, a signal higher in switching frequency of the limited frequency and the output signal of the frequency-modulated signal generation circuit is selected as a signal to be supplied to the dead time generation circuit in accordance with time having passed, so that the selected signal is changed over gradually to the output signal of the frequency-modulated signal generation circuit.

27. The high-frequency heating apparatus according to claim 3, wherein the dead time generation circuit generates a dead time increased in accordance with increase of a switching frequency.

30. The high-frequency heating apparatus according to claim 3, wherein the dead time generation circuit generates a dead time based on positive and negative offset voltages each varying with a first inclination in proportion to increase of a switching frequency and varying with a second inclination when the switching frequency reaches a predetermined frequency or higher.

31. The high-frequency heating apparatus according to claim 3, wherein the dead time generation circuit includes a VCC power supply, a duty control power supply, a first current varying in proportion to a switching frequency, a second current beginning to flow at a predetermined frequency and varying in proportion to the switching frequency, a third current obtaining by and multiplying a combining current of the two currents by a predetermined coefficient, and a upper and lower potential generation unit for generating two upper and lower potentials obtained by adding positive and negative offset voltages proportional to the third current, to the duty control power supply respectively, and a dead time is generated based on the two upper and lower potentials.

10-12. -12. (canceled)

15. (canceled)

20. The high-frequency heating apparatus according to claim 15, wherein the dead time generation circuit fixes or marginally increases the dead time at a switching frequency not higher than a predetermined frequency.

21. The high-frequency heating apparatus according to claim 15, wherein the dead time generation circuit suddenly increases the dead time at a switching frequency not lower than a predetermined frequency.

25. The high-frequency heating apparatus according to claim 20, wherein the lowest frequency limiting circuit has a capacitor, the capacitor is charged during suspension of the high-frequency heating apparatus, and as soon as the high-frequency heating apparatus begins to operate, a voltage of the capacitor is supplied to the dead time generation circuit, and charges accumulated in the capacitor are discharged.

26. The high-frequency heating apparatus according to claim 20, wherein the dead time generation circuit generates a fixed or marginally increased dead time regardless of a switching frequency.