JP3072122B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating apparatus that heats and cooks food by using dielectric heating. The present invention relates to a high-frequency heating device using an inverter circuit that converts a DC power supply obtained by the above into high-frequency AC power.

2. Description of the Related Art Hereinafter, a configuration of a conventional high-frequency heating device will be described with reference to the drawings.

FIG. 3 is a diagram showing a circuit configuration of a conventional high-frequency heating device. In the figure, a commercial power supply 31 is rectified into DC by a rectifier 32, and is converted into high-frequency AC power by an inverter circuit 33 including a capacitor and a semiconductor switching element. The high-frequency AC power obtained by the inverter circuit is
Applied to the transformer 34. The transformer 34 includes a primary winding that applies a high-frequency AC output generated by the inverter circuit 33,
A secondary winding that boosts and generates a high voltage, and a magnetron 36
And a tertiary winding for supplying current to the filament.

The high AC voltage generated by the secondary winding is converted into a high DC voltage by the voltage doubler rectifier circuit 35, and the high DC voltage is applied between the anode and the cathode of the magnetron 36 to energize the magnetron 36.

The fan 37 for cooling the inverter circuit 33, the transformer 34, and the magnetron 36 is driven using a shaded AC motor. Electric power for the AC motor is supplied from a commercial power supply 31.

Problems to be Solved by the Invention An AC motor that drives a fan for cooling an inverter circuit, a transformer, and a magnetron is very large,
It is large. Therefore, when reducing the size and weight of the power supply of the high-frequency heating device, the size and weight of the AC motor have become a major issue. Therefore, it was considered to use a small, lightweight, and low-cost DC motor.

In order to drive a fan for sufficiently cooling an inverter circuit, a transformer, and a magnetron by using a DC motor, a DC voltage of about 7 to 24 V is required, and 10
Large electric power of about watts is required.

For this reason, a driving circuit for driving a DC motor by dropping a voltage from a commercial power supply of AC 100V AC and rectifying the DC voltage to generate a low voltage is large.

Therefore, by providing the transformer with a winding for a DC motor having a smaller number of turns than the primary winding of the transformer,
A method of generating a low-voltage AC voltage, rectifying this voltage, and supplying a low-voltage DC voltage to a DC motor has been adopted.

However, when the output of the inverter circuit is changed to control the microwave output of the magnetron, the output of the DC motor winding also changes.

That is, when the output of the inverter circuit is reduced, the output of the motor winding is also reduced, the DC voltage supplied to the DC motor is also reduced, the rotational speed of the DC motor is reduced, and the cooling capacity is reduced.

When the microwave output of the magnetron is reduced, the power handled by the magnetron and the transformer is reduced, so that the loss is reduced and the cooling capacity may be reduced.

A voltage resonance circuit system with a single inverter circuit is adopted. That is, the switching loss is reduced by performing zero-voltage switching for turning on the semiconductor switching device when the voltage applied to the semiconductor switching device of the inverter circuit becomes zero.

However, if the output of the inverter circuit is reduced, the above-mentioned zero voltage switching cannot be performed. Therefore, when the output of the inverter circuit is reduced, the loss of the semiconductor switching device may increase.

Therefore, for the inverter circuit, when the microwave output of the magnetron is reduced, the output of the transformer is also reduced, so that the cooling capacity is reduced, and an abnormal temperature rise of the semiconductor switching device, which causes an increase in loss, is caused to be destroyed. there were.

Means for Solving the Problems A DC power supply obtained by rectifying a battery or a commercial power supply, an inverter circuit that converts the power of the DC power supply into high-frequency AC power, a transformer that boosts the output of the inverter circuit, A magnetron energized by the output of the transformer, and a DC motor that receives power supply from a DC motor winding provided in the transformer and drives a cooling fan, the DC motor winding and the DC A configuration in which a circuit element whose impedance is variable between motors is provided.

Specifically, a resonance circuit including a capacitor and an inductor is used as a circuit element whose impedance is variable, and the impedance of the resonance circuit is changed according to the operating frequency of the inverter circuit.

When controlling the microwave output of the magnetron, when the microwave output is at the maximum output, that is, when the inverter circuit is operating at the maximum output, the impedance of the resonance circuit is increased, and the microwave output is changed from the maximum output to the minimum output. When the inverter circuit operates from the maximum output to the minimum output, the impedance of the resonance circuit is changed from a high impedance to a low impedance. In this case, even if the output voltage of the DC motor winding provided in the transformer is reduced when the microwave output is reduced, the impedance of the resonance circuit is reduced, so that the power supplied to the DC motor is reduced. Be kept constant.

Effects The present invention has the following effects.

A DC motor winding provided in a transformer for boosting the output of the inverter circuit, and a circuit element capable of changing the impedance between the DC motor are inserted to control the microwave output of the magnetron and at the same time, the impedance of the circuit element By controlling the power supply, the power supplied to the DC motor that drives the cooling fan can be kept almost constant, so that the cooling capacity of the cooling fan can be stabilized and the inverter circuit during microwave output control can be controlled. An abnormal temperature rise of the semiconductor switching device can be prevented, and the reliability can be improved.

If a resonance circuit including a capacitor and an inductor is used as a circuit element that can change the impedance, the impedance of the resonance circuit can be changed by changing the operation frequency of the inverter circuit.

Embodiments A high-frequency heating device according to one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a high-frequency heating device according to one embodiment of the present invention. In the figure, a commercial power supply 1 is rectified into a direct current by a rectifier 2 and converted into a high-frequency AC power by an inverter circuit 3 including a capacitor and a semiconductor switching element. The inverter circuit 3 uses a single-pole voltage resonance type circuit configuration. The high-frequency AC power obtained by the inverter circuit is applied to the transformer 4. The transformer 4 includes a primary winding for applying a high-frequency AC output generated by the inverter circuit 3, a secondary winding for generating a high voltage by boosting, a tertiary winding for generating a low voltage, and a cooling fan. It comprises a motor winding 5 for supplying power to a DC motor for driving.

The AC high voltage generated in the secondary winding is converted into a DC high voltage by the voltage doubler rectifier circuit 6, and the DC high voltage is applied between the anode and the cathode of the magnetron 12 to energize the magnetron 12.

The tertiary winding supplies a low voltage to the cathode of the magnetron 12 and heats the filament.

Between the motor winding 5 and the DC motor 9, a circuit element 10 whose impedance can be varied and a rectifier circuit 11 are connected.

The inverter circuit uses a single-type voltage resonance type circuit configuration, and the microwave output generated by the magnetron can be varied by controlling the on-time of the semiconductor switching device 7 by the control circuit 8.

To increase the microwave output, the on-time may be increased. Therefore, the frequency of the drive signal supplied from the control circuit 8 to the semiconductor switching device 7 decreases, and the operating frequency of the inverter circuit decreases. Conversely, when it is desired to reduce the microwave output, the on-time may be shortened. Therefore, the frequency of the drive signal provided from the control circuit 8 to the semiconductor switching device 7 increases, and the operating frequency of the inverter circuit increases.

As described above, a resonance circuit including a capacitor, an inductor, and a resistor is connected between the motor winding 5 and the DC motor 9 as a circuit element 10 whose impedance can be varied. A rectifier 11 for applying a voltage is connected. Therefore, when the operating frequency of the inverter circuit changes, the impedance of the resonance circuit also changes. Since the resonance circuit is a series resonance of an inductor, a capacitor, and a resistor, the relationship between frequency and impedance is as shown in FIG. Therefore, if the operating frequency range of the inverter circuit is set to the shaded portion in the figure, the operating frequency of the inverter circuit is lowered to increase the microwave output, and even if the output of the motor winding 5 increases,
Since the impedance of the resonance circuit is high, a rectifier 11 is connected in parallel with the resistor to apply DC voltage to the DC motor.
Is kept almost constant without increasing. Conversely, when the microwave output is reduced, the operating frequency of the inverter circuit increases, and the output of the motor winding 5 decreases.
Since the impedance of the resonant circuit is low, a rectifier 11 is connected in parallel with the resistor to apply DC voltage to the DC motor.
Is kept almost constant without increasing.

Since the sharpness of the resonance circuit varies depending on the size of the inductor and the capacitor, the sharpness may be determined so that the voltage extracted from the resistance of the resonance circuit is constant within the operating frequency range of the inverter circuit.

Effects of the Invention According to the present invention, the following effects are obtained.

A DC motor winding provided in a transformer for boosting the output of the inverter circuit, and a circuit element capable of changing the impedance between the DC motor are inserted to control the microwave output of the magnetron and at the same time, the impedance of the circuit element , The power supplied to the DC motor driven by the cooling fan can be kept substantially constant.

In addition, as a circuit element that can change the impedance,
If a resonance circuit including a capacitor and an inductor is used, the impedance of the resonance circuit can be changed by changing the operating frequency of the inverter circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing characteristics of a resonance circuit of the device, and FIG. 3 shows a configuration of a conventional high-frequency heating device. It is a circuit diagram. 3 ... Inverter circuit, 4 ... Transformer, 5 ... Motor winding, 9 ... DC motor, 10 ... Circuit element with variable impedance, 11 ... Rectifier, 12 ... Magnetron.

 ──────────────────────────────────────────────────の Continued on the front page (72) Takahiro Matsumoto, Inventor 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-52-64032 (JP, A) JP-A-60-131996 (JP, U) JP-A-57-44304 (JP, U)

Claims (1)

(57) [Claims] A DC power supply obtained by rectifying a battery or a commercial power supply; an inverter circuit for converting the power of the DC power supply into high-frequency AC power; a transformer for boosting an output of the inverter circuit; A magnetron whose output is variable in accordance with the output of the DC motor, a DC motor that receives power supplied from a motor winding provided in the transformer and drives a cooling fan, and a DC motor winding between the DC motor winding and the DC motor. A high frequency heating device comprising: a resonance circuit including a capacitor and an inductor, wherein the impedance of the resonance circuit is varied by changing an operating frequency of the inverter circuit.