JPS6248354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heating device that radiates microwave power with an antenna in the oven to heat food in the oven, and operates with the best power efficiency depending on the load condition of the food. With the goal.

Conventional high-frequency heating devices use a magnetron as a heating power source, and radiate oscillation output with a fixed frequency from an antenna inside the oven to heat the food inside the oven. For this reason, power efficiency varies depending on the ingredients, size, weight, and location of the food. For example, the power supply and load impedance are matched so that maximum efficiency can be obtained for a water load of 2 liters as a food load (this is determined by the standard for microwave ovens), so the load is light (500 grams). , the efficiency is about 20 to 30% lower than the maximum efficiency, and
gram load, efficiency decreases by about 30-40%.
Also, depending on the ingredients of the food and the location where the food is placed,
For the same reason, power efficiency decreases from maximum efficiency. Current microwave ovens have these drawbacks.

The present invention has a microwave heating power source that can vary the oscillation frequency, and measures the reflected power that changes depending on the shape, size, position, composition, and heating state of the food, and the reflected power reaches the minimum value. By tracking the oscillation frequency of the power source and driving the power source in the vicinity of the oscillation frequency, the above-mentioned conventional drawbacks are solved.

In addition, conventionally, a magnetron whose tuning frequency can be varied by voltage is used as a microwave heating power source, a step wave voltage is applied at intervals of several seconds, and the tuning frequency of the power source is swept over the required bandwidth.
A method has been proposed in which when the reflected power passes through a minimum value that is smaller than in the previous sweep, the corresponding step of the staircase voltage is memorized, set as a new tuning frequency, and held at this frequency until the next sweep.

In contrast to this method, the present invention provides for similar purposes:
This paper proposes another means of operating the power supply so that the oscillation frequency of the power supply is such that the reflected power becomes the minimum value.
That is, in contrast to the conventional method, which was a complicated method of checking and updating the minimum value of reflected power every few seconds in response to fluctuations in reflection conditions due to changes in food load, the present invention constantly monitors the reflected power. This paper proposes a simpler means of tracking the oscillation frequency of the power supply at which the power reaches the stated value and driving the power supply in the vicinity of the oscillation frequency. Hereinafter, the first embodiment of the present invention will be described.
This will be explained based on FIGS.

In Figure 1, the (a) curve is an example of the change in reflected power with respect to the oscillation frequency of the microwave heating power source when a food load is placed in an oven and heated, and the (b) curve is an example of the change in reflected power with respect to the oscillation frequency of the microwave heating power source when a food load is placed in an oven and heated. This is an example of a change in reflected power when any of the positions, components, and heating conditions of the food differ. The reflected powers are different, and in particular, the oscillation frequency ₀ , which shows the minimum value, is significantly different. Also, (1), (2), (3), (4), ... indicate each step of sweeping the oscillation frequency in the case of curve (a). Initially, in the first step (1), the oscillation frequency starts from an oscillation frequency _s far away from _zero and sweeps to a frequency slightly beyond _zero . Then, in the second step (2), the frequency sweep is reversed and sweeps to a frequency slightly above _zero . Further, after the third step (3), the power supply is similarly reversed and swept, and the power supply is driven at a frequency that reciprocates very close to _zero .

In FIGS. 2 and 3, 1 is a voltage control signal generator that outputs a negative voltage control signal in response to the input of a start pulse, and 2 is a voltage control signal generator that generates a positive slope wave voltage by inputting the voltage control signal. a frequency control voltage generator that outputs an oscillation frequency control voltage that is
3 is a microwave heating power source whose oscillation frequency is changed by an oscillation frequency control voltage; 4 is a directional coupler through which the output power of the microwave heating power source is passed;
Inside the oven 5, microwave power is transmitted to an radiating antenna 6. 7 is a detector, and the reflected power from the oven side is reflected at reflection port a of the directional coupler.
The signal is then detected by this detector. Reference numeral 8 denotes a terminator, which terminates the output obtained at the b port to which the output power of the microwave heating power source, that is, a part of the input power of the directional coupler 4 is coupled, without reflection. 9 is a minimum value search circuit, into which the detected output of the reflected power is input;
An inverted pulse is output when the detected output exceeds the minimum value by a threshold value ΔV. This inverted pulse is also used to erase the held voltage held in the minimum value search circuit. Also, this inverted pulse is input to the voltage control signal generator and sets the output reset by the start pulse.
Then for each reversal pulse, the reset,
Used to repeat the set.

FIG. 4 shows a specific embodiment of the present invention regarding the voltage control signal generator 1, frequency control voltage generator 2, and microwave heating power source 3 in FIG. 2, and FIGS. Minimum value search circuit 9
A specific example of the present invention will be shown below.

In FIG. 4, 11 in the voltage control signal generator 1 represents an OR gate, and 12 represents a counter. The frequency control voltage generator 2 includes an input resistor 21, an operational amplifier 22, a feedback capacitor 23, and a protection resistor 24, and constitutes an integrating circuit. The microwave heating power source 3 includes a chiyoke coil 31, a voltage variable capacitance diode 32, a DC blocking capacitor 33, a capacitor 34, a coil 35, a capacitor 36, a transistor 37, a capacitor 38, and a chiyoke coil 3.
9, a resistor 40, a choke coil 41, a capacitor 42, and a supply DC voltage Vcc.

The oscillation frequency can be changed by a voltage variable capacitance diode, and is determined by this diode, capacitor 34, coil 35, capacitor 36, and capacitor 38. The oscillation circuit has a capacity of 38
This is a wrap circuit consisting of a combined capacitance of capacitors 32, 33, and 34, and a series circuit of a coil 35 and a capacitor 36, and the oscillation frequency changes as the diode capacitance 32 changes. The structure of these coils and capacitors may include strip line elements.

In Figures 5 and 6, 91 is a first amplifier that receives the detected voltage of the reflected power, subtracts the bias voltage +V _B from it, and amplifies it to obtain a polarity-inverted output voltage, and 92 is the maximum polarity-inverted output voltage. A maximum value holding circuit stores and holds the value and outputs the maximum value holding voltage. 93 is a subtracter that subtracts the maximum value holding voltage from the polarity inverted output voltage. 94 is a subtracter that subtracts the threshold voltage ΔSH from the subtracted output voltage. , a second amplifier which inverts the polarity, amplifies the pulse, and outputs it as an inverted pulse. Further, this inversion pulse erases the maximum value holding voltage held in the maximum value holding circuit, and becomes the same level as the polarity inverted output voltage at that time.

In addition, (1), (2), (3), (4)... show the time course of the voltage waveforms at each part corresponding to each step of sweeping the oscillation frequency shown in Figure 1. .

In the above configuration, the operation of the high frequency heating device of the present invention will be explained.

When a food load is placed in the oven and heating is started, a start pulse is input to the voltage control signal generator 1. The start pulse is OR gate 11
The counter 12 is reset through the . Therefore, at this initial point, the output of the frequency control voltage generator is at zero level, and the microwave heating power source 3
There is no voltage applied to the voltage controlled variable capacitance diode. Therefore, since this capacitance diode has the maximum capacity, the oscillation frequency of the power supply 3 determined by this is the lowest frequency, which is the lowest frequency _s in Figure 1.
corresponds to this frequency, the power source 3 is driven at this frequency, and the power obtained by the power source 3 is radiated from the antenna in the oven containing the food. At this time, the reflected power from the oven side is relatively large.

Thereafter, in the first step, the frequency control voltage generator 2 integrates the input from the counter 12, and
A frequency control voltage which is a positive ramp voltage shown in FIG. 3 is output. This voltage is applied to the variable capacitance diode 32. As this voltage increases, the capacitance of the diode 32 decreases, so the oscillation frequency of the power supply 3 increases. Further, as the frequency increases, as shown in FIG. 1, the reflected power from the oven side changes in a direction of decreasing, reaches a minimum at frequency ₀ , and increases thereafter. The oscillation frequency continues to rise until the reflected power increases by the threshold value ΔW from the minimum value, and the first step of the frequency sweep ends. In addition, in this first step, as shown in Figure 3, the detected voltage of the reflected power decreases as the frequency increases and reaches the minimum value, and furthermore,
This continues until it increases from the minimum value to the threshold value ΔV (which corresponds to the reflected power threshold value ΔW). Further, the first amplifier 91 of the minimum value search circuit 9 receives the detected voltage of the reflected power, subtracts the bias voltage +V _B from it, and amplifies it. One of the resulting polarity inverted outputs is directly sent to a subtracter 93, the other is held at its maximum value in a maximum value holding circuit 92, and a subtracter 93 subtracts it from the polarity inverted output to obtain a subtracted output voltage. There is. Furthermore, the portion of this subtracted output voltage exceeding the threshold value ΔSH is amplified to obtain an inverted pulse. This inverted pulse erases the maximum holding voltage held in the maximum value holding circuit 92, and also erases the maximum held voltage held in the maximum value holding circuit 92, and also
Set 2. That is, the first step is completed by detecting that the detected voltage of the reflected power reaches a minimum value, that is, frequency ₀ , and conversely exceeds the threshold value, resulting in a slight deviation from frequency ₀ .

Next, when the voltage control signal is set, the output of the frequency control generator 2 falls as a ramp voltage due to the negative voltage, so the oscillation frequency of the power supply 3 changes in the lower direction, and as shown in FIG. This becomes the frequency sweep of step (2). In this case, the reflected power decreases and reaches a minimum value at frequency ₀ .
Thereafter, the frequency is lowered, and the oscillation frequency continues to decrease until the reflected power increases by the threshold value ΔW from the minimum value. That is, the second step of the frequency sweep is completed. Also, in this step, the detected voltage of the reflected power decreases as the frequency decreases,
becomes the minimum value, and then from that minimum value the threshold △V
(corresponds to ΔW). Further, in this second step, the operation of the minimum value search circuit 9 is performed in the same manner as in the first step, and an inverted pulse is obtained. This inverted pulse also erases the minimum holding voltage held in the maximum value holding circuit, and the counter 1 of the voltage control signal generator 1
Reset 2. That is, after the detected voltage of the reflected power reaches a minimum value of frequency ₀ , it is detected that this voltage exceeds the threshold value and becomes a slight deviation from frequency ₀ , and the second step is completed. .

Next, when the voltage control signal is reset,
Because of that zero voltage, the output of the frequency control generator 2 rises as a ramp voltage, so the oscillation frequency of the power supply 3 changes towards the higher side, resulting in the frequency sweep of step (3) in FIG. Thereafter, the operations after this step (3) are a repetition of the operations from step (1) to step (2).

In this way, in step (1), the oscillation frequency of the power supply at which the reflected power from the oven side is the minimum value is determined.
Sweep from the frequency _s far away from ₀ to detect ₀ , and from step (2) onwards, this ₀
The power source is driven by an operation that tracks the oscillation frequency of the power source at which the reflected power newly becomes the minimum value while reciprocating slightly in the vicinity of the power source.

Therefore, the heating power source is best matched to the load impedance, which varies depending on the composition, size, and weight of the food to be heated, the position where the food is placed, and changes in load conditions as the food heats. Therefore, it is possible to always drive with maximum power efficiency.

[Brief explanation of the drawing]

FIG. 1 is a change curve of reflected power with respect to the oscillation frequency of the power source for explaining the operation of the high-frequency heating device of the present invention, FIG. 2 is a block diagram of the high-frequency heating device according to an embodiment of the present invention, and FIG. The figure shows an input/output voltage waveform diagram of each block in the block configuration diagram of Fig. 2, and Fig. 4 shows a specific example of the voltage control signal generator, frequency control voltage generator, and microwave heating power supply of Fig. 2. 5 is a detailed diagram showing a specific embodiment of the minimum value search circuit of FIG. 2, and FIG. 6 is an input/output voltage waveform diagram of each part of FIG. 5. 12...Counter, 43...Capacitor, 32
... Voltage controlled variable capacitance diode, 37 ... Transistor, 4 ... Directional coupler, 5 ... Oven, 6 ... Antenna, 7 ... Detector, 92 ... Maximum value holding circuit.

Claims (1)

[Claims] 1. A microwave heating power source that can vary the oscillation frequency by changing the capacitance of an oscillation circuit, and microwave power at this oscillation frequency is radiated by an antenna in the oven to heat food placed in the oven. In a high-frequency heating device that heats food, the reflected power that changes depending on the shape, size, position, composition, and heating state of the food is measured, and the oscillation frequency of the power source at which the reflected power becomes the minimum value is tracked and the A high-frequency heating device characterized by driving a power source nearby. 2. A microwave heating power source whose oscillation frequency can be varied by changing the capacitance value of the oscillation circuit, an antenna to which the oscillation power is transmitted, an oven to which the microwave power is radiated from the antenna, and a power reflected from the antenna. a directional coupler that outputs, a detector that detects reflected power from the directional coupler,
A minimum value search circuit that receives the output voltage from the detector and generates an output when the output voltage increases from the minimum value by a threshold value, and a counter output that operates based on the output. It consists of a voltage control signal generator that obtains the voltage control signal, and a frequency control voltage generator that receives the output voltage control signal and outputs a ramp voltage obtained by integrating this signal. A high-frequency heating device characterized in that the oscillation frequency of the microwave heating power source is changed. 3. In claim 2, the microwave heating power source is configured with a π-type oscillator including a voltage-controlled variable capacitance diode that changes depending on the output voltage of the frequency-controlled voltage generator. Device. 4. In claim 2, the minimum value search circuit receives the detected voltage of the reflected power and amplifies the detected voltage by adding a bias voltage to the first amplifier to obtain a polarity inverted output; a maximum value holding circuit that stores and holds the value, a comparator that subtracts the maximum value holding voltage from the output of the first amplifier, and a second comparator that receives this comparison output, subtracts the threshold value, inverts the polarity, and amplifies the The high-frequency heating system is characterized in that the amplified output erases the power held in the maximum value holding circuit, and that the amplified output is used as an inverted pulse of a voltage control signal generator. Device. 5 In claim 2, the voltage control signal generator consists of one gate and a one-stage counter; first, the first-stage counter is reset by a heating start pulse, and thereafter is reset by an inversion pulse. 1. A high-frequency heating device characterized in that setting and resetting are repeated, and the resulting rectangular wave voltage is output.