JP2009283221A - High-frequency heating power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of controlling a high-frequency output depending on power source voltage plus cooling capacity, for a high-frequency heating device driving a magnetron such as a microwave oven. <P>SOLUTION: A PWM signal of a microcomputer for controlling a high-frequency output can be changed based on information obtained from an input power source voltage detection circuit back to the original. However, a PWM value is made constant in the vicinity of the rating in consideration of variation of parts and read-in variation due to power source impedance. Further, the PWM value at the rating can be set at maximum with other points decreased (especially, at the maximum output), in consideration of the cooling capacity and absolute safety at parts destruction. Thus, an optimum high-frequency output can be set in accordance with cooling capacity for each power source voltage. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention proposes an improvement related to the control of the high frequency output depending on the input power supply voltage in the field of a high frequency heating apparatus that performs dielectric heating by driving a magnetron like a microwave oven.

  As a power source used for high-frequency heating cooking equipment such as a microwave oven used in general homes, it is desirable to have a small machine room space that is easy to carry and has a built-in power source in order to enlarge the cooking chamber. ), Small and light has been desired. Therefore, downsizing and weight reduction and cost reduction are being promoted by switching the power source, and the inverter power source is becoming mainstream.

  In addition, there is a demand for higher output, and an inverter power supply having many heat generating parts is required to have the same cooling performance with respect to input voltage fluctuation.

  There is also a change in the total input power due to the input voltage fluctuation, that is, it causes a variation in the high frequency output. As a method for ensuring performance with respect to the variation as a cooker, a method of changing the cooking time has been proposed (see, for example, Patent Document 1).

  In addition, there has also been proposed a method in which the high-frequency output is uniformly made variable according to the input power supply voltage (see, for example, Patent Document 2).

  An example of the inverter power supply will be described with reference to the block diagram shown in FIG. 8. The commercial power supply 1 is rectified by the rectifier 2 and converted into a DC voltage, and power is supplied from the commercial power supply 1. The DC voltage is applied to the capacitor 4 and the inductor 13 and the inverter resonance circuit 5 of the semiconductor switching element 3 through the filter circuit 11 including the choke coil 9 and the capacitor 10.

  In the inverter resonance circuit 5, the semiconductor switching element 3 switches at a frequency of 20 to 45 kilohertz to create a high frequency alternating current. Since the inductor 13 also serves as a primary winding of the high-voltage transformer 6, high-frequency alternating current generated in the inductor 13 is boosted to a high voltage by the high-voltage transformer 6.

  The high voltage boosted by the high voltage transformer 6 is rectified to a DC high voltage by the high voltage rectifier circuit 7. The control circuit unit 14 gives a signal for obtaining a desired high-frequency output to the semiconductor switching element 3 in a form reflecting the input current information obtained from the current transformer 12, and drives it.

  A command signal for determining a desired output is externally given to the control circuit unit 14 by an insulation interface (not shown) such as a photocoupler by the microcomputer 19 to obtain high-frequency outputs such as 1000 W, 800 W, and 600 W.

  These electric component parts constitute the inverter power supply 18. The DC high voltage rectified by the high voltage rectifier circuit 7 is applied between the anode portion 17 and the cathode portion 16 of the magnetron 8. The high-voltage transformer 6 is provided with another auxiliary secondary winding, and this auxiliary secondary winding constitutes a heating current supply line 15 that supplies power as a heating current to the cathode portion 16 of the magnetron 8. .

The magnetron 8 is supplied with electric power to the cathode portion 16, oscillates and generates microwaves when the cathode temperature rises and a high voltage is applied between the anode portion 17 and the cathode portion 16. Microwaves generated by the magnetron 8 are applied to an object to be heated such as food in a heating chamber to perform dielectric heating cooking.

  Since the high frequency output naturally changes depending on the input power, the dependence on the power supply voltage is high. That is, in the case of the same current value, the input power decreases when the voltage decreases, and increases when the voltage increases. Therefore, it is required to control the input power depending on the power supply voltage in order to minimize the high frequency output fluctuation.

However, in terms of cooling, the input power change described above is desirable in the case of a component whose rotational speed changes depending on the input power supply voltage, such as a sirocco fan or a propeller fan. There is a need for a system that can control these conflicting events according to the development of each occasion.
JP-A-6-111104 JP-A-7-35352

  However, the above configuration has the following problems. That is, the configuration in which the current value is kept constant without changing according to the input power supply voltage has a problem that the fluctuation of the high frequency output becomes large and the high frequency output cannot be adjusted according to the cooling performance.

  Some methods have been proposed to make the current value variable according to the input power supply voltage, but due to the linear change, the input may be lowered in the rating depending on the component variation and the reading variation due to the power supply impedance, ensuring the nominal high frequency output. There was a problem that there was a fear of not being able to.

  The present invention solves the above-mentioned conventional problems, and controls the input power so as to obtain an optimum high-frequency output in consideration of the cooling capacity in accordance with the input power supply voltage, and also ensures the nominal high-frequency output at the rating. A control method is proposed.

  In order to solve the conventional problems, the inverter power supply of the present invention is realized by making the command signal (PWM) from the microcomputer for determining the high frequency output variable depending on the input power supply voltage. In addition, by fixing the PWM value in the range near the rated voltage, the nominal high-frequency output is secured in response to the component variation and the reading variation due to the power source impedance.

  According to the present invention, since the command signal (PWM) from the microcomputer for determining the high frequency output can be made variable according to the input power supply voltage, the nominal high frequency output can be easily guaranteed when the voltage fluctuates. This is because the input power can be controlled.

  When an AC motor is used as the cooling fan, the rotational speed naturally changes due to fluctuations in the input power supply voltage, that is, the cooling capacity also changes. Also in this case, in the present invention in which the input power can be controlled, it is possible to determine the optimum input power according to the cooling capacity.

  Furthermore, since it is fixed to the same PWM in the vicinity of the rated voltage, a nominal high-frequency output can be ensured by corresponding to variations in parts and reading variations due to power source impedance.

A first invention has an inverter power supply for driving a magnetron, a microcomputer for sending a command signal for determining a high frequency output to the inverter power supply, an input power supply voltage detection circuit for identifying an input power supply voltage, and a range in the vicinity of the rated voltage Is fixed, and the command signal of the microcomputer is changed even at the same high frequency output at the power supply voltage before and after that.

  According to a second invention, in the first invention, the command signal of the microcomputer is controlled so as to lower the high-frequency output only when the input power supply voltage is higher than the rated voltage.

  According to a third invention, in the first invention, the command signal of the microcomputer is controlled so as to lower the high-frequency output only when the input power supply voltage is reduced below the rating.

  According to a fourth invention, in the first invention, the command signal of the microcomputer is controlled so as to increase the high-frequency output only when the input power supply voltage is reduced below the rating.

  The fifth invention is characterized in that, in the first invention, the command signal of the microcomputer is controlled so as to lower the high-frequency output when the input power supply voltage is increased / decreased outside the rating.

  According to a sixth aspect of the present invention, in the first or second aspect, when the input power supply voltage is increased beyond a certain level, the control value of the microcomputer command signal is changed in a direction to further reduce the high-frequency output to notify the abnormality. A buzzer is provided.

  According to a seventh aspect of the present invention, in the first or fourth aspect of the present invention, when the input power supply voltage is reduced beyond a certain level, a limit is set on the control value of the microcomputer command signal in a direction to lower the high-frequency output, and an abnormality is detected. It features a buzzer to inform you.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that this embodiment is merely an exemplification that embodies the present invention, and the present invention includes various modes in which changes are made within the scope of the configurations described in the claims.

(Embodiment 1)
FIG. 1 is a block diagram according to the first embodiment of the present invention. Compared with the conventional high-frequency heating power supply device, an input power supply voltage detection unit 20 is added.

  That is, the information obtained by the input power supply voltage detection unit 20 can be fed back to the microcomputer 19. Using this information, the command signal (PWM) that determines the high-frequency output from the microcomputer 19 is made variable.

  FIG. 2 shows a PWM change in the case of a rating of 100V. Voltage is plotted on the horizontal axis, PWM is plotted on the vertical axis, and the standard rated PWM is a change when the on-duty is 80%. It can be said that PWM, which has been constant with respect to input voltage fluctuations, is variable according to the input voltage. Naturally, if PWM is large, the high frequency output is high, and if it is small, the high frequency output is low. PWM is a command signal that can determine a high-frequency output, and is a method of power control.

  At this time, it is defined as ± 5V because it is in the vicinity of the rating, that is, between 95V and 105V is the same PWM. Therefore, even if there is a reading variation due to component variation or power supply impedance, it is possible to ensure the nominal high-frequency output at the rating without extremely changing the PWM.

  Further, the PWM is lowered on the voltage increase side, that is, it can be said that the input power is brought close to the same as the rated vicinity. Therefore, the merit that the quality of cooking is exactly the same regardless of voltage fluctuation is born. Of course, without the hassle of changing the cooking time.

  Of course, these change characteristics may be the same according to the PWM corresponding to each high-frequency output, or may be changed in all high-frequency output bands.

(Embodiment 2)
FIG. 3 shows the characteristics of the input voltage -PWM in the second embodiment of the present invention. The PWM is lowered when the voltage is reduced, and this control is effective when the input current has an upper limit value (15A for household equipment in Japan, etc.) or when the cooling performance of parts is weak. That is, if the PWM is raised, the input current naturally increases, and there is a risk of breaking the breaker or exceeding the rated current value of the power cord, which can be used to avoid this.

(Embodiment 3)
FIG. 4 shows the characteristics of the input voltage-PWM in the third embodiment of the present invention. The PWM is raised when the voltage is reduced, and this control is effective when it is desired to keep the input power constant. That is, there is no restriction on the upper limit value of the input current, and there is a feature that the cooking quality with respect to voltage fluctuation is not affected.

  It has excellent cooling performance and can be used when there is room for the upper limit current. Of course, this PWM change may be set separately for each high-frequency output (for example, 1000 W, 800 W, 500 W, etc.).

(Embodiment 4)
FIG. 5 shows the characteristics of the input voltage-PWM in the fourth embodiment of the present invention. Both PWM are lowered when the voltage is increased or decreased outside the vicinity of the rating, and this control is suitable when you want to control the input power to be constant when the voltage is increased and to keep the temperature of the component below the upper limit current while reducing the voltage. . It can be said to be the safest control method that can control the current and power not exceeding the rating even when the voltage increases or decreases while securing the input power near the rating.

(Embodiment 5)
FIG. 6 shows the characteristics of the input voltage-PWM in the fifth embodiment of the present invention. The feature is that the amount of change in PWM is greatly reduced over an increased voltage (for example, 115 V) that is similar to the first embodiment.

  Then, as a process inside the microcomputer 19, for example, if it reaches a trigger voltage increase and operates for 60 seconds, it is possible to perform a safety measure such as sounding and stopping the buzzer (not shown). It is safer because of It can be used effectively in areas where power supply conditions are not stable.

(Embodiment 6)
FIG. 7 shows the characteristics of the input voltage-PWM in the sixth embodiment of the present invention. The characteristic is that the voltage lower than the reduced voltage (for example, 85V), which is similar to the third embodiment, is changed to decrease as the change in PWM.

  Then, as a process inside the microcomputer 19, for example, when the current voltage as a trigger is reached and the operation is performed for 60 seconds, it is possible to take a safety measure such as sounding and stopping the buzzer (not shown). It is safer because of It can be used effectively in areas where octopus foot wiring and power supply conditions are not stable.

As described above, according to the high-frequency heating device of the present invention, the command signal (PWM) from the microcomputer that controls the high-frequency output can be made variable according to the input power supply voltage. Can also be used as a protection function when abnormal voltage increases or decreases. Furthermore, since the vicinity of the rating is constant, it is possible to take into account variations in reading due to component variations and power source impedance, and it is easy to ensure a nominal high frequency output.

1 is a block diagram of a high-frequency heating power supply device according to a first embodiment of the present invention. Input voltage-PWM characteristic diagram in Embodiment 1 of the present invention Input voltage-PWM characteristic diagram in Embodiment 2 of the present invention Input voltage-PWM characteristic diagram in Embodiment 3 of the present invention Input voltage-PWM characteristic diagram in Embodiment 4 of the present invention Input voltage-PWM characteristic diagram in Embodiment 5 of the present invention Input voltage-PWM characteristic diagram in Embodiment 6 of the present invention Block diagram of a conventional high-frequency heating power supply device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectifier 3 Semiconductor switching element 4 Capacitor 5 Inverter resonance circuit 6 High voltage transformer 7 High voltage rectifier circuit 8 Magnetron 9 Choke coil 10 Capacitor 11 Filter circuit 12 Current transformer 13 Inductor 14 Control circuit part 15 Heating current supply line 16 Cathode part 17 Anode section 18 Inverter power supply 19 Microcomputer 20 Input power supply voltage detection section

Claims (7)

It has an inverter power supply that drives the magnetron, a microcomputer that sends a command signal for determining a high frequency output to the inverter power supply, and an input power supply voltage detection circuit that identifies the input power supply voltage. A high frequency heating apparatus characterized in that the command signal of the microcomputer is changed even at the same high frequency output at the power supply voltage. 2. The high frequency heating apparatus according to claim 1, wherein the command signal of the microcomputer is controlled so as to decrease the high frequency output only when the voltage of the input power supply is higher than the rated voltage. 2. The high frequency heating apparatus according to claim 1, wherein the command signal of the microcomputer is controlled so as to decrease the high frequency output only when the input power supply voltage is reduced below the rating. 2. The high frequency heating apparatus according to claim 1, wherein the command signal of the microcomputer is controlled so as to increase the high frequency output only when the voltage of the input power source is lower than the rated voltage. 2. The high frequency heating apparatus according to claim 1, wherein a command signal of the microcomputer is controlled so as to decrease the high frequency output when the input power supply voltage is increased or decreased except for the rating. 3. The buzzer according to claim 1, further comprising a buzzer for notifying an abnormality by changing the control value of the microcomputer command signal in a direction to further reduce the high-frequency output when the input power supply voltage exceeds a certain level. The high-frequency heating device described. 5. A buzzer for notifying abnormality by providing a limit to the control value of the microcomputer command signal in a direction to lower the high-frequency output when the input power supply voltage is reduced beyond a certain level. The high-frequency heating device described in 1.

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