JPH01687A - High frequency heating device - 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 Industrial Application The present invention relates to a high frequency heating device equipped with a microcomputer.

Conventional technology FIG. 4 is a control circuit diagram of a conventional high-frequency heating device.

Reference numeral 1 denotes a control unit, ie, a microcomputer, which controls relays, display tubes, etc. 2 is a relay for phase control of the high voltage transformer,
3 is a relay for controlling lamps, fan motors, etc., 4 is a magnetron, and 5 is a high voltage transformer. 7 is an unstabilized relay power source, 9 is a commercial power source, and 10 is a start switch. The operation of the control circuit configured as described above will be explained below.

First, by pressing the start switch 10, a command to start heating is input to the microcomputer 1. Then, the microcomputer first sets the control signals R1 and R2 of the lamp, turntable, and fan motor control relay 3 to Hlgh, and then sets the control signal R3 of the phase control relay 2 of the high voltage transformer to Hlgh. Then, the contact of the relay 2 is turned on, voltage is applied to the primary side of the high voltage transformer 5, and power supply to the magnetron 4 is started. The high frequency output is switched by switching the ON time of the relay 2, that is, the duty, as shown in FIG. When voltage is applied to the primary side of the high-voltage transformer 5, current flows into the primary side of the transformer 5 (hereinafter abbreviated as "rush current").
flows, and the resulting magnetic field attracts the metal oven wall or the metal external box on the side of the high-voltage transformer, producing a loud ``ton'' sound. (not shown)
Here, rush current will be explained using FIGS. 6 and 7. FIG. 6(a) shows the relationship between the primary voltage of the transformer 5 and the magnetic flux Φ1 of the iron core of the transformer 5 when the transformer 5 is excited. Thereby, the relationship between the ON phase of the relay 2 and the magnetic flux Φ1 can be found.

FIG. 6(b) shows the relationship between the primary voltage v2 and the magnetic flux amount Φ2 when the transformer 5 is saturated. Is this supposed to be it? - shows the relationship between the off-phase of relay 2 and magnetic flux Φ2. FIG. 7 shows the B-8 curve of this transformer 5 and the magnitude of the rush current with respect to the ON phase of the relay 2. Now, Figure 6(a).

As shown in Figure 3), the on point of the relay 2 is set to one point (ie, the point where the on phase is 0), and the off point is set to point b (ie, the point where the off phase is 1/4π). The magnitude of the inrush current is the sum of the amount of change in magnetic flux ΔΦ1 from one point, which is the ON point, to the point where the direction of voltage v1 is reversed, and the magnetic flux Φ2 at point b, which is the OFF point, that is, the magnetic flux (ΔΦ1 + Φ2). It will be proportional to. Now, from ΔΦ1=2·Φ□, Φ2=0, and Φ□=·am (here, 8□ is the magnetic flux density, which is a constant), an inrush current proportional to the magnetic flux density of +28 m flows. As shown in FIG. 7, this magnitude can be determined from a single point plotted on the B-H curve as the magnetic field strength Hl and the inrush current 11. This value is more than ten times the normal current lff1. The relationship between the on-phase of relay 2 and the inrush current is as follows:
If we now consider Φ2=o, the result will be as shown in the lower part of FIG. Therefore, in order to keep this inrush current low,
It is necessary to control the on-phase and off-phase of the relay 2. Therefore, emphasis has been placed on phase control of the relay 2 using a microcomputer. FIG. 8 shows the timing chart. INT is a power supply clock signal used for clocks and timers. After time TSIG, the microcomputer takes the falling point of the INT signal, that is, the point A, as a reference.
The relay 2 control signal R3 is set to Hl, h, and the contact is further turned on after the relay operating time TOI. In addition, here T
SIG is determined by a microcomputer program and is always constant. The problem here is the variation in relay operating time.

Problems to be Solved by the Invention A particular problem in the phase control of the relay 2 is the above-mentioned fluctuation in the operating time of the relay. FIG. 9 shows the relationship between the relay coil drive voltage (i.e., relay control power supply voltage) and the relay operating time.
If there is even a slight change in the relay operating time, the relay operating time will change significantly. FIG. 10 shows the relationship between relay 3 (control signals R1 and R2), relay 2 (control signal R3), and relay control power source at the time of starting cooking. Relay 2 is turned on after a time T1 after relay 3 is turned on. The relay control power supply VM was at vO before the start, but after T1 after the start, that is, the relay 2 control signal R3 became Hlg.
When the voltage reaches h, the voltage becomes vl, and finally the voltage stabilizes at v2. In this way, the control power supply VM for the relay is not stabilized, and as shown in FIGS. 11 and 12, it fluctuates greatly depending on the current consumption of the relay and the like. If we consider stabilizing the power supply, it would lead to a significant increase in cost, and it would also lead to an increase in the size and capacity of the low-voltage transformer, so there is no possibility of realizing it. Figure 13 shows relay 2 (
That is, it shows the relationship between each signal and the relay control power supply pressure when the control signal R3) is intermittent during cooking and the output is switched. In this case, relay a is continuously turned on, and only relay 2 repeatedly disconnects.

At this time, the voltage at the time when the relay 2 control signal R3 becomes Hlgh becomes v1', and eventually stabilizes at voltage v2 when the relay is completely operated. Therefore, as shown in FIGS. 9, 10, and 13, the voltage at the time when the relay 2 control signal R3 becomes Hlgh at the start of cooking and when the relay is in the intermittent state. is v1 at the start and v1' at the time of intermittent operation. Then, from FIG. 9, the relay operation time is TQI at the start time and Tol at the intermittent time, and is longer at the intermittent time. That is, TOI<701' and &ru・8th
Based on the relationship with the inrush current shown in the figure, if the inrush current is suppressed during discontinuation, the relay contacts will be turned on at TSIG+Tδ1' during discontinuation, and the inrush current will be reduced to lFl. However, when starting cooking, To
l<Tot' and T! 51G +T01 Kuding SI
G + T01', the on-phase of the relay becomes early, and the rush current becomes 1P, which is significantly larger than the value of TofuV.

Here, the conventional method has the following drawbacks.

(1) The inrush current becomes large either at the start of cooking or when the relay is intermittent, and the adhesion noise due to the generated magnetic field is large.

(2) i4 [Large noise occurs on the line, causing the microcomputer to malfunction.

(3) Relays with large contact ratings and capacities are required, resulting in a significant increase in cost.

4) There is a risk of relay contacts welding, etc.

(5) When considering stabilization of the power supply voltage for the relay, it is necessary to add a constant voltage element and improve the regulation of the low voltage transformer, resulting in a significant increase in cost.

Means for Solving the Problems The present invention provides a heating chamber for accommodating an object to be heated, a heating means provided in the heating chamber, a high-voltage transformer for supplying power to the heating means, and a phase shifter for the high-voltage transformer. first to control
relay, and a second one that controls the lamp, fan motor, etc.
, a control power supply for the unregulated relay, and
a microcomputer that controls the relay, and the microcomputer controls the first relay at a certain predetermined level after the second relay operates and the control power supply voltage for the relay decreases and reaches an equilibrium state. This is a high-frequency heating device configured to operate after a certain period of time.

Function The high-frequency heating device of the present invention improves the method of phase control of a relay for suppressing inrush current to a high-voltage transformer.

At the start of cooking, after the other relays are turned on and the relay control power supply voltage becomes stable, relay 2 is turned on to equalize the voltage applied to the relay at the start of cooking and during intermittent cooking, ] The operating time can be made equal, and the inrush current at both start and intermittent times can be reduced.

EXAMPLE An example of the present invention will be described below. Figure 1 shows
FIG. 2 is a control circuit diagram of the high-frequency heating device of the present invention. 1 is a microcomputer, 2 is a phase control relay for a high voltage transformer, ie, a first relay, 4 is a magnetron, and 5 is a high voltage transformer. 7 is a control power supply for the relay, 8 is A
/D circuit. The A/D circuit 8 inputs the relay control power supply voltage (LJ) to the microcomputer, and the microcomputer determines the value of the relay control power supply voltage VM.

To ensure phase control of the high-voltage transformer at the start of cooking and during intermittent cooking (that is, to match the on-phase of the relay contacts at a point where the inrush current is low).
As shown in FIGS. 10 and 13, the voltages v1 and v immediately after the control signal R3 of the first relay 2 is turned on are
1' must be made equal, and the relay operating times of relay 2 must be made equal. However, the voltage v1' during intermittent operation is
The control power supply voltage for the relay has reached an equilibrium state and is constant.

Therefore, when starting cooking, the control signals R1 and R2 of the second relay that controls the lamp, fan motor, etc. are turned on, and the contacts of these relays are turned on reliably.
After the control power supply voltage VM for the relay reaches equilibrium after decreasing, (
In other words, the time Tsi = after 3 days), and a certain predetermined time Δ
After T, the control signal R3 of the first relay 2 is turned on. As shown in FIG. 2, at this time, the relay control power supply voltage VM is v1', which is equal to the voltage when the control signal R3 of the first relay is turned on during the intermittent operation. Therefore, the operation time of the relays and - is the same both at the start of cooking and at the time of intermittent cooking. Here, the time T1' from when the second relay 3 is turned on until the first relay 2 is turned on is the time from when the second relay is turned on until the control power supply voltage VM for the relay reaches an equilibrium state. Then, if a certain predetermined time (approximately 100 m5eo) is two guns, then Tl'
=TSET+ΔT. This time TI' is determined by the relationship between the current and voltage of the control power supply voltage for the relay, and can be written in the microcomputer as a constant. Therefore, as shown in Fig. 3, the first
The relay control power supply voltage VM when the relay turns on is
By setting VM=V1' equal, the operating time of the first relay at the start of cooking and during intermittent cooking is 7.
61 = r6I', the on phase of the first relay is the same at the start of cooking and at the time of intermittent cooking, and the phase angle is 2.
The angle was close to 70°, and the inrush current was 1F/, which was extremely small.

Furthermore, as shown in Fig. 1, if a microcomputer with an A/D function is used and the voltage detection means 8 is used, the control power supply voltage VM for the relay reaches equilibrium after the second relay is turned on. The microcomputer can automatically recognize the time TSET. This is for the relay. - The control power supply voltage VM is input to the microcomputer A/D input terminal J1 through two resistors P1 and r2. Since the microcomputer is equipped with an internal A/D converter, it converts it into a digital quantity internally. Now, if we assume that the relay control power supply voltage VM is in an equilibrium state when it reaches v1', the level 1 at which the microcomputer determines that the VM is in an equilibrium state is as follows.

Now, if the power supply voltage of the microcontroller is VDO, then (256
level division). Therefore, the input port 1 microcomputer of the microcomputer calculates that the level is LST, and determines that the relay control power supply voltage is in a balanced state. Therefore, after a predetermined time ΔT, the control signal R3 of the first relay 2 is turned on. Therefore, even in this case, the first
The voltage when the relay is turned on is the same both at the start of cooking and when cooking is interrupted, the operating time of the first relay is the same, and the inrush current is also suppressed to a low level.

By the way, depending on the power supply, it takes a long time for the control power supply voltage VM for the relay to reach an equilibrium state. In such a case, whether VM has almost reached an equilibrium state can be determined by using the VM reduction curve 0. If it is 5V/1 second, it is determined that the state is almost in equilibrium, and TSET is determined.

Effect of the invention With the above configuration, the present invention has the following effects.

(1) The inrush current of the high-voltage transformer is always small at the start of cooking and during intermittent cooking, making it possible to reduce the adhesion noise caused by the generated magnetic field.

(2) Relays with smaller contact ratings and rated capacities are better, making it possible to significantly reduce costs and downsize.

(3) The critical problem of relay contact welding has been completely eliminated, and the number of guaranteed durability has been dramatically improved.

(4) Changing the phase control sequence by changing the power supply circuit or changing the relays requires only changing one constant in the microcomputer, resulting in a significant increase in design efficiency.

(5) Since the control power supply voltage for the relay is a balanced (that is, stable) voltage at the time the relay operates, the bouncing time of the relay is reduced and reliability is improved.

[Brief explanation of drawings]

FIG. 1 is a control circuit diagram of a high-frequency heating device in an embodiment of the present invention, FIG. 2 is a timing chart of in-phase control,
Figure 3 is a timing chart of the same phase control sequence.
Fig. 4 is a control circuit diagram of a conventional high-frequency heating device, Fig. 5 is a timing chart of the microwave thawing sequence,
6(a), (b), and 7 are waveform diagrams showing the relationship between voltage phase, magnetic flux, and inrush current, and FIG. 8 is a timing chart of conventional phase control. Fig. 9 is a graph showing the relationship between the operating time and drive voltage of the same relay, Fig. 10 is a timing chart of conventional phase control, Fig. 11 is a power supply circuit diagram of the same, and Fig. 12 is a graph showing the voltage and current of the same power supply circuit. Characteristic diagram, 1st
FIG. 3 is a timing chart of in-phase control. 1...Microcomputer, 2...Relay for phase control, a...Relay for controlling lamps, motors, etc.
4... Magnetron, 5... High voltage transformer, 7... Control power supply for relay, 8...
A/D circuit. Name of agent: Patent attorney Toshio Nakao Haka 1 person 4 people
- Magnetron Figure 1 1g 2 Figure 7? lr+ = n5+' Figure 4 Figure 5 Figure 6 680 X yc 3. ．． 2. c Fig. 7 To+-5TARTk Fig. 8 T6+' - On the way - time zone 〉Δ-&Au ¥1!2゜':y' Mound Fig. 11 Fig. 12 Current IM Fig. 13 T.

Claims (2)

[Claims] (1) a heating chamber for accommodating an object to be heated; a heating means provided in the heating chamber; a high voltage transformer for supplying power to the heating means; a first relay for controlling the phase of the high voltage transformer; A second relay that controls a controlled object other than a high-voltage transformer, an unstabilized relay control power source, and a control unit that controls the first and second relays, the control unit comprising: The high frequency heating device is configured to operate the first relay after a certain predetermined time after the second relay operates and the control power supply voltage for the relay decreases and reaches an equilibrium state. (2) a heating chamber for accommodating an object to be heated; a heating means provided in the heating chamber; a high-voltage transformer for supplying power to the heating means; a first relay for controlling the phase of the high-voltage transformer; a second relay that controls a controlled object other than the high-voltage transformer; an unstabilized relay control power source; a power supply voltage detection means connected to the relay control power supply; and an output from the power supply voltage detection means. a control section that controls the first and second relays by inputting the output from the power supply detection means, and the control section controls the first relay by inputting the output from the power supply detection means. A high-frequency heating device configured to operate a relay a certain predetermined time after the relay operates and the control power supply voltage for the relay decreases and reaches an equilibrium state.