JPH0546676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control device for a means for opening and closing the power supply of a power transformer in a high frequency output variable method for a high frequency heater.

Conventional technology In high-frequency heaters, the type of food to be cooked,
It has become common practice to set the high-frequency output to an appropriate level depending on the quality and finished product, and this is useful for improving cooking performance. As a means of varying the high-frequency output to an appropriate level as described above, two methods have been developed: one in which the high-voltage power supply to the high-frequency oscillator that emits the high-frequency output is intermittent, and the other in which the power supply side of the power transformer is intermittent. The latter is the mainstream in terms of performance, configuration, and cost.

Conventionally, there has been provided a power transformer that supplies power to a high-frequency oscillator, an A switch that cuts off the power on the power supply side of the power transformer, and an inrush current suppression load that is connected in series with the primary winding of the power transformer. , a B switch for intermittent power supply to the inrush current suppression load, and a series connection portion of the inrush current suppression load and the B switch is connected in parallel with the A switch. It was hot.

The operation of this conventional example is that the B switch, which controls the inrush current suppression load, is turned on a predetermined time before the A switch is turned on, and the excitation current of the power transformer rapidly increases.
In other words, generation of a large inrush current was prevented to some extent.

Problems to be Solved by the Invention However, with respect to the A switch, no measures have been taken to extend the life of the contacts of the switch by controlling its opening timing and closing timing in accordance with the power supply voltage phase. However, regarding the control of the B switch connected in series with the inrush current suppression load, it closes and closes at a predetermined timing, regardless of the opening phase of the A switch.
In addition, an opening operation was being performed.

Therefore, depending on the opening phase of the A switch, the residual magnetic flux of the power transformer may be affected, and a large inrush current may occur when the B switch is closed. In addition to having to use a device with a large capacity, there were problems such as noise generation due to the large pulsed current.

The present invention solves these conventional problems, and provides a high-frequency heating device that significantly reduces inrush current and incorporates a control device that enables the use of switches with small contact capacity. It is something.

Means for Solving the Problems The high-frequency heating device of the present invention includes a power transformer for supplying power to a high-frequency oscillator, a switching means for intermittent power supply on the power supply side of the power transformer, and a switching means connected in parallel with the switching means. an inrush current suppression load and its switching means, the switching means;
The main control section for controlling the power supply voltage phase detection section, the timer section, the deciding means for deciding the opening/closing timing of the opening/closing means, and the timing control section for controlling the opening/closing means based on the signal of the deciding means. It is composed of.

Effect: The high-frequency heating device of the present invention causes the switching means that controls the inrush current suppression load to perform the closing operation in response to the opening operation phase of the switching means controlled by the signal from the determining means in the main control section. Therefore, the inrush current can be significantly reduced, and a switching means with a small current capacity can be used.

Embodiments Hereinafter, the high frequency heating device of the present invention will be explained with reference to the drawings.

FIG. 2 shows an external view of one embodiment. 1
1 is a main body of a high-frequency heater, and a heating chamber 2 made of a ferromagnetic material is provided within this main body 1. A door 3 that can be opened and closed at will is provided at the opening of the heating chamber 2 to take food in and out of the heating chamber 2. On the front of the main body 1, there are controls for setting and displaying cooking time, output, etc. An operating section 4 is provided to perform the operations.

Next, FIG. 1 shows a block diagram of the main components of the high frequency heating device of the present invention. 5 is a high frequency oscillator that supplies high frequency output to the heating chamber 2; 6 is a power transformer that supplies power to the high frequency oscillator 5; and 7 is a power supply section. Reference numeral 8 denotes a switching means for intermittent power supply on the power supply side of the power transformer 6, 9 a load for inrush current suppression connected in series with the primary winding of the power transformer 6, and 10 for the load for inrush current suppression. As shown in the drawing, the series connection portion of the load 9 and the switching means 10 is connected in parallel with the switching means. 11 is a main control unit that controls the opening/closing timing of the opening/closing means 8, 10, which includes a power supply voltage phase detection unit 12, a timer unit 1;
3. The main components are a determining means 14 that determines the opening/closing timing of the opening/closing means, and a timing control section 15 that outputs a control signal based on the signal from the determining means 14. A signal from the power supply unit 7 is input to a power supply voltage phase detection unit 12, which determines which phase the power supply voltage is in. The determining means 14 determines when to turn on and off the power to the power transformer 6 in order to supply an appropriate high frequency level, and also determines when to open and close the switching means. That is, when power is supplied to the power transformer 6, the opening/closing means 10 is first closed at a predetermined voltage phase, and then the opening/closing means 8 is closed after a predetermined time when the excitation current is approximately stabilized. With this operation, the voltage of the power supply section is directly applied to the power transformer 6.
Thereafter, after another predetermined period of time, the opening/closing means 10 is operated to open, and the power supply to the rush current suppressing load 9 is stopped. In response to the signal from the aforementioned determining means, the timing control section 15 outputs a control signal to the opening/closing means 8 and 10. The output timing of this control signal is based on the signal from the power supply voltage phase detection section 12 and
It is managed by a signal from the timer section 13. That is, if the signal of the power supply voltage zero cross point is input from the phase detection section 12 and the elapsed time from that point is counted and synchronized with the signal of the timer section 13, the switching means 8 and 10 are operated at a predetermined power supply voltage phase. It can be controlled. Further, the timing of outputting the control signal may be determined by taking into consideration the operation delay time of each opening/closing means 8, 10.
1, it is possible.

Next, a specific embodiment of the present invention will be described with reference to FIG. Components with the same numbers as in the previous figure are components having the same functions. One side of the commercial power source 16 is connected to one side of the primary winding of the power transformer 6 via a latch switch 17 that detects door opening/closing and the opening/closing means 8 and 10, and the other side of the commercial power source 16 is connected to the current fuse 18 and the It is connected to the other end of the primary side of the power transformer 6 via a latch switch 19 that operates similarly. Reference numeral 20 denotes a short switch, which operates with a time lag from the latch switch 17.
7 is turned off when the door is open, whereas this shot switch 20 is turned on. 21 is an internal lamp, 22 is a cooling fan motor, and switch contact 2
Controlled by 3a. 24 is a low voltage power transformer,
The diode 25, the smoothing capacitor 26, and the constant voltage power source 27 constitute the main control section 11 and a low voltage power source for the switch. A door switch 28 operates in synchronization with the latch switch 17, and a connection point with a resistor 29 is input to the control section 30 as a door opening/closing signal. In addition, diodes 32, 3
4 and resistors 31 and 33 constitute a power supply voltage phase detection section 12 that detects zero crosses of the power supply voltage. The capacitors 35 and 36 and the oscillator 37 generate a reference clock for the timer section 13. The inverter buffers of 38, 39, and 40 are
This is a drive section for the switch contact drive coils 10b, 8b, and 23b, and is operated by a signal from the control section 30. Further, a capacitor 41 and a diode 42 in the figure are for driving the high frequency oscillator 5.

Here, the control section 30 includes a determining section 14 that determines the control timing of the above-mentioned opening/closing means 8 and 10, a timer section 13, and a timing control section 15.
It is included. These controls are processed by, for example, a predetermined program stored in a microcomputer.

FIG. 4 illustrates the control program flow of this embodiment. First, the power supply clock is taken in and a predetermined phase of the power supply voltage waveform is used as the reference point for controlling the opening/closing means. Next, determine whether it is necessary to operate the switch from on to off or from off to on,
When operation is necessary, first determine whether or not the internal timer is activated, and if not activated, determine the internal timer time to operate at a predetermined phase depending on the switch to be controlled, Perform initial settings. After startup, while performing other processes, it waits for the internal timer time to elapse, and when it elapses, it outputs a signal to drive the switch coil shown in FIG. 3. As mentioned above, if the operating time of the switch itself is a problem, it is only necessary to set the internal timer in consideration of it.

In FIG. 5, the operating states of the opening/closing means 8 and 10 are shown in a timing chart. a is a power supply voltage waveform, b is an operation signal of the switching means 8, and c is an operation signal of the switching means 10. In order to obtain an appropriate high frequency output level, the time of the high frequency oscillator is controlled, but the phase θ1
At time t ₁ , the opening/closing means 8 performs an opening operation to stop the power supply to the power transformer 6 . Next, after a predetermined off time has elapsed, the opening/closing means 10 is closed at time _t2 of θ2, which corresponds to the phase θ1 and is earlier by θ3. Thereafter, when T ₁ has passed, the opening/closing means is operated to close, and further after T ₂ has passed, the opening/closing means 10 is operated to open. Thereafter, the opening/closing means 8 is operated to open after a predetermined on-time period has elapsed. By the way, when the primary side of the power transformer 6, which has inductance, is turned off, if the switching means 8 is constituted by a relay or the like, arc discharge occurs at the contacts, causing the contacts to wear out. Therefore, a method is used in which the positive and negative phases of the power supply voltage are alternately cut off every predetermined number of times.
The closing phase θ2 is also determined corresponding to the shutoff phase θ1.

Next, regarding the closing phase and the opening operation phase of the switching means, it will be shown that the inrush current is reduced according to the content of the present invention.

When a voltage is applied to the power transformer 6 due to the zero phase of the power supply voltage, the transient excitation magnetic flux Φ generated in the iron core
If the maximum magnetic flux in the steady state is Φm, then the magnetic flux changes until the direction of the excitation magnetic flux is reversed. Further, when the power transformer 6 that is energized is cut off at an arbitrary phase, residual magnetic flux remains in the iron core. The rush current that occurs when power is applied to the power transformer 6 is:
It is determined by the magnitude of the transient magnetic flux Φ generated in the iron core when it is turned on.

To further explain with reference to FIG. 6, this transient magnetic flux Φ
is given by the sum of the amount of change in the excitation magnetic flux at the time of input and the residual magnetic flux Φr remaining in the iron core, and when this transient magnetic flux Φ exceeds the saturation magnetic flux, the excitation current, that is, the rush current increases rapidly. If the circuit is interrupted at point A in the same figure, a residual magnetic flux Φr will remain, and then, if the opening/closing means 10 is closed at a predetermined phase corresponding to point A, here, at point B, which is approximately π/2 ahead of phase. , a magnetic flux Φx' corresponding to the applied voltage reduced by the inrush current suppressing load 9 corresponding to the excitation magnetic flux Φx is generated. The transient magnetic flux Φ at this time
becomes as shown in equation (1).

Φ=[Φm′−Φx′]+(+Φr) −(1) Here, Φm′...Magnetic flux via the inrush current suppression load corresponding to the maximum magnetic flux Φm Φm′−Φx′...At phase B Amount of change until the magnetic flux is reversed after turning on
If point B has a phase advanced by π/2, the residual magnetic flux Φr
has the maximum value Φrmax (<Φm), and since the excitation magnetic flux at the time of input is zero, the amount of change is Φm'. Substituting into (1), we get Φo = Φm′−Φrmax −(2), and the inrush current is suppressed.

Next, if point A is set to π/2, the residual magnetic flux Φr is zero and the amount of change in the excitation magnetic flux is 2Φm'. Substituting it into (1), Φπ/2 = 2Φm' + O, resulting in an extremely large inrush current level. Must not be.

Effects of the Invention As described above, the high-frequency heating device of the present invention includes a main control section that includes a power supply voltage phase detection section, a timer section, a determining means for determining the opening/closing timing of the opening/closing means, and a determining means for determining the opening/closing timing of the opening/closing means. and a timing control section that controls the opening/closing means.The following effects can be obtained.

(1) Regarding the operation of the switching means, inrush current can be significantly reduced or eliminated by controlling the voltage phase corresponding to the opening operation of the switching means.

(2) Since inrush current is suppressed, it is possible to use a switch with relatively small contact capacity,
This allows for thorough design considerations.

(3) By reducing inrush current, it is possible to prevent magnetic vibration noise from heating chambers, etc.

(4) By reducing inrush current, impulsive noise is minimized, and noise resistance performance can be improved.

[Brief explanation of the drawing]

Fig. 1 is a main block diagram of the high frequency heating device of the present invention, Fig. 2 is an external view of the high frequency heating device which is an embodiment of the present invention, and Fig. 3 is a specific circuit diagram of the high frequency heating device which is an embodiment of the present invention. Fig. 4 is a control flow diagram of an embodiment of the present invention, Fig. 5 is a timing chart of an embodiment of the invention, and Fig. 6 is a voltage phase opening/closing phase of the power transformer. It is a figure showing the relationship of magnetic flux. 2...Heating chamber, 5...High frequency oscillator, 6...Power transformer, 8...Switching means, 9...Load for inrush current suppression, 10...Switching means, 11...Main control section, 12...Power source Voltage phase detection section, 13...timer section, 14...determining means, 15...timing control section.

Claims (1)

[Scope of Claims] 1. A heating chamber for storing food, a high-frequency oscillator that supplies high-frequency output to the heating chamber, a power transformer that supplies power to the high-frequency oscillator, and a primary winding on the power supply side of the power transformer. a switching means for intermittent power supply to the line; an inrush current suppression load connected in series with the primary winding of the power transformer; and a power supply to the inrush current suppression load and the primary winding of the power transformer. and a main control section that controls the opening/closing timing of the switching means in relation to the power supply phase, and the series connection part of the inrush current suppression load and the switching means is connected in parallel to the switching means. The main control section includes a power supply voltage phase detection section that detects the phase of the power supply supplied to the power transformer, and a timer section that receives a signal from the power supply voltage phase detection section and measures time. A high-frequency heating device comprising: a determining means for calculating and determining the opening/closing timing of the opening/closing means; and a timing control section for controlling the opening/closing means based on a signal from the determining means and a signal from the timer section. 2. After controlling the opening/closing means to stop the power supply to the high frequency oscillator, when controlling the switching means to close the switching means to supply power to the high frequency oscillator again, the switching means is in the off phase (opening phase). 2. The high-frequency heating device according to claim 1, wherein the opening/closing means is controlled in a corresponding on phase (closed phase). 3. The high-frequency heating device according to claim 2, wherein the opening/closing means is closed at a phase that is approximately π/2 ahead of the opening phase of the opening/closing means.