JPH01276587A - 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 phase control of a power relay used as a means for opening and closing the power supply of a high-voltage transformer in a high-frequency output variable method for a high-frequency heating device.

In conventional high-frequency heating devices, it has become common practice to set the high-frequency output to an appropriate level depending on the type, quality, and finished state of the food to be cooked, which is useful for improving cooking performance. As a means of changing the high-frequency output to an appropriate level, two methods have been developed: one in which the high-voltage transformer that supplies the high-frequency oscillator that emits the high-frequency output is switched on and off, and the other on the primary side of the high-voltage transformer. In particular, the latter primary-side intermittent method has become mainstream from the viewpoint of cost, insulation performance, and configuration.

A conventional example is shown in FIG.

High-power electronic components (for example, triacs, etc.) and power relays are used as means for disconnecting the primary side of a high-voltage transformer that supplies power to a high-frequency oscillator. Using a triac has the advantage of being able to accurately control the power-on phase when turning on the power to the high-voltage transformer, and keeping the inrush current of the high-voltage transformer low, but it also has the advantage of being able to keep the inrush current of the high-voltage transformer low; There is a high risk that the triac will be easily damaged due to the surge voltage generated inside the main body, and the failure mode will be short circuit, and power will be constantly supplied to the high voltage transformer, creating a dangerous situation where high frequency oscillation will occur. To prevent this, it is necessary to improve the protection circuit. Additionally, auxiliary parts such as photocouplers are required to insulate between the power supply circuit and the control circuit, making the configuration complicated.

FIG. 6 shows a conventional example using a power relay.

Reference numeral 5 denotes a main circuit, which connects the contacts of a power relay 8 to the primary side of a high-frequency oscillator 6 that irradiates high-frequency output to the heating chamber and a high-voltage transformer 7 that supplies power to the high-frequency oscillator 6, and opens the contacts.
The high frequency output is made variable by turning on the power. Reference numeral 9 indicates a control circuit that controls the power relay 8. low voltage transformer 10
The commercial power supply is stepped down to about 30V and is used to supply power to the control circuit. The power relay power supply circuit 11 half-wave rectifies the alternating current power to create a voltage to be supplied to the operating coil of the power relay 8. The microcomputer power supply circuit 12 generates the voltage necessary to operate the microcomputer 13. The microcomputer 13 controls the opening and closing phases of the power relay 8 and performs a series of operations based on a predetermined sequence, and is the core of the control circuit. The power supply clock circuit 15 is a waveform shaping circuit that converts a commercial power supply waveform into a voltage waveform that can be recognized by the microcomputer, and serves as a reference for controlling the phase of the power relay 8. The power relay drive circuit 16 is
This is a control circuit that controls the power relay 8 connected to the primary side of the high voltage transformer 8.

Problems to be Solved by the Invention FIG. 7 shows a timing chart showing a conventional phase control method. When a magnetic material is used for the core of a transformer, the magnetic field H
and has hysteresis characteristics in magnetic flux density. Furthermore, even if the external magnetic field (current on the primary side of the high-voltage transformer) is cut off, a residual magnetic flux ±Φr remains inside the transformer core. (a) When the voltage waveform of the high-voltage transformer is turned on at the 0 phase, the excitation flux generated in the core of the power transformer will be at most 1Φm until the direction of the excitation flux is reversed, assuming that the steady maximum magnetic flux is Φm. It changes up to +Φm. Next, when the high-voltage transformer is turned on, for example, when it is opened, the residual magnetic flux will be +Φr
becomes. Next, if it is turned on at point A, the magnetic flux at the time of turning on is Φ
becomes Φ=-Φm+Φr. By reversing the opening and closing phases, the magnetic flux inside the core can be reduced, but Φm~
Φr, it is not possible to completely prevent inrush current when turning on. In addition, an example is shown when the closing phase angle is set to 0 point (π) in (1+1).If the closing phase angle is set to π, the excitation flux at closing becomes 0 and there is only residual magnetic flux Φr, but at closing,
This Φr causes an inrush current to flow. If the phase control is incorrect, the core of the high-voltage transformer becomes saturated, and the inrush current value reaches about ten times the steady state value, which may blow the fuse or turn off the breaker of the home power supply.

The present invention is intended to solve such conventional problems, and aims to suppress the inrush current value by creating a phase in which the residual magnetic flux when the high-voltage transformer is opened and the excitation flux when it is turned on completely cancel each other out.

Means for Solving the Problems In order to solve the above problems, the high-frequency heating device of the present invention includes a heating chamber for heating food, a high-frequency oscillator that supplies high-frequency output to the heating chamber, and a high-frequency oscillator that supplies power to the high-frequency oscillator. It has a high-voltage transformer, a power relay that connects the power to the high-voltage transformer, and a control unit that controls the power relay. The system is equipped with a phase setting circuit that sets the phase of the power relay to a phase in which the residual magnetic flux caused by turning on the high-voltage transformer and the excitation flux caused by the opening of the high-voltage transformer cancel each other out.

Effect of the Invention With the above-described configuration, the present invention suppresses the inrush current by suppressing the magnetic flux of the high-voltage transformer core to O when the power relay is turned on, improves the contact durability of the power relay, increases reliability, and reduces ferromagnetism caused by the inrush current. This also has the effect of preventing magnetic vibrations in the heating chamber, etc., which is made up of the body.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 2 shows an external view of one embodiment. Reference numeral 1 denotes a main body of a high-frequency heating device, and a heating chamber 2 made of a ferromagnetic material is provided within this main body 1. A fan 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, and an operating section 4 on the front of the main body 1 is used to set cooking time, output, etc. A display section 5 is provided to display the information.

FIG. 3 shows an example of a circuit diagram of the present invention. This circuit example uses a microcomputer (hereinafter referred to as microcomputer), and may be constructed using discrete components. 5 is a main body circuit, which connects the contacts of a power relay 8 to the primary side of a high-frequency oscillator 6 that irradiates high-frequency output to the heating chamber 2 and a high-voltage transformer 7 that supplies power to the high-frequency oscillator 6, and operates by opening and closing the contacts. The high frequency output is variable. 9 is power relay 8
The control circuit that controls the is shown. The low voltage transformer 10 steps down the voltage of the commercial power supply to about 30V and supplies power to the control circuit. The power relay power supply circuit 11 half-wave rectifies the alternating current power to create a supply voltage for the operating coil of the power relay 8. The microcomputer power supply circuit 12 is connected to the microcomputer 13
It creates the voltage necessary to operate. The microcomputer 13 includes a power supply phase monitoring circuit 14a that detects the phase of the commercial power supply using a power supply clock circuit 15 (described later), and indirectly recognizes the residual magnetic flux and excitation flux of the high-voltage transformer, and outputs power to phases that cancel each other out. It has a phase setting circuit 14 that sets the phase of the relay. The power supply clock circuit 15 is a waveform shaping circuit that converts a commercial power supply waveform into a voltage waveform that can be recognized by the microcomputer 13, and serves as a reference for controlling the phase of the power relay. The power relay drive circuit 16 is a control circuit that controls the power relay 8 connected to the primary side of the high voltage transformer.

FIG. 3 shows a timing chart showing the phase control method of the present invention. When the power relay is opened at an arbitrary phase of a high voltage transformer that is energized, the high voltage transformer core will be
A residual magnetic flux Φr remains. Therefore, the inrush current that occurs when power is applied to the high-voltage transformer is determined by the magnitude of the transient magnetic flux Φ that occurs when the power is turned on. This transient magnetic flux is determined by the sum of the excitation flux at the time of input and the residual magnetic flux remaining in the core. When this transient magnetic flux exceeds the saturation magnetic flux of the core, the excitation current increases rapidly and appears as an inrush current.

The timing for preventing inrush current will be explained with reference to FIG. 3(a). The left diagram shows the relationship between the magnetic flux density of the core and the magnetic field H.

Magnetic flux is proportional to the current flowing through the high voltage transformer. When an alternating magnetic field is applied to the core, a magnetic flux with a certain hysteresis is generated. The figure on the right shows the voltage waveform and current (magnetic flux) waveform of the high-voltage transformer.

Current has a characteristic that its phase lags behind voltage by π. When the power supply is opened at point A, the residual magnetic flux Φr at point A' remains in the core. Next, if the point at which the power to the high-voltage transformer is turned on is set to timing A or 2, an excitation flux of A' or G is generated. Therefore, the generated magnetic flux Φ becomes Φ=(-Φ')+Φr=0, and the rush current can be suppressed to a small value.

A phase control method using this configuration will be explained. (b) is
This shows the waveform of a low-voltage transformer that steps down commercial power.

(0) is a waveform obtained by shaping the stepped-down power supply waveform to a level that can be recognized by the microcomputer.

This is input to the INT terminal of the microcomputer, and the opening and closing phases are determined based on the rising edge of this waveform. (d+ indicates the opening timing, and τ1 is stored in the memory of the microcomputer. T is the return FF return time of the power relay, and the opening timing of the power relay is τ from the standard.
After +T, the power supply is opened. (e) is 1
OFF Indicates the input timing and stores 2 in the microcomputer memory. "ON" indicates the operating time of the power relay.The timing of turning on the power relay is that the power is turned on after τ2+ToN from the standard.

FIG. 4 shows a case where the opening phase is reversed (positive polarity).

Similar to FIG. 3, the closing phase has two valid points. The timing is as described above. By using such phase timing, inrush current can be suppressed to a minimum. Also, when the /X'l power relay is opened, an arc occurs between the contacts. Silver alloy is often used as the contact material, but if the opening phase is fixed, when an arc occurs,
Silver is consumed in only one direction, causing contact failure. Therefore, contact failure can be improved by setting the opening phases to the positive electrode side and the negative electrode side.

As described above, according to this embodiment, it is possible to eliminate inrush current caused by the opening/closing operation of the power relay that opens and closes the power supply of the high-voltage transformer, improves the contact durability of the power relay, and has excellent insulation performance and anti-noise performance. The power relay can be used as a switching element for the power supply of a high-voltage transformer, and can be configured at low cost.

Effect of the invention As described above, the present invention has the following effects.

(1) By turning on the power at a timing that cancels out the residual magnetic flux generated by the opening phase of the high-voltage transformer, the inrush current of the high-voltage transformer can be eliminated, making it possible to control the phase of the power relay, and Contact durability can be significantly improved. Further, it is possible to eliminate the unpleasant vibration noise of the heating chamber and the like.

(2) By setting the opening phase to the positive pole side and the negative pole side, it is possible to reduce contact wear of the power relay and to significantly improve the contact durability.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of an embodiment of the present invention.
The external view of the present invention, FIGS. 3 and 4, and FIG. 7 are timing charts showing the conventional opening and closing phases. 2... Heating chamber, 6... High frequency oscillator,
7... High voltage transformer, 8... Power relay, 9... Control circuit, 14... Phase setting circuit, 14m... Power supply phase monitoring circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
・-Body 2-m! 'fi Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) A heating chamber that stores food, a high-frequency oscillator that supplies high-frequency output to the heating chamber, a high-voltage transformer that supplies power to the high-frequency oscillator, a power relay that connects the power to the high-voltage transformer, and this power and a control circuit that controls the relay, and the control circuit uses a power supply phase monitoring circuit that detects the phase of a commercial power supply, and the power supply phase monitoring circuit to excite the high voltage transformer by applying residual magnetic flux due to opening of the high voltage transformer. and a phase setting circuit that sets the phase of the power relay to a phase where the power relays cancel each other out. (2) The phase setting circuit recognizes the polarity of the residual magnetic flux due to the opening of the high voltage transformer by the power supply phase monitoring circuit, and
2. The high-frequency heating device according to claim 1, wherein the high-frequency heating device has two input phases with respect to the negative electrode. (3) The high frequency heating device according to claim 1, wherein the phase setting circuit sets the opening phase of the high voltage transformer to the positive electrode side and the negative electrode side by the power supply phase monitoring circuit. (4) The high-frequency heating device according to claim 1, wherein the phase setting circuit alternately sets the opening phase of the high voltage transformer to the positive electrode side and the negative electrode side by the power supply phase monitoring circuit.