JPH077708B2 - High frequency heating device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to phase control of a power relay used as means for opening and closing a power supply of a high voltage transformer in a high frequency output varying method for a high frequency heating device.

2. Description of the Related Art In a high-frequency heating device, it is general to set a high-frequency output at an appropriate level according to the type, quality, and completion of an object to be cooked, which is useful for improving cooking performance. As a means for changing the high-frequency output to an appropriate level in this way, a method of disconnecting the secondary side of the high-voltage transformer that supplies the high-frequency oscillator that emits the high-frequency output and a method of disconnecting the primary side of the high-voltage transformer have been developed. . Especially cost, insulation performance,
From the point of view of configuration, the latter intermittent method on the primary side has become the mainstream. The primary-side intermittent method will be described below.

FIG. 5 shows a conventional example.

Reference numeral 5 denotes a main circuit, which connects a contact of a power relay 8 to a primary side of a high-frequency oscillator 6 that irradiates a heating chamber with a high-frequency output and a high-voltage transformer 7 that supplies power to the heating chamber.
The high frequency output is made variable by turning on. Reference numeral 9 indicates a control circuit for controlling the power relay 8. Transformer 10
Supplies the power to the control circuit unit by stepping down the commercial power supply. The power relay power supply circuit 11 half-wave rectifies the AC power supply to generate a supply voltage to the operation coil of the power relay 8. Then, the microcomputer power supply circuit 12 produces a voltage necessary for operating the microcomputer 13. This microcomputer 13
Is a center of the control circuit section, which performs a series of operations based on a predetermined sequence of opening and closing phase control of the power relay 8 and a predetermined sequence. The power clock circuit 15 is
It is a circuit that shapes the commercial power supply waveform into a voltage waveform that can be recognized by the microcomputer, and serves as a reference for controlling the opening and closing phases of the power relay 8. The power relay drive circuit 16
This circuit controls the power relay 8 connected to the primary side of the high voltage transformer.

FIG. 6 is a timing chart showing a conventional phase control method for a power relay. Since the transformer uses a magnetic material for the core, it has a hysteresis characteristic in the magnetic field H and the magnetic flux density B. Further, even if the external magnetic field (current on the primary side of the high voltage transformer) is cut off, the residual magnetic flux ± Φr remains inside the transformer core. The steady-state magnetic flux of the high-voltage transformer is -Φ at maximum before the direction of the exciting magnetic flux is reversed.
It changes from m to + Φm. The inrush current generated when the high voltage transformer is turned on is generated when the sum of the residual magnetic flux and the exciting magnetic flux is not zero. It is controlled so that this total becomes zero. (a) shows the voltage and current characteristics of the high voltage transformer,
The change of the excitation magnetic flux in a steady state is shown. The left figure of (a) is
Due to the relationship between the magnetic flux density B of the core and the magnetic field H, the magnetic flux is proportional to the current flowing through the high voltage transformer. When an AC magnetic field is applied to the core, a magnetic flux with a certain hysteresis is generated. And
The right figure in (a) shows the voltage waveform and current (magnetic flux) waveform of the high-voltage transformer. The current has a characteristic that the phase lags behind the voltage by π. When the contact is opened at the point a, the residual magnetic flux Φr at the point a ′ remains in the core. Next, when the timing of point a or point c when the high voltage transformer is turned on is point a'or point c '
Exciting magnetic flux is generated. Therefore, the generated magnetic flux Φ becomes Φ = (− Φr) + Φr = 0, and the inrush current can be suppressed to a small value. (b) is
The waveform of the low-voltage transformer which steps down commercial power is shown.
(c) is a waveform obtained by shaping the reduced power supply waveform to a level that can be recognized by the microcomputer. The opening and closing phases are determined based on the rising edge of this waveform input to the INT pin of the microcomputer. (d) shows the opening timing, and Z ₁ is stored in the memory of the microcomputer. T _OFF is the recovery time of the power relay, and the power relay opening timing is Z ₁ + T _OFF from the reference and the power supply is opened. (e) shows the input timing, and Z ₂ is stored in the memory of the microcomputer. T _ON indicates the operating time of the power relay. The power relay will be turned on after Z ₂ + T _ON from the standard. By controlling the power relay at such timing, the inrush power supply of the high voltage transformer is kept small.

Problems to be Solved by the Invention However, the above configuration has the following problems.
FIG. 4 shows the exciting magnetic flux characteristics in the transient state. As described above, in the steady state of the magnetic flux, for example, when the magnetic flux is opened at the timing of A ′, the residual magnetic flux −Φr remains. If the residual magnetic flux is applied at a timing to cancel it, the residual magnetic flux −Φr
Is And reaches an equilibrium state after T seconds. Here, considering the case where the contacts are opened within T seconds after the power relay is turned on,
For example, when the contact is opened by d ', the residual magnetic flux becomes -Φr', which is different from the residual magnetic flux -Φr in the equilibrium state. Therefore, when the next closing phase is fixed to a ', | -Φr' | ≈ | + Φr |, and the balance of the magnetic flux at the time of closing is broken, and an inrush current is generated.

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 for supplying a high-frequency output to the heating chamber, and a power source for the high-frequency oscillator. A high-voltage transformer, a power relay that connects and disconnects this high-voltage transformer, and a control unit that controls this power relay, and the control unit has a power supply phase monitoring unit that detects the phase of the commercial power supply,
Equipped with a timer unit that detects the time from turning on the power relay to opening the contact, and a phase setting unit that sets the next closing to the maximum phase of the commercial power supply voltage when the detection time of this timer unit is within a predetermined time It is a thing.

Action The present invention, with the above configuration, when the time to the next opening after the power relay is turned on is within a predetermined time, that is, when the magnetic flux of the high-voltage transformer has not reached the equilibrium state, the next turn-on phase is set to the commercial power source. Maximum phase of voltage (minimum phase of exciting magnetic flux)
The configuration is performed in. Therefore, it has an effect of suppressing the inrush current to be low, improving contact durability performance of the power relay, improving reliability, and preventing magnetic vibration such as heating due to the inrush current which is formed of a ferromagnetic material.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows an external view of one embodiment. Reference numeral 1 is a main body of the high-frequency heating device, and in the main body 1, a heating chamber 2 made of a ferromagnetic material is provided. At the opening of the heating chamber 2,
A fan 3 that can be freely opened and closed is provided for loading and unloading the food in the heating chamber 2, and an operation unit 4 for setting a cooking time, an output and the like is provided on the front surface of the main body 1.

FIG. 1 shows a circuit embodiment of the present invention. This circuit example
It is an embodiment using a microcomputer (hereinafter referred to as a microcomputer) and may have a discrete configuration. Reference numeral 5 is a main circuit, which is a high-frequency oscillator 6 for irradiating the heating 2 with high-frequency output.
Then, the primary side of the high-voltage transformer 7 that supplies power to this is connected to the contact of the power relay 8 and the high frequency output is made variable by opening and closing the contact. Reference numeral 9 indicates a control circuit for controlling the power relay 8. The low-voltage transformer 10 steps down commercial power to about 30 V and supplies power to the control circuit. The power relay power supply circuit 11 half-wave rectifies the AC power supply to generate the operating coil supply voltage of the power relay 8. The microcomputer power supply 12 produces a voltage required to operate the microcomputer 13. This microcomputer 13 has a power supply phase monitoring unit 14a which detects a phase of a commercial power supply by a power supply clock circuit 15 which will be described later, a timer unit 14b which measures a time from turning on of a power relay to opening, and a timer unit of this timer unit. If the value is within a predetermined time, within a predetermined time, that is, if the excitation state of the high voltage transformer has not reached equilibrium, by the power supply phase monitoring unit 14a, the maximum phase of the commercial power supply voltage It has a phase setting unit 14c for setting. The power supply clock circuit 15 serves as a reference for controlling the phase of the power relay by a waveform shaping circuit into a voltage waveform that the microcomputer 13 can recognize as a commercial power supply waveform. 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 is a timing chart showing the phase control method of the present invention. When a high-voltage transformer whose magnetic flux has reached the equilibrium state is opened at an arbitrary phase during energization, a constant residual magnetic flux | Φr | remains inside the core of the high-voltage transformer, but the transient state in which the magnetic flux has not reached the equilibrium state. When the power relay is opened in this state, various amounts of residual magnetic flux | Φr ′ | that are not in balance remain in the core of the high voltage transformer. The phase control in such a state will be described.

In (a), the left diagram shows the relationship between the magnetic flux density B of the core and the magnetic field H. The magnetic flux is proportional to the current flowing through the high voltage transformer, and when an alternating magnetic field is applied to the core, a magnetic flux having a certain hysteresis is generated. The figure on the right shows the voltage waveform and current (magnetic flux) waveform of the high-voltage transformer. When the power relay is turned on, the magnetic flux gradually increases and reaches the equilibrium state after T seconds. When the contact is opened at point d in the transient state,
The residual magnetic flux of -Φr 'remains. (b) shows the waveform of the low-voltage transformer that steps down the commercial power supply. (c)
Is a waveform obtained by shaping the reduced power supply waveform into a level that can be recognized by the microcomputer. The opening and closing phases are determined based on the rising edge of this waveform input to the INT pin of the microcomputer. (d) shows the opening timing, and Z ₁ is stored in the memory of the microcomputer. T _OFF , power relay recovery time
The contact is opened after Z ₁ + T _OFF . The timer unit determines whether the opening timing is within T seconds after the power relay is turned on. (e) shows the closing timing, and when the timer unit judges that it is in the transient state, the next closing phase is closed at the maximum phase of the voltage, that is, the minimum phase of the magnetic flux (current) phase. T ₂ is stored in the memory of the microcomputer, and it is turned on after t ₂ + T _ON from the reference by the operation time T _ON of the power relay.

As described above, according to the present embodiment, it is possible to suppress the inrush current at the next power-on when the power of the high-voltage transformer is turned off when the magnetic flux is in a transient state, and to open and close the power supply of the high-voltage transformer. The contact durability of can be improved.

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

After the high voltage transformer is turned on, by making the next closing phase at the maximum voltage phase for the opening in the transient state, the inrush current of the high voltage transformer can be suppressed to a small value, and the contact durability of the power relay is significantly improved. be able to. In addition, it is possible to eliminate the vibration noise of the heating chamber and the like, which is uncomfortable.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an external view of the present invention, and FIGS. 3 and 4 are timing charts showing opening and closing of a power relay of the present invention. FIG. 5 is a circuit diagram of a conventional example, and FIG. 6 is a timing chart showing the conventional opening and closing. 2 ... Heating chamber, 6 ... High frequency oscillator, 7 ... High voltage transformer, 8 ... Power relay, 9 ... Control circuit, 14a ... Power supply phase monitoring unit, 14b ... Timer unit, 14c ... Phase setting unit .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-12691 (JP, A) JP-A-63-205088 (JP, A) JP-A-60-12693 (JP, A)

Claims (1)

[Claims] 1. A heating chamber for containing food, a high-frequency oscillator for supplying a high-frequency output to the heating chamber, a high-voltage transformer for supplying electric power to the high-frequency oscillator, and a power relay for connecting and disconnecting the power supply of the high-voltage transformer. A control circuit for controlling the power relay, wherein the control circuit detects a phase of a commercial power source, a power supply phase monitoring unit, a timer unit for detecting a time from turning on of the power relay to opening of the power relay, and A high-frequency heating device comprising: a phase setting unit that sets the next turn-on to the maximum phase of the commercial power supply voltage when the value of the timer unit is within a predetermined time.