JP2651927B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION (Industrial application field) The present invention relates to a high-frequency heating device for driving a magnetron by an inverter circuit, and particularly to an improved abnormality detection function of the inverter circuit.

(Conventional technology) An inverter circuit that rectifies a commercial AC power supply voltage and converts it to AC power with a frequency (several tens of KHz) according to the magnetron output set by the customer by turning on and off a switching element. In a high-frequency heating device that supplies power to a magnetron by a circuit,
As a means for detecting an abnormal operation of a circuit, a system as shown in FIG. 3 is conventionally used.

In FIG. 3, the power converted into an AC of several tens of KHz by turning on / off the switching element 1 is boosted by a high-voltage transformer 2 and then supplied to a magnetron 3. The secondary side of the high-voltage transformer 2 The voltage generated at the resistor 4 inserted in the circuit (high voltage circuit) is compared with the reference voltage Vs by the comparison circuit 5.

When an abnormal current occurs in the circuit and an excessive current flows to the secondary side, the voltage generated in the resistor 4 exceeds the reference voltage Vs. As a result, the output Vo of the comparison circuit 5 is inverted with respect to the normal state. The field back is performed to stop the operation of the switching element 1.

(Problems to be Solved by the Invention) However, this method is for detecting an excessive current, and is not a single magnetron output, but a variable output high-frequency heating that allows a customer to freely select a magnetron output according to cooking. In the device, even if it operates with an output different from the selected output value due to a circuit abnormality, it cannot detect this, and not only fails cooking, but in the worst case, the output value far exceeds the selected value. Heating may cause dangerous modes such as smoking of food.

(Means for Solving the Problems) Whether the inverter circuit operates at the selected output value can be determined by measuring the current value supplied to the inverter circuit, and this value is determined by the selected output value. Since it is conceivable that even the same is different depending on the power supply voltage applied to the inverter circuit, it is necessary to judge both. If the detected current value is not different from the inverter circuit current value expected when operating at the output value selected at the detected power supply voltage value By determining whether or not the inverter circuit is operating according to the selected output.

(Operation) A current detection circuit for detecting a current flowing through the inverter circuit and a voltage detection circuit for detecting a power supply voltage supplied to the inverter circuit are also provided, and the current value and the voltage value detected by both circuits are used to operate the switching element. Feedback to the control circuit that controls The control circuit calculates the current value that should flow through the inverter circuit when operating at the output value selected by the customer at the input power supply voltage value,
This value is compared with the input current value, and if the difference is equal to or more than a predetermined value, it is determined that there is an abnormality in the circuit, the operation of the switching element is stopped, and the heating is stopped.

(Embodiment) FIG. 1 shows an embodiment of the present invention. 1 is a switching element, 2 is a high-voltage transformer, 3 is a magnetron, 6 is a control circuit, the center of which is a microcomputer 6a having a built-in A / D conversion function. Reference numeral 7 denotes a magnetron output setting circuit, and an output value p to be set is input to the drive circuit 6b and the microcomputer 6a as a signal S (p).

In order to detect a current flowing through the inverter circuit D and a supplied power supply voltage, a current detection circuit 8 and a voltage detection circuit 9 are incorporated in an AC circuit before the rectifier.
The current detecting circuit 8 includes a current transformer 8a and a rectifying / smoothing circuit 8b. The AC voltage generated in the current transformer 8a when an AC current i flows is supplied to the rectifying / smoothing circuit 8b.
And converts it into a DC voltage V (i), which is input to the A / D conversion port of the microcomputer 6a. The voltage detecting circuit 9 is composed of a transformer 9a and a rectifying / smoothing circuit 9b. Input to A / D conversion port of microcomputer. The memory of the microcomputer 6a has a power supply voltage and a reference current value i for a set output value p.
(V, p) is stored.

FIG. 2 shows a processing flow in the microcomputer 6a in this embodiment. The microcomputer 6a simultaneously A / D-converts the signal V (v) from the voltage detection circuit 9 and the signal V (i) from the current detection circuit 8 and performs a predetermined operation on each of the converted values to obtain a power supply voltage. In addition, a measured value vd, id of the current flowing in the inverter circuit is calculated. Further, based on the calculated power supply voltage value vd and the output value p set by the customer, the current to flow in the inverter circuit is determined by the reference value is (v
d, p) is determined.

It is determined whether or not the absolute value of the difference between the reference value is (vd, p) and the actual measured value id obtained from V (i) satisfies the following expression.

| idp−is (vd, p9) | ≦ △ i Here, △ i is a constant determined in consideration of a measurement error and a calculation error.

If the difference is larger than △ i, it is determined that there is an abnormality, that is, the inverter circuit is not operating at the set output value, and the microcomputer 6a sends a signal to the drive circuit 6b that turns the switching element 1 on and off. An off signal is output as the output control signal c to stop the operation of the switching element 1.

The checking operation of the inverter circuit current by the microcomputer is always performed, and the abnormality of the circuit is detected at an early stage.

(Effect of the Invention) As described above, according to the present invention, an erroneous output operation that could not be detected conventionally can be detected, and an inverter circuit type high-frequency heating device excellent in safety and reliability is realized. can do.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of the embodiment, FIG. 2 is an explanatory diagram showing processing in a microcomputer in the embodiment, and FIG. 3 is a control circuit diagram of a conventional example. DESCRIPTION OF SYMBOLS 1 ... Switching element, 2 ... High voltage transformer, 3 ... Magnetron, 4 ... Current detection resistor, 5 ... Comparison circuit, 6 ... Control circuit, 6a ... Microcomputer, 6b ... Drive circuit, 7
…… Output setting circuit, 8 …… Current detection circuit, 8a …… Current transformer, 8b …… Rectification / smoothing circuit, 9 …… Voltage detection circuit, 9a
…… Transformer, 9b …… Rectifier smoothing circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kiyoshi Ozawa 3-1, Shinjuyoji, Kashiwa-shi, Chiba Examiner, Hitachi Heating Equipment Co., Ltd. Yutaka Ogawara (56) References JP-A-1-12495 (JP, A) JP-A-62-198082 (JP, A)

Claims (1)

(57) [Claims] 1. An inverter power supply for rectifying a commercial AC power supply voltage and converting the rectified AC power into AC power of an arbitrary frequency to drive a magnetron, and controlling the frequency according to a set output value of the magnetron. A control circuit, a voltage detection circuit that detects the commercial AC power supply voltage and inputs the voltage value to the control circuit, and detects a current supplied from the commercial AC power supply to the inverter power supply, and detects the current value. A current detection circuit input to the control circuit, wherein a reference current value calculated based on the voltage value input to the control circuit and an output set value of the magnetron; Wherein the control circuit stops the operation of the inverter power supply when the difference from the detected current value becomes equal to or greater than a predetermined value. Location.