JPH03114194A - Induction heating cooking apparatus - Google Patents

Abstract

PURPOSE:To prevent excessive current from flowing in a switching element whichever material and shape a pan placed as the load is made of/in by sensing the current at the time of turn-on and -off of No.1 and No.2 switching element, increasing the turn-on delay times of these switching elements, and thereby decreasing the current value. CONSTITUTION:A current sensing part 9 senses the amperages at the time of turn-on and -off of No.2 switching element 3. When the amperages at these times of turn-on and -off senses by the amperage sensing part 9 exceed a preset value, a control part 6 transmits increase in the delay time of turn-on to No.1 and No.2 variable delay time generator part 7, 8, and the turn-on delay times of the No.1 and No.2 switching element 2, 3 are increased. Thus the amperage of the turn-on or -off of each switching element is oscillation controlled under the preset value, so that heating of a pan can be operated safely whichever material and shape it is made of/in.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction heating cooker used in general households.

BACKGROUND OF THE INVENTION In recent years, induction heating cookers have been recognized for their excellent features of safety, cleanliness, and high efficiency, and are becoming popular as main cooking devices replacing gas cookers. A main cooker is required to have 20 or more burners, but according to the conventional control method for induction heating cookers, the frequency of the high-frequency current applied to the heating coil changes depending on the material of the load pot or the input power. There is a problem in that when used at the same time, interference noise is generated due to the difference in their frequencies, which is harsh on the ears.

In order to solve this problem, a method has been proposed in which the frequency of the high-frequency current applied to the heating coil is constant regardless of the material of the pot or the input power, and this will be explained based on FIG. 4. In Figure 4, 1 is a DC power supply, 2 and 3 are the first
and a second nutwitching element, which are connected in series and connected to the DC power supply 1. A heating coil 4 and a resonant capacitor 6 are connected in series to form a resonant circuit.

Reference numeral 11 denotes a control unit that controls on/off of the first and second switching elements 2.3 at a constant frequency.

Reference numerals 12 and 13 denote first and second fixed delay time generators, which have a function of delaying the turn-on of each by a certain period of time in order to prevent the first and second switching elements 2゜3 from being turned on at the same time. .

1o is the load pot.

Next, the operation of the conventional example will be explained based on FIG.

FIG. 5 C1d is a time chart of on/off of the first and second switching elements 2 and 3 when the input power is large, and FIG. 5 C1d is a time chart when the input power is small. As shown in FIG. 6, the input power is adjusted by changing the ratio of on-times of the first and second switching elements 2 and 3.
, 3 are turned on at the same time, each turn-on is the first turn-on.
and the delay time set by the second fixed delay time generating section 12.13, that is, the delay time td1 of the first switching element, and the delay time t of the second switching element.
Delay by d2.

Problems to be Solved by the Invention In such a conventional induction heating cooker, the first and second
Since the turn-on delay time of the switching elements 2 and 3 is fixed, when a stainless steel pot or the like is placed as the load 10, the inductance of the heating coil 4 decreases, and as a result, the difference between the operating frequency and the resonant frequency increases. becomes larger, the turn-on or turn-off current becomes larger,
There have been problems in that the switching element loss increases and the switching element may be destroyed.

The present invention is intended to solve the above problems, and enables safe operation by preventing excessive turn-on/turn-off current from being applied to the switching element no matter what material or shape is placed as the load pot. The purpose is to provide an induction heating cooker that can.

Means for Solving the Problems In order to achieve the above object, the present invention includes a DC power supply, a series circuit of a first switching element and a second switching element connected to the DC power supply, and one of which is connected to the first switching element. A series circuit of a heating coil and a resonant capacitor, the other of which is connected to the DC power source at the midpoint of the switching element and the second switching element, and the on/off of the first and second switching elements are controlled at the same frequency. a control unit, first and second variable delay time generating units that arbitrarily delay turn-on of the first and second switching elements, and a control unit that detects the applied current of the first or second switching element and detects the current applied to the first or second switching element at turn-on. and a current detection unit that detects the magnitude of the current at the time of turn-off, and the first and second The configuration is such that the turn-on delay time of the second switching element is varied.

Function: With the above-described configuration, the present invention detects the currents during turn-on and turn-off of the first and second switching elements, and when these currents exceed a predetermined value set in advance, the currents of the first and second switching elements are detected. This increases the turn-on delay time and decreases these current values,
This makes it possible to prevent excessive turn-on and turn-off currents from being applied to the switching element no matter what material or shape of pot is placed as a load.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an induction heating cooker according to an embodiment of the present invention. In FIG. 1, 1 is a DC power source, and 2 and 3 are first and second switching elements connected in series and connected to the DC power source 1. In FIG. A heating coil 4 and a resonant capacitor 6 are connected in series to form a resonant circuit. 6 is a control unit that includes first and second switching elements 2;
．． Input power is controlled by changing the ratio of on/off of 3 at the same frequency. 7 and 8 are the first and second
The variable delay time generating section has the function of delaying the turn-on of the first and second switching elements 2 and 3 by an arbitrary period, and its setting is controlled by the control section 6. 9
1 is a current detection section, which detects the current when the second switching element 3 is turned on and turned off. When the current detected by the current detection section 9 during turn-on and turn-off exceeds a predetermined value, the control section 6 sends a signal to the first and second variable delay time generation sections 7 and 8 to increase the turn-on delay period. is transmitted to the first and second
The turn-on delay period of the switching elements 2, 3 is increased.

FIG. 2 is a time chart showing on/off of the first and second switching elements 23, and shows a control method when the turn-off current exceeds a large predetermined value. A and b are time charts when the turn-off current is large, and c and d are time charts when the delay time of the second switching element 3 is increased according to this embodiment in order to reduce the turn-off current.

FIG. 3 shows the first and second switching elements 2 at that time.
．． 3 shows the current applied to 3. a and b are waveforms when the turn-off current is large, and c and di are waveforms when the turn-off current is small and negative. Although the waveform shown here shows the waveform when it reaches a negative value, it is possible to turn on or turn off near zero by controlling it appropriately.

Effects of the Invention As is clear from the above embodiments, according to the induction heating cooker of the present invention, the turn-on or turn-off current of the switching element is controlled to oscillate below a preset value. It can also be operated safely.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an induction heating cooker according to an embodiment of the present invention, Fig. 2 is an on/off pattern diagram of the switching element, and Fig. 3 is a current waveform diagram of the switching element.
FIG. 4 is a block diagram of a conventional induction heating cooker, and FIG. 6 is a timing chart for explaining the operation of the conventional example. 1... DC power supply, 2... First switching element, 3... Second switching element,
4... Heating coil, 6... Resonant capacitor, 6... Control section, 7... First variable delay time generating section, 8... ...Second variable delay time generating section, 9...Current detection section, 10...
pot.

Claims (1)

[Claims] a DC power supply, a series circuit of a first switching element and a second switching element connected to the DC power supply, one connected to the midpoint of the first switching element and the second switching element, and the other connected to the DC power supply; a series circuit of a heating coil and a resonant capacitor connected to a controller; a controller that controls on/off of the first and second switching elements at the same frequency; and a control unit that arbitrarily turns on the first and second switching elements. It has first and second variable delay time generation sections that delay the switching element, and a current detection section that detects the current applied to the first or second switching element and detects the magnitude of the current at turn-on and turn-off. , an induction characterized in that the turn-on delay time of the first and second switching elements is changed so that the magnitude of the current at the time of turn-off or turn-off detected by the current detection section is equal to or less than a predetermined value. Heating cooker.