JPH01260785A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To enable an input to be changed with the oscillation frequency of an inverter circuit maintained constant as well as to eliminate the occurrence of interference sound even when plural numbers of inverters are simultaneously operated by changing the ratio of the conducting period between two switching elements with the sum of the conducting period left constant. CONSTITUTION:A variable conduction ratio setting section 9g connected with an oscillator 9f oscillating a constant oscillation frequency allows a comparator section 9c to compare an input set value set in an input setting section 9a with an actual input detected by an input detecting section 9b so that a conduction ratio between No.1 switching element 3 and No.2 switching element 4 is changed depending on outputted error voltage (e). An input electric power return loop as set forth herein above allows the conduction ratio between No.1 switching element 3 and No.2 switching element 4 to be controlled in such a way that the actual input is equal to the input set value. By this constitution, the input can be changed with the oscillation frequency maintained identical, and heating can thereby be processed without the occurrence of interference sound even when plural numbers of inverter circuits are operated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction heating cooker characterized by input control.

2. Description of the Related Art Conventionally, a common method for changing the input of an induction heating cooker is to change the oscillation frequency of an inverter circuit. This configuration will be explained based on FIG. 6. In the figure, 1 is a DC power supply, 2 is an inverter circuit, which includes a first switching element 3 and a second switching element 4 connected in series, a heating coil 5, a resonant capacitor 6 connected in series with the heating coil 6, and an inverter circuit 2. It is composed of a diode 7 and a second diode 8. Reference numeral 9 denotes a control circuit for the inverter circuit 2, which includes an input setting section 9a, an input detection section 9b, a comparison section 9c, a variable frequency oscillation section 9d, and a conduction ratio setting section 9e.

The operation of the induction heating cooker configured as above will be explained below.

In FIG. 6, a high frequency current is supplied to the heating coil 5 and the resonant capacitor 6 by alternately turning on and off the first switching element 3 and the second switching element 4 of the DC power supply 1 whose power supply voltage is E. . At that time, the voltage vcE1 across the first switching element 3, the voltage vcE2 across the second switching element 4, the sum IC1 of the currents of the first switching element 3 and the first diode 7, the voltage between the second switching element 4 and the first diode 7. The sum of the currents of 2 diodes 8 IC
2 becomes as shown in Figure 7. In FIG. 7, a shows the operating waveform when the oscillation period T is smaller than the resonance period T0 determined by the conditions of the inverter circuit and load, and b shows the operating waveform when the oscillation period T is the resonance period T. This is the operating waveform when . As shown in FIG. 7, in the conventional example, the conduction periods of the first switching element 3 and the second switching element 4 are controlled to be equal even if the oscillation frequency f changes. As can be seen from the characteristic curve diagram in Figure 8, if the oscillation period T changes, the oscillation frequency f and the input P change, so in Figure 7, a is the operating waveform at low input, and b is at high input. Operating waveforms are shown. Next, the operation of the control circuit 9 will be explained. First, the input setting value set in the input setting section 9a from the outside and the input detection section 9b
The comparator 9C compares the detected input with the actual input, and generates an error voltage e. The variable frequency oscillator 9d oscillates at an oscillation frequency depending on the error voltage e. This oscillation output drives the inverter circuit 2 in the conduction ratio setting section 9e so that the first switching element 3 and the second switching element have the same phase. This input power feedback loop controls the oscillation frequency to the oscillation frequency that provides the set input setting value. As can be seen from FIG. 8, when the user changes the input setting value of the input setting section 9a, the oscillation period T changes and the oscillation frequency f changes.

As described above, in the conventional configuration, the input P is controlled by making the conduction periods of the first switching element 3 and the second switching element 4 equal and changing the oscillation frequency f.

Problems to be Solved by the Invention However, in the conventional input control method described above, the oscillation frequency f changes, so in a multi-burner induction heating cooker with a plurality of inverter circuits, the difference Δ between the oscillation frequencies
There was a problem in that the interference sound f was generated from the pot which was the heating load.

The present invention solves the above conventional problems, and aims to provide an induction heating cooker that does not generate interference noise even when a plurality of inverter circuits are operated simultaneously.

Means for Solving the Problems In order to achieve this object, the induction heating cooker of the present invention is designed so that the conduction ratio of the switching element is made variable so that the input can be changed at a constant oscillation frequency.

Function: With this configuration, the input can be changed at the same oscillation frequency, and even if a plurality of inverter circuits are operated, heating can be performed without causing interference noise.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 6. Parts that are the same as those in the prior art will be given the same weight, detailed explanation will be omitted, and the explanation will focus on the differences. In FIG. 1, 9f is an oscillator, and 9q is a variable conduction ratio setting section. Then, the voltage e of the comparison section 9c is determined by the variable conduction ratio setting section 9q.
has been entered. Moreover, the circuit shown in FIG. 1 has a plurality of circuits, and constitutes a plurality of burners.

The operation of the induction heating cooker of this embodiment configured as described above will be described below.

Oscillator 9g that oscillates at a constant oscillation frequency in Figure 1
The variable conduction ratio setting unit 9q connected to the input setting unit 9a compares the input setting value set in the input setting unit 9a with the actual input detected by the input detection unit 9b in the comparison unit 9c, and outputs an error voltage e.
The conduction ratio between the first switching element 3 and the second switching element 4 is changed accordingly. Through this input power feedback loop, the conduction ratio of the first switching element 3 and the second switching element 4 is controlled so that the actual input becomes equal to the input setting value.

This is based on the fact that the relationship between the ratio T2/T of the conduction period T2 and the oscillation period T1 of the first switching element 3, the input P, and the oscillation frequency f is as shown in the characteristic curve diagram in FIG. The oscillation period is T.

By changing the conduction period of the first switching element 3 while keeping it constant, it is possible to change the input P while keeping the oscillation frequency f constant. At this time, the conduction period T3 of the second switching element 4 is necessarily controlled to T1-T2. Figure 2a shows low input (
Figure 2 shows the operating waveforms when T2/T1<o, ts), and the operating waveforms when the input is high (T2/T1=0.5). Although this embodiment has a plurality of circuits shown in FIG.
Since the oscillation frequencies of the oscillator 9f are set to be the same, no interference noise is generated due to the difference in oscillation frequencies even if both inverter circuits 2 are operated simultaneously.

Note that the same effect can be obtained even if the resonant capacitors of the inverter circuit of this embodiment are connected as shown in 6a in FIG. 4 and ab and 6c in FIG. 6.

Effects of the Invention The present invention provides a control unit that controls an inverter circuit by changing the ratio of the conduction periods of two switching elements of the inverter circuit while keeping the total of the conduction periods of the two switching elements constant. The input can be changed at a fixed oscillation frequency, and if the oscillation frequencies of multiple inverter circuits are made the same, there will be no interference noise even when multiple inverter circuits are operated at the same time. Excellent multi-burner induction heating cooking. It is something that can be realized by a vessel.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention, Fig. 2 a and b are respective operation waveform charts, Fig. 3 is a characteristic curve chart, and Figs. 4 and 5 are other charts. FIG. 6 is a circuit diagram showing an example of the conventional induction heating cooker, and FIG. 7a is a circuit diagram showing an example of
, b are waveform diagrams of the same operation, and FIG. 8 is a diagram of the characteristic curves. DESCRIPTION OF SYMBOLS 1...DC power supply, 2...Inverter circuit, 3...First switching element, 4...
...Second switching element, 5...Heating coil, 6...Resonance capacitor, 9...
Control circuit, 9f...Oscillator, 9q...
Variable conduction ratio setting section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure u
J Fig. 2 Tz/Tt -6,5n Last 31!1 θS Tz/Tt Fig. 4 Fig. 7 T<To no Gin T ” To's special Fig. 8

Claims (1)

[Claims] It has a DC power supply, an inverter circuit that converts the DC current into a high-frequency current, and a control circuit thereof, and the inverter circuit has a heating coil, a resonant capacitor connected to the heating coil, and two switching elements. , the control circuit includes an oscillator and a variable conduction ratio setting section, and the variable conduction ratio setting section alternately conducts the two switching elements at the oscillation frequency of the oscillator and makes the conduction ratio variable. Heating cooker.