JPS5812835B2 - Inverter touch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device, and more particularly to an inverter device for an induction heating cooker that heats a household pot made of metal using an eddy current generated by a high-frequency magnetic field.

Conventionally, in a household induction heating cooker using an inverter device, a plurality of heating parts are required, and therefore, the number of inverter devices equal to the number of heating coils is required, which poses an economical problem.

Therefore, the present invention provides an automatic frequency tracking type induction heating inverter device that has a plurality of heating coils and is capable of operating a plurality of heating coils at the same time or operating only a part of the heating coils. That is.

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

In Fig. 1, when a DC voltage is applied to the inverter circuit 2 from the DC power supply 1, the inverter circuit 2 converts the DC current into a high frequency current, and the high frequency magnetic field caused by the high frequency current causes the inverter circuit 2 to
Eddy currents are generated in metals such as household pots, and the resulting Joule heat is used to heat them.

In this case, the positive side of the DC power source 1 is connected to the anode of the thyristor 22 via the current limiting inductor 21, and the cathode of the thyristor 22 is connected to the negative side of the DC power source 1.

Further, a diode 23 is connected antiparallel to the thyristor 22, and a series circuit of a commutating inductor 24 and a commutating capacitor 25 is connected in parallel with the thyristor 22.

Furthermore, a series circuit of a filter capacitor 26, a heating coil 27, and a switch 28 is connected in parallel with the commutation capacitor 25.

Similarly, a series circuit of filter capacitor 26', heating coil 27, and switch 28' is connected in parallel with commutating capacitor 25.

If you want to operate the heating coil 27 now, switch 28
When the interlocking switch 29 is turned on at the same time and the heating coil 27' is also operated, the switch 28 is turned on.
' and the interlocking switch 29' are also turned on.

Note that the filter capacitor 26 cuts direct current to the heating coil 27 and allows only high-frequency current to flow therethrough, and the series resonance frequency f3 of the filter capacitor 26 and the heating coil 27 is set to a value that is approximately equal to or lower than the inverter oscillation frequency f0. .

Furthermore, similar values are selected for the series resonance frequencies of the filter converter 26' and the heating coil 27'.

Therefore, the switches 28, 28' and the interlocking switch 2
9, 29' are in the ON state, the filter capacitors 26, 26' are connected in parallel, and the heating coils 27, 2 are connected in parallel.
7' is also connected in parallel, but the output circuit resonance frequency hardly changes.

and switches 27, 27' and interlocking switch 29,
The switching of 29' is performed by stopping the oscillation of the inverter.

The heating coils 27, 27' are spiral disc coils, and have a shape that makes it easy to heat an iron plate like a household pot.

Next, to explain the control part of the inverter, first,
The output voltage detection circuit 3 detects the terminal voltage of the heating coils 27, 27', and the input voltage detection circuit 4 extracts a voltage proportional to the input voltage of the inverter circuit 2.

The bridge circuit 5 is configured so that the input side has a positive potential and the output side has a negative potential, and the output voltage of the bridge circuit 5 is zero potential under the balanced condition of the bridge. Set it so that

Then, depending on the output voltage of the bridge circuit 5, the oscillation period of the gate trigger circuit 7 is changed by a Vf converter circuit 6 having the characteristics shown in FIG. 2, thereby forming an automatic frequency tracking circuit.

The gate trigger circuit 7 periodically triggers the Cyrisk 22, and the oscillation frequency of the inverter circuit 2 is the same as the oscillation frequency of the gate trigger circuit 7.

The characteristics of the V-f converter circuit 5 are determined by setting the limiter A on the low frequency side and the limiter B on the high frequency side as shown in Figure 2.
When the input voltage of the -f converter circuit 6 is zero, it oscillates at frequency C.

Limiter A is to prevent the oscillation frequency of the inverter circuit 2 from reaching the audible range, and limiter B is designed to prevent the oscillation frequency of the inverter circuit 2 from reaching the audible range.As the oscillation frequency increases, the switching loss of the thyristor 22 increases, the junction temperature Ti rises, and it becomes impossible to turn off. Therefore, the maximum frequency at which the thyristor 22 can be turned off is set.

Now, when the thyristor 22 is periodically triggered by the gate trigger circuit 7 and turned on, it is turned off by the current limiting inductor 21, the commutating inductor 24, and the commutating capacitor 25.

At this time, the commutating capacitor 25 can be regarded as a high frequency power source, and a substantially sinusoidal current flows through the output circuit of the filter capacitor 26 and the heating coil 27.

The output current largely depends on the impedance of the output circuit,
When the resonant frequency of the output circuit approaches the oscillation frequency of the inverter circuit 2, the impedance becomes low and the output voltage also increases.

Conversely, when the inverter oscillation frequency is brought closer to the resonant frequency of the output circuit, the output current and output voltage increase, so by changing the gate trigger period of the inverter circuit 2, the output voltage, that is, the heating coil terminal voltage can be controlled.

Therefore, when the oscillation frequency of the inverter circuit 2 is controlled by the -f converter circuit 6 so that the output voltage of the bridge circuit 5 becomes zero by the automatic frequency tracking circuit shown in FIG. The ratio of voltage to input voltage is always constant.

Even if the heating coil is disconnected by switch 28 or switch 28', the heating coil terminal voltage remains constant, so if the load condition is constant, the heating coil current remains constant and the output does not change.

In other words, switch 28 or switch 28'
Although the load condition of the inverter circuit 2 changes greatly depending on whether the switch 28 is turned on or off, the terminal voltage of the heating coils 27, 27' is always constant. ,28'
It is not affected by the on/off status of the heating coil or the load condition of one heating coil.

As described above, according to the present invention, the ratio between the inverter input voltage and the heating coil terminal voltage becomes constant, and a plurality of series circuits of the filter capacitor, the heating coil, and the switch are connected in parallel with the commutating capacitor. It is possible to have a plurality of output circuits with one commutation circuit and one thyristor, and the number of output circuits can be increased or decreased as desired.

Also, even if only the input voltage changes, the oscillation frequency does not change.
The oscillation frequency changes depending on the load conditions, resulting in stable operation.

Furthermore, even if a pan made of a non-magnetic material such as aluminum is brought close to the heating coil, the oscillation frequency increases, the device operates stably, and does not fail in commutation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an inverter device showing one embodiment of the present invention, and FIG. 2 is a characteristic diagram of the same Vf converter circuit. 3... Output voltage detection circuit, 4... Input voltage detection circuit, 5... Bridge circuit, 6...
...V-f converter circuit, 7... Gate trigger circuit, 26, 26'... Capacitor, 27
, 27'... Heating coil, 28, 28'...
...Switch, 29, 29'...Interlocked switch.

Claims (1)

[Claims] 1. In an inverter device in which a series circuit of a heating coil and a filter capacitor is connected in parallel with a commutating capacitor, a plurality of output circuits each including the filter capacitor, the heating coil, and a switch are connected in parallel to the commutating capacitor, Each of these output circuits is provided with an interlocking switch that operates in conjunction with the switch, connects the heating coils in parallel, and also serves as a voltage detection section, while the output voltage detection circuit and the input voltage detection circuit to the inverter device An inverter device comprising: a bridge circuit whose input voltage is a detected voltage; and a Vf converter circuit which changes the oscillation frequency of a gate trigger circuit according to the output voltage of the bridge circuit.