JP4492559B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker.

Conventionally, an induction heating cooker changes an oscillation frequency according to a set heating output, as typified by a monolithic resonance type inverter. In order to maximize the heating efficiency, the oscillation frequency is set to be as low as possible and about 20 kHz at the maximum heating output so as to be outside the audible frequency. When this is applied to a multi-mouth induction heating cooker having a plurality of heating parts, there is a problem that interference sounds generated from the oscillation frequency difference of each heating part due to the pot material and heating output when the plurality of heating parts are used simultaneously, In order to suppress interference noise, multi-mouth induction heating cookers that have become widespread in recent years are set by changing the on / off time ratio of the switching element with a fixed oscillation frequency, such as a half-bridge inverter. The heating output was realized. Further, in order to maximize the heating efficiency, the oscillation frequency is set to about 20 kHz so as to be as low as possible and out of the audible frequency (see, for example, Patent Document 1).
JP 2003-17234 A

  However, in the conventional configuration, interference noise due to frequency control is generated, and even if constant frequency control is performed, the switching element generates heat at a low heating output, and the generated noise increases. It had the problem that.

  This invention solves the said conventional subject, and it aims at providing the induction heating cooking appliance which reduced the unpleasant interference sound generated from a cooking appliance or a pan at the time of cooking by easy structure.

In order to solve the above conventional problems, the induction heating apparatus of the present invention a heating coil for magnetically coupling the load to a resonant circuit of the resonant capacitor in series, an inverter supplying power to the heating coil, the heating coil a plurality heating output control means, the induction heating unit with a controlling the heating output of the inverter of at least two of said induction heating unit, in the case of heating the load material is aluminum, the inverter switching elements of the inverter when the power cycle shorter than 50kHz with the frequency of the resonant current of the resonant circuit than the driving period of the switching element is supplied to the heating coil, heating the load material is iron 50kHz at least the maximum heating output of the drive period as a resonance frequency of the resonant circuit It has a structure that is characterized in that to supply power at a frequency above the heating coil. With this configuration, the amplitude of the fundamental vibration of the load is reduced by induction heating at a frequency of 50 kHz or higher, and therefore the amplitude is reduced even if interference frequency is generated due to the difference in frequency due to the material or the like. Therefore, unpleasant interference sound generated from the cooker or pan during cooking can be reduced.

  The induction cooking device of the present invention can reduce unpleasant interference sound generated from the cooking device or pan during cooking with an easy configuration.

The first invention includes a heating coil to magnetically couple the structure to load the resonant circuit of the resonant capacitor in series, an inverter supplying power to the heating coil, a heating output control means for controlling the heating output of the heating coil The inverter of the at least two induction heating units includes a plurality of induction heating units, and when the load is made of aluminum, the inverter of the resonance circuit is driven by a switching period of the switching element of the inverter. When the period of the resonance current is shortened and power having a frequency of 50 kHz or more is supplied to the heating coil and the load made of iron is heated , the drive period of the switching element of the inverter is set as the resonance frequency of the resonance circuit. It becomes way powering of 50kHz or more frequency at least up to the heating output to the heating coil It is possible to reduce the unpleasant interference noise generated from the cooker or pot during cooking in a simple configuration by Rukoto.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 shows a circuit configuration diagram of an induction heating unit of the induction heating cooker according to the first embodiment of the present invention.

  In FIG. 1, a power source 51 is a 200 V commercial power source, and a power factor improvement circuit (a power factor improvement circuit ( The power source is converted into a boosted direct current by the power factor improving means 71 and stored in the second smoothing capacitor 73 so that the power factor of the commercial power source becomes close to 1. It is converted into a high frequency by the inverter 70, and a high frequency magnetic field is generated in the heating coil 59. A pan (not shown), which is a load, is installed facing the heating coil 59. The resonance capacitor 60 forms a series resonance circuit together with the heating coil 59. The resonance frequency of the resonance circuit is set to about 90 kHz. The inverter 70 is connected to the first switching element 74, the second switching element 75, the third switching element 76, and the fourth switching element 77 so as to form a full bridge circuit having the resonance circuit as an output. The switching elements 74, 75, 76, and 77 are formed of IGBTs and diodes connected in antiparallel to the IGBTs. When the output is increased by alternately driving the first switching element 74 and the fourth switching element 77 or the second switching element 75 and the third switching element 76 by the heating output control circuit (heating output control means) 63. In this case, the switching element is driven by the heating output control circuit 63 so that the driving frequency of the switching element approaches the resonance frequency, and the heating output is detected by the heating output detecting means 67 comprising a current transformer so that a predetermined heating output can be obtained. It is a frequency controlled inverter. At the start-up, the heating output control circuit 63 alternately drives the first switching element 74 and the fourth switching element 77 or the second switching element 75 and the third switching element 76 at a constant frequency (about 60 kHz). To do.

  About the induction heating cooking appliance comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  FIG. 2 is a characteristic diagram of the detection input of the load material detection means 72. The drive period of the first switching element 74 and the fourth switching element 77 is driven in a mode shorter than the resonance period of the resonance current, the drive time ratio is minimized, and the drive time ratio is gradually increased after the minimum output is achieved. In the meantime, the load material detection means 72 detects the load material from the detection output of the current transformer 67 and the detection output of the resonance voltage detection means 68 comprising the second current transformer. When the load material detection means 72 determines that the material of the load is magnetic (iron), the load material detection means 72 increases the drive frequency and starts heating at a low output again. Low conductivity material mode in which the driving frequency of the switching elements 74, 75, 76, 77 is about 90 kHz, which is the resonance frequency of the resonance circuit, and is gradually increased from the minimum output to a predetermined output by frequency control. Operate with. At this time, each part operates as shown in FIG. At this time, the power factor correction circuit 71 can boost the voltage to 450 V and obtain a sufficient heating output. Further, when the load material detecting means 72 detects that the material is of low to medium conductivity such as a non-magnetic stainless steel thin plate, the power factor correction circuit 71 boosts the voltage to 330 V and operates in the low to medium conductivity mode. . At this time, each part operates as shown in FIG. Switching loss is reduced by lowering the voltage applied to the switching elements 74, 75, 76, 77 from the low conductivity material mode.

  Here, by another induction heating unit (not shown), another load is independently heated by controlling the heating output. Even if the load is the same material and the heating output is the same, the drive frequency of each induction heating unit differs due to variations, etc., but in this embodiment, the frequency is controlled near 90 kHz, and the difference in drive frequency The interference sound due to is small and practically no problem.

  On the other hand, when it is detected that the load is an aluminum load, when a predetermined drive time ratio is reached, the mode shifts to a mode in which the resonance current cycle is shorter than the drive period of the first switching element 74 and the fourth switching element 77. To do. At this time, the drive period is set so that the output is in a low output state. The drive frequency of the switching elements 74, 75, 76, 77 is set to about 30 kHz which is 1/3 of the resonance frequency of the resonance circuit. At this time, each part operates as shown in FIG. The power factor correction circuit 71 operates to improve the power factor of the commercial power supply while boosting the voltage to 400V. In this way, by increasing the pressure while reducing the loss of the switching elements 74, 75, 76, 77, the metal is operated in a high conductivity material mode that can heat a metal having low magnetic permeability and high conductivity such as aluminum. It is what.

  Furthermore, when it is detected as a composite material in which a high conductivity material such as aluminum or copper is placed on an aluminum-based and iron-based intermediate material, that is, a non-magnetic stainless steel plate or a thin non-magnetic stainless steel plate, the switching element 74, 75, 76 and 77 are driven as shown in FIG. The first switching element is driven by passing a resonance current in the latter half period of driving the first switching element 74 and the fourth switching element 77 so that the driving frequency is about 45 kHz which is ½ of the resonance frequency of the resonance circuit. 74 and the fourth switching element 77 are stopped, and the second switching element 75 and the third switching element 76 are started to be driven. The third switching element 76 is operated in a medium conductivity material mode that repeatedly stops driving. At this time, the power factor correction circuit 71 operates so as to be stepped up and smoothed to 330 V, and the drive frequency is increased from the high conductivity material mode, but the voltage applied to the switching element is decreased from the high conductivity material mode. This reduces switching loss.

  As described above, in the present embodiment, power having a frequency of about 90 kHz is supplied to the heating coil, and the load is made of a magnetic material or a low-conductivity material. Unpleasant interference sound can be reduced.

  In the present embodiment, the driving frequency is 90 kHz, but if it is 50 kHz or more, the basic amplitude of the load is small, so that the interference sound is small and there is no practical problem.

  As described above, since the induction heating cooker according to the present invention can reduce interference noise regardless of the material of the load even if there are a plurality of induction heating units, it can be used for industrial induction heating and the like. Is also applicable.

The circuit block diagram of the induction heating unit of the induction heating cooking appliance in the 1st Embodiment of this invention Characteristic diagram of detection input of load material detection means of the same induction heating cooker The figure which shows each part waveform of the circuit of the induction heating cooking appliance The figure which shows each part waveform of the circuit of the induction heating cooking appliance The figure which shows each part waveform of the circuit of the induction heating cooking appliance

Explanation of symbols

59 Heating coil 60 Resonant capacitor 63 Heating output control circuit (heating output control means)
70 Inverter 71 Power factor improvement circuit (Power factor improvement means)
72 Load material detection means 74 1st switching element 75 2nd switching element 76 3rd switching element 77 4th switching element

Claims (1)

A heating coil that was a resonant capacitor in series with the resonant circuit load is magnetically coupled, the inverter supplies power to the heating coils, induction with a heating output control means for controlling the heating output of the heating coil heating The inverter of at least two induction heating units has a plurality of units, and when the load made of aluminum is heated, the period of the resonance current of the resonance circuit is made shorter than the drive period of the switching element of the inverter. Then, when supplying electric power having a frequency of 50 kHz or more to the heating coil and heating the load made of iron, the drive period of the switching element of the inverter is at least maximized so as to be the resonance frequency of the resonance circuit. Supplying electric power having a frequency of 50 kHz or more to the heating coil in the heating output The induction heating cooker.