JP2009252565A - Induction heating device - Google Patents

Abstract

An object of the present invention is to prevent the generation of interference sound when using a plurality of heating coils at the same time and reduce circuit loss at high heating power.
A serial body of first and second semiconductor switches 5 and 6 connected in parallel to a DC power source 1 and third and fourth semiconductor switches 15 and 16 connected in parallel to the DC power source. A series body, a first resonance circuit 9 having one end connected to the midpoint of the series body of the first and second semiconductor switches, and one end at the midpoint of the series body of the third and fourth semiconductor switches. The connected second resonance circuit 19 and switching means 4 for connecting one end to the connection point of the first resonance circuit and the second resonance circuit and connecting the other end to one end of the DC power source are provided.
[Selection] Figure 1

Description

  The present invention relates to an induction heating apparatus that heats an object to be heated using induction heating by a high-frequency magnetic field.

  Conventionally, some induction heating apparatuses of this type have inverter circuits arranged in parallel (see, for example, Patent Document 1).

  FIG. 3 shows a conventional induction heating apparatus described in Patent Document 1. In FIG. As shown in FIG. 3, a series body of a first semiconductor switch 5 and a second semiconductor switch 6 is connected in parallel with the DC power source 1, and the first heating coil 3 and the first semiconductor switch 6 are connected to the second semiconductor switch 6. The series connection body of the resonance capacitor 2 and the first snubber capacitor 7 are connected, and the series body of the third semiconductor switch 15 and the fourth semiconductor switch 16 is connected in parallel with the DC power source 1. The fourth semiconductor switch 16 is connected to the series connection body of the second heating coil 13 and the second resonance capacitor 12 and the second snubber capacitor 17.

  The first to fourth semiconductor switches have a conduction time and a control means 8 so that predetermined power can be supplied to a load such as a pan magnetically coupled to the first heating coil 3 and the second heating coil 13. The operating frequency is controlled.

  The operation of the conventional example will be described. This operation description is made up of a DC power source 1, a first semiconductor switch 5, a second semiconductor switch 6, a first heating coil 3, a first resonant capacitor 2, a first snubber capacitor 7, and a control means 8. To do with the circuit.

  The same applies to the circuit constituted by the DC power source 1, the third semiconductor switch 15, the fourth semiconductor switch 16, the second heating coil 13, the second resonance capacitor 12, the second snubber capacitor 17 and the control means 8. It will work.

  When the first semiconductor switch 5 is turned on, a current determined by the voltage difference between the DC power source 1 and the first resonant capacitor 2 is supplied to the first heating coil 3.

  Next, when the first semiconductor switch 5 is turned off, the electric charge stored in the first snubber capacitor 7 moves to the first resonant capacitor 2 through the first heating coil 3, and the first snubber capacitor 7 After the charge disappears, the reverse conducting element in the second semiconductor switch 6 is turned on, so that a current flows from the first heating coil 3 to the first resonant capacitor 2.

  By setting the second semiconductor switch 6 in a conductive state at the timing when the reverse conducting element is conducting, the first resonance after the electric power of the first heating coil 3 has transitioned to the first resonant capacitor 2. Electric power is supplied to the first heating coil 3 using the capacitor 2 as a power source.

  Further, when the second semiconductor switch 6 is turned off after a predetermined time has elapsed, the first snubber capacitor 7 stores electric charge, and then passes through the reverse conducting element in the first semiconductor switch 5. The electric power stored in the heating coil 3 is regenerated in the DC power source 1.

  In this regeneration period, the first semiconductor switch 5 is turned on again to return to the initial operation.

  By performing this series of operations at a frequency of about 20 to 50 kHz, a high frequency current is supplied to the first heating coil 3, and a high frequency magnetic field generated by the high frequency current is magnetically coupled to the first heating coil 3. When entering a load such as a pan, an eddy current is generated in the load by the high-frequency magnetic field, and the pan itself generates heat due to the eddy current and the skin resistance of the pan itself.

  The first snubber capacitor 7 serves to reduce the loss when the semiconductor switch is turned off by gradually increasing the voltage when the first semiconductor switch 5 and the second semiconductor switch 6 are turned off. Is responsible.

  Further, in the induction heating apparatus of the present embodiment, the capacity of the first resonance capacitor 2 must be set in the vicinity of the resonance frequency of the resonance circuit formed by the first heating coil 3 and the first resonance capacitor 2. The necessary power is not secured, and on the other hand, the resonance frequency varies greatly depending on the type of pan or the like that is magnetically coupled to the first heating coil 3, so that the control means 8 brings the drive frequency close to the resonance frequency. In addition, control is performed by changing the driving frequency.

Here, the 1st heating coil 3 and the 2nd heating coil 12 are arrange | positioned at the lower part of one pan, and heat one load alternately or simultaneously.
JP-A-5-114474

  However, in the conventional configuration, for example, when heating a pan having a large outer diameter, when each heating coil operates independently when simultaneously heating using a plurality of heating coils, the current supplied to each heating coil If the frequency is different, the difference between the frequencies of the currents flowing in the heating coils can be heard by the device user, which makes it uncomfortable.

  On the other hand, when a heating coil combined with a large outer diameter is used alone, when the pan with a small outer diameter is heated, the outer diameter of the heating coil becomes larger and efficient heating cannot be performed.

  Furthermore, in the case where there are a plurality of heating coils, there is a problem that if a high output is obtained with only one of the heating coils, the loss of the semiconductor switch becomes large and the cooling design becomes difficult.

  In order to solve the conventional problems, an induction heating apparatus according to the present invention includes a DC power source, a series body of a first semiconductor switch and a second semiconductor switch connected in parallel to the DC power source, and the DC power source. And a first heating unit in which one end of the third semiconductor switch and the fourth semiconductor switch connected in parallel is connected to a midpoint of the series body of the first semiconductor switch and the second semiconductor switch. A first resonance circuit constituted by a series circuit of a coil and a first resonance capacitor; one end of the first resonance circuit and the other end of the third semiconductor switch and the fourth semiconductor switch in series; A second resonance circuit composed of a series circuit of a second heating coil and a second resonance capacitor connected to the other end of the resonance capacitor, and one end connected to the first resonance circuit and the second resonance circuit Connect the point and forward the other end Switching means connected to one end of a DC power supply, control of conduction time and operating frequency of the first semiconductor switch, the second semiconductor switch, the third semiconductor switch, the fourth semiconductor switch, and the switching means Control means for instructing the operation of the first heating coil, and the switching means is in a short-circuit state when supplying power to only one of the first heating coil and the second heating coil, and the first heating coil and When power is simultaneously supplied to the second heating coil, the second heating coil is opened.

As a result, when the first heating coil and the second heating coil heat the same load independently, each can be operated as an independent half-bridge circuit, and the first
When heating one load at the same time with the heating coil and the second heating coil, the first heating coil, the second heating coil, the first resonance capacitor, and the second resonance capacitor are connected in series and Since it operates as a bridge circuit, the same current flows through the first heating coil and the second heating coil, so heating without interference noise caused by the difference in operating frequency can be achieved, and circuit loss is also reduced. Therefore, it is possible to reduce the interference noise and the air volume of the cooling fan, and to realize an optimum heating configuration suitable for the load.

  The induction heating device of the present invention can select a heating coil to be used according to the shape of a load such as a pan, etc. When using the heating coil at the same time, no interference noise of the pan is generated, and further high heating power Since circuit loss can sometimes be reduced by switching the circuit system, it is possible to realize an induction heating device that is easy to use with little noise when using the equipment.

  According to a first aspect of the present invention, there is provided a DC power source, a series body of first and second semiconductor switches connected in parallel to the DC power source, and third and fourth semiconductor switches connected in parallel to the DC power source. A first resonance circuit including a series body, a first heating coil having one end connected to a midpoint of the series body of the first and second semiconductor switches, and a first resonance capacitor; and one end Is constituted by a series circuit of a second heating coil and a second resonance capacitor, in which the other end of the first resonance capacitor is connected to the midpoint of the series body of the third and fourth semiconductor switches. A second resonance circuit, switching means having one end connected to a connection point of the first resonance circuit and the second resonance circuit, and the other end connected to one end of the DC power supply, the first semiconductor switch, The second semiconductor switch, the third semiconductor switch Control means for controlling the conduction time and operating frequency of the fourth semiconductor switch and the operation of the switching means, and the switching means supplies power only to one of the first and second heating coils. When the first and second heating coils heat the same load by short-circuiting them and opening them when supplying power to the first and second heating coils simultaneously. Can be operated as independent half-bridge circuits, and when heating one load simultaneously with the first and second heating coils, the first and second heating coils and the first and second heating coils are used. Because the same current flows through the first and second heating coils because the resonant capacitors are connected in series and operate as a full bridge circuit, interference occurs due to the difference in the operating frequency of each other. It can be heated in the absence of heat and circuit loss can be reduced, so that interference noise and cooling fan airflow can be reduced, and an optimal heating configuration suitable for the load can be realized, making it easy to use. A good induction heating device can be realized.

  In the second invention, in particular, the switching of the circuit system can be realized at low cost by using the electromagnetic switch as the switching means of the first invention.

  In the third invention, in particular, by using the semiconductor switch as the switching means of the first invention, the durability at the time of switching can be remarkably increased, so that a highly reliable induction heating apparatus can be realized. .

  In particular, the fourth invention provides a capacitor in parallel with at least one of the first and second semiconductor switches of any one of the first to third inventions and at least one semiconductor switch of the third and fourth semiconductor switches. By connecting, the loss of the semiconductor switch can be reduced and the noise during the switching operation can be reduced, so that an induction heating apparatus with high efficiency and low noise can be realized.

In the fifth invention, in particular, the first and second heating coils are arranged concentrically to heat the same load, and the outer diameter of the first heating coil is made smaller than the inner diameter of the second heating coil. Since one load can be heated with good distribution, an induction heating device with excellent cooking performance can be realized.

  In the sixth invention, in particular, the first and second heating coils are arranged on a concentric plane so as to heat the same load, so that the heating coil can be arranged on one table and the heating coil. Since a magnetic-shielding component such as ferrite disposed on the back surface can be shared, an inexpensive configuration can be realized.

  In the seventh aspect of the invention, in particular, the control means switches the switching means without charge accumulated in the first and second resonance capacitors by stopping heating for a certain period of time when operating the switching means. Therefore, since an overcurrent does not occur in the switching means, a highly reliable induction heating device can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

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

  FIG. 2 is a configuration diagram of a heating coil of the induction heating apparatus in the first embodiment.

  In FIG. 1, a series body of a first semiconductor switch 5 and a second semiconductor switch 6 and a series body of a third semiconductor switch 15 and a fourth semiconductor switch 16 are connected in parallel with the DC power source 1.

  At the midpoint of the first semiconductor switch 5 and the second semiconductor switch 6 and at the midpoint of the third semiconductor switch 15 and the fourth semiconductor switch 16, the first heating coil 3 and the first resonant capacitor 2 are provided. A series circuit of a first resonance circuit 9 formed by connecting in series, a second heating coil 13 and a second resonance circuit 19 formed by connecting the second resonance capacitor 12 in series is connected. The switching means 4 is connected to a connection point between the resonance circuit 9 and the second resonance circuit 19 and one end of the DC power supply 1.

  The first to fourth semiconductor switches are operated by the control means 8 so that predetermined power can be supplied to a load such as a pan magnetically coupled to the first heating coil 3 and the second heating coil 13. The frequency is controlled. In the present embodiment, the switching means 4 is configured by an electromagnetic switch such as a relay.

  The first to fourth semiconductor switches are usually composed of a semiconductor switch for controlling a forward current such as an IGBT or an FET, a reverse blocking diode for passing a current in the reverse direction to the semiconductor switch, and a parallel circuit. The configuration is not limited to this.

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

  At least one of the first semiconductor switch 5 and the second semiconductor switch 6, and at least one of the third semiconductor switch 15 and the fourth semiconductor switch 16 have a first snubber capacitor 7 and a second snubber capacitor 17. Are connected in parallel, the rise of the voltage when the first to fourth semiconductor switches are turned off can be moderated, so that the switching loss during turn-off can be reduced, and the semiconductor switch The noise generated from the can also be kept low.

  Here, when the first heating coil 3 and the second heating coil 13 heat a load such as the same pan, when heating is performed by supplying power to only one heating coil or alternately to the heating coil. The switching means 4 is in a closed state, and includes a first resonance circuit 9 including a first heating coil 3 and a first resonance capacitor 2, a second heating coil 13 and a second resonance capacitor 12. The second resonance circuit 19 is connected to one end of the DC power source 1 to supply power necessary for a load such as a pan through each heating coil.

  At this time, in order to obtain a predetermined electric power, the control means 8 independently varies the driving frequency of the first and second semiconductor switches and the driving frequency of the third and fourth semiconductor switches, so that each heating is performed. Electric power required for the coil is generated.

  On the other hand, when the first heating coil 3 and the second heating coil 13 heat the same load at the same time, the switching means 4 is opened, and the first heating coil 3 and the first resonant capacitor 2 are configured. Since the second resonance circuit 19 composed of the first resonance circuit 9, the second heating coil 13, and the second resonance capacitor 12 is connected in series, the first to fourth semiconductor switches Both heating coils and a resonant capacitor are connected between the midpoints to form a full bridge circuit.

  At this time, in order to obtain a predetermined power, the control means 8 operates the first to fourth semiconductor switches alternately, and the first heating coil 3 and the second heating coil 13 are identical. Current will flow.

  In this case, the power distribution on the load such as the pan depends on the ratios of the shape and the number of turns of the first heating coil 3 and the second heating coil 13.

  In addition, as shown in FIG. 2, the first heating coil 3 and the second heating coil 13 are arranged concentrically so that a heating distribution can be obtained evenly with respect to the load, and further arranged on the same plane. Thus, the heating coil can be arranged on one table, and a magnetic-shielding component such as ferrite arranged on the back surface of the heating coil can be shared.

  Further, when the first heating coil 3 and the second heating coil 13 are connected in series, the heating coil is operated with a full bridge circuit, so even if the inductance of the heating coil is large, twice the voltage is applied to the heating coil. The generated power can be increased.

  As a result, a large amount of generated magnetic field can be obtained with a small current, and circuit loss can be reduced.

  Therefore, when large power is required, the circuit can be cooled with a small amount of cooling air by adopting a configuration in which the first heating coil 3 and the second heating coil 13 are arranged in series. A heating device can be provided.

  When the outer diameter of the load such as a pan is small, heating is performed only with the inner heating coil (first heating coil 3 in FIG. 2), and when the outer diameter of the load is larger, the inner heating coil ( In FIG. 2, the first heating coil 3) and the outer heating coil (second heating coil 13 in FIG. 2) are configured in series to realize an optimum heating configuration in accordance with the shape of the pan.

In addition, as a method of detecting the diameter of the pan, a method of detecting a leakage magnetic field from the heating coil with a pickup coil, a method of detecting a temperature distribution on the top plate on which the pan is mounted, or a current flowing through the heating coil and generation There is a method of estimating from the voltage relationship, but it is not particularly limited.

  Further, when a relay is used for the switching means 4, it is desirable to increase the reliability of the relay after the power supply to the load such as a pan is stopped for a predetermined time, especially when the relay is switched.

  In addition, it is possible to use a semiconductor switch without using a relay for the switching means 4, and by adopting this configuration, the durability with respect to the number of times of use is improved compared to the mechanical contact switching means, thereby improving the reliability. Can do.

  Note that the switching means 4 and the first to fourth semiconductor switches perform a switching operation based on a command from the control means 8.

  As described above, in the present embodiment, when the first heating coil 3 and the second heating coil 13 are independently heating the same load depending on the state of the switching means 4, each is an independent half-bridge circuit. Works as.

  Further, when the same load is simultaneously heated by the first heating coil 3 and the second heating coil 13, the first heating coil 3, the second heating coil 13, the first resonant capacitor 2 and the second heating coil 3 are used. The resonance capacitors 12 are connected in series and the first to fourth semiconductor switches operate as a full bridge circuit, so that the same current flows through the heating coil, so that there is no interference sound caused by the difference between the operating frequencies of each other. Can be heated.

  Further, since the required power can be obtained in the state where the inductances of the first heating coil 3 and the second heating coil 13 are added together, a large amount of generated magnetic field can be obtained with a small current, and the circuit loss can be reduced. Therefore, since there is no interference sound and the air volume of the cooling fan can be reduced, a user-friendly induction heating device can be realized.

  As described above, the induction heating device according to the present invention is effective for cooking appliances such as induction heating because the heating coil to be used can be selected according to the shape of a load such as a pan.

The circuit block diagram of the induction heating apparatus in Embodiment 1 of this invention The block diagram of the heating coil of the induction heating apparatus in Embodiment 1 of this invention Circuit diagram of a conventional induction heating device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 1st resonance capacitor 3 1st heating coil 4 Switching means 5 1st semiconductor switch 6 2nd semiconductor switch 8 Control means 9 1st resonance circuit 12 2nd resonance capacitor 13 2nd heating Coil 15 Third semiconductor switch 16 Fourth semiconductor switch 19 Second resonance circuit

Claims (7)

A DC power source, a series body of a first semiconductor switch and a second semiconductor switch connected in parallel to the DC power source, and a third semiconductor switch and a fourth semiconductor switch connected in parallel to the DC power source. A first resonance composed of a series body, a series circuit of a first heating coil and a first resonance capacitor, one end of which is connected to a midpoint of the series body of the first semiconductor switch and the second semiconductor switch. A circuit, a second heating coil having one end connected to the midpoint of a series body of the third semiconductor switch and the fourth semiconductor switch and the other end connected to the other end of the first resonance capacitor, and a second resonance A second resonance circuit constituted by a series circuit of capacitors, and switching means for connecting one end to a connection point of the first resonance circuit and the second resonance circuit and connecting the other end to one end of the DC power supply; , The first semiconductor device Control means for controlling the conduction time and operating frequency of the second semiconductor switch, the third semiconductor switch, the fourth semiconductor switch, and the operation of the switching means, and the switching means When power is supplied to only one of the first heating coil and the second heating coil, it is in a short-circuit state, and when power is supplied simultaneously to the first heating coil and the second heating coil. Induction heating device to be opened. The induction heating apparatus according to claim 1, wherein the switching unit uses an electromagnetic switch. The induction heating apparatus according to claim 1, wherein the switching means uses a semiconductor switch. 4. The capacitor according to claim 1, wherein a capacitor is connected in parallel to at least one of the first semiconductor switch and the second semiconductor switch and at least one semiconductor switch of the third semiconductor switch and the fourth semiconductor switch. The induction heating apparatus described. The first heating coil and the second heating coil are arranged concentrically to heat the same load, and the outer diameter of the first heating coil is made smaller than the inner diameter of the second heating coil. The induction heating device according to any one of the above. The induction heating apparatus according to any one of claims 1 to 5, wherein the first heating coil and the second heating coil are arranged on a concentric plane so as to heat the same load. The induction heating apparatus according to any one of claims 1 to 6, wherein the control means stops heating for a predetermined time when operating the switching means.

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