JP2013012308A - Induction heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating apparatus which can set a plurality of patterns of a ratio of an electric power supplied from a plurality of heating coils to heating objects by an easy and inexpensive configuration and control of an inverter circuit.SOLUTION: An induction heating apparatus comprises an inverter circuit 40 to which two resonance circuits are connected in parallel. The resonance circuits respectively include a first heating coil 48 provided on an inner side and a second heating coil 49 provided on an outer side to which resonance capacitors are connected in parallel, respectively. Between a resonance frequency of a first resonance circuit 56 including the first heating coil and a first resonance capacitor 50 connected to the first heating coil in series, and a resonance frequency of a second resonance circuit 57 including the second heating coil and a second resonance capacitor 51 connected to the second heating coil in series, switching means 60 is connected in series between the resonance circuit having a higher resonance frequency and the inverter circuit. An operation frequency of the inverter circuit and switching of the switching means are controlled depending on a set heating pattern.

Description

  The present invention relates to an apparatus for induction heating an object to be heated using a plurality of heating coils including an induction heating cooker, and particularly relates to a circuit configuration and a control method of the induction heating apparatus.

  Conventionally, in this type of induction heating device, there are some which connect two resonance circuits composed of a heating coil and a resonance capacitor to the same inverter circuit, and each resonance circuit has a different resonance frequency (for example, Patent Document 1). FIG. 7 is a characteristic diagram showing frequency impedance characteristics of the inner resonance circuit and the outer resonance circuit in this induction heating apparatus.

  This induction heating device can vary the ratio of the heating power by operating the inverter circuit at a frequency corresponding to the ratio of the power supplied from the heating coil included in each resonance circuit to the object to be heated.

  For example, the impedances of the inner resonance circuit and the outer resonance circuit substantially coincide with each other in the frequency range of the A region in FIG. 7, and the inner resonance circuit and the outer resonance circuit are operated by operating the inverter circuit at the frequency of the A region. Are supplied with substantially the same current. As a result, the electric power supplied to the inner heating coil and the outer heating coil becomes substantially the same value, and the entire heating area is heated substantially uniformly.

  Further, in the frequency range of region B in FIG. 7, the impedance of the outer resonance circuit is higher than the impedance of the inner resonance circuit. By operating the inverter circuit at the frequency in the region B, almost no current is supplied to the outer resonance circuit. That is, the current supplied to the inner heating coil is larger than the current supplied to the outer heating coil, and as a result, the inside of the object to be heated is heated more than the outside of the object to be heated in the frequency range of the B region. To do.

JP 2001-353063 A

  However, in the conventional configuration, whether the power supplied to the inner heating coil and the outer heating coil is substantially the same, or whether the power supplied to the inner heating coil is larger than the power supplied to the outer heating coil. However, it does not have a heating pattern that increases the power supplied to the outer heating coil as compared with the power supplied to the inner heating coil. For example, in order to improve the rice cooking performance, there is an optimum heating pattern according to the rice cooking process or the amount of rice cooking, and the power supplied to the outer heating coil is supplied to the inner heating coil in the heating pattern. Since the heating pattern which increases compared with electric power is also required, the rice cooking performance was not able to be improved with the said conventional structure.

Further, in Patent Document 1 described in the prior art document, the electric power supplied to the inner heating coil and the outer heating coil is substantially matched, or the electric power supplied to the outer heating coil is the electric power supplied to the inner heating coil. It has also been proposed to realize two heating patterns that are greater than those of the heating coil, but in this case, heating that increases the power supplied to the inner heating coil compared to the power supplied to the outer heating coil. Since it has no pattern, three heating patterns could not be realized as described above.

  In order to realize the three heating patterns, an inverter circuit is connected to each of the inner heating coil and the outer heating coil, and means for independently controlling the power supplied to each heating coil can be considered. The number of parts that constitutes a large number, and three heating patterns could not be realized at low cost.

  Also, three heating patterns are realized by connecting the same number of switching means as the number of resonance circuits or heating coils, and selectively conducting the switching means connected to the resonance circuits or heating coils to which power is to be supplied. In addition to the fact that a large number of switching means were required and the circuit could not be constructed at low cost, a switching means mounting space corresponding to the number of switching means was required on the circuit board, and thus the circuit board was made compact. Could not be converted.

  The present invention solves the above-described conventional problems, and substantially matches the power supplied to the inner heating coil and the outer heating coil, or changes the power supplied to the inner heating coil to the power supplied to the outer heating coil. Induction heating apparatus capable of realizing a total of three heating patterns at a low cost, that is, a larger number compared with the power supplied to the outer heating coil or a larger amount compared to the power supplied to the inner heating coil. The purpose is to provide.

  In order to solve the above-described conventional problems, an induction heating apparatus according to the present invention includes a first heating coil provided inside a heating region and a first heating coil that is substantially concentric with the first heating coil and outside the first heating coil. Two resonance circuits in which a resonance capacitor is connected in series to each of the second heating coils provided in, and two resonance circuits connected in parallel and converting the output of the power supply into alternating current of a set frequency. An inverter circuit that outputs to the connected resonance circuit section, a switching means that electrically opens and closes the resonance circuit and the inverter circuit, a drive signal is supplied to the inverter circuit to control the operation of the inverter circuit, and the switching means is arbitrarily switched A control means for controlling, a resonance frequency of a first resonance circuit comprising a first heating coil and a first resonance capacitor connected in series to the first heating coil, and a second heating coil. And the second resonant circuit composed of the second resonant capacitor connected in series to the second heating coil are set to be different from each other, and the resonant frequency of the first resonant circuit and the resonant frequency of the second resonant circuit are set. Among the frequencies, switching means is connected in series between the resonance circuit having a higher resonance frequency and the inverter circuit, and the operation frequency of the inverter circuit and the opening / closing of the switching means are controlled according to the set heating pattern.

  Accordingly, the power supplied to the heating coil in the resonance circuit on the higher resonance frequency side and the heating coil in the resonance circuit on the lower resonance frequency side are substantially matched, or the heating coil in the resonance circuit on the higher resonance frequency side is matched. When the power supplied to the heating coil is increased as compared with the power supplied to the heating coil in the resonance circuit on the low resonance frequency side, the switching means is closed (turned on) and the resonance circuit and the inverter circuit When the two operating patterns are realized by changing the operating frequency of the inverter circuit in a state in which the power is connected, and power is supplied only to the heating coil in the resonance circuit on the low resonance frequency side, the switching means is opened ( By disconnecting the resonant circuit from the inverter circuit (off), a total of three heating patterns can be realized.

The induction heating device of the present invention has a total of three heating patterns with an easy and inexpensive configuration when supplying substantially the same power to two heating coils and when supplying a large amount of power to one of the heating coils. By realizing, for example, this induction heating apparatus is applied to a rice cooker, and rice is cooked with an optimal heating pattern according to the rice cooking process or the amount of rice cooking, so that rice cooking performance can be improved and delicious rice can be cooked.

The inverter circuit block diagram of the induction heating apparatus in Embodiment 1 of this invention The characteristic view which shows the relationship between the operating frequency of the inverter circuit of the induction heating apparatus at the time of the switching means conduction | electrical_connection in Embodiment 1 of this invention, and supply electric power The characteristic view which shows the relationship between the operating frequency of the inverter circuit of the induction heating apparatus at the time of switching means cutting | disconnection in Embodiment 1 of this invention, and supply electric power The characteristic view which shows the relationship between the elapsed time at the time of rice cooking of the rice cooker which applied the induction heating apparatus in Embodiment 2 of this invention, and the bottom temperature sensor, and the relationship of the operation area | region of the inverter circuit for every rice cooking process. The characteristic view which shows the relationship between the elapsed time at the time of the convection mode heating of the induction heating cooking appliance which applied the induction heating apparatus in Embodiment 3 of this invention, and the electric power supplied from each heating coil The characteristic view which shows the relationship between the elapsed time at the time of the uniform mode heating of the induction heating cooking appliance which applied the induction heating apparatus in Embodiment 3 of this invention, and the electric power supplied from each heating coil A characteristic diagram showing the relationship between the operating frequency and impedance of an inverter circuit of a conventional induction heating device

  In the first invention, each of the first heating coil provided inside the heating region and the second heating coil provided substantially outside the first heating coil and concentrically with the first heating coil. Two resonant circuits formed by connecting resonant capacitors in series; an inverter circuit that is connected to a power source and converts the output of the power source into alternating current of a set frequency and outputs the two resonant circuits to a resonant circuit unit connected in parallel; A switching means for electrically opening and closing the resonance circuit and the inverter circuit; and a control means for controlling the operation of the inverter circuit by supplying a drive signal to the inverter circuit and controlling the switching means arbitrarily. A resonance frequency of a first resonant circuit comprising a coil and a first resonant capacitor connected in series to the first heating coil; a second heating coil and a second connected in series to the second heating coil; The resonance frequency of the second resonance circuit composed of the resonance capacitor is set to be different from each other, and the resonance circuit and inverter on the higher resonance frequency side of the resonance frequency of the first resonance circuit and the resonance frequency of the second resonance circuit Switching means are connected in series between the circuits, and the operating frequency of the inverter circuit and the opening and closing of the switching means are controlled according to the set heating pattern.

  Accordingly, the power supplied to the heating coil in the resonance circuit on the higher resonance frequency side and the heating coil in the resonance circuit on the lower resonance frequency side are substantially matched, or the heating coil in the resonance circuit on the higher resonance frequency side is matched. When the power supplied to the heating coil is increased compared to the power supplied to the heating coil in the resonance circuit on the low resonance frequency side, the switching means is turned on and the resonance circuit and the inverter circuit are connected. In the case where two heating patterns are realized by changing the operating frequency of the inverter circuit and power is supplied only to the heating coil in the resonance circuit on the low resonance frequency side, the switching means is turned off and the resonance circuit is switched to the inverter. By disconnecting from the circuit, a total of three heating patterns can be realized.

In the second invention, in particular, in the first invention, the operating frequency of the inverter circuit when the resonance circuit is electrically disconnected from the inverter circuit by the switching means is electrically connected between the inverter circuit and the resonance circuit by the switching means. The switching circuit is turned off by disconnecting the resonant circuit from the inverter circuit by lowering the operating frequency of the inverter circuit at that time, and power is supplied only to the heating coil in the resonant circuit on the lower resonant frequency side. In the case, the supplied power is the first when the switching means is turned on and the resonance circuit is in conduction with the inverter circuit, and the power supplied to the first heating coil and the second heating coil substantially coincides with each other. The sum of the power supplied to the first heating coil and the power supplied to the second heating coil, or the heating coil included in the resonance circuit on the higher resonance frequency side. The power supplied to the first heating coil and the power supplied to the second heating coil in the case where the power to be supplied is increased as compared with the power supplied to the heating coil included in the resonance circuit on the low resonance frequency side. Can be supplied to the heating coil in the resonance circuit on the low resonance frequency side.

  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 is an inverter circuit configuration diagram of the induction heating apparatus according to the first embodiment of the present invention, and shows a configuration of an inverter circuit and a connection relationship between a plurality of heating coils and a resonant capacitor.

  FIG. 2 is a characteristic diagram showing the relationship between the operating frequency of the inverter circuit of the induction heating device and the maximum power that can be supplied to the object to be heated when the switching means in the first embodiment of the present invention is conductive. Yes, it shows the power characteristics of each resonance circuit.

  In FIG. 1, a commercial power source 41 is an AC power source, and a diode bridge 42 is connected to convert the AC power source into a DC power source. In order to smooth the full-wave rectified power source output from the diode bridge 42 and to prevent electromagnetic noise generated by the switching operation of the switching element from propagating to the commercial power source 41 at the output end of the diode bridge 42, A first filter capacitor 43, a filter inductor 44, and a second filter capacitor 45 are connected.

  A reverse conducting diode is connected to both ends of the second filter capacitor 45 (hereinafter, the high potential side to which the filter inductor 44 is connected is referred to as a positive bus and the other low potential side is referred to as a negative bus). A first switching element 46 connected in parallel with 54 and a second switching element 47 similarly connected in parallel with a reverse conducting diode 55 are connected in series to form an inverter circuit 40. Yes.

  At the connection point of the first switching element 46 and the second switching element 47, one end of the first resonance circuit 56 in which the first heating coil 48 and the first resonance capacitor 50 are connected in series and the second heating coil One end of a second resonance circuit 57 in which 49 and the second resonance capacitor 51 are connected in series is connected. Then, the other terminal of the first resonance circuit 56 and the other terminal of the second resonance circuit 57 are connected to the negative bus line, so that a circuit configuration based on a circuit configuration called SEPP type is obtained.

  Further, in order to reduce switching loss and electromagnetic noise generated by the switching operation of the first switching element 46 and the second switching element 47, the snubber capacitor 53 is electrically connected in parallel with the second switching element 47. Yes.

  In the present embodiment, the inductance of the heating coil and the capacitance of the resonance capacitor are set so that the resonance frequency of the first resonance circuit 56 is higher than the resonance frequency of the second resonance circuit 57. A switching means 60 for switching whether the first resonance circuit 56 and the inverter circuit 40 are electrically connected or disconnected is connected in series between the first resonance circuit 56 and the negative bus.

A temperature detecting means 62 for detecting the temperature of the heated object 61 is arranged in contact with or not in contact with the heated object 61 at the bottom of the heated object 61 such as a rice cooker or a pan. The circuit of the induction heating apparatus according to the present embodiment is configured by including a control unit 59 that drives and controls the first switching element 46 and the second switching element 47 based on the output value of the detection signal.

  In addition, the other terminal of the first resonance circuit 56 and the other terminal of the second resonance circuit 57 are not negative buses, and power is supplied from the inverter circuit 40 to the resonance circuit even when connected to a positive bus. Can do.

  Furthermore, the induction heating apparatus of the present embodiment has a circuit configuration in which two resonance circuits are connected to the SEPP type inverter circuit 40 using two switching elements, but is a full bridge type using four switching elements. A circuit configuration in which two resonance circuits are connected to the inverter circuit may be used.

  In the induction heating apparatus of the present embodiment, the switching means 60 is connected between the negative bus and the first resonance circuit 56, but the first resonance circuit 56 is electrically disconnected from the inverter circuit 40. It may be anywhere as long as the switching means 60 is connected to a position where it can be performed.

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

  First, the operation of the inverter circuit 40 in the present embodiment will be described. The inverter circuit 40 according to the present embodiment changes the operating frequency of the first switching element 46 and the second switching element 47 and the ratio between the conduction time and the non-conduction time (0 <Duty <1) by changing the first switching element 46 and the second switching element 47. By controlling the current flowing through the resonance circuit 56 and the current flowing through the second resonance circuit 57, the power supplied from the first heating coil 48 and the second heating coil 49 to the heated object 61 can be adjusted. . Here, it goes without saying that the first switching element 46 and the second switching element 47 operate exclusively without being simultaneously conducted.

  When adjusting the power supplied from the heating coil to the object to be heated 61 by changing the duty, under the condition that the potential difference between the positive bus and the negative bus is constant, when the duty is 0.5, the heating coil The electric power supplied to the heated object 61 becomes the maximum. On the other hand, as the duty of the first switching element 46 and the second switching element 47 is increased from 0.5, such as 0.1 or 0.9, the power supplied from the heating coil to the heated object 61 becomes smaller.

  FIG. 2 shows the operating frequency of the inverter circuit 40 and the first heating coil 48 in the first resonance circuit 56 in a state where the switching means 60 is turned on and the first resonance circuit 56 and the inverter circuit 40 are conducted. 2 shows the relationship between the electric power that the second heating coil 49 in the second resonance circuit 57 can supply to the object 61 to be heated, and a waveform 83 in FIG. 2 indicates that the first heating coil 48 has the object 61 to be heated. The waveform 87 shows the relationship of the power that can be supplied to the object 61 to be heated by the waveform 87. Since the resonance characteristics such as the resonance frequency and the power that can be supplied to the object to be heated differ depending on the inductance of the heating coil in the resonance circuit, the capacitance of the resonance capacitor, and the magnetic coupling degree between the heating coil and the object to be heated, the waveform 83 and The waveform 87 has different characteristics. In FIG. 2, the potential difference between the positive bus and the negative bus is always constant.

  A waveform 88 in FIG. 2 indicates the power supplied from the first heating coil 48 to the heated object 61 and the power supplied from the second heating coil 49 to the heated object 61 at each operating frequency of the inverter circuit 40. Is the sum of When one object 61 is heated using the first heating coil 48 and the second heating coil 49, the electric power supplied to the object 61 is supplied from the first heating coil 48 to the object 61. The waveform 88 shows the power characteristic supplied from the power source 41 to the heated object 61 because it is the sum of the generated electric power and the electric power supplied from the second heating coil 49 to the heated object 61.

  An operation region A in FIG. 2 is an operation region in the case where the electric power supplied to the first heating coil 48 and the second heating coil 49 substantially match. The operation region B is an operation region when the power supplied to the first heating coil 48 is increased as compared with the power supplied to the second heating coil 49. In this case, by setting the operating frequency of the inverter circuit 40 to the operating region A, the object to be heated 61 is heated in a state where the power supplied to the first heating coil 48 and the second heating coil 49 is substantially matched. be able to. Further, since the resonance frequency of the first resonance circuit 56 including the first heating coil 48 is set higher than the resonance frequency of the second resonance circuit 57 including the second heating coil 49, the inverter circuit By setting the operation frequency of 40 in the operation region B, the object 61 is heated in a state in which the power supplied to the first heating coil 48 is higher than the power supplied to the second heating coil 49. be able to.

  A waveform 88 indicates the sum of the electric power supplied from the first heating coil 48 to the object to be heated 61 and the electric power supplied from the second heating coil 49 to the object to be heated 61. It can be seen from FIG. 2 that the power supplied to the article 61 to be heated (the value of the waveform 88) and the electric power supplied to the article to be heated 61 in the operation region A (the value of the waveform 88) are substantially the same. By setting such a relationship between the operation areas, the ratio of the electric power supplied from the heating coil to the object to be heated 61 varies between the operation area A and the operation area B, but the electric power supplied to the object to be heated 61 Since the sum can be substantially matched, even if the operating region is changed to change the heating pattern, the supplied power can be made constant at all times. Such a relationship between the operation regions is particularly effective when changing the heating pattern while constantly heating the object to be heated 61 with the rated power. If the operation region is set ignoring this relationship, changing the heating pattern may cause a situation in which, for example, the power supplied to the article 61 to be heated increases and exceeds the rated power. It may be a product defect. Conversely, by changing the heating pattern, the power supplied to the object to be heated 61 decreases, and it may be impossible to perform when cooking with high power. In order to avoid this, it is necessary to set the operation area described above.

  However, when the electric power supplied to the article 61 to be heated may vary with the change of the operation region depending on the product, it is not necessary to set the operation region along this condition.

  The relationship between the resonance characteristics of the first resonance circuit 56 including the first heating coil 48 and the resonance characteristics of the second resonance circuit 57 including the second heating coil 49 is the inductance of the heating coil, the capacitance of the resonance capacitor, Since it is determined by the equivalent resistance of the object to be heated as viewed from the heating coil, in order to set the relationship of the operation region, first, the power supplied to the first heating coil 48 and the second heating coil 49 is made to substantially match. It is necessary to clarify the operation area A. After the operation area A is set and the sum of the electric power (waveform 88) supplied from the first heating coil 48 and the second heating coil 49 in the operation area A is clarified, the sum of the electric power is abbreviated. An induction heating device having this function can be designed by setting the matching operation region B.

  Here, when the object to be heated is fixed, the induction heating apparatus having this function can be easily implemented by measuring the characteristics in advance and storing them in the control means 59.

  The induction heating apparatus according to the present embodiment includes a first resonance circuit 56 including a first heating coil 48 having a resonance frequency higher than that of a second resonance circuit 57 including a second heating coil 49. Since the switching means 60 is connected in series, the switching means 60 is turned off and the first resonance circuit 56 is electrically disconnected from the inverter circuit 40, so that no power is supplied to the first resonance circuit 56. You can avoid it.

FIG. 3 shows the operating frequency of the inverter circuit 40 and the power supplied to the second heating coil 49 when the switching means 60 is turned off and the first resonance circuit 56 is electrically disconnected from the inverter circuit 40. Yes. Here, the waveform 87 in FIG. 3 and the waveform 87 in FIG. 2 have the same characteristics because the value of the second resonance circuit 57 is not changed. By turning off the switching means 60 and electrically disconnecting the first resonance circuit 56 from the inverter circuit 40, no power is supplied to the first resonance circuit 56. As a result, the second heating circuit The heated object 61 can be heated in a state in which the power supplied to the coil 49 is higher (100% supplied to the second heating coil 49) than the power supplied to the first heating coil 48.

  In addition, when the switching means 60 is turned on and the first resonance circuit 56 is electrically connected to the inverter circuit 40, the power supplied to the first heating coil 48 and the second heating coil 49 is substantially matched. In addition to the state and the two heating pattern control methods for heating the object to be heated 61 in a state where the power supplied to the first heating coil 48 is higher than the power supplied to the second heating coil 49, the switching means When the first resonance circuit 56 is electrically disconnected from the inverter circuit 40 by turning off 60, the power supplied to the second heating coil 49 is higher than the power supplied to the first heating coil 48. A total of three patterns of heating the object to be heated 61 in a state can be realized, and the object to be heated 61 can be heated at a desired power ratio.

  When the switching means 60 is turned off and the first resonance circuit 56 is electrically disconnected from the inverter circuit 40, no power is supplied to the first resonance circuit 56. Therefore, the power supplied to the object to be heated 61 is All are supplied from the second heating coil 49 included in the second resonance circuit 57. Therefore, when the inverter circuit 40 is operated in the operation region A even when the switching means 60 is turned off and the first resonance circuit 56 is electrically disconnected from the inverter circuit 40, the electric power supplied to the heated object 61 Will drop to almost half. For this reason, even when three heating patterns are used, in order to be able to constantly supply the set power even if the heating pattern is changed, the object 61 to be heated is only required by the second heating coil 49. The operation region C in the case of heating needs to be a frequency region lower than the operation region A in the case of heating by substantially matching the power supplied to the first heating coil 48 and the second heating coil 49. .

  Thereby, by changing a heating pattern, it can avoid that the electric power supplied to the to-be-heated material 61 increases, and it can avoid exceeding rated power. Further, by changing the heating pattern, it is possible to avoid that the power supplied to the article 61 to be heated is reduced, and it is possible to maintain the cooking performance even when it is desired to continue cooking with high power, for example.

  However, similarly to the above, when the three heating patterns are used, it is not necessary to set the operation area in this condition when the power supplied to the object to be heated 61 may vary with the change of the operation area depending on the product. .

(Embodiment 2)
FIG. 4: is a characteristic view which shows the relationship between each rice cooking process and the operation area | region of an inverter circuit at the time of applying the induction heating apparatus of this invention in the 2nd Embodiment of this invention to a rice cooker.

  In cooking rice with a rice cooker, after the rice cooker containing rice and water is set in the rice cooker, the rice cooker is pre-programmed with a pre-programmed rice cooking sequence (for example, a soaking process, a cooking process, boiling) The process is performed in the order of the process, the unevenness process, and the heat retention process), and the temperature adjustment suitable for each process and the amount of cooked rice and the adjustment of the supplied power are performed.

In any rice cooking process, the temperature of rice and water in the rice cooker is uniform everywhere, which is a necessary condition for cooking rice deliciously. Because it changes, the entire rice cooker is always heated uniformly, or the rice cooker is always heated locally to cause convection. Rice cooking performance is not obtained.

  FIG. 4 is a characteristic diagram showing the relationship between the rice cooking time (elapsed time from the start of rice cooking) and the bottom sensor temperature of the rice cooking pot obtained by the temperature detecting means 62, and shows each rice cooking step.

  After the water immersion process (maintained at a constant temperature in the present embodiment), in the cooking process, the first heating coil 48 disposed inside the bottom of the rice cooker has the second heating coil 48 disposed outside the bottom of the rice cooking pot. By supplying more electric power than the heating coil 49, it is possible to secure a passage of high-temperature liquid or bubbles generated in the subsequent boiling process. A sufficient amount of heat can be supplied to the rice located in the rice cooker, and the rice located in the central part of the rice cooker and the rice located in the outer peripheral part of the rice cooker can be heated uniformly.

  After the cooking process, in the boiling process, with the switching means 60 turned on, the operating frequency of the inverter circuit 40 is operated in the operation area A lower than that in the cooking process, so that the entire rice cooker is now It can be heated uniformly. Here, as described above, since the passage of the liquid or bubbles generated during the boiling process is secured in the central portion of the cooking pot in the cooking process, bubbles are generated only along the cooking pot by uniformly heating the entire cooking pot. It is possible to cook delicious rice by suppressing the rise in the amount of heat and equalizing the amount of heat applied to the rice in the outer peripheral part and the central part of the rice cooker.

  Also, after the boiling process, in the mura process, the rice cooker is steamed with preheating, so only a small amount of electricity is supplied to the rice cooker. However, since the rice is in a high temperature state near 100 ° C, a lot of steam is generated and the steam is cooked. If it contacts the side of the kettle, it will be cooled and condensed. The condensation eventually drips down the side of the rice cooker, and as a result, the rice located on the outer periphery of the rice cooker is crushed. Therefore, in the unevenness process, by switching off the switching means 60 and operating the inverter circuit 40 in the operation region C, only the outer peripheral portion of the rice cooker can be heated, and the rice on the outer peripheral portion is not sticky. Overall delicious rice can be cooked.

  Here, since there is less electric power to supply to the rice cooker in the uneven process than in the cooking process or boiling process, the electric power supplied by operating the inverter circuit 40 at a higher frequency than the operation region C can be reduced. Alternatively, the average value of the power supplied to the rice cooker may be lowered by operating the inverter circuit 40 in the operation region C and intermittently operating the inverter circuit 40.

  The above-described various processes and the corresponding operation areas are merely examples, and the present invention invents an induction heating apparatus that can realize three heating patterns with a small number of parts and a low cost and a simple configuration. Because it achieves a rice cooker that can be cooked deliciously using an induction heating device, if there is a sequence that can cook more deliciously than the above sequence, it may be changed to it, and the order of the rice cooking process and operation area The amount of power is not limited.

Furthermore, the power supplied to the first heating coil 48 is higher than the power supplied to the second heating coil 49, and the power to be supplied to the second heating coil 49 is heated. In the case where the object to be heated 61 is heated in a higher state than the power supplied to the first heating coil 48, whether or not the low power is supplied completely depending on whether the switching means 60 is on or off. For example, in the unevenness process, power is not supplied to the second heating coil 49 only to heat the outside of the rice cooker extremely, but the first disposed on the inside. When it is desired to supply a small amount of power to the heating coil 48 to heat the inside of the rice cooker, the magnitude relationship between the resonance frequencies of the first resonance circuit 56 and the second resonance circuit 57 is reversed, and the switching means 60 is changed. Second additive with high resonant frequency By connecting in series with the coil 49, power is supplied only to the first heating coil 48 this time in the cooking process, but while supplying much power to the second heating coil 49 in the unevenness process, A small amount of power can be supplied to the first heating coil 48. As described above, by adjusting the resonance characteristics, it is possible to select heating suitable for each process.

(Embodiment 3)
FIG. 5 shows a case where the induction heating apparatus according to the third embodiment of the present invention is applied to an induction heating cooker and is supplied to the first heating coil 48 and the second heating coil 49 when convection is desired. It is a characteristic view which shows the time change of electric power.

  Moreover, FIG. 6 is supplied to the 1st heating coil 48 and the 2nd heating coil 49 when applying the induction heating apparatus in the 3rd Embodiment of this invention to an induction heating cooking appliance, and making it want to heat uniformly. It is a characteristic view which shows the time change of the electric power.

  In the induction heating cooker, in order to accelerate the soaking of the taste of the cooked food in the pan, which is the heated object 61 placed on the cooker, increase the flow rate of the liquid present in the pan during heating. Is effective. Therefore, by clarifying the part that is heated and the part that is not heated in the surface direction of the placement area (that is, the pan bottom), the part that is not heated from the part that is heated after the heated liquid rises to the top of the liquid The liquid can flow smoothly to the bottom, resulting in convection.

  In the induction heating apparatus of the present invention, a large amount of electric power can be supplied to the first heating coil 48 by operating the inverter circuit 40 in the operation region B, and the inverter circuit 40 is operated in the operation region C. Thus, since power can be supplied only to the second heating coil 49, large convection can be generated in the liquid in the pan in any heating.

  Here, when operating the inverter circuit 40 in the operation region B, a small amount of power is supplied from the second heating coil 49 to the pan, but compared with the power supplied from the first heating coil 48 to the pan. Therefore, since there is a large difference, generation of convection is not greatly inhibited.

  In FIG. 5, the magnitude relationship between the power supplied from the first heating coil 48 to the pan and the power supplied from the second heating coil 49 to the pan is switched every certain period. The purpose of the present invention is to prevent the object from being biased to the inside or outside of the pan, and the present invention proposes an induction heating device that can realize the magnitude relationship of heating with a low cost and simple configuration with a small number of parts. Since it is what implement | achieves the induction heating cooking appliance which can be used and is deliciously cooked, it does not limit the switching timing or the necessity of switching.

  The cooking performed by the induction heating cooker includes not only stewed cooking that requires the soaking of taste as described above, but also cooking such as grilled food and fried food. For example, when such cooking is performed using a frying pan, it is desirable that the temperature of the frying pan be uniform from the viewpoint of reducing uneven baking. In the induction heating apparatus of the present invention, in addition to realizing the above-described heating bias, the inverter circuit 40 is operated in the operation region A to be supplied from the first heating coil 48 and the second heating coil 49. As a result, the frying pan as the article to be heated 61 can be heated uniformly.

  Therefore, by applying the induction heating device of the present invention to the induction heating cooker, it is possible to realize an induction heating cooker with high cooking performance that can selectively use the heating method according to the cooking scene.

In all the embodiments described above, the number of switching elements in the inverter circuit is two, which is the same as the number of switching elements in the conventional SEPP type inverter circuit, although the currents flowing through the two heating coils are controlled. Can be controlled at low cost. Furthermore, the number of resonance circuits or the same number of switching means as the number of heating coils are connected to each of them, and the switching means connected to the resonance circuits or heating coils to be supplied with power are selectively switched over the conventional method. From this point, it can be constructed at low cost. In addition, the circuit board can be reduced in size.

  In all the above embodiments, the resonance frequency of the first resonance circuit including the first heating coil arranged on the inner side is the resonance frequency of the second resonance circuit including the second heating coil arranged on the outer side. However, even if the resonance frequency of the second resonance circuit is set higher than that of the first resonance circuit, the same effect as described above can be obtained.

  In all the above embodiments, the control method in the case of having two resonance circuits has been described, but even in the case of having three or more resonance circuits, the resonance frequency is between two adjacent resonance circuits. Among them, by connecting the switching means to a resonance circuit having a high resonance frequency, the same effect as described above can be obtained between two resonance circuits having adjacent resonance frequencies.

  As described above, the induction heating device according to the present invention controls the power supplied from the plurality of heating coils to the object to be heated by the same inverter circuit, and can constitute the inverter circuit at low cost. Since the required three heating patterns can be realized, it is effective not only for consumer use and industrial use but also for all induction heating apparatuses that require a change in the heating pattern.

40 Inverter circuit 46 1st switching element 47 2nd switching element 48 1st heating coil 49 2nd heating coil 50 1st resonance capacitor 51 2nd resonance capacitor 56 1st resonance circuit 57 2nd resonance Circuit 59 Control means 60 Switching means 61 Object to be heated 62 Temperature detection means

Claims (2)

Two resonant circuits formed by connecting a resonant capacitor to each of the first heating coil and the second heating coil for heating the same object to be heated;
An inverter circuit connected to a power source and converting the output of the power source into an alternating current of a set frequency and outputting the two resonant circuits to a resonant circuit unit connected in parallel;
Switching means for electrically opening and closing the resonant circuit and the inverter circuit;
Control means for controlling the operation of the inverter circuit by supplying a drive signal to the inverter circuit and arbitrarily switching the switching means;
A resonance frequency of a first resonance circuit including a first resonance capacitor connected in series to the first heating coil and the first heating coil, and a series of the second heating coil and the second heating coil. Of the resonance frequency of the second resonance circuit composed of the connected second resonance capacitors, the switching means is connected between the resonance circuit having the higher resonance frequency and the inverter circuit, and according to the set heating pattern. An induction heating device that controls the operating frequency of the inverter circuit and the switching of the switching means. The operating frequency of the inverter circuit when the resonance circuit is electrically disconnected from the inverter circuit by the switching means is that of the inverter circuit when the inverter circuit and the resonance circuit are electrically connected by the switching means. The induction heating device according to claim 1, wherein the induction heating device is set lower than the operating frequency.