JP5605198B2 - Induction heating device - Google Patents

Description

The present invention is 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 kind of induction heating apparatus, 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, patents) Reference 1). FIG. 9 is a characteristic diagram of the operating frequency of the inverter circuit in this induction heating apparatus and the electric power that can be supplied from each heating coil to the object to be heated.

  This induction heating device can arbitrarily change the ratio of the heating power by operating the inverter circuit at a frequency corresponding to the ratio of the power supplied from the respective heating coils to the object to be heated.

  For example, when it is desired to set the heating power from one heating coil to 1000 W and the heating power from the other heating coil to 600 W, that is, to set the heating power ratio to 5 to 3, the frequency at which the heating power ratio is 5 to 3 The inverter circuit is operated at 26 kHz.

  In addition, by adjusting the thyristor of the DC power supply to set the output voltage of the DC power supply to 85V, the absolute value of the heating power is adjusted and set to the desired heating power of 1000 W and 600 W.

Japanese Patent No. 2722738

  However, in the conventional configuration, for example, even if the ratio of the heating power from the two heating coils is the same 5 to 3, if the absolute value of the heating power is set to 678 W and 407 W, the output voltage of the DC power supply is It is necessary to make it 70V.

  In order to adjust the output voltage of the DC power supply in this way, a switching element that can control the output voltage of the DC power supply by a control signal from the control circuit is required, so that the circuit configuration is expensive.

  Also, for example, when the material, thickness, shape, placement position, etc. of the object to be heated change, such as an induction heating cooker, the resonance characteristics also change accordingly, so the operating frequency is set in advance at the design stage. It cannot be decided.

  For this reason, it is necessary to determine the frequency so that the ratio of the heating power from the two heating coils that cannot discriminate the object to be heated is satisfied. However, in the conventional circuit configuration, the induction heating apparatus in which the object to be heated changes. The determination means is not specified, and it cannot be put into practical use as an inverter circuit.

  Furthermore, for example, when the heating output from the first heating coil is set to 600 W and the heating output from the second heating coil is set to 1000 W, the switching operation is performed in a state where no current flows through the switching element. There is a possibility that the switching loss is increased and the switching noise is increased or the switching noise is increased due to an increase in switching noise generated during switching.

  For this reason, control is not possible in the entire frequency region between the resonance frequencies of the two heating coils, but the conventional invention does not specify that region and has a problem that it cannot be put into practical use as an inverter circuit. It was.

  The present invention solves the above-described conventional problems, and can detect an object to be heated that has not been possible with the conventional configuration, and can perform an optimum operation on any object that can be heated. The purpose is to provide.

In order to solve the above-described conventional problems, an induction heating apparatus according to the present invention includes an inverter circuit connected to a power source and having at least one switching element, a heating coil and a resonance capacitor for induction heating each object to be heated. Including at least two resonance circuits connected to each other in parallel from the switching element, control means for controlling on / off of the switching element, and an object to be heated that is heated by induction by each of the heating coils. A heating object discriminating means for discriminating characteristics, and the resonance frequency when the heating object that can be induction-heated by one heating coil is magnetically coupled to the heating coil can be induction-heated by the other heating coil. The heating coil or the heating coil so that the heated object is always higher than the resonance frequency when magnetically coupled to the heating coil The value of the resonant capacitor is set, and at least before starting the induction heating, the heated object discriminating means discriminates the characteristics of the heated object magnetically coupled to the respective heating coils, and the heated object discriminating means. On the basis of the determination result, the operating frequency of the switching element is set between two different resonance frequencies, and the respective heating coils are simultaneously induction-heated with respect to the object to be heated .

  As a result, the operating frequency range can be set according to the material, shape, thickness, etc. of the object to be heated, so that it is possible to put to practical use an inverter circuit with an inexpensive configuration and low loss generated in the switching element. .

  The induction heating device of the present invention can perform optimum control based on the result obtained by the detection means, and can reduce switching loss.

The inverter circuit block diagram of the induction heating apparatus in Embodiment 1 of this invention The figure which shows the relationship between the operating frequency of the inverter circuit of the induction heating apparatus in Embodiment 1 of this invention, and maximum electric power. The figure which shows the relationship between the output of the input current detection means in Embodiment 1 of this invention, and the output of a resonance output detection means The figure which shows the relationship between the operating frequency of the inverter circuit of the induction heating apparatus in Embodiment 2 of this invention, and electric power. The figure which shows the relationship between the operating frequency and maximum current of the inverter circuit of the induction heating apparatus in Embodiment 3 of this invention. The figure which shows the relationship between the coil current of the induction heating apparatus in Embodiment 3 of this invention, and the electric current which flows into the switching element of an inverter circuit. The figure which shows the relationship between the coil current of the induction heating apparatus in Embodiment 3 of this invention, and the electric current which flows into the switching element of an inverter circuit. The figure which shows the relationship between the coil current of the induction heating apparatus in Embodiment 3 of this invention, and the electric current which flows into the switching element of an inverter circuit. The figure which shows the relationship between the operating frequency of the inverter circuit of the conventional induction heating apparatus, and electric power

The first invention includes an inverter circuit connected to a power source and having at least one switching element, a heating coil for induction heating of an object to be heated, and a resonance capacitor, each having a different resonance frequency, And at least two resonance circuits connected in parallel from the switching elements, control means for controlling on / off of the switching elements, and heated object determining means for determining characteristics of the heated object that is heated by induction by the respective heating coils. The resonance frequency when the object to be heated that can be induction-heated by one heating coil is magnetically coupled to the heating coil is the resonance frequency when the object to be heated that is induction-heated by the other heating coil is magnetically coupled to the heating coil. Set the value of the heating coil or the resonance capacitor so that it always becomes higher than the resonance frequency of Before starting the induction heating, the heated object discriminating means discriminates the characteristics of the heated object magnetically coupled to the respective heating coils, and the switching element of the switching element is determined based on the discrimination result of the heated object discriminating means. The operating frequency is set between two different resonance frequencies, and the respective heating coils simultaneously inductively heat the object to be heated, thereby adjusting the operation frequency of the inverter circuit according to the state of the object to be heated. be able to.

Further , the current flowing through the switching element can be reduced to increase the power conversion efficiency of the inverter circuit.

In particular, according to the second invention, in the first invention, the ratio of the conduction state and the non-conduction state of the inverter circuit is adjusted to control the power supplied to the load from the first resonance circuit and the second resonance circuit. Thus, desired power can be supplied to the object to be heated.

  Further, even if there is no switching element for controlling the output voltage of the DC power supply and the output voltage is constant, the power supplied from the heating coil to the object to be heated can be controlled.

According to a third aspect of the invention, in particular, in the first or second aspect of the invention, when at least a part of power is supplied, at a timing when the switching element transitions from a conductive state to a non-conductive state, a current equal to or greater than a threshold value in the switching element. By setting the operating frequency of the switching element so that it flows, switching loss that occurs during switching can be suppressed, simplifying the cooling device, and preventing destruction of the switching element due to heat generation and switching noise be able to.

  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.

  Moreover, FIG. 2 is a figure which shows the relationship between the operating frequency of the inverter circuit of the induction heating apparatus in the 1st Embodiment of this invention, and the maximum electric power which can be supplied to a to-be-heated object for every resonance circuit and to-be-heated object It shows the power characteristic of.

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 output from the diode bridge 42 and to prevent electromagnetic noise generated by the switching operation of the inverter circuit 40 from propagating to the commercial power supply 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 54 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). The first switching element 46 connected in parallel and the second switching element 47 similarly connected in parallel with the reverse conducting diode 55 are connected in series to constitute the inverter circuit 40.

  At the connection point between the first switching element 46 and the second switching element 47, one end of the first resonance circuit 56 including the first heating coil 48 and the first resonance capacitor 50 and the second heating coil 49 are connected. One end of the second resonance circuit 57 including the second resonance capacitor 51 is connected.

  The other terminal of the first resonance circuit 56 and the other terminal of the second resonance circuit 57 are connected to a negative bus. Further, the snubber capacitor 53 is electrically connected in parallel with the second switching element 47 in order to reduce the switching loss caused by the switching operation of the first switching element 46 and the second switching element 47.

  Between the commercial power supply 41 and the inverter circuit 40, an input current detection means 60 using a current transformer is connected to measure the value of the current flowing from the commercial power supply 41 to the inverter circuit 40.

  In addition, a first resonance output detection means 61 and a second resonance output detection means 62 for measuring the magnitude of the resonance voltage are connected to each of the first resonance circuit and the second resonance circuit.

  Further, the control means 59 for driving and controlling the first switching element 46 and the second switching element 47 based on the detection values of the input current detection means 60, the first resonance output detection means 61, and the second resonance output detection means. The circuit of the induction heating apparatus of this Embodiment is comprised by having.

  The input current detection means 60 may be any means as long as it can detect the input current, and is not limited to a system using a current transformer. Similarly, the first resonance output detection means 61 and the second resonance output detection means 62 may be any means as long as the resonance output can be detected. For example, a current value flowing through the resonance circuit may be used as the detection value.

  Further, the other terminal of the first resonance circuit 56 and the other terminal of the second resonance circuit 57 can operate in the same manner when connected to a positive bus instead of a negative bus.

  Further, the induction heating apparatus of the present embodiment has a circuit configuration in which two resonance circuits are connected to an SEPP type inverter circuit using two switching elements, but a full bridge type inverter using four switching elements. A circuit configuration in which two resonant circuits are connected to the circuit may be used, and the configuration of the inverter circuit itself is not limited.

  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 in this 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. The electric current supplied to the object to be heated from the first heating coil 48 and the second heating coil 49 can be adjusted by controlling the current flowing through the resonance circuit 56 and the current flowing through the second resonance circuit 57. 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 by changing the duty, the heating coil is heated from the heating coil when the duty difference is 0.5 under the condition that the potential difference between the positive bus and the negative bus is constant. The power supplied to the object is maximized.

  On the other hand, the power supplied from the heating coil to the object to be heated decreases as the duty of the first switching element 46 or the second switching element 47 is increased from 0.5 such as 0.1 or 0.9.

  In addition, when adjusting the power supplied to the object to be heated from the heating coil by changing the operating frequency, the difference in the resonance circuit and the material of the object to be heated must be maintained under the condition that the potential difference between the positive bus and the negative bus is constant. The power characteristics are as shown in FIG. 2 for the difference.

  The maximum power can be supplied to the object to be heated when the operating frequency of the inverter circuit 40 coincides with the resonant frequency of the resonant circuit, and the maximum point of each waveform in FIG. 2 becomes the resonant frequency of the resonant circuit.

  Here, the waveforms 80, 81, 82 in the region of the resonance characteristic 83 of the first resonance circuit 56 are power characteristics supplied from the first heating coil 48 to the object to be heated. Waveforms 84, 85, 86 in the region of the resonance characteristic 87 are power characteristics supplied from the second heating coil 49 to the object to be heated.

  Waveforms 80 and 84 show power characteristics when magnetic stainless steel is used as an object to be heated, waveforms 81 and 85 show power characteristics when iron is used as an object to be heated, and waveforms 82 and 86 show nonmagnetic stainless steel. It is an electric power characteristic when it is set as a to-be-heated object.

  Even for the same object to be heated, power characteristics having different resonance frequencies can be obtained by setting the capacitance of the resonance capacitor included in each resonance circuit or the inductance of the heating coil to different values. In addition, it goes without saying that power characteristics having different resonance frequencies can be obtained even if the degree of magnetic coupling is changed by changing the distance between the heating coil and the object to be heated.

  FIG. 3 is a diagram showing the relationship between the detection value of the input current detection means 60 and the detection values of the first resonance output detection means 61 and the second resonance output detection means 62 in the first embodiment of the present invention. This shows one method for discriminating an object to be heated.

  The resistance component of the heated object measured from the heating coil magnetically coupled to the heated object has different characteristics depending on the material of the heated object. In general, an object to be heated with a large resistance component tends to have a small detection value of the resonance output detection means even if the detection value of the input current detection means becomes large, while an object to be heated with a small resistance component detects the input current. When the detection value of the means increases, the detection value of the resonance output detection means tends to increase.

Therefore, as shown in FIG. 3, a material discrimination threshold is provided in the relationship between the detection value of the input current detection means 60 and the detection value of the resonance output detection means, and if it is lower than the material discrimination threshold Ath, for example, the material Am (eg, magnetic stainless steel) ), And if it is higher than the material determination threshold Ath and lower than the material determination threshold Bth, it is determined that the material is Bm (for example, nonmagnetic stainless steel), and the detected value of the input current detection means 60 and the first resonance output detection means 61 are detected. The control circuit 59 having the heated object discriminating means discriminates in which material discriminating area the relationship of the detection values of the second resonance output detecting means 62 is, so that the inverter circuit is operated at the operating frequency suitable for the material. 40 can be operated.

  In FIG. 2, the operation region Ar is an operation frequency region of the inverter circuit 40 when the first heating coil 48 and the second heating coil 49 are both nonmagnetic stainless steels to be heated. The operating region Br is the operating frequency region of the inverter circuit 40 when the first heating coil 48 uses non-magnetic stainless steel as the object to be heated, whereas the second heating coil 49 uses iron as the object to be heated. It is.

  In the resonance circuit, when the operating frequency of the inverter circuit 40 is higher than the resonance frequency of the resonance circuit, the current is delayed with respect to the voltage applied to the resonance circuit. On the other hand, when the operating frequency of the inverter circuit 40 is lower than the resonant frequency of the resonant circuit, the current advances and becomes a phase with respect to the voltage applied to the resonant circuit.

  In addition, since the induction heating apparatus according to the present embodiment shares the inverter circuit 40 and connects the two first resonance circuits 56 and 57 in parallel, the two first resonance circuits 56 and the second resonance circuit 57 are connected. The sum of the currents flowing through the two resonance circuits flows through the first switching element 46 and the second switching element 47.

  Therefore, by setting the operating frequency of the inverter circuit 40 between two different resonance frequencies, a lagging phase current and a leading phase current flow through the switching element. Under this condition, at a certain moment, one resonance circuit acts so that a positive current flows through the switching element, and the other resonance circuit flows a negative current through the switching element (using the IGBT shown in FIG. 1). In the switching element, the negative current does not flow, so it actually flows in the antiparallel diode).

  Then, the current flowing through the switching element has a smaller current value when the two resonance circuits are heated in parallel than the sum of the current values when power is supplied to each resonance circuit independently. .

  By reducing the value of the current flowing through the switching element, the conduction loss caused by the current flowing through the switching element can be reduced, and the cooling configuration can be simplified and made inexpensive. Alternatively, by reducing the air volume of the cooling fan, a low noise induction heating device can be realized.

  In order to reduce conduction loss compared to when power is supplied to each resonance circuit independently, the operating frequency of the inverter circuit 40 needs to be between two resonance frequencies. Therefore, the operating frequency of the inverter circuit 40 when the first heating coil 48 and the second heating coil 49 are both nonmagnetic stainless steels to be heated must be in the operating region Ar, and the first heating coil In 48, the operating frequency of the inverter circuit 40 when the non-magnetic stainless steel is the object to be heated and the second heating coil 49 is iron is the operating region Br. For this reason, in an induction heating apparatus that needs to heat an object to be heated having various characteristics, an object to be heated discrimination means is required to determine the operating frequency region of the inverter circuit.

  In this embodiment, only two types of combinations of objects to be heated have been described, and the operation area has been described. However, in all objects to be heated, operation areas suitable for each combination of objects to be heated are described. By setting this, the effect of the present invention can be obtained.

Further, in the present embodiment, the change in characteristics due to the difference in material has been described, but any conditions that cause differences in the characteristics of the heated object as seen from the heating coil, such as the size and thickness of the heated object, The same determination can be made according to the threshold setting.

(Embodiment 2)
FIG. 4 is a diagram showing the relationship between the operating frequency of the inverter circuit of the induction heating device and the power that can be supplied to the object to be heated in the second embodiment of the present invention, and shows a method for controlling the power.

  4 is different from FIG. 2 in that the relationship between the operating frequency of the inverter circuit and the power that can be supplied to the object to be heated when nonmagnetic stainless steel is heated at a duty of 0.3.

  The operation and action of the relationship between the operating frequency and power will be described below.

  In addition to adjusting the operating frequency, the inverter circuit 40 such as the SEPP type as shown in FIG. 1 supplies the object to be heated by adjusting the duty ratio between the conduction time and the non-conduction time of the first switching element 46. Power to be controlled.

  Even if two first resonance circuits 56 and second resonance circuits 57 are connected in parallel to the same inverter circuit 40 as in the present embodiment, the inverter circuit 40 viewed from the respective resonance circuits Since the operation is the same, power control by adjusting the duty is possible.

  For example, when the nonmagnetic stainless steel is heated at a duty of 0.3, the power that can be supplied from the first heating coil 48 to the nonmagnetic stainless steel is as shown by the waveform 88. The electric power that can be supplied to the non-magnetic stainless steel has characteristics as shown by a waveform 89.

  It can be seen that both are lower than the characteristics of the waveform 82 and the waveform 86 heated at a duty of 0.5. Power adjustment by duty control is possible, eliminating the need to change the output voltage of the DC power supply, eliminating the need for switching elements and control circuits for changing the output voltage of the DC power supply, and controlling heating power with an inexpensive circuit configuration can do.

(Embodiment 3)
FIG. 5 is a diagram showing the relationship between the operating frequency of the inverter circuit of the induction heating device and the current flowing through the object to be heated in the third embodiment of the present invention, and shows the selection criteria for the operating frequency of the inverter circuit. is there.

  FIGS. 6, 7 and 8 are diagrams showing the relationship between the current flowing in the switching element of the inverter circuit of the induction heating device and the current flowing in the resonance circuit in the third embodiment of the present invention. The current value at the time is shown.

  FIG. 5 differs from FIG. 2 in that the power characteristics with respect to the operating frequency are converted into current characteristics.

  6 is a waveform when the inverter circuit is operated with the frequency Af and the duty is 0.5 in FIG. 5, and FIG. 7 is the waveform when the inverter circuit is operated with the frequency Af and the duty is 0.3 in FIG. FIG. 8 is different from FIG. 8 in that the waveform is obtained when the inverter circuit is operated with the frequency Bf and the duty of 0.5 in FIG.

  The operation and action of the relationship between the above conditions and current values will be described below.

In FIG. 6, a current waveform 100 is a current waveform that flows in the first heating coil 48 when the nonmagnetic stainless steel is heated by the first heating coil 48, and a current waveform 101 is the nonmagnetic stainless steel in the second heating coil 49. It is the electric current waveform which flows into the 2nd heating coil 49 when heating is carried out.

  Since the resonance frequency of the first resonance circuit 56 including the first heating coil 48 is lower than the frequency Af, the phase of the current waveform flowing through the first heating coil 48 is delayed with respect to the voltage. The current value Ac flowing at the point Atr is positive, that is, a current flows through the first switching element 46 from the positive bus to the connection point of the resonance circuit.

  On the other hand, since the resonance frequency of the second resonance circuit 57 including the second heating coil 49 is higher than the frequency Af, the phase of the current waveform flowing through the second heating coil 49 becomes a leading phase with respect to the voltage. The current value Bc flowing at the transition point Atr is negative, that is, a current flows through the first switching element 46 from the connection point of the resonance circuit to the positive bus.

  In the induction heating device of the present embodiment, since the two first resonance circuits 56 and the second resonance circuit 57 are connected in parallel, the current flowing through the switching element is the same as the current flowing through the first resonance circuit 56. Since it is the sum of the currents flowing through the second resonance circuit 57, the current waveform 102 flowing through the first switching element is as shown in FIG.

  When the switching element transitions from a conducting state to a non-conducting state, the more current flowing through the switching element, the greater the switching loss that occurs during switching. As shown in FIG. 6, the induction heating device of the present embodiment cancels out the current flowing through the switching element at least at the transition point Atr at the time of switching by taking the sum of the currents of the leading phase and the lagging phase. By performing a switching operation with a current value Cc that is smaller than the current flowing through the first heating coil and a positive current value Cc, switching loss can be reduced, and each object to be heated can be reduced. It becomes possible to make the power conversion efficiency higher than the sum when heated alone or to simplify the heat dissipation configuration of the switching element.

  In addition, in the inverter circuit 40 using the voltage source as a power source, if the operating frequency is lower than the resonant frequency of the resonant circuit, a current flows through the reverse conducting diode connected in parallel with the switching element during switching. As a result, the switching element becomes large.

  However, in one of the resonance circuits, by operating the inverter circuit 40 at a frequency higher than the resonance frequency, when the switching element transitions from a conduction state to a non-conduction state, a current flows through the switching element. Therefore, the current during the transition flows to the snubber capacitor 53, and the voltage applied to the switching element varies with a constant change amount associated with the charging / discharging of the snubber capacitor 53, so that the current is applied to the switching element. Switching loss generated by the product of the voltage and the current flowing through the switching element can be reduced, power conversion efficiency can be increased, or the heat dissipation configuration of the switching element can be simplified.

  Here, as an index for determining whether or not a positive current is flowing through the switching element during switching, there is a current characteristic shown in FIG. It is a resonance circuit having a resonance frequency lower than the operating frequency that causes a positive current to flow through the switching element at the time of switching, including the current waveform 100, and a negative current to flow through the switching element at the time of switching, including the current waveform 101. Since the resonance circuit has a resonance frequency higher than the operating frequency, in order for the sum of the currents flowing through the switching elements during switching to be positive, the current flowing through the first resonance circuit at the operating frequency is The condition is that the current is larger than the current flowing in the resonance circuit 2.

  That is, by setting the operating frequency between the resonance frequency of the first resonance circuit 56 and the above condition, the sum of the currents flowing through the switching elements during switching is obtained when the first resonance circuit 56 is heated alone. Therefore, switching loss can be reduced because switching can be performed with a positive current flowing through the switching element.

  In addition, since the relationship between the operating frequency and the current flowing through the resonance circuit can be predicted based on the detected value of the heated object discriminating means, it is not necessary to take a current characteristic value by actual operation. Of course, if the current value can be measured in real time, it can be controlled with higher accuracy.

  As shown in FIG. 7, for example, even when Duty (= Ton / T) operates at 0.7, the current (current waveform 102) flowing through the first switching element 46 and the second switching element 47 Since any of the flowing currents (current waveform 103) can perform a switching operation in a state where a positive current is flowing through the switching element, it is possible to prevent a significant increase in switching loss or reduce the occurrence of switching noise. can do.

  FIG. 8 shows the current flowing through the switching element when the inverter circuit is operated at a frequency Bf in which the current flowing through the resonance circuit having a low resonance frequency in FIG. 5 is less than the current flowing through the resonance circuit having a high resonance frequency.

  In FIG. 8, at the transition point Atr at the time of switching, the current flowing through the first switching element has a negative value (actually, it flows through a reverse conducting diode connected in parallel).

  If the switching operation is performed in this state, the snubber capacitor 53 is short-circuited, and switching loss and switching noise increase, which is not desirable.

  Even when the current flowing through the resonance circuit having a low resonance frequency is greater than the current flowing through the resonance circuit having a high resonance frequency, a condition occurs in which the current during switching becomes negative as the duty is moved away from 0.5. .

  However, by operating the inverter circuit so as to reduce the switching loss in the vicinity of the rated power where at least a part of the power, preferably the most current needs to flow, the maximum value of the loss generated by the switching element is suppressed. Therefore, the operation of the present invention is effective.

  The index in FIG. 5 is merely an example, and in short, any means may be used as long as the current value flowing at the time of switching can be roughly grasped.

  In all the embodiments described above, the number of switching elements in the inverter circuit is controlled by two without changing the number of switching elements in the conventional inverter circuit, although the currents flowing through the two heating coils are controlled. Therefore, it can be configured at low cost.

  Further, in all the above embodiments, the difference in characteristics with respect to the material of the object to be heated is illustrated, but it is possible to similarly determine and control the change in characteristics due to the difference in the shape and thickness of the object to be heated. is there.

Furthermore, although all the above embodiments have described the case where different objects to be heated are heated, for example, two heating coils having different diameters are arranged concentrically to heat the same object to be heated. The configuration of the heating coil or the like is not limited as long as two or more resonance circuits are connected to the same inverter circuit.

  Further, even if three or more resonant circuits are connected, the number of resonant circuits is not limited because all the above effects are obtained between two resonant circuits having adjacent resonant 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 loss generated in the switching element is smaller than the sum of the loss when heated independently, it is effective not only for consumer and industrial use but also for all induction heating devices.

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 Input current detection means 61 First resonance output detection means 62 Second resonance output detection means 70 Heated object discrimination means

Claims (3)

An inverter circuit connected to a power source and having at least one switching element, each including a heating coil and a resonance capacitor for inductively heating an object to be heated, each having a different resonance frequency and connected in parallel from the switching element And at least two resonance circuits, control means for controlling on / off of the switching element, and heated object discriminating means for determining the characteristics of the heated object that is heated by each of the heating coils. The resonance frequency when the object to be heated that can be induction heated is magnetically coupled to the heating coil is always higher than the resonance frequency when the object to be heated that can be induction heated by the other heating coil is magnetically coupled to the heating coil. Set the value of the heating coil or the resonant capacitor so that it is higher, and at least start induction heating. Before you determine the properties of the object to be heated is magnetically coupled to the respective heating coils by the heated object determination means, different operating frequencies of the switching elements based on the discrimination result of the object to be heated discrimination means An induction heating apparatus that is set between two resonance frequencies and in which each of the heating coils is induction-heated simultaneously with respect to an object to be heated . The induction heating device according to claim 1, wherein the electric power supplied to the load from the first resonance circuit and the second resonance circuit is controlled by adjusting a ratio between the conduction state and the non-conduction state of the inverter circuit. The operating frequency of the switching element is set so that a current equal to or greater than a threshold value flows in the switching element at a timing when the switching element transitions from a conductive state to a non-conductive state at least when a part of power is supplied. The induction heating apparatus according to 1 or 2 .