Induction heating device

Abstract

[Problem] To provide an induction heating device capable of improving the effect of inhibiting uneven heating when heating an object to be heated with coils. [Solution] This heating device according to one embodiment is provided with a first coil for heating an object to be heated by receiving a supply of a first coil current, and a second coil being disposed inside the first coil and for heating the object to be heated by receiving a supply of a second coil current. The second coil has a first portion and a second portion in which the winding direction is opposite of that in the first portion.

Description

induction heating device

[0001] The present invention relates to an induction heating device capable of suppressing uneven heating when heating an object with a coil.

[0002] In conventional induction heating devices, which heat an object using the principle of induction heating, the object to be heated is heated by a single circular coil. In this case, the amount of heat inside the circular coil is smaller than that of the surrounding area, resulting in uneven heating. This uneven heating can lead to deformation or cracking of the object being heated.

[0003] In contrast, Patent Document 1 discloses an induction heating cooker in which two circular coils of different diameters are arranged concentrically. With this induction heating cooker, the inside of the larger diameter circular coil is heated by the smaller diameter circular coil. Therefore, it is possible to suppress uneven heating of the food being heated.

[0004] International Publication No. 2011 / 070785

[0005] As in the induction heating cooker proposed in Patent Document 1, when multiple circular coils are arranged in close proximity, mutual induction is likely to occur. When mutual induction occurs, it becomes difficult to control the current in each circular coil, which can result in a reduced effect in suppressing uneven heating.

[0006] The present invention aims to provide an induction heating device that can improve the effect of suppressing uneven heating when heating an object with a coil.

[0007] An induction heating device according to one embodiment of the present invention comprises a first coil that heats an object to be heated by receiving a first coil current, and a second coil disposed inside the first coil and heating an object to be heated by receiving a second coil current. The second coil has a first portion and a second portion whose winding direction is opposite to that of the first portion.

[0008] Furthermore, in the induction heating device, the shape of the first coil may be circular, the first part and the second part may each be semicircular, and the first part and the second part may be arranged back-to-back with respect to the center of the first coil to form a circle.

[0009] Furthermore, in the induction heating device, the first coil, the first portion, and the second portion may each be rectangular, and the first portion and the second portion may be arranged symmetrically with respect to the center of the first coil.

[0010] Furthermore, in the induction heating device, the shape of the first coil may be circular, the first part and the second part may each be semicircular, and the first part and the second part may be arranged symmetrically with respect to the center of the first coil with their arc portions facing back to back.

[0011] Furthermore, in the induction heating device, the phase difference between the first coil current and the second coil current may be 90 degrees.

[0012] Furthermore, the induction heating device may further include a first drive circuit that supplies the first coil current to the first coil, and a second drive circuit that supplies the second coil current to the second coil, wherein the circuit configuration of the first drive circuit may be the same as that of the second drive circuit.

[0013] Furthermore, in the induction heating device, the inductance of the first portion may be equal to the inductance of the second portion.

[0014] Furthermore, in the induction heating device, the first part and the second part may be connected in series.

[0015] Furthermore, in the induction heating device, the first part and the second part may be connected in parallel.

[0016] According to the present invention, it is possible to improve the effect of suppressing uneven heating.

[0017] This figure shows a schematic circuit configuration of an induction heating device according to the first embodiment. This is a plan view showing the arrangement of the first coil and the second coil. (a) is a schematic diagram illustrating the magnetic flux when the second coil is energized, and (b) is a schematic diagram illustrating the magnetic flux when the first coil is energized. (a) is a plan view showing the heating distribution when the phase difference of the coil current between the first coil and the second coil is set to 0 degrees. (b) is a plan view showing the heating distribution when the phase difference of the coil current between the first coil and the second coil is set to 180 degrees. This figure shows the current waveform and heating distribution when the phase difference of the coil current between the first coil and the second coil is set to 90 degrees. This is a plan view showing the temperature measurement locations. This is a graph showing the experimental results of temperature measurement of the heated object when the phase difference of the coil current is 0 degrees. This is a graph showing the experimental results of temperature measurement of the heated object when the phase difference of the coil current is 180 degrees. This is a graph showing the experimental results of temperature measurement of the heated object when the phase difference of the coil current is 90 degrees. This is a plan view showing the arrangement of coils according to a modified example. This is a plan view showing the arrangement of coils according to another modified example. This is a plan view of the second coil of the induction heating device according to the second embodiment. This is a diagram showing the equivalent circuit related to the heat generation of an object being heated using the induction heating device according to the second embodiment. This is a plan view of the second coil of the induction heating device according to the third embodiment. This is a diagram showing the equivalent circuit related to the heat generation of an object being heated using the induction heating device according to the third embodiment.

[0018] Embodiments of the present invention will be described below with reference to the drawings. In each figure, components having equivalent functions are denoted by the same reference numerals.

[0019] (First Embodiment) Figure 1 is a diagram showing a schematic circuit configuration of an induction heating device according to the first embodiment. The induction heating device 1 shown in Figure 1 comprises a first coil 11, a second coil 12, a first drive circuit 21, and a second drive circuit 22.

[0020] The first coil 11 receives an alternating current (AC) first coil current from the first drive circuit 21 to heat the object to be heated 40. The second coil 12 receives an alternating current (AC) second coil current from the second drive circuit 22 to heat the object to be heated 40.

[0021] The first drive circuit 21 includes a first semiconductor switch S1, a second semiconductor switch S2, a first diode D1, a second diode D2, and a first resonant capacitor C1. The second drive circuit 22 includes a third semiconductor switch S3, a fourth semiconductor switch S4, a third diode D3, a fourth diode D4, and a second resonant capacitor C2.

[0022] As shown in Figure 1, the circuit configuration of the first drive circuit 21 is the same as that of the second drive circuit 22. In this embodiment, the first semiconductor switch S1 to the fourth semiconductor switch S4 are N-channel type MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). However, each semiconductor switch is not limited to MOSFETs and may be other semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistors). The first semiconductor switch S1 to the fourth semiconductor switch S4 are switched on or off depending on the level of the control signal input to their respective gates.

[0023] The first semiconductor switch S1 and the second semiconductor switch S2 are connected in series. Specifically, the drain of the first semiconductor switch S1 is connected to the positive terminal of the single-phase DC power supply 30, and the source of the first semiconductor switch S1 is connected to the drain of the second semiconductor switch S2. The source of the second semiconductor switch S2 is connected to the negative terminal of the DC power supply 30.

[0024] The first diode D1 is connected in antiparallel between the drain and source of the first semiconductor switch S1. The second diode D2 is connected in antiparallel between the drain and source of the second semiconductor switch S2. The first diode D1 and the second diode D2 are freewheeling diodes that return the energy stored in the first coil 11 to the DC power supply 30 when the first semiconductor switch S1 or the second semiconductor switch S2 is in the off state.

[0025] The third semiconductor switch S3 and the fourth semiconductor switch S4 are connected in series. Specifically, the drain of the third semiconductor switch S3 is connected to the positive terminal of the DC power supply 30, and the source of the third semiconductor switch S3 is connected to the drain of the fourth semiconductor switch S4. The source of the fourth semiconductor switch S4 is connected to the negative terminal of the DC power supply 30.

[0026] The third diode D3 is connected in antiparallel between the drain and source of the third semiconductor switch S3. The fourth diode D4 is connected in antiparallel between the drain and source of the fourth semiconductor switch S4. The third diode D3 and the fourth diode D4 are freewheeling diodes that return the energy stored in the second coil 12 to the DC power supply 30 when the third semiconductor switch S3 or the fourth semiconductor switch S4 is in the off state.

[0027] The first resonant capacitor C1 is positioned between the connection point of the source of the first semiconductor switch S1 and the drain of the second semiconductor switch S2 and the first coil 11. On the other hand, the second resonant capacitor C2 is positioned between the connection point of the source of the third semiconductor switch S3 and the drain of the fourth semiconductor switch S4 and the second coil 12.

[0028] Figure 2 is a plan view showing the arrangement of the first coil 11 and the second coil 12. The first coil 11 is a so-called Q coil. In the first coil 11, a metal wire is wound in a circular shape.

[0029] On the other hand, the second coil 12 is a so-called DD coil. The second coil 12 is composed of a D-shaped (semicircular) first part 121 and a D-shaped (semicircular) second part 122. The winding direction of the first part 121 is opposite to the winding direction of the second part 122. The first part 121 is located on one side (left) of the interior of the first coil 11, which is divided into left and right halves, and the second part 122 is located on the other side (right). Specifically, the first part 121 and the second part 122 are placed back to back to form a circle, and are arranged symmetrically with respect to the center of the first coil 11. It is desirable that the inductance of the second coil 12 be equal between the first part 121 and the second part 122.

[0030] Figure 3(a) is a schematic diagram illustrating the magnetic flux when current is passed through the second coil 12. When current is passed through the second coil 12, the direction of the current is the same in the linear region where the first part 121 and the second part 122 face each other, and the direction of the current is opposite in the circumferential region. As a result, the net flux linkage between the magnetic flux φ1 generated in the first part 121 and the magnetic flux φ2 generated in the second part 122 becomes zero. Consequently, the magnetic flux generated by the current passing through the second coil 12 does not affect the first coil 11.

[0031] Figure 3(b) is a schematic diagram illustrating the magnetic flux when current is passed through the first coil 11. When current is passed through the first coil 11, a magnetic flux φ3 is generated. This magnetic flux φ3 induces currents in the first portion 121 and the second portion 122 of the second coil 12. However, in the linear region where the first portion 121 and the second portion 122 face each other, the current directions are opposite, so the induced currents cancel each other out. As a result, the magnetic flux generated by the current flowing through the first coil 11 does not affect the second coil 12.

[0032] Figure 4(a) is a plan view showing the heating distribution when the phase difference of the coil current between the first coil 11 and the second coil 12 is set to 0 degrees.

[0033] When the phase difference between the first coil current I1 of the first coil 11 and the second coil current I2 of the second coil 12 is set to 0 degrees, as shown in Figure 4(a), the direction of the first coil current I1 between the first coil 11 and the first part 121 is opposite to the direction of the second coil current I2. On the other hand, between the first coil 11 and the second part 122, the direction of the first coil current I1 is the same as the direction of the second coil current I2. As a result, the amount of heating in the first heating region R1 generated by the heat generated between the first coil 11 and the first part 121 is lower than the amount of heating in the second heating region R2 generated by the heat generated between the first coil 11 and the second part 122.

[0034] Figure 4(b) is a plan view showing the heating distribution when the phase difference of the coil currents between the first coil 11 and the second coil 12 is set to 180 degrees.

[0035] When the phase difference between the first coil current I1 and the second coil current I2 is set to 180 degrees, as shown in Figure 4(b), the direction of the first coil current I1 becomes the same as the direction of the second coil current I2 between the first coil 11 and the first part 121. On the other hand, between the first coil 11 and the second part 122, the direction of the first coil current I1 becomes the opposite direction to the direction of the second coil current I2. As a result, the amount of heating in the first heating region R1 becomes higher than the amount of heating in the second heating region R2.

[0036] As described above, when the phase difference of the coil current between the first coil 11 and the second coil 12 is set to 0 degrees or 180 degrees, as shown in Figures 4(a) and 4(b), one of the first heating region R1 and the second heating region R2 becomes a high-temperature region, and the other becomes a low-temperature region. Therefore, it becomes difficult to heat the object to be heated 40 uniformly.

[0037] Figure 5 shows the current waveform and heating distribution when the phase difference of the coil currents between the first coil 11 and the second coil 12 is set to 90 degrees.

[0038] When the phase difference between the first coil current I1 and the second coil current I2 is set to 90 degrees, as shown in Figure 5, within the half-cycle range where the phase difference angle is 0 to 180 degrees, there are both phase angles in which the first heating region R1 is in a higher temperature region than the second heating region R2, and phase angles in which the first heating region R1 is in a lower temperature region than the second heating region R2. Therefore, after a certain amount of time has passed, the temperature difference between the first heating region R1 and the second heating region R2 decreases, and the object to be heated 40 is heated uniformly.

[0039] (Example) The following describes the experimental results of the heating distribution when the phase difference of the coil current between the first coil 11 and the second coil 12 is set to 0 degrees, 180 degrees, and 90 degrees, respectively.

[0040] First, the experimental conditions will be described. The first coil 11 is a Q coil with an outer diameter of 230 mm and an inner diameter of 110 mm. The second coil 12 is a DD coil with an outer diameter of 80 mm. The capacitance of the first resonant capacitor C1 is 30 μF. The capacitance of the second resonant capacitor C2 is 0.47 μF. The object to be heated 40 is an iron plate with a length of 304 mm, a width of 798 mm, and a thickness of 1 mm. A 60 V DC power supply and a 230 V DC power supply are used for the DC power supply 30. The frequency (switching frequency) of the pulsed control signals input to the gates of the first semiconductor switch S1 to the fourth semiconductor switch S4 is 40 kHz.

[0041] Figure 6 is a plan view showing the temperature measurement locations. In this embodiment, the temperature at three measurement locations is measured using a thermoviewer. The first measurement location P1 is the center of the first coil 11 and the second coil 12. The second measurement location P2 is a measurement location within the range of the first heating region R1. The third measurement location P3 is a measurement location within the range of the second heating region R2.

[0042] Figure 7 is a graph showing the experimental results of temperature measurement of the heated object 40 when the phase difference of the coil current is 0 degrees. Figure 8 is a graph showing the experimental results of temperature measurement of the heated object 40 when the phase difference of the coil current is 180 degrees. Figure 9 is a graph showing the experimental results of temperature measurement of the heated object 40 when the phase difference of the coil current is 180 degrees. In Figures 7 to 9, the horizontal axis represents the heating time, and the vertical axis represents the temperature of the heated object 40.

[0043] When the phase difference between the first coil current I1 and the second coil current I2 is 0 degrees, the temperature T1 at the first measurement point P1 after 2 minutes of heating is 49.9°C, the temperature T2 at the second measurement point P2 is 46.9°C, and the temperature at the third measurement point P3 is 43.1°C. Therefore, the temperature difference (T1-T2) between the center of the coil and the first heating region R1 is 3.0°C, and the temperature difference (T1-T3) between the center of the coil and the second heating region R2 is 6.8°C. As a result, when the phase difference of the coil currents is 0 degrees, a temperature difference of 3.8°C occurs between the first heating region R1 and the second heating region R2.

[0044] When the phase difference between the first coil current I1 and the second coil current I2 is 180 degrees, the temperature T1 at the first measurement point P1 after 2 minutes of heating was 50.1°C, the temperature T2 at the second measurement point P2 was 43.1°C, and the temperature at the third measurement point P3 was 46.5°C. Therefore, the temperature difference (T1-T2) between the center of the coil and the first heating region R1 is 7.0°C, and the temperature difference (T1-T3) between the center of the coil and the second heating region R2 is 3.6°C. As a result, when the phase difference between the coil currents is 180 degrees, a temperature difference of 3.4°C occurs between the first heating region R1 and the second heating region R2.

[0045] In contrast, when the phase difference between the first coil current I1 and the second coil current I2 is 90 degrees, the temperature T1 at the first measurement point P1 after 2 minutes of heating is 50.0°C, the temperature T2 at the second measurement point P2 is 44.9°C, and the temperature at the third measurement point P3 is 45.0°C. Therefore, the temperature difference (T1-T2) between the center of the coil and the first heating region R1 is 5.1°C, and the temperature difference (T1-T3) between the center of the coil and the second heating region R2 is 5.0°C. As a result, when the phase difference of the coil currents is 90 degrees, the temperature difference between the first heating region R1 and the second heating region R2 is 0.1°C. Therefore, compared to when the phase difference of the coil currents is 0 degrees or 180 degrees, the temperature difference between the first heating region R1 and the second heating region R2 is significantly reduced, so the object to be heated 40 is heated uniformly.

[0046] According to the embodiment described above, the second coil 12 is arranged concentrically inside the first coil 11. Furthermore, the second coil 12 is composed of a first portion 121 and a second portion 122, the winding directions of the coils being opposite to each other. Therefore, no mutual induction occurs between the first coil 11 and the second coil 12. Thus, when heating the object to be heated 40 with the first coil 11 and the second coil 12, it is possible to improve the effect of suppressing uneven heating.

[0047] In particular, in this embodiment, when the phase difference between the first coil current I1 and the second coil current I2 is set to 90 degrees, the temperature difference between the first heating region R1 generated by the heat generated by the first coil 11 and the first portion 121 and the second heating region R2 generated by the heat generated by the first coil 11 and the second portion 122 is significantly reduced. Therefore, it becomes possible to heat the object to be heated 40 uniformly.

[0048] (Modified Version) Figure 10 is a plan view showing the arrangement of coils according to the modified version. In this modified version, as shown in Figure 10, the first coil 11a is rectangular.

[0049] On the other hand, the second coil 12a is composed of a first portion 121a and a second portion 122a, which are arranged symmetrically with respect to the center of the first coil 11a inside the first coil 11a. Both the first portion 121a and the second portion 122a are rectangular in shape. Furthermore, the winding direction of the first portion 121a is opposite to that of the second portion 122a.

[0050] As a result, in this modified example, no mutual induction occurs between the first coil 11a and the second coil 12a. Therefore, when heating the object to be heated 40 with the first coil 11a and the second coil 12a, it is possible to improve the effect of suppressing uneven heating.

[0051] Furthermore, by setting the phase difference of the coil currents between the first coil 11a and the second coil 12a to 90 degrees, the temperature difference between the first heating region R1 and the second heating region R2 is significantly reduced. Therefore, it becomes possible to heat the object to be heated 40 uniformly.

[0052] Figure 11 is a plan view showing the arrangement of coils according to another modified example. In this modified example, as shown in Figure 11, the first coil 11 is circular. However, the first coil 11 may be rectangular, similar to the first coil 11a shown in Figure 10.

[0053] On the other hand, the second coil 12b is composed of a first portion 121b and a second portion 122b, which are arranged symmetrically inside the first coil 11b. Both the first portion 121b and the second portion 122b are semicircular, and their arc portions are placed back-to-back, arranged symmetrically with respect to the center of the first coil 11. Furthermore, the winding direction of the first portion 121b is opposite to that of the second portion 122b.

[0054] As a result, in this modified example, no mutual induction occurs between the first coil 11 and the second coil 12b. Therefore, when heating the object to be heated 40 with the first coil 11 and the second coil 12b, it is possible to improve the effect of suppressing uneven heating.

[0055] Furthermore, by setting the phase difference of the coil currents between the first coil 11 and the second coil 12b to 90 degrees, the temperature difference between the first heating region R1 and the second heating region R2 is significantly reduced. Therefore, it becomes possible to heat the object to be heated 40 uniformly.

[0056] (Second Embodiment) Figure 12 is a plan view of the second coil of the induction heating device according to the second embodiment. The second coil 12 shown in Figure 12 is a series-type DD coil in which a first portion 121 and a second portion 122 are connected in series to a DC power supply. In the second coil 12 according to this embodiment, the first portion is wound clockwise, while the second portion 122 is wound counterclockwise. That is, the winding direction of the first portion 121 is opposite to the winding direction of the second portion 122.

[0057] In this embodiment, the second coil 12 is arranged inside the circular first coil 11, similar to the first embodiment. Therefore, the object to be heated 40 is heated by the first coil 11, which is supplied with a first coil current from the first drive circuit 21, and the second coil 12, which is supplied with a second coil current from the second drive circuit 22. Now, with reference to Figure 13, an equivalent circuit related to the heating of the object to be heated 40 will be described.

[0058] Figure 13 is a diagram showing the equivalent circuit related to the heat generation of the object to be heated 40 using the induction heating device 2 according to the second embodiment. M shown in Figure 13 １２Ｌ and M １２Ｒrepresents the mutual inductance between the first coil 11 and the second coil 12 and is divided into left and right parts for the symmetry of the equivalent circuit. However, M １２Ｌ and M １２Ｒ are almost equal to zero. This is because the magnetic coupling between the first coil 11 and the second coil 12 is negligibly small. R ｒ１２Ｌ and R ｒ１２Ｒ represent the resistance components of the heated object 40 shared by the first coil 11 and the second coil 12 and are equally divided into left and right parts for the same reason.

[0059] Next, the part specific to the first coil 11 will be described. L ｒ１ −M １２Ｌ −M １２Ｒ represents the inductance component specific to the first coil 11 and is equal to the self-inductance L ｒ１ . This is because the mutual inductances M １２Ｌ and M １２Ｒ are almost equal to zero. R ｒ１ａ and R ｒ１ｂ represent the resistance components of the heated object 40 specific to the first coil 11 and are divided for analysis.

[0060] Next, the part specific to the second coil 12 will be described. L ｒ２Ｌ −M[[ID=Z3]] １２Ｌ and L ｒ２Ｒ −M １２Ｒ represent the inductance components specific to the second coil 12 and are equally divided into left and right parts for the symmetry of the equivalent circuit. Similar to the case of the first coil 11, L ｒ２Ｌ −M １２Ｌ and L ｒ２Ｒ −M １２Ｒ are respectively the divided self-inductances L ｒ２Ｌ and L ｒ２Ｒ . R ｒ２ａ , R ｒ２ｂ , R ｒ２ｃ , and then R ｒ２ｄ represent the resistance components of the heated object 40 specific to the second coil 12 and are divided into four equal parts for analysis.

[0061] Next, the path of the coil current i ｏｕｔ１ flowing through the first coil 11 will be described. The coil current i ｏｕｔ１If the condition is positive, then there are two paths: the first path and the second path. The first path is L ｒ１ , R ｒ１ａ M １２Ｌ , R ｒ１２Ｌ , R ｒ１ｂ , R ｒ１２Ｒ , and M １２Ｒ This is the route that passes through L. On the other hand, the second route is L ｒ１ , R ｒ１ａ , R ｒ２ｂ , L ｒ２Ｒ , R ｒ２ｃ , R ｒ１２Ｒ , and M １２Ｒ This is a route that passes through [location].

[0062] Coil current i ｏｕｔ１ If is negative, there exists a first reverse path through which current flows in the reverse direction of the first path, and a second reverse path through which current flows in the reverse direction of the second path. In Figure 13, the current flowing through the first path is i ｏｕｔ１ａ It is shown that the current flowing through the second path is i ｏｕｔ１ｂ This is shown by i. ｏｕｔ１ = i ｏｕｔ１ａ +i ｏｕｔ１ｂ That is the case.

[0063] Next, the coil current i flowing through the second coil 12 ｏｕｔ２ Let's explain the path. Coil current i ｏｕｔ２ If the condition is positive, then there are two paths: the third path and the fourth path. The third path is L ｒ２Ｌ , R ｒ２ａ , R ｒ１２Ｌ M １２Ｌ , R ｒ２ｂ , L ｒ２Ｒ , R ｒ２ｃ , R ｒ１２Ｒ M １２Ｒ , and R ｒ２ｄ This is the route that passes through L. On the other hand, the fourth route is L ｒ２Ｌ , R ｒ２ａ , R ｒ１ｂ , R ｒ１２Ｒ M １２Ｒ , and R ｒ２ｄ This is a route that passes through [location].

[0064] Coil current i ｏｕｔ２If is negative, there exists a third reverse path through which the current flows in the reverse direction of the third path, and a fourth reverse path through which the current flows in the reverse direction of the fourth path. In Figure 13, the current flowing through the third path is i ｏｕｔ２ａ As shown above, the current flowing through the fourth path is i ｏｕｔ２ｂ This is shown. However, i ｏｕｔ２ = i ｏｕｔ２ａ +i ｏｕｔ２ｂ In the diagram, the currents indicated by arrows are the coil currents flowing through each branched path, superimposed with the arrow direction being positive.

[0065] According to the induction heating device 2 of this embodiment described above, the second coil 12 is arranged inside the first coil 11, similar to the first embodiment. Furthermore, the second coil 12 is composed of a first portion 121 and a second portion 122 whose winding directions are opposite to each other. Therefore, mutual induction does not occur between the first coil 11 and the second coil 12, making it possible to improve the effect of suppressing uneven heating.

[0066] (Third Embodiment) Figure 14 is a plan view of the second coil of the induction heating device according to the third embodiment. The second coil 12 shown in Figure 14 is a parallel-type DD coil in which a first portion 121 and a second portion 122 are connected in parallel to a DC power supply. In the second coil 12 according to this embodiment, the first portion is wound clockwise, while the second portion 122 is wound counterclockwise. That is, the winding direction of the first portion 121 is opposite to the winding direction of the second portion 122.

[0067] In this embodiment, the second coil 12 is arranged inside the circular first coil 11, similar to the first embodiment. Therefore, the object to be heated 40 is heated by the first coil 11, which is supplied with a first coil current from the first drive circuit 21, and the second coil 12, which is supplied with a second coil current from the second drive circuit 22. Now, with reference to Figure 15, an equivalent circuit related to the heating of the object to be heated 40 will be described.

[0068] Figure 15 is a diagram showing an equivalent circuit related to the heat generation of an object 40 to be heated using the induction heating device 3 according to the third embodiment. In Figure 15, the same reference numerals are used for the same circuit elements as in the equivalent circuit shown in Figure 13, and redundant explanations are omitted.

[0069] First, the path of the coil current i flowing through the first coil 11 will be described. ｏｕｔ１ For the path of the coil current i ｏｕｔ１ When it is positive, there are three paths: the first path, the second path, and the third path. The first path is the path passing through L ｒ１ , R ｒ１ａ , M １２Ｌ , R ｒ１２Ｌ , R ｒ１ｂ , R ｒ１２Ｒ , and M １２Ｒ . The second path is the path passing through L ｒ１ , R ｒ１ａ , M １２Ｌ , R ｒ１２Ｌ , R ｒ２ａ , L ｒ２Ｌ , L ｒ２Ｒ , R ｒ２ｃ , R ｒ１２Ｒ , and M １２Ｒ . The third path is the path passing through L ｒ１ , R ｒ１ａ , R ｒ２ｂ , and R ｒ２ｄ .

[0070] When the coil current i ｏｕｔ１ is negative, there are the first reverse path flowing in the reverse direction of the first path, the second reverse path flowing in the reverse direction of the second path, and the third reverse path flowing in the reverse direction of the third path. In FIG. 15, the current flowing through the first path is indicated by i ｏｕｔ１ａ , the current flowing through the second path is indicated by i ｏｕｔ１ｂ , and the current flowing through the third path is indicated by i ｏｕｔ１ｃ . However, i ｏｕｔ１ = i ｏｕｔ１ａ + i ｏｕｔ１ｂ + i ｏｕｔ１ｃ .

[0071] Next, the path of the coil current i ｏｕｔ２ flowing through the second coil 12 will be described. When the coil current i ｏｕｔ２ is positive, there are two paths: the fourth path and the fifth path. The fourth path is the path passing through L ｒ２Ｌ , R ｒ２ａ , R ｒ１２Ｌ , M １２Ｌ , and R ｒ２ｂThis is the route that passes through L. On the other hand, the fifth route is L ｒ２Ｒ , R ｒ２ｃ , R ｒ１２Ｒ M １２Ｒ , and R ｒ２ｄ This is the path through which the coil current i passes. ｏｕｔ２ If the value is negative, there exists a fourth reverse path that flows in the opposite direction to the fourth path, and a fifth reverse path that flows in the opposite direction to the fifth path.

[0072] The equivalent circuit shown in Figure 15 is symmetrical, therefore R ｒ１ No potential difference is generated across b. Therefore, the coil current i ｏｕｔ２ R ｒ１ｂ There is no path through. For the same reason, the current through the first path is equal to the current through the second path, so the current flowing through each path is i ｏｕｔ２ This corresponds to / 2. The currents shown by arrows in the diagram are the coil currents flowing through each branched path, superimposed with the arrow direction being positive.

[0073] In the induction heating device 3 according to the present embodiment described above, the second coil 12 is arranged inside the first coil 11, similar to the second embodiment. Furthermore, the second coil 12 is composed of a first portion 121 and a second portion 122 whose winding directions are opposite to each other. Therefore, mutual induction does not occur between the first coil 11 and the second coil 12, making it possible to improve the effect of suppressing uneven heating.

[0074] Furthermore, in this embodiment, the second coil 12 is a parallel DD coil. Therefore, the symmetry of the coil connection is superior to that of the series DD coil described in the third embodiment. As a result, according to this embodiment, it is possible to further reduce uneven heating.

[0075] In this invention, the first portion 121 and the second portion 122 of the second coil 12 do not necessarily have to be symmetrical. However, if the first portion 121 and the second portion 122 are asymmetrical, it is desirable that the inductance be equal between the first portion 121 and the second portion 122 in order to avoid mutual induction.

[0076] Based on the above description, those skilled in the art may conceive of additional effects and various modifications of the present invention, but the embodiments of the present invention are not limited to those described above. Various additions, modifications, and partial deletions are possible without departing from the conceptual idea and spirit of the present invention derived from the claims and their equivalents.

[0077] 1: Induction heating device 11, 11a: First coil 12, 12a, 12b: Second coil 21: First drive circuit 22: Second drive circuit 121, 121a, 121b: First part 122, 122a, 122b: Second part 40: Object to be heated

Claims

1. An induction heating device comprising: a first coil that heats an object to be heated by receiving a first coil current; and a second coil disposed inside the first coil and that heats the object to be heated by receiving a second coil current, wherein the second coil has a first portion and a second portion whose winding direction is opposite to that of the first portion.

2. The induction heating apparatus according to claim 1, wherein the shape of the first coil is circular, the first portion and the second portion are each semicircular, and the first portion and the second portion are arranged back-to-back with respect to the center of the first coil to form a circle.

3. The induction heating apparatus according to claim 1, wherein each of the first coil, the first portion, and the second portion is rectangular, and the first portion and the second portion are arranged symmetrically with respect to the center of the first coil.

4. The induction heating apparatus according to claim 1, wherein the shape of the first coil is circular, the first portion and the second portion are each semicircular, and the first portion and the second portion are arranged symmetrically with respect to the center of the first coil with their arc portions facing back to back.

5. The induction heating apparatus according to any one of claims 1 to 4, wherein the phase difference between the first coil current and the second coil current is 90 degrees.

6. An induction heating device according to any one of claims 1 to 4, further comprising a first drive circuit for supplying the first coil current to the first coil, and a second drive circuit for supplying the second coil current to the second coil, wherein the circuit configuration of the first drive circuit is the same as the circuit configuration of the second drive circuit.

7. The induction heating apparatus according to any one of claims 1 to 4, wherein the inductance of the first portion is equal to the inductance of the second portion.

8. The induction heating apparatus according to claim 2, wherein the first part and the second part are connected in series.

9. The induction heating apparatus according to claim 2, wherein the first part and the second part are connected in parallel.

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