Induction heating device

Abstract

To reduce inverter current in heating operation of an induction heating device.SOLUTION: An induction heating device A includes a parallel resonance circuit 20 including an inductor with a heating coil C, and a resonance capacitor 26, an inverter circuit 1 that supplies the parallel resonance circuit 20 with electric power, first current detection means 35 that detects output current output from the inverter circuit 1 to the parallel resonance circuit 20, and control means 40 that controls drive frequency of the inverter circuit 1 so as to reduce a peak current value of the output current detected by the first current detection means 35.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an induction heating device using a heating coil.

Background Art

[0002] Patent Document 1 discloses a technique for operating at a resonance frequency by matching the voltage phase of a heating coil and the inverter output voltage phase in an inverter device that is PWM-controlled and connected to a resonant load. In Patent Document 1, a short pulse width is output, and the drive frequency is shifted so that the phase of the pulse width matches the voltage phase of the resonant circuit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the technique of Patent Document 1, since it is difficult to detect the phase state of the output voltage of the inverter during heating, the drive frequency is locked and not changed during the heating operation. Then, when the object to be heated moves during heating and the resonance point shifts, there is a problem that the drive frequency of the inverter deviates from the resonance frequency and the efficiency deteriorates. Further, when applying the technique of Patent Document 1 to a high-frequency induction heating device, there is a problem that high-speed phase detection means is required to accurately detect the phase.

[0005] The present invention has been made in view of such points, and an object thereof is to reduce the inverter current with respect to the current flowing through the heating coil during the heating operation of the induction heating device.

Means for Solving the Problems

[0006] To solve the above problems, an induction heating device according to a first aspect of the present invention comprises a heating coil for induction heating of an object to be heated, a parallel resonant circuit including an inductor and a resonant capacitor that include the heating coil, an inverter circuit that supplies power to the parallel resonant circuit, a current detection means for detecting the output current output from the inverter circuit to the parallel resonant circuit, and a control means for controlling the output current detected by the current detection means so that the peak current becomes smaller.

[0007] According to the above embodiment, for example, when the resonant frequency and the minimum value of the peak current coincide, the peak current of the output current detected by the current detection means is controlled to be small. Therefore, even if the resonant point of the parallel resonant circuit changes during operation, it is possible to track the changed resonant point, and continuous operation near the resonant frequency becomes possible. Furthermore, unlike the conventional technology, there is no need to detect the phase, and only the peak current of the inverter needs to be acquired, making it easy to control the resonant frequency.

[0008] In a second aspect of the present invention, in the first aspect, the control means controls the drive frequency of the inverter circuit in a direction that reduces the slope of the output current with respect to the change in the drive frequency, while varying the drive frequency of the inverter circuit.

[0009] In a third aspect of the present invention, in the first aspect, the control means controls the drive frequency of the inverter circuit so that the peak current of the output current detected by the current detection means is less than or equal to a predetermined threshold.

[0010] The second and third embodiments described above specify concrete forms of control by the control means.

[0011] According to the second embodiment, the control means can control the current peak with the minimum current more reliably in order to control the current change in response to time fluctuations. In contrast, in the third embodiment, a threshold value for controlling the current peak is determined, making control easier compared to the second embodiment.

[0012] In a fourth aspect of the present invention, in the first aspect, a filter means is provided between the inverter circuit and the parallel resonant circuit to smooth out the rectangular output voltage output from the inverter circuit and convert it into a sinusoidal waveform.

[0013] This makes it easier to detect peak current even when the effective value of the inverter's output voltage is small relative to the input voltage to the inverter circuit, enabling control based on peak current. Furthermore, it allows for control of the resonant frequency over a wide range of the inverter circuit's output voltage duty cycle. In addition, it enables broad control of thermal power.

[0014] In a fifth aspect of the present invention, as in the first to fourth aspects, the control means includes an input voltage control unit that changes the input voltage of the inverter circuit according to the set heat amount of the heating coil.

[0015] This allows the inverter circuit to maintain a large duty cycle for its output voltage, and the thermal power can be controlled by changing the input voltage in the input voltage control unit, thus enabling a wide range of thermal power control.

[0016] In a sixth aspect of the present invention, in the first aspect, a second current detection means for detecting the current flowing through the parallel resonant circuit is provided, and the control means controls the drive frequency of the inverter circuit to decrease when the peak current of the output current detected by the first current detection means exceeds a predetermined first threshold, and controls the drive frequency of the inverter circuit to increase when the current detected by the second current detection means falls below a predetermined second threshold.

[0017] As a result, even when the RMS value of the inverter circuit's output voltage is small compared to the inverter circuit's input voltage, if the resonance point of the parallel resonant circuit changes during operation, it is possible to track the changed resonance point and continue operating near the resonant frequency.

[0018] An induction heating device according to a seventh aspect of the present invention comprises a heating coil, a parallel resonant circuit including an inductor and a resonant capacitor that include the heating coil, and an inverter circuit that supplies power to the parallel resonant circuit, wherein the parallel resonant circuit is a parallel circuit of a first circuit which is one side of a circuit branched from the output of the inverter circuit and a second circuit which is the other side, and further comprises a first current detection means for detecting the current of the first circuit, a second current detection means for detecting the current of the second circuit, and a control means for controlling the drive frequency of the inverter circuit so that the difference between the first peak current value of the current detected by the first current detection means and the second peak current value of the current detected by the second current detection means is within a predetermined range, so as to reduce the difference between the first peak current value of the current detected by the first current detection means and the second peak current value of the current detected by the second current detection means.

[0019] Here, when the parallel resonant circuit is in resonance, the waveform of the branch current flowing through the first circuit and the waveform of the branch current flowing through the second circuit are ideally the same. Therefore, the control means controls the drive frequency of the inverter circuit so that the difference between the first peak current value and the second peak current value is within a predetermined range. In this way, the drive frequency of the inverter circuit can be brought closer to the resonant frequency of the parallel resonant circuit. Furthermore, since the drive frequency can be adjusted even during heating, even if the pot moves and the resonance point shifts, the operation can be automatically readjusted to match the resonance point.

[0020] In a sixth aspect of the present invention, in the first aspect, the control means compares the first peak current value and the second peak current value and controls the drive frequency of the inverter circuit so that the error between them is within 20%.

[0021] Here, the specified scope of the seventh aspect is specifically defined. [Effects of the Invention]

[0022] According to the present invention, in an induction heating device, since the control frequency of the inverter can be controlled to follow the parallel resonance frequency, the inverter current can be reduced with respect to the current flowing through the heating coil during the heating operation of the induction heating device.

Brief Description of the Drawings

[0023] [Figure 1] Equivalent circuit configuration diagram of the induction heating device according to the embodiment [Figure 2] Diagram showing a specific configuration example of the induction heating device in FIG. 1 [Figure 3] Diagram showing the frequency-impedance characteristics of the parallel resonance circuit [Figure 4] Simulation waveform diagram when the effective value of the output voltage of the inverter circuit is large [Figure 5] Diagram showing the change in current with respect to the driving frequency of the inverter circuit [Figure 6] Diagram comparing the current when a coil (filter means) is provided and when it is not provided [Figure 7] Diagram summarizing the cases when the effective value of the output voltage of the inverter circuit is large and small [Figure 8] Equivalent circuit configuration diagram showing another example of the induction heating device [Figure 9] Diagram for explaining the operation of the induction heating device in FIG. 8 [Figure 10] Equivalent circuit configuration diagram showing another example of the induction heating device [Figure 11] Diagram for explaining the operation of the induction heating device in FIG. 10 [Figure 12] Diagram showing another configuration example of the parallel resonance circuit [Figure 13] Equivalent circuit configuration diagram showing another example of the induction heating device [Figure 14] Equivalent circuit configuration diagram showing another example of the induction heating device

Embodiments for Carrying Out the Invention

[0024] Embodiments of the present invention will be described below with reference to the drawings. The following description of preferred embodiments is essentially illustrative and is not intended to limit the present invention, its applications, or its uses.

[0025] As shown in Figures 1 and 2, the induction heating device A comprises a heating coil C, a parallel resonant circuit 20 composed of inductors 24, 25 including the heating coil C and a resonant capacitor 26, an inverter circuit 1 that supplies power to the parallel resonant circuit 20, a first current detection means 35 that detects the output current of the inverter circuit 1 (hereinafter referred to as "inverter current I3"), and a control means 40.

[0026] -Inverter- The circuit configuration of the inverter circuit 1 is not particularly limited, and conventionally known configurations can be applied. In this embodiment, an example of an inverter circuit 1 in a full-bridge configuration in which arms 11 and 12 are connected in parallel is shown.

[0027] Arms 11 and 12 each have two switching elements 13 connected in series. More specifically, the two switching elements 13 of arm 11 are connected by a first wiring N1, and the two switching elements 13 of arm 12 are connected by a second wiring N2. Each switching element 13 is a parallel circuit of a transistor and a diode connected in parallel and in the opposite direction to the transistor. The switching element 13 of arm 11 performs switching operations in response to a drive signal from a driver 61 that operates under the control of a CPU 42 (described later). Similarly, the switching element 13 of arm 12 performs switching operations in response to a drive signal from a driver 62 that operates under the control of a CPU 42. Through the switching operation of arms 11 and 12, DC power is converted into AC power and output.

[0028] Between the first wiring N1 and the second wiring N2, a voltage filter coil 31, a parallel resonant circuit 20, and a first current detection means 35 are connected in series. The first current detection means 35 has a conventionally known configuration, and a detailed explanation of its specific configuration is omitted here.

[0029] -Coil for voltage filter- Coil 31 (voltage filter) is inserted between the output of inverter circuit 1 and parallel resonant circuit 20, and acts to make the inverter current I3 approximate a sine wave (see the embodiment in Figure 3). This makes it possible to control the resonant frequency based on the peak current, even when the effective value of the output voltage of inverter circuit 1 (hereinafter referred to as "inverter voltage Vo") is small relative to the input voltage from DC power supply 5. The inverter voltage Vo is square wave shaped. Alternatively, another filter circuit that removes the harmonic components of the inverter voltage Vo and smooths the waveform to make it sinusoidal may be used instead of coil 31. Control of the resonant frequency based on the peak current will be explained later.

[0030] -Parallel resonant circuit- The parallel resonant circuit 20 has a configuration in which an inductor 25 is connected in parallel to the first circuit 21, which has an inductor 24 and a resonant capacitor 26 connected in series.

[0031] Figures 2(a) and 2(b) show specific configuration examples of the parallel resonant circuit 20 shown in the equivalent circuit of Figure 1. In Figures 2(a) and 2(b), the heating coil C is wound spirally in a predetermined one direction.

[0032] In Figure 2(a), one end of the heating coil C is connected to the second wiring N2 via the first current detection means 35, and the other end is connected to the second wiring N2 via the resonant capacitor 26 and the first current detection means 35. An intermediate point P1 located in the middle of the heating coil C is connected to the first wiring N1 via the coil 31. That is, the heating coil 3 is divided into a first heating coil C1 and a second heating coil C2 at the intermediate point P1. The first heating coil C1 constitutes an inductor 24, and the second heating coil C2 constitutes an inductor 25.

[0033] In Figure 2(b), the parallel resonant circuit 20 is configured by connecting in parallel a first circuit 21, in which a heating coil C and a resonant capacitor 26 are connected in series, and a second circuit 22, which is composed of an inductor 25. In Figure 2(b), the heating coil C constitutes the inductor 24.

[0034] -Control means- Returning to Figure 1, the control means 40 comprises a peak current conversion circuit 41 and a CPU 42, and controls the drive frequency of the inverter circuit 1 so that the peak current of the output current detected by the first current detection means 35 becomes smaller.

[0035] The peak current conversion circuit 41 is a circuit that converts the output current detected by the first current detection means 35 into a peak current; in other words, it is a circuit that detects the peak current value of the inverter current I3. The peak current conversion circuit 41 outputs the peak current value (hereinafter simply referred to as "peak current value") for each period of the drive frequency of the inverter circuit 1 to the CPU 42.

[0036] Based on the peak current value received from the peak current conversion circuit 41, the CPU 42 controls the drive frequency of the inverter circuit 1 so that the peak current value is minimized or within a certain threshold range, under the condition that the effective value of the inverter voltage Vo is fixed. As shown in Figure 1, the CPU 42 outputs a voltage phase difference control command to control the drive frequency of the inverter circuit 1.

[0037] <Impedance of a parallel resonant circuit> Figure 3 shows an example of the frequency-impedance characteristics of a parallel resonant circuit 20. In Figure 3, the thick solid line shows the characteristics of the parallel resonant circuit 20, the dashed line shows the characteristics of the first circuit 21, and the thin solid line shows the characteristics of the second circuit 22.

[0038] Here, in the parallel resonant circuit 20, when the impedance Z20 resonates at the resonant frequency fo where the impedance Z20 is at its maximum value, the impedance Z21 of the first circuit 21 and the impedance Z22 of the second circuit 22 are approximated by the following equation (1). Also, the impedance Z20 of the parallel resonant circuit 20 is approximated by the following equation (2).

[0039]

number

[0040]

number

[0041] In equation (1), Lm is the inductance of the first circuit 21 (inductor 24 in this case), Ls is the inductance of the second circuit 22 (inductor 25 in this case), M is the mutual inductance of the first circuit 21 and the second circuit 22, and Cm is the capacitance value of the first circuit 21 (resonant capacitor 26 in this case). Equation (2) is the equation for when a pot is placed on the heating coil C, where Rm is the resistance component of the first circuit 21 including the effect of the pot, Rs is the resistance component of the second circuit 22 including the effect of the pot, and Rt is the resistance component corresponding to the mutual inductance.

[0042] The impedance Z21 in equation (1) is determined by the number of turns of the heating coil C and the size of the pot being heated, and is largely independent of the material of the pot. The value of impedance Z21 is designed to be, for example, around 3 to 10 [Ω].

[0043] In the case of an aluminum pot, (Rm + Rs + 2Rt) is approximately 1 [Ω], and from equations (1) and (2) above, the impedance Z20 is approximately 10 to 100 [Ω]. That is, in the case of an aluminum pot, the relationship between impedance Z20 and impedances Z21 and Z22 is (Z20 > Z21, Z22).

[0044] In the case of a stainless steel pot, (Rm + Rs + 2Rt) is approximately 20 [Ω], and from equations (1) and (2) above, the impedance Z20 is approximately 0.05 to 5 [Ω]. That is, the relationship between impedance Z20 and impedances Z21 and Z22 in the case of a stainless steel pot is (Z20 <Z21,Z22)となる。

[0045] To summarize the impedance of the parallel resonant circuit 20, in the case of a non-magnetic pot such as an aluminum pot, at the parallel resonant frequency, the impedance Z20 of the parallel resonant circuit 20 is greater than the impedance Z21 of the first circuit 21 and also greater than the impedance Z22 of the second circuit 22.

[0046] <Drive frequency control of inverter circuits> Next, the drive frequency control of inverter circuit 1 will be explained in detail. Note that in the circuit shown in Figure 1, coil 31 may be omitted. The drive frequency control of inverter circuit 1 will be explained in the following sections, with different cases to consider.

[0047] In this embodiment, the control means 40 performs different control depending on whether (1) a coil 31 is provided or the coil 31 is not provided but the effective value of the inverter voltage Vo is relatively large, or (2) a coil 31 is not provided and the effective value of the inverter voltage Vo is relatively small.

[0048] The boundary between the relative magnitude of the effective value of the inverter voltage Vo can be arbitrarily set according to the circuit configuration, etc. For example, the control means 40 determines that the effective value of the inverter voltage Vo is relatively large (hereinafter simply referred to as "large effective value") when the effective value of the inverter voltage Vo is 60% or more of the input voltage Vi of the inverter circuit 1, and determines that the effective value of the inverter voltage Vo is relatively small (hereinafter simply referred to as "small effective value") when it is less than 60%.

[0049] -Inverter circuit drive frequency control (1)- First, we will explain the drive frequency control of the inverter circuit 1 when a coil 31 is provided in the first circuit 21, or when the effective value of the inverter voltage Vo is large.

[0050] Figure 4 shows the simulated waveforms of the branch current I1 flowing through the first circuit 21, the branch current I2 flowing through the second circuit 22, and the inverter current I3. In Figure 4, the upper figure shows the time variation of the inverter voltage Vo, and the lower figure shows the time variation of the branch currents I1, I2 and the inverter current I3.

[0051] Furthermore, in Figure 5, the upper waveform shows the results of the AC analysis of the branch currents I1, I2 and inverter current I3 with respect to the drive frequency near the resonant frequency fo, while the lower waveform shows an example of the change in the measured peak current value Ip with respect to the drive frequency.

[0052] As shown in Figure 4, when a coil 31 is provided in the first circuit 21, or when the effective value of the inverter voltage Vo is large, the inverter current I3 approaches a sine wave. Furthermore, as shown in the upper waveform of Figure 5, when the branch current I1 of the first circuit and the branch current I2 of the second circuit 22 are substantially equal, the parallel resonant circuit 20 is in resonance, and heating is performed most efficiently.

[0053] As can be seen from Figure 5, the frequency at which the inverter current I3 is at its minimum in the AC analysis above almost coincides with the frequency at which the output current I3 is at its minimum in actual operation, which is the resonant frequency fo. Specifically, for example, when the resonant frequency fo of the parallel resonant circuit 20 determined by the AC analysis is 75.95 [kHz], the drive frequency calculated from the minimum value of the output current I3 (measured value) is 76.0 [kHz], confirming that operation at the resonant frequency is practically possible by minimizing the peak current value Ip.

[0054] Therefore, when the effective value of the inverter voltage Vo is large, the CPU 42 controls the drive frequency of the inverter circuit 1 so that the peak current value Ip, based on the detection result of the first current detection means 35, is minimized. This makes it possible to operate the induction heating device A at its resonant frequency.

[0055] The specific method for controlling the drive frequency of the inverter circuit 1 by the CPU 42 is not particularly limited.

[0056] For example, the CPU 42 controls the drive frequency of the inverter circuit 1. number The drive frequency of the inverter circuit 1 is controlled in a direction that reduces the slope ΔI of the output current with respect to the change in drive frequency Δf, while constantly varying it by a small amount (for example, less than 1 kHz). In other words, it is controlled so that ΔI / Δf approaches "0".

[0057] Furthermore, for example, the CPU 42 sets a threshold Ith1 for the inverter current I3 according to the output level of the induction heating device A, and controls the inverter circuit 1 so that its drive frequency is less than or equal to the threshold Ith1.

[0058] To explain using a specific example, if the output power of induction heating device A is 2500[W], and a standard-sized aluminum pot is installed, and the resistance value of the heating coil at the driving frequency is designed to be 1[Ω], then the current flowing through the heating coil will be 50[A]. Here, the impedance values ​​when an aluminum pot is installed are correlated with the size of the pot, so for a standard-sized pot, the values ​​of equations (1) and (2) above can be obtained. For example, Z21=Z22=6[Ω] and Z20=36[Ω]. In this case, the theoretically obtainable inverter current I3 is "output current × Z21 / Z20", which is 8.3[A]. Therefore, the theoretically determined peak current is 11.7[A]. If we then set a control threshold of 14[A], which is about 20% larger than this theoretical value, we can control the drive frequency of inverter circuit 1 within the range of the resonant frequency fo ± 350[Hz].

[0059] -Inverter circuit drive frequency control (2)- Next, we will explain the drive frequency control of the inverter circuit 1 when coil 31 is not provided in Figure 1 and the effective value of the inverter voltage Vo is relatively small.

[0060] As shown in Figure 6, when the effective value of the inverter voltage Vo is large (see left column), the inverter current I3 has a sinusoidal waveform, and the frequency at which the inverter current I3 is at its minimum value in the AC analysis and the frequency at which the output current I3 is at its minimum value in actual operation almost coincide with the resonant frequency fo.

[0061] In contrast, when the effective value of the inverter voltage Vo is small (see the right column), the inverter current I3 does not form a sinusoidal waveform, and the frequency at which the output current I3 is at its minimum value during actual operation does not coincide with the resonant frequency fo. Therefore, when the coil 31 is not provided, a different method is adopted when the effective value of the inverter voltage is small compared to when the effective value of the inverter voltage is large.

[0062] Specifically, as shown in Figure 8, in addition to the first current detection means 35, a second current detection means 36 is provided to detect the current flowing through the parallel resonant circuit 20. The second current detection means 36 may be provided in the first circuit 21 or in the second circuit 22.

[0063] Furthermore, as shown in Figure 10, the first circuit 21 may be provided with a first current detection means 37, and the second circuit 22 may be provided with a second current detection means 38.

[0064] The following sections will explain each method with reference to the diagrams.

[0065] First, let's describe the induction heating device A shown in Figure 8. In Figure 8, components common to both Figure 1 and Figure 1 are denoted by the same reference numerals, and here we will focus on the differences. Figure 9 shows the changes in branch currents I1, I2 and inverter current I3 with respect to the drive frequency on the horizontal axis in the configuration of Figure 8.

[0066] As described above, the induction heating device A in FIG. 8 includes, in addition to the first current detection means 35, second current detection means 36 for detecting the current flowing through the parallel resonance circuit 20. In the example of FIG. 8, an example where the second current detection means 36 is provided in the second circuit 22 is shown.

[0067] Furthermore, the control means 40 includes a peak current conversion circuit 43 that converts the output current detected by the second current detection means 36 into a peak current. Also, the CPU 42 controls the drive frequency of the inverter circuit 1 based on the peak current value of the inverter current I3 received from the peak current conversion circuit 41 and the peak current value of the branch current I2 flowing through the second circuit 22 received from the peak current conversion circuit 43.

[0068] Specifically, when the inverter current I3 exceeds a predetermined threshold Ith2, the CPU 42 controls to lower the drive frequency of the inverter circuit 1. In FIG. 9, since the drive frequency at the threshold Ith2 is f2 (where f2 > fo), the control is to lower the drive frequency below f2.

[0069] Also, when the branch current I2 flowing through the second circuit 22 exceeds a predetermined threshold Ith3 (where Ith3 > Ith2), the CPU 42 controls to increase the drive frequency of the inverter circuit 1. In FIG. 9, since the drive frequency at the threshold Ith3 is f1 (where f1 < fo < f2), the control is to increase the drive frequency above f1.

[0070] Thereby, the CPU 42 can adjust the drive frequency of the inverter circuit 1 between f1 and f2. That is, the CPU 42 can bring the drive frequency of the inverter circuit 1 closer to the resonance frequency fo of the parallel resonance circuit 20. Also, even during heating, the drive frequency can be adjusted, so that even when the pan moves and the resonance point shifts, it can be automatically adjusted to operate at the resonance point.

[0071] Furthermore, since the drive frequencies f1 and f2 can be set to any value using thresholds Ith2 and Ith3, respectively, the frequency interval between drive frequency f1 and drive frequency f2 can be adjusted.

[0072] Next, the induction heating device A shown in Figure 10 will be described. In Figure 10, components common to Figure 1 are denoted by the same reference numerals as in Figure 1, and the differences will be the focus of this explanation. Figure 11 shows the changes in branch currents I1, I2 and inverter current I3 with respect to time on the horizontal axis in the configuration of Figure 10.

[0073] As described above, the induction heating device A in Figure 10 includes a first current detection means 37 for detecting the branch current I1 flowing through the first circuit 21, and a second current detection means 38 for detecting the branch current I2 flowing through the second circuit 22.

[0074] Furthermore, the control means 40 includes a peak current conversion circuit 44 that converts the branch current I1 detected by the first current detection means 37 into a peak current, and a peak current conversion circuit 45 that converts the branch current I2 detected by the second current detection means 38 into a peak current. The CPU 42 controls the drive frequency of the inverter circuit 1 based on the peak current value of the branch current I1 received from the peak current conversion circuit 44 and the peak current value of the branch current I2 received from the peak current conversion circuit 45.

[0075] Here, when the parallel resonant circuit 20 is in resonance, the inverter current I3 becomes the minimum value, and ideally the waveform of the branch current I1 flowing through the first circuit 21 and the waveform of the branch current I2 flowing through the second circuit 22 become the same.

[0076] Therefore, the CPU 42 controls the drive frequency of the inverter circuit 1 so that the peak current of branch current I1 matches the peak current of branch current I2, or so that the peak currents of branch current I1 and branch current I2 are within a predetermined range.

[0077] By doing so, the drive frequency of the inverter circuit 1 can be brought closer to the resonant frequency fo of the parallel resonant circuit 20. Furthermore, since the drive frequency can be adjusted even during heating, if the pot moves and the resonant point shifts, the system can automatically readjust to operate at the resonant point.

[0078] As described above, preferred embodiments have been explained as examples of the technology of this disclosure. However, the technology of this disclosure is not limited thereto and can be applied to embodiments that have been modified, replaced, added, or omitted as appropriate. Furthermore, some of the components described in the accompanying drawings and detailed description may not be essential for solving the problem. Therefore, the mere presence of such non-essential components in the accompanying drawings and detailed description should not be immediately assumed to mean that they are essential.

[0079] For example, the above embodiment may have the following configuration.

[0080] In the above embodiment, an example of a full-bridge type inverter circuit 1 was described, but as shown in Figure 12, a half-bridge type inverter circuit 1 may also be used, and the same effects as in the above embodiment can be obtained.

[0081] Furthermore, a parallel resonant circuit 20 different from the above embodiment may be used. For example, in Figure 13(a), the first circuit 21 of the parallel resonant circuit 20 is composed of a resonant capacitor 26, and the second circuit 22 is composed of an inductor 24 consisting of a heating coil C. Also, for example, in Figure 13(b), the first circuit 21 of the parallel resonant circuit 20 is composed of an inductor 24 consisting of a heating coil C and a resonant capacitor 26, and the second circuit 22 is composed of a resonant capacitor 27. Thus, even when the parallel resonant circuit 20 is different, the technology of this disclosure can be applied and similar effects can be obtained.

[0082] Alternatively, the configuration shown in Figure 14 may be used. In Figure 14, the control means 40 includes an input voltage control means that changes the input voltage Vi of the inverter circuit 1 according to the set heat amount of the heating coil C. In the example in Figure 14, the CPU 42 is shown to function as the input voltage control means.

[0083] This allows the inverter circuit to maintain a large duty cycle for its output voltage, and the thermal power can be controlled by changing the input voltage in the input voltage control unit, thus enabling a wide range of thermal power control. [Industrial applicability]

[0084] As described above, the present invention is extremely useful and has high industrial applicability because, in an induction heating device using a heating coil, it can contribute to improving the heating efficiency of aluminum pots (reducing heating time), miniaturizing the housing by reducing the number of parts, reducing costs, and reducing noise. [Explanation of symbols]

[0085] A induction heating device C Heating coil 1. Inverter Circuit 4. Control means 13 Switching elements 24,25 Inductor 35 First current detection means 36. Second current detection means 37 First current detection means 38 Second current detection means

Claims

1. Heating coil and A parallel resonant circuit is formed by connecting in parallel a first circuit in which a part of the heating coil and a resonant capacitor are provided in series, and a second circuit having the remaining part of the heating coil. An inverter circuit that supplies power to the parallel resonant circuit, A first current detection means for detecting the output current output from the inverter circuit to the parallel resonant circuit, An induction heating device comprising a peak current conversion circuit that converts the output current detected by the first current detection means into a peak current, and a control means that controls the drive frequency of the inverter circuit so that the peak current converted by the peak current conversion circuit becomes small.

2. Heating coil and A parallel resonant circuit is formed by connecting a first circuit, in which the heating coil and the resonant capacitor are provided in series, and a second circuit, in which an inductor is provided, in parallel. An inverter circuit that supplies power to the parallel resonant circuit, A first current detection means for detecting the output current output from the inverter circuit to the parallel resonant circuit, An induction heating device comprising a peak current conversion circuit that converts the output current detected by the first current detection means into a peak current, and a control means that controls the drive frequency of the inverter circuit so that the peak current converted by the peak current conversion circuit becomes small.

3. Heating coil and A parallel resonant circuit is formed by connecting a first circuit equipped with a resonant capacitor and a second circuit equipped with the heating coil in parallel. An inverter circuit that supplies power to the parallel resonant circuit, A first current detection means for detecting the output current output from the inverter circuit to the parallel resonant circuit, An induction heating device comprising a peak current conversion circuit that converts the output current detected by the first current detection means into a peak current, and a control means that controls the drive frequency of the inverter circuit so that the peak current converted by the peak current conversion circuit becomes small.

4. Heating coil and A parallel resonant circuit is formed by connecting in parallel a first circuit in which the heating coil and the first resonant capacitor are provided in series, and a second circuit in which the second capacitor is provided, An inverter circuit that supplies power to the parallel resonant circuit, A first current detection means for detecting the output current output from the inverter circuit to the parallel resonant circuit, An induction heating device comprising a peak current conversion circuit that converts the output current detected by the first current detection means into a peak current, and a control means that controls the drive frequency of the inverter circuit so that the peak current converted by the peak current conversion circuit becomes small.

5. In an induction heating apparatus according to any one of claims 1 to 4, The control means controls the drive frequency of the inverter circuit in a direction that reduces the slope of the output current with respect to the change in the drive frequency, while varying the drive frequency of the inverter circuit.

6. In an induction heating apparatus according to any one of claims 1 to 4, The control means controls the drive frequency of the inverter circuit so that the peak current of the output current detected by the first current detection means is less than or equal to a predetermined threshold, in an induction heating device.

7. In an induction heating apparatus according to any one of claims 1 to 4, An induction heating device comprising a filter means between the inverter circuit and the parallel resonant circuit, which smooths out the rectangular output voltage output from the inverter circuit to form a sinusoidal waveform.

8. In an induction heating apparatus according to any one of claims 1 to 4, The control means comprises an input voltage control means for changing the input voltage of the inverter circuit according to the set heat amount of the heating coil, in an induction heating device.

9. In an induction heating apparatus according to any one of claims 1 to 4, The system includes a second current detection means for detecting the current flowing through the first circuit or the second circuit, An induction heating device wherein the control means controls the drive frequency of the inverter circuit to decrease when the peak current of the output current detected by the first current detection means exceeds a predetermined first threshold, and controls the drive frequency of the inverter circuit to increase when the current detected by the second current detection means falls below a predetermined second threshold.

10. Heating coil and A parallel resonant circuit including an inductor containing the heating coil and a resonant capacitor, The system includes an inverter circuit that supplies power to the parallel resonant circuit, The parallel resonant circuit is a parallel circuit comprising a first circuit, which is one side of the circuit branched from the output of the inverter circuit and in which a part of the heating coil and the resonant capacitor are provided in series, and a second circuit, which is the other side and in which the remaining part of the heating coil is provided. A first current detection means for detecting the current of the first circuit, A second current detection means for detecting the current of the second circuit, An induction heating device further comprising: a first peak current conversion circuit that converts the output current detected by the first current detection means into a first peak current; and a second peak current conversion circuit that converts the output current detected by the second current detection means into a second peak current; and a control means that controls the drive frequency of the inverter circuit so that the difference between the first peak current converted by the first peak current conversion circuit and the second peak current converted by the second peak current conversion circuit becomes small.

11. In the induction heating apparatus according to claim 10, The control means compares the first peak current and the second peak current and controls the drive frequency of the inverter circuit so that the error between them is within 20%, in an induction heating device.

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