JP3833159B2 - Induction heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating cooker, an induction heating type water heater, a humidifier, an iron, or the like which can efficiently heat an object to be heated having high conductivity and low permeability such as an aluminum pan. It is about.
[0002]
[Prior art]
Conventionally, as this type of induction heating device, for example, a technique for suppressing a squealing noise when an aluminum pan is heated with respect to an induction heating cooker and a power factor reduction is disclosed (for example, Patent Document 1). In addition, a technique for suppressing the switching loss and heating the aluminum pan at a high frequency is disclosed (for example, see Patent Document 2).
[0003]
FIG. 9 is a circuit diagram showing the contents disclosed in Patent Document 1. In FIG. In FIG. 9, a thyristor 3, a thyristor 4, a diode 5, and a diode 6 constitute a bridge circuit 2 that inputs the voltage of an AC power supply 1 of 100 V and rectifies it into a DC voltage. Thyristor 3 and thyristor 4 control the conduction angle so that the DC power supply voltage of the inverter is reduced to about 20 V when the inverter is started and the output power is set to a low value so that the load detection means 24 has an appropriate heated object. Is determined, the output control circuit 26 operates, and thereafter the output is changed by changing the DC voltage.
[0004]
The input waveform shaping means 23 improves the power factor by driving the transistor 10 so that the input current has a predetermined waveform based on the signal from the input setting means 25 and the signal from the current transformer 22. . This is performed by the action of the choke coil 8 storing energy in the choke coil 8 when the transistor 10 is turned on and releasing the energy to the capacitor 11 via the diode 9 when the transistor 10 is turned off.
[0005]
Moreover, in order to heat an aluminum pan, the frequency of the electric current of the heating coil 18 is switched from 20 kHz to 50 kHz. This is done by changing the number of turns of the heating coil 18 and the capacity of the resonant capacitor 19.
[0006]
However, in the above conventional technique, it is necessary to switch the number of turns of the heating coil in order to heat the aluminum pan and the iron-based pan, which is structurally complicated and costly, and the resonance frequency is 50 kHz. In order to reduce the switching loss, the driving frequency of the switching elements 15 and 17 must be the same frequency (50 kHz), and the switching loss becomes large. In addition, there is a problem that a power supply voltage changing means for changing the output is required.
[0007]
As a method for solving the above problems, there is a technique disclosed in Patent Document 2. The circuit diagram of FIG. 10 and the waveforms of FIGS. 11 and 12 show the contents of this technique.
[0008]
A feature of this technique is that a signal is received by a current transformer 30 that detects a current flowing through the heating coil 18, and the frequency of the resonance current formed by the heating coil 18 and the resonance capacitor 19 is compared with the drive signals of the transistors 15 and 17. By setting it twice or more, the aluminum pan can be heated by increasing the frequency supplied to the heating coil while suppressing the switching loss of the transistors 15 and 17.
[0009]
In the output control method shown in the waveform of FIG. 11, when the power is small, the transistor 15 is turned off when the current reaches the zero point for the first time, and the transistor 17 is turned on when the current reaches the third time. Control to turn off. When the power is large, the transistor 15 is controlled to be turned off when the current reaches the zero point for the second time, and the transistor 17 is controlled to be turned off when the current reaches the second time.
[0010]
In the output control method shown in FIG. 12, when the power is small, the transistor 15 is turned off after lapse of t1 time (shorter than 1/2 period of the resonance current) after the conduction, and the transistor 17 is turned on for the third time. It is controlled to turn off when it reaches the zero point. When the power is high, the transistor 15 is turned off when the current reaches the zero point for the first time (1/2 period of the resonance current), and the transistor 17 is turned on for the third time. It is controlled to turn off when it reaches.
[0011]
[Patent Document 1]
JP-A-1-246683
[Patent Document 2]
JP 2001-160484 A
[0012]
[Problems to be solved by the invention]
The conventional induction heating apparatus as described in Patent Document 2 has a problem that the output cannot be continuously adjusted by the control method of FIG. 11, and the control method of FIG. There has been a problem that the output change becomes too large to control delicate output. Moreover, in any control method, since the envelope of the current of the heating coil 18 is not smoothed, a beat sound generated at a frequency twice as high as the commercial frequency is generated from the pan (hereinafter referred to as a pot sound). There was also. As a method for preventing the squealing noise, a technique as described in the above-mentioned Patent Document 1 is conceivable, but this technique is a method of adjusting the output by lowering the input power supply of the inverter to a lower level. Even when combined with the method described in the above-mentioned Special Reference 2, the resonance current is attenuated and does not continue, so that sufficient output control cannot be performed.
[0013]
The present invention solves the above-mentioned problem, suppresses the switching loss of the switching element of the inverter without generating a pot sound and controls the aluminum pan continuously with a sufficiently large output with good controllability. It aims at providing the induction heating apparatus which can be heated.
[0014]
[Means for Solving the Problems]
  In order to solve the above-described problems, the induction heating device of the present invention is characterized in that, particularly when the magnetic field generated by the heating coil heats an iron-based load or a non-magnetic stainless steel load, the resonance current is the first switching element or the second switching element. When the iron-type load or the non-magnetic stainless steel load is heated at the maximum output, the first switching element and the second switching element are supplied with current in the forward direction. Since the resonance capacitor is switched to a larger capacity than when heating a load with high conductivity and low permeability so that the switching element can be cut off at the timing when the current flows, the resonance capacitor and the correction capacitor are It is connected in series with the heating coil and its capacity can be switched to heat iron-type loads or non-magnetic stainless steel loads. ToThe DC voltage is boosted by the boosting smoothing means and supplied to the inverter; andBy switching the resonance capacitor to a larger capacity than when heating a load with high conductivity and low permeability, the resonance frequency becomes longer and the current increases, further boostingsmoothSince the DC power supply voltage is boosted by the means, the resonance current value increases. Therefore, the maximum output is set within a range in which the switching element can be cut off at the timing when the current flows through the switching element in the forward direction. When suppressing an increase in switching loss at turn-on, the maximum output can be made larger than that of the conventional configuration. Also, when heating an object with high conductivity and low permeability such as aluminum and an iron-based object to be heated with the same inverter, conventionally, the number of turns of the heating coil is switched to the object to be heated. The intensity of the radiated magnetic field (ampere turn) has been switched, but the action can be replaced by boosting the boosting means. Therefore, if the resonant capacitor is switched without switching the heating coil, high conductivity such as aluminum can be achieved. In addition, there is an effect that an object to be heated and an iron-based object to be heated can be heated.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The invention according to claim 1 is a series connection body of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and the second switching element. A DC voltage having a second reverse conducting element connected in parallel to the switching element; and a resonance circuit including a heating coil and a resonance capacitor connected in parallel to the first switching element or the second switching element. And an inverter that resonates by conduction between the first switching element and the second switching element, and a control circuit that exclusively controls conduction of the first switching element and the second switching element, The resonance current that flows through the first switching element or the first reverse conducting element causes a magnetic field generated by the heating coil to induce a load with high conductivity and low permeability. When heated, the DC voltage is boosted and smoothed by the boosting smoothing means so as to resonate with a period shorter than the driving period of the first switching element and maintain the resonance current with a predetermined amplitude or more in the driving period. By being supplied to the inverter, since there are a plurality of switching elements as compared with a single switching element, the duty is reduced, and the output control can be performed by changing the drive time ratio or the drive frequency. It can be done finely according to the load.
[0016]
  In addition, when heating a load with high conductivity and low permeability, the DC voltage input by the inverter is set so that the peak value of the resonance current does not decay and become zero during the switching element drive period.To be higher than the peak value of the input DC voltage of pulsating currentSince boosting and smoothing means for boosting and smoothing is provided, the switching element driving period is changed and the output is stably controlled while the resonance current is generated for one cycle or more during the switching element driving period, or It becomes possible to control so as not to increase the duty of the switching element (occurrence of turn-on loss).
[0017]
In particular, when the magnetic field generated by the heating coil heats an iron-based load or a nonmagnetic stainless steel load, the resonance current resonates at a period longer than the conduction period of the first switching element or the second switching element. When the iron-based load or the non-magnetic stainless steel load is heated at the maximum output, the switching element can be shut off at the timing when the current flows in the forward direction to the first switching element and the second switching element. The resonance capacitor is switched to a larger capacity than when heating a load with high conductivity and low permeability, so the resonance capacitor and the correction capacitor are connected in series with the heating coil and the capacity can be switched. When heating an iron load or a non-magnetic stainless steel loadDC voltage is boosted and smoothed by the boost smoothing means and supplied to the inverter; andBy switching the resonant capacitor to a larger capacity than when heating a load with high conductivity and low permeability, the resonance frequency becomes longer and the current increases, and the DC power supply voltage is boosted by boosting means. Therefore, since the resonance current value increases, set the maximum output within the range where the switching element can be cut off at the timing when the current flows in the forward direction to the switching element to suppress the increase in switching loss when the switching element is turned on. In this case, the maximum output can be made larger than that of the conventional configuration. Also, when heating an object with high conductivity and low permeability such as aluminum and an iron-based object to be heated with the same inverter, conventionally, the number of turns of the heating coil is switched to the object to be heated. The intensity of the radiated magnetic field (ampere turn) has been switched, but the action can be replaced by boosting the boosting means. Therefore, if the resonant capacitor is switched without switching the heating coil, high conductivity such as aluminum can be achieved. In addition, there is an effect that an object to be heated and an iron-based object to be heated can be heated.
[0018]
Further, the invention according to claim 2 starts with a resonant capacitor having a small capacity, and gradually increases the output, and determines whether it is an iron-based load or a load with high conductivity and low permeability during the process. However, if it is determined that the load is iron-based, after the drive is stopped, the resonance capacitor is switched so that the capacity becomes large, and the drive frequency is re-driven at a low frequency, resulting in a load with high conductivity and low magnetic permeability. If the output is continuously increased to a predetermined drive time ratio or a predetermined output, the drive time ratio is substantially fixed, the conduction time is changed, and the output reaches the predetermined output. To distinguish between low-power, high-conductivity, low-permeability load and iron-based load, and to select a suitable resonant capacitor according to the detection result and to select a drive method to reach a predetermined output It is something that can be done.
[0019]
【Example】
(Example 1)
A first embodiment of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a diagram showing a circuit configuration of the induction heating apparatus of this embodiment. The power source 51 is a 200 V commercial power source that is a low-frequency AC power source, and is connected to an input terminal of a rectifier circuit 52 that is a bridge diode. A first smoothing capacitor 53 is connected between the output terminals of the rectifier circuit 52. A series connection body of the choke coil 54 and the second switching element 57 is further connected between the output terminals of the rectifier circuit 52. The heating coil 59 is arranged to face the aluminum pan 61 that is the object to be heated.
[0021]
50 is an inverter, the low potential side terminal (emitter) of the second smoothing capacitor 62 is connected to the negative terminal of the rectifier circuit 52, and the high potential side terminal of the second smoothing capacitor 62 is the first switching element (IGBT). ) 55 is connected to the high potential side terminal (collector) of the first switching element (IGBT) 55 and the low potential side terminal of the first switching element (IGBT) 55 is the high potential side terminal (collector) of the choke coil 54 and the second switching element (IGBT) 57. Connected to the connection point. A series connection body of the heating coil 59 and the resonance capacitor 60 is connected to the second switching element 57 in parallel.
[0022]
The first diode 56 (first reverse conducting element) is connected in antiparallel to the first switching element 57 (the cathode of the first diode 56 and the collector of the first switching element 57 are connected), and the second The diode 58 (second reverse conducting element) is connected to the second switching element 57 in antiparallel. The snubber capacitor 64 is connected in parallel to the second switching element 57. A series connection body of the correcting resonance capacitor 65 and the relay 66 is connected to the resonance capacitor 60 in parallel. The control circuit 63 inputs detection signals of a current transformer 67 that detects an input current from the power source 51 and a current transformer 68 that detects a current of the heating coil 59, and the first switching element 55 and the second switching element. A signal is output to a gate 57 and a drive coil (not shown) of the relay 66.
[0023]
The operation of the induction heating apparatus configured as described above will be described below. The power source 1 is full-wave rectified by a rectifier circuit 52 and supplied to a first smoothing capacitor 53 connected to the output terminal of the rectifier circuit 52. The first smoothing capacitor 53 serves as a supply source for supplying a high-frequency current to the inverter.
[0024]
FIG. 2 is a diagram showing the waveform of each part in the above circuit, and FIG. 2 (A) is the one when the output is 2 kW, which is a large output. FIG. 4A shows the current waveform Ic1 flowing through the first switching element 55 and the first diode 56, and FIG. 4B shows the current waveform Ic2 flowing through the second switching element 57 and the second diode 58. FIG. 4C shows the voltage Vce2 generated between the collector and the emitter of the second switching element 57, FIG. 4D shows the drive voltage Vg1 applied to the gate of the first switching element 55, and FIG. The driving voltage Vg <b> 2 applied to the gate of the second switching element 57 and the current IL flowing through the heating coil 59 are shown in FIG.
[0025]
When the output is 2 kW (FIG. 2A), the control circuit 63 has a drive period T2 (about 24 μsec) at the gate of the second switching element 57 as shown in (e) from time t0 to time t1. Outputs an on signal. During this driving period T2, the second switching element 57 and the second diode 58, the heating coil 59, and the resonant capacitor 60 resonate in a closed circuit, and the pot 61 is an aluminum pot. The number of turns of the heating coil 59 (40T), the capacity of the resonant capacitor 60 (0.04 μF), and the driving period so that the resonance period (1 / f) is about 2/3 times (about 16 μs) the driving period T2. T2 is set. The choke coil 54 stores the electrostatic energy of the smoothing capacitor 53 as magnetic energy during the driving period T2 of the second switching element 57.
[0026]
Next, the collector current is applied at the time t1, which is the timing between the second peak of the resonance current flowing in the second switching element 57 and the resonance current next becoming zero, that is, in the forward direction of the second switching element 57. At the time of flowing, the driving of the second switching element 57 is stopped.
[0027]
Then, since the second switching element 57 is turned off, the potential of the terminal of the choke coil 54 connected to the collector of the second switching element 57 rises, and when this potential exceeds the potential of the second smoothing capacitor 62, The second smoothing capacitor 62 is charged through the first diode 56 to release the magnetic energy stored in the choke coil 54. The voltage of the second smoothing capacitor 62 is boosted so as to be higher than the peak value (283 V) of the DC output voltage Vdc of the rectifier 52 (500 V in this embodiment). The level to be boosted depends on the conduction time of the second switching element 58, and the voltage generated in the second smoothing capacitor 62 tends to increase as the conduction time increases.
[0028]
As described above, the second smoothing capacitor 62, the first switching element 55, the first diode 56, the heating coil 59, and the second smoothing functioning as a DC power source when resonating in a closed circuit formed by the resonance capacitor 60. By increasing the voltage level of the capacitor 62, the peak value (peak value) of the resonance current flowing through the first switching element 55 and the resonance path shown in FIG. In such a manner that the peak value of the resonance current flowing through the second switching element 57 of FIG. 5B that resonates does not become zero or does not become small, the aluminum pan is induction-heated with high output, In addition, the output can be controlled by increasing or decreasing continuously.
[0029]
Then, as shown in (d) and (e) of FIG. 2 (A), the control circuit 63 starts at time t2 after an idle period provided to prevent both switching elements from conducting simultaneously from time t1. A drive signal is output to the gate of the first switching element 55. As a result, as shown in FIG. 5A, the path is changed to a closed circuit composed of the heating coil 59, the resonance capacitor 60, the first switching element 55 or the first diode 56, and the second smoothing capacitor 62, and the resonance current is changed. Will flow. In this case, the drive period T2 of the drive signal is set to substantially the same period as T1, so that the drive period T2 is about 2/3 of the drive period T1, as in the case where the second switching element 58 is conductive. Periodic resonance current flows.
[0030]
Accordingly, the current IL flowing through the heating coil 59 has a waveform as shown in (f) of FIG. 2A, and the drive periods of the first and second switching elements (the sum of T1, T2, and the idle period) are resonant. If the current period is about three times and the first and second drive frequencies are about 20 kHz, the frequency of the resonant current flowing through the heating coil 59 is about 60 kHz.
[0031]
3A shows the voltage waveform of the commercial power supply 51, FIG. 3B shows the voltage Vce2 applied to the series connection body of the heating coil 59 and the resonant capacitor 60, FIG. 3C shows the current IL flowing through the heating coil 59, and FIG. Show. As described above, the output voltage of the rectifier 52 by the second smoothing capacitor 62 is a pulsating waveform obtained by full-wave rectification of the commercial power source shown in FIG. Since the line is smoothed as shown in FIG. 3 (c), the squealing noise generated at a frequency twice the commercial power supply frequency as generated by the heating coil current shown in FIG. 13 (c) of the conventional example is suppressed. become.
[0032]
The waveform in FIG. 2B is obtained when the output is 450 W, which is a low output. (A ′) to (e ′) in FIG. 2B are waveforms corresponding to (a) to (e) in FIG. As shown in FIG. 2B, the output power is controlled by changing the drive time (T1 ′) of the first switching element 55 and the drive time (T2 ′) of the second switching element 57 at the time of 2 kW output. This is done by making the driving time shorter than T1 and T2.
[0033]
2A, when the second switching element 58 is turned on at the time when the current flowing through the first diode 56 reaches a peak (time t5 in FIG. 2A), the output power is the minimum output power. Or a value close to that. On the other hand, the first switching element 56 is turned off at the time (not shown) at which resonance again becomes zero (from the time indicated by t6 in the figure) after starting to flow through the first switching element 56 for the second time. When the second switching element 58 is controlled to be turned on, the maximum output power can be obtained (resonance point power control).
[0034]
When the output setting is 450 W, which is a low output, according to the above principle, as shown in FIG. 2B (a ′), the drive time (T1 ′) is set to be longer than when the output setting is 2 kW, which is the maximum output setting. Although shortened, the first switching element 55 is turned off at the time (t3 ′) when the forward current flows through the first switching element 55. By doing so, the energy stored in the heating coil 59 is caused to resonate with the snubber capacitor 64 when the first switching element 55 is turned off, regardless of whether the maximum output is set or the low output is set. It is possible to reduce the switching loss by lowering the collector potential of one switching element 55 and slowing the rise of the voltage between the collector and emitter.
[0035]
As a result, the voltage is not applied in the forward direction when the second switching element 57 to be turned on is turned on, or the level is reduced even if the voltage is applied, and the turn-on loss is suppressed or the noise at the turn-on is reduced. In addition to being able to prevent the occurrence, the turn-off loss of the first switching element 55 can be reduced.
[0036]
Next, at the time of start-up, the control circuit 63 turns off the relay 66 and drives the first switching element 55 and the second switching element 57 alternately at a constant frequency (about 21 kHz). The drive period of the first switching element 55 is driven in a mode shorter than the resonance period of the resonance current, the drive time ratio is minimized, and the drive time ratio is gradually increased after the minimum output is achieved. 63 detects the material of the load pan 61 from the detection output of the current transformer 67 and the detection output of the current transformer 68. When the control circuit 63 determines that the material of the load pan 61 is iron-based, the heating is stopped, the relay 66 is turned on, and heating is started again at a low output. At this time, the control circuit 63 gradually increases the first switching element 55 and the second switching element 57 from a minimum output at a constant frequency (about 21 kHz) with a minimum drive time ratio to a predetermined output.
[0037]
On the other hand, when it is not detected that the load is iron-based, when the predetermined drive time ratio is reached, the period of the resonance current is shorter than the drive period of the first switching element 57 as shown in FIG. Enter mode. At this time, the drive period is set so that the output is in a low output state.
[0038]
FIG. 4 is a diagram showing the relationship between the on-time of the second switching element 57 and the input power when the drive frequency of the first switching element 55 and the second switching element 57 is constant (20 kHz). As shown in this figure, in this embodiment, a heating output of about 2 kW is obtained in the vicinity of a half of the cycle, and the output is obtained by shortening the driving period of the second switching element from the peak in the vicinity. It can be reduced linearly. Accordingly, stable control can be performed by setting the lower limit Tonmin and the upper limit Tonmax of the drive time or drive time ratio limiter as shown in FIG.
[0039]
As described above, according to the present embodiment, when a high-conductivity and low-permeability load such as aluminum or copper is heated by the magnetic field generated by the heating coil 59, the first switching element 55 and the first diode 56 flow. Since the resonance current generated by the heating coil 59 and the resonance capacitor 60 resonates at a cycle shorter than the drive period (T1) of each of the switching elements, a frequency higher than the drive frequency of the first switching element 55 (1 in this embodiment). .5 times) current can be supplied to the heating coil 59 for heating, and a choke coil 54 as a boosting means and a second smoothing capacitor 62 as a smoothing means are provided to provide a smoothing capacitor as a high-frequency power source. The voltage of 62 is boosted and smoothed, and the amplitude of the resonance current is increased in each drive period (T and T ′). The first cycle ends after the current starts to flow, and the resonance current having a sufficiently large amplitude is continued after the second cycle is reached, and the drive stop timing of each switching element is changed after the second cycle. A variable range of output can be obtained.
[0040]
Further, the choke coil 54, which is a boosting means, is obtained by changing the magnitude of the boosting so as to be related to the driving period of the second switching element 58. That is, the conduction time of the second switching element 57 is, for example, If it becomes longer, the boosting action of the choke coil 54 becomes larger, and the voltage of the smoothing capacitor 62, which is a smoothing means, becomes higher.
[0041]
In addition, the boosting unit 54 is configured to move the energy accumulated in the choke coil 54 by the conduction of the second switching element 57 to the second smoothing capacitor 62 via the first diode 56, thereby simplifying the operation. With this configuration, a high-voltage power supply can be obtained by smoothing the input DC voltage of the pulsating current, and it is converted to a high-frequency current with a smooth envelope based on this power supply and supplied to the heating coil 59, thus suppressing the squealing noise. can do.
[0042]
The resonance current flowing through the second switching element 57 or the second diode 58 is generated when the load having high conductivity and low magnetic permeability such as aluminum or copper is heated by the magnetic field generated by the heating coil 59. By resonating at a cycle shorter than the drive period (T2) of 57, the resonance current flowing through the first switching element 55 or the first diode 56 is combined and further within the drive period of the first and second switching elements. The wave number of the resonance frequency can be increased.
[0043]
In addition, when the second switching element 57 is turned on, the first smoothing capacitor 53 that gives energy to the choke coil 54 has a high frequency component leaking to the power source 51 when energy is stored in the choke coil 54. Can be suppressed.
[0044]
In addition, when the maximum output is set, the control circuit 63 performs the first switching within a period in which the resonance current is flowing in the first switching element 55 after the start of driving of the first switching element 55. A signal that cuts off the conduction of the element 55 is output, or after the second switching element 57 starts to be driven, the resonance current is flowing in the second switching element 57 after the second period and flowing through the second switching element 57. Since the signal for shutting off the conduction of the second switching element is output, an increase in turn-on loss of the second switching element 57 or the first switching element 55 at the maximum output can be suppressed.
[0045]
Further, the control circuit 63 shuts off the first switching element 55 after the start of driving of the first switching element 55 until the resonance current passes the peak phase in the second cycle and reaches the zero point when the maximum output is set. Or a signal that shuts off the first switching element 55 after the start of driving of the second switching element 57 until the resonance current passes through the peak phase of the second and subsequent cycles and reaches the zero point. , The generation of turn-on loss of the second switching element 57 or the first switching element 55 at the maximum output can be suppressed, and the output can be reduced by shortening the drive period thereof. Even if the output is low, the turn-on mode of each switching element hardly occurs and the turn-on loss hardly occurs.
[0046]
Further, when the ratio of the conduction period of the first switching element 55 and the second switching element 57 is substantially 1, and when a high conductivity and low permeability load is heated by the magnetic field generated by the heating coil 59, the first The resonance current flowing in the switching element 55 and the first diode 56 resonates at a period of about 2/3 times the driving period of the first switching element 55, thereby causing the first switching element 55 and the second diode 56 to The wave number of three resonance currents can be generated during the driving period of the switching element, and a high frequency current about three times the driving frequency can be supplied to the heating coil 59, and the first switching element 55 can be driven. Is started at the timing when the current flows through the first diode 56, and the stop of driving is stopped at the timing when the current flows through the first switching element 55 in the forward direction. Can be performed, the second control can be the same for the switching element 57 and second diode 58 is stabilized.
[0047]
  In addition, at the time of start-up, load ratio is detected by changing the driving time ratio of the first switching element 55 and the second switching element 57 to increase the heating output and changing the driving frequency from the middle to increase the heating output. It can be made easier. In other words, by changing the drive time ratio, it is possible to achieve a low output state with both high-conductivity and low-permeability aluminum loads and iron-based loads.Therefore, as shown in FIG. 4, if the lower limit Tonmin and the upper limit Tonmax of the drive time or drive time ratio limiter are set,The output can be changed monotonously, and the control circuit 63 can accurately detect the load in a low output state. Also, after reaching a predetermined drive time ratio, drive time, or heating output, the drive time ratio is constant so that the switching element can be driven and shut off in a specific phase range in the case of a load with high conductivity and low magnetic permeability. Thus, by changing the cutoff phase and changing the drive frequency, the output can be varied while suppressing a sudden increase in the loss of the switching element.
[0048]
Further, at the time of startup, the driving time ratio of the first switching element 55 and the second switching element 57 is changed to increase the heating output so that the driving period of the first switching element 55 is shorter than the resonance period of the resonance current. When the predetermined driving time or the predetermined driving time ratio is reached, the driving period of the first switching element 55 is changed to be discretely longer so as to be longer than the period of the resonance current and lower, and then the driving period is gradually increased. The heating output is increased from a low output value to a predetermined output value by shortening to a predetermined output value, so that the load 61 is a load having a high conductivity and a low magnetic permeability before reaching a predetermined drive time or a predetermined drive time ratio. When the load 61 is a load with high conductivity and low magnetic permeability, the driving period is discretely lengthened and the state shifts to a low output state and reaches a predetermined value. In which it increased to a constant can reach.
[0049]
Further, when an iron-based load or a nonmagnetic stainless steel load 61 is heated by the magnetic field generated by the heating coil 59, the resonance current resonates at a period longer than the conduction period of the first switching element 55 and the second switching element 57. When the iron-based load or the non-magnetic stainless steel load 61 is heated at the maximum output, the switching element is activated at the timing when the current flows in the first switching element 55 and the second switching element 57 in the forward direction. The correction resonance capacitor 65 is connected in parallel to the resonance capacitor 60 so as to be able to cut off, and the capacitance is switched to a larger capacity than when heating a load with high conductivity and low magnetic permeability. The correction capacitor 64 is connected in series with the heating coil 59 and has a switchable capacity. By switching the resonant capacitor 60 to a larger capacity than when heating a load with high conductivity and low permeability when heating a magnetic stainless steel load, the resonance frequency becomes longer and the current increases. Since the DC voltage Vdc is boosted by the choke coil 54, the amplitude of the resonance current increases, so the maximum output is set within a range in which the switching element can be cut off at the timing when the current flows through the switching element in the forward direction. Therefore, when it is intended to suppress an increase in switching loss when the switching element is turned on, the maximum output can be made larger than that of the conventional configuration. Further, when an aluminum pan and an iron pan are to be heated by the same inverter, conventionally, the number of turns of the heating coil 59 and the resonance capacitor are switched simultaneously to radiate the resonance frequency and the magnetic field to the object 61 to be heated. However, the coil winding number switching action can be replaced by the boosting action of the choke coil 54 and the first switching means 57, and the resonance capacitor 60 can be replaced by the same heating coil 59. By switching, there is an effect that an object to be heated of a wide range of materials can be heated.
[0050]
Further, the correction resonance capacitor 65 is started without being connected to the resonance capacitor 60, that is, is started with the resonance capacitor 60 having a small capacity, and the output is gradually increased. It is determined whether it has conductivity and low magnetic permeability. If it is determined that the load is an iron-based load, after the drive is stopped, the relay 60 is turned on and the correcting resonance capacitor 65 is connected in parallel. Since the capacitor 60 is switched to have a large capacity and the drive frequency is re-driven at a low frequency, the resonance frequency is increased and the current is increased. Further, the choke coil 54 as the boosting means and the second smoothing capacitor 62 are used for direct current. Since the power supply voltage is boosted, the resonance current value increases, so that the switching element is switched at the timing when the current flows in the forward direction to the first switching element 55. The when the extent possible blocking by setting the maximum output attempts to suppress the increase in switching loss at turn-on of the switching element 57 can be made larger than that of the conventional configuration the maximum output. If it is determined that the load has high conductivity and low permeability, the drive time ratio is continuously fixed and the conduction time is changed by increasing the output to a predetermined drive time ratio or a predetermined output. Since the output reaches a predetermined output, so-called soft start operation is possible to start at a low output at any load, determine the load, and stably reach the predetermined output value or limit value. It becomes.
[0051]
In FIG. 1, the ratio of the capacitances of the first smoothing capacitor and the second smoothing capacitor may be appropriately determined depending on the case. For example, if the former is 1000 microfarads and the latter is 15 microfarads, the smoothness of the envelope of the heating coil current is increased. In this case, a choke coil may be inserted into the power supply line on the input side of the first smoothing capacitor 53. Conversely, if the former is set to about 10 microfarads and the latter is set to about 100 microfarads, the power factor can be prevented from lowering. However, the latter requires a high withstand voltage and may be expensive.
[0052]
In FIG. 1, the second smoothing capacitor 62 may be connected at the low potential side to the positive electrode of the rectifier circuit 52, and the snubber capacitor 64 may be connected in parallel to the first switching element 55. The effect is obtained.
[0053]
Further, the low potential side terminal of the resonant capacitor 60 may be connected to the high potential side terminal (collector) of the first switching element 55, and the capacitance is divided so that the high potential side terminal of the first switching element 55 The same operation is performed even if they are simultaneously connected to the low potential side terminal (emitter) of the second switching element 57. The resonance circuit connected in parallel to the first switching element 55 or the second switching element 57 is not limited to the one in this embodiment, and the technique of this embodiment can be applied as appropriate.
[0054]
Further, although the induction heating cooker has been described in the above embodiment, the present invention can be applied to other types of induction heating apparatuses such as an iron or a water heater for heating a high conductivity and low magnetic permeability material such as aluminum.
[0055]
(Example 2)
A second embodiment of the induction heating apparatus of the present invention will be described with reference to the drawings. FIG. 5 is a diagram showing a circuit configuration of this embodiment. This embodiment differs from the configuration of the first embodiment in that the first smoothing capacitor 71 and the choke coil 72 are arranged between the power supply 51 and the rectifier circuit 52.
[0056]
The operation in this embodiment will be described. Reference numeral 50 denotes an inverter, and the operation of the control circuit 63 alternately turns on / off the first switching element 55 and the second switching element 57 in order to ensure necessary input power, as in the first embodiment. At this time, when the first switching element 55 is turned on, in the first embodiment, a current flows through the heating coil 59 and a part of the current is regenerated from the choke coil 72 to the first smoothing capacitor 71. Therefore, by adopting the configuration of the present embodiment, the rectifier circuit 52 works to prevent the regenerative current, so that the current is not regenerated in the first smoothing capacitor 71 and the input power is supplied to the heating coil 59 and the pan 61. Can be communicated to. The diode used in the rectifier circuit 52 is preferably a high-speed diode because high-frequency current passes therethrough.
[0057]
As described above, according to the present embodiment, since the current is not regenerated in the first smoothing capacitor 71, the input power is supplied to the circuit without waste, so that the induction heating device that can efficiently heat the aluminum pan is possible. Can be realized.
[0058]
(Examples related to the present invention)
An example related to the induction heating apparatus of the present invention will be described with reference to the drawings. FIG. 6 shows a circuit configuration of this example. The power source 51 is a commercial power source and is rectified by the rectifier circuit 52 and applied to the series circuit of the choke coil 80 and the transistor 87. The collector of the transistor 87 is connected to the anode of the diode 82, and the cathode of the diode 82 is connected to the high potential side of the smoothing capacitor 81. The low potential side of the smoothing capacitor 81 is connected to the negative electrode side of the rectifier 52.
[0059]
Reference numeral 79 denotes an inverter, and a series connection body of the choke coil 83 and the transistor 88 is connected to both ends of the smoothing capacitor 81. A series connection body of the heating coil 89 and the resonance capacitor 91 is connected to both ends of the transistor 88, and a series connection body of the resonance capacitor 92 and the relay 93 is connected in parallel to the resonance capacitor 91. The control circuit 85 drives the transistor 88 and inputs detection signals from the current transformer 67 that detects the input current from the power source 51 and the current transformer 94 that detects the current in the heating coil 89 to determine the material of the load pan 90. Load detection function. The control circuit 85 outputs a control signal or a drive signal to the boost control circuit 86, the relay 93, and the transistor 88 according to the detection result of the load detection function. The boost control circuit 86 outputs a drive signal for the transistor 87 based on the control signal from the control circuit 85.
[0060]
The operation of the above configuration will be described. The control circuit 85 performs on / off control of the transistor 87 so that the choke coil 80 functions as a step-up chopper. As a result, the output voltage Vdc of the rectifier 52 is boosted and smoothed across the smoothing capacitor 81 via the diode 82. This smoothed voltage serves as a supply source for supplying high frequency current of the inverter. The choke coil 83 is connected to the positive electrode of the rectifier 52 and is used for zero current switching when the transistor 88 is turned off.
[0061]
A diode 84 is connected to the transistor 88 in antiparallel, and is used to circulate the current when the resonance current flows in the opposite direction to the transistor 88. The transistor 88 generates a resonance current that resonates at a resonance frequency determined by the heating coil 89 and the resonance capacitor 91 when the transistor 88 is on, and supplies a high-frequency magnetic field to the pan 90.
[0062]
The control circuit 85 causes the transistor 88 to perform control according to input power using a microcomputer or the like. When the control circuit 85 determines that the pot 90 heated by the heating coil 89 is made of a material having high conductivity and low permeability such as aluminum by the load detection function, the drive control as shown in FIG. When the pot 90 is determined to be an iron-based pot, the relay 93 is turned on, and the drive control as shown in FIG.
[0063]
FIG. 7 is a diagram showing the waveform of each part in this example. Waveform (a) shows current waveform Ic flowing through transistor 88 and diode 84, waveform (b) shows voltage Vce generated between the collector and emitter of transistor 88, and waveform (c) shows current IL flowing through heating coil 89. A waveform (d) shows a drive waveform VGE given to the transistor 88 by the control circuit 85.
[0064]
The control circuit 85 gives a gate signal to the transistor 88 so that the transistor 88 is turned on. At this time, the resonance current generated by the heating coil 89 and the resonance capacitor 91 flows through the transistor 88. Here, since the frequency of the resonance current is at least twice as high as the drive frequency, the resonance current eventually becomes zero, and this time, the current flows through the diode 84 in the opposite direction. During this time, since a resonance current continues to flow through the heating coil 89, a high frequency magnetic field determined by the resonance frequency decision is supplied to the pan 90. That is, the same effect as that in the state of driving at a frequency that is twice or more the normal frequency can be obtained.
[0065]
Thereafter, after supplying necessary power, the control circuit 85 turns off the transistor 88 at the timing when the current flows through the diode 84, and after a certain period, the control circuit 85 is turned on again and repeats this.
[0066]
As shown in FIG. 8, when the material is an iron pan, the driving period (T ′) of the transistor 88 is a capacitance obtained by adding the capacitance of the resonance capacitor 92 to the inductance of the heating coil 89 and the capacitance of the resonance capacitor 91. The sum of the resonance period (T1 ′) and the idle period (T2 ′) determined by is set so that the frequency (1 / T ′) is normally 20 to 30 kHz in consideration of switching loss and the like.
[0067]
On the other hand, when the control circuit 85 determines that the pan 90 is made of a material such as aluminum, the resonance frequency is increased without adding the resonance capacitor 92 and the boosting level by the transistor 86 and the choke coil 80 is increased. increase.
[0068]
This is because the vibration of Ic in FIG. 7A does not decrease due to attenuation, and a resonance current is required as shown in FIG. 7 during the driving period (T) of the transistor 88 when the maximum output is set. The maximum output is obtained by continuing the amplitude with a predetermined amplitude or more for the wave number to be shortened and shortening the pause period T2.
[0069]
At this time, the resonance frequency determined by the inductance of the heating coil 89 coupled to the pan 90 and the capacitance of the resonance capacitor 91 is equal to or more than twice the operating frequency (1 / T ′) of the transistor 88, that is, two or more waveforms. The constant is such that it flows in a single switching operation. This is intended to generate heat using the feature that the skin resistance of the pan is proportional to the square root of the frequency when heating an aluminum pan, etc., and does not increase the skin resistance and increase the switching loss. In this way, heating of aluminum pans and multilayer pans is possible.
[0070]
As described above, according to this example, when the load 90 having high conductivity and low permeability is heated by the magnetic field generated by the heating coil 89, the resonance current flowing through the switching element 88 and the diode 84 causes the switching element 88 to drive. The resonance current is boosted by the choke coil 80, the switching element 87, the diode 82, and the boosting means, which are boosting means for boosting the DC voltage Vdc so as to continue the driving period. By providing a smoothing capacitor 81 which is a smoothing means for smoothing the voltage, the resonance current can be switched to zero current, the driving frequency of the switching element 88 is made lower than the resonance frequency, and zero current switching is performed. The aluminum pan reduces the switching loss and prevents the pot noise. In which it can be heated.
[0071]
In addition, the following induction heating cooking appliances are contained in this application. That is, a rectifier circuit connected in parallel to the power source, a first smoothing capacitor connected in parallel to the DC output terminal of the rectifier circuit, and one end thereof connected to the positive electrode side of the DC output terminal of the rectifier circuit A choke coil; a first semiconductor switching element having an emitter connected to the other end of the choke coil; a collector connected to the other end of the choke coil; and an emitter connected to the negative electrode side of the DC end. A second semiconductor switching element, a first diode connected in parallel to the first semiconductor switching element, a second diode connected in parallel to the second semiconductor switching element, and the second A heating coil and a resonant capacitor series circuit connected in parallel with each other and in series with each other, and the first half A second smoothing capacitor connected to the collector of the body switching element and the emitter of the second semiconductor switching element; and control means for controlling the first and second semiconductor switching elements so as to obtain a predetermined output. And an induction heating cooker.
[0072]
A filter capacitor connected in parallel to the power supply; a choke coil connected in series to the power supply; a rectifier circuit connected to the choke coil;
A first semiconductor switching element having an emitter connected to a positive electrode side of a DC output terminal of the rectifier circuit, a collector connected to a positive electrode side of the DC output terminal of the rectifier circuit, and a negative electrode side of the DC terminal; A second semiconductor switching element connected to an emitter; a first diode connected in parallel to the first semiconductor switching element; a second diode connected in parallel to the second semiconductor switching element; A heating coil and a resonance capacitor series circuit connected in parallel with each other and connected in series to the second semiconductor switching element, and connected to the collector of the first semiconductor switching element and the emitter of the second semiconductor switching element Second smoothing capacitor and the first and second semiconductor switching so as to obtain a predetermined output Induction heating cooker comprising a control means for controlling the child, the include.
[0073]
【The invention's effect】
  As described above, according to the present invention, an aluminum pan having a high heating efficiency with less noise generated by supplying a current with little change in amplitude to the heating coil and no noise is generated, and there is little loss of switching elements.It is an induction heating device that can heat an iron-based material pan without switching the number of turns of the heating coilCan be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of an induction heating apparatus in Embodiment 1 of the present invention.
FIG. 2 is a waveform diagram showing the operation of each part of the induction heating apparatus in Embodiment 1 of the present invention.
FIG. 3 is another waveform diagram showing the operation of each part of the induction heating apparatus in Embodiment 1 of the present invention.
FIG. 4 is a diagram showing input power control characteristics of the induction heating apparatus in Embodiment 1 of the present invention.
FIG. 5 is a diagram showing a circuit configuration of an induction heating device in a second embodiment of the present invention.
FIG. 6 is a waveform diagram showing the operation of each part of the induction heating apparatus in an example related to the present invention.
FIG. 7 is a diagram showing a circuit configuration of an induction heating device in an example related to the present invention.
FIG. 8 is a diagram showing waveforms of respective parts of the induction heating device in an example related to the present invention.
FIG. 9 is a diagram showing an example of a circuit configuration of a conventional induction heating device
FIG. 10 is a diagram showing an example of a circuit configuration of a conventional induction heating device.
FIG. 11 is a diagram showing waveforms of respective parts of a conventional induction heating apparatus.
FIG. 12 is a diagram showing waveforms of respective parts of a conventional induction heating device.
FIG. 13 is a diagram showing waveforms of respective parts of a conventional induction heating apparatus.
[Explanation of symbols]
50 inverter
51 AC power supply
52 Rectifier circuit
53 First smoothing capacitor
54 Choke coil (pressure booster)
55 1st switching element
56 First diode (first reverse conducting element)
57 Second switching element
58 Second diode (second reverse conducting element)
59 Heating coil
60 Resonant capacitor
61 Pan (load)
62 Second smoothing capacitor (smoothing means)
63 Control circuit
71 First smoothing capacitor
72 choke coil
80 choke coil
81 Smoothing capacitor
83 Choke coil
84 Diode (rectifier)
85 Control circuit
88 Switching element
89 Heating coil
90 pan (load)
91 Resonant capacitor

Claims (2)

A series connection body of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and a first connected in parallel to the second switching element A first reverse switching element, a heating circuit connected in parallel to the first switching element or the second switching element, and a resonance circuit including a resonance capacitor to input a DC voltage to the first switching element. An inverter that resonates by conduction between the first switching element and the second switching element, and a control circuit that exclusively controls conduction of the first switching element and the second switching element. When the magnetic field generated by the heating coil inductively heats a load having a high conductivity and a low magnetic permeability, The DC voltage to the resonant current in conjunction with the driving period resonate at a period shorter than the drive period of the switching element is to maintain resonance at a predetermined higher amplitude is higher than the peak value of the input DC voltage pulsating by boosting smoothing means the boosted and is smoothed is supplied to the inverter so, and the magnetic field generated by the heating coil, heating the load or load of a non-magnetic stainless steel iron, resonance current of the first switching element or the The DC voltage is boosted by the boosting smoothing means when the iron-type load or the non-magnetic stainless steel load is heated at the maximum output, and resonates at a cycle longer than the conduction period of the second switching element. current flows in the forward direction to the supplied, and the first switching element and the second switching element A resonance capacitor to enable blocking the switching element in timing, comprising switching to a larger capacity than the case of heating the load of the high conductivity and low permeability induction heating device. When starting with a resonant capacitor with a small capacity and gradually increasing the output, determine whether it is an iron-based load or a load with high conductivity and low permeability, and if it is determined to be an iron-based load After stopping driving, switch the resonance capacitor so that the capacity becomes large, re-drive the driving frequency at a low frequency, and if it is determined that the load has high conductivity and low magnetic permeability, continue the predetermined driving time The induction heating apparatus according to claim 1, wherein the drive time ratio is substantially fixed after the output is increased to a ratio or a predetermined output, and the conduction time is changed so that the output reaches the predetermined output.

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