JP3460997B2 - Induction heating device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker, an induction heating type water heater, and a humidifier capable of efficiently inductively heating an object to be heated having high conductivity and low magnetic permeability such as an aluminum pot. Alternatively, it relates to an induction heating device such as an iron.

[0002]

2. Description of the Related Art Conventionally, as an induction heating device of this type, for example, a technique for suppressing the noise of a pan when an aluminum pan is heated in an induction heating cooker and suppressing a reduction in power factor has been disclosed ( For example, a technique for suppressing switching loss and heating an aluminum pot with high frequency is disclosed (see, for example, Patent Document 2).

FIG. 9 is a circuit diagram showing the contents disclosed in Patent Document 1. In FIG. 9, the thyristor 3, the thyristor 4, the diode 5 and the diode 6 form a bridge circuit 2 which receives the voltage of the AC power supply 1 of 100V and rectifies it into a DC voltage. The thyristor 3 and the thyristor 4 control the conduction angle to reduce the DC power supply voltage of the inverter to about 20 V at the time of starting the inverter and set the output power to a low value so that the load detection means 24 has an appropriate heated object. The output control circuit 26 operates when the judgment is made, and thereafter, the output is changed by changing the DC voltage.

Further, the input waveform shaping means 23 drives 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, thereby increasing the power factor. Be improved.
This is done by the action that the choke coil 8 stores energy in the choke coil 8 when the transistor 10 is turned on and releases the energy to the capacitor 11 via the diode 9 when the transistor 10 is turned off.

In order to heat the aluminum pot,
The frequency of the current of the heating coil 18 is 20 kHz to 50 k
Switch to Hz. This is performed by changing the number of turns of the heating coil 18 and the capacity of the resonance capacitor 19.

However, in the above-mentioned conventional technique, in order to heat the aluminum pot and the iron pot, it is necessary to switch the number of windings of the heating coil, which is structurally complicated and burdens the cost. In order to set the frequency to 50 kHz, the drive frequencies of the switching elements 15 and 17 also need to be set to the same frequency (50 kHz), resulting in a large switching loss, and if the resonance point tracking method is adopted to reduce the switching loss, However, there is a problem that the control circuit and the power supply voltage changing means for changing the output are required.

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.

The feature of this technique is that the current transformer 30 for detecting the current flowing to the heating coil 18 receives a signal, and the resonance current formed by the heating coil 18 and the resonance capacitor 19 is higher than the drive signal of the transistors 15 and 17. By setting the frequency of 2 times or more,
While suppressing the switching loss of the transistors 15 and 17, the frequency supplied to the heating coil can be increased to heat the aluminum pot.

In the output control method shown by the waveform in FIG. 11, when the power is small, the transistor 15 turns off when the current reaches the zero point for the first time, and the transistor 17 turns the current for the third time. It is controlled to turn off when it reaches. When the power is large, the transistor 15 is turned off when the current reaches the zero point for the second time, and the transistor 17 is turned off when the current reaches the second time.

In the output control method shown in FIG. 12, when the power is small, the transistor 15 turns off after t1 time (time shorter than 1/2 cycle of the resonance current) after conduction, and the transistor 17 turns off the current. It is controlled so that it turns off at the time of reaching the zero point for the third time and reaching the zero point. When the power is large, the transistor 15 is turned off when the current reaches the zero point for the first time and reaches the zero point (1/2 cycle of the resonance current),
The transistor 17 is controlled so as to turn off when the current reaches the third time.

[0011]

[Patent Document 1] Japanese Patent Laid-Open No. 1-248783

[Patent Document 2] Japanese Patent Laid-Open No. 2001-160484

[0012]

The conventional induction heating device as described in Patent Document 2 has a problem that the output cannot be continuously adjusted by the control method shown in FIG. The control method has a problem that a change in the output with respect to a change in the conduction time becomes too large and a delicate output cannot be controlled. In addition, since the envelope of the current of the heating coil 18 is not smoothed by any of the control methods, a problem that a roaring sound generated at a frequency twice the commercial frequency is generated from the pan (hereinafter referred to as a pan noise) is a problem. There was also. As a method for preventing the noise of the pot, the above Patent Document 1
Although the technology described in can be considered, this technology
This is a method of adjusting the output by lowering the input power source of the inverter, and even if this method and the method described in the above-mentioned special reference 2 are combined, the resonance current is attenuated and does not continue, so sufficient output control is possible. could not.

The present invention solves the above-mentioned problems. It suppresses the switching loss of the switching element of the inverter without generating the ringing noise of the pot, and outputs the aluminum pot with a sufficiently large output continuously and with good controllability. It is an object of the present invention to provide an induction heating device capable of controlled heating.

[0014]

In order to solve the above-mentioned problems, the induction heating device of the present invention uses a switching element or reverse conduction when a magnetic field generated by a heating coil induces heating of a load having high conductivity and low magnetic permeability. The resonance current flowing through the element resonates in a cycle shorter than the driving period of the switching element, and the DC voltage is boosted by the step-up smoothing means in order to maintain the resonance current at the amplitude of a predetermined magnitude or more during the driving period. By being smoothed and supplied to the inverter, the drive frequency of the switching element is lowered to suppress the switching loss of the switching element, and the heating coil is supplied with a resonance current having a frequency higher than the drive frequency of the switching element. , A load of high conductivity and low magnetic permeability such as aluminum can be heated with high output.

Further, in the case of heating the load of high conductivity and low permeability, the pulse DC voltage inverter inputs
Boosted so that it is higher than the peak value of the input DC voltage.
And a control circuit with a step-up smoothing means for smoothing
Is the resonance current after starting the driving of the first switching element.
It has reached the second cycle since it started flowing into the first switching element.
After that, current flows through the first switching element.
Drives the first switching element within the specified period
Since a signal for stopping the output of the switching element is output, the driving period of the switching element is changed while the resonance current is generated for one cycle or more during the driving period to stably control the output.
Alternatively, it becomes possible to perform control so that the duty of the switching element (generation of turn-on loss) is not increased.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a series connection body of a first switching element and a second switching element, and a first reverse conducting element connected in parallel to the first switching element. A resonant circuit including a second reverse conducting element connected in parallel to the second switching element, a heating coil connected in parallel to the first switching element or the second switching element, and a resonance capacitor. And an inverter that receives a DC voltage and resonates due to conduction between the first switching element and the second switching element, and exclusively controls conduction between the first switching element and the second switching element. A resonance circuit that flows through the first switching element or the first reverse conducting element, and the magnetic field generated by the heating coil has a high conductivity. By the DC voltage boosted smoothing means to maintain the resonance in amplitude the resonance current is equal to or larger than the predetermined in the driving period with resonate at a period shorter than the drive period of the first switching element to induce heating load of the permeability Higher than the peak value of pulsating input DC voltage
Ri boosted and is smoothed name is supplied to the inverter so that the control circuit, the first switching
After the driving of the switching element is started, the resonance current is changed to the first switch.
After reaching the second cycle after starting to flow to the ching element
There is a current flowing through the first switching element.
The drive of the first switching element is stopped within the period.
By outputting a signal to stop the switching element, the driving frequency of the switching element is reduced to suppress the switching loss of the switching element, and the heating coil is supplied with a resonance current having a frequency higher than the driving frequency of the switching element, so that the aluminum It is possible to heat a load having high conductivity and low magnetic permeability with high output. In addition, since there are a plurality of switching elements as compared with a single switching element, the duty of the switching elements is reduced, and the output control can be finely adjusted according to the load by changing the drive time ratio or the drive frequency.

Further, when heating a load having high conductivity and low magnetic permeability, the peak value of the input DC voltage of the pulsating current
As it is also high, and boosts the DC voltage inverter inputs and with formed by providing a step-up smoothing means for smoothing,
After the control circuit starts driving the first switching element,
2 laps after the oscillating current begins to flow in the first switching element
After reaching the first period, the first switching element
The first switching element in the period in which the current flows
Since the signal for stopping the driving of the child is output , the driving period of the switching element is changed to stably control the output while the resonance current is generated for one cycle or more during the driving period of the switching element, or The responsibility of the switching element (the occurrence of turn-on loss) can be controlled without increasing it.

According to a second aspect of the present invention, in particular, the control circuit has a resonance current after the driving of the first switching element is started.
By heating output obtained by varying the <br/> which varying smoking a driving stop timing of the first switching element in later reached the second cycle from the start to flow to the first switching element, made of aluminum The pan can be induction-heated with a high output, a large output variable range can be obtained, and the output can be controlled by continuously increasing and decreasing to finely control the output according to the load.

According to the third aspect of the present invention, in particular, in the step-up smoothing means, the driving period of the second switching element becomes long.
By greatly changing the boosting action , it is possible to improve the controllability of the output by simultaneously changing the driving period and the boosting level.

The invention according to claim 4 is the first switch.
A series connection of the switching element and the second switching element, and
The first reverse connected in parallel with the first switching element.
Connected in parallel with the conduction element and the second switching element
Second reverse conducting element and the first switching element
Connected in parallel to the child or the second switching element
With a heating coil and a resonant circuit including a resonant capacitor
DC voltage is input to the first switching element and the second switching element.
Inverter that resonates due to conduction of switching elements
And the first switching element and the second switch
And a control circuit for exclusively controlling conduction of the switching element,
The first switching element or the first reverse conducting element
The resonance current flowing in the
When a load having high conductivity and low magnetic permeability is induction-heated, the first
Resonates in a cycle shorter than the driving period of the switching element
Along with the driving period, the resonance current is more than a predetermined value.
The DC voltage is boosted and smoothed to maintain resonance at the amplitude of
Boosted and smoothed by the
In addition, the step-up smoothing means includes a second smoothing capacitor connected in parallel with a series connection body of the first switching element and the second switching element, and a choke connected in series with the second switching element. A coil, and stores energy in the choke coil by conduction of the second switching element.
By switching off the switching element of the
By moving to the second smoothing capacitor via the reverse conducting element of, the envelope of the DC voltage of the pulsating current input to the choke coil is smoothed and boosted, and The smoothed DC power can be stored in the smoothing capacitor and can be supplied to the resonant circuit including the first and second switching elements as a power source. It was but <br/>, those that can be achieved in a stable manner and a simple circuit configuration the induction heating device.

According to a fifth aspect of the invention, in particular, the resonance current flowing through the second switching element or the second reverse conducting element induces a load whose magnetic field generated by the heating coil has high conductivity and low magnetic permeability. resonates with a period shorter than the drive period of the second switching element on heating Ri Na, the said control circuit
After starting driving the second switching element,
After the oscillating current begins to flow in the second switching element
The second switch after the second cycle is reached
During the period when current is flowing through the switching element, the second switch
By outputting the signal for stopping the driving of the switching element, it becomes easy to increase the frequency of the resonance current while equalizing the duty with the first switching element , and at the same time
In the case of the structure according to claim 4, since the driving period of the second switching means is longer than the cycle of the resonance current, the energy accumulated in the choke coil is increased and the boost level can be increased. peak value of the resonance current flowing through the first switching element is one that can be easily realized Udo operation have to be so as not zero during the driving period of the first switching element.

According to the sixth aspect of the present invention, in particular, the first smoothing capacitor that gives energy to the choke coil by the conduction of the second switching element is provided.
By bypassing the current when energy is stored in the choke coil, it is possible to suppress the high frequency noise from leaking to the input power source side as conduction noise.

[0023]

First Embodiment A first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the circuit configuration of the induction heating apparatus of this embodiment. The power source 51 is a low frequency AC power source 20
It is a 0V commercial power source and is connected to the input terminal of the rectifier circuit 52 which is a bridge diode. The first smoothing capacitor 53 is connected between the output terminals of the rectifier circuit 52. Rectifier circuit 5
The choke coil 54 and the second
The switching element 57 is connected in series. The heating coil 59 is an aluminum pan 61 which is an object to be heated.
It is arranged opposite to.

Reference numeral 50 is an inverter, and the low potential side terminal (emitter) of the second smoothing capacitor 62 is a rectifier circuit 52.
Connected to the negative electrode terminal of the second smoothing capacitor 62, and the high potential side terminal of the second smoothing capacitor 62 is connected to the first switching element (IGBT) 55.
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 choke coil 54 and the second switching element (IGBT) 57.
Is connected to the connection point with the high potential side terminal (collector).
A series connection body of the heating coil 59 and the resonance capacitor 60 is connected in parallel to the second switching element 57.

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). , The second diode 5
8 (second reverse conducting element) is the second switching element 57.
Are connected in anti-parallel to. The snubber capacitor 64 is the second
Is connected in parallel to the switching element 57. A series connection body of the correction resonance capacitor 65 and the relay 66 is connected in parallel to the resonance capacitor 60. The control circuit 63
Current transformer 6 that detects the input current from the power supply 51
7 and the detection signal of the current transformer 68 which detects the current of the heating coil 59, and signals to the gates of the first switching element 55 and the second switching element 57 and the drive coil (not shown) of the relay 66. Is output.

The operation of the induction heating device constructed as above will be described below. The power supply 1 is full-wave rectified by the rectifier circuit 52 and supplied to the first smoothing capacitor 53 connected to the output terminal of the rectifier circuit 52. The first smoothing capacitor 53 works as a supply source for supplying a high frequency current to the inverter.

FIG. 2 is a diagram showing waveforms at various points in the above circuit, and FIG. 2 (A) shows a case where the output is a large output of 2 kW. FIG. 3A shows the first switching element 55.
And the current waveform Ic1 flowing through the first diode 56,
The figure (b) shows the current waveform Ic2 flowing through the second switching element 57 and the second diode 58, and the figure (c) shows the voltage Vce2 generated between the collector and the emitter of the second switching element 57. (D) shows the drive voltage Vg1 applied to the gate of the first switching element 55, (e) shows the drive voltage Vg2 applied to the gate of the second switching element 57, and (f) shows the heating coil 59. Each of the flowing currents IL is shown.

When the output is 2 kW (FIG. 2 (A)), the control circuit 63 causes the gate of the second switching element 57 to have a driving period T for the period from time t0 to time t1 as shown in (e).
An ON signal of 2 (about 24 μsec) is output. During the driving period T2, the second switching element 57 and the second switching element 57
The diode 58, the heating coil 59, and the resonance capacitor 60 resonate in a closed circuit, and the resonance cycle (1 / f) when the pot 61 is an aluminum pot is about 2/3 of the driving period T2. The number of turns of the heating coil 59 (40T), the capacity of the resonance capacitor 60 (0.04 μF), and the driving period T2 are set so as to double (about 16 μsec).
The choke coil 54 has the second switching element 57.
In the driving period T2 of, the electrostatic energy of the smoothing capacitor 53 is stored as magnetic energy.

Next, at time t1 which is the timing between the second peak of the resonance current flowing through the second switching element 57 and the resonance current next becoming zero, that is, in the forward direction of the second switching element 57. The driving of the second switching element 57 is stopped when the collector current is flowing.

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 this potential becomes the potential of the second smoothing capacitor 62. When it exceeds, the second smoothing capacitor 62 is charged through the first diode 56, and the magnetic energy stored in the choke coil 54 is released. The voltage of the second smoothing capacitor 62 is the peak value of the DC output voltage Vdc of the rectifier 52 (28
The voltage is increased to be higher than 3 V (500 V in this embodiment). The boosted level depends on the conduction time of the second switching element 58, and if the conduction time becomes longer, the second
The voltage generated in the smoothing capacitor 62 tends to increase.

In this way, the second smoothing capacitor 62-
By boosting the voltage level of the second smoothing capacitor 62 that functions as a DC power source when resonating in the closed circuit formed by the first switching element 55 or the first diode 56-heating coil 59-resonance capacitor 60. ,
The first switching element 55 shown in (a) of FIG.
The peak value (peak value) of the resonance current flowing through the second switching element 57 and the peak value of the resonance current flowing through the second switching element 57 in FIG. In addition, the pan made of aluminum can be induction-heated with a high output, and the output can be continuously increased or decreased so as not to be reduced.

Then, as shown in (d) and (e) of FIG. 2A, the control circuit 63 is provided after the idle period provided to prevent simultaneous conduction of both switching elements from the time t1. At time t2, the drive signal is output to the gate of the first switching element 55. As a result, the heating coil 59-resonance capacitor 60 as shown in FIG.
Resonance current flows by changing the path to a closed circuit composed of the first switching element 55 or the first diode 56 and the second smoothing capacitor 62. In this case, the driving period T2 of this driving signal is set to substantially the same period as T1. Therefore, as in the case where the second switching element 58 is conducting, it is about 2/3 of the driving period T1. A periodic resonant current flows.

Therefore, the current IL flowing through the heating coil 59
Has a waveform as shown in (f) of FIG.
The driving cycle of the second switching element (the sum of T1 and T2 and the rest period) is about three times the cycle of the resonance current.
If the second drive frequency is about 20 kHz, the frequency of the resonance current flowing through the heating coil 59 is about 60 kHz.

FIG. 3 shows the voltage waveform of the commercial power source 51 (a).
Further, the voltage Vce2 applied to the series connection body of the heating coil 59 and the resonance capacitor 60 is shown in (b), and the waveform (c) shows the current IL flowing in the heating coil 59. As described above, the output voltage of the rectifier 52 by the second smoothing capacitor 62 is a pulsating current waveform obtained by full-wave rectifying the commercial power supply shown in FIG. 3A, while the envelope of the current flowing through the heating coil 59. Since the line is smoothed as shown in FIG. 3 (c), the pan noise that occurs at a frequency twice as high as the commercial power supply frequency, which is caused by the heating coil current of the conventional example shown in FIG. 13 (c), can be suppressed. become.

In the waveform of FIG. 2B, the output is low 4
It is for 50W. 2 (B) (a ')-
(E ') is a waveform corresponding to (a) to (e) of FIG. The output power is controlled as shown in FIG.
The drive time (T1 ′) of the first switching element 55 and the drive time (T2 ′) of the second switching element 57 are set to 2
This is performed by making each drive time T1 and T2 at the time of kW output shorter.

In FIG. 2A, the first diode 5
When the second switching element 58 is turned on at the time when the current flowing through 6 reaches a peak (time t5 in FIG. 2A), the output power becomes the minimum output power or a value close to it. On the other hand, the first switching element 56 is turned off at the time (not shown) at which the resonance becomes zero again after the second switching element 56 starts to flow (at the time indicated by t6 in the figure). When the second switching element 58 is controlled to be turned on, the maximum output power can be obtained (resonance point power control).

When the output setting is 450 W which is a low output, the driving time (T1 ') is set to the maximum output setting of 2 kW as shown in (a') of FIG. Although it is shorter than that at the time, the first switching element 55 is turned off at the time point (t3 ′) when the forward current flows through the first switching element 55.

By doing so, the first switching element 5 is set regardless of whether the maximum output is set or the low output is set.
In accordance with the turn-off of No. 5, the energy stored in the heating coil 59 resonates with the snubber capacitor 64 to lower the collector potential of the first switching element 55 and to gently increase the voltage between the collector and emitter of the first switching element 55 for switching. The loss can be reduced.

As a result, the voltage is not applied in the forward direction at the time of turning on the second switching element 57 which is to be turned on continuously, or the level thereof is made small even if it is applied to suppress the turn-on loss or at the time of turning on. Noise can be prevented, and the turn-off loss of the first switching element 55 can be reduced.

Next, at the time of start-up, the control circuit 63 turns off the relay 66 and sets the constant frequency (about 21 kHz).
In z), the first switching element 55 and the second switching element 57 are alternately driven. The drive period of the first switching element 55 is driven in a mode shorter than the resonance cycle of the resonance current, the drive time ratio is minimized, and the drive time ratio is gradually increased after the output is minimized. 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, it stops heating and then turns on the relay 66,
Start heating again at low power. At this time, the control circuit 63
Causes the first switching element 55 and the second switching element 57 to start again from the minimum output at the constant frequency (about 21 kHz) at the minimum drive time ratio and gradually increase to the predetermined output.

On the other hand, when it is not detected that the load is an iron-based load, when the predetermined drive time ratio is reached, the resonance current of the resonance current is changed from the drive period of the first switching element 57 as shown in FIG. 2B. Move to short cycle mode. At this time, the driving period is set so that the output is in the low output state.

FIG. 4 shows the first switching element 55 and the second switching element 55.
The drive frequency of the switching element 57 of is constant (20 kHz
It is a figure which shows the relationship of the ON time of the 2nd switching element 57 at the time of z), and input electric power. As shown in this figure, in the present embodiment, about 2 kW is around ½ of the cycle.
Heating output is obtained, and the output can be linearly reduced by shortening the driving period of the second switching element from the peak in the vicinity thereof. Therefore, as shown in FIG. 4, the lower limit Tonmi of the limiter for the drive time or the drive time ratio is
If n and the upper limit Tonmax are set, stable control can be performed.

As described above, according to the present embodiment, when a load having a high conductivity and a low magnetic permeability 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 are heated. Since the resonance current due to the heating coil 59 and the resonance capacitor 60 flowing through 56 resonates in a cycle shorter than the driving period (T1) of each switching element, a frequency higher than the driving frequency of the first switching element 55 (this implementation). An electric current of 1.5 times) is supplied to the heating coil 59 to heat it, and a choke coil 54 as a boosting means and a second smoothing capacitor 62 as a smoothing means are further provided so that a high frequency power supply can be used. The voltage of a certain smoothing capacitor 62 is boosted and smoothed, and the amplitude of the resonance current is increased in each driving period (T and T ′). After the start, the first cycle ends after the resonance current begins to flow, and the resonance current with a sufficiently large amplitude is continued after reaching the second cycle, and the drive stop timing of each switching element is changed after the second cycle. By doing so, a large variable range of output can be obtained.

Further, the choke coil 54 which is a step-up means.
Is obtained by changing the boosting level in association with the driving period of the second switching element 58, that is, the second
When the conduction time of the switching element 57 becomes long, for example, the boosting action of the choke coil 54 becomes large and the voltage of the smoothing capacitor 62 as the smoothing means becomes high, so that it can be used for output control.

Further, the boosting means 54 moves the energy accumulated in the choke coil 54 due to the conduction of the second switching element 57 to the second smoothing capacitor 62 via the first diode 56. With a simple configuration, a pulsating input DC voltage can be smoothed into a high-voltage power supply, and based on this power supply, a high-frequency current with a smoothed envelope is converted and supplied to the heating coil 59. The sound can be suppressed.

Further, the resonance current flowing through the second switching element 57 or the second diode 58 is the second when the load of high conductivity and low permeability such as aluminum or copper is heated by the magnetic field generated by the heating coil 59. Of the first switching element 55 or the first switching element 57 by resonating in a cycle shorter than the driving period (T2) of the switching element 57 of
In addition to the resonance current flowing through the diode 56 of
Also, the wave number of the resonance frequency within the drive cycle of the second switching element can be increased.

When the second switching element 57 is turned on, the first choke coil 54 is energized by the first energy.
By having the smoothing capacitor 53, it is possible to suppress the high frequency component from leaking to the power supply 51 when the energy is stored in the choke coil 54.

Further, when the maximum output is set, the control circuit 63 causes the first switching element 55 to have a resonance current after the second cycle after the driving of the first switching element 55 is started.
A signal for cutting off the conduction of the first switching element 55 is output within the period of flowing into the second switching element 57, or the resonance current after the driving of the second switching element 57 is started after the second cycle and the second Since the signal that cuts off the conduction of the second switching element is output during the period when the current flows through the switching element 57, the turn-on loss of the second switching element 57 or the first switching element 55 at the maximum output increases. Can be suppressed.

Further, when the maximum output is set, the control circuit 63 allows the first switching element 55 to drive the first switching element 55 before the resonance current passes through the peak phase after the second cycle and reaches the zero point. A signal for shutting off 55 is output, or the first switching element 55 is turned on until the resonance current after the start of driving the second switching element 57 passes the peak phase after the second cycle and reaches the zero point. By outputting a signal to cut off, the occurrence of turn-on loss of the second switching element 57 or the first switching element 55 at the time of maximum output is suppressed, and
The output can be reduced by shortening the driving period thereof, and the turn-on loss of each switching element is unlikely to occur even if the output is low.

The first switching element 55 and the second switching element 55
When the ratio of the conduction period of the switching element 57 is set to about 1 and the load of high conductivity and low magnetic permeability is heated by the magnetic field generated by the heating coil 59, the load flows to the first switching element 55 and the first diode 56. Since the resonance current resonates at a period that is approximately ⅔ times the driving period of the first switching element 55, three resonance currents are generated during the driving period of the first switching element 55 and the second switching element. The wave number of the current can be generated, and the high frequency current of about three times the driving frequency can be supplied to the heating coil 59, and the driving of the first switching element 55 causes the current to flow through the first diode 56. The driving can be stopped at the timing when a current flows in the first switching element 55 in the forward direction, and the driving can be stopped at the timing when the second switching is performed. Control can be similar to stable for the child 57 and the second diode 58.

At the time of startup, the first switching element 5
The load detection can be facilitated by changing the driving time ratio of the switching element 57 and the second switching element 57 to increase the heating output and changing the driving frequency from the middle to increase the heating output. That is, by changing the drive time ratio, it is possible to monotonically change the output in a low output state under a load of a material such as aluminum having high conductivity and low magnetic permeability or an iron-based load. Can be done accurately and in a low output state. Further, after reaching a predetermined drive time ratio, drive time or heating output, the drive time ratio is kept constant so that the switching element can be driven and cut off in a specific phase range in the case of a load having high conductivity and low magnetic permeability. By changing the cut-off phase and changing the drive frequency, it is possible to suppress a sudden increase in the loss of the switching element and change the output.

At the time of startup, the first switching element 5
The driving time of No. 5 is shorter than the resonance cycle of the resonance current, the heating time is increased by changing the driving time ratio of the first switching element 55 and the second switching element 57, and a predetermined driving time or a predetermined driving time. When the ratio is reached, the drive period of the first switching element 55 is discretely changed to be longer than the cycle of the resonance current and low output, and then the drive period is gradually shortened to reduce the heating output to a low output value. To a predetermined output value, it is possible to accurately and stably determine whether the load 61 has a high conductivity and a low magnetic permeability by the time the predetermined drive time or the predetermined drive time ratio is reached. When 61 is a load having high conductivity and low magnetic permeability, it is possible to lengthen the driving period discretely to shift to a low output state and stably increase to a predetermined value from the low output state. It is.

When the iron-based load or the non-magnetic stainless load 61 is heated by the magnetic field generated by the heating coil 59, the resonance current has a cycle 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 to the maximum output, the current flows in the first switching element 55 and the second switching element 57 in the forward direction. The resonance capacitor for correction 65 is connected in parallel to the resonance capacitor 60 so that the switching element can be cut off, and the capacitance is switched to a larger capacity than that when heating a load having high conductivity and low magnetic permeability. The capacitor 60 and the correction capacitor 64 are connected in series with the heating coil 59 and are capable of switching their capacities. When the load or the load made of non-magnetic stainless steel is heated, the resonance capacitor 60 is switched to a larger capacity than that when a load having high conductivity and low magnetic permeability is switched, so that the resonance frequency becomes longer and the current flows. Since the DC voltage Vdc is boosted by the choke coil 54, the amplitude of the resonance current is increased, so that the maximum output within the range in which the switching element can be interrupted at the timing when the current flows in the forward direction in the switching element. Is set 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-based pot and an iron-based pot are to be heated by the same inverter, conventionally, the number of turns of the heating coil 59 and the resonance capacitor are simultaneously switched so that the resonance frequency and the magnetic field radiated to the object to be heated 61 are radiated. Although the strength (ampere turn) of the resonance coil 60 is switched, the operation of switching the number of coil turns can be replaced by the boosting effect of the choke coil 54 and the first switching means 57. There is an effect that the objects to be heated of a wide range of materials can be heated by switching the above.

Further, the correction resonance capacitor 65 is started without being connected to the resonance capacitor 60, that is, it is started by the resonance capacitor 60 having a small capacity, and the output is gradually increased. If it is determined that the load is iron-based, it is determined that the load is iron-based, and after driving is stopped, the relay 60 is turned on and the correction resonance capacitor 65 is connected in parallel. That is, since the resonance capacitor 60 is switched to have a large capacity and the drive frequency is re-driven at a low frequency, the resonance frequency becomes longer and the current increases, and further, the choke coil 54 and the second smoothing capacitor as the boosting means. Since the DC power supply voltage is boosted by 62, the resonance current value increases, so
In order to suppress an increase in switching loss at the time of turning on the switching element 57 by setting the maximum output within a range in which the switching element can be interrupted at the timing when the current flows in the switching element 55 and the forward direction,
The maximum output can be made larger than that of the conventional configuration.

When it is determined that the load has high conductivity and low magnetic permeability, the output is continuously increased to a predetermined drive time ratio or a predetermined output, and then the drive time ratio is fixed to reduce the conduction time. Since the output is changed to reach a predetermined output, so-called soft start that starts at a low output for any load to judge the load and stably reaches a predetermined output value or limit value It becomes possible to operate.

In FIG. 1, the capacitance ratio 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 becomes high. In this case, a choke coil may be inserted in the power supply line on the input side of the first smoothing capacitor 53. On the contrary, if the former is set to about 10 microfarads and the latter is set to about 100 microfarads, the reduction of the power factor can be suppressed, but the latter may be expensive since it requires a large withstand voltage.

Further, in FIG. 1, the second smoothing capacitor 62 may connect 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. However, the same effect can be obtained.

Further, the low potential side terminal of the resonance 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 of the first switching element 55. And the second switching element 5
The same operation is performed even when simultaneously connected to the low potential side terminal (emitter) of 7. The resonance circuit connected in parallel to the first switching element 55 or the second switching element 57 is not limited to that of this embodiment, and the technique of this embodiment can be applied as appropriate.

Although the induction heating cooker has been described in the above embodiment, it can be applied to other types of induction heating devices such as an iron and a water heater for heating a material having high conductivity and low magnetic permeability such as aluminum.

(Second Embodiment) 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 the circuit configuration of this embodiment. The first embodiment is different from the configuration of the first embodiment in the first
The smoothing capacitor 71 and the choke coil 72 of the power source 5
1 and the rectifier circuit 52.

The operation of this embodiment will be described. Reference numeral 50 denotes an inverter, and the operation of the control circuit 63 is the same as in the first embodiment, in which the first switching element 55 and the second switching element 57 are alternately turned on and off in order to secure necessary input power.
Turn off. At this time, the first switching element 55
When the switch 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 this embodiment, the rectifier circuit 5
Since 2 works so as to block the regenerative current, the current is not regenerated in the first smoothing capacitor 71, and the input power can be transmitted to the heating coil 59 and the pan 61.
Since a high frequency current passes through the diode used in the rectifier circuit 52, a high speed diode is desirable.

As described above, according to the present embodiment, since the current is not regenerated in the first smoothing capacitor 71 and the input power is supplied to the circuit without waste, it is possible to efficiently heat the aluminum pot. The induction heating device can be realized.

(Embodiment 3) A third embodiment of the induction heating apparatus of the present invention will be described with reference to the drawings. FIG. 6 shows the circuit configuration of this embodiment. The power supply 51 is a commercial power supply, is rectified by the rectification circuit 52, and is 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 side of the rectifier 52.

Reference numeral 79 is an inverter, and the 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. Control circuit 85
Loads the detection signal from the current transformer 67 that detects the input current from the power supply 51 and the current transformer 94 that detects the current in the heating coil 89 while driving the transistor 88, and determines the material of the load pan 90. Have a function. Then, the control circuit 85, in accordance with the detection result of the load detection function, the boost control circuit 86, the relay 93,
A control signal or a drive signal is output to the transistor 88. The boost control circuit 86 outputs a drive signal for the transistor 87 based on the control signal from the control circuit 85.

The operation of the above configuration will be described. The control circuit 85 controls on / off of the transistor 87 so that the choke coil 80 functions as a step-up chopper. As a result, the output Vdc of the rectifier 52 is boosted and a smoothed voltage is applied across the smoothing capacitor 81 via the diode 82. This smoothed voltage acts as a supply source for supplying the high frequency current of the inverter. The choke coil 83 is connected to the positive electrode of the rectifier 52 and is connected to the transistor 88.
Is used for zero current switching at turn-off.

The transistor 88 has a diode 8
4 are connected in anti-parallel and are used to circulate the resonant current when it flows in the opposite direction of 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 in the ON state, and supplies a high frequency magnetic field to the pan 90.

The control circuit 85 uses a microcomputer or the like to control the transistor 88 according to the input power. When the control circuit 85 determines that the pot 90 heated by the heating coil 89 by the load detection function is made of a material such as aluminum having high conductivity and low permeability, the relay 93 is used.
When the pot 90 is judged to be an iron pot, the relay 93 is turned on and the capacity of the resonance capacitor 91 is increased, as shown in FIG. The maximum output is obtained by performing such drive control.

FIG. 7 is a diagram showing waveforms at various points in this embodiment. The waveform (a) shows the current waveform Ic flowing through the transistor 88 and the diode 84, the waveform (b) shows the voltage Vce generated between the collector and the emitter of the transistor 88, and the waveform (c) shows the current IL flowing through the heating coil 89. The waveform (d) is shown in FIG.
8 shows the drive waveform VGE given to the No. 8.

The control circuit 85 supplies a gate signal to the transistor 88 to make the transistor 88 conductive. At this time, the resonance current generated in the heating coil 89 and the resonance capacitor 91 flows in the transistor 88. Here, since the frequency of the resonance current is more than twice as high as the drive frequency, the resonance current eventually becomes zero, and this time the diode 84
Through, the current will flow in the opposite direction. During this time, the resonance current continues to flow in the heating coil 89, so that the pan 90 is supplied with the high-frequency magnetic field determined by the resonance frequency determination. That is, the same effect as in the case of driving at a frequency twice or more the normal frequency can be obtained.

Then, after supplying the necessary power, the control circuit 85 turns off the transistor 88 at the timing when the current is flowing through the diode 84, and after a certain period of time, turns on again and repeats this.

As shown in FIG. 8, when the material is an iron-based pot, the driving period (T ') of the transistor 88 is the inductance of the heating coil 89 and the capacitance of the resonance capacitor 91, and the capacitance of the resonance capacitor 92. The sum of the resonance period (T1 ′) and the rest period (T2 ′) determined by the added capacitance is the frequency (1 /
T ') is usually set to 20 to 30 kHz.

On the other hand, when the control circuit 85 determines that the pot 90 is made of a material such as aluminum, the resonance capacitor 92 is not added, the resonance frequency is increased, and the transistor 86 and the choke coil 80 are used. Increase boost level.

This is because the oscillation of Ic in FIG. 7 (a) is not reduced by the attenuation so that the resonance current as shown in FIG. 7 is generated during the driving period (T) of the transistor 88 at the maximum output setting. Is continued at a predetermined amplitude or more for the required wave number, and the rest period is shortened to obtain the maximum output.

At this time, the heating coil 8 combined with the pan 90
The resonance frequency determined by the inductance of 9 and the capacitance of the resonance capacitor 91 is the operating frequency of the transistor 88 (1 /
T ') is twice or more, that is, a constant such that two or more resonance currents flow in one switching operation.
This is intended to generate heat by using the characteristic 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. This makes it possible to heat aluminum pans and multi-layer pans in this way.

As described above, according to the present embodiment, when the load 90 having high conductivity and low magnetic 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 is switched. A choke coil 80, a switching element 87, a diode 82, and a booster, which is a booster that boosts the DC voltage Vdc so that the resonance current resonates in a cycle shorter than the drive period of the element 88 and the drive current continues for the drive period. Smoothing capacitor 8 which is a smoothing means for smoothing the voltage boosted by the means.
By providing 1, the resonance current can be zero-current switched, the drive frequency of the switching element 88 can be lower than the resonance frequency, and the zero-current switching can be performed to reduce the switching loss. , It is possible to prevent the noise of the pot and heat the aluminum pot.

The present application includes the following induction heating cooker. That is, a rectifier circuit connected in parallel to a power source, a first smoothing capacitor connected in parallel to the DC output end of the rectifier circuit, and one end of which is connected to the positive electrode side of the DC output end of the rectifier circuit. A choke coil, a first semiconductor switching element having the 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 resonance capacitor series circuit connected in parallel with each other and connected 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 a control means for controlling the first and second semiconductor switching elements so as to obtain a predetermined output. And an induction heating cooker including.

Further, 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, and a positive electrode side of the DC output terminal of the rectifier circuit. A first semiconductor switching element having its emitter connected, and a second semiconductor switching element having its collector connected to the positive electrode side of the DC output terminal of the rectifier circuit and its emitter connected to the negative electrode side of the DC terminal. 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 connected in parallel to the second semiconductor switching element. The series connection of the heating coil and the resonance capacitor series circuit, and the core of the first semiconductor switching element. And a second smoothing capacitor connected to 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. A heating cooker is included.

[0079]

As described above, according to the present invention, a heating coil is supplied with a current with a small change in amplitude, so that a pan noise does not occur and the noise is small, and the switching element loss is small and the heating efficiency is high. An induction heating device capable of heating an aluminum pot can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an induction heating device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing the operation of each part of the induction heating device in Embodiment 1 of the present invention.

FIG. 3 is another waveform diagram showing the operation of each part of the induction heating device in Embodiment 1 of the present invention.

FIG. 4 is a diagram showing an input power control characteristic of the induction heating device according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a circuit configuration of an induction heating device according to a second embodiment of the present invention.

FIG. 6 is a waveform diagram showing the operation of each part of the induction heating device in the third embodiment of the present invention.

FIG. 7 is a diagram showing a circuit configuration of an induction heating device according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a waveform of each part of the induction heating device in the third embodiment of 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 various parts of a conventional induction heating device.

FIG. 12 is a diagram showing waveforms of various parts of a conventional induction heating device.

FIG. 13 is a diagram showing waveforms of various parts of a conventional induction heating device.

[Explanation of symbols]

50 inverter 51 AC power supply 52 Rectifier circuit 53 First Smoothing Capacitor 54 Choke coil (step-up means) 55 First 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 capacitors 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 (rectifying element) 85 Control circuit 88 switching elements 89 heating coil 90 pans (load) 91 Resonant capacitor

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Kitazumi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yuji Fujii 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Koji Niiyama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 2001-160484 (JP, A) JP 1-31588 (JP, A) Special Open 2002-75620 (JP, A) JP 2002-246161 (JP, A) JP 2003-77626 (JP, A) JP 2003-77639 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05B 6/12 H05B 6/00

Claims (6)

(57) [Claims] 1. 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 parallel connection to the second switching element. A second reverse conducting element connected to the first switching element, a heating coil connected in parallel to the first switching element or the second switching element, and a resonance circuit including a resonance capacitor, An inverter that resonates when the first switching element and the second switching element are electrically connected; and a control circuit that exclusively controls the conduction of the first switching element and the second switching element. Resonance current flowing through the switching element or the first reverse conducting element is generated when the magnetic field generated by the heating coil induces heating of a load having high conductivity and low permeability. The first of the said DC voltage the resonance current to maintain the resonant at a predetermined higher amplitude in the driving period is input DC voltage pulsating by boosting the smoothing means with resonate at a period shorter than the drive period of the switching element
Of Ri Na is supplied to the inverter is boosted and smoothed so as to be higher than the peak value, the control circuit,
After starting driving the first switching element,
2 laps after the flow starts to flow in the first switching element
The first switching element after the first period is reached
During the period in which the current is flowing through the child, the first switch
An induction heating device that outputs a signal for stopping the driving of a ching element . 2. The control circuit, wherein after the drive of the first switching element is started, the resonance current reaches the second cycle after the resonance current begins to flow in the first switching element, and thereafter, the first switching is performed. and change the driving stop timing of the element
The induction heating device according to claim 1, wherein the heating output is variable . 3. The induction heating device according to claim 1, wherein the step-up smoothing means largely changes the step-up action when the driving period of the second switching element becomes long . 4. A first switching element and a second switch.
And a first switching element connected in series
A first reverse conducting element connected in parallel to the child;
Second reverse conducting element connected in parallel to the switching element
And the first switching element or the second switching element.
A heating coil and a resonance capacitor connected in parallel to the switching element.
A resonance circuit including a capacitor and a DC voltage input
Conduction of the first switching element and the second switching element
An inverter that resonates by communication, and the first switch
The switching element and the second switching element exclusively for conduction.
And a control circuit for controlling the first switching element.
Alternatively, the resonance current flowing in the first reverse conducting element is
The magnetic field generated by the heating coil is negative with high conductivity and low permeability.
Induction heating of the load drives the first switching element
It resonates in a cycle shorter than the period and during the driving period.
In order to maintain the resonance with the amplitude of the resonance current above a predetermined level,
The DC voltage is boosted and smoothed by boosting smoothing means.
Are together formed by supplying to the inverter, the temperature <br/> applanation slip means, said first of said switching element and the second
Connected in parallel to the series connection body of the switching elements of the second
Smoothing capacitor and a choke coil connected in series with the second switching element, and stores energy in the choke coil due to conduction of the second switching element, and cuts off the second switching element. induction heating apparatus ing with the energy via the first reverse conducting element moves to the second smoothing capacitor by. 5. A resonance current flowing through the second switching element or the second reverse conducting element causes the magnetic field generated by the heating coil to inductively heat a load having high conductivity and low permeability. Ri Na resonates shorter than the drive period cycle, the control circuit, the second switching element
After the start of driving the child, the resonance current changes to the second switching
After reaching the second cycle from the beginning
Period during which current flows through the second switching element
Driving of the second switching element is stopped within
The cooking device according to any one of claims 1 to 4, which outputs a signal indicating that the cooking device is a cooking device. 6. The induction heating device according to claim 4, further comprising a first smoothing capacitor that applies energy to the choke coil by the conduction of the second switching element.