JP3443448B2 - Inverter 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 inverter device having an inverter circuit for generating a high-frequency output in a resonance coil by performing on / off control of a switching element to connect and disconnect a resonance circuit composed of a resonance coil and a resonance capacitor. .

[0002]

2. Description of the Related Art For example, in an inverter device used for an induction heating cooker, a resonance circuit composed of a heating coil as a resonance coil and a resonance capacitor, a switching element such as a transistor, and a flyhole diode for reverse conduction are provided. There is a so-called single-ended type inverter circuit which is a combination of the above-mentioned ones, and a transistor is turned on / off to generate a resonance current in the resonance circuit, thereby giving a high frequency output to the heating coil.

In this case, since the switching element is turned on and off according to the oscillation frequency, if the on timing is deviated, an overvoltage may be applied between the terminals of the switching element and the element may be destroyed. Therefore, in order to protect the switching element from such overvoltage breakdown, it is necessary to properly set the on timing of the switching element.

Therefore, conventionally, in order to deal with such a problem, an inverter device as disclosed in, for example, Japanese Patent Publication No. Sho 58-36473 has been considered. That is, this device detects that the collector voltage of the transistor as the switching element has reached the DC power supply voltage, and supplies the base drive current after a predetermined time based on the result.

In this structure, the on-timing of the switching element is set according to the fluctuation of the DC power supply voltage, instead of detecting the timing when the voltage applied to the collector of the transistor becomes zero.
It is intended to obtain a stable oscillation state in response to various load conditions.

In the inverter device disclosed in Japanese Patent Publication No. 61-42392, the terminal voltage of the switching element is detected and the terminal voltage is integrated, and the terminal voltage of the switching element is compared with the integrated voltage. Then, when the terminal voltage becomes lower than the integrated voltage, the switching element is made conductive. With such a configuration, even if the oscillation frequency of the inverter circuit changes, the integrated voltage at that time can be changed following the change, so that the on-timing of the switching element can be kept constant. It is possible to reduce the switching loss at the time of ON operation of and to improve the operation efficiency.

[0007]

However, the above conventional structure has the following problems. That is, first, both types have a configuration in which the on-timing of the switching element is determined based on the terminal voltage. Therefore, for example, when a surge voltage such as a lightning surge is superimposed on the DC power supply circuit, the surge The voltage charges the smoothing capacitor via the choke coil provided in the DC power supply circuit, which causes the input voltage of the inverter circuit to rise sharply. Generally, surge voltage is very fast with a rise time of several μsec.
It rises faster than the oscillation cycle during induction heating (for example, about several tens of μsec).

When a surge voltage is applied, the choke coil and the smoothing capacitor resonate, so that the DC power supply circuit outputs a DC voltage on which a high-voltage harmonic component is superimposed. Therefore, when the switching element is turned on, the magnitude of the current flowing through the heating coil is about several times larger than in the normal state, and when the switching element is turned off, the heating coil and the resonance capacitor are used. Since the resonance voltage of the resonance circuit also becomes large, the amplitude of the terminal voltage of the switching element becomes a very large value. In addition, there is a problem in that the resonance voltage changes depending on the timing of the harmonics generated by the resonance caused by the lightning surge.

In this case, in the one disclosed in Japanese Patent Publication No. 58-36473, the output voltage of the DC power supply circuit fluctuates rapidly and the collector voltage of the switching element fluctuates, so that the switching element is turned on. Since the timing is disturbed, the switching element may be destroyed. In addition, Japanese Examined Japanese Patent Publication 61-42392
In the one disclosed in the publication, since the collector voltage of the switching element is integrated, it is not possible to obtain an integrated voltage that follows the collector voltage that fluctuates in each oscillation cycle. Disruption of the on-timing may lead to destruction.

In addition to the lightning surge, for example,
The on-timing of the switching element is also disturbed in the same manner as described above due to the sudden fluctuation of the power supply voltage caused by the occurrence of the momentary power failure or the disconnection accident of the ground power supply line in the configuration of the single-phase three-wire system. There is a defect.

Secondly, in the DC power supply circuit, the output of the full-wave rectification of the AC power supply by the full-wave rectification circuit is smoothed by the smoothing circuit to obtain the DC output voltage. Has an output that fluctuates according to the waveform when the AC power supply is full-wave rectified, so that the output of the DC power supply circuit drops to a very low value of about several volts at the zero crossing point of the AC power supply input. On the other hand, since the saturation voltage in the ON state of the switching element is also about several volts, the voltage actually applied to the heating coil is the difference between the output voltage of the DC power supply circuit and the saturation voltage when the switching element is turned on. Therefore, in the method of detecting the terminal voltage of the switching element as in the conventional configuration described above,
It is difficult to detect the voltage to get accurate on-timing,
As a result, the ON timing of the switching element may be deviated.

Thirdly, there is a so-called slow start system in which the ON time of the switching element is set to be very short when the oscillation operation of the inverter circuit is started, and thereafter the ON time is controlled to be gradually increased. However, at this time, if the on-time is short, the amplitude of the resonance voltage generated in the heating coil becomes small. Therefore, in the conventional configuration, the on-timing cannot be set accurately, and the on-timing of the switching element may shift. There is.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a DC power supply circuit with a simple configuration in which a surge voltage is applied to cause a sudden change in the output voltage of the DC power supply circuit or a DC power supply circuit. Even when the output voltage is small or when the switching element ON time is set to be extremely short, the ON timing of the switching element can be set appropriately, and overvoltage breakdown when the switching element is ON can be prevented. It is possible to provide an inverter device that can obtain a stable oscillation state.

[0014]

An inverter device according to the present invention is provided with a DC power supply circuit in which a smoothing capacitor is connected to an output stage, and a resonance coil which is provided so as to convert a DC output of the DC power supply circuit into high frequency power. A resonance capacitor that forms a resonance circuit together with the resonance coil, a switching element that is connected between the output terminals of the DC power supply circuit via the resonance coil in series, and a rectifying element that is connected in antiparallel to the switching element. An inverter circuit comprising: a resonance current phase detecting means for detecting a change in a resonance current flowing through the resonance capacitor when the switching element is off;
A phase shift circuit that inputs the detection output of the resonance current phase detection means and generates an output signal in which the phase when the maximum value of the resonance current flowing from the resonance capacitor to the resonance coil is the zero cross phase, and this phase shift circuit It is the ON timing of the switching element that is set within a period in which the terminal voltage when the switching element is OFF, which is obtained based on the detection time point of the zero-cross phase of the output signal, becomes substantially zero, and the switching element is actually turned ON. characterized in was equipped with the on timing setting means for setting a timing in consideration of the delayed by a delay time ([Delta] T) that occurs on the circuit arrangement with respect to the timing.

In the above structure, the resonance current phase detecting means is provided with a detection capacitor for shunting the resonance current flowing through the resonance capacitor, and the resonance current of the resonance capacitor is detected by detecting a change in the current of the detection capacitor. It may be configured to detect a change in

Further, the resonance current phase detection means is provided with a detection resistor for detecting a change in the current of the detection capacitor, and the change in the resonance current of the resonance capacitor is detected based on the terminal voltage of the detection resistor. It can also be configured.

In the above structure, the resonance circuit is in a state in which a resonance coil and a resonance capacitor are connected in parallel,
The detection capacitor may be provided so as to detect the change in the resonance current of the resonance capacitor via the smoothing capacitor of the DC power supply circuit.

Further, the resonance current phase detection means is provided with a current transformer for detecting the resonance current of the resonance capacitor, and is configured to detect the change of the resonance current based on the detection output of the current transformer. You can

[0019]

[0020]

[0021]

According to the inverter device of the present invention, in the inverter circuit, when the switching element is turned on, power is supplied to the resonance coil from the DC power supply circuit, and thereafter, when the switching element is turned off. Then
Even when the power supply from the DC power supply circuit is stopped, the current flowing through the resonance coil does not suddenly become zero, but flows into the resonance capacitor side forming the resonance circuit as a resonance current. Then, when the terminal voltage of the resonance capacitor rises to a predetermined voltage due to this resonance current, the resonance current flows reversely from the resonance capacitor side to the resonance coil side.

At this time, when the terminal voltage of the resonant capacitor decreases until the voltage between the terminals of the switching element in the off state becomes zero, thereafter, the voltage is forwardly applied to the rectifying element connected in antiparallel to the switching element. As a result, the terminal voltage of the resonance capacitor does not drop any further, and the current flowing from the resonance capacitor to the resonance coil becomes zero. However, in the resonance coil, the resonance current does not suddenly become zero, and from then on, the current continues to flow from the path passing through the DC power supply and the rectifying element.

On the other hand, the phase shift circuit includes a resonance capacitor
When exhibiting the maximum value of the resonance current flowing toward the vibration coil
Phase of the resonance current phase detection means
The zero-cross phase is detected, and the on-timing setting means is
Resonance current phase detecting means off when the terminal voltage is a set value or less and Do that life of switch <br/> quenching element obtained on the basis of a detection signal of a change of the resonant current of the resonant capacitor to be detected by
Since the on-timing of the switching element is set within the interval, the oscillation control means controls the on-off of the switching element at the on-time corresponding to the set on-timing and the predetermined oscillation frequency. As a result, the switching element is turned on each time at the on-timing at which the inter-terminal voltage based on the resonance current is minimized, and the switching element is prevented from being destroyed by overvoltage and always performs the resonance operation at an appropriate on-timing. Will be able to.

As a result, for example, even when a surge voltage is superimposed on the DC power supply, an overvoltage is not applied when the switching element is turned on, and the switching element is not likely to be destroyed, so that the operating state can be reliably performed. Can be held. Further, when the DC power supply is generated by rectifying and smoothing the AC power supply, even when the output voltage of the DC power supply circuit becomes low according to the frequency of the AC power supply, or the on-time of the switching element according to the set frequency Even when it is set to be extremely short, the ON operation can be performed with the voltage applied to the switching element always set to the minimum, and the overvoltage breakdown of the switching element can be prevented.

According to the inverter device of the second aspect,
Since the resonance current phase detecting means divides the resonance current of the resonance capacitor into the detection capacitor and detects the change in the current, it is possible to detect a current smaller than the resonance current itself flowing in the resonance capacitor, and It becomes possible to adopt a structure using a small current detecting means.

According to the inverter device of the third aspect,
The resonance current phase detection means divides the resonance current of the resonance capacitor into the detection capacitor and detects the current flowing through the detection capacitor based on the terminal voltage of the detection resistor, so that the resonance current changes with a simple configuration. Can be detected. In this case, the detection resistor can detect the phase of the resonance current without any trouble by setting a resistance value such that the shunted current is out of phase with the resonance current of the resonance capacitor.

According to the inverter device of the fourth aspect,
When the resonance circuit is configured with the resonance coil and the resonance capacitor connected in parallel, the resonance current flowing in the resonance capacitor can be obtained by connecting the detection capacitor in parallel with the resonance capacitor. Even when the smoothing capacitor of the power supply circuit is connected in a state including the smoothing capacitor, it can be considered that the smoothing capacitor is AC short-circuited, and thus the resonance current can be detected. By connecting the detection capacitor in this manner, for example, compared to the case of connecting between the terminals of the resonance capacitor, one end side can be grounded, so that the phase of the resonance current can be changed. The electrical configuration for detection can be simple.

According to the inverter device of the fifth aspect,
In the resonance current phase detection means, the resonance current flowing through the resonance capacitor can be detected by providing a current transformer. If the current transformer is provided with a detection capacitor, it should be installed so as to detect the current of the detection capacitor, so that a capacitor with a smaller capacity than that used for directly detecting the resonance current should be used. Will be able to.

[0029]

[0030]

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the present invention is applied to an inverter device for an induction heating cooker will be described below with reference to FIGS. In FIG. 1 showing an electrical configuration, an output terminal of a commercial power supply 1 is connected between both terminals of an input capacitor 2 and is connected between AC input terminals of a full-wave rectifier circuit 3 formed by bridge-connecting diodes. .
The positive output terminal 3a of the full-wave rectifier circuit 3 is a choke coil 4
To the DC power supply line 5a, and the negative output terminal 3b is connected to the DC power supply line 5b. A smoothing capacitor 6 is connected between the DC power supply lines 5a and 5b. The full-wave rectifier circuit 3, the choke coil 4, and the smoothing capacitor 6 constitute a DC power supply circuit 7.

The heating coil 8 as a resonance coil constitutes a resonance circuit 10 together with the resonance capacitor 9, and the resonance circuit 10 and an IGBT (insulated gate bipolar transistor; Insulated gate) as a switching element.
an inverter circuit 13 including a bipolar transistor 11 and a flywheel diode 12 as a rectifying element.
Is configured. A stainless steel pan A for cooking is placed on the heating coil 8 through a top plate (not shown), and the stainless steel pan A is induced in the stainless steel pan A by the high-frequency current supplied to the heating coil 8. An electric current flows and the resistance loss heats the stainless steel pan A. The DC power supply line 5a is connected to the DC power supply line 5b via the heating coil 8 and the IGBT 11, the resonance capacitor 9 is connected in parallel to the heating coil 8, and the flywheel diode 12 is connected to the IGBT 11.
Are connected in anti-parallel to.

Next, the configuration of the control system will be described. The input setting unit 14 includes a current transformer 15 that detects an input current, an input current detection circuit 16, an input setting circuit 17, and an input comparison circuit 18, and detects the input current from the commercial power supply 1 and preliminarily detects it. The difference from the set input current level is calculated and output to the output side as an input setting signal. In this case, the input current detection circuit 16 detects the input current level based on the detection signal of the current transformer 15 provided on one output line of the commercial power supply 1. The input comparison circuit 18 compares the input level set in the input setting circuit 17 with the input current level detected by the input detection circuit 16 and outputs an input setting signal of a level corresponding to the difference. There is.

The oscillation control section 19 includes a current transformer 20 as a resonance current phase detection means, a phase detection circuit 21 as an on-timing setting means, an oscillation circuit 22, an output control circuit 23 as an oscillation control means, and a drive circuit 24. The on-timing and on-time of the IGBT 11 are set as will be described later based on the resonance current of the resonance capacitor 9. The current transformer 20 is provided so as to detect the resonance current of the resonance capacitor 9, and the phase detection circuit 21 outputs a phase detection signal indicating the peak value of the negative current based on the detection signal of the current transformer 20. Is configured to.

The oscillation circuit 22 outputs a sawtooth wave signal for setting the ON timing for the IGBT 11 for each cycle based on the phase detection signal output from the phase detection circuit 21. The output control circuit 23 compares the sawtooth wave signal output from the oscillation circuit 22 with the input setting signal output from the input comparison circuit 18, and sets the ON timing and the ON time of the IGBT 11 as a control signal.
The signal is output to the gate of the IGBT 11 via the signal line 4.

FIG. 2 shows a specific electrical configuration of the oscillation control section 19, which is constructed as follows. The current transformer 20 is connected between the input terminals 21a and 21b of the phase detection circuit 21. In this phase detection circuit 21, a resistor 25 is connected between the input terminals 21a and 21b, and the input terminal 21b is grounded. Also, the input terminal 21a
Is a phase shift circuit 28 including a resistor 26 and a capacitor 27.
It is connected to the input terminal 21b via.

The output terminal 28a of the phase shift circuit 28 (resistor 26a
And a capacitor 27) are connected to the non-inverting input terminal of the comparison circuit 30 via the resistor 29. The non-inverting input terminal of the comparison circuit 30 is connected to the constant voltage output terminal VCC via the protective diode 31 of the illustrated polarity, and is also grounded via the protective diode 32 of the illustrated polarity. It is grounded. The output terminal of the comparison circuit 30 is connected to the constant voltage output terminal VCC via the pull-up resistor 33 and the input terminal 22a of the oscillation circuit 22.

In the oscillator circuit 22, the input terminal 22a is connected to the constant voltage output terminal VCC through a differentiating circuit 36 consisting of a capacitor 34 and a resistor 35, and its output terminal 36a is the non-inverting input terminal of the comparator circuit 37. It is connected. The non-inverting input terminal of the comparator circuit 37 is connected to the constant voltage output terminal VCC via the protective diode 38 of the illustrated polarity, and the inverting input terminal is connected to the constant voltage output terminal VCC via the resistor 39 and the resistance. It is grounded through 40.

The inverting input terminal of the comparator circuit 41 performing the oscillating operation has a constant voltage output terminal V via resistors 42 and 43 connected in series.
It is connected to CC and grounded via a capacitor 44. The common connection point of the resistors 42 and 43 is connected to the output terminal of the comparison circuit 37 via the reverse current blocking diode 45 having the illustrated polarity. The non-inverting input terminal of the comparison circuit 41 is connected to the constant voltage output terminal VCC via the resistor 46, and is also grounded via the resistor 47. The output terminal of the comparison circuit 41 is connected to the output terminal of the comparison circuit 37 and also connected to the non-inverting input terminal via the resistor 48.

The output control circuit 23 is composed of a comparison circuit 49, the inverting input terminal of the comparison circuit 49 is connected to the inverting input terminal of the comparison circuit 41, and the non-inverting input terminal of the comparison circuit 49 is It is connected to the output terminal of the input comparison circuit 18 of the input setting unit 14 (see also FIG. 1).
The output terminal of the comparison circuit 49 is connected to the input terminal of the drive circuit 24.

Next, the operation of the present embodiment will be described with reference to the waveform diagram showing the changes over time in the current and voltage of each part shown in FIG. First, the oscillation operation of the inverter circuit 13 will be described. That is, the gate-on signal Vj of the “H” level is output from the drive circuit 24 at the on-timing Ton described later.
When (FIG. 3 (j)) is output, the IGBT 11 is turned on and the heating coil 8 outputs the output voltage V V of the DC power supply circuit 7.
DC is applied. As a result, the current Ia such that the current value gradually increases flows through the heating coil 8 as shown in FIG. At this time, I
The current Ib (I in FIG. 1) shown in FIG.
The current flowing through the GBT 11 is Ib1 and the current flowing through the flywheel diode 12 is Ib2).

Next, in this state, when the output of the gate-on signal Vj is inverted to the "L" level from the drive circuit 24 at an off timing Toff described later (see (j) in the same figure), IG is set.
BT11 is turned off and current Ia flowing from the heating coil 8
Comes to shut off. However, in the heating coil 8, the current Ia that is flowing now does not suddenly become zero,
The current Ia flows into the resonance capacitor 9 as the resonance current Ic (see FIG. 7C). Then, when the terminal voltage of the resonance capacitor 9 reaches a predetermined voltage, the resonance current Ic generates a current flowing in the opposite direction because the charge is saturated.

At this time, the terminal voltage Vd of the IGBT 11
Is highest at time T1 when the current Ic flowing from the heating coil 8 to the resonance capacitor 9 becomes zero, as shown in FIG. When it starts flowing, IGBT1
The terminal voltage Vd of 1 decreases. And IGBT1
At time T2 when the terminal voltage Vd of 1 becomes equal to the output voltage VDC of the DC power supply circuit 7, that is, when the voltage applied between both terminals of the resonance capacitor 9 becomes zero, the current Ic flowing into the heating coil 8 becomes negative. Is the peak value of.

Then, at time T3 when the terminal voltage Vd of the IBGT 11 becomes zero, when the current Ic is about to flow from the resonance capacitor 9 toward the heating coil 8, the flywheel diode 12 is turned on.
The current Ic is stopped, and instead, the regenerative current Ib2 flows from the smoothing capacitor 6 side to the heating coil 8 via the flywheel diode 12.

Then, at a later-described on-timing Ton during the period when the regenerative current Ib2 is flowing in this way, the gate-on signal Vj is again given to the IGBT 11 from the drive circuit 24, and the IGBT 11 is turned on.
The heating coil 8 is energized. After that, the same operation as described above is repeated, so that the high-frequency current is applied to the heating coil 8, the induction current is generated in the pan A, and the heating operation is performed by the resistance loss thereof.

In this way, the drive circuit 24 causes the IGBT
Since the gate-on signal Vj to 11 is applied, the IGBT 11 is turned on when the terminal voltage of the IGBT 11 is substantially zero, and when the IGBT 11 is turned on, the resonance capacitor 9 is fed from the heating coil 8 side. The charging current that flows into the battery suddenly flows between the drain and source,
Alternatively, when the electric charge charged in the resonance capacitor 9 flows to the heating coil 8 side, the charging current does not suddenly flow and destruction does not occur.

Now, in the above high-frequency oscillation operation, I
The output timings Ton and Toff of the gate-on signal Vj given to the GBT 11 will be described in detail below. That is, the current Ic flowing in the resonance capacitor 9 is detected by the current transformer 20, and the resistor 25 of the input current detection circuit 16 is detected.
A detection voltage Vc having the same phase as the current Ic is obtained between the terminals (see FIG. 3C). The detected voltage Vc is phase-shifted by the phase shift circuit 28 so as to be delayed by 90 °, and the voltage Ve
(See (e) in the figure).

That is, at the time T2 when the current Ic flowing from the resonance capacitor 9 toward the heating coil 8 becomes maximum, the voltage Ve changes from a positive value to zero, and at the time T3, the voltage Ve exhibits a negative peak value. Like In the comparison circuit 30, the signal Vf at the "H" level (see (f) in the figure) is output during the positive period of the output voltage Ve. Therefore, the output signal Vf of the comparison circuit 30
Changes to "L" level at time T2 when the voltage Ve becomes zero.

Next, in the oscillating circuit 22, the signal Vf output from the comparing circuit 30 is differentiated by the differentiating circuit 36, and then the output signal is compared with a predetermined reference voltage by the comparing circuit 37. To output the signal Vg (see (g) in the figure). In this case, the differentiating circuit 36 changes the output signal Vf from the comparing circuit 30 from the “H” level to the “L” level.
Since a pulse that changes to the negative side is generated at the time point T2 when the level changes to the level, the level of the input signal to the non-inverting input terminal of the comparison circuit 37 becomes lower than the reference voltage, and the output signal Vg is Time T in the output state of "H" level
In 2, the pulse signal of "L" level is output for a short time.

Now, when the output signal Vg of the comparison circuit 37 is at the "H" level, the capacitor 44 is connected to the resistor 43,
Since the charging operation is being performed from the constant voltage output terminal VCC with a time constant via 42, the terminal voltage Vh of the capacitor 44 is
Indicates a state in which it gradually rises with the passage of time (see (h) in the figure). The voltage of the constant voltage output terminal VCC is applied to the resistors 46, 47, 4 at the non-inverting input terminal of the comparator circuit 41.
The voltage divided by the circuit composed of 8 is applied, and the comparison circuit 41 outputs a signal of "H" level until the terminal voltage Vh of the capacitor 44 exceeds the voltage.

However, when the output signal Vg of the comparison circuit 37 is inverted to the "L" level, the electric charge charged in the capacitor 44 is rapidly discharged through the resistor 42 and the diode 45, and at this time, the comparison circuit 41 is charged. The output terminal is inverted to "L" level. Then, the input voltage to the non-inverting input terminal of the comparison circuit 41 also decreases, so that the discharging operation is continued until the terminal voltage Vh of the capacitor 44 decreases to the voltage value at that time, and then the charging operation is started again. become.

In this case, the charging time constant of the capacitor 44 is set by the capacitance value of the capacitor 44 and the resistance values of the resistors 42 and 43, and the discharge time constant is determined by the capacitance value of the capacitor 44 and the resistance value of the resistor 42. Since it is set, the discharging operation is performed rapidly and the charging operation is performed at a slower speed. After that, the charging / discharging operation described above is repeated in the cycle of the negative pulse signal output from the comparison circuit 37, and the terminal voltage Vh of the capacitor 44 is shown in FIG.
The signal is output as a sawtooth signal as shown in.

Then, in the output control circuit 23, the comparison circuit 49 causes the input comparison circuit 18 of the input setting section 14 to operate.
Control signal Vi of "H" level at the timing (between time TS and TE) at which the terminal voltage Vh of the capacitor 44 becomes larger than the level of the input setting signal VS output from
Will be output (see (i) in the figure). The control signal Vi comes to be supplied to the IGBT 11 via the drive circuit 24. At this time, in the drive circuit 24, a predetermined delay time ΔT generated on the circuit configuration when the drive signal Vj is generated. It will be output at a timing delayed by just that. Therefore, the rising timing of the drive signal Vj obtained in this manner is determined by the above-mentioned IGB.
This is the on-timing Ton of T11 and the falling timing is the off-timing Toff. The value of the above-mentioned delay time ΔT is changed by changing the circuit constant.
It is a value that can be adjusted so as to be set appropriately large.

The input setting signal VS generated by the input setting section 14 is set as follows. The output signal of the current transformer 15 that detects the input current is input to the input current detection circuit 16, where the level of the current input from the commercial power supply 1 to the DC power supply circuit 7 side is detected. Further, the input setting circuit 17 is input with a signal of a level according to the set heating amount by the heating coil 8. And
The input comparison circuit 18 compares the levels of the detection signal of the input current detection circuit 16 and the setting signal of the input setting circuit 17 and outputs the input setting signal VS corresponding to the value of the difference between them. As a result, the input comparison circuit 18 outputs the input setting signal VS corresponding to the deviation of the actual heating amount from the set heating amount to the output control circuit 23, and the input setting signal VS corresponding to the set heating amount is always output. The signal VS is output.

According to this embodiment, the IGBT 1
The resonance current flowing through the resonance coil 9 during the off period of 1 is detected by the current transformer 20, and the I current is detected by the phase detection circuit 21.
Since the on-timing Ton is set so as to be turned on when the terminal voltage Vd becomes zero, which is equal to or less than the set value, the on-timing of the IGBT 11 can be set based only on the phase of the resonance current. Therefore, the voltage applied at the time of the ON operation of the IGBT 11 can be always minimized in response to a sudden change in the input voltage or the load change.

As a result, even when a surge voltage such as a lightning surge is superposed on the DC power supply circuit 7 side, the ON timing is set without being adversely affected by the fluctuation of the voltage level at that time, and the IGBT 11 is turned on. It becomes possible to prevent the overvoltage breakdown during the on-operation and to surely perform the oscillation operation. Further, even when the output voltage VDC of the DC power supply circuit 7, that is, the input voltage of the inverter circuit 13 is small, an accurate on-timing can always be set. Further, even when the on period of the IGBT 11 is short, such as when the inverter circuit 13 is slowly started, or when there is a sudden change, the accurate on timing can always be set.

In the case of the configuration of this embodiment, the IG
Since the on timing of the BT11 is not set based on the output voltage VDC of the DC power supply circuit 7 or the integrated voltage of the terminal voltage Vd of the IGBT11, the entire circuit configuration of the oscillation control unit 19 is simple and inexpensive. It is possible,
Moreover, it is possible to reduce adverse effects due to variations in parts and the like.

Further, according to this embodiment, the on-timing Ton of the IGBT 11 is based on the detection signal of the current transformer 20.
When setting, the phase detection circuit 21 detects the phase at which the resonance current flowing from the resonance capacitor 9 to the heating coil 8 is maximum, that is, the phase of the negative peak value of the resonance current Ic, and Is obtained by detecting the zero-cross phase of the signal phase-shifted by 90 ° using the phase shift circuit 28, and there is a predetermined delay time based on the zero-cross phase detection time T2. Since the on-timing Ton is set by
It becomes possible to set the ON timing of the IGBT 11 with certainty while ensuring a simple configuration.

FIG. 4 shows a second embodiment of the present invention. Hereinafter, parts different from the first embodiment will be described. That is, in the present embodiment, the resonance capacitor 9 forming the resonance circuit 10 has both terminals of the heating coil 8.
And a smoothing capacitor 6 are connected in series, and a resonance capacitor 9 is connected in parallel with a series circuit of a detecting capacitor 50 and a detecting resistor 51.

In this case, the capacitance of the detection capacitor 50 is set to a value much smaller than the capacitance of the resonance capacitor 9, and the resistance value of the detection resistor 51 is compared to the impedance of the resonance capacitor 9. And is set to a very small value. Therefore, the detection capacitor 50
The resonance current shunted to is much smaller than the resonance current Ic flowing to the resonance capacitor 9, and the resonance current shunted to the detection capacitor 50 is detected from the terminal voltage generated in the detection resistor 51. ing.

According to the above configuration, the resonance capacitor 9 of the resonance circuit 10 is the same as the resonance capacitor 9 of the first embodiment.
On the other hand, the configuration is such that the smoothing capacitor 6 is included and connected in parallel to the heating coil 8. However, the resonance current Ic generated by the ON operation of the IGBT 11 is very high in frequency as compared with the frequency of the commercial power source 1. Since it is a current, it can be considered that the smoothing capacitor 6 of the DC power supply circuit 7 is short-circuited in terms of an AC circuit, so that it is understood that the oscillation operation is performed in exactly the same way as in the first embodiment.

According to the present embodiment, the resonance current Ic flowing through the resonance capacitor 9 is converted into the detection capacitor 5
Since it is possible to detect a resonance current with a small in-phase, which is shunted to 0, as a voltage signal, a simpler and cheaper configuration can be achieved as compared with the first embodiment.

In the case of the above configuration, the detection resistor 51
Therefore, in order to detect the phase of the resonance current more accurately, the resistance value R51 is set to be much smaller than the resistance value R25 of the resistor 25 used in the phase shift circuit 28 of the phase detection circuit 21. And (R51 << R25), the impedance X27 of the capacitor 27 of the phase shift circuit 28 is also set.
If (= 1 / (ωC25)) is set to be sufficiently smaller than the resistance value R25 of the resistor 25 (X27 << R25),
It becomes possible to reduce the phase detection error due to the dispersion of these values.

The value P50 of the ratio between the impedance X50 of the detecting capacitor 50 and the resistance value R51 of the detecting resistor 51.
If (= X50 / R51) is set so that the value P28 (= X27 / R26) of the ratio of the impedance X27 of the capacitor 27 of the phase shift circuit 28 and the resistance value R26 of the resistor 26 becomes the same value (P50 = P28) Since impedance matching can be achieved between the two, it is possible to detect the accurate phase of the resonance current Ic.

FIG. 5 shows a third embodiment of the present invention. Hereinafter, parts different from the first and second embodiments will be described. That is, the connection configuration of the detection capacitor 50 and the detection resistor 51 is the same as that of the second embodiment, and the resonance circuit 10 is connected in parallel to the heating coil 8 as in the first embodiment. It is a thing.

Also according to this embodiment having such a configuration, in the process of detecting the resonance current Ic, it can be considered that the smoothing capacitor 6 is in a short-circuited state in terms of an AC circuit. The resonance current can be detected in the same manner as in the example. Further, when the resonance circuit 10 is configured as described above, a series circuit of the resonance current of the detection capacitor 50 and the detection resistor 51 is not connected in parallel to the resonance capacitor 9 but a smoothing capacitor. The reason for connecting via 6 is as follows.

That is, when the series circuit of the detecting capacitor 50 and the detecting resistor 51 is connected in parallel to the resonant capacitor 9 to divide the resonant current, the terminal voltage of the detecting resistor 51 is DC. Output voltage VD of power supply circuit 7
Although it is obtained as the voltage value of the difference from C, unlike the configuration of the present embodiment, the phase detection circuit 21 cannot be configured to perform voltage detection with reference to the ground potential, and the DC power supply This is because it is necessary to detect the output voltage VDC of the circuit 7 and detect the voltage of the difference between them, and the circuit structure becomes complicated as a whole.

In other words, even when the resonance circuit 10 is configured in this way, it is not necessary to connect a series circuit of the detection capacitor 50 and the detection resistor 51 in parallel to the resonance capacitor 9, and the earth level is set. The reference detection circuit configuration can be used, and the configuration of the detection circuit can be simplified.

FIG. 6 shows a fourth embodiment of the present invention. The difference from the third embodiment is that a current transformer 52 for detecting the current flowing through the detecting capacitor 50 instead of the detecting resistor 51. Has been installed. Thereby, the resonance current can be accurately detected in the same manner as in the third embodiment, and
Different from the first embodiment in which the resonance current flowing through the resonance capacitor 9 is directly detected, the current capacity of the current transformer 52 is set to such an extent that a low level resonance current shunted by the detection capacitor 50 can be detected. Therefore, the configuration can be made inexpensive.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. In addition to IGBT11, switching elements are FET
Alternatively, a bipolar transistor or the like may be used. In addition to the inverter device for induction heating, it can be applied to, for example, an inverter device for a microwave oven or an inverter device such as a switching regulator. The phase shift circuit can be appropriately provided as needed. The smoothing circuit of the DC power supply circuit 7 can be configured to use a resistor instead of the choke coil 4.

[0071]

As described above, according to the inverter device of the present invention, the following effects can be obtained.
That is, according to the inverter device of the first aspect, the resonance current phase detecting means detects a change in the resonance current flowing through the resonance capacitor when the switching element is off, and the phase shift circuit causes the resonance coil to move to the resonance coil.
Phase when the maximum value of the resonance current flowing toward the
The phase of the detection signal of the resonance current phase detection means
Detected by loss phase, on of the switching element based on a detection output of the resonance current phase detecting means by the timing setting means during off-voltage between terminals of the switching elements in a period in <br/> that Do a set value or less Since the on-timing is set, the switching element can be turned on at each on-timing at which the terminal voltage based on the resonance current is minimized every time.For example, a surge voltage is applied to the DC power supply. Even in the case, the overvoltage is not applied at the time of turning on, and there is no fear that the switching element will be destroyed, and the operating state can be reliably maintained. Also, when the DC power supply is generated by rectifying and smoothing the AC power supply, even if the output voltage becomes low according to the frequency of the AC power supply, or the switching element ON time is set to be extremely short according to the set frequency. Even in such a case, there is an excellent effect that the ON operation can be performed with the voltage applied to the switching element always set to the minimum.

According to the inverter device of the second aspect,
Since the detection capacitor is connected in parallel with the resonance capacitor and the resonance current phase detection means divides the resonance current of the resonance capacitor into the detection capacitor to detect the change in the current, a current smaller than the current flowing in the resonance capacitor. It is possible to obtain the excellent effect that the current detection means for detecting the resonance current flowing through the detection capacitor can be configured to have a small current capacity.

According to the inverter device of the third aspect,
Since a detection resistor is connected in series to the detection capacitor and the resonance current flowing through the resonance capacitor is detected based on the terminal voltage of the detection resistor, changes in the resonance current can be detected with a simple configuration. In such a case, the excellent effect that the phase of the resonance current can be detected without any trouble by setting the resistance value of the detection resistor so that the shunted current is not out of phase with the resonance current of the resonance capacitor. Play.

According to the inverter device of the fourth aspect,
Even when the detection capacitor is connected in a state including the smoothing capacitor of the DC power supply circuit, it can be considered that the smoothing capacitor is AC short-circuited, so the resonance current can be detected by the detection capacitor. As a result, for example, compared to the case of connecting between the terminals of the resonance capacitor, one end side can be configured to be grounded, so that the electrical configuration for detecting the phase of the resonance current is simpler. There is an excellent effect that it can be.

According to the inverter device of the fifth aspect,
In the resonance current phase detection means, the resonance current flowing through the resonance capacitor is detected by the current transformer.Therefore, the on-timing that does not apply the overvoltage to the switching element can be achieved while the simple configuration using the small-capacity current transformer is adopted. It has an excellent effect that it can be set.

[0076]

[0077]

[Brief description of drawings]

FIG. 1 is an overall electrical configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an electrical configuration diagram of an inverter oscillation control circuit.

FIG. 3 is a diagram for explaining a temporal transition of current and voltage of each part.

FIG. 4 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 5 is a diagram corresponding to FIG. 1 showing a third embodiment of the present invention.

FIG. 6 is a diagram corresponding to FIG. 1 showing a fourth embodiment of the present invention.

[Explanation of symbols]

1 is a commercial power supply, 2 is an input capacitor, 3 is a full-wave rectifier circuit, 4 is a choke coil, 5a and 5b are DC power supply lines, 6 is a smoothing capacitor, 7 is a DC power supply circuit, 8 is a heating coil (resonance coil), Reference numeral 9 is a resonance capacitor, 10 is a resonance circuit, 11 is an IGBT (switching element), 12 is a flywheel diode (rectifying element), 13 is an inverter circuit, 14 is an input setting unit, 15 is a current transformer, and 16 is input current detection. Reference numeral 17 is an input setting circuit, 18 is an input comparison circuit, 19 is an oscillation control unit (oscillation control means), 20 is a current transformer (resonance current phase detection means), 21 is a phase detection circuit (on-timing setting means), 22 is an oscillation circuit, 23 is an output control circuit, 24 is a drive circuit, 28 is a phase shift circuit, 30, 3
Reference numerals 7, 41 and 49 are comparison circuits, 36 is a differentiating circuit, 50 is a detecting capacitor, 51 is a detecting resistor, and 52 is a current transformer.

Claims (5)

(57) [Claims] 1. A direct current power supply circuit having a smoothing capacitor connected to an output stage, a resonance coil provided so as to convert a direct current output of the direct current power supply circuit into high frequency power, and a resonance coil which forms a resonance circuit together with the resonance coil. A capacitor, an inverter circuit including a switching element connected between the output terminals of the DC power supply circuit via the resonance coil in series, and a rectifying element connected in antiparallel to the switching element; When the resonance current phase detecting means for detecting a change in the resonance current flowing in the resonance capacitor at the time of off and the detection output of the resonance current phase detecting means are input and the maximum value of the resonance current flowing from the resonance capacitor to the resonance coil is exhibited. A phase shift circuit that generates an output signal whose phase is the zero cross phase, and the zero cross phase of the output signal of this phase shift circuit Circuit configuration with respect to the on-timing of the switching element, which is set within a period in which the terminal voltage when the switching element is off, which is obtained based on the detection time point, is substantially zero, and the timing when the switching element is actually turned on inverter apparatus characterized by comprising an on timing setting means for setting a timing in consideration of the delayed by a delay time that occurs in the above ([Delta] T). 2. A resonance current phase detection means is a detection capacitor for shunting a resonance current flowing through a resonance capacitor.
It is equipped with a capacitor and detects changes in the current of the detection capacitor.
To detect changes in the resonance current of the resonance capacitor.
2. The inn according to claim 1, wherein
Verta device. 3. The resonance current phase detection means includes a detection resistor for detecting a change in current of the detection capacitor.
Of the resonance capacitor based on the terminal voltage of the detection resistor.
3. The method according to claim 2, wherein a change in resonance current is detected.
Inverter device installed. 4. The resonance circuit comprises a resonance coil and a resonance capacitor.
Are connected in parallel, and the detection capacitor is the smoothing capacitor of the DC power supply circuit.
To detect the change of the resonance current of the resonance capacitor.
3. Also, it is provided so that
Is an inverter device described in 3. 5. The resonance current phase detection means includes a current transformer that detects the resonance current of the resonance capacitor, and changes the resonance current based on the detection output of the current transformer.
Any of claims 1, 2 or 4 characterized by detecting
Inverter device described there.