JPH04274189A - High frequency inverter - Google Patents

Abstract

PURPOSE:To form an electromagnetic cooking device or the like without generating inteference noise by setting a high frequency inverter to change a power easily at a constant frequency using an inverse continuity switching element for a first switching element, and a bidirectional switching element for a second switching element. CONSTITUTION:Switching elements 15, 19 are continuous at a period t0-t1, the element is discontinuous at a period t1-t2, and currents IQD1, IQD2 at the elements 15, 19 become zero. At a period t2-t3, both the elements 15, 19 are continuous. A DC voltage E us applied to a resonance coil 16 at this time. At a period t3-t4, the element is discontinuous, while the element 19 is continuous, the coil 16 and a capacitor 17 are in a resonating condition. and VQD1 is increased in resonarjce to reach a peak value Vp at a period t4. At a period t5-t6 the element 19 becomes continuous, and the coil 16 and the capacitor 17 resonate. By controlling to reduce a cyclic period TrOFF1 or TOFF2 corresponding to an increase of a cyclic period TcON, therefore, a cyclic period T0 can be constant. An output can thus be changed keeping the frequency constant.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency inverter constituting an electromagnetic cooker, an induction heating rice cooker, or a microwave oven used in general households.

0002

2. Description of the Related Art Conventionally, this type of high frequency inverter was constructed as shown in FIG. In the figure, 1 is a DC power supply consisting of a rectifier stack 3 connected to an AC power supply 2 and a smoothing capacitor 4 connected to this, and 5 is a switching element consisting of a transistor 6 and an anti-parallel diode 7, which is a reverse conduction switching element. . 8 is a resonant coil, 9 is a resonant capacitor, and 10 is a control circuit. The resonant coil 8 is a heating coil in the case of an electromagnetic cooker or an induction heating rice cooker, and a step-up transformer in the case of a microwave oven.

FIG. 10 shows operating waveforms of the conventional example shown in FIG.
IC is the current of the switching element 6 shown in FIG. 9, and VCE is the voltage across the switching element 6. Control circuit 10
controls conduction/cutoff of the switching element 6 as indicated by Q in FIG. During the conduction period TON of the switching element 6, the DC voltage VDC is applied to the resonant coil 8 shown in FIG. 9, and the IC increases. When the switching element 6 is turned off, the resonant coil 8 and the resonant capacitor 9 enter a resonant state, and VCE reaches a peak as shown in FIG. 10 and then becomes zero again. When VCE reaches zero, the switching element 6 becomes conductive again and oscillation continues. By changing the TON shown in the figure, the power supplied from the DC power supply 1 to the high frequency inverter, that is, the output of the high frequency inverter can be varied.

0004

However, in such a conventional configuration, when TON is changed in an attempt to vary the output of the high frequency inverter, the operating frequency 1/(TO
N+TOFF) changes, which poses the following problems. (1) For example, 1 like a multi-burner electromagnetic cooker.
When multiple high-frequency inverters are installed in one device,
When devices equipped with high-frequency inverters are placed close to each other, the difference in operating frequency of each inverter is within the audible range (several 10
Hz to 20kHz) and becomes interference noise. (2) Power supply filters become expensive because the operating frequency becomes broadband.

The present invention has solved the above-mentioned conventional problems, and aims to provide a high frequency inverter that eliminates interference noise and eliminates the need for expensive filters.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a high frequency inverter of a first invention includes a first switching element connected to a DC power supply, and a link between the first switching element and the DC power supply. A series circuit of a connected resonant coil and a second switching element, a resonant capacitor connected in parallel to the series circuit or the first switching element, and a control circuit connected to the first switching element and the second switching element. The first switching element is a reverse conduction switching element, and the second switching element is a bidirectional switching element.

A high frequency inverter according to a second aspect of the invention includes a series circuit including a first switching element connected to a DC power supply, a resonant coil connected between the first switching element and the DC power supply, and a second switching element. and a resonant capacitor connected in parallel to the series circuit or the first switching element, and a control circuit connected to the first switching element and the second switching element,
The switching element and the second switching element are reverse conduction switching elements, and the first switching element and the second switching element are connected so that they conduct in the same direction.

[0008] In the high frequency inverter of the third invention, the control circuit detects the reverse conduction period of the first switching element and the second switching element, and the control circuit detects the reverse conduction period of the first switching element and the second switching element. The first switching element is turned on until the switching element is turned on, and the second switching element is turned off during the reverse conduction period of the second switching element.

A high frequency inverter according to a fourth aspect of the invention includes a series circuit including a first switching element connected to a DC power supply, a resonant coil connected between the first switching element and the DC power supply, and a second switching element. a resonant capacitor connected in parallel to the series circuit or the first switching element, and a control circuit connected to the first switching element and the second switching element, the first switching element and the The second switching element is a reverse conduction switching element, and the first switching element and the second switching element are connected in opposite conduction directions.

[0010] In the high frequency inverter of the fifth aspect of the invention, the control circuit detects the reverse conduction period of the first switching element and the second switching element, and during the reverse conduction period of the first switching element, the control circuit detects the reverse conduction period of the first switching element and the second switching element. The switching element is turned on, and the second switching element is turned off during the reverse conduction period of the second switching element.

[0011]

[Operation] The high frequency inverter of the first invention includes a reverse conduction switching element as the first switching element, and a reverse conduction switching element as the first switching element.
By applying a bidirectional switching element as the switching element, power can be easily varied at a constant frequency.

[0012] In the high-frequency inverter of the second invention, the first switching element and the second switching element are reverse conduction switching elements, and the first switching element and the second switching element are conductive in the same direction. By connecting them in such a manner, it is possible to realize variable power at a constant frequency with a simpler configuration.

[0013] In the high-frequency inverter of the third invention, the control circuit detects the reverse conduction period of the first switching element and the second switching element, and the control circuit detects the reverse conduction period of the first switching element and the second switching element. By turning on the first switching element before turning on the switching element and turning off the second switching element during the reverse conduction period of the second switching element,
It is possible to realize stable operation during sudden changes in power supply or startup.

[0014] In the high frequency inverter of the fourth invention, the first switching element and the second switching element are reverse conduction switching elements, and the first switching element and the second switching element are conductive in opposite directions. By connecting the second switching element in such a manner, the second switching element can be driven more stably and easily.

[0015] In the high frequency inverter of the fifth aspect of the invention, the control circuit detects the reverse conduction period of the first switching element and the second switching element, and during the reverse conduction period of the first switching element, the control circuit detects the reverse conduction period of the first switching element and the second switching element. by turning on a switching element and turning off a second switching element during a reverse conduction period of the second switching element;
It is possible to realize stable operation during sudden changes in power supply or startup.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a high frequency inverter according to the first invention, in which 11 is a rectifier stack 13 connected to an AC power supply 12, a DC power supply consisting of a smoothing capacitor 14 connected to this, 15 a transistor Q1, Anti-parallel diode D
1, which is a reverse conduction switching element. 16 is a resonant coil, 17 is a resonant capacitor, and 18 is a control circuit. 19 is a second switching element, which includes transistors 20 connected in series in the opposite direction;
21, a bidirectional switching element consisting of diodes 22 and 23.

FIG. 2 shows operating waveforms of the high frequency inverter in FIG. 1, and IQD1 is the first switching element 15 in FIG.
The current VQD1 is the voltage across the first switching element 15. QD1 indicates conduction/cutoff of the first switching element 15 controlled by the control circuit 18. I
Q2 is the current of the second switching element 19 in FIG. 1, VQ
2 is the voltage across the second switching element 19. Q2 indicates conduction/cutoff of the second switching element 19 controlled by the control circuit 18.

From time t0 to time t1, both the first switching element 15 and the second switching element 19 are conductive. At this time, the DC voltage E shown in FIG. 1 is applied to the resonant coil 16, and IQD1=IQ2 increases and reaches zero at time t1.

From time t1 to time t2, the second switching element 19 is cut off, and both IQD1 and IQ2 become zero. Since the current in the resonant coil becomes zero, the voltage across it also becomes zero, and since the first switching element 15 is conductive, VQ2=E. As you can easily see, this IQD
The states of 1=0, IQ2=0, VQD1=0, and VQ2=E are maintained regardless of the magnitude of the cutoff period TOFF1 in FIG. Therefore, TOFF1 can be set freely.

[0020] From time t2 to t3, both the first switching element 15 and the second switching element 19 are conductive. At this time, the DC voltage E shown in FIG. 1 is applied to the resonant coil 16, and IQD1=IQ2 increases.

[0021] From time t3 to t4, the first switching element 15 is cut off and the second switching element 19 is conductive, so that the resonant coil 16 and the resonant capacitor 17 are in a resonant state, and VQD1 increases resonantly. After reaching its peak, IQ2 reaches zero again at time t4. VQ at time t4
D1 becomes the peak value VP.

[0022] From time t4 to time t5, both the first switching element 15 and the second switching element 19 are cut off. Therefore, the voltage of the resonant capacitor 17 at time t4 -VP
+E becomes a held state and is held at VQD1=VP. Also, since the voltage of the resonant coil is zero, VQ2=-VP+
It is held at E. As can be easily seen, in principle, this state is held constant regardless of the magnitude of the cutoff period TOFF2 in FIG. Therefore, TOFF2 can be set freely.

From time t5 to time t6, the first switching element 15 is cut off, the second switching element 19 is conductive, the resonant coil 16 and the resonant capacitor 17 are in a resonant state, and VQD1 decreases resonantly. reaches zero. At time t6, the first switching element 15 becomes conductive, returning to the initial state at time t0, and oscillation continues.

[0024] In the above operation, the first switching element turns on and turns off at zero voltage, that is, performs zero voltage switching, and the second switching element turns on and turns off at zero current, that is, performs zero current switching. It has small element duty, low loss, and low noise.

When TON in FIG. 2 is changed, the DC power supply 11
The power supplied to the high frequency inverter from the high frequency inverter, that is, the output of the high frequency inverter can be varied. At this time, the cycle T0 is kept constant by controlling TOFF1 or TOFF2 to decrease in accordance with the increase in TON. Therefore, the output can be varied while keeping the operating frequency 1/T0 constant.

FIG. 3 shows a high frequency inverter according to the second invention, in which 24 is a rectifier stack 26 connected to an AC power source 25.
, a DC power supply consisting of a smoothing capacitor 27 connected thereto, and a first switching element 28 consisting of a transistor Q1 and an anti-parallel diode D1, which is a reverse conduction switching element. 29 is a resonant coil, 30 is a resonant capacitor, and 31 is a control circuit. A second switching element 32 is a reverse conduction switching element composed of a transistor Q2 and an anti-parallel diode D2. The first switching element and the second switching element are connected in the same conduction direction.

FIG. 4 shows operating waveforms of the high frequency inverter of FIG. 3, and IQD1 is the first switching element 28 of FIG.
The current VQD1 is the voltage across the first switching element 28. QD1 indicates conduction/cutoff of the first switching element 28 controlled by the control circuit 31. I
QD2 is the current of the second switching element 32 in FIG.
QD2 is the voltage across the second switching element 32. QD2 indicates conduction/cutoff of the second switching element 32 controlled by the control circuit 31.

From time t0 to time t1, both the first switching element 28 and the second switching element 32 are conductive. At this time, the DC voltage E shown in FIG. 3 is applied to the resonant coil 29, and IQD1=IQD2 increases and reaches zero at time t1. From time t1 to t2, the second switching element 3
2 is blocked, and both IQD1 and IQD2 become zero. Since the current in the resonant coil 29 becomes zero, the voltage across it also becomes zero, and since the first switching element 28 is conductive, VQD2=E. As you can easily see, this
IQD1=0, IQD2=0, VQD1=0, VQD2
The state of =E is maintained regardless of the magnitude of the cutoff period TOFF in FIG. Therefore, TOFF can be set freely.

From time t2 to time t3, both the first switching element 28 and the second switching element 32 are conductive. At this time, the DC voltage E shown in FIG. 3 is applied to the resonant coil 29, and IQD1=IQD2 increases. Time t3-t
4, the first switching element 28 is cut off, the second switching element 32 is conductive, the resonant coil 29 and the resonant capacitor 30 are in a resonant state, and VQD1 increases resonantly and reaches its peak. It reaches zero again. IQD
2 oscillates negatively after reaching zero. At time t4, the first switching element 28 becomes conductive, returning to the initial state at time t0, and oscillation continues.

In the above operation, the first switching element is turned on and turned off at zero voltage, ie, performs zero voltage switching, and the second switching element is turned on and turned off at zero current, ie, performs zero current switching. Switching element responsibility is small, low loss,
Low noise.

When TON in FIG. 4 is changed, the DC power supply 24
The power supplied to the high frequency inverter from the high frequency inverter, that is, the output of the high frequency inverter can be varied. At this time, the cycle T0 is kept constant by controlling TOFF to decrease in accordance with the increase in TON. Therefore, the operating frequency 1
The output can be varied while keeping /T0 constant.

In the case of the configuration shown in FIG. 3, since a reverse conduction switching element is used as the second switching element 32,
When IQD2 reaches zero between times t3 and t4 in FIG. 4, the current cannot be cut off and the anti-parallel diode D2 naturally becomes conductive. Therefore, since there is no freely settable period corresponding to TOFF2 in FIG. 2, the degree of freedom in control is slightly lower than in the high frequency inverter in FIG. 1. However, in the configuration of FIG. 3, the number of components constituting the second switching element is small, so it is inexpensive and highly reliable.

FIG. 5 shows operating waveforms of the control circuit of the third invention, and Q1 and Q2 indicate conduction (ON) and cutoff (OFF) of the transistors Q1 and Q2 of FIG. The control circuit detects the reverse conduction period of the first switching element 28 and the second switching element 32, and starts the reverse conduction period of the first switching element 28 from t0 to the time of the second switching element 32. The transistor Q1 is turned on until turn-on t2. Further, the second switching element is turned off during the reverse conduction period t5 to t4 of the second switching element. The reverse conduction period of the first switching element 28 can be easily detected by inserting a current transformer or a microresistance into the first switching element 28 and detecting the current IQD1. 28 zero points of the voltage VQD1 may be detected. Further, the reverse conduction period of the second switching element 32 can be easily detected by inserting a current transformer or a microresistance into the second switching element 32 and detecting the current IQD2. The peak point of the voltage VQD1 of the switching element 28 (dVDQ1
/dt=0) may be detected. By controlling in this manner, the necessary switching timing can be reliably maintained even when the power supply suddenly changes or when the inverter starts up.

FIG. 6 shows the configuration of a high frequency inverter according to the fourth invention, in which 33 is a rectifier stack 35 connected to an AC power supply 34, a DC power supply consisting of a smoothing capacitor 36 connected to this, 37 is a transistor Q1, and an inverse A first switching element consisting of a parallel diode D1, which is a reverse conduction switching element. 38 is a resonant coil, 39 is a resonant capacitor, and 40 is a control circuit. 41 is a second switching element, which includes a transistor Q2 and an anti-parallel diode D2.
This is a reverse conduction switching element consisting of. The first switching element and the second switching element are connected in opposite conduction directions.

FIG. 7 shows operating waveforms of the high frequency inverter of FIG. 6, and IQD1 is the first switching element 37 of FIG.
The current VQD1 is the voltage across the first switching element 37. QD1 indicates conduction/cutoff of the first switching element 37 controlled by the control circuit 40. I
QD2 is the current of the second switching element 41 in FIG. 6, V
QD2 is the voltage across the second switching element 41. QD2 indicates conduction/cutoff of the second switching element 41 controlled by the control circuit 40.

From time t0 to time t1 to time t2, both the first switching element 37 and the second switching element 41 are conductive. At this time, the DC voltage E shown in FIG. 6 is applied to the resonant coil 38, and IQD1=-IQD2 increases and reaches zero at time t1.

From time t2 to t3, the first switching element 37 is cut off, the second switching element 41 is conductive, the resonant coil 38 and the resonant capacitor 39 are in a resonant state, and VQD1 increases resonantly. The peak value VP is reached. At this time, IQD1 reaches zero. From time t3 to t4, the second switching element 41 is cut off, and the IQD
1 and IQD2 both become zero. Therefore, the resonant capacitor 29
voltage is maintained, VQD1=VP, VQD2=VP-
maintained at E. As you can easily see, this IQD1=
0, IQD2=0, VQD1=VP, VQD2=VP-
The state E is maintained regardless of the magnitude of the cutoff period TOFF in FIG. Therefore, TOFF can be set freely.

[0038] From time t4 to t5, the first switching element 37 is cut off and the second switching element 41 is conductive, so that the resonant coil 38 and the resonant capacitor 39 are in a resonant state, and VQD1 decreases resonantly. , reaches zero. I
QD2 vibrates positively. At time t5, the first switching element 37 becomes conductive, returning to the initial state at time t0, and oscillation continues.

In the above operation, the first switching element turns on and turns off at zero voltage, that is, performs zero voltage switching, and the second switching element turns on and turns off at zero current, that is, performs zero current switching. Switching element responsibility is small, low loss,
Low noise.

When TON in FIG. 7 is changed, the DC power supply 33
The power supplied to the high frequency inverter from the high frequency inverter, that is, the output of the high frequency inverter can be varied. At this time, the cycle T0 is kept constant by controlling TOFF to decrease in accordance with the increase in TON. Therefore, the operating frequency 1
The output can be varied while keeping /T0 constant.

In the configuration shown in FIG. 6, since a reverse conduction switching element is used as the second switching element 41,
When IQD2 reaches zero at time t1 in FIG. 4, the current cannot be cut off and the anti-parallel diode D2 naturally becomes conductive. Therefore, since there is no freely settable period corresponding to TOFF1 in FIG. 2, the degree of freedom in control is slightly lower than in the high frequency inverter in FIG. However, in the configuration of FIG. 6, the number of components constituting the second switching element is small, so it is inexpensive and highly reliable. Furthermore, compared to the high frequency inverter of FIG. 3, the emitter of the transistor Q2 constituting the second switching element is directly connected to the output of the DC power supply 36, so the emitter potential is stable. Therefore, driving Q2 is easy.

FIG. 8 shows operating waveforms of the control circuit of the fifth invention, and Q1 and Q2 indicate conduction (ON) and cutoff (OFF) of the transistors Q1 and Q2 of FIG. 6. The control circuit detects the reverse conduction period of the first switching element 37 and the second switching element 41, and turns on the transistor Q1 during the reverse conduction period of the first switching element 37 from t0 to t1. Also, during the reverse conduction period t1 to t2 to t3 of the second switching element, the transistor Q
Turn off 2. the first switching element 3
7, the detection of the reverse conduction period is performed by the first switching element 37.
Insert a current transformer or microresistance into the current IQD1
This can be easily done by detecting the zero point of the voltage VQD1 of the first switching element 37. Further, the reverse conduction period of the second switching element 41 can be easily detected by inserting a current transformer or a microresistance into the second switching element 41 and detecting the current IQD2. By inserting a current transformer or a microresistance into the switching element 37, the current IQ
D1 may also be detected. By controlling in this manner, the necessary switching timing can be reliably maintained even when the power supply suddenly changes or when the inverter starts up.

Note that in the embodiments shown in FIGS. 1, 3, and 6, the first
The switching element and the second switching element were explained using a bipolar transistor and an anti-parallel diode, but
MOSFET, IGBT, SIT, SI thyristor, G
Any switching element may be used as long as it is a self-turn-off element such as a TO thyristor, and since the second switching element performs zero-current switching, it may be composed of a commutating turn-off element such as a thyristor. Further, the DC power supply is composed of an AC power supply, a rectifier stack, and a smoothing capacitor, but the smoothing capacitor has a size similar to that of a high-frequency filter and may be a pulsating current power supply (unsmoothed power supply) or a battery. Furthermore, although the resonant capacitor is connected in parallel to the series circuit of the heating coil and the second switching element, it may also be connected in parallel to the first switching element, and the resonant capacitor may be connected in parallel to the series circuit of the heating coil and the second switching element, and One switching element may be connected in parallel to each of the switching elements.

[0044]

[Effect of the invention] As is clear from the above embodiments, the first
The high-frequency inverter invented by can easily vary the power at a constant frequency, solving problems such as interference noise and expensive filters, and producing high-quality and inexpensive induction cookers.
It is possible to realize induction heating rice cookers, microwave ovens, etc.

[0045] The high-frequency inverter of the second invention can realize variable power at a constant frequency with a simpler configuration than the first invention, so it can be used for high-quality and cheaper electromagnetic cookers and induction heating rice cookers. It is possible to realize a container, a microwave oven, etc.

The high-frequency inverter of the third invention can realize more stable operation during sudden changes in power supply or startup than the second invention, so it can be used in high-quality, inexpensive, and reliable electromagnetic cookers, induction heating type It can be used as a rice cooker, microwave oven, etc.

[0047] The high-frequency inverter of the fourth invention can drive the second switching element more stably and easily than the second invention, so that a high-quality, cheaper, and more reliable electromagnetic cooker can be obtained. , induction heating rice cookers, microwave ovens, etc.

The high-frequency inverter of the fifth invention can achieve more stable operation during sudden power changes or startup than the fourth invention, so it can be used in high-quality, inexpensive, and more reliable electromagnetic cookers and induction heating. It is possible to realize rice cookers, microwave ovens, etc.

[Brief explanation of the drawing]

[Fig. 1] A circuit configuration diagram showing an embodiment of the first invention.

[Figure 2
] An operation waveform diagram explaining the operation of the embodiment shown in FIG.

[Figure 3]
Circuit configuration diagram showing an embodiment of the second invention

FIG. 4 is an operation waveform diagram explaining the operation of one embodiment of FIG. 3;

[Fig. 5] Operation waveform diagram showing the control circuit of the third invention

FIG. 6 is a circuit configuration diagram showing an embodiment of the fourth invention.

FIG. 7 is an operation waveform diagram explaining the operation of the embodiment in FIG. 6;

[Fig. 8] Operation waveform diagram showing the control circuit of the fifth invention

[Figure 9] Circuit configuration diagram showing a conventional example

[Fig. 10] Operation waveform diagram explaining the operation of the conventional example shown in Fig. 9.

[Explanation of symbols]

11, 24, 33 DC power supply 15, 28, 37 First switching element 16, 2
9, 38 Resonance coil 17, 30, 39 Resonance capacitor 18, 31, 40 Control circuit

Claims (5)

[Claims] 1. A first switching element connected to a DC power source; a series circuit of a resonant coil and a second switching element connected between the first switching element and the DC power source; a resonant capacitor connected in parallel to the first switching element and a control circuit connected to the first switching element and the second switching element, wherein the first switching element is a reverse conducting switching element and the second switching element is connected to the second switching element. The switching element is a high frequency inverter that uses bidirectional switching elements. 2. A first switching element connected to a DC power supply, a series circuit of a resonant coil and a second switching element connected between the first switching element and the DC power supply, and a first switching element connected to the first switching element and the second switching element; a resonant capacitor connected in parallel to the first switching element and a control circuit connected to the first switching element and the second switching element, the first switching element and the second switching element having reverse conduction. Applying switching elements,
A high frequency inverter in which the first switching element and the second switching element are connected in the same conduction direction. 3. The control circuit detects a reverse conduction period of the first switching element and the second switching element, and detects the reverse conduction period of the first switching element until the turn-on of the second switching element. 3. The high frequency inverter according to claim 2, wherein the first switching element is turned on during the reverse conduction period of the second switching element, and the second switching element is turned off during the reverse conduction period of the second switching element. 4. A first switching element connected to a DC power supply, a series circuit of a resonant coil and a second switching element connected between the first switching element and the DC power supply, and a first switching element connected to the first switching element and the DC power supply; a resonant capacitor connected in parallel to the first switching element and a control circuit connected to the first switching element and the second switching element;
The switching element is a reverse conduction switching element, and the first switching element and the second switching element are connected in opposite conduction directions. 5. The control circuit detects a reverse conduction period of the first switching element and the second switching element, and turns on the first switching element during the reverse conduction period of the first switching element, The high frequency inverter according to claim 4, wherein the second switching element is turned off during a reverse conduction period of the second switching element.