JP3602332B2 - High frequency voltage type inverter device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency voltage type inverter device that outputs a high-frequency voltage necessary for driving an induction heating device or the like.
[0002]
[Background Art]
2. Description of the Related Art Conventionally, in controlling the output of an induction load such as an induction heating device having an inductance component, a high-frequency voltage inverter device capable of adjusting the frequency of AC power supplied to the load has been used.
The high frequency voltage type inverter device converts AC power supplied from a commercial power supply into DC power once by a forward conversion circuit, and further converts this DC power into AC power by an inverse conversion circuit, thereby obtaining a required frequency, For example, an induction heating device outputs high-frequency power of about 50 to 200 kHz.
In a high-frequency voltage type inverter device, a MOSFET capable of a high-speed switching operation is often employed as a power control switching element employed in an inverse conversion circuit.
Further, as the forward conversion circuit, it is common to employ either a chopper type forward conversion circuit combining a rectifier diode and a chopper, or a thyristor type forward conversion circuit for controlling the phase of a thyristor as a rectifying element. .
[0003]
FIG. 2 shows an example of a high-frequency voltage type inverter device provided with a chopper type forward conversion circuit. In the figure, the high-frequency voltage type inverter device 50 includes a rectifier circuit 51 for rectifying an AC voltage from an AC power supply 1 by a diode 51A which is a passive element, and an intermittent connection with a subsequent stage. And a chopper circuit 52 for adjusting the DC voltage to a desired voltage level.
The high-frequency voltage type inverter device 50 is provided with an inverse conversion circuit 54 for converting a DC voltage output from the forward conversion circuit 53 into a high-frequency voltage by high-speed switching of the MOSFET 54A.
[0004]
FIG. 3 shows an example of a high-frequency voltage type inverter device provided with a thyristor type forward conversion circuit. In this figure, a high-frequency voltage type inverter device 60 rectifies an AC voltage from an AC power supply 1 with a thyristor 55A, which is an active element, and controls the phase of the thyristor 55A to intermittently connect to a subsequent stage. And a forward conversion circuit 55 for outputting a DC voltage of a desired voltage level.
The high frequency voltage type inverter device 60 is provided with an inverse conversion circuit 54 for converting the DC voltage output from the forward conversion circuit 55 into a high frequency voltage by high-speed switching of the MOSFET 54A, similarly to the high frequency voltage type inverter device 50 described above. Have been.
According to the high-frequency voltage type inverter device 60 provided with such a thyristor-type forward conversion circuit, the number and types of circuit elements forming the entire device are reduced and the circuit configuration is simplified, so that the reliability as a power source is improved. In addition, the efficiency and the manufacturing efficiency and the productivity are superior to the high-frequency voltage type inverter device 50 including the chopper type forward conversion circuit.
[0005]
Here, in the inverter device, a protection means such as a fuse or a circuit breaker is generally provided to protect each electric element from an overcurrent or the like. Since the time is long and it is not possible to cope with the high-speed switching operation of the switching element of the inverter circuit provided in the high-frequency voltage type inverter device, the switching element of the inverter circuit may be destroyed before the cutoff of the circuit is completed. In addition, sufficient protection of the switching element cannot be achieved.
On the other hand, in a high-frequency voltage type inverter device equipped with a chopper-type forward conversion circuit, the chopper of the forward conversion circuit enables high-speed circuit shutdown (shutdown completed in a few μs), so the chopper is forcibly shut down by detecting an overcurrent. If such a circuit is provided, destruction of the switching element of the inverse conversion circuit can be prevented, and sufficient protection of the switching element can be achieved.
[0006]
In a high-frequency voltage type inverter device provided with a thyristor-type forward conversion circuit, the thyristor has no self-extinguishing property and has a low cutoff speed (several tens of ms). Since the high-speed cutoff cannot be performed by itself, it is necessary to provide a protection circuit separately from the forward conversion circuit and the reverse conversion circuit.
FIG. 4 shows a high-frequency voltage type inverter device 71 having a general protection circuit 70. In the figure, a protection circuit 70 is connected between a thyristor-type forward conversion circuit 55 and an inverse conversion circuit 54, and has a thyristor 72 and a DC resistance element 73 connected in series.
If such a protection circuit 70 is provided, the thyristor 72 is turned on when an abnormality occurs, and the input current to the reverse conversion circuit 54 is bypassed to the ground side. In addition, the destruction of the switching element of the inverse conversion circuit 54 is prevented, and the switching element can be protected.
[0007]
[Problems to be solved by the invention]
In such a protection circuit 70, since the inverter device 71 is of a voltage type, the inductance 74 on the output side of the forward conversion circuit 55 is small, and when the protection circuit 70 becomes conductive, the input side of the inversion circuit 54 Since the charge of the capacitor 75 is discharged to the protection circuit 70 side, when the thyristor 72 is turned on at the time of abnormality, a large surge current flows through the protection circuit 70, and the surge current destroys the thyristor 72, and the protection circuit 70 There is a problem that 70 may be damaged.
In addition, the above-described surge current causes an AC overcurrent on the side of the AC power supply 1, and thus causes a problem that an overcurrent breaker or the like malfunctions.
In order to prevent such a large surge current, it is conceivable to set the DC resistance element 73 of the protection circuit 70 to be large. However, if the DC resistance element 73 is increased and the current flowing through the protection circuit 70 is reduced, the DC resistance element 73 can be reduced accordingly. However, the current flowing to the inversion circuit 54 increases, and the original function of the protection circuit 70 is impaired, and the possibility that the switching element of the inversion circuit is destroyed increases.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a high-frequency voltage type inverter device that protects a switching element of an inverting circuit by operation of a protection circuit and avoids damage to the protection circuit itself without complicating the entire circuit configuration. To provide.
[0009]
[Means for Solving the Problems]
The present invention provides a high-frequency voltage-type inverter including a forward conversion circuit that converts AC power supplied from an AC power supply into DC power, and an inverse conversion circuit that converts DC power from the forward conversion circuit into predetermined high-frequency power. A device, wherein a switching element is connected between the forward conversion circuit and the reverse conversion circuit, and by turning on the switching element, the reverse conversion circuit can be coupled to the forward conversion circuit. Do Ri, the switching element is the IGBT (Insulated Gate Bipolar Transistor), the forward conversion circuit, which has a thyristor as a rectifier element, which the thyristor is phase-controlled, an output current of the inverse transform circuit detecting, when the output current becomes larger than a predetermined value, the abnormality detecting trip circuit for the switching element to the off state is provided And it features.
In the present invention, a MOSFET and an IGBT capable of performing a high-speed switching operation can be adopted as the switching element. According to such a high-speed switching element, the connection between the forward conversion circuit and the reverse conversion circuit can be established. High-speed cutoff (shutdown completed in a few μs) becomes possible. If the switching element is turned off by detecting an overcurrent, the overcurrent does not flow to the reverse conversion circuit, and the switching element of the reverse conversion circuit is destroyed. Is prevented, and sufficient protection of the switching element can be achieved.
Then, during normal operation, the switching element of the protection circuit is in the ON state, so that a current larger than the rated current does not flow through the switching element. Since the switching element is turned off, no current flows through the switching element, a large surge current does not occur, and the switching element is not destroyed by an overcurrent.
Moreover, since the protection circuit is formed only by the switching elements connected between the forward conversion circuit and the reverse conversion circuit, the circuit configuration of the entire high-frequency voltage inverter device is not complicated at all.
[0010]
In the above, an IGBT that is a high-speed switching element is employed as the switching element . Here, since the IGBT has a large current capacity and a small on-resistance, the power loss in the on state is small, the input impedance is large, and the power required for the control operation is small.
For this reason, since the IGBT is employed , the power consumed by the IGBT is small . Therefore , as described above, even if the protection circuit in which the switching element is turned on during the normal operation is provided, the high-frequency voltage type inverter device can be used. Efficiency loss is minimized.
[0011]
Further, the forward conversion circuit, which has a thyristor as a rectifier element, the thyristor is phase-controlled.
Because it uses a forward conversion circuit for such a thyristor type, number and type of circuit elements forming the entire high-frequency voltage-type inverter device is reduced, since the circuit configuration is simplified, high-frequency voltage-type inverter device Thus, the reliability and efficiency as a power source, and the manufacturing efficiency and productivity are improved.
Furthermore, the detected output current of the inverse transform circuit, the output current becomes larger than a predetermined value, that have abnormality detecting trip circuit is provided for the switching element to the off state.
An overcurrent that can destroy the switching element of the inverting circuit often occurs due to an accident on the load side, such as a short circuit in a part of the load. Is quickly detected when the value exceeds the allowable value, the switching element of the protection circuit is quickly turned off, and the destruction of the switching element of the inverse conversion circuit is reliably prevented.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an inverter device 10 according to the present embodiment. The inverter device 10 is a high-frequency voltage type inverter device that converts AC power supplied from the three-phase AC power supply 1 into high-frequency power required for driving an induction heating device or the like. A forward conversion circuit 11 that outputs a current and an inverse conversion circuit 12 that converts DC power output by the forward conversion circuit 11 into AC power are provided.
The inverter device 10 includes, in addition to the forward conversion circuit 11 and the inverse conversion circuit 12, a protection circuit 13 connected between the forward conversion circuit 11 and the inverse conversion circuit 12, and an operation signal for driving control provided to the protection circuit 13. And an abnormality detection trip circuit 14 for sending out an alarm.
[0013]
The forward conversion circuit 11 includes a rectifier circuit 16 including a thyristor 15 which is an active rectifier having a gate serving as a control electrode, and a reactor for smoothing pulsating DC power rectified by the rectifier circuit 16. 17 and a capacitor 18 are provided. The inductance of the reactor 17 is set to a relatively small value so that the inverter device 10 is of a voltage type.
Here, the phase of the thyristor 15 of the rectifier circuit 16 is controlled during operation so that the output voltage thereof becomes a predetermined voltage.
[0014]
The inversion circuit 12 is provided with a switching circuit 19 for generating a square wave high-frequency voltage and a capacitor 20 for cutting off the high frequency to the switching circuit 19. The switching circuit 19 includes a MOSFET 21 that is a switching element capable of performing a high-speed switching operation.
The control voltage signal transmitted by a phase-locked loop circuit (not shown) is input to the gate of the MOSFET 21 of the inverse conversion circuit 15. The phase-locked loop circuit controls the frequency of the AC power output from the inverter device 10 to be equal to the resonance frequency of the load.
[0015]
The protection circuit 13 includes an IGBT 22 that is a high-speed switching element. The protection circuit 13 is turned on during normal operation, and connects the forward conversion circuit 11 and the inverse conversion circuit 12 to each other. The connection between the circuit 11 and the inverter circuit 12 is cut off, and the MOSFET 21 of the inverter circuit 12 is protected from overcurrent.
The abnormality detection trip circuit 14 includes a current transformer 23 for detecting an output current of the inverse conversion circuit 12, detects an abnormality based on an output signal of the current transformer 23, and when the abnormality is detected, the IGBT 22 of the protection circuit 13. Is forcibly shut off.
More specifically, the abnormality detection trip circuit 14 applies a drive operation voltage to the gate of the IGBT 22 provided in the protection circuit 13 when the output current of the inverse conversion circuit 12 is in a normal range, and the IGBT 22 It is set to be turned on.
On the other hand, when the output current of the inversion circuit 12 deviates from the normal range and becomes an overcurrent, the driving operation voltage applied to the gate of the IGBT 22 is released and the IGBT 22 is forcibly turned off. It is set as follows.
[0016]
According to the above-described embodiment, the following effects can be obtained.
That is, a high-speed switching element is provided between the forward conversion circuit 11 and the reverse conversion circuit 12 in order to protect the MOSFET 21 as a switching element provided in the reverse conversion circuit 12 of the high-frequency voltage type inverter device 10 from overcurrent. Since the IGBT 22 is connected, and the forward conversion circuit 11 and the reverse conversion circuit 12 are coupled to each other by the IGBT 22, it is possible to turn off the IGBT 22 at high speed by detecting an overcurrent. The reverse conversion circuit 12 is shut off, no overcurrent flows through the reverse conversion circuit 12, and the destruction of the MOSFET 21 of the reverse conversion circuit 12 is prevented, so that the MOSFET 21 can be reliably protected.
During normal operation, the IGBT 22 of the protection circuit 13 is in the ON state, so that a current larger than the rated current does not flow through the IGBT 22. In an abnormal state, the IGBT 22 is in the OFF state. A large surge current does not flow through the IGBT 22, and the IGBT 22 is not destroyed by the overcurrent, so that the protection circuit 13 itself can be prevented from being damaged.
Moreover, since the protection circuit 13 is simply formed by the IGBT 22 connected between the forward conversion circuit 11 and the inverse conversion circuit 12, the circuit configuration of the high frequency voltage type inverter device 10 is not complicated at all. .
[0017]
Further, since the IGBT 22 having a large current capacity is adopted as a switching element of the protection circuit 13 to suppress the power loss in the ON state, the protection circuit 13 in which the IGBT 22 is turned ON during normal operation is also used as the high-frequency voltage type inverter. The reduction in efficiency of the device 10 can be minimized.
Further, since such a protection circuit 13 and the forward conversion circuit 11 for controlling the phase of the thyristor 15 as a rectifier are combined, the number and types of circuit elements forming the entire high-frequency voltage type inverter device 10 are reduced, and The configuration is simplified, and the reliability and efficiency as a power source of the high-frequency voltage type inverter device 10, and the manufacturing efficiency and productivity can be improved.
[0018]
Further, the output current of the inverting circuit 21 is detected by the current transformer 23, and when the output current exceeds a predetermined value, the abnormality detecting trip circuit 14 for turning off the IGBT 22 is provided. Occurrence of an overcurrent due to an accident on the load side that causes an overcurrent that causes the element to be destroyed can be quickly detected, the IGBT 22 of the protection circuit 13 is quickly turned off, and the destruction of the MOSFET 21 of the reverse conversion circuit 12 is ensured. Can be prevented.
[0019]
As described above, the present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the embodiments, and various improvements and design changes can be made without departing from the gist of the present invention. .
In other words, the switching element of the protection circuit is not limited to the IGBT, but may be any element that can perform high-speed switching operation such as a MOSFET. Since the capacity is large, an effect is obtained that a reduction in efficiency of the high-frequency voltage type inverter device can be minimized.
Further, the forward conversion circuit is not limited to a thyristor type in which a thyristor as a rectifying element is phase-controlled to secure a predetermined output voltage, but may be a chopper type in which a predetermined output voltage is secured by a chopper. By employing a thyristor-type forward conversion circuit, as described above, it is possible to obtain an effect that the reliability and efficiency as a power source of the high-frequency voltage type inverter device 10 and the manufacturing efficiency and productivity can be improved.
[0020]
【The invention's effect】
As described above, according to the present invention, the switching element of the inverting circuit can be protected by the operation of the protection circuit and the protection circuit itself can be prevented from being damaged without complicating the entire circuit configuration.
[Brief description of the drawings]
FIG. 1 is a single connection diagram illustrating an embodiment of the present invention.
FIG. 2 is a single connection diagram showing a conventional example.
FIG. 3 is a single connection diagram showing another conventional example.
FIG. 4 is a single connection diagram showing still another conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 AC power supply 10 High frequency voltage type inverter device 11 Forward conversion circuit 12 Reverse conversion circuit 14 Abnormality detection trip circuit 15 Thyristor 22 as a rectifier element IGBT as a switching element

Claims (1)

A high-frequency voltage type inverter device comprising: a forward conversion circuit that converts AC power supplied from an AC power supply into DC power; and an inverse conversion circuit that converts the DC power from the forward conversion circuit into a predetermined high-frequency power. ,
A switching element is connected between the forward conversion circuit and the inverse conversion circuit, and by turning on the switching element, the inverse conversion circuit can be coupled to the forward conversion circuit,
The switching element is a IGBT (Insulated Gate Bipolar Transi st or ),
The forward conversion circuit has a thyristor as a rectifying element, and the thyristor is phase-controlled,
A high frequency voltage type inverter device comprising an abnormality detection trip circuit which detects an output current of the inversion circuit and turns off the switching element when the output current becomes larger than a predetermined value.

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