JP2007333553A - Resonance frequency measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonance frequency measuring method which prevents a self-arc-suppressing type switching element from breaking down, and can measure the resonance frequency of a resonance circuit with high accuracy, by using an oscillating current waveform output from an inverter. <P>SOLUTION: A high-frequency power supply is equipped with a single-phase output voltage type full bridge inverter 100, wherein two element pairs which are composed of MOSFETs 2, 3 and MOSFETs 8, 9 respectively connected in series, are connected to a DC power supply 1 in parallel, and connection points of MOSFETs of respective element pairs are used as a pair of AC output terminals. In the high-frequency power supply, an inductive impedance 4 and a parallel circuit of a resonance capacitor 5 and a load 200 are connected in series between the pair of AC output terminals. A positive or a negative DC voltage signal is output from the inverter 100 for a prescribed period, and then the output current of the inverter 100 is oscillated, by controlling the MOSFETs 2, 3, 8 and 9 to be turned on/off so that the output voltage becomes zero; and the oscillation frequency is measured, thereby obtaining the resonance frequency of the resonance circuit, including the load 200. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of measuring a resonance frequency of a resonance circuit including a load by a high-frequency power supply device including a single-phase output voltage type full-bridge inverter or a single-phase output voltage type half-bridge inverter.

  In a high frequency power supply apparatus having an output frequency of several tens of kHz to several hundreds of kHz, the load circuit is constituted by a resonance circuit. This type of power supply device uses a voltage source inverter that uses a self-extinguishing switching element, and operates at an output frequency higher than the resonance frequency so that the output current is always in a lagging phase with respect to the output voltage. I have to do it.

When a MOSFET is used as a self-extinguishing switching element of a voltage type inverter and a parasitic diode of a MOSFET is used as a freewheeling diode connected in reverse parallel to this element, if the inverter is operated at an output frequency lower than the resonance frequency, the output of the inverter The output current advances in phase with respect to the voltage, causing the parasitic diode to sharply reversely recover and destroy the MOSFET.
For this reason, it is very important to accurately grasp the resonance frequency of the load circuit in this type of high-frequency power supply device.

When the load circuit is inductive, the actual load circuit constant is determined by calculating the capacitance of the resonance capacitor for resonating at a frequency lower than the output frequency of the high frequency power supply device from the inductance of the load circuit.
Here, in order to obtain the required resonance frequency, it is necessary to determine the inductance and resistance of the load circuit. However, the load circuit may include a metal heated by a coil, and the inductance is unknown. There are many things. In addition, the inductance of the load circuit may be 1 μH or less, and the inductance of the load circuit viewed from the power supply device is usually changed to a degree that cannot be ignored due to the influence of the wiring inductance or the like.
On the other hand, even if the constant of the load circuit is to be measured with an LCR meter or the like, the load circuit of the high frequency power supply device with an output of several tens to several hundred kW has a total length of several meters in a high frequency resistance welding machine for an electric resistance steel pipe, for example. The measurement work is difficult and takes a lot of time.

  As described above, since it is difficult to accurately grasp the resonance frequency of the load circuit of the high frequency power supply device at the design stage, it is more reliable to measure the resonance frequency after manufacture. As one of the methods, there is a method of actually flowing a current from an inverter to a load circuit and measuring a resonance frequency from the current waveform.

Here, FIG. 4 shows a main circuit configuration of the high-frequency power supply device for explaining the background art.
In FIG. 4, a voltage source inverter 100 includes an element pair in which self-extinguishing switching elements 2 and 3 made of MOSFETs are connected in series and an element pair in which self-extinguishing switching elements 8 and 9 are connected in series. This is a so-called single-phase output voltage type full-bridge inverter that is configured to be connected in parallel to the DC voltage source 1 and that uses the connection point between the elements of each element pair as an AC output terminal.
A pair of AC output terminals of the inverter 100 is connected to a resonance capacitor 10 and a load 200 composed of an inductive impedance 6 and a resistance component 7 in series. A series resonance circuit is formed by the resonance capacitor 10 and the load 200. It is configured.

FIG. 5 is a waveform diagram showing the operation of FIG.
As shown in FIG. 5, when turning on the element 2,9 of the inverter 100 at time _{t 0,} a DC voltage is output as a voltage _{V o.} As is well known, when a DC voltage is applied to a series circuit composed of a capacitor, an inductance, and a resistor, the current oscillates at a frequency substantially equal to the resonance frequency when the circuit constant is oscillating. However, the output current _Io oscillates substantially at the resonance frequency, and this can be measured.

Further, FIG. 6 shows a main circuit configuration of another high frequency power supply device for explaining the background art.
The configuration of the inverter 100 is the same as that in FIG.
A parallel circuit of a resonant capacitor 5 and a load 200 is connected to a pair of AC output terminals of the inverter 100 via an inductive impedance 4, and the load 200 has an inductive impedance 6 and a resistance component 7 as described above. And a series circuit.
In this case, a series-parallel resonant circuit is configured by the inductive impedance 4 and the parallel circuit of the resonant capacitor 5 and the load 200.

FIG. 7 is a waveform diagram showing the operation of FIG.
In the same manner as in FIG. 5, when turning on the element 2,9 of the inverter 100 at time t _0, but the DC voltage is output as a voltage V _o, for this DC voltage component, to the output side of the inverter 100 Inductive impedance 4, inductive impedance 6, and resistance component 7 are connected in series. Therefore, the output current _Io increases as shown in FIG. 7 and finally becomes a current value determined by the resistance value of the resistance component 7. Here, since the resistance value of the resistance component 7 is usually several tens of mΩ to several hundreds of mΩ, the output current I _o is several thousand A to several tens of thousands A with respect to several hundreds V of the output voltage V _o , and the allowable value of the inverter 100 As a result of exceeding the current, the inverter 100 is stopped by the overcurrent protection operation.
Therefore, in the high frequency power supply device as shown in FIG. 6, as long as the inverter 100 is normally operated, it is impossible to obtain the resonance frequency from the output current waveform.

  On the other hand, in a discharge lamp lighting device as a high-frequency power supply device, by detecting that the phase of the output current has advanced with respect to the inverter output voltage in the event of an abnormality due to the end of life of the discharge lamp, Patent Document 1 discloses a technique for preventing an excessive voltage from being applied to a discharge lamp or a resonant capacitor.

Japanese Patent Laying-Open No. 2003-224981 (paragraphs [0015] to [0018], FIG. 28, etc.)

As shown in FIG. 6, when a MOSFET is used for the voltage source inverter 100, after the output current has advanced and reached the phase with respect to the output voltage of the inverter 100, the parasitic diode steeply reversely recovers as described above. May be destroyed.
For this reason, the prior art described in Patent Document 1 cannot protect the element, and the resonance frequency cannot be obtained based on the output current waveform.

  Accordingly, the problem to be solved by the present invention is to provide a resonance frequency measuring method capable of measuring the resonance frequency of a resonance circuit including an inductive impedance, a resonance capacitor and a load with high accuracy while preventing destruction of the switching element. is there.

In order to solve the above-mentioned problems, the invention described in claim 1 is characterized in that two element pairs each comprising a self-extinguishing switching element connected in series are connected in parallel to a DC voltage source, and the switching of each element pair is performed. Equipped with a single-phase output voltage type full bridge inverter with the connection point between elements as a pair of AC output terminals,
In the high frequency power supply apparatus in which the inductive impedance and the parallel circuit of the resonant capacitor and the load are connected in series between the pair of AC output terminals,
The inverter output current is vibrated by controlling on and off of the switching element so that the output voltage of the inverter becomes zero after outputting a positive or negative DC voltage from the inverter for a predetermined period. By measuring the resonance frequency of the resonance circuit including the inductive impedance, the resonance capacitor, and the load.

According to a second aspect of the present invention, an element pair composed of self-extinguishing switching elements connected in series is connected to both ends of a DC voltage source, and a connection point between the switching elements and one end of the DC voltage source are paired. It is equipped with a single-phase output voltage type half-bridge inverter as an AC output terminal of
In the high frequency power supply apparatus in which the inductive impedance and the parallel circuit of the resonant capacitor and the load are connected in series between the pair of AC output terminals,
After a positive DC voltage is output from the inverter for a predetermined period, the switching element is turned on and off so that the output voltage of the inverter becomes zero, and the output current of the inverter is vibrated and the frequency is measured. Thus, the resonance frequency of the resonance circuit including the inductive impedance, the resonance capacitor, and the load is obtained.

The invention described in claim 3 is the resonance frequency measuring method according to claim 1 or 2, wherein
The predetermined period is a period within a half cycle of the output current of the inverter.

The invention described in claim 4 is the resonance frequency measuring method according to any one of claims 1 to 3,
The self-extinguishing type switching element is a MOSFET having a parasitic diode.

According to the present invention, the resonance frequency of the resonance circuit including the load can be measured before the normal operation of the inverter, and if the output frequency of the inverter is appropriately set based on the resonance frequency, the output voltage of the inverter Thus, it is possible to operate the output current with a delayed phase.
For this reason, for example, when a MOSFET element is used as a self-extinguishing switching element of an inverter and a parasitic diode of the MOSFET is used as a freewheeling diode, there is no possibility of destroying the MOSFET, and the reliability of the high-frequency power supply device is improved. be able to. In addition, the resonance frequency can be easily measured as compared with a frequency calculation method using a constant measurement of a load circuit using an LCR meter or the like, so that measurement time can be shortened and measurement equipment can be simplified.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a waveform diagram showing the operation of the first embodiment of the present invention. The main circuit configuration of the high-frequency power supply apparatus to which this embodiment is applied is the same as that of FIG. Single-phase output voltage type full-bridge inverter 100, inductive impedance 4 having one end connected to one AC output terminal of inverter 100, and the other end of impedance 4 and the other AC output terminal of inverter 100 The resonance capacitor 5 is connected, and the load 200 is connected in parallel to the capacitor 5 and is composed of a series circuit of an inductive impedance 6 and a resistance component 7.

Next, a resonance frequency measuring method according to this embodiment will be described.
First, when turning on the device 2, 9 which constitute the inverter 100 at time t _0, a DC voltage is output as well as voltage V _o and 7, the output current I _o is increases. Here, the element 9 is turned off at an arbitrary time t ₁ before the phase of I _o advances to the output voltage V _o , that is, before the polarity of I _o is reversed. A certain element 8 is turned on. Thus, a pair of AC output terminals of the inverter 100 will be both through the element 2 or 8 is connected to the positive pole of the DC voltage source 1, the output voltage V _o becomes zero voltage.
That is, since the inverter 100 does not continue to output a DC voltage as shown in FIG. 7, there is no possibility that the output current _Io becomes an overcurrent. For this reason, the operation of the inverter 100 can be continued without stopping.

Further, by continuing to turn on the elements 2 and 8 after the time t ₁ , the output side of the inverter 100 is short-circuited through these elements 2 and 8. Therefore, the vibration of the resonance circuit constituted by the inductive impedance 4, the resonance capacitor 5, and the load 200 in which the inductive impedance 6 and the resistance component 7 are connected in series is sustained, and vibrates substantially at the resonance frequency. It is possible to measure the frequency of the output current _Io . In addition, after frequency measurement, it shifts to normal operation and the elements 2, 3, 8, and 9 of the inverter 100 may be switched at a frequency higher than the measured frequency.
In this way, the frequency of the output current _Io is measured, and the inverter 100 is switched at a frequency higher than that frequency, so that the steep reverse recovery of the parasitic diode is prevented and the overvoltage of the elements 2, 3, 8, and 9 is reduced. Destruction can be prevented.

  Here, for example, in Japanese Patent Laid-Open No. 2003-33030, in a power supply system that supplies an AC voltage from a single-phase output voltage type full-bridge inverter to a resonance circuit having a transformer, the resonance current flowing to the primary side of the transformer is measured. Thus, a power supply system is disclosed in which the resonance frequency, resonance impedance, and the like are measured. In this power supply system, the resonance frequency is measured by turning on the switching elements on the diagonals of the upper and lower arms of different inverters for a certain period and then turning them off. Since it is regenerated to the DC power supply via a diode connected in reverse parallel to the switching element, it rapidly decreases. For this reason, there is a problem that the time for which the current oscillation continues is short and the measurement of the resonance frequency is not easy.

On the other hand, in the present embodiment, after the elements 2 and 9 are turned on for a short period (time t _{0 to} t ₁ ) as described above, the AC output terminals of the inverter 100 are short-circuited to output zero voltage. As shown in FIG. 1, the oscillation of the output current can be continued over a plurality of periods. For this reason, a plurality of cycles of the output current can be measured, and the resonance frequency can be measured with higher accuracy.

In this embodiment, the elements 2 and 9 are turned on at time t ₀ , the element 9 is turned off and the element 8 is turned on at time t ₁ , so that a positive voltage V _o as shown in FIG. Although is output to turn on the device 3 and 8 at time t _0, off elements 8 at time t _1, by turning on the device 9, it may be output a negative voltage V _o from the inverter 100.

Next, FIG. 2 is a main circuit configuration diagram of the high frequency power supply device for explaining the second embodiment of the present invention.
In the inverter 110 in this embodiment, both ends of an element pair in which self-extinguishing switching elements 2 and 3 are connected in series are connected to a DC voltage source 1, a connection point between elements of the element pair and a negative electrode of the DC voltage source 1. Is a so-called single-phase output voltage type half-bridge inverter.
On the load side, similarly to FIG. 6, an inductive impedance 4 having one end connected to the connection point between the elements, and a resonance connected between the other end of the impedance 4 and the negative electrode of the DC voltage source 1. A capacitor 5 and a load 200 connected in parallel to the capacitor 5 and composed of a series circuit of an inductive impedance 6 and a resistance component 7 are included.

FIG. 3 is a waveform diagram showing the operation of this embodiment.
To explain the operation, when the upper arm element 2 constituting the inverter 110 is turned on at time t ₀ , a DC voltage is output as the output voltage V _o and the output current I _o increases as described above. Before the output voltage V _o with respect to I _o is advanced phase, i.e. off the element 2 at an arbitrary time t ₁ before the polarity of the I _o is inverted to turn on the element 3 of the lower arm. As a result, the output voltage V _o of the inverter 110 becomes zero voltage and does not continue to output a DC voltage, so there is no possibility that the output current I _o becomes an overcurrent. Therefore, the operation of the inverter 110 can be continued without stopping.

Further, the output side of the inverter 110 is short-circuited through the element 3 by continuing to turn on the element 3 after the time t ₁ . Therefore, similarly to the first embodiment, the vibration of the resonance circuit constituted by the inductive impedance 4, the resonance capacitor 5, and the load 200 in which the inductive impedance 6 and the resistance component 7 are connected in series continues. In other _words , it becomes possible to measure the frequency of the output current Io that vibrates substantially at the resonance frequency. In addition, after frequency measurement, it shifts to normal operation and the elements 2 and 3 may be switched at a frequency higher than the measured frequency.
Also in the present embodiment, by making the output frequency of the inverter 110 higher than the measured frequency of the output current _Io , it is possible to prevent a sudden reverse recovery of the parasitic diode and prevent overvoltage breakdown of the elements 2 and 3. it can.

In FIG. 2, the resonance circuit including the inductive impedance 4, the resonance capacitor 5, and the load 200 is connected to both ends of the element 3. However, the resonance circuit may be connected to both ends of the element 2. In that case, the element 3 is turned on at time t _0, off element 3 at time t _1, it is sufficient on the element 2, the output voltage V _o becomes the voltage across the element 2.

It is a wave form diagram which shows operation | movement of 1st Embodiment of this invention. It is a main circuit block diagram of the high frequency power supply device with which 2nd Embodiment of this invention is applied. It is a wave form diagram which shows operation | movement of 2nd Embodiment of this invention. It is a main circuit block diagram of the high frequency power supply device for demonstrating background art. It is a wave form diagram which shows the operation | movement of FIG. It is a main circuit block diagram of the other high frequency power supply device for demonstrating background art. It is a wave form diagram which shows the operation | movement of FIG.

Explanation of symbols

1: DC voltage sources 2, 3, 8, 9: self-extinguishing switching elements 4, 6: inductive impedance 5: resonant capacitor 7: resistance component 100: single-phase output voltage type full-bridge inverter 110: single-phase output voltage Half-bridge inverter 200: Load

Claims (4)

Single-phase output with two pairs of self-extinguishing switching elements connected in series, connected in parallel to a DC voltage source, and a connection point between the switching elements of each element pair as a pair of AC output terminals It has a voltage-type full-bridge inverter,
In the high frequency power supply apparatus in which the inductive impedance and the parallel circuit of the resonant capacitor and the load are connected in series between the pair of AC output terminals,
The inverter output current is vibrated by controlling on and off of the switching element so that the output voltage of the inverter becomes zero after outputting a positive or negative DC voltage from the inverter for a predetermined period. The resonance frequency measurement method is characterized in that the resonance frequency of the resonance circuit including the inductive impedance, the resonance capacitor, and the load is obtained by measuring. A single-phase output in which a pair of self-extinguishing switching elements connected in series is connected to both ends of a DC voltage source, and a connection point between the switching elements and one end of the DC voltage source are used as a pair of AC output terminals Equipped with a voltage type half bridge inverter,
In the high frequency power supply apparatus in which the inductive impedance and the parallel circuit of the resonant capacitor and the load are connected in series between the pair of AC output terminals,
After a positive DC voltage is output from the inverter for a predetermined period, the switching element is turned on and off so that the output voltage of the inverter becomes zero, and the output current of the inverter is vibrated and the frequency is measured. To obtain a resonance frequency of a resonance circuit including the inductive impedance, the resonance capacitor, and a load. In the resonance frequency measuring method according to claim 1 or 2,
The method for measuring a resonance frequency, wherein the predetermined period is a period within a half cycle of an output current of the inverter. In the resonance frequency measuring method according to any one of claims 1 to 3,
The self-extinguishing type switching element is a MOSFET having a parasitic diode.

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