JP2002270433A - Reactor and dc-dc converter using the same and x-ray high-voltage apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact, light, efficient large-output DC-DC converter by reducing the loss in a reactor having a core with a gap for miniaturizing the reactor, and using the reactor for a zero voltage switching means, and to provide an inverter type X-ray high-voltage apparatus using the DC-DC converter. SOLUTION: Winding is farmed around a core having a gap, and a conductive layer is provided along the direction of the magnetic flux in the core for composing the reactor. The reactor is used for the zero voltages switching means of the DC-DC converter. Then, by setting the load of the DC-DC converter that is composed in this manner to an X-ray tube, the inverter-type X-ray high- voltage apparatus is composed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor, a DC-DC converter using the same, and an X-ray high-voltage device. The present invention relates to a technique suitable for obtaining a DC-DC converter and an X-ray high-voltage device using the same.

[0002]

2. Description of the Related Art In recent years, for the purpose of reducing power loss and electromagnetic noise, software for turning on and off the switching element in a state where a voltage applied to the switching element is zero or a state in which a current flowing through the switching element is zero is used. DC using a technique called switching
-DC converters are being developed. Conventional DC of this type
As a DC converter, there is one disclosed in Japanese Patent Application Laid-Open No. 6-22551.

[0003] The DC-DC converter described in the above publication includes zero voltage switching means for turning on and off the switching element by making the voltage of the power semiconductor switching element substantially zero, and the switching by the zero voltage switching means. An inverter that turns the element on and off to convert the voltage of the DC power supply to an AC voltage, a transformer connected to the output side of the inverter, a rectifier that converts the output of the transformer to DC, and an output of the rectifier And a means for controlling the turn-on and turn-off timings of the switching elements of the inverter according to a setting signal of a voltage applied to the load and a current flowing to the load. The inverter provided with the zero-voltage switching means has a first series connection including a first switch connected to a positive electrode of the DC power supply and a second switch connected to the negative electrode, and is connected to the positive electrode. A third switch connected to the first switch and a fourth switch connected to the negative electrode of the switch, and a second switch connected in parallel to the first switch. It has first to fourth diodes connected in anti-parallel and a capacitor as a lossless snubber, and in the forward direction of the first and second diodes when the switching elements of the first and second switches are turned on and off. First auxiliary current supply means for supplying current;
Second auxiliary current supply means for supplying a current in a forward direction of the third and fourth diodes when the switching elements of the third and fourth switches are turned on and off.

The first auxiliary current supply means includes:
A first reactor is connected between a connection point of the first and second switches and a neutral point of the DC power supply, and the second auxiliary current supply unit is configured to connect the third and fourth switches with each other. A second reactor is connected between a connection point and a neutral point of the DC power supply, and the first to fourth switches are turned on and turned off via the first and second reactors when the first to fourth switches are turned off. It is configured such that a current flows in a forward direction of the first to fourth diodes (a direction in which the diodes conduct).

By applying the phase shift PWM (Puls Width Modulation) control disclosed in Japanese Patent Application Laid-Open No. 63-190556 to the conventional DC-DC converter thus configured, the first and second reactors are used. If the inductance value is appropriately selected, the first to fourth switches of the inverter are turned on with current always flowing through the anti-parallel diode, and with the current flowing in the forward direction of the switch. It is possible to turn off the power supply, and a dead time period (the first and second switches and the third and fourth switches provided to prevent a power supply short circuit caused by turning on simultaneously). During which both the first switch and the second switch and the third and fourth switches are turned off). Soft switching operation using manner can be realized.

However, when this DC-DC converter is used in a medical X-ray high-voltage device having a very wide load range, the first and second reactors become unnecessary depending on the operating phase shift angle and load conditions. A large current flows, and as a result, there is much waste in terms of conduction loss of the first to fourth switches and loss of the first and second reactors.

Therefore, in order to improve this point, a current is supplied only when necessary for the first and second reactors, that is, only when the first to fourth switches are turned on and off. "RWDe D
oncker, et al: “The AuXillary Resonant Commutated
Pole Converter ”, IEEE-IAS (1990), pp.1228-1235”
Is known.

In this circuit, a bidirectional switch is connected in series to both the first reactor and the second reactor, and these bidirectional switches are turned on and off by the first to fourth switches. The continuity is controlled in accordance with the timing.

More specifically, the bidirectional operation is performed only for a certain period before and after the ON / OFF timing of the first and second switches and the third and fourth switches (this period is denoted by Δt). Turn on the switch. Then, by controlling the Δt according to the current state of the first and second switches and the current states of the third and fourth switches, the current (for the first to fourth switches) is reduced by an amount necessary for realizing soft switching. Less than,
The power conversion efficiency is improved by using a circuit through which an auxiliary current can flow. This circuit, when applied to an X-ray high-voltage device with a very wide load range (changes by a factor of 10 ⁴ as load resistance), can always operate efficiently under all load conditions. There are great benefits.

[0010]

As described above, the above D
By applying the C-DC converter to an X-ray high-voltage device for medical diagnosis, it is possible to reduce electromagnetic noise and switching loss generated by switching of a switching element of an inverter circuit. As a result, the reduction of electromagnetic noise contributes to the improvement of the image quality of the X-ray image, and the reduction of switching loss increases the operating frequency of the inverter circuit to reduce the size of the high-voltage transformer. Contributes to

In particular, the medical diagnostic X-ray CT apparatus has an X-ray high-voltage device mounted on the scanner to reduce the installation space, and thus has three units of a console, a scanner, a table, and an image processing unit. Only X-ray images are becoming mainstream, and further improvement in image quality of X-ray images is desired. Further, in such an X-ray CT apparatus, it is possible to "scan a wide range in a short time", "obtain continuous data in the body axis direction, and thereby generate a three-dimensional image". Due to its characteristics, spiral CT called helical scan or spiral scan has rapidly spread.

In the spiral CT, the time required for multilayer imaging from a wide range is greatly reduced by actively moving the imaging position during imaging, thereby enabling three-dimensional CT imaging.

In the spiral CT having such a characteristic, the fixed scanner main body performs a continuous rotation scan, and at the same time, the bed is continuously moved in the body axis direction, so that the X-ray tube is relatively moved with respect to the subject. Due to the turning motion, the continuous rotation scan time becomes longer. Furthermore, in recent years, scan times have tended to become increasingly faster in order to enable the diagnosis of the heart without motion artifacts, and a scan time of less than 0.5 seconds has been demanded. .

If the scan time is shortened, the X-ray dose applied to the subject must be the same when the imaging region of the subject and the thickness of the subject are the same and the imaging technique is the same. . Therefore, in order to make the time integration value of the current flowing between the anode and the cathode of the X-ray tube (hereinafter referred to as the tube current) the same as in the case where the conventional one scan time is long, the scanner rotating disk is required. The tube current must be increased as much as the rotation speed of the camera increases and the photographing time decreases.

As described above, a large capacity of the X-ray tube is required due to an increase in the tube current due to the increase in the scan time and the increase in the imaging time due to the spiral scan, and power is supplied to the X-ray tube. An inverter type X-ray high voltage apparatus to be supplied also needs to have a high output. Specifically, 60 kW
An X-ray high-voltage device capable of continuously outputting for one minute or more is required. If the above DC-DC converter is used in this X-ray high-voltage device, it is possible to reduce electromagnetic noise and switching loss of the switching element. The temperature of the first and second reactors that supply the auxiliary current for performing the operation is increased. These reactors require an inductance of 5 μH, an operating frequency of 20 kHz, and an effective value of 150 A. However, if a conventional normal air-core reactor or a reactor with an iron core is used, the power of the winding is reduced in the case of the air-core reactor. Heat generated by the loss is large, and in the case of a reactor with an iron core, the heat generated by the loss of the iron core is large.If the heat generated by these power losses is to be kept within an allowable value, the reactor becomes large, and as a result, the equipment becomes large. Becomes Therefore, in order to utilize the effect of the soft switching, it is necessary to reduce the power loss of the reactor, and conventionally, no consideration has been given to this point.

The inductance of the reactor is represented by magnetic permeability,
It is proportional to the magnetic path cross-sectional area and the square of the number of turns, and inversely proportional to the magnetic path length. The air-core reactor has the advantage that it is lightweight and has no magnetic saturation due to the absence of an iron core. However, since the magnetic permeability is as low as 1, a magnetic path cross-sectional area is required to produce a reactor with a large inductance. Or the number of turns must be increased.

If the magnetic path cross-sectional area is increased, the reactor naturally becomes larger, and if the number of turns is increased, the reactor becomes larger and the resistance of the winding becomes larger. As in the case of the X-ray high-voltage apparatus used in the above-mentioned X-ray CT apparatus, when the energizing current is large and the energizing time is long, the power loss of the winding increases and heat generation of the reactor becomes a problem. For example,
When an air-core reactor with an inductance value of 5 μH is manufactured so that it fits in a cube with one side of 80 mm, the effective value is 15
When a current of 0 A and a frequency of 20 kHz flows, the temperature becomes about 100 ° C. in several tens of seconds, and the temperature of the reactor winding increases.

In such a case, if a core-containing reactor using an iron core having a high magnetic permeability is used, the magnetic resistance of the magnetic path is reduced and the number of windings can be reduced. However, the magnetic flux passing through the core increases the loss of the core. This loss increases as the operating frequency increases and the magnetic flux density increases.
This magnetic flux density is inversely proportional to the number of turns. In other words, in the case of a reactor with an iron core, it is better to reduce the number of turns in order to suppress the heat generation of the windings.However, if the number of turns is too small, the magnetic flux density must be increased. It will overheat.

Therefore, there is a method of adjusting the magnetic resistance of the magnetic path by providing a gap in the iron core in consideration of the number of turns and the core loss at which the required inductance is obtained.

However, in such a reactor with a core having a gap, a loss occurs due to the magnetic flux leaking at the gap. This is because the magnetic flux leaked into the air from the end face of the iron core returns to the iron core on the opposite side of the gap, and eddy current loss occurs in the iron core. In this case, if the gap is increased, the number of turns can be increased to reduce the magnetic flux density of the iron core, and the iron core loss decreases.However, the vicinity of the gap is locally heated by the eddy current loss due to the leakage magnetic flux near the gap. Is done. Therefore, the gap cannot be increased so much that the iron core has to be eventually enlarged, and the reactor becomes larger.

Therefore, the present invention aims at the following. (1) Reducing the loss of a reactor with a core with a gap to reduce the size of the reactor, and using this reactor for a DC-DC converter having zero voltage switching means to reduce the size, weight, and loss of the DC-DC converter Aim. (2) A small, lightweight, high-output X-ray high-voltage device is provided by using the DC-DC converter with reduced loss for the X-ray high-voltage device.

[0022]

The above object is achieved by the following means.

(1) In a reactor comprising a core having a gap and a winding wound around the core, a reactor is formed by providing a conductor layer along the direction of magnetic flux running in the core.

(2) DC power supply and zero voltage switching means for turning on and off the switching element by making the voltage of the power semiconductor switching element substantially zero, and turning on and off the switching element by the zero voltage switching means. An inverter for converting the voltage of the DC power supply to an AC voltage, a transformer connected to the output side of the inverter, a rectifier for converting the output of the transformer to DC, and a rectifier connected to the output side of the rectifier. And a means for controlling the turn-on and turn-off timings of the switching elements of the inverter in accordance with a setting signal of a voltage applied to the load and a current flowing to the load. (1) above for zero voltage switching means
Of the reactor is used.

(3) The inverter provided with the zero voltage switching means includes a first series connected body comprising a first switch connected to the positive electrode of the DC power supply and a second switch connected to the negative electrode. A third switch connected to the positive electrode and a fourth switch connected to the negative electrode, a second switch connected in parallel to the first switch, and a second switch connected in parallel to the first switch. To a fourth switch and a first to fourth diode and a capacitor respectively connected in anti-parallel to the fourth switch, and the first and second diodes are turned on and off when the switching elements of the first and second switches are turned on and off. First auxiliary current supply means for supplying a current in the forward direction, and the third auxiliary current supply means for turning on and off the switching elements of the third and fourth switches. And second auxiliary current supply means for supplying a current in the forward direction of the fourth diode.

(4) The first auxiliary current supply means includes a first reactor and a first bidirectional switch between a connection point of the first and second switches and a neutral point of the DC power supply. And the second auxiliary current supply means is connected between a connection point of the third and fourth switches and a neutral point of the DC power supply, and a second reactor is connected to the second auxiliary current supply means. A series connection of two bidirectional switches is connected, and the reactor of (1) is used as the first reactor and the second reactor.

(5) An inverter type X-ray high voltage device is constituted by using the load of the DC-DC converter as an X-ray tube.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<< Reactor with iron core with gap >>
Is a first embodiment of a reactor with a core with a gap according to the present invention. 31 and 32 are iron cores. A gap 30 is provided between these iron cores, and copper plates 35 and 36 are arranged around the gap 30 to form a U-shaped iron core. A winding 33 is wound around the U-shaped iron core. Make up the reactor. When an electric current is applied to the winding 33, a magnetic flux 34 is generated in the direction shown in the figure, and a reactor having an inductance proportional to the magnetic permeability, the magnetic path cross-sectional area, and the square of the number of turns and inversely proportional to the magnetic path length is obtained.

In the case of the conventional reactor shown in FIG. 2 (without the copper plates 35 and 36 shown in FIG. 1), the magnetic flux generated by the current flowing through the winding 33 is different from the reactor having such a configuration.
34 passes through the gap 30 from the cut surface of the core 31 and
Since the magnetic resistance of the magnetic path reaching the iron core 31 is large, the magnetic flux leaks out of the core from the side surface of the iron core 31, and the leaked magnetic flux enters the inside of the iron core 32 from the side surface of the iron core 32. For example, when the iron cores 31 and 32 are of a laminated type, the eddy current does not flow with respect to the magnetic flux leaking out from the cut surface of the iron core 31 and entering the cut surface of the iron core 32 through the gap 30. Leak from the side of
An eddy current very easily flows in the magnetic flux that enters the side surface of the iron core 32. Such leakage magnetic flux causes eddy current loss near the gap between the cores 31 and 32, and the eddy current loss causes the core to generate heat.

On the other hand, in the case of the first embodiment of the present invention shown in FIG. 1, the provision of the copper plates 35 and 36
Magnetic flux from the side of 31 hardly leaks. In addition, iron core 31
The magnetic flux leaked out of the core from the cut surface hardly enters the inside of the core 32 from the side surface of the core 32 because of the presence of the copper plates 35 and 36. The reason is that the magnetic flux leaking out of the core 31
This is because, when trying to cross the 5, 36, an eddy current is generated in the copper plate, and a magnetic flux in the opposite direction to the traversing magnetic flux is generated in the copper plates 35, 36 and acts to cancel the traversing magnetic flux. By acting in this way, the leakage flux is reduced by the copper plates 35, 36
, The magnetic flux of the iron core 31 reaches the iron core 32, the loss near the gap 30 is reduced, and the iron cores 31, 32 may be locally heated. Disappears.

FIG. 3 shows a second embodiment of the reactor with a gapped iron core according to the present invention. In the first embodiment of FIG. 1 described above, copper plates 35 and 36 are provided near the gap to prevent heat generation due to leakage magnetic flux near the gap, but in FIG. Wrap tape 37,
The effect of preventing heat generation due to eddy current generated by magnetic flux leaking from the entire iron cores 31, 32 is obtained. Although not shown, if the copper tape is wound around the entire inside of the iron cores 31, 32, the effect is further enhanced.

FIG. 4 shows a third embodiment of the reactor with a gapped iron core according to the present invention. In this embodiment, a gap 39 is provided in a toroidal iron core 38, and a winding 40 is wound around the gap 39,
This is a reactor having a configuration in which the entire iron core 38 including the gap 39 is covered with a copper tape 42. Thus, iron core with copper tape 42
By covering the whole 38, the main magnetic flux 41 can be prevented from leaking from the gap 39, and the loss due to the leakage magnetic flux can be reduced.

FIG. 5 shows a fourth embodiment of the reactor with a gapped iron core according to the present invention. A winding 44 is wound around a laminated I-shaped iron core 43 having a large gap in the magnetic path.
This is a reactor in which an electric current is caused to flow through 44 to generate a magnetic flux 46, and an iron core 43 is sandwiched between copper plates 45 in the stacking direction. With this configuration, it is possible to prevent magnetic flux from penetrating in the direction in which the magnetic flux is laminated on the side surface of the iron core 43, thereby reducing loss.

As described above, various embodiments of the present invention are shown in FIGS. 1 and 3 to 5. However, the reactor with a core with a gap of the present invention is not limited to the above-described embodiment.
There are various modifications as follows.

(1) In the embodiment of FIG. 1, a laminated iron core is used. However, a copper plate may be provided in the vicinity of the gap to prevent generation of leakage magnetic flux even if it is not a laminated iron core.
Any iron core is acceptable.

(2) In the embodiment shown in FIG.
Although the magnetic path is formed by using the individual pieces, any magnetic path may be used as long as the reactor is a cored reactor with a gap.
For example, a magnetic path formed by using an I-shaped iron core as in the fourth embodiment shown in FIG. 5 may be used.

(3) In the embodiment shown in FIG. 1, the copper plates 35 and 36 are provided inside and outside the U-shaped iron core.
Even when the copper plate 35 is provided only on the outside without the 36, any material can be used as long as the effect of reducing the loss due to the leakage magnetic flux generated due to the gap can be obtained.

In the embodiment described above, the conductor layers (the copper plates 35, 3 in FIG. 1) are arranged along the running direction of the main magnetic flux in the iron core.
6, a copper tape 37 in FIG. 3, a copper tape 42 in FIG. 4, and a copper plate 45 in FIG. 5, thereby reducing the leakage magnetic flux near the gap and reducing the size of the reactor with a core with a gap. It is assumed that. At this time, it is more effective to select a conductor layer having a smaller electric resistance to prevent the passage of magnetic flux, and eddy current loss caused by eddy current flowing at that time is smaller. However, it is not always necessary to use a copper plate as the conductor layer.
Other materials having high electric conductivity such as silver may be used.

In mounting, it is advantageous that the thickness of the conductor layer is small. However, in order to reduce the loss caused by the eddy current, it is necessary to reduce the electric resistance to a certain thickness. There is also.

<< DC-DC Converter and Inverter-Type X-ray High-Voltage Apparatus Using the Same >> FIG. 6 shows a DC-DC converter according to the present invention using the above-described reactor with a gapped iron core as a zero-voltage switching means of the DC-DC converter. FIG. 2 is a circuit diagram showing a DC converter and an inverter type X-ray high voltage device applied to the DC converter.

An X-ray high-voltage device using this DC-DC converter converts a DC voltage from a converter that converts commercial power into DC to an AC voltage by using an inverter circuit, boosts the output, and then converts this to an AC voltage. It rectifies and applies a high DC voltage to the X-ray tube to emit X-rays. The DC power supply 1, the inverter 4, the reactor 5, and the capacitor 6
A high voltage transformer 7, a high voltage rectifier 8, an X-ray tube 17 as a load, a phase determination circuit 18 and a phase control circuit 19,
It has a GBT drive circuit 21 (21a to 21h) and is called a resonance type inverter type X-ray high voltage device.
Next, each function of the above components will be briefly described. The DC power supply 1 is a device for supplying a DC voltage, and is a DC voltage obtained by rectifying the voltage of a commercial AC power supply of 50 Hz or 60 Hz or a DC voltage supplied from a battery or the like. In FIG. The two power supply voltages E / 2 are shown symmetrically.

The inverter 4 receives a DC voltage, converts the DC voltage into a high-frequency AC voltage, and controls the output. The inverter 4 is connected to the IGBT 20a as a first switch connected to the positive electrode of the DC power supply 1 and its negative electrode. A first series connected body composed of an IGBT 20b as a second switch connected thereto and an IG as a third switch connected to the positive electrode.
A BT20c and an IGBT 20d as a fourth switch, a second series-connected body connected in parallel to the first series-connected body, and first to fourth diodes connected in anti-parallel to the IGBTs 20a to 20d, respectively. 3a to 3d. Each of the IGBTs 20a to 20d is an insulated gate bipolar transistor, and is a power semiconductor switching element having a self-extinguishing function of turning on / off by applying a drive signal to each. The first arm 10a is connected to the first IGBT 20a and the first diode 3a, and the second IGBT 20b and the second diode 3b.
And the third arm 10c with the third IGBT 20c and the third diode 3c.
T20d and the fourth diode 3d form a fourth arm 10d, respectively, and the first to fourth IGBTs 20a to 20d
The capacitor 22a used as a lossless snubber circuit
To 22d are connected in parallel, respectively, between the connection point of the first and second IGBTs 20a and 20b and the neutral point (potential E / 2) of the DC power supply 1, and between the third and fourth IGBTs 2a and 2b.
A first auxiliary circuit 27a and a second auxiliary circuit 27b are connected between a connection point of 0c and 20d and a neutral point of the DC power supply 1, respectively. As the first auxiliary circuit 27a,
One end of a reactor 23a is connected to the neutral point of the DC power supply 1, and two sets of IGBTs 24a1 and 24a2 as auxiliary switches and diodes 25a1 and 25a2 connected in anti-parallel to the other end of the reactor 23a are provided. A two-way switch 26a connected in series in the opposite direction is connected in series, and the other end of the two-way switch 26a is connected to a connection point of the first and second IGBTs 20a and 20b. On the other hand, the configuration of the second auxiliary circuit 27b is the same as that of the first auxiliary circuit 27a.

A reactor 5 is connected to the output side of the inverter 4.
Is connected, and this reactor 5 has a capacitor 6
Are connected in series. A resonance circuit is formed by the inductance of the reactor 5 and the capacitance of the capacitor 6. Reactor 5 and capacitor 6 above
Is connected to a high-voltage transformer 7, which boosts the output voltage from the inverter 4 and insulates the output. The rectifier 8 converts the output voltage from the transformer 7 into a direct current by full-wave rectification, and includes four diodes 11a to 11d. Further, an X-ray tube 17 is connected to the output side of the rectifier 8 as a load. Numeral 12 indicates the capacitance of a high-voltage cable for applying the output voltage of the rectifier 8 to the X-ray tube 17,
This has the function of smoothing the output from the rectifier 8. In addition,
The reactor 5 is not necessarily required if resonance operation is possible only with the leakage inductance of the high-voltage transformer 7 and the capacitor 6.

The capacitor 6 is inserted for the purpose of improving that a high-frequency current does not sufficiently flow through the winding of the high-voltage transformer 7 due to the influence of the leakage inductance of the high-voltage transformer 7. If not, it does not need to be inserted.

The phase determination circuit 18 and the phase control circuit
Reference numeral 19 denotes the first to fourth IGBTs 20a according to a setting signal of a voltage applied to the X-ray tube 17 and a current flowing through the X-ray tube 17.
The phase determining circuit 18 determines the operation phase of the IGBTs 20a to 20d as switches based on the tube voltage setting signal S1 and the tube current setting signal S2. The phase control circuit 19 outputs the output signal S3 from the phase determination circuit 18.
IGBTs 24a1 and 24 as auxiliary switches and signals for controlling the phases at which the IGBTs 20a to 20d operate according to
A signal for controlling the on / off timing of a2, 24b1, 24b2 is output when an X-ray irradiation signal S4 input from a controller (not shown) is input. In addition,
Reference numerals 21a to 21h denote IGBTs as switches according to the respective control signals output from the phase control circuit 19.
20a to 20d and IGBTs 24a1,2 as auxiliary switches
This is a drive circuit for driving 4a2, 24b1, 24b2.

According to the present invention, the DC-DC converter having the above-described configuration uses the above-described reactor having a core with a gap as the reactor 23a of the first auxiliary circuit 27a and the reactor 23b of the second auxiliary circuit 27b. A device that obtains a small X-ray high-voltage device even with a large output by reducing the switching loss of the first switch IGBT20a, the second switch IGBT20b, the third switch IGBT20c, and the fourth switch IGBT20d of the inverter 4 of the DC converter. It is.

Next, the operation of the DC-DC converter thus configured will be described.

In the circuit shown in FIG. 6, the normal (basic) operation in which the IGBTs 24a1, 24a2, 24b1, and 24b2 as the auxiliary switches perform zero-voltage switching is described in the above-cited reference "RWDe Doncker, et al:" The Au Xillary Resonator ".
ant Commutated Pole Converter ”, IEEE-IAS (1990),
pp. 1228-1235 ", and is controlled to supply a minimum auxiliary current capable of realizing soft switching to the IGBTs 20a to 20d as switches according to the operation conditions. IGBTs 24a1, 24a as auxiliary switches
The on / off timing of 2, 24b1, 24b2 is determined by the IGBT as a switch determined by the phase determination circuit 18.
A certain period Δt (minimum period necessary for soft switching) is provided before and after the ON / OFF timing of 20a to 20d as a reference, and the IGBT 24a1 as an auxiliary switch is provided only during this period Δt. , 24a2, 24b
Soft switching is enabled by turning on 1, 24b2.

That is, as shown in FIG. 7, the ON / OFF timing of the first and second switches is set as a reference, and only during a certain period (Δt in FIG. 7) before and after the ON / OFF timing (Δt in FIG. 7). Turn on the auxiliary switch 24a1 or 24a2. Then, according to the current state of each switch of the first and second arms 10a and 10b, the above-mentioned △
By controlling the t, the current (hereinafter, referred to as the amount necessary for realizing the soft switching for the switches 20a and 20b,
The power conversion efficiency is improved by using a circuit through which an auxiliary current can flow.

The switches 20c and 20 of the third and fourth arms
Soft switching can be realized by operating d in the same manner. The DC-DC converter shown in FIG. 6 has a very wide load range (10 ⁴
When applied to an X-ray high-voltage device (which changes by a factor of two), there is a great merit in that efficient operation is always possible under all load conditions.

The inverter type X-ray high-voltage device having this configuration is
For use in an X-ray CT apparatus that performs a spiral scan of 1 minute or more with a scan time of 0.5 seconds, it is necessary that a 60 kW output can be continuously output for 1 minute or more. In order to mount this X-ray high-voltage device on the scanner rotating part of the X-ray CT device, the reactors 23a and 23b of the first and second auxiliary circuits 27a and 27b have a cube size of 80 mm on a side. Is required. If a conventional air-core reactor or a reactor with a core with a gap is used, heat is generated in several tens of seconds due to the large loss of 200 watts, making it impossible to fit in a cube with one side of 80 mm. is there.
On the other hand, when the reactor with a core with a gap according to the present invention is used, the loss is reduced to 100 watts,
The X-ray high-voltage device can be mounted on the scanner rotating part of the X-ray CT device because it can be accommodated in a cube with one side of 80 mm. A line CT apparatus becomes possible.

In the embodiment of FIG. 6, as means for controlling the on / off timing of the first to fourth switches, the phase shift PWM control disclosed in Japanese Patent Application Laid-Open No. 63-190556 is used. Although the applied example has been described, this is a method of controlling the operating frequency of the first to fourth switches according to the setting signal of the voltage applied to the load and the current flowing to the load, or using both the frequency and the phase. It can also be applied to a control method.

Also, in the circuit of FIG. 6, an auxiliary circuit for realizing soft switching, in which a reactor and a bidirectional switch are connected in series, is used in both the first series connection body and the second series connection body. However, one of them may be used as an auxiliary circuit of only the reactor 23a or 23b according to the current waveform of each of the arms 10a to 10d, or soft switching may be performed even if one of the auxiliary circuits is removed. This may be done where possible. Further, the soft switching means is not limited to the above embodiment, and any circuit may be used as long as an auxiliary current is flown by using a reactor, thereby making the voltage of the switching element of the inverter zero and turning on / off the switching element. Any circuit may be used. Furthermore, IGBTs are connected to the first to fourth switches 20a to 20d and the auxiliary switches 24a1, 24a2, 24b1, 24b2.
Was used, but here the MO
It is also possible to use other switching elements such as SFETs and bipolar transistors.

[0055]

The effects of the present invention described above are summarized as follows.

(1) The conductor layer provided in the iron core of the reactor with the iron core with a gap parallel to the magnetic flux running direction can reduce the loss due to the leakage magnetic flux generated by the gap to greatly reduce the size of the reactor. it can.

(2) By using the reactor of the above (1) for a DC-DC converter having zero voltage switching means, the loss of the DC-DC converter can be reduced and the DC-DC converter can be made small and lightweight. .

(3) By using the DC-DC converter of (2) above for an inverter type X-ray high voltage device, a small and light X-ray high voltage device can be obtained even if the output is increased.

[Brief description of the drawings]

FIG. 1 is a first embodiment of a reactor with a gapped iron core according to the present invention.

FIG. 2 shows a conventional reactor with a core with a gap.

FIG. 3 is a second embodiment of the reactor with a gapped iron core according to the present invention.

FIG. 4 is a third embodiment of the reactor with a gapped iron core according to the present invention.

FIG. 5 is a fourth embodiment of the reactor with a gapped iron core according to the present invention.

FIG. 6 is a DC-DC converter using a reactor with a core with a gap according to the present invention as a zero voltage switching means of a DC-DC converter, and an inverter type X-DC converter.
FIG. 3 is a circuit configuration diagram used in a line high-voltage device.

FIG. 7 is a timing chart for explaining the operation (normal operation) of the circuit of FIG. 6;

[Explanation of symbols]

1 DC power supply, 3a first diode, 3b second diode, 3c third diode, 3d fourth diode, 4 inverter, 5 reactor, 6 capacitor, 7
... Transformer, 8 ... Rectifier, 17 ... X-ray tube as load, 18 ...
Phase determining circuit, 19 ... Phase control circuit, 20a-20d ... IGBT (insulated gate bipolar transistor) as a switch, 21a-21h ... IGBT drive circuit, 22a-22d ... Capacitor as a lossless snubber circuit, 23a ... First Reactor, 23b… Second reactor, 24a1, 24a2, 25a1, 25a
2 IGBT and diode constituting first bidirectional switch 26a, 24b1, 24b2, 25b1, 25b2 IGBT and diode constituting second bidirectional switch 26b, 27a first auxiliary circuit, 27b second Second auxiliary circuit, 30 ... gap, 31, 3
2 ... iron core, 33 ... winding, 34 ... magnetic flux, 35, 36 ... copper plate, 37 ... copper tape, 38 ... iron core, 39 ... gap, 40 ... winding, 41 ... magnetic flux, 42 ... copper tape, 43 ... iron core, 44 ... winding, 45 ... copper plate, 46
... magnetic flux

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) H01F 27/24 K F term (reference) 4C092 AA01 AB27 AC17 BB13 BB36 5H730 AA02 AA14 AA20 AS16 BB27 BB63 BB66 DD03 DD41 EE04 EE07 FG07 FG10 ZZ09 ZZ17

Claims (5)

[Claims] 1. A reactor comprising a core having a gap and a winding wound around the core, wherein a conductor layer is provided along a direction in which magnetic flux runs in the core. 2. A DC power supply, and zero voltage switching means for turning on and off the switching element by making the voltage of the power semiconductor switching element substantially zero, and turning on and off the switching element by the zero voltage switching means. An inverter for converting the voltage of the DC power supply to an AC voltage, a transformer connected to an output side of the inverter, a rectifier for converting the output of the transformer to DC, and an output side of the rectifier. A DC-DC converter comprising: a load; and means for controlling timing of turning on and off a switching element of the inverter according to a setting signal of a voltage applied to the load and a current flowing to the load. The reactor according to claim 1, wherein the zero voltage switching means is provided. DC characterized by the use of
-DC converter. 3. The inverter provided with the zero-voltage switching means has a first series connection including a first switch connected to a positive electrode of the DC power supply and a second switch connected to a negative electrode thereof. A third series connected to the positive electrode and a fourth series connected to the negative electrode, and a second series connected body connected in parallel to the first series connected body. It has first to fourth diodes and capacitors respectively connected in anti-parallel to the fourth switch, and turns on the first and second diodes when the switching elements of the first and second switches are turned on and off. First auxiliary current supply means for supplying a current in the direction, and the third and fourth switching elements of the third and fourth switches when the third and fourth switches are turned on and off. The DC-DC converter according to claim 2, further comprising a second auxiliary current supply unit that supplies a current in a forward direction of the fourth diode. 4. The first auxiliary current supply means includes a first reactor and a first bidirectional switch between a connection point of the first and second switches and a neutral point of the DC power supply. The second auxiliary current supply means is provided between the connection point of the third and fourth switches and the neutral point of the DC power supply, the second reactor and the second 4. The DC-to-DC converter according to claim 3, wherein the first and second reactors are connected to each other in series.
DC converter. 5. The DC-DC according to claim 1, wherein:
An X-ray high-voltage device, wherein the load of the converter is an X-ray tube.