JP3714745B2 - Inverter X-ray high voltage device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention converts a DC power source into high-frequency AC, boosts the output voltage with a high-voltage transformer and then rectifies it to generate a DC high voltage, which is applied to an X-ray tube to emit X-rays. The present invention relates to an inverter type X-ray high voltage apparatus.
[0002]
[Prior art]
FIG. 6 shows a main circuit diagram of an inverter type X-ray high voltage apparatus according to the prior art.
In FIG. 6, a commercial power supply voltage is converted into a DC voltage by the rectifier circuit 1, smoothed by the smoothing capacitor 11, and input to the inverter circuit 2. This inverter circuit 2 uses the resonance phenomenon between the capacitor 10 and the leakage inductance of the high voltage transformer 3 to convert it into a high frequency alternating current, boosts this with the high voltage transformer 3, and outputs this output to the high voltage rectifier circuit. 4 is converted into a DC high voltage and applied to the X-ray tube 6 via the high-voltage cable 5 to emit X-rays. The high voltage (abbreviated as tube voltage) applied to the X-ray tube is variable by controlling the phase difference, frequency, pulse width, etc. of the inverter circuit 2. The high voltage transformer 3 is usually installed in a tank 12 filled with insulating oil together with a high voltage rectifier 4 and a tube voltage detector 8 to be described later for the purpose of ensuring and cooling the withstand voltage. Further, the high voltage cable 5 has a capacitance, which brings about a smoothing action of the tube voltage.
[0003]
The tube voltage feedback control circuit 9 for stabilizing the tube voltage detects the actual tube voltage Vx with the tube voltage detector 8 and inputs this and the target tube voltage signal Vr to obtain the phase difference of the inverter 2 and the like. The frequency or pulse width is obtained, and this is controlled so that the detected tube voltage Vx matches the target tube voltage Vr. The tube current is controlled by adjusting the filament temperature of the X-ray tube 6 using a filament heating circuit (not shown).
[0004]
In the conventional inverter type X-ray high voltage apparatus having the above-described configuration, the switching element of the inverter circuit 2, for example, the insulated gate bipolar transistor IGBT, generates heat due to switching loss and conduction loss during X-ray exposure. It is fixed to a metal having a large heat capacity called a heat sink with heat radiation fins, and at the same time, the heat sink is cooled by using a method of forcibly air cooling using a cooling fan or the like. Since the heat sink and the cooling fan require a relatively large volume and weight, the high voltage transformer tank 12 and the other circuit 31 including the inverter circuit 2 are separately arranged and accommodated in the same casing.
[0005]
[Problems to be solved by the invention]
Thus, the cooling component not only requires a large space but also is expensive. Further, the X-ray high voltage apparatus has an imaging mode in which a large output is exposed for a short time and a fluoroscopic mode in which a small output is exposed for a long time. In the imaging mode, the IGBT temperature is abrupt because of a large loss of the IGBT. However, since the temperature of the high voltage transformer tank 12 is relatively large (having a large heat capacity) and is oil-cooled, it hardly increases.
[0006]
On the other hand, since the power loss is small in the fluoroscopic mode, the temperature of the inverter 2 hardly rises, and the high voltage transformer tank 12 also rises slightly compared with the time of shooting, but the rise is very slight. It was. Therefore, the heat sink and the cooling fan are necessary mainly for suppressing the temperature rise of the inverter 2 during photographing. On the other hand, the insulating oil injected into the high voltage transformer tank 12 has the two purposes of securing the withstand voltage and cooling the high voltage transformer 3 as described above. The amount was determined only from the viewpoint of ensuring withstand voltage. That is, for example, in order to ensure the withstand voltage between the secondary winding of the high-voltage transformer reaching a maximum of 150 kV and the high-voltage transformer tank 12 that is normally at the ground potential, a corresponding large insulation distance must be provided. The space was filled with insulating oil.
[0007]
However, the temperature rise of the insulating oil and the high voltage transformer tank 12 as above mentioned is very small, just when viewed only purpose of cooling, the injected insulating oil is a large amount more than necessary, over in that sense It was spec.
[0008]
On the other hand, in recent medical X-ray apparatuses, in order to take sharp X-ray photographs with high diagnostic ability, high-current, short-time control with high accuracy and good reproducibility is required for X-ray high voltage apparatuses. Therefore, a tube voltage waveform having a high rise and no pulsation is required (a comparison between an ideal tube voltage waveform and an actual tube voltage waveform is shown in FIG. 7). Therefore, increasing the rise and fall times of the tube voltage is also strongly demanded from the viewpoint of improving the photographic effect and reducing the exposure caused by soft X-rays. As a means for realizing them, the operating frequency of the inverter circuit is increased. Progressing. However, one factor that hinders the high frequency is the presence of wiring from the inverter circuit to the high voltage transformer. If the operating frequency of the inverter circuit is increased while the inductance is large, the impedance of the inductance is proportional to the frequency, so that a sufficient current does not flow to the load, and a predetermined X-ray output cannot be obtained. Therefore, the reduction of the inductance has become an indispensable problem for increasing the frequency. Furthermore, recent medical X-ray apparatuses are not only in terms of performance as described above, but also demands for reduction in installation area, reduction in size and weight, and price reduction are increasing. Among them, high-voltage transformers are increasing in volume. The ratio is high, and higher frequencies are required to reduce the size of high-voltage transformers.
[0009]
As described above, the prior art has the following problems and points to be improved.
(1) Although the switching element of the inverter circuit is cooled by the heat sink and the cooling fan, the space occupied by these cooling components is very large and expensive.
(2) The insulating oil injected into the high-voltage transformer tank has the two purposes of securing the withstand voltage and simultaneously cooling the high-voltage transformer. It is determined only from the point of securing, and if viewed only from the purpose of cooling, the amount of insulating oil is larger than necessary, and the insulating oil cannot be used sufficiently effectively.
(3) Since the inverter circuit 2 and the high voltage transformer tank 12 are separately arranged, there is a limit to the reduction of the inductance of the wiring between the inverter circuit 2 and the high voltage transformer 3. For this reason, there is a limit to increasing the frequency, and it is necessary to shorten this distance in order to obtain a tube voltage waveform that is close to the required ideal, and at the same time to reduce the size of the high-voltage transformer.
[0010]
An object of the present invention is to provide an inverter type X-ray high voltage apparatus that is small and inexpensive and can obtain a tube voltage waveform close to ideal required for a medical X-ray apparatus.
[0011]
[Means for Solving the Problems]
The purpose is to provide a direct current power supply, an inverter circuit for converting the direct current power supply to a high frequency alternating current, a high voltage transformer for boosting the output voltage of the inverter circuit, and an X-ray by rectifying the output of the high voltage transformer. In an inverter type X-ray high voltage apparatus comprising a high voltage rectifier circuit applied to a tube, the switching element of the inverter circuit is fixed to a metal plate having a higher thermal conductivity than the element, and the fixed This is achieved by bringing a metal plate into close contact with one outer wall surface of the high voltage transformer tank and conducting heat generated by the switching element to insulating oil in the high voltage transformer tank.
[0012]
Further, the above-mentioned DC power source is the above-mentioned IGBT when the commercial power source is converted into DC using a pulse width modulation control type converter (Japanese Patent Application No. 6-71303) using a IGBT, a rectifier circuit such as a diode or a thyristor, etc. In the same way as above, the diode, the thyristor, etc. are fixed to a metal plate having higher thermal conductivity than the above, and the fixed metal plate is fixed to the high plate. This is achieved by closely contacting one outer wall surface of the voltage transformer tank and efficiently conducting heat generated by the switching element to the insulating oil in the high voltage transformer tank.
[0013]
The inverter type X-ray high voltage apparatus of the present invention configured as described above is
(1) Since the heat sink and cooling fan of the rectifier circuit (converter circuit) and inverter circuit can be removed, it is possible to reduce the cost while reducing the size and weight.
(2) The heat generated in the switching element of the rectifier circuit (converter circuit) and the inverter circuit at the time of photographing can be efficiently conducted to the insulating oil in the high voltage transformer tank, and the temperature rise of the switching element is minimized. Can be suppressed. At the same time, insulating oil, which is more than necessary in terms of conventional cooling, can be effectively used for cooling the rectifier circuit (converter circuit) and the inverter circuit.
(3) Since the wiring between the inverter circuit and the high-voltage transformer can be shortened, the inductance between them can be reduced, and a tube voltage waveform close to ideal can be obtained by increasing the operating frequency of the inverter circuit. In addition, the high voltage transformer can be further downsized.
[0014]
As a result, it is possible to provide an inverter type X-ray high voltage apparatus that has a small installation area, is small, light, and inexpensive, and obtains a tube voltage waveform that is close to the ideal required for medical X-ray apparatuses.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an embodiment of the mounting arrangement of an inverter type X-ray high voltage apparatus according to the present invention.
[0016]
This X-ray high voltage device converts a DC voltage from a rectifier circuit into an AC voltage using an inverter, boosts the output voltage, rectifies it, supplies the DC voltage to the X-ray tube, and emits X-rays. As shown in the circuit diagram of FIG. A rectifier circuit 1, an inverter 2, a high voltage transformer 3, a high voltage rectifier circuit 4, a high voltage cable 5, an X-ray tube 6, a tube voltage detector 8, a tube voltage feedback control device 9, etc. It is prepared for. In FIG. 1, the X-ray tube 6 is excluded. Since the function of this circuit is the same as that of the prior art, the description thereof is omitted.
[0017]
Next, the configurations of the inverter circuit 2 and the tank 12 of the high voltage transformer 3 which are the main parts of the present invention will be roughly described first. In FIG. 1, an inverter circuit 2 according to the present invention is fixed together with a smoothing capacitor 11 with a bolt on a fixing plate 15 made of metal or the like having a relatively high thermal conductivity so that the IGBT 13 as a switching element can withstand mechanical strength. The fixing plate 15 is also in close contact with one outer wall surface of the high-voltage transformer tank 12 in which the high-voltage transformer 3 and the high-voltage rectifier 4 and the like are made of a metal having high thermal conductivity and the insulating oil 24 is injected. Fix and hold with. Further, the wiring 14 from the inverter circuit 2 to the high voltage transformer 3 reaches the inside of the tank via a connection terminal 17 provided in the vicinity of the IGBT 13 in order to reduce leakage inductance and wiring resistance, and the high voltage transformer tank. 12 reaches the high voltage transformer 3 installed in the shortest distance. On the other hand, the X-ray control circuit 9 is supported by the support 16 and fixed to the front surface of the IGBT 13.
[0018]
Subsequently, an arrangement example of the smoothing capacitor 11 and the IGBT 13 will be described in more detail with reference to FIGS. The capacitor 11 that smoothes the output voltage of the rectifier circuit uses an aluminum electrolytic capacitor. In order to suppress the surge voltage at the time of switching of the IGBT 13 by reducing the inductance component of the wiring, components are placed in a minimum space. Thus, it arrange | positions as close as possible to IGBT13. The capacitors 11 are arranged in series in order to increase the withstand voltage, and the axis thereof is installed on the fixed plate 15 by a support 22 or the like along the surface of the fixed plate 15.
[0019]
The capacitor 11 is electrically connected to the IGBT 13 by using a bent copper plate 21 or the like as shown in FIG. In the embodiment of FIG. 2, two modules of a type in which two switches are incorporated in one package are used, and a full-bridge inverter is constituted by these two modules. FIG. 3 shows an equivalent circuit of this module having three terminals. The terminals in FIG. 2 correspond to the terminals C1, E2, and C2E1 in FIG. 3 in order from the right. The fixing plate 15 to which the capacitor 11 and the IGBT 13 are fixed is fixed and held on one outer wall surface of the high voltage transformer tank 12 provided with a screw hole by a fixing bolt 23 or the like.
[0020]
Next, the heat conduction path and the IGBT cooling effect in the inverter circuit 2 and the high voltage transformer tank 12 configured as described above will be described in detail. A part of the heat generation in the IGBT 13 is directly conducted to the surrounding air, the electric wiring path, the support of each component, etc. in each process of the path described below, but most of the heat generation is transferred to the case of the IGBT 13 from the case. Conducted to the fixed plate 15, from the fixed plate 15 to the wall surface of the high voltage transformer tank 12, and from the wall surface of the high voltage transformer tank 12 to the insulating oil 24 inside the high voltage transformer tank 12. For example, silicon grease or the like is applied to the gap between the IGBT 13 and the fixed plate 15 and the gap between the fixed plate 15 and the outer wall surface of the high voltage transformer tank 12 to increase the degree of close contact with each other (the contact area is reduced). The contact heat resistance is reduced by increasing the heat resistance, and the heat generated in the IGBT 13 is efficiently conducted to the high voltage transformer tank 12 having a large heat capacity, thereby enhancing the cooling effect of the IGBT 13. As described above, the insulating oil 24 in the high voltage transformer tank 12 is larger than necessary for the purpose of cooling only the conventional high voltage transformer 3 and has not been effectively utilized. With this configuration, the insulating oil 24 can be effectively used not only for cooling the high-voltage transformer 3 but also for the IGBT 13, and a well-balanced thermal design can be realized for the inverter type X-ray high-voltage device.
[0021]
In the second embodiment of the present invention, the rectifier circuit 1 is integrated with the inverter circuit 2 of the present invention, which will be described with reference to FIGS. FIG. 4 shows an example in which a pulse width modulation control system converter circuit (Japanese Patent Application No. 6-71303) is applied to the rectifier circuit 1. FIG. 5 is a configuration diagram of the main part of the second embodiment of the present invention, and FIG. Is shown. As in the case of the inverter circuit 2 in the first embodiment, the switching element of the converter circuit uses two IGBT modules in which two switches are incorporated in one package. The converter circuit IGBT module is also fixed in close contact with the fixing plate 15 in the same manner as the inverter circuit IGBT module of the first embodiment, and the generated heat is transferred to the insulating oil 24 in the high voltage transformer tank 12 having a large heat capacity. It is designed to conduct efficiently. In order to make wiring resistance and inductance components as small as possible, the IGBT module is also arranged in the vicinity of the smoothing capacitor 11 and electrically connected by a copper plate. A snubber circuit for suppressing the surge voltage at the time of switching is arranged on the top surface of the IGBT, and wiring for driving the IGBT (not shown) is necessary, so that the space on the top surface of the IGBT is not so complicated. . For this reason, in the example of FIG. 4, the “E2” terminal of the IGBT module for converter circuit is the minus of the smoothing capacitor (2) 11 through a copper plate provided along the side surface of the IGBT module close to the smoothing capacitor 11. Electrically connect to the terminal. With the above-described configuration, the insulating oil 24 can be effectively used not only for cooling the rectifier circuit 1 and the inverter circuit 2 but also the high-voltage transformer 3. At the same time, not only can the space be saved, the wiring from the rectifier circuit 1 to the inverter circuit 2 can be shortened, and the power loss of the apparatus can be reduced.
[0022]
In the second embodiment, the rectifier circuit 1 is a pulse width modulation control type converter circuit that uses IGBTs for all four switches of the bridge. This is slightly different from the converter circuit of FIG. Although the power factor decreases, a converter circuit in which one of the two IGBT modules for converter circuit is a diode module may be applied. Alternatively, an IGBT is not used at all, and a diode module or a thyristor module is arranged in place of the IGBT module, its input side is connected to a commercial power source, and one output side is connected to the plus terminal of the smoothing capacitor 11 (the C1 terminal in FIG. 4). And a negative terminal of the capacitor 11 (a terminal connected to the E2 terminal in FIG. 4), and the present invention can be applied even if a full-wave rectifier circuit is configured. However, in this case, since the diode or thyristor operates only at the commercial frequency, heat generation is not a major problem, and it is not always necessary to enhance the cooling effect by installing it on the fixed plate 15, taking into consideration the balance with other components. What is necessary is just to arrange | position in the place which is easy to install. Furthermore, in the above-described embodiments, the copper modules are used for the electrical connection between the IGBT modules and between the IGBT module and the smoothing capacitor 11, but an electric wire may be used for this electrical connection.
[0023]
Further, in FIG. 1, the output voltage of the high voltage rectifier 4 is output to the high voltage cable 5 via the upper surface of the high voltage transformer tank 12, but it is desired to effectively use the space above the high voltage transformer tank 12. In some cases, the voltage may be output through the side surface of the high voltage transformer tank 12.
[0024]
In FIG. 6, the resonance capacitor 10 is connected to the output side of the inverter 2. However, the capacitor 10 has a high frequency current due to the leakage inductance of the high voltage transformer 3. It is inserted for the purpose of improving the fact that it does not sufficiently flow into the winding of the transformer 3, and may not be inserted if the above improvement is not necessary.
[0025]
【The invention's effect】
As explained above, according to the present invention,
(1) Since the heat sink and cooling fan of the rectifier circuit (converter circuit) and inverter circuit can be removed, it is possible to reduce the cost while reducing the size and weight.
(2) Since heat generated in the switching element of the inverter at the time of photographing can be efficiently conducted to the high voltage transformer tank having a large heat capacity, an increase in temperature of the switching element can be suppressed to a minimum.
(3) Since the wiring between the inverter circuit and the high-voltage transformer can be shortened, the inductance between them can be reduced, the inverter operation can be performed at a high frequency, the miniaturization of the high-voltage transformer can be realized, and the ideal required A close tube voltage waveform can be obtained.
[0026]
With the above three points, it is possible to obtain an ideal tube voltage waveform required for a medical X-ray apparatus, and to provide an inverter type X-ray high voltage apparatus that has a small installation area, is small and light, and is inexpensive. Can do.
[Brief description of the drawings]
FIG. 1 is a mounting layout diagram of an inverter type X-ray high voltage apparatus showing a first embodiment of the present invention.
FIG. 2 is a diagram showing a mounted state of the smoothing capacitor and the IGBT in the first embodiment of the present invention.
FIG. 3 is an equivalent circuit diagram of an IGBT module used in the embodiment shown in FIG.
FIG. 4 is a diagram showing a mounted state of a converter circuit, a smoothing capacitor, and an inverter circuit in a second embodiment of the present invention.
5 is a circuit diagram from a converter circuit to an inverter circuit in the embodiment shown in FIG. 4;
FIG. 6 is a circuit configuration diagram of a conventional inverter type X-ray high voltage device.
FIG. 7 is an ideal waveform diagram and an actual waveform diagram of a tube voltage in a medical X-ray apparatus.
[Explanation of symbols]
1 Rectifier circuit (converter circuit)
2 Inverter circuit 3 High voltage transformer 4 High voltage rectifier 5 High voltage cable 6 X-ray tube 8 Tube voltage detector 11 Smoothing capacitor 12 High voltage transformer tank 13 IGBT
14 Wiring from inverter to high voltage transformer 15 Fixing plate 19 Heat sink 20 Cooling fan 24 Insulating oil

Claims (2)

A DC power supply, applies the DC power supply and the inverter circuit that converts the alternating current of high frequency, high voltage transformer for boosting the output voltage of the inverter circuit, the X-ray tube by rectifying the output of the high voltage transformer In the inverter type X-ray high voltage apparatus comprising the high voltage rectifier circuit, the switching element of the inverter circuit is fixed to a metal plate having a higher thermal conductivity than the element, and the fixed metal plate The inverter type X-ray high voltage apparatus is characterized in that the heat generated by the switching element is conducted to the insulating oil in the high voltage transformer tank by adhering to the outer wall surface of the high voltage transformer tank. The DC power source is composed of a rectifier circuit that receives a commercial power source and rectifies the commercial power source. The inverter type X-ray high voltage device according to claim 1 , wherein the inverter type X-ray high voltage device is conducted to insulating oil in a transformer tank.

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