JPH09134793A - Inverter type x-ray high voltage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the supply voltage distortion and apparent power and reduce the loss and electromagnetic noises in an inverter. SOLUTION: A converter 1 is equipped with a full bridge circuit including self-extinguishing switch, a DC reactor 54 connected in series with the DC output end of the full bridge circuit, a diode 30 in which a cathode side terminal is connected with an input side terminal of the DC reactor, and a DC capacitor 6 connected to part between the anode side terminal of the diode and the output side terminal of the DC reactor 54. A converter control circuit 31 controls the converter 1 so that its output voltage is identical to the target voltage value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an AC power supply,
It is converted into direct current, this direct current is converted into high frequency alternating current using an inverter, the output voltage is boosted by a high voltage transformer and rectified to generate high direct current voltage, which is applied to an X-ray tube. The present invention relates to an inverter type X-ray high voltage device that radiates X-rays by means of an inverter.

[0002]

2. Description of the Related Art Conventionally, an inverter type X-ray high voltage apparatus of this type has a commercial three-phase AC power source U, V, W as shown in FIG.
AC voltage from the diode 40 to 45 composed of 3
A full-wave full-wave rectifier circuit (hereinafter, simply referred to as a converter) 1'converts it into a DC voltage, which is smoothed by a capacitor 6 and input to an inverter 2. The inverter 2 applies a tube voltage to the X-ray tube 4, which is a load, by controlling the phase difference and frequency of the inverter 2 by utilizing the resonance phenomenon between the capacitor 7 and the leakage inductance of the high voltage transformer 5. is there. That is, the AC voltage output from the inverter 2 is boosted by the high voltage transformer 5, converted into high voltage DC by the high voltage rectifier circuit 3, and applied to the X-ray tube 4.
The output voltage of the converter 1'has a peak value of the line voltage of U, V, W as the maximum voltage, and is slightly reduced according to the capacity of the smoothing capacitor 6 and the power supplied to the inverter 2, and is the same as the line voltage. The degree is a minimum voltage, and the voltage is in the range of approximately line voltage to line voltage × √2, and this cannot be actively controlled.

In FIG. 6, the inverter 2 detects the actual tube voltage value Vx, inputs this and the target value kVr to the inverter control circuit 32, obtains the phase difference and frequency of the inverter 2, and controls this. . The tube current is controlled by adjusting the temperature of the filament of the X-ray tube 4 by a filament heating circuit (not shown).

[0004]

In the above conventional device, the output voltage of the converter 1 ', that is, the input voltage of the inverter 2 cannot be arbitrarily set, which causes a large power loss in the inverter 2. However, there is a problem that electromagnetic noise occurs. In addition, AC power supply U,
There is also a problem in that the current supplied from V and W to the converter 1'abruptly changes, causing voltage distortion in the power supply voltage, or increasing apparent power and increasing the burden on the power supply equipment. Hereinafter, these problems will be described in detail.

First, the problem that power loss and electromagnetic noise occur because the input voltage of the inverter 2 cannot be set arbitrarily will be described. FIG. 7 is a timing chart showing an inverter operation for explaining the principle of controlling the output voltage of the inverter 2 by the phase difference of the inverter 2 and consequently controlling the tube voltage. As shown in FIGS. 7A to 7D, the switches 16 to 19 of the inverter 2 in FIG. 6 delay the switch 19 by a phase difference φ1 with respect to the switch 16 and place the switch 18 with respect to the switch 17. Turn on and off with a phase difference of φ1. Also, the upper and lower switches, that is, switches 16 and 17, switches 18 and 19
And turn on and off with a 90 ° phase shift. At this time,
A resonance current flows due to the capacitor 7 connected to the output side of the inverter 2 and the leakage inductance of the high-voltage transformer 5,
The currents flowing through the switches 16 to 19 and the anti-parallel diodes 26 to 29 are as shown in FIGS. 7 (e) to 7 (h), respectively. The output voltage of the inverter 2 is as shown in FIG. 7 (j), and the output current is as shown in FIG. 7 (i).

FIG. 8 shows the relationship between the phase difference φ and the tube voltage at this time. The smaller the phase difference φ, the higher the tube voltage is output, and the output becomes zero when φ is 180 °. Further, the output voltage is different when the current flowing through the X-ray tube 4 (hereinafter referred to as the tube current) is large and when it is small, even if the phase difference is the same. Furthermore,
In FIG. 8, the solid line shows the characteristics when the converter output voltage (tube voltage) is low, and the dotted line when the converter output voltage (tube voltage) is high. In this way, a desired tube voltage can be obtained by changing the phase difference φ or the converter output voltage. For example, when the tube current is small, to obtain a certain tube voltage, the converter output voltage may be lowered and the phase difference may be φ1, or the converter output voltage may be increased and the phase difference may be φ2.

Next, returning to FIG. 7, it will be described that the current and voltage waveforms of the switches 16 to 19 of the inverter 2 differ depending on the magnitude of the converter output voltage. In FIG.
The waveforms shown by the dotted lines show the current and voltage of each part when the converter output voltage is high. When the converter output voltage is high, the phase difference is set to φ2, which is larger than φ1, and the overlap between the switches 16 and 19 or the switches 17 and 18 is reduced to set the output voltage of the inverter as shown by the dotted line in FIG. 7 (j). As a result, a desired tube voltage is obtained. However, at this time, a current flows through the switches 16 to 19 forming the inverter 2 in a waveform as shown by the dotted lines in FIGS. This is the switch 16,17
In addition to the large turn-off current for switches 18 and 19 and the large peak value of the current, losses generated in switches 16 to 19 and high-voltage transformer 5 are higher than those when the converter output voltage is low. And electromagnetic noise are extremely large.

The conventional device, as shown in FIG.
Since the converter 1'is composed of diodes,
The input voltage of the inverter 2 is appropriately controlled to reduce the phase difference φ, that is, the switch 16 generated in the inverter 2
The loss of 19 and electromagnetic noise could not be minimized. Therefore, particularly when the power supplied to the X-ray tube 4 is small, the switches 16 to 19 of the inverter 2 generate heat, and electromagnetic noise adversely affects monitors (not shown) and various image processing devices around the inverter type device. Was to give. Next, in the conventional device that uses the converter 1'composed of the full-wave rectifier circuit including the diodes 40 to 45, the AC input current changes abruptly, the apparent power increases, and the AC power supplies U, V, W are changed. A problem that causes a large distortion will be described.

FIG. 9 shows an AC input voltage (expressed here as a phase voltage instead of a line voltage) of the U phase and an AC input current in the conventional device. Diodes 40-4
In the converter 1'which rectifies by 5 and smoothes the output voltage by the smoothing capacitor 6, the AC input current has a waveform with a large peak. Such a steep current causes distortion in the phase voltage as shown in FIG. This voltage distortion also fluctuates the power supply voltage of the peripheral equipment connected to the same power supply equipment (not shown), which causes failure or malfunction. Also, in FIG. 9, the apparent power obtained from the product of the phase voltage and the AC input current at each time is very large, and is a force that is a ratio to the effective power that can be actually taken in the inverter type X-ray high-voltage device as energy. The rate (= active power / apparent power) is about 0.3 to 0.8. Therefore, it is necessary to supply the apparent power 1.3 to 3 times as much as the required power from the power supply facility, which requires a great deal of cost for installation and maintenance of the power supply facility.

Further, as described above, the output voltage of the converter 1'has a peak value of the line voltage of U, V, W as the maximum voltage, and is slightly depending on the capacity of the smoothing capacitor 6 and the power supplied to the inverter 2. The voltage decreases, and the line voltage becomes the line voltage to the line voltage × √2, with the minimum voltage being approximately the same as the line voltage, and this cannot be positively controlled. In order to solve this, the inventions of Japanese Patent Application No. 5-194544 and Japanese Patent Application No. 6-3092 have been proposed.
In the system according to the invention of 194544 (hereinafter, this system is referred to as a boost converter), the output voltage can be set only to a voltage which is approximately equal to or higher than the interphase voltage of the AC power source, and Japanese Patent Application No. 6- In the invention of No. 3092, the output voltage can be set only to a voltage equal to or lower than the interphase voltage of the AC power supplies U, V, W (hereinafter, this method is referred to as a step-down converter). Therefore, the AC power supply U,
The desired output voltage could not be obtained depending on the difference in the voltage values of V and W. That is, the conventional three-phase AC power supplies U, V, W used for the X-ray high-voltage device are mainly 20
There are 0V system and 400V system.
For 00V power supply equipment, use a boost converter 4
Power supply equipment to be used (AC power supply voltage value), for example, a step-down converter must be applied to the 00V power supply.
Different types of converters have to be used depending on the type, and improvement of this point has been desired.

An object of the present invention is to provide an inverter type X-ray high voltage device capable of reducing loss and electromagnetic noise generated in an inverter, and reducing distortion of power supply voltage and apparent power. . It is an object of the invention of claim 2 to provide an inverter type X-ray high voltage device which is extremely convenient in practical use, in which it is not necessary to properly use different types of converters depending on the power supply equipment (AC power supply voltage value) used.

[0012]

An object of the present invention is to provide a converter for receiving an AC power source and rectifying the AC power source, an inverter for converting a DC voltage from the converter side into a high-frequency AC voltage, and this inverter. High voltage transformer for boosting the output voltage of the high voltage transformer, a high voltage rectifier circuit for rectifying the output voltage of the high voltage transformer and applying it to the X-ray tube, and a target tube voltage value inputted to the high voltage transformer and the X-ray tube. An inverter type X-ray high-voltage device comprising an inverter control circuit for controlling the above-mentioned inverter so that the actual tube voltage values match,
The converter is a full bridge circuit using a switch capable of self-extinguishing, a DC reactor connected in parallel to the DC output end of this full bridge circuit, and a cathode side terminal connected to the input side terminal of this DC reactor. A converter control that includes a diode and a DC capacitor connected between the anode side terminal of the diode and the output side terminal of the DC reactor, and controls the converter so that the output voltage thereof matches the target voltage value. This is achieved by providing a circuit. According to the invention of claim 1, the current supplied from the AC power supply can be appropriately controlled by the self-extinguishing switch connected to the AC power supply. As a result, power can be received while suppressing sharp changes and high peak currents, and the AC input current can be changed in a sinusoidal manner and can be synchronized with the phase voltage. Distortion and apparent power can be reduced. Further, since the output voltage of the converter can be controlled arbitrarily, the output voltage of the converter can be adjusted and optimized, and the loss and electromagnetic noise generated in the switch of the inverter can be suppressed to the minimum.

It is an object of the invention of claim 2 that, in the converter, as an operation mode of the switch, at least one of the switches capable of self-extinguishing each phase for flowing a current to the positive side of the DC capacitor is always conductive. The first operation mode in which one of the self-extinguishing switches that keeps the current flowing from the negative side of the DC capacitor to the AC power supply side is always in the conducting state, and all the self-extinguishing switches are in the OFF state. And a second mode of operation in. By providing the converter with the two modes as described above, it is not necessary to use different types of converters depending on the power supply equipment (AC power supply voltage value) used, which is extremely convenient in practice.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an inverter type X according to the present invention.
It is a circuit diagram which shows the 1st Example of a line high voltage apparatus. In FIG. 1, 51 to 53 are reactors inserted in the respective phases U, V, W of the AC power supplies U, V, W. Reference numerals 61 to 63 are capacitors connected to the reactors 51 to 53, and the capacitors 51 to 53 are star-connected. 10
Reference numeral 15 is a switch capable of self-extinguishing, here an insulated gate bipolar transistor (hereinafter referred to as IGBT), 2
0 to 25 are diodes connected in series to the IGBTs 10 to 15. These IGBTs 10 to 15 and the diodes 20 to 25 respectively form a self-extinguishing type switch, and these 6 sets of self-turning-off type switches constitute a 3-phase full bridge circuit.

Reference numeral 54 is a DC reactor, and 6 is a smoothing DC capacitor (also called a smoothing capacitor). The converter 1 is composed of the full bridge circuit, the DC reactor 54, the diode 30, and the DC capacitor 6. Reference numeral 7 is a resonance capacitor inserted in the output side of the inverter 2, and 5 is an inverter 2 and a resonance capacitor 7
And a high voltage transformer for boosting the inverter output voltage to generate a high frequency AC high voltage, 3 is a high voltage rectifier circuit connected to the secondary side of the high voltage transformer 5, and 4 is a high voltage. It is an X-ray tube connected to the rectifier circuit 3. Reference numeral 31 is a converter control circuit for controlling the IGBTs 10 to 15 of the converter 1, the details of which will be described later. 32 detects the voltage across the X-ray tube 4 (actual tube voltage value) Vx, and this and the target value kVr
Is an inverter control circuit for controlling the IGBTs 16 to 19 of the inverter 2 by means of.

The operation of the device of the present invention having the above-described structure will be described below. However, the operation of each part after the smoothing capacitor 6 is the same as that of the conventional device, and the description thereof will be omitted. That is, the device of the present invention is characterized in that the converter 1 is configured by using a switch capable of self-extinguishing. First, the operation of the converter 1 will be described together with FIG. FIG. 2 is a timing diagram conceptually showing the operation (switching operation) of the IGBTs 10 to 15 of the converter 1.

The converter 1 has an "AC side connection mode" in which the DC reactor 54 is connected to the AC input side and a "DC side connection mode" in which it is connected to the DC input side by the operation of the full bridge circuit. The DC reactor 54 of No. 1 operates while the above two modes are alternately selected, and temporarily stores energy input from the power supply side during the former "AC side connection mode" period and the latter "DC side connection mode". "During the period, the energy is transferred to the DC capacitor 6
To be released. The converter output voltage is controlled by the duty ratio for selecting the "AC side connection mode" or "DC side connection mode". In the "AC side connection mode", the IGBTs 10 to 15 are turned on and off at regular intervals according to the following rules (1) to (3). On the other hand, in the "DC side connection mode", all the IGBTs 10 to 15 are off. In this embodiment, the IGBTs 10 to 15 are operated at regular intervals for the sake of simplicity of explanation, but this is not always necessary.

(1) At least one of the lower IGBTs 10, 12, 14 is turned on, and the upper IGBTs 11, 12,
By turning on at least one of 3, 15
An electric current is continuously supplied to the reactor 54. (2) In FIG. 2, for example, in the section I, when it is desired to increase the current supplied from the U phase, the ON time of the IGBT 10 is lengthened. Similarly, when it is desired to increase the current supplied from the V phase, the ON time of the IGBT 14 is lengthened.
Then, the IGBT 12 is turned on for the remaining time. (3) The IGBT 13 is turned on during this period. The converter control circuit 31 controls ON / OFF of the IGBTs 10 to 15 which are the switches configuring the converter 1 based on the above-mentioned operation principle, and outputs the output of the converter 1 so as to match the target value V1 of the converter output voltage. The voltage (voltage Vc across the smoothing capacitor 6) is detected to perform the above control. As described above, the device of the present invention controls the converter 1 (IGBTs 10 to 15) as shown in FIG. 2 corresponding to the sections I to VI in FIG. 2, whereby the AC input current is freely controlled. To be able to
The AC input current can be changed sinusoidally and synchronized with the phase voltage. The output voltage control range is
In principle, it can be lower or higher than the interphase voltage. For example, even for three-phase 200V, 400V, etc., a constant output voltage can be obtained with the apparent power minimized. It is possible to support various power supply equipment (AC power supply voltage value).

FIG. 3 is a diagram showing the phase voltage and the input current waveform of the AC power supplies U, V, W in the first embodiment of the present invention. As shown in FIG. 3, the power supply according to the present invention is used. It is possible to reduce voltage distortion and apparent power. Further, when the AC input current can be controlled, the output voltage of the converter 1 can be adjusted and optimized as a result, and the loss and electromagnetic noise in the inverter 2 can be reduced.

The AC reactors 51 to 53 are added as necessary so that the inductance of the power supply equipment (not shown) of the device of the present invention and the voltage fluctuation caused by the switching of the converter 1 are not returned to the power supply side. It represents "and" and is not always necessary in the operation principle. Similarly, the capacitors 61 to 63 prevent the high frequency voltage fluctuation due to the switching of the converter 1 from returning to the power supply side together with the reactors 51 to 53, and the surge current is generated by continuing the current flowing through the reactors 51 to 53. It is provided for the purpose of preventing this, and is not necessarily required in the operation principle. The diodes 20 to 25 are inserted so that the currents flowing through the IGBTs 10 to 15 are in a fixed direction and no reverse voltage is applied. Gate turn-off thyristor (GT
This is not necessary when using a switch that originally allows a current to flow only in one direction, as represented by O).

FIG. 4 is a circuit diagram showing a second embodiment of the device of the present invention in which the capacitors 61 to 63 at the connection between the AC power supplies U, V and W and the converter 1 are inserted between the lines. is there. The connection method of these capacitors 61 to 63 may be a delta type or a star type.

FIG. 5 is a circuit diagram showing a third embodiment in which the present invention is applied to an inverter type X-ray high voltage device for a single-phase AC power supply. In the single-phase AC power supplies U and W, I
The converter 1 is composed of four sets of self-extinguishing type switches formed by the GBTs 10 to 15 and the diodes 20 to 25. For each phase of input, reactors 51 and 53, a capacitor 6 between the lines
1 is inserted to prevent high frequency voltage fluctuations from returning to the power supply side. The reactor 54 and the smoothing capacitor 6 are the same as those in the first embodiment.

In the above-mentioned embodiment, the IGBT is used as the switch which constitutes the converter 1. However, instead of the IGBT, another self-extinguishing type switch such as a bipolar transistor or a field effect transistor (MOS-FET) is used. May be. In addition, MOS controlled thyristors (
When a switch such as an MCT) or a gate turn-off thyristor (GTO) in which a current does not flow in the reverse direction is used, a diode for blocking a reverse current connected to the IGBT becomes unnecessary. Further, in the above embodiment, the inverter 2 controls the tube voltage by the phase difference, but other control methods such as pulse width modulation and frequency modulation may be used.
Alternatively, the inverter 2 may not control the tube voltage, but may only perform the DC-AC conversion, and the converter 1 may control the tube voltage. Furthermore, although the resonance capacitor 7 is provided on the output side of the inverter 2 in the above-described embodiment, this is not always necessary.

[0024]

According to the invention of claim 1, the AC input current can be changed in a sinusoidal manner and can be synchronized with the phase voltage. Therefore, harmful power supply voltage distortion and apparent power can be reduced. Further, there is an effect that the output voltage of the converter is adjusted and optimized to reduce loss and electromagnetic noise in the inverter. According to the invention of claim 2, since it is not necessary to provide the converter with two operation modes and use different types of converters depending on the power supply equipment (AC power supply voltage value) to be used, it is extremely convenient in practice. There is.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the device of the present invention.

FIG. 2 is a timing diagram showing an operation of an IGBT of the converter shown in FIG.

FIG. 3 is a waveform diagram of a phase voltage and an AC input current according to the device of the present invention.

FIG. 4 is a circuit diagram showing a main part of a second embodiment of the device of the present invention.

FIG. 5 is a circuit diagram showing an essential part of a third embodiment of the device of the present invention.

FIG. 6 is a circuit diagram showing a conventional device.

FIG. 7 is a timing diagram showing an operation of the inverter in FIG.

8 is a graph showing the relationship between the phase difference φ in FIG. 7 and the tube voltage.

FIG. 9 is a waveform diagram of a phase voltage and an AC input current according to a conventional device.

[Explanation of symbols]

U, V, W ... AC power supply, 1, 1 '... Converter, 2 ... Inverter, 3 ... High-voltage rectifier circuit, 4 ... X-ray tube, 5 ... High-voltage transformer, 6 ... DC capacitor (smoothing capacitor), 7
... Resonant capacitors, 10-19 ... Switches (IGB
T) 20-29 ... Diode, 31 ... Converter control circuit, 32 ... Inverter control circuit, 54 ... DC reactor, 61-63 ... Capacitor.

Claims (2)

[Claims] 1. A converter for receiving an AC power source and rectifying the AC power source, an inverter for converting a DC voltage from the converter side into a high frequency AC voltage, a high voltage transformer for boosting an output voltage of the inverter, and A high-voltage rectifier circuit that rectifies the output voltage of the high-voltage transformer and applies it to the X-ray tube, and the inverter so that the target tube voltage value is input and the actual tube voltage value of the X-ray tube matches. In an inverter type X-ray high voltage apparatus comprising an inverter control circuit for controlling, the converter is connected in parallel to a full bridge circuit using a switch capable of self-extinguishing and a DC output terminal of the full bridge circuit. DC reactor, a diode in which the cathode side terminal is connected to the input side terminal of this DC reactor, the anode side terminal of this diode and the above DC reactor And a DC capacitor connected between output terminals of the converter, and a converter control circuit for controlling the converter so that its output voltage matches a target voltage value. High voltage device. 2. In the converter, as an operation mode of the switch, at least one of the switches capable of self-extinguishing each phase for flowing a current to the positive side of the DC capacitor is always in a conductive state, and the DC capacitor A first operation mode in which one of the self-extinguishing switches that allows a current to flow from the negative side to the AC power supply side is always in a conductive state, and a second operation mode in which all the self-extinguishing switches are in the off state. The inverter type X-ray high voltage apparatus according to claim 1, further comprising: