JP4169221B2 - Inverter X-ray high voltage device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention converts a commercial alternating current power source into a direct current with a converter circuit, converts the direct current into a high frequency alternating current with an inverter circuit, boosts the output voltage with a high voltage transformer, and rectifies the high voltage direct current. The present invention relates to an inverter type X-ray high voltage apparatus that generates a voltage and applies it to an X-ray tube to emit X-rays. In particular, it reduces the equipment capacity and harmonics of the AC power supply, converter circuit, inverter circuit and high voltage. The present invention relates to an inverter type X-ray high voltage device suitable for miniaturization of a transformer.
[0002]
[Prior art]
An inverter X-ray high-voltage device converts an AC voltage from a commercial AC power source into a DC voltage via an AC reactor by a converter circuit using a full-wave rectifier circuit composed of a thyristor or a diode, and smoothes this. Smoothed with a capacitor and input to the inverter circuit.
[0003]
This inverter circuit controls the phase difference and frequency of the inverter circuit by utilizing the resonance phenomenon between the resonant capacitor and the leakage inductance of the high voltage transformer, as described in, for example, Japanese Patent Laid-Open No. 63-190556. Thus, a high DC voltage (hereinafter referred to as tube voltage) is applied to the X-ray tube as a load. That is, the high-frequency AC voltage output from the inverter circuit is boosted by the high-voltage transformer, converted into DC by the high-voltage rectifier circuit, and applied to the X-ray tube. The inverter circuit detects the actual tube voltage, inputs this and the target value to the inverter control circuit, and obtains and controls the phase difference and frequency of the inverter.
[0004]
The tube current is controlled by adjusting the filament temperature of the X-ray tube by a filament heating circuit. Such X-ray high voltage apparatuses are widely applied from general X-ray imaging apparatuses to circulatory X-ray imaging apparatuses, X-ray CT apparatuses, etc., but recent medical X-ray high voltage apparatuses are only in terms of performance. However, the demand for reducing the installation area and reducing the size and weight is increasing. In particular, high-voltage transformers account for a large percentage of the equipment volume, and downsizing the high-voltage transformer is effective for downsizing the equipment. In order to achieve this, it is necessary to reduce the current of the inverter circuit and use a switching element of this circuit with a small current capacity, to reduce the turn ratio of the high voltage transformer and to reduce the size of the transformer. .
[0005]
Reducing the turns ratio leads to reduced loss of eddy current loss caused by the leakage flux of the high voltage transformer interlinked with the primary winding, etc., improving efficiency, thereby reducing the inverter circuit current. In addition, the current capacity of the switching element is also reduced. Furthermore, the leakage inductance of the high voltage transformer is reduced, and the high voltage transformer can be expected to be miniaturized by further increasing the frequency. The current capacity of the switching element of the inverter circuit and the turns ratio of the high voltage transformer are the magnitude of the input voltage of the inverter circuit, that is, the voltage obtained by full-wave rectification of the AC power supply voltage (the line voltage peak value of the AC power supply). The maximum voltage is determined in the range of approximately 0 (V) to line voltage × √2 (V), and when the power supplied to the inverter circuit is large, the voltage is lowered. There was a limit to the miniaturization of inverter circuits and high voltage transformers by reducing the turn ratio of high voltage transformers.
[0006]
Therefore, in such a case, a transformer for boosting the AC power supply voltage (for example, boosting to 400 V when the AC power supply voltage is 200 V) is connected between the AC power supply and the converter circuit, and this The output voltage of the transformer may be rectified by a full-wave rectifier circuit and input to the inverter circuit. However, since the transformer for boosting the AC power supply voltage requires a large capacity, the size of the device is greatly increased. This is not preferable because it increases costs. As another method, there is a method of increasing the input voltage of the inverter circuit by using the voltage doubler rectifier circuit shown in FIG. 3, but this also can increase the input voltage of the inverter only up to twice that during full-wave rectification. However, there is a limit even if the input voltage of the inverter circuit is further increased to reduce the size.
[0007]
Further, the inverter type X-ray high voltage apparatus using a full-wave rectification type converter circuit composed of a conventional thyristor or diode has a problem of power factor reduction and power supply harmonics. That is, because the phase of the gate control signal of the thyristor of the converter circuit is given as a delayed phase with respect to the phase of the AC power supply voltage, for example, as shown in FIG. 4, the current waveform is delayed in phase by φ from the voltage waveform, The power factor was decreasing. For this reason, reactive power is large, and the installation capacity of the AC power source must be increased accordingly.
[0008]
Furthermore, the phase current waveform of the AC power supply is also distorted and has many harmonic components. This may cause the harmonic current to flow into the power supply system, and thus cause troubles to other devices connected to the power supply system.
[0009]
In view of this, an inverter type X-ray high voltage apparatus using a converter circuit capable of increasing the input voltage of the inverter circuit to a predetermined value and improving the power factor and reducing the power supply harmonics is disclosed in Japanese Patent Laid-Open Nos. 7-263175 and It is disclosed in Japanese Patent Application No. 7-272891. In these publications, pulse width modulation control (hereinafter abbreviated as PWM control) that can increase the input voltage of the inverter circuit and eliminate the delay of the phase of the voltage and current of the AC power supply to improve the power factor and reduce the power supply harmonics. Inverter X-ray high-voltage devices using full-bridge or mixed-bridge type converter circuits have been proposed.
[0010]
[Problems to be solved by the invention]
However, the inverter type X-ray high voltage apparatus using the PWM control converter circuit described in Japanese Patent Application Laid-Open Nos. 7-263175 and 7-272891 has the following problems.
[0011]
(1) Problems of the converter circuit disclosed in Japanese Patent Laid-Open No. 7-263175
Since this converter circuit forms a full bridge type by combining four switching elements made of self-extinguishing switching elements, for example, IGBTs (insulated gate bipolar transistors), there are many switching elements and there is a difficulty in economical efficiency. is there.
[0012]
(2) Problems with the converter circuit of Japanese Patent Laid-Open No. 7-272891
This converter circuit uses a switching element capable of self-extinguishing only in two arms on the AC side or DC side of four full-bridge type arms (mixed bridge type), and the number of switching elements capable of self-extinguishing There are few advantages in terms of economy.
[0013]
However, since the power regeneration that returns the load power of the converter circuit to the power supply side cannot be performed, it cannot be reduced when it is desired to reduce the output voltage of the converter circuit, which is the input power of the inverter circuit, and the current waveform near zero of the phase current of the AC power supply Cannot be a sine wave (this current waveform is shown in FIG. 6), and therefore has a disadvantage that the power factor is lower and the power harmonics are larger than the full bridge type.
[0014]
(3) Problems common to JP-A-7-263175 and JP-A-7-272891
1. In general, a commercial AC power supply having a V-phase ground is used. For the PWM control system converter circuit having the above-described full bridge type and mixed bridge type boosting functions, a bridge of the converter circuit is configured. The connection point of any one of the series connection bodies of the set of self-extinguishing switching elements is grounded. From this, the positive terminal of the DC output of the converter circuit is in the range from zero volt to VDC volt when viewed from the ground point with the DC output voltage as VDC, and the negative terminal of the DC output of the converter circuit is Since the voltage change rate (dv / dt) is large due to the switching of the switching element, it often causes malfunction due to noise generated by the switching element, and many countermeasures are taken. The effort is spent.
[0015]
2. In the inverter type X-ray high voltage apparatus using the PWM control type converter circuit, the converter circuit and the inverter circuit are configured by combining an IGBT and a switching module including a diode connected in reverse parallel thereto, and these converters The circuit and the inverter circuit were arranged separately. In addition, since the switching module has a size corresponding to a withstand voltage and a current capacity and requires a corresponding space, the size of the switching module almost determines the size of the entire main circuit, so that the size can be reduced. There was also a limit. Further, since each of the switching modules is arranged separately, an inductance component exists in the wiring connecting them, which increases the surge voltage at the time of switching and increases the switching loss. For this reason, mounting of the means for suppressing the surge voltage and the means for cooling the switching element has become a major issue.
[0016]
An object of the present invention is to provide an inverter-type X-ray high-voltage apparatus that can reduce power supply capacity and power supply harmonics, is small and inexpensive, and has higher reliability.
[0017]
[Means for Solving the Problems]
  The purpose of the present invention is to receive an AC power supply and rectify the converter circuit, an inverter circuit that replaces the output voltage of the converter circuit with a high-frequency AC, a high-voltage transformer that boosts the output voltage of the inverter circuit, Inverter-type X-ray high voltage comprising a high-voltage rectifier circuit that rectifies the output voltage of the high-voltage transformer, and an X-ray tube that applies a DC voltage that is the output voltage of the high-voltage rectifier circuit to emit X-rays In the deviceThe converter circuit is achieved by matching the phase of the voltage and current of the AC power supply and making the input voltage to the inverter circuit equal to a predetermined set value.
  In particular,The converter circuit includes a switching module series connection body in which two sets of switching modules each including a self-extinguishing switching element and a diode connected in reverse parallel to the switching element, and the switching module series connection body, A capacitor series connection body in which two capacitors are connected in series in parallel, one end of the AC reactor is connected to the connection point of the switching module series connection body, the other end of the AC reactor and the capacitor series connection body The AC power source is connected to the connection point of the AC power source, and the pulse width modulation control of the two sets of switching modules is performed in accordance with an error between the voltage of the AC power source and the phase difference and the set value of the voltage across the capacitor series connection body. To match the phase of the voltage and current of the AC power supply and Comprising a pulse width modulation control circuit for controlling the voltage across the series connection body to the set value, the voltage across the capacitor series connection is accomplished by input to the inverter circuit.
[0018]
The inverter type X-ray high-voltage apparatus configured as described above is a converter circuit having a minimum circuit configuration including two self-extinguishing switching elements and diodes, two capacitors, and one AC reactor. The switching element is subjected to pulse width modulation control in accordance with an error between the phase difference between the voltage and the voltage across the two capacitors (the input voltage of the inverter circuit) to match the phase of the current and voltage of the AC power supply. The input voltage of the inverter circuit is controlled to be equal to the set value. As a result, the phase of the current and the voltage of the AC power supply coincide with each other, and the current waveform becomes a sine wave without distortion. Accordingly, the power factor is improved, the apparent power is reduced, the capacity of the power supply facility can be reduced, and the power supply harmonics are also eliminated.
[0019]
The above converter circuit is smaller, lighter and cheaper than the conventional full bridge type or mixed bridge type pulse width modulation control type converter circuit, and is different from the mixed bridge type in which one phase is composed of a diode. Power regeneration is possible, and even when the phase current is near zero, the phase current waveform can be made closer to a sine wave, reducing power consumption especially when X-rays are exposed for a long time, such as during fluoroscopy. This is advantageous.
[0020]
Normally, a V-phase grounded one is used as the AC power source, and the midpoint of the bridge on one side of the converter circuit is grounded for the above-mentioned full bridge type and mixed bridge type converter circuit. From this, the output terminal on the positive side of the full-bridge type and mixed-bridge type converter circuit has a DC output voltage as VDC, in the range from zero volt to VDC volt when viewed from the ground, and the negative output of the converter circuit. The terminal greatly changes in the range of -VDC volt to zero volt to generate switching noise, and this noise sometimes causes malfunction. However, with this configuration, the midpoint of the smoothing capacitor (capacitor series connection body) of the converter circuit can be dropped to the ground potential, so that the output terminal on the positive side of the converter circuit has a DC output voltage as VDC, The range of approximately zero volts to VDC / 2 volts as viewed from the ground, and the negative output terminal of the converter circuit will change only in the range of -VDC / 2 volts to zero volts. That is, the change range is almost halved compared to the full bridge type and the mixed bridge type, which is advantageous in that the circuit system can be made stronger against switching noise.
[0021]
Also, the input voltage of the inverter circuit is increased to an optimum value by using the boosting function of the converter circuit. As a result, not only miniaturization by reducing the turn ratio of the high voltage transformer, but also leakage flux of the high voltage transformer is reduced, thereby reducing power loss and improving efficiency. The inverter circuit can be reduced in size by reducing the circuit current by increasing the input voltage of the inverter circuit and increasing the input voltage of the inverter circuit, and the switching noise is also reduced, so that the reliability is improved.
[0022]
In addition, two sets of switching modules, each of which includes a switching element capable of self-extinguishing and a diode connected in antiparallel with the switching element, are connected in series, or two sets of switching module series connection bodies are connected in parallel. A circuit is configured, and these two sets are connected in parallel or a set of switching modules are connected in parallel with a series connection body and a switching module series connection body of the converter circuit to form a three-phase switching module or a single-phase switching module. .
[0023]
By configuring the converter circuit and the inverter circuit using the three-phase switching module or the single-phase switching module configured as described above, it is possible to reduce the space and cost required for the main circuit components, and between the converter circuit and the inverter circuit. As a result, the inductance of the wiring can be reduced, the reliability can be improved by reducing the surge voltage during switching, and the cooling and mounting of the element can be simplified by reducing the loss of the switching element.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a first embodiment of an inverter type X-ray high voltage apparatus according to the present invention. This X-ray high-voltage device converts the output voltage (DC voltage) of a converter circuit that converts commercial power into DC to an AC voltage of high frequency using an inverter circuit, boosts the output voltage with a transformer, and then rectifies it. A DC high voltage is applied to the X-ray tube to emit X-rays. The converter circuit 1, the inverter circuit 2, the high voltage transformer 3, the high voltage rectifier circuit 4, and the high voltage cable 5 , An X-ray tube 6, a converter control circuit 9, an inverter control circuit 10 and the like.
[0025]
Next, the function of each component will be briefly described. The converter circuit 1 is a device that supplies a DC voltage, and rectifies the AC voltage of a commercial AC power supply 30 of 50 Hz or 60 Hz. The inverter circuit 2 receives the DC voltage output from the converter circuit 1 and converts it into a high-frequency AC voltage and controls the tube voltage. The inverter circuit 2 receives the DC voltage output from the converter circuit 1 and converts it into a high-frequency AC voltage and controls the tube voltage.
[0026]
The high voltage transformer 3 boosts the AC voltage from the inverter circuit 2, and its primary side is connected to the output of the inverter circuit 2. The X-ray tube 6 emits X-rays from the high voltage rectifier circuit 4 via the high voltage cable 5, and is connected to the output side of the high voltage rectifier circuit 4. Further, the converter circuit 1 includes an IGBT 13 which is a switching element of the converter circuit 1 according to a difference between a current and voltage phase of the AC power supply 30 and a set value of the output voltage of the converter circuit 1 and an actual output voltage. 14 is subjected to pulse width modulation control to match the phase of the current and voltage of the AC power supply 30, and at the same time, the control signal S1 is generated so that the output voltage of the converter circuit 1 matches the set value.
[0027]
The inverter control circuit 10 receives the target tube voltage signal Vr and the tube voltage detection signal Vx, compares the target tube voltage signal Vr and the tube voltage detection signal Vx, and calculates the tube voltage of the X-ray tube 6 as a target. The control signal S2 is generated so as to coincide with the tube voltage.
Reference numeral 26 denotes a resonance capacitor inserted on the output side of the inverter circuit 2, and it is confirmed that a high frequency current does not sufficiently flow through the winding of the high voltage transformer 3 due to the leakage inductance of the high voltage transformer 3. It is inserted for the purpose of improvement, and may not be inserted if the above is not necessary.
[0028]
Then, the structure and function of the converter circuit 1 and the inverter circuit 2 which are the principal parts of this invention are demonstrated using FIG. Reference numerals 11 and 12 are capacitors connected in series with one phase of one side of the commercial power supply 30 as a midpoint, 13 to 18 are power semiconductor switches, here IGBTs, and 19 to 24 are connected in reverse parallel to the IGBTs 13 to 18, respectively. Diode. The IGBTs 13 and 14 and the diodes 19 and 20 constitute the converter circuit 1 together with the capacitors 11 and 12, and the IGBTs 15 to 18 and the diodes 21 to 24 constitute the inverter circuit 2. In the present embodiment, the same type can be applied to the switching modules (IGBT and diodes connected in reverse parallel thereto) used in the converter circuit 1 and the inverter circuit 2, and the orientations thereof can be aligned. The three-phase switching module 25 in which a total of six pairs of IGBTs and diodes connected in reverse parallel thereto (two sets of series-connected bodies are connected in parallel) is applied to reduce the size and cost. Further, by applying the three-phase switching module in this way, the amount of inductance of the wiring between the converter circuit 1 and the inverter circuit 2 is reduced to reduce the surge voltage due to switching, thereby reducing the switching loss. .
[0029]
Reference numeral 7 denotes a capacitor inserted between the phases, which is provided for the purpose of preventing high-frequency power supply fluctuations due to switching of the converter circuit 1 from returning to the power supply side, and is not necessarily required in terms of the operation principle. Reference numeral 8 denotes an AC reactor inserted between the commercial power supply 30 and the converter circuit 2. As will be described later, the converter circuit 1 has a boosting function, and at the same time, voltage fluctuations caused by switching of the converter circuit 1 are returned to the power supply side. It is provided so that there is no. Hereinafter, the operation of the main part of the device of the present invention having the above-described configuration will be described. Since the operation after the converter circuit 1 is the same as that of the conventional device, the description thereof will be omitted.
[0030]
The device according to the present invention is greatly characterized in that the converter circuit 1 is configured by using a self-extinguishing switching element. The operation of the converter circuit 1 will be described with reference to FIG.
[0031]
FIG. 2 shows all the operation modes in this circuit. If the direction of the phase current is classified, (a) and (b) are when the phase current is positive, and (c) and (d) are when the phase current is negative. In addition, if classified according to the operating state of the switch, (a) and (c) indicate that the upper switch is on and the lower switch is off, and (b) and (d) indicate that the upper switch is off. The lower switch is on. Speaking of the operation of charging or discharging the capacitor 11 or 12, (a) and (d) are modes in which the capacitor is charged (output voltage is increased), and (b) and (c) are the modes in which the capacitor is discharged (output). Voltage decreases: mode in which power is regenerated on the power supply side. The basic algorithm of this converter control is an operation in which the upper switch 13 and the lower switch 14 are alternately turned on and off.
[0032]
First, output voltage control and boosting operation will be described. Considering when the phase current is positive, the output voltage can be controlled by controlling the time ratio between the charge / discharge modes of (a) and (b), but the current path changes each time the switch is switched, Each time the power supply voltage is short-circuited via the capacitor 11 or 12, the voltage at both ends of the AC reactor 8 is greatly increased at the same time as the phase current increases rapidly (the voltage at both ends of the AC reactor 8 is Lu · diu / dt). However, Lu is the value of the inductance of the AC reactor 8).
[0033]
In this state, since the charging mode (a) is set, a high voltage is generated at both ends of the reactor 8, so that the capacitor 11 is charged until the capacitor 11 becomes a high voltage by being added to the power supply voltage. As a result, a voltage higher than the peak value of the AC power supply voltage can be obtained (step-up operation: an infinite voltage can be theoretically obtained, but there are actually limitations due to the loss of the AC reactor 8 and the switching element). It becomes possible. The same applies to the case where the direction of the phase current is reversed (negative).
[0034]
Next, phase current control and higher power factor will be described. The middle point a of the output pressure VDC is set as a reference potential (ground), the potential on the collector side of the upper switch 13 is + VDC / 2, and the potential on the emitter side of the lower switch 14 is -VDC / 2. The ratio of the time during which the upper switch 13 is turned on with respect to one cycle of the AC power supply 30 is referred to as duty here. Controlling this duty is the same as controlling the charge / discharge mode ratio described above. is there.
[0035]
The potential at the middle point a of the upper switch 13 and the lower switch 14 becomes + VDC / 2 and −VDC / 2 each time the upper switch 13 and the lower switch 14 are alternately turned on.
Therefore, when the duty is controlled, the average potential at the middle point a can be controlled to + VDC / 2 to -VDC / 2, and when the average potential at the middle point a is controlled as described above, the current flows to the AC reactor 8 as well as the output voltage. The current iu can also be controlled. In addition, by observing the AC power supply voltage and performing pulse width modulation control so that the waveform and the phase current have the same phase, it becomes possible to obtain a phase current waveform having substantially the same phase as the AC power supply voltage, The converter circuit 1 can receive high power factor power. The converter circuit 1 also reverses the direction of the phase current in the same current path when the phase current is inverted (for example, when shifting from mode (a) to mode (c)). Since continuous control is possible, the phase current waveform can be controlled in a sine wave shape even when the phase current value is near zero.
[0036]
FIG. 5 shows a waveform diagram of the phase current and pulse width modulation signal of the single-phase AC power supply 30 in the apparatus of the present invention. A smoother sine wave current can be obtained by increasing the modulation frequency of the pulse width modulation control or adjusting the constant of the filter on the AC side.
[0037]
In this way, the input voltage of the inverter circuit is increased to reduce the turn ratio of the high voltage transformer and the current of the inverter circuit, and the high voltage transformer and the inverter circuit can be miniaturized. In addition, a high power factor by matching the phase of the voltage and current of the AC power supply and a sine wave of the phase current greatly contribute to a reduction in power supply facility capacity and a reduction in power supply harmonics.
[0038]
Next, the converter circuit 1 and the inverter circuit 2 are integrated by a three-phase switching module to reduce the size of these circuits and reduce the switching noise by reducing the wiring inductance between these circuits. Normally, the breakdown voltage types of switching elements prepared by power semiconductor switching element manufacturers are relatively rough, such as 600V below 1200V, while current ratings are, for example, 50A, 75A, 100A, 150A, 200A, 300A, and 400A are relatively finely divided. In the conventional device, for example, when a single-phase 200V power source is used, the output voltage of the converter circuit is about 450V at the maximum even in the case of the voltage doubler rectifier circuit (FIG. 3), but the withstand voltage of the switching element is 1200V. Even with consideration of surge voltage during switching and abnormal operation, there was too much room in terms of breakdown voltage.
[0039]
However, the 600V withstand voltage below the 1200V withstand has no margin, and the specification cannot be reduced, and a large 1200V withstand voltage may have to be adopted.
[0040]
Therefore, according to the present invention, the input voltage of the inverter circuit is boosted to a voltage corresponding to the element withstand voltage, and the current of the inverter circuit is reduced by that amount (the final output power is approximately proportional to the value of voltage × current. If a current rating that is finely classified is selected, an optimum switching element corresponding to the rating of the X-ray high-voltage device can be selected. If the switching elements are selected in this way and the converter circuit 1 and the inverter circuit 2 are mounted with one three-phase switching module, the size of these circuits and the wiring inductance between these circuits can be reduced. Mounting for reducing the switching noise and cooling the switching element is simplified, and the circuit is greatly reduced in size. Further, by using the converter circuit 1 of FIG. 1, the midpoint of the smoothing capacitors 11 and 12 of the converter circuit 1 can be dropped to the ground potential, so that the output terminal on the positive side of the converter circuit 1 has a DC output voltage. As the VDC, the range from approximately zero volts to VDC / 2 volts as viewed from the ground, and the negative output terminal of the converter circuit 1 is in the range of -VDC / 2 volts to zero volts, that is, a full bridge type and a mixed bridge type. Compared with a voltage change that is almost a half of the voltage change, a circuit system that is strong against switching noise can be obtained.
[0041]
FIG. 7 shows an inverter type X-ray high-voltage apparatus that combines the converter circuit 1 and the half-bridge type inverter circuit 40 described above.
The inverter circuit 40 of this inverter type X-ray high-voltage device has a series resonance capacitor 26 connecting a connection point of a series connection body of an IGBT 50 and a diode 60 connected in reverse parallel thereto and an IGBT 51 and a diode 61 connected in reverse parallel thereto. One end of the primary winding of the high-voltage transformer 3 is connected to the connection point between the capacitors 11 and 12 to constitute a half-bridge type inverter circuit. The rest of the configuration is the same as that shown in FIG.
[0042]
Since the output voltage of the half-bridge type inverter circuit 40 is ½ that of the full-bridge type in FIG. 1, the inverter circuit 40 is used to make the voltage input to the high-voltage transformer 3 the same as that of the full-bridge type. The operating point of the converter circuit 1 may be set so that the input voltage of the converter circuit 1, that is, the output voltage of the converter circuit 1 is double that of FIG. In this way, the current of the inverter circuit can be made the same as that in FIG.
[0043]
Further, the same type of switches can be used for the switches used in the converter circuit 1 and the inverter circuit 40, and the orientations thereof can be made uniform. Therefore, a total of four sets of IGBTs and diodes connected in reverse parallel thereto (two sets). By applying the built-in single-phase switching module 70, it is possible to achieve further miniaturization and cost reduction than those of FIG. Furthermore, by applying the single-phase switching module in this way, the inductance of the wiring between the converter circuit 1 and the inverter circuit 2 can be reduced to reduce the surge voltage due to switching, thereby reducing the switching loss. This is the same as the first embodiment.
[0044]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0045]
(1) Effects of pulse width modulation control of converter circuit
Since the phase of the AC power supply voltage and current match and the current of the AC power supply can be made sinusoidal, the power factor is increased to reduce the capacity of the AC power supply and the influence on peripheral devices due to the reduction of power supply harmonics. Can be removed.
[0046]
(2) Effect of boost function of converter circuit
The X-ray high voltage device can be selected by reducing the inverter circuit current by boosting the input voltage of the inverter circuit to a voltage corresponding to the withstand voltage of the switching element with a converter circuit with the minimum configuration and selecting an element with a finely classified current rating. Since an optimum switching element can be selected according to the rating of the inverter, the inverter circuit can be downsized. At the same time, the turn ratio of the high-voltage transformer is reduced, and the high-voltage transformer can be reduced in size. Further, the magnetic flux is reduced by greatly reducing the turn ratio of the high-voltage transformer, thereby reducing the transformer loss. Inverter circuits and high voltage transformers can be made smaller.
[0047]
(3) Effect of integration of converter circuit and inverter circuit
Since the converter circuit can be configured with two elements, when a full-bridge inverter circuit is applied, the converter circuit and the inverter circuit need only have six switching elements, and the series connection body of two sets of switching elements. A three-phase switching module in which three sets are connected in parallel can be applied. In addition, when a half-bridge type inverter circuit is applied, the number of switching elements of the converter circuit and the inverter circuit is four, and a single unit in which two sets of series connection bodies of two sets of switching elements are connected in parallel is integrated. Phase switching module can be applied. Therefore, the converter circuit and the inverter circuit are modularized, and these circuits can be significantly downsized. In addition, by modularizing in this way, the inductance of the wiring between the converter circuit and the inverter circuit is reduced, so that switching noise and loss of the switching element are reduced, and noise absorption and circuit cooling are achieved by simplifying the cooling and mounting of the element. This greatly contributes to further miniaturization and improved reliability of X-ray high voltage devices.
[0048]
(4) Effects of grounding method
Since the midpoint of the smoothing capacitor of the converter circuit of the present invention can be dropped to the ground potential, the output terminal on the positive side of the converter circuit has a DC output voltage of VDC and is approximately zero volts to VDC / 2 volts as viewed from the ground. And the negative output terminal of the converter circuit has a voltage change in the range of -VDC / 2 volts to zero volts, that is, almost half of the voltage change compared to the conventional full bridge type and the mixed bridge type, A circuit system that is strong against switching noise can be obtained, and the reliability of the apparatus is improved.
[0049]
To summarize the above effects, it is possible to reduce the size, reduce the capacity of the power supply facility, and improve the reliability (noise reduction, power supply harmonic reduction).
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an inverter type X-ray high voltage apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the converter circuit of FIG. 1 of the present invention.
FIG. 3 is a diagram showing a conventional single-phase voltage doubler rectification converter circuit.
FIG. 4 is a waveform diagram of current and voltage of a single-phase AC power supply when a conventional full-wave rectification type converter circuit using a thyristor or a diode is used.
FIG. 5 is a waveform diagram of a current of a single-phase AC power supply and a pulse width modulation signal when the converter circuit of FIG. 1 of the present invention is used.
FIG. 6 is a current waveform diagram of a single-phase AC power source when a conventional converter circuit having a mixed bridge type boosting function is used.
FIG. 7 is a circuit configuration diagram of an inverter type X-ray high voltage apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
1 Converter circuit
2 Inverter circuit (full bridge type)
3 High voltage transformer
4 High voltage rectifier circuit
6 X-ray tube
7 capacitors
8 AC reactor
9 Converter control circuit
10 Inverter control circuit
11,12 capacitor
13-18, 50, 51 IGBT
19-24, 60, 61 Diode
25 Three-phase module
30 Single-phase AC power supply
40 Inverter circuit (half-bridge type)
70 single-phase module

Claims (2)

A converter circuit that receives and rectifies an AC power supply, an inverter circuit that converts the output voltage of the converter circuit into a high-frequency AC, a high-voltage transformer that boosts the output voltage of the inverter circuit, and the high-voltage transformer In an inverter type X-ray high-voltage apparatus comprising a high-voltage rectifier circuit that rectifies the output voltage and an X-ray tube that applies a DC high voltage that is an output voltage of the high-voltage rectifier circuit to emit X-rays,
The converter circuit is
A switching module series connection body in which two sets of switching modules each consisting of a self-extinguishing switching element and a diode connected in reverse parallel to the switching element are connected in series, and two capacitors are connected in parallel with the switching module series connection body. Is connected to the connection point of the switching module series connection body, and one end of the AC reactor is connected to the connection point of the switching module series connection body, and the other end of the AC reactor is connected to the connection point of the capacitor series connection body. An AC power supply is connected, and the AC voltage is controlled by performing pulse width modulation control on the two sets of switching modules in accordance with the phase difference between the voltage and current of the AC power supply and the set value of the voltage across the capacitor series connection body. Match the phase of the voltage and current of the power supply and Comprising a pulse width modulation control circuit for controlling the voltage at the end of the setting value, enter the voltage across the capacitor series connection to said inverter circuit,
The inverter X-ray high-voltage apparatus characterized in that the converter circuit makes the phase of the voltage and current of the AC power supply coincide with each other and makes the input voltage to the inverter circuit equal to a predetermined set value. Two sets of the switching module series connection bodies are connected in parallel or one set constitutes the inverter circuit, and these two sets are connected in parallel or one set of switching module series connection bodies and the switching circuit series connection body of the converter circuit. are connected in parallel to configure a three-phase switching modules or single phase switching module, the inverter type X-ray high voltage apparatus according to this claim 1, characterized in that used in the converter circuit and the inverter circuit.

Images