JP2000252094A - Inverter type x-ray high-voltage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of safely obtaining the stabilized tube voltage waveform without overshooting the output voltage by switching the control gain so that a target value and the real output voltage of the direction current output voltage of a converter circuit coincide with each other, and controlling the output voltage while setting it at a value corresponding to each period of a series X-ray exposing operation and the load condition of the X-ray. SOLUTION: An X-ray control circuit 12 sets the exposing condition such as tube voltage, tube current, and exposing time. A converter control circuit 10 computes a deviation while inputting the target converter output voltage signal Vr1 corresponding to the set condition and the real output voltage Vc to a comparing means 26 of an output voltage adjusting unit 23. An X-ray control circuit 12 sends the status signal (X-ray exposing condition, operating condition) of a high-voltage device, and a gain switching means 14 obtains the optimal control gain in response to the status signal, and sets a proportional gain Kp and an integral gain Ki inside of the output voltage adjusting unit 23 and the proportional gain Kc inside of an input current adjusting unit 24 so as to control a converter circuit 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a commercial AC power supply, which is converted into DC by a converter circuit, the DC is converted into a high-frequency AC by using an inverter circuit, and the output voltage is boosted by a high-voltage transformer. The present invention relates to an inverter-type X-ray high-voltage device that rectifies and generates a DC high voltage and applies this to an X-ray tube to emit X-rays. When using a boost type high power factor converter circuit disclosed in Japanese Unexamined Patent Publication No. 7-272891, the output voltage of the converter circuit is not overshoot, is safe and reliable, and is applied to the X-ray tube. The present invention relates to an inverter type X-ray high voltage device capable of stabilizing a voltage to be generated.

[0002]

2. Description of the Related Art Generally, an inverter type X-ray high voltage apparatus converts an AC voltage from a commercial AC power supply into a DC voltage by a converter circuit using a full-wave rectifier circuit composed of a thyristor or a diode via an AC reactor. This is converted, smoothed by a smoothing capacitor, and input to an inverter circuit. This inverter circuit is disclosed in, for example,
As described in the bulletin of No. 556, the X-ray which is the load is controlled by controlling the phase difference, frequency or pulse width of the inverter circuit using the resonance phenomenon of the resonance capacitor and the leakage inductance of the high voltage transformer. It applies a high DC voltage (hereinafter referred to as a tube voltage) to the tube. That is, the high-frequency AC voltage output from the inverter circuit is boosted by the high-voltage transformer, converted into DC by a high-voltage rectifier circuit, and applied to the X-ray tube. The inverter control circuit detects an actual tube voltage, obtains a phase difference, a frequency, or a pulse width of the inverter circuit for matching this with a target value, and controls the same. The tube current is controlled by adjusting the temperature of the X-ray tube filament in a filament heating circuit. Such an X-ray high-voltage device is widely applied to general X-ray imaging devices, circulatory organ X-ray devices, X-ray CT devices, and the like. Demands for reduction in installation area and reduction in size and weight are increasing. Above all, the high-voltage transformer occupies a large volume in the device volume, and miniaturization of the high-voltage transformer is particularly effective for miniaturization of the device.

However, there is a limit to this method, and in order to further reduce the size of the device, the current of the inverter circuit is reduced, and a switching element having a small current capacity is used for the switching element of the inverter circuit. It is necessary to reduce the turns ratio of the high voltage transformer. Decreasing the turns ratio leads to a reduction in eddy current loss generated by leakage magnetic flux of the high voltage transformer linked to the primary winding and the like, thereby improving the efficiency of the high voltage transformer. The current of the inverter circuit is also reduced, which is effective in reducing the current capacity of the switching element.

Further, the leakage inductance of the high-voltage transformer can be reduced, and the downsizing of the high-voltage transformer due to the further increase in the frequency can be expected. The current capacity of the switching element of the inverter circuit and the turns ratio of the high-voltage transformer are determined by the input voltage of the inverter circuit, that is, the magnitude of the full-wave rectified voltage of the AC power supply voltage (the peak value of the line voltage of the AC power supply). The maximum value is determined by the range of approximately 0 (V) to the line voltage × √2 (V)). Therefore, the inverter circuit and the high-voltage transformer are formed by reducing the current capacity of the switching element and the turns ratio of the high-voltage transformer. There was a limit to miniaturization of the vessel. Therefore, in such a case, a transformer for boosting the AC power supply (for example, when the AC power supply voltage is 200 V, boosting to 400 V) is connected between the AC power supply and the converter circuit. The output voltage of the transformer may be rectified by a full-wave rectifier circuit and input to the inverter circuit. However, a large-capacity transformer is required to boost the AC power supply voltage. It is not preferable because it causes up. As another method, there is a method of increasing the input voltage of the inverter circuit by using a voltage doubler rectifier circuit.However, since the voltage can be boosted only up to twice that at the time of full-wave rectification, the input voltage of the inverter circuit is increased. There is a limit even if the size is made higher than this and the size is reduced.

Further, as another problem of the conventional system, there is a conventional inverter type X-ray high voltage device using a full-wave rectifier type converter circuit composed of a thyristor or a diode. There's a problem. That is, since the phase of the gate 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, the current of the AC power supply is delayed in phase from the power supply voltage,
The power factor was decreasing. For this reason, the reactive power is large, and the installed capacity of the AC power supply must be increased accordingly. Furthermore, the current waveform of the AC power supply is also distorted and has many harmonic components, which may cause the harmonic current to flow into the power supply system, and thus may impair other devices connected to the power supply system. However, this measure was expensive. Therefore, as a means for solving the above-described restrictions on the input voltage to the inverter circuit and the problem of power supply harmonics, it is necessary to increase the input voltage of the inverter circuit to a predetermined value, and to improve the power factor and reduce the power supply harmonics. An inverter X-ray high-voltage device using a boost type high power factor converter circuit that can be used is disclosed in JP-A-7-263175 and JP-A-7-272891. These publications disclose pulse width modulation control (hereinafter abbreviated as PWM control) that can increase the input voltage of an inverter circuit, improve the power factor and reduce power supply harmonics by eliminating the phase shift between the voltage and current of an AC power supply. ), An inverter type X-ray high voltage device using a full bridge type or mixed bridge type converter circuit has been proposed.

[0006]

According to the circumstances described above,
A step-up type high power factor converter disclosed in the above-mentioned JP-A-7-263175 and JP-A-7-272891 has been introduced.
This has a great effect on reducing the size and weight of the device, improving the power factor, and reducing power supply harmonics. However, when the above method is actually applied to a medical device that requires a high degree of reliability and stability, the following considerations have been insufficient.

When the above-mentioned step-up type high power factor converter circuit is used for a medical X-ray high-voltage device, the output voltage of the converter circuit is usually set to a predetermined value after power is turned on, and thereafter,
Through the process of operating the inverter circuit and outputting X-rays for a predetermined period. That is, the converter circuit boosts its output voltage to a set value in a substantially no-load state, and thereafter the load is applied to the converter circuit (up to 100 kW) with the start of the operation of the inverter circuit, and after a predetermined exposure time, There is no load again. In such an operation, the converter control circuit that controls the converter circuit sets an X-ray irradiation condition such as a tube voltage value, a tube current value, and an irradiation time in a console that controls the entire high-voltage device. Then, an output voltage command value of the converter circuit determined from the condition and an output voltage detection value (actual value) of the converter circuit are input and compared, and the difference is used as a deviation value of the output voltage of the converter circuit. The feedback control is performed so that this deviation value becomes zero. In general, the control system of the converter control circuit includes a proportional control and an integral control (the integral control has a large effect on the rise time of the output voltage of the converter circuit) in order to suppress and stabilize a sharp increase in the output voltage of the converter circuit. Influence, the larger the value, the faster the rise is.), Which is often used.

In the conventional thyristor control method, when the output voltage of the converter circuit is raised from zero volt and set to the final target value, for example, the target value is gradually (may be stepwise) in order to prevent an inrush current. A kind of soft start method or the like in which the control phase angle of the thyristor is gradually increased by increasing the value so as to approach the final target value has been adopted. Thus, a series of exposure operations could be performed.

[0009] Such a soft start method is referred to as the PWM
When applied to a boost converter by control, the following problems occur. That is, when the output voltage of the converter circuit is set from zero volts to the target value, if a method similar to the above-described soft start method is adopted, an inrush current can be prevented, and the output voltage of the PWM control boost converter can be safely increased. Although it is possible to set the target value, on the other hand, at the end of X-ray irradiation, the output voltage of the converter circuit may overshoot.
This is because if the output power (tube voltage x tube current) is large, X
During the X-ray irradiation period, the output voltage is lower than the target set value, and in this state, when the X-ray irradiation is completed and the state shifts to the no-load state, the output voltage below the target value reaches the target value at that moment. The output voltage may overshoot at a stretch (the boost converter can theoretically boost the voltage to infinity), and in some cases, the switching element constituting the converter circuit May be destroyed. Although this phenomenon at the end of irradiation was slightly overshoot in the output voltage even in the conventional thyristor method, compared with a boost converter that can theoretically boost to infinity, , It was slight and not at a level that would cause operational problems. And this means that the PWM
Improvements have been strongly desired from the viewpoints of safety and reliability of an X-ray high-voltage device to which a controlled boost converter is applied.

Accordingly, an object of the present invention is to provide a converter circuit for converting a commercial AC power supply into a DC power supply by using a PWM control type booster disclosed in Japanese Patent Application Laid-Open Nos. 7-263175 and 7-272891. Provided is an inverter-type X-ray high-voltage device that does not overshoot the output voltage of the converter circuit even when a high power factor type converter circuit is used, and that can obtain a safe, reliable, and stable tube voltage waveform. Is to do.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a step-up converter circuit of a pulse width modulation control system for receiving and rectifying an AC power supply, and an inverter for converting a DC output voltage of the converter circuit into a high-frequency AC. Circuit, a high-voltage transformer that boosts the output voltage of the inverter circuit, a high-voltage rectifier circuit that rectifies the output of the high-voltage transformer, and an output voltage (tube voltage) of the high-voltage rectifier circuit. An X-ray tube that emits X-rays; and a converter control circuit that inputs a target value of the DC output voltage of the converter circuit and controls the converter circuit so that the target value matches the actual DC output voltage of the converter circuit. Inverter type X provided
In the line high voltage device, a target value of a DC output voltage of the converter circuit and an actual DC output of the converter circuit are provided to the converter control circuit in accordance with each period of a series of X-ray exposure operations and X-ray load conditions. A control gain for controlling the voltages to be equal to each other; and switching means for switching the control gain. The switching means controls the control gain according to each period of a series of X-ray exposure operations and X-ray load conditions. This is achieved by controlling the output voltage of the converter circuit by setting the value to the above-mentioned value.

The inverter type X-ray high-voltage device having the above-described configuration is capable of controlling the control gain of the converter circuit in a series of X-ray exposure operations, that is, during an X-ray exposure preparation period before X-ray exposure,
The output voltage of the converter circuit can be set to an optimum value according to the X-ray exposure period, after the X-ray exposure is completed, and according to the magnitude of the X-ray load. Inverter that does not have a drop in irradiation period and no overshoot (bounce) at the end of X-ray exposure. By inputting this DC voltage to the inverter circuit, a safe, reliable, and stable tube voltage waveform can be obtained. It can be a formula X-ray high voltage device.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of an overall configuration showing an embodiment of an inverter type X-ray high voltage device according to the present invention. This X-ray high-voltage device receives AC power, converts it to DC by a converter circuit, converts the DC voltage from the converter circuit to a high-frequency AC voltage by using an inverter circuit, and converts this output voltage to a high-voltage transformer. The converter circuit is rectified and then rectified to supply a high DC voltage to the X-ray tube to emit X-rays. As shown in the figure, a converter circuit 1 including insulated gate bipolar transistors IGBTs 16 to 21 and , An inverter circuit 2, a high-voltage transformer 3,
High voltage rectifier circuit 4, high voltage cable 5, XX ray tube 6
, A tube voltage detector 7, current detectors 8a and 8b, a smoothing capacitor 9, a converter control circuit 10 using a digital control method, a tube voltage feedback control circuit 11 also using a digital control method, and an X-ray high voltage device. An X-ray control circuit 12 for controlling the entire movement, and an AC reactor 1
5 a, 15 b, and 15 c and a resonance capacitor 22.

Next, the functions of the above components will be briefly described. The converter circuit 1 is a device that supplies a DC voltage to the inverter circuit 2, and obtains a DC voltage by rectifying an AC commercial power supply voltage of 50 Hz or 60 Hz and smoothing it with a smoothing element such as a capacitor. In the embodiment shown in FIG.
A high power factor converter circuit based on PWM control disclosed in JP-A-7-263175 and JP-A-7-272891, which has a step-up function applying the above, is adopted. The inverter circuit 2 receives the DC voltage output from the converter circuit 1, converts the DC voltage into a high-frequency AC voltage, and controls the voltage (tube voltage) applied to the X-ray tube. The high-voltage transformer 3 boosts the high-frequency AC voltage from the inverter circuit 2, and has a primary winding connected to the output side of the inverter circuit 2. The X-ray tube 6 emits X-rays by applying the output voltage from the rectifier circuit 4 to the X-ray tube via the high-voltage cable 5 and is connected to the output side of the high-voltage rectifier circuit 4. .

Further, the tube voltage detector 7 is provided with the X-ray tube 6.
And sends a tube voltage detection signal Vx to the tube voltage control circuit 11. The output side of the rectifier circuit 4 is connected to the input side of the X-ray tube 6. . The converter control circuit 10 outputs the target output voltage signal Vr1
And the output voltage signal Vc of the converter circuit and the current value (iu, iv) detected by the current detector 8 to set the output voltage of the converter circuit 1 to a target value, and
u, iv), and sends a control signal S1 to the converter circuit 1 so that there is no phase delay with the AC power supply voltage. Then, the tube voltage control circuit 11 is connected to the target tube voltage signal Vr2 and the tube voltage detector 7.
The control signal S2 is sent to the inverter circuit 2 so that the difference between the tube voltage detection signal Vx and the detected tube voltage detection signal Vx is calculated, and the difference therebetween becomes zero.

Next, the configuration of the converter control circuit 10 which is a main part of the present invention will be described with reference to FIG. The converter control circuit 10 in the present embodiment employs a digital feedback control method using a microcontroller having an A / D converter. The converter control circuit 10 based on this software includes first comparing means 26,
An output voltage regulator 23 comprising a proportional adjusting means 28, an integrating adjusting means 29, etc., a second comparing means 27, and an input current regulator 24 comprising a proportional adjusting means 30a, etc.
, A pulse distributor 25, and a gain switching means 14. In the present invention, this gain switching means 1
4, the converter control circuit 10 changes the control gains of the output voltage regulator 23 and the input current regulator 24 between when the output voltage of the converter circuit is set (when preparing for X-ray irradiation) and when the X-ray irradiation ends. It has a function of switching between X-ray irradiation and a function of freely selecting an optimum control gain for both of them according to X-ray irradiation conditions.

Next, the specific operation of the converter control circuit of the inverter type X-ray high voltage device having the above configuration will be described in detail. First, when performing X-ray irradiation, the X-ray control circuit 12 sets irradiation conditions such as a tube voltage, a tube current, and an irradiation time. Thereafter, when a command to start feedback control is issued from the X-ray control circuit 12 to the converter control circuit 10, a target converter output voltage signal Vr1 corresponding to the above set conditions is output from the converter control circuit 1.
It is input to the first comparison means 26 of the output voltage regulator 23 within 0. At the same time, the converter output voltage signal Vc, which has detected the actual output voltage of the converter circuit, is input to the first comparing means 26, and the deviation from the target converter output voltage signal Vr1 is calculated. Then, the calculation result from the first comparing means 26 is input to the proportional adjusting means 28, and the proportional adjusting means 28 multiplies the deviation ecle generated by the comparing means 26 by a proportional gain Kp. A current command ir is obtained by adding a value obtained by multiplying the integral value of the deviation ecle by the integral gain Ki. Subsequently, an input current regulator 24 for matching the phase voltage and the phase current of the AC power supply and controlling the phase current to a sine wave is provided inside the converter circuit control system to improve the power factor. The current command ir sent from the output voltage regulator 23 is input to the input current regulator 24, where sin (ωt) and sin (ωt-2π / 3) are input.
To obtain the respective current commands iur and ivr of the u-phase and the v-phase. The comparing means 27 so that the phase currents iu and iv detected by the current detectors 8a and 8b match the current commands iur and ivr.
The deviation is calculated by using a and 27b (iue, ive), and the deviation is calculated by multiplying the deviation by the gain Kc of the proportional controller 30 to obtain the current control amount. The control amount of the current obtained in this way is sent to the pulse distributor 25, and the converter control signal S1 corresponding to the processing result is output. This converter control signal S1 is output from the converter circuit 1 according to the output voltage signal Vr1 of the target converter circuit.
The switching timing of each of the switches IGBTs 16 to 21 is determined. In this embodiment, only two phases (U-phase and V-phase) of the three-phase input current are detected and feedback-controlled, but if the movement of the two phases of the three phases is determined, the remaining two phases are determined. One is inevitable, so we do so. As a result, the converter circuit 1
When a commercial AC power supply is received and rectified, its output voltage can be matched with the target output voltage, and the input current is made sinusoidal and its power factor is increased without phase lag. It becomes possible.

Next, the operation of switching the control gain by the gain switching means 14 in the converter feedback control device 10 will be described. The X-ray control circuit 12 for controlling the operation of the whole X-ray apparatus sends not only the target output voltage signal Vr1 but also the status signal of the high-voltage apparatus to the gain switching means 14 as described above. The status signal includes X-ray irradiation conditions such as a tube voltage, a tube current, and an irradiation time, and the high-voltage device is set to “not operating the converter circuit” and “setting the output voltage of the converter circuit (X-ray irradiation preparation). Medium) "," X-ray exposure (during inverter operation) "," X
The operation status in a series of processes of X-ray irradiation in the X-ray high-voltage device, such as "end of X-ray irradiation" is included. Then, the gain switching means 14 determines an optimum control gain according to the status signal, and
Are set, and the proportional gain Kc in the input current controller 24 is set. In the case of medical X-ray high-voltage equipment, the X-ray load range is very wide, and the output power varies from several hundred watts to 100 kW by as much as three orders of magnitude. Each gain adjustment according to the X-ray exposure conditions However, since the present apparatus uses digital control by software, it can be handled relatively easily by means such as preparing a control gain table that matches the load conditions. According to the method described above, it is possible to switch the control gain of the converter control circuit according to the X-ray irradiation conditions and the operation status of the X-ray high-voltage device.

If a means for switching the control gain as described above in accordance with the status signal is provided, the converter circuit can be controlled with an optimum control gain in each status. That is, in the no-load state, the output voltage Vc changes sensitively even with a slight change in the control amount. Therefore, particularly when the output voltage Vc rises, an overshoot that places a heavy burden on the switching elements 16 to 21 or If the control gain is set to a relatively low value to suppress the inrush current, the target value Vr as in the conventional method can be set.
A method of gradually increasing 0 and approaching the final target value Vr becomes unnecessary. On the other hand, when the operation of the inverter circuit 2 is started while maintaining such a low control gain and X-ray irradiation is started, the response speed is slow, so that the X-ray load (output power =
The larger the (tube voltage × tube current) is, the more the output voltage of the converter circuit drops, and after that, not only does it take time to match the output voltage with the target value for a while, but in the worst case, sufficient X-ray output is obtained. In some cases, the output voltage Vc of the converter circuit drops to such an extent that it cannot be obtained. The output voltage of the converter circuit of such operation,
The tube voltage waveform is shown in FIG. If the control gain of the converter control circuit is set high to eliminate this drop,
When the operation of the inverter circuit 3 is stopped at the end of the X-ray exposure, the converter circuit 2 is in a no-load state, and as shown in FIG. When the rated voltage of the switching element IGBT of the circuit is exceeded, the switching element may be destroyed.

For this reason, according to the present invention, the control gain (particularly the integral gain K) is higher during X-ray irradiation than during non-exposure.
By setting i) large, even if the load is heavy, V
The drop of c can be suppressed to a small value. Further, at the end of the X-ray irradiation, there is no load again, so that the control gain is reduced (about the same as when the output voltage Vc rises) to prevent overshoot of Vc after the end of the irradiation. It is possible to do. in this way,
If the control gain is optimally set in accordance with the status, as shown in FIG. 4, the output voltage of the converter circuit becomes larger than that of the overshoot at the time of preparation for X-ray irradiation before X-ray irradiation and at the end of X-ray irradiation. Suppression and drop during X-ray exposure are suppressed, and by controlling the inverter circuit 3 using this voltage as the DC power supply voltage of the inverter circuit 3, it is possible to obtain a tube voltage waveform that matches the target tube voltage and has no fluctuation. Can be. That is, in the related art, the control gain of the converter control circuit is set such that the output voltage is set when the converter circuit is not loaded (when the X-ray irradiation is prepared and when the X-ray irradiation is completed) and the X-ray irradiation state when the converter circuit is loaded. In the present invention, the converter circuit and the inverter circuit using the output voltage of the converter circuit as a DC power supply operate stably by switching to the value corresponding to the status. It is something to do.

As described above in detail, according to the present invention, a X-ray converter using a PWM control boost type converter which has a great effect on reducing the size and weight of the device, improving the power factor, and reducing power supply harmonics is provided. When the conventional method is applied to a line high-voltage device, there is a problem that sufficient safety cannot be ensured, especially at the end of irradiation, but this point will be solved.

In the converter feedback control device 10, the output voltage regulator 23 is shown as a combination of a proportional regulator and an integral regulator, and the input current regulator 24 is shown only as a proportional regulator.
The present invention is not limited to this, and any of the above-mentioned adjusting means may be omitted, or a combination of further adjusting means may be used. May be set to any optimal value according to the magnitude of the load condition. In the present embodiment, a three-phase power supply is used. However, the present invention can be applied to a single-phase power supply. In this case, the current detector only needs to detect and control only one phase, and can be configured more simply than the control system shown in FIG.

Further, in the above embodiment, the digital control is applied. However, even in the case of using the analog control, for example, if the switching of the integral gain is to be performed, the capacitor of the integrator using the operational amplifier is required. This can be implemented by providing means such as switching at time. Although FIG. 1 shows that the resonance capacitor 22 is connected to the output side of the inverter circuit 2, the high-frequency current is affected by the leakage inductance of the high-voltage transformer 3. It is inserted for the purpose of improving that the current does not sufficiently flow through the winding of the high-voltage transformer 3, and may not be inserted if the above-mentioned improvement is not necessary.

[0024]

As described above, according to the present invention,
In an X-ray high-voltage device to which a PWM control step-up converter is applied, which has a great effect on reducing the size and weight of the device, improving the power factor, and reducing power supply harmonics, the control gain of the converter circuit is changed to the X-ray irradiation operation. For each process of X
An inverter type that can obtain a safe, reliable, and stable tube voltage waveform that does not overshoot the output voltage of the converter circuit by setting it to any optimal value according to the line exposure conditions An X-ray high voltage device can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an inverter type X-ray high voltage device showing an embodiment of the present invention.

FIG. 2 shows a converter control circuit which is a main part of the present invention.

FIG. 3 is a waveform diagram of an output voltage and a tube voltage of a conventional converter circuit.

FIG. 4 is a waveform diagram of an output voltage and a tube voltage of a converter circuit when the present invention is applied.

FIG. 5 is a waveform diagram of the output voltage and the tube voltage of the converter circuit when the converter control circuit is operated without switching the control gain.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Converter circuit 2 Inverter circuit 3 High voltage transformer 4 High voltage rectifier 5 High voltage cable 6 X-ray tube 7 Tube voltage detector 8a, 8b Current detector 9 Smoothing capacitor 10 Converter control circuit 11 Tube voltage control circuit 12 X-ray control Circuit 13 Control unit 14 Control gain switching means 15a, 15b, 15c AC reactor 16-21 Insulated gate bipolar transistor IGBT 22 Resonant capacitor 23 Output voltage regulator 24 Input current regulator 25 Pulse distributor 26 First comparison means 27 Second comparison means 28 Proportional adjustment means 29 Integral adjustment means 30 Proportional adjustment means

Claims (1)

[Claims] 1. A step-up converter circuit of a pulse width modulation control system for receiving and rectifying an AC power supply, an inverter circuit for converting a DC output voltage of the converter circuit into a high-frequency AC, and an output of the inverter circuit. A high-voltage transformer for boosting a voltage, a high-voltage rectifier circuit for rectifying the output of the high-voltage transformer, and an X-ray tube for applying the output voltage (tube voltage) of the high-voltage rectifier circuit to emit X-rays And a converter control circuit for inputting a target value of the DC output voltage of the converter circuit and controlling the converter circuit so that the target value matches the actual DC output voltage of the converter circuit. In the voltage device, the converter control circuit is provided with a target value of a DC output voltage of the converter circuit and a target value of the DC output voltage of the converter circuit in accordance with each period of a series of X-ray irradiation operations and X-ray load conditions. A control gain for controlling the actual DC output voltage of the converter circuit so that the actual DC output voltage coincides with the control circuit, and switching means for switching the control gain. The switching means changes the control gain during each of a series of X-ray irradiation operations. And an output voltage of the converter circuit is set to a value corresponding to a load condition of the X-ray to control the output voltage of the converter circuit.