JPH0765987A - Inverter type x-ray high voltage device - Google Patents

Abstract

PURPOSE:To allow the capacity of a power supply facility to be reduced, save the equipment costs for the power supply, remove the power supply higher harmonic barriers, and decrease or eliminate provision of booster transformer(s) by improving the power facor, turning the AC input current into sine wave, and boosting the inverter input voltage. CONSTITUTION:An inverter type X-ray high voltage device is so structured that AC power as given to the first rectifier circuit 13 through an AC reactor 1 and converted into DC, which is turned into high frequency AC by an inverter circuit 4, and the resultant is boosted, rectified, and impressed on an X-ray tube 8. The first rectifier circuit 13 is made in a full bridge form consisting in a combination of switching elements 131-136 capable of self-extinction and diodes D1-D6 connected with them in counter-parallelism. Control signal is given to this first rectifier circuit 13 through a gate drive circuit 16, and the line current phase of the AC power supply is put identical to the phase voltage phase, and the output voltage of the first rectifier circuit 13 is controlled to the set value by a current/voltage control circuit 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts an alternating current power source into direct current, converts the direct current into high frequency alternating current using an inverter circuit, boosts the output voltage of the alternating current and rectifies it and applies it to an X-ray tube. The present invention relates to an inverter type X-ray high voltage device that generates X-rays.

[0002]

2. Description of the Related Art Conventionally, this type of inverter type X-ray high voltage apparatus has been constructed as shown in FIG. That is,
An AC voltage from a commercial three-phase AC power supply U, V, W is converted into a DC voltage by a three-phase full-wave rectifier circuit 2 composed of a thyristor via an AC reactor 1, and this is smoothed by a smoothing capacitor 3
Smoothed by and input to the full-bridge type inverter circuit 4 using an IGBT (insulated gate type bipolar transistor).

This inverter circuit 4 is disclosed in Japanese Patent Laid-Open No. 63-1.
As described in Japanese Patent No. 90556, by controlling the phase difference and frequency of the inverter circuit 4 by utilizing the resonance phenomenon between the resonance capacitor 5 and the leakage inductance, stray capacitance, etc. of the high voltage transformer 6. , A high voltage is applied to the X-ray tube 8 which is a load.
The high-voltage transformer 6 boosts the AC voltage from the DC voltage, the rectifier circuit 7 converts the AC voltage to DC, and the DC voltage is applied to the X-ray tube 8.

Voltage applied to the X-ray tube 8 (tube voltage)
Are controlled as follows. First, the set value VS1 of the tube voltage and the set value IS1 of the current (tube current) flowing in the X-ray tube 8 are set.
The gate control circuit 10 sets the gate control phase angle of each thyristor of the three-phase full-wave rectifier circuit 2 in accordance with the above, and the gate drive circuit 9 amplifies this to the gate of each thyristor of the three-phase full-wave rectifier circuit 2. give. Thereby, the gate phase of each thyristor of the three-phase full-wave rectifier circuit 2 is controlled, and the voltage according to the load condition is input to the inverter circuit 4.

The inverter circuit 4 is a three-phase full-wave rectifier circuit 2.
For the DC output of (smoothing capacitor 3), the tube voltage is set value V
It is converted to high-frequency alternating current while controlling to become S1.
That is, the phase difference / frequency control circuit 12 detects the detected values VS2 and IS2 of the tube voltage and the tube current and their set values VS1 and VS1, respectively.
IS1 is input, and with respect to the tube voltage, the frequency of the inverter circuit 4 and the phase differences of the switching elements 41 and 4 and 42 and 43 are feedback-controlled so that it becomes a set value. The output signal of the phase difference and frequency control circuit 12 is amplified by the gate drive circuit 11 and is output to the inverter circuit 4
Are applied to the gates of the IGBTs of and are driven.
As a result, the inverter circuit 4 sets the tube voltage to the set value VS1.
The DC output of the three-phase full-wave rectifier circuit 2 (smoothing capacitor 3) is converted into high-frequency AC while controlling so that The tube current is controlled by controlling the heating amount of the filament of the X-ray tube 8.

Such an inverter type X-ray high voltage apparatus is used for general X-ray imaging apparatus, circulator X-ray imaging apparatus, X-ray C
It is applied to T-devices, etc., and its AC power supply can handle three-phase power supply and single-phase power supply depending on the output and the application. Further, for applications in which a predetermined load range can be controlled by controlling the phase difference and frequency of the inverter circuit 4, the thyristor of the rectifier circuit 2 may be replaced with a diode so that the input voltage of the inverter circuit 4 cannot be controlled.

The AC power supplies U, V, W are 200V.
In this case, if this is rectified and input to the inverter circuit 4 as it is, the inverter circuit current becomes large, an IGBT as an inverter switching element needs to have a large current capacity, and the voltage is low, so a high voltage transformer is required. Since the turns ratio of 6 must also be increased, the inverter circuit 4 and the high voltage transformer 6 become very large.

Therefore, in such a case, the AC power source U,
Boost the voltage of V and W above a specified value (for example, 200 V is 4
A method of connecting a transformer (not shown) for boosting the voltage to 00V, rectifying the output voltage by the rectifying circuit 2 and inputting the rectified voltage to the inverter circuit 4 has been adopted.

[0009]

[Problems to be Solved by the Invention] Conventional inverter type X
In the line high voltage device, since the phase of the gate control signal of the thyristor of the rectifier circuit 2 is given in a delayed phase with respect to the phase of the phase voltage of the AC power supplies U, V, W, as shown in FIG. 5, for example, The phase of the U-phase line current a was delayed by φ compared to the phase voltage b, and the power factor was reduced. Therefore, the reactive power is large, and the installed capacities of the AC power supplies U, V, and W are correspondingly increased. In addition, the current waveform is also distorted and has many harmonic components, which may cause inflow of the harmonic current into the power supply system and, in turn, interference with other devices connected to the power supply system.

Further, when the AC power supply voltage is 200 V, a large-capacity and large-sized transformer is required for boosting this voltage to a predetermined value or more, which is a problem in terms of economy and space saving. .

These problems were almost the same even when the thyristor of the rectifier circuit 2 was replaced with a diode.

An object of the present invention is to reduce a power supply equipment capacity by improving a rectifier circuit for converting an AC power supply into a DC power supply by improving a power factor, a sine wave of an AC input current, and a boosting circuit. An object of the present invention is to provide an inverter type X-ray high-voltage device capable of cost reduction and space saving by eliminating the step-up transformer, and further elimination of obstacles by reducing power source harmonics.

[0013]

The object is to rectify an AC power supply, a first rectifier circuit, an AC reactor connected between the first rectifier circuit and the AC power supply, and the first rectifier circuit.
The smoothing capacitor that smoothes the output voltage of the rectifier circuit, the inverter circuit that converts the output of this smoothing capacitor into high-frequency AC, the high-voltage transformer that boosts the output voltage of this inverter circuit, and the high-voltage transformer An inverter type X which is provided with a second rectifier circuit for rectifying an output, and applies an output voltage of the second rectifier circuit to an X-ray tube to generate X-rays.
In the line high-voltage device, the first rectifier circuit is provided between the AC reactor and the first rectifier circuit positive side output end, and between the AC reactor and the first rectifier circuit negative side output end. Each of the switching elements is connected in a forward direction and is capable of self-extinguishing, and diodes respectively connected in anti-parallel to these switching elements. The phase difference between the line current and the phase voltage of the AC power supply and the smoothing capacitor are provided. Pulse width modulation control of the switching element of the first rectifier circuit according to the error with the set value of the output voltage of the AC power supply to match the phase of the line current of the AC power supply with the phase of the phase voltage and the output voltage of the smoothing capacitor. This is achieved by providing a current and voltage control circuit that controls to a set value.

[0014]

The current / voltage control circuit controls the pulse width modulation of the switching element of the first rectifier circuit in accordance with the error between the line current of the AC power supply and the phase difference between the phase voltages and the set value of the output voltage of the smoothing capacitor. , The line current of the AC power supply and the phase of the phase voltage are matched, and the output voltage of the smoothing capacitor is controlled to a set value.

As a result, the line current of the AC power supply and the phase of the phase voltage are in phase with each other, and a sine wave with no distortion is obtained. Therefore, the power factor is improved, the apparent power is reduced, the power supply capacity is reduced, and the power supply harmonics are also removed.

An AC reactor is provided between the AC power supply and the first rectifier circuit, and the AC reactor and the first rectifier circuit are connected to each other.
To the positive side output terminal of the rectifier circuit, and between the AC reactor and the first negative side output terminal of the rectifier circuit, the switching elements and the switching elements capable of self-extinguishing respectively connected in the forward direction. The first rectifier circuit is configured by including diodes connected in antiparallel. With such a configuration and the pulse width modulation control, electromagnetic energy is stored in the AC reactor, the electromagnetic energy is discharged to the smoothing capacitor, and the smoothing capacitor is charged with a voltage higher than the power supply voltage.

As a result, the input voltage of the inverter circuit can be made higher than the power supply voltage, and the cost of the inverter circuit can be reduced, the step-up transformer can be eliminated, and the winding ratio of the high-voltage transformer can be reduced. Can be realized.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of an inverter type X-ray high voltage device according to the present invention. In this FIG.
U, V and W are three-phase AC power sources, 1 is an AC reactor, 3 is a smoothing capacitor, 4 is a full bridge type inverter circuit using an IGBT, 5 is a resonance capacitor, 6 is a high voltage transformer, and 7 is a high voltage. Voltage rectification circuit (second rectification circuit), 8 is an X-ray tube as a load, 11 is a second gate drive circuit,
12 is a phase difference of the inverter circuit 4, a frequency control circuit, 1
3 is a first rectifier circuit (3-phase full-wave rectifier circuit), 14 is a line current detector for the three-phase AC power supplies U, V, W, 15 is a phase voltage detector for the three-phase AC power supplies U, V, W, Reference numeral 16 is a first gate drive circuit, 17 is a current for controlling the line currents of the three-phase AC power supplies U, V, W and the output voltage of the first rectifier circuit 13,
It is a voltage control circuit.

Here, the first rectifying circuit 13 is a three-phase AC power source U, V, which is input via the AC reactor 1.
A rectifier that rectifies an AC voltage from W into a DC voltage, and is a self-extinguishing switching element, here, six switching elements 131 to 136 composed of an IGBT (insulated gate bipolar transistor) are combined to form a full bridge type. Together with those switching elements 131-
The diode D1 to D6 is connected in anti-parallel to 136.

These switching elements 131 to 136 are controlled as follows. That is, the current / voltage control circuit 1
Reference numeral 7 creates a pulse width modulation control pulse to match the phase of the line currents of the three-phase AC power supplies U, V, W with the phase of the phase voltage and to control the output voltage of the first rectifier circuit 13 to a set value. Then, this is amplified by the first gate drive circuit 16 and given to each gate of the switching elements 131 to 136,
The switching elements 131 to 136 are switching-controlled.

FIG. 2 is a diagram showing a specific example of the current / voltage control circuit 17 together with its peripheral circuit portion. Here, the current / voltage control circuit 17 includes a three-phase sine wave generator 20, an error amplifier 21, and a multiplier. 22, an error amplifier 23, a sawtooth wave generator 24, and a comparator 25, and operates as follows.

First, the output voltage of the first rectifier circuit 13, that is, the voltage VS4 of the smoothing capacitor 3 is detected, and this and a set value VS3 (set according to the tube voltage and the tube current) are subjected to voltage feedback control. Error amplifier 2 for performing
Compare and amplify at 1.

On the other hand, the phase voltage of the three-phase AC power supply U, V, W is detected by the phase voltage detector 15, and this is input to the three-phase sine wave generator 20 to generate a three-phase sine wave reference synchronized with the phase voltage. Create a signal. This three-phase sine wave reference signal and the error amplification 2
The signal from 1 is multiplied by the multiplier 22, and the three-phase AC power supply U,
A three-phase line current reference signal for controlling the V and W line currents (a line current command waveform of a sinusoidal AC power supply synchronized with the phase voltage waveforms of the AC power supplies U, V, and W) is created, and this and the line The line current signal (actual line current waveform) from the current detector 14 is input to the error amplifier 23 to generate a current feedback control deviation (error signal between the line current command waveform and the actual line current waveform).

A comparator 25 compares the control deviation with the sawtooth wave from the sawtooth wave generator 24 to create a modulated wave signal.
This is the switching element 131 of the first rectifier circuit 13.
The signal is output as a signal that determines the switching timing of ~ 136.

This modulated wave signal is amplified by the first gate drive circuit 16 to switch the switching element (IGBT) 131.
To 136 gates, and the output voltage (voltage of the smoothing capacitor 3) VS4 of the first rectifier circuit 13 is set value VS3.
And the switching elements 131 to 1 so that the phases of the line currents of the three-phase AC power supplies U, V, and W and the phase voltages match.
36 is switching-controlled.

FIG. 3 shows a line current C for one phase of the three-phase AC power supplies U, V and W, and a pulse width modulation signal (current to the first gate drive circuit 16, output pulse of the voltage control circuit 17. The fundamental wave of the signal has the same phase as the phase voltage.) FIG.

The waveform of the line current C is the phase voltage when the inverter circuit 4 operates to supply power to the X-ray tube 8 and the input voltage of the inverter circuit (voltage of the smoothing capacitor 3) drops below the set value. It is in phase with AC power source U,
Supply from V and W to the smoothing capacitor 3 side. When the input voltage of the inverter circuit rises above the set value, the waveform of the line current C becomes opposite in phase to the phase voltage, and power is regenerated from the smoothing capacitor 3 side to the AC power supplies U, V, W.

Even in the pulse width modulation (PWM) control of the sine wave, a ripple component corresponding to the PWM frequency is included, but a filter (not shown) is inserted on the AC power sources U, V, W side or the PWM frequency is changed. A smooth sinusoidal current can be obtained by increasing it.

Returning to FIG. 1, the inverter circuit 4
Is to control the power supplied to the X-ray tube 8 by utilizing the resonance phenomenon while receiving the DC voltage thus obtained and converting it to an AC voltage. Here, four switching circuits composed of IGBTs are used. The elements 41, 42, 43, and 44 are combined to form a full-bridge type, and diodes D7 to D10 are connected in antiparallel to the switching elements 41 to 44, respectively.

The capacitor 5 is one of the resonance elements that generate a resonance current by the output voltage of the inverter circuit 4. The high voltage transformer 6 has its primary winding connected in series with the capacitor 5, causes resonance with the capacitor 5 and leakage inductance, and boosts the resonance output.

The second rectifier circuit 7 includes the high voltage transformer 6
It is connected to the secondary winding of and converts the output AC voltage into DC. The X-ray tube 8 serves as a load of the device of the present invention, and the output voltage of the second rectifier circuit 7 is applied to generate X-rays.

Next, the operation of the apparatus of the present invention will be described. When conditions such as a tube voltage and a tube current are set on a console (not shown), these are the current of the first rectifier circuit 13,
The phase difference between the voltage control circuit 17 and the inverter circuit 4 is input to the frequency control circuit 12. The current / voltage control circuit 17 sets the input voltage VS3 of the inverter circuit 4 corresponding to the set values VS1 and IS1 of the tube voltage and the tube current, and compares this with the actual input voltage VS4 of the inverter circuit 4 to perform feedback control. As described above, the three-phase AC power supply U,
The switching elements 131 to 136 of the first rectifier circuit 13 are switching-controlled so that the phase voltages of V and W and the phase of the line current are matched and the input voltage VS4 of the inverter circuit 4 becomes the set value VS3.

The inverter circuit 4 converts the direct current output of the first rectifying circuit 13 (smoothing capacitor 3) into high frequency alternating current while controlling the tube voltage to the set value VS1. That is, the phase difference / frequency control circuit 12 detects the detected values VS2 and IS2 of the tube voltage and the tube current and the set values V thereof.
S1 and IS1 are input, and with respect to the tube voltage, feedback control is performed on the frequency of the inverter circuit 4 and the phase difference between the switching elements 41 and 44 and 42 and 43 so that the tube voltage becomes the set value VS1. The output signal of the phase difference and frequency control circuit 12 is amplified by the second gate drive circuit 11 and given to the gates of the switching elements 41 to 4 4 of the inverter circuit 4 to drive them. As a result, the inverter circuit 4 converts the DC output of the first rectifier circuit 13 (smoothing capacitor 3) into high-frequency AC while controlling the tube voltage to be the set value VS1. The tube current is controlled by controlling the heating amount of the filament of the X-ray tube 8.

As described above, in the device of the present invention, the phase voltage of the AC power supplies U, V, W and the line current are in phase, the power factor is 1, and the line current can be controlled to a sine wave. The power supply equipment cost can be saved and the harmonic interference of the power supply can be eliminated.

Further, electromagnetic energy is stored in the AC reactor 1 by the pulse width modulation control and is released to the smoothing capacitor 3, whereby the smoothing capacitor 3 is charged with a voltage higher than the power supply voltage. That is,
The device of the present invention has a step-up function, and in the case of 200 V AC power sources U, V, W, 282 V (effective value of 1.414).
It is possible to control in the range of 564V, which is twice as much as that of 564V.
Therefore, by increasing the input voltage of the inverter circuit 4 to about twice the power supply voltage, the conventionally used transformer (not shown) for boosting the voltage of the AC power supplies U, V, W is not required. As a result, cost reduction and size reduction are possible, and an economical and space-saving inverter type X-ray high-voltage device can be realized.

Further, in the case of a light load in which the tube voltage is low and the tube current is small, conventionally, the input voltage of the inverter circuit 4 is controlled below the peak value of the power supply voltage by the thyristor of the three-phase full-wave rectifier circuit 2 of FIG. Although the inverter circuit 4 is controlled only by the phase difference, in the present invention, not only the phase difference of the inverter circuit 4 but also the frequency is controlled to expand the control range of the inverter circuit 4 so that a wide range can be obtained as in the conventional case. Can handle loads.

In the above-mentioned embodiment, the three-phase AC power supplies U, V and W have been described as an AC power supply by way of example, but a single-phase AC power supply may be used. Various configurations using a full-wave bridge, a composite bridge of a diode and an IGBT, and the like are possible.

[0038]

As described above, according to the present invention, the phase voltage and line current of an AC power supply are in phase, the power factor is 1, the apparent power is reduced, and the power supply equipment capacity is reduced. You can save money. Moreover, since the waveform of the line current is also a sine wave, the power source harmonic interference is eliminated. Furthermore, since the input voltage of the inverter circuit can be raised to the required voltage, 200
In the case of the V power supply, the step-up transformer which is required is not necessary, and there are effects such as cost reduction and space saving.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a specific example of the current / voltage control circuit in FIG. 1 together with its peripheral circuit portion.

3 is a waveform diagram of a line current and a pulse width modulation signal for one phase of the three-phase AC power supply in FIG.

FIG. 4 is a circuit diagram of a conventional device.

FIG. 5 is a waveform diagram of a line current and a phase voltage for one phase of a three-phase AC power supply in a conventional device.

[Explanation of symbols]

U, V, W 3-phase AC power supply 1 AC reactor 2 3-phase full-wave rectifier circuit by thyristor 3 Smoothing capacitor 4 Full bridge type inverter circuit using IGBT 5 Resonant capacitor 6 High voltage transformer 7 High voltage rectifier circuit 8 X-ray tube 11 Gate drive circuit (second gate drive circuit) 12 Phase difference and frequency control circuit of inverter circuit 13 First rectifier circuit (3-phase full-wave rectifier circuit by IGBT) 14 Line current detection of 3-phase AC power supply 15 Phase voltage detector for 3-phase AC power supply 16 First gate drive circuit 17 Current and voltage control circuit for controlling line current of 3-phase AC power supply and output voltage of first rectifier circuit 20 3-phase sine wave generator 21,23 Error amplifier 22 Multiplier 24 Sawtooth wave generator 25 Comparator

Claims (2)

[Claims] 1. A first rectifying circuit for rectifying an AC power supply,
An AC reactor connected between the first rectifier circuit and the AC power source, a smoothing capacitor that smoothes the output voltage of the first rectifier circuit, and an inverter circuit that converts the output of the smoothing capacitor into high-frequency AC. A high-voltage transformer for boosting the output voltage of the inverter circuit and a second rectifier circuit for rectifying the output of the high-voltage transformer, and applying the output voltage of the second rectifier circuit to the X-ray tube. In the inverter-type X-ray high-voltage device for generating X-rays, the first rectifier circuit includes the AC reactor and the first rectifier circuit positive side output terminal, and the AC reactor and the first rectifier. A self-extinguishing switching element respectively connected in the forward direction between the circuit negative side output terminal and a diode respectively connected in anti-parallel to these switching elements; In response to said error between the phase difference and the set value of the output voltage of the smoothing capacitor line current and phase voltage source first
Pulse width modulation control of the switching element of the rectifier circuit of
An inverter type X-ray high voltage device comprising a current and voltage control circuit for matching the phase of the phase voltage with the line current of the AC power supply and controlling the output voltage of the smoothing capacitor to a set value. 2. A first rectifier circuit and an inverter circuit are created in accordance with a set voltage and a set current of an X-ray tube, a current, a control signal for a voltage control circuit and a control circuit for an inverter circuit are created. The inverter type X-ray high voltage device according to claim 1, wherein the X-ray high voltage device is controlled.