JPH05159893A - Inverter controlled x-ray high voltage generator - Google Patents

Abstract

PURPOSE:To miniaturize a generator by boosting the extent of supply voltage twice as large with a three-phase AC supply voltage rectifier circuit. CONSTITUTION:Three-phase 200V AC voltage is rectified to the extent of double voltage by a specified rectifier circuit 26, and converted into a DC voltage of about 400V. This voltage is smoothed by a reactor 9 and a capacity 10 and fed to an inverter circuit 27. A voltage control circuit 24 determines the operating frequency of an inverter corresponding to a voltage conversion rate at the inverter circuit 27 from a relationship between pressure rise ratio of a high voltage transformer 20 and setting tube voltage, controlling a transistor in the inverter circuit 27 via a base drive circuit 25. The inverter circuit 27 and the transformer 20 are resonated together, and thereby a high frequency voltage is produced at the secondary side. This voltage is converted into DC by a rectifier circuit 21, and smoothed by a high tension cable, thus it is impressed on an X-ray tube 23 as tube voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray high-voltage apparatus using an inverter circuit which uses a three-phase AC power supply as an input power supply and rectifies it to convert it into an AC voltage higher than the AC power supply frequency. The present invention relates to an inverter type X-ray high voltage device in which the voltage input to an inverter circuit is increased to reduce the size and efficiency of the device.

[0002]

2. Description of the Related Art As a compact and high-performance X-ray high-voltage device,
An inverter circuit using a power semiconductor device, which has developed remarkably in recent years, converts the commercial power supply voltage into an AC voltage higher than the commercial power supply frequency, and inputs this to a high voltage transformer to boost the voltage.
An inverter type X-ray high voltage device for applying to a wire tube has been developed and put into practical use. More specifically, this method rectifies a commercial power supply voltage (hereinafter referred to as an AC power supply voltage) into a direct current, which is converted into a high frequency alternating voltage by an inverter circuit, and this voltage is boosted by a high voltage transformer. Then, the AC power source is rectified and applied to the X-ray tube, and there is an advantage that the AC power source can be used in a single phase or a three phase.

In this inverter type X-ray apparatus, in order to make the inverter circuit and the high-voltage transformer small, the input voltage of the inverter circuit and the high-voltage transformer is increased to reduce the current of the inverter circuit. It is necessary to reduce the turns ratio of the high voltage transformer. For this reason, the following method was used when the AC power supply voltage was 200V. In the case of a single-phase 200 V power supply, the AC power supply voltage is doubled and rectified, and the inverter input voltage is boosted to about twice that in full-wave rectification. In the case of three-phase power supply There was no circuit method to boost by a rectifier circuit, so whether to change existing 200V power supply equipment to 400V power supply, or to boost from 200V to 400V with a boost transformer and full-wave rectify this voltage. Alternatively, the voltage is boosted by the boost chopper circuit.

[0004]

In the above-mentioned prior art, a three-phase 200V power source requires a step-up chopper circuit and a step-up transformer, which makes the apparatus large and expensive. That is, the method using the boost chopper circuit requires a large-capacity self-turn-off semiconductor switching element such as a transistor or an insulated gate bipolar transistor and its control circuit, and a plurality of large passive components such as a reactor and a capacitor. .. The method using the step-up transformer requires a transformer having the same capacity as that of the AC power supply, and thus the apparatus is more expensive and larger than the method using the step-up chopper circuit. Also, if the power supply is changed to 400V, the cost of remodeling will be enormous. As described above, in applications such as an X-ray diagnostic apparatus that handles a large amount of power, no consideration has been given to the fact that a newly added device or facility is expensive and large, and actually involves many difficulties. there were. An object of the present invention is to provide a large-capacity inverter type X-ray high-voltage device that is small and inexpensive even in the case of a three-phase AC power supply.

[0005]

In order to achieve the above object, a first rectifier circuit that receives a three-phase AC power source and rectifies it, and a smoothing circuit that smoothes the output voltage of the first rectifier circuit. An inverter circuit that converts the output voltage of the smoothing circuit into a high-frequency alternating current, a high-voltage transformer that boosts the output voltage of the inverter circuit, and a second rectifier circuit that rectifies the output voltage of the high-voltage transformer, In an inverter type X-ray high-voltage device including an X-ray tube to which the output voltage of the second rectifier circuit is applied, a voltage doubler rectifier circuit is configured by the first rectifier circuit and the smoothing circuit. This is achieved by setting the output voltage as the input voltage of the inverter circuit.

More specifically, in the voltage doubler rectifier circuit, the DC output terminals of a pair of rectifiers or control rectifiers connected in series are connected to both ends of a pair of capacitors connected in series, and the connection point of the rectifiers or control rectifiers is connected. And at least two sets of single-phase voltage doubler rectifier circuits each of which is formed by connecting an arbitrary single phase of the three-phase AC power supply to a connection point of the capacitor and the capacitor,
An arbitrary single-phase AC power supply having a different phase among the three-phase AC power supplies is connected to the AC power supply terminals of the two sets of single-phase voltage doubler rectifier circuits.

[0007]

According to the above structure, the input voltage to the inverter circuit and the high voltage transformer is boosted to about 400V when the AC power supply voltage is 200V, for example. Therefore, the step-up ratio in the high-voltage transformer can be reduced to 20
Taking the case of using a 0V power source as an example, when the present invention is implemented,
The turns ratio of the high-voltage transformer is about 1/2 that of the conventional device, and the high-voltage transformer can be made smaller and lighter. Further, since the input voltage to the inverter circuit is increased, the current of the inverter circuit is reduced, and a semiconductor switch having a small capacity can be used.

[0008]

EXAMPLES Examples of the present invention will be described in detail below. FIG. 1 shows a main circuit of an inverter type X-ray high voltage device according to an embodiment of the present invention. In the figure, 7 is a three-phase AC power supply, and a three-phase voltage rectifier circuit 26 is connected to a three-phase rectifier circuit 26 via reactors 8u, 8v, 8w for suppressing harmonics generated on the power supply side from each phase of u, v, w. Supply AC power. This rectifier circuit uses a diode (rectifier element) 2u, 3u and capacitors 5u, 6u to form a single-phase voltage doubler rectifier circuit and diodes 2v, 3v and capacitors 5v, 6v 1u, 1
v and 4u, 4v are combined, and this output is smoothed by a smoothing circuit composed of the DC reactor 9 and the capacitor 10 and supplied to the inverter circuit 27.

The inverter circuit 27 includes transistors 11 to 11.
14 is a full-bridge inverter circuit composed of 14 and diodes 15-18 connected in antiparallel to these transistors, the output of which is connected to the resonance capacitor 19 and the primary winding of the high-voltage transformer 20. Reference numeral 21 is a full-wave rectifier circuit, 22 is a resistor for detecting a voltage (hereinafter, referred to as a tube voltage) applied between the anode and the cathode of the X-ray tube 23, 2
Reference numeral 4 denotes a voltage controller that compares the tube voltage setting value with the tube voltage detection value detected by the resistor 22 and generates a signal for controlling the inverter circuit 27 so that the two match.
Is a base drive circuit that amplifies the output of the voltage controller 24 and supplies it to the bases of the transistors 11 to 14 of the inverter circuit 27.

In the above configuration, u- of the three-phase AC power supply 7
When the voltage euv between v is positive, the diode 2u becomes conductive and the capacitor 5u is charged, and when it is negative, the diode 3u is charged.
u conducts and the capacitor 6u is charged, and the capacitor 5
Both ends of u and the capacitor 6u are charged with a voltage approximately twice the peak value of the uv voltage euv. Similarly, when the voltage evw between v and w of the three-phase AC power supply 7 is positive, the diode 2v conducts and charges the condenser 5v, and when it is negative, the diode 3v conducts and the capacitor 6v charges.
Both ends of the capacitors 5v and 6v are charged with a voltage that is approximately twice the peak value of the v-w voltage evw. Then, when the voltages across the capacitors 5u and 6u and the voltages across the capacitors 5v and 6v are combined by the diodes 1u, 1v and 4u, 4v, the output voltage of the rectifier circuit 26 is as shown by edc in FIG. The DC voltage becomes about twice the peak value of the AC power supply voltage, which is smoothed by the reactor 9 and the capacitor 10 and input to the inverter circuit 27.

Next, the operation of the inverter type X-ray high voltage device having the configuration shown in FIG. 1 will be described. First, among these X-ray conditions for setting conditions of X-rays to be emitted to the subject (tube voltage, tube current and imaging time), FIG. 1 shows setting and control of only tube voltage. When a desired tube voltage is set and an X-ray exposure start signal is given, the voltage controller 24 is set by the tube voltage setting signal.
Gives a signal for controlling the inverter circuit 27 to the base drive circuit 25. The base drive circuit 25 amplifies it and outputs it to the bases of the transistors 11 to 14 of the inverter circuit 27. Then, the inverter circuit 27 causes the transistors 11 and 14, at a predetermined cycle for setting the tube voltage,
A switching operation for alternately turning on and off 12 and 13 is started, whereby a current (resonance current) having an oscillation cycle determined by the capacitor and the inductance is applied to the high voltage transformer 2
It flows to 0.

Of the capacitors and the inductances that determine the vibration period, the capacitors are present between the resonance capacitor 19 connected in series with the primary winding of the high-voltage transformer 20 and the secondary winding of the high-voltage transformer 20. The stray capacitance is the stray capacitance of the high-voltage cable (not shown), and the inductance is the leakage inductance of the high-voltage transformer 20 and the wiring inductance. In the half cycle of the predetermined cycle in which the transistors 11 and 14 are driven, the resonance current is
Transistor 11 → Resonant capacitor 19 → High-voltage transformer 20 primary winding → Traffic current flows in a circuit of transistor 14 in an arc of resonance frequency, and the resonance current becomes zero after a certain time (1/2 of the half cycle) has elapsed. , Diode 1 going backwards
8 → Primary winding of high voltage transformer 20 → Resonant capacitor 19
→ It flows in the circuit of diode 15. Then, the transistors 11 and 14 are turned off, and the transistors 12 and 13 are turned on in the next half cycle. Then, in contrast to the above, a resonance current flows in the circuit in which the transistor and the diode are exchanged.

An AC current obtained by subtracting the exciting current of the high voltage transformer 20 and the current flowing in the stray capacitance of the secondary winding from the primary current flowing through the primary winding of the high voltage transformer 20 is a rectifier circuit 2.
It is rectified by 1 and smoothed by the stray capacitance of the high voltage cable and X
It is applied to the wire tube 23. The signal corresponding to the actual tube voltage detected by the tube voltage detection resistor 22 is the voltage control circuit 2.
4, a signal for controlling the operating frequency or pulse width of the inverter is created so that the difference between the set tube voltage signal and the set tube voltage signal becomes zero, and this signal is transmitted via the base drive circuit 25 to the transistors 11 to 11. Give to 14 bases. As a result, the operating frequency of the inverter 27 in the next cycle is corrected, and the tube voltage is accurately controlled with respect to the set value.

In the above operation, the voltage conversion from the three-phase 200V power source to the application to the X-ray tube which is a load is in the following order. The three-phase 200V AC voltage is double-voltage rectified by the rectifier circuit 26 and converted into a DC voltage of approximately 400V. The DC voltage of about 400 V is smoothed by the reactor 9 and the capacitor 10 and input to the inverter circuit 27. The voltage control circuit 24 uses the inverter circuit 27 based on the relationship between the step-up ratio of the high-voltage transformer 20 and the set tube voltage.
Then, the operating frequency of the inverter corresponding to the voltage conversion rate is determined, and the transistor of the inverter circuit 27 is controlled via the base drive circuit 25. The inverter circuit 27 and the high-voltage transformer 20 to which the DC voltage of approximately 400 V is applied generate high-frequency AC voltage on the secondary side of the high-voltage transformer 20 due to the resonance described above. This high-frequency AC voltage is converted into a DC voltage by the rectifier circuit 21, smoothed by a high-voltage cable, and applied to the X-ray tube 23 as a tube voltage.

According to the present invention, when a three-phase 200V power supply is used, the input voltage of the inverter circuit can be increased by the voltage doubler rectifier circuit without using a step-up chopper circuit or step-up transformer. The current of the circuit and the turns ratio of the high-voltage transformer are approximately halved, and a compact and economical large-capacity inverter type X-ray high-voltage device can be realized. When the inverter input voltage is changed in the embodiment of FIG. 1, the diode of each single-phase voltage doubler rectifier circuit may be replaced with a thyristor (controlled rectifier element). This is because the diodes 2u and 3u of FIG. 1 are connected to the thyristor 2 as shown in FIG.
The diodes 2v and 3v are connected to u'and 3u ', respectively.
In the case of replacing with v ′ and 3v ′, the control range can be further widened by controlling the phase angle of the gate of each thyristor as compared with the case of controlling only by the inverter circuit.

[0016]

According to the present invention, a voltage doubler rectifier circuit in which a diode is added to a conventional three-phase rectifier circuit can convert an AC voltage into a DC voltage twice the power supply voltage and supply the voltage to an inverter circuit. Therefore, even when the power source at the device installation location is a three-phase 200V power source, the current of the inverter circuit and the turns ratio of the high-voltage transformer are small, and a small-sized and inexpensive large-capacity inverter type X-ray high-voltage device is possible. ..

[Brief description of drawings]

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

FIG. 2 is a waveform diagram of input voltage and output voltage of the rectifier circuit of FIG.

FIG. 3 is a circuit configuration diagram of another embodiment of the present invention.

[Explanation of symbols]

 1u diode 2u diode 3u diode 4u diode 1v diode 2v diode 3v diode 4v diode 2u 'thyristor 2v' thyristor 3u 'thyristor 3v' thyristor 5u capacitor 5v capacitor 6u capacitor 6v capacitor 7 three-phase AC power supply 21 high voltage AC power supply 20 Rectifier circuit 23 X-ray tube 26 Three-phase voltage doubler rectifier circuit 27 Inverter circuit 28 Three-phase voltage doubler rectifier circuit

Claims (1)

[Claims] 1. A voltage doubler rectifier circuit comprising a first rectifier circuit which receives a three-phase AC power source and rectifies the same, and a smoothing circuit which smoothes an output voltage of the first rectifier circuit, and the smoothing circuit. An inverter circuit for converting the output voltage of the inverter into a high frequency AC, a high voltage transformer for boosting the output voltage of the inverter circuit, a second rectifier circuit for rectifying the output voltage of the high voltage transformer, and a second rectifier circuit for rectifying the output voltage of the high voltage transformer. In an inverter type X-ray high-voltage device equipped with an X-ray tube to which an output voltage of a rectifier circuit is applied, the voltage doubler rectifier circuit has a DC output terminal of a pair of serially connected rectifier elements or a pair of control rectifier elements. A single-phase voltage doubler rectifier that is connected to both ends of a pair of capacitors connected in series, and an arbitrary single phase of the three-phase AC power source is connected to the connection point of the rectifying element or control rectifying element and the connection point of the capacitor. circuit At least two sets are prepared, and any single-phase AC power supply having a different phase among the three-phase AC power supplies is connected to the AC power supply terminals of these single-phase voltage doubler rectification circuits, and the output of each single-phase voltage doubler rectification circuit. An inverter type X-ray high voltage device characterized by synthesizing voltages and using this voltage as an input voltage of an inverter circuit.