JPH04262397A - Inverter type x-ray device - Google Patents

Abstract

PURPOSE:To stabilize the voltage of an X--ray tube by feedback controlling a rectifier circuit on the input side of a resonant type inverter, keeping the input voltage of the inverter at optimum value, and suppressing noise or loss generated in a switch part of the inverter. CONSTITUTION:The wide voltage range inherent in an X-ray device is covered only by phase difference control of a resonant type inverter 3a, wherein the inverter phase difference theta is selected to around 0.3pi when the tube voltage Vh is in steady state with turbulence and power variation taken into consideration. When the phase difference is constant, the input voltage of the inverter 3a is approx. proportional. to the tube voltage. Therefore, the inverter input voltages Vinhi, Vinlo with max. and min. tube voltages are determined experimentally tube current by current, and in this interval the tube voltage Vh is proportionally calculated using the max. and min. tube voltages Vhhi, Vhlo. A rectifier circuit 2a is feedback controlled with the determined target inverter input voltage Vin. This reduces noise and loss of resonant type inverter 3a in the steady state, which should give a stable tube voltage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type X-ray apparatus in which loss and noise generated in an inverter switch are reduced and tube voltage is stabilized.

0002

[Prior Art] Japanese Patent Application Laid-Open No. 63-276292 states that
It is stated that by controlling the operating phase difference and operating frequency of the inverter using the resonance phenomenon, it is possible to supply voltage (tube voltage) to the X-ray tube, which is the load, and to control the tube voltage. ing.

[0003] A conventional inverter-type X-ray apparatus using a phase difference control method that utilizes a resonance phenomenon, as shown in FIG. A resonant inverter 3b that converts the DC output rectified by the resonant inverter 2b into alternating current and controls power by using resonance phenomena, a transformer 4b that steps up the AC voltage obtained by the resonant inverter 3b, and this transformer. A rectifier circuit 5b that converts the output of the rectifier 4b into direct current, an X-ray tube 6b that converts the output of the rectifier circuit 5b into X-rays, a tube voltage detector 10b that detects tube voltage, and this tube voltage detector 10b. The feedback control device 11b determines an inverter control signal so that the difference between the tube voltage detected by and the desired tube voltage, that is, the target tube voltage, becomes small.

0004

[Problems to be Solved by the Invention] In the above-mentioned conventional inverter type X-ray apparatus, by controlling only the phase difference of the resonant inverter 3b, the
Since a wide range of kV and 0.5 mA to 1000 mA is controlled, the phase difference of the resonant inverter 3b must be used over the entire range from the minimum to the maximum.

[0005] However, if the inverter phase difference is used to reduce the output, the resonance phenomenon cannot be effectively utilized, and the switching current and peak current increase, resulting in an increase in loss and noise generated in the switches of the resonant inverter 3b. . Also,
The relationship between the phase difference and the output of the resonant inverter 3b is not linear, and the control gain changes depending on the phase difference, resulting in the problem that a good tube voltage waveform may not be obtained, and a stable tube voltage cannot be applied. Ta.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter-type X-ray apparatus that can reduce loss and noise generated in a switch of a resonant inverter and can provide a stable tube voltage to an X-ray tube.

[0007]

[Means for Solving the Problems] The above object is to provide a first rectifier circuit that can convert commercial power to direct current and adjust its output voltage, and convert the direct current output rectified by this first rectifier circuit into alternating current. A resonant inverter using phase difference control that converts and controls tube voltage, a transformer that boosts the output voltage of this resonant inverter, and a second rectifier connected to this transformer that converts the output to direct current. an X-ray tube to which the output voltage of the second rectifier circuit is applied and which emits X-rays;
an inverter input voltage detector connected between the first rectifier circuit and the resonant inverter to detect the input voltage of the resonant inverter; a detection signal of the inverter input voltage detector; and a target inverter input voltage signal. a rectifier circuit feedback control device that inputs a difference signal between the two and outputs a control signal to the first rectifier circuit so that the inverter input voltage becomes a target voltage; an inverter operating range setting means for setting an operating range of the resonant inverter; an inverter operating range set by the inverter operating range setting means;
an inverter input voltage setting means for determining a target inverter input voltage from the target tube voltage and the target tube current and outputting the target inverter input voltage signal to the rectifier circuit feedback control device; A tube voltage detector is connected between the tube voltage detector and the target tube voltage to detect the tube voltage. This is achieved by providing an inverter feedback control device that outputs an inverter control signal to the resonant inverter so that the voltage becomes the target tube voltage.

[0008]

[Operation] By feedback-controlling the input voltage of the resonant inverter to an optimal voltage, the phase difference of the resonant inverter can be maintained at an optimal state during steady state.

[0009] This makes it possible to minimize losses in the switches and transformers of the resonant inverter. Furthermore, since the nonlinear nature of the resonant inverter can be suppressed, a stable tube voltage can be obtained through phase difference feedback control.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an inverter type X-ray apparatus according to the present invention. In this Figure 1, 1
a is a commercial power source; 2a is a first rectifier circuit that converts the commercial power source 1a into direct current and can adjust its output voltage; 3;
a is a resonant inverter using phase difference control that converts the DC output rectified by the first rectifier circuit 2a into alternating current and controls the tube voltage, and 4a is a transformer that boosts the output voltage of the resonant inverter 3a. It is.

5a is a second rectifier circuit connected to the transformer 4a and converts its output into direct current; 6a is an X-ray tube to which the output voltage of the second rectifier circuit 5a is applied and emits X-rays; 7a is the first rectifier circuit 2a and the resonant inverter 3.
8a is a rectifier circuit feedback control device that detects the difference signal between the detection signal of the inverter input voltage detector 7a and the target inverter input voltage signal. A control signal is input to the first rectifier circuit 2a so that the inverter input voltage becomes a target voltage.

12a is inverter operating range setting means for setting the operating range of the resonance type inverter 3a from arbitrarily set target tube voltage and target tube current; 9a is inverter input voltage setting means;
A target inverter input voltage is determined from the inverter operating range set in step 2a, the target tube voltage, and the target tube current, and the target inverter input voltage signal is output to the rectifier circuit feedback control device 8a.

10a is a tube voltage detector connected between the second rectifier circuit 5a and the X-ray tube 6a to detect tube voltage; 11a is an inverter feedback control device which detects the detection signal of the tube voltage detector 10a; and the target tube voltage signal, and outputs an inverter control signal to the resonant inverter 3a so that the tube voltage actually applied to the X-ray tube becomes the target tube voltage. .

Next, the principle of controlling the tube voltage by controlling the current flowing through the transformer 4a by controlling the phase difference of the resonant inverter 3a will be explained with reference to FIGS. 2 and 3.

FIG. 2 shows an example of the configuration of the resonant inverter 3a, in which 311 to 314 are switches;
- 324 are diodes connected in parallel with the switches 311 - 314, the switch 311 and the diode 321 constitute the first arm 31, and the switches 312 - 31 similarly constitute the first arm 31.
4 and diodes 322 to 324 to form the second to fourth arms 32
~34. 35 is a resonant capacitor, and 36 is a resonant inductance, both of which are connected in series with the transformer 4a to form a resonant circuit.

A switch drive circuit 37 drives the switches 311 to 314 from the inverter control signal output from the inverter feedback control device 11a.

Switches 311 and 314, switch 312
and 313 are turned on with their phases shifted by π [rad], respectively.
Works off. Switches 311 and 312, switch 31
When 3 and 314 are operated with a phase difference of φ [rad], the current flowing through the arms 31 to 34, the output voltage Vh of the resonant inverter 3a, and the resonant current ih are as follows.
It will look like Figure 3. At this time, as the phase difference φ increases, the period T1 during which the output voltage Vh of the resonant inverter 3a is equal to the inverter input voltage Vin becomes shorter, and the resonant current ih also becomes smaller accordingly.

If the resonant current ih and the output voltage Vh of the resonant inverter 3a can be controlled by the phase difference φ in this manner, the tube voltage supplied to the X-ray tube 6a can be controlled.

FIG. 4 shows the phase difference φ= of the resonant inverter 3a.
This is the waveform of the current flowing through the arm 31 when the current is 0.3π, 0.5π, and 0.7π [rad]. It can be seen that when the phase difference is changed as shown in the figure, not only the amount of current flowing through the arm 31 but also the waveform changes significantly. The issue here is the amount of current flowing during switching of the transistors that constitute the switch 311. In the case of an X-ray device, a maximum current of 500 A or more may flow through a transistor. Switching the transistor with such a large current places a heavy burden on the transistor, causing loss and noise. FIG. 5 shows the phase difference φ and the arm 3 when turning off the switch 311.
1, and the phase difference φ=0
．． Below 4π [rad], the load on the switch 311 becomes small. FIG. 6 shows the relationship between the inverter phase difference φ and the tube voltage. Phase difference φ of resonance type inverter 3a
The relationship between and tube voltage has non-linearity as shown in the figure.
Particularly in a range where the ratio of tube voltage to tube current (hereinafter referred to as load resistance) is large, the phase difference is discontinuous around φ=0.5π [rad]. Therefore, if this range is used in a steady state, it will have a negative effect on the output (tube voltage) waveform (making the tube voltage unstable).

For these reasons, if control is performed only by the phase difference of the resonant inverter 3a in all ranges, the loss and noise of the switches of the inverter 3a will increase, and parts of the output waveform characteristic curve will not be smooth. The tube voltage becomes unstable, and it can be said that it is difficult to control the wide range of 20 to 150 kV peculiar to the X-ray apparatus only by controlling the phase difference of the resonant inverter 3a. Therefore, considering disturbances and power supply fluctuations, the inverter phase difference φ in the steady state of tube voltage is
=0.3π [rad] is desirable.

In the present invention, in order to keep the phase difference φ of the resonant inverter 3a in an optimal state, the input voltage Vin of the resonant inverter 3a is determined for each tube voltage and tube current from a numerical table obtained by calculation or experiment. The inverter input voltage setting means 9a obtains a target inverter input voltage signal at that time, and outputs it to the rectifier circuit feedback control device 8a to control the input voltage Vin of the resonant inverter 3a.

That is, the inverter input voltage setting means 9
a determines the target inverter input voltage and outputs the target inverter input voltage signal to the rectifier circuit feedback control device 8a. In this embodiment, the input voltage of the resonant inverter 3a is calculated according to the following equation (1). be.

Vin=Vinlo+(Vinhi−Vinlo)*(
Vh-Vhlo)/(Vhhi-Vhlo)


‥‥(1) However, Vin: Desired input voltage of the resonant inverter
Vh: Desired tube voltage Vinlo: Input voltage of resonant inverter with minimum tube voltage Vhl
o: Minimum tube voltage Vinhi: Input voltage of the resonant inverter at maximum tube voltage Vhhi: Maximum tube voltage.

The target inverter input voltage outputted from the inverter input voltage setting means 9a is determined for each tube voltage and tube current, and a predetermined tube voltage is set to a phase difference of φ=0.3π[r
The voltage required to output the voltage at [ad] must be determined experimentally, and in reality, the range is wide and there are a huge number of voltages. However, if the phase difference of the resonant inverter 3a is constant, it can be said that the input voltage of the resonant inverter 3a and the tube voltage are approximately proportional to each other. It is practical to find it by experiment, and find the difference between them by calculating the above equation (1).

By feedback-controlling the rectifier circuit 2a using the target inverter input voltage determined by the above equation (1), the phase difference of the resonant inverter 3a in a steady state can be maintained at an optimum value, and the resonant inverter 3a
It is possible to obtain a stable tube voltage waveform with less loss and noise.

Note that the inverter input voltage setting means 9a
may be constructed using a microprocessor or signal processor, or may be constructed using an operational amplifier or the like.

[0027]

[Effects of the Invention] As explained above, according to the present invention, the rectifier circuit on the input side of a resonant inverter is feedback-controlled, and the input voltage of the inverter is maintained at the optimum voltage, thereby maintaining the inverter phase difference at an optimum value. Since this is controlled, it is possible to suppress the loss and noise generated in the switch section of the inverter, and it is possible to obtain the effect that a stable tube voltage can be applied to the X-ray tube.

[Brief explanation of the drawing]

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

FIG. 2 is a circuit diagram showing a configuration example of a resonant inverter.

FIG. 3 is a time chart for explaining the operation of a phase difference control type resonant inverter.

4 is a time chart of current flowing through an arm made up of one transistor and a diode that constitute the resonant inverter in FIG. 2; FIG.

FIG. 5 is a diagram showing the relationship between an inverter phase difference and a current flowing when one transistor of the inverter is off.

FIG. 6 is a diagram showing the relationship between inverter phase difference and tube voltage.

FIG. 7 is a block diagram of a conventional device.

[Explanation of symbols]

1a Commercial power supply 2a Rectifier circuit 3a Inverter 4a High voltage transformer 5a High voltage rectifier 6a X-ray tube 7a Inverter input voltage detector 8a Rectifier circuit feedback control device 9a Inverter input voltage setting means 10a Tube voltage detector

Claims (1)

[Claims] Claims 1: A first rectifier circuit that converts a commercial power source into direct current and is capable of adjusting its output voltage; and a first rectifier circuit that converts the direct current output rectified by the first rectifier circuit into alternating current and controls the tube voltage. A resonant inverter that uses phase difference control, a transformer that boosts the output voltage of this resonant inverter, and a second transformer that is connected to this transformer and converts its output to DC.
a rectifier circuit, an X-ray tube to which the output voltage of the second rectifier circuit is applied and emits X-rays, and an X-ray tube that is connected between the first rectifier circuit and the resonant inverter; an inverter input voltage detector that detects the input voltage, and the first rectifier that inputs a difference signal between the detection signal of the inverter input voltage detector and the target inverter input voltage signal so that the inverter input voltage becomes the target voltage. a rectifier circuit feedback control device that outputs a control signal to the circuit;
an inverter operating range setting means for setting the operating range of the resonant inverter from an arbitrarily set target tube voltage and target tube current; and an inverter operating range set by the inverter operating range setting means, the target tube voltage and the target. an inverter input voltage setting means for determining a target inverter input voltage from the tube current and outputting the target inverter input voltage signal to the rectifier circuit feedback control device;
A tube voltage detector is connected between the rectifier circuit and the X-ray tube to detect the tube voltage, and a difference signal between the detection signal of the tube voltage detector and the target tube voltage signal is inputted to the X-ray tube. An inverter-type X-ray apparatus comprising: an inverter feedback control device that outputs an inverter control signal to the resonant inverter so that the tube voltage actually applied to the tube becomes the target tube voltage.