WO2012123232A1

WO2012123232A1 - Circuit assembly comprising inverters for supplying an x-ray tube with power and associated method

Info

Publication number: WO2012123232A1
Application number: PCT/EP2012/053152
Authority: WO
Inventors: Walter Beyerlein
Original assignee: Siemens Aktiengesellschaft
Priority date: 2011-03-11
Filing date: 2012-02-24
Publication date: 2012-09-20
Also published as: DE102011005446A1

Abstract

The invention relates to a circuit assembly and to an associated method for generating an X-ray tube voltage (U_hv). The assembly comprises a mains input circuit (1) for generating a DC link voltage (U_dc), an inverter circuit (2) for converting the DC link voltage (U_dc) to a high-frequency AC voltage (U_ac), and a high-voltage generator (6), which converts the high-frequency AC voltage (U_ac) to a high voltage (U_hv) for the X-ray tube (5), wherein the high-voltage generator (6) comprises a transformer (3) and a high-voltage capacitor (7) which is connected in parallel to the secondary winding of the transformer (3) and which, together with the inductance of the secondary winding, forms an oscillating circuit having the natural frequency thereof in the frequency range between 10 kHz and 500 kHz. The invention offers the advantage that the existing parasitic winding capacitance of the transformer is optionally increased by an additional capacitor so much that it can be beneficially utilized as a component for increasing the voltage of a high-voltage source.

Description

description

Circuit arrangement with inverter for powering an X-ray tube and associated method

The invention relates to a circuit arrangement for generating an X-ray tube voltage with an input circuit for generating a DC link voltage, with an inverter circuit for converting the DC link voltage into a high-frequency AC voltage and with a high-voltage generator, which converts the high-frequency AC voltage with a certain gear ratio in a high voltage for the X-ray tube. Moreover, the invention relates to an X-ray generator with such a circuit arrangement and to a corresponding method for generating an X-ray tube voltage.

Modern generators often have circuit arrangements of the type mentioned for generating an X-ray tube voltage. Since the network frequency is first rectified and then converted back into a high-frequency AC voltage, which is finally trans ^¬ formed to the desired voltage, such generators are also referred to as Hochfre ^¬ frequency generators. Compared with conventional generators, in which the high voltage is first transformed with the present network frequency, then rectified and finally fed to the X-ray tube, such a circuit arrangement has the advantage that they are made almost independent by a fast control loop of changes in both the mains voltage and the tube current can and therefore the tube voltage is very well reproducible and can be kept constant. Compared to the well-known so-called DC voltage generators, in which a transformed with line frequency and rectified high ^¬ voltage is finely controlled by means of triodes, the high-frequency generators have the advantage of a relatively small volume and lower manufacturing costs. These advantages These are the reasons for the preferred use of such circuits in today's X-ray generators.

The circuit arrangements must in this case be dimensioned such that they provide a constant power over a very large voltage range. The voltage range used in medical diagnostics for x-ray tubes usually ranges from 40 kV to 150 kV. In order to deliver constant power over this range, the current at the lowest voltage level of 40 kV must be nearly four times higher than at the upper limit of 150 kV.

The high voltage generator must be chosen in its transmission ratio so that the highest required tube voltage is achieved at a given by the available mains voltage DC link voltage. The transmission ratio of the high voltage generator is usually defined in such X-ray generators as the ratio ^¬ nis the output voltage to the input voltage of the high voltage generator. In general, the high-tension voltage generator ^¬ essentially consists of a transformer and a downstream rectifying and smoothing circuit. If it is assumed that the effective voltage is close to the inverter circuit in such as the intermediate circuit voltage corresponds, and that the high-voltage generator is designed so that by a suitable transformer nachge ^¬ switched rectifier circuit, a voltage doubling is achieved, it follows for the transmission ratio ü of the transformer of the high voltage generator:

2 - U _dc

wherein U _{dc is} the rectified ^{DC link} voltage and U _{t is} the voltage applied to the X-ray tube, rectified high ^¬ voltage. At a desired tube current I _t is therefore consequently the average current I _avg strain _WR for the primary side of the high voltage generator and the front switched AC Rich ^¬ terschaltung

! avg WR ^{= I} t -2-Ü (2)

It can be seen that at a constant output power P _t = U _t 'I _{t of} the circuit arrangement of the inverter is loaded with a high current, in particular when the X-ray tube voltage U _{t is set} relatively low. As a result, the inverter with its passive components and power semiconductors as well as the intermediate circuit and the high voltage generator must be designed for these currents. In addition to higher costs for the components, this leads to the fact that in addition to the active power and much reactive power in the inverter and transformer is processed.

It is therefore an object of the present invention to provide an alternative to the cited prior art, which avoids these disadvantages.

According to the invention, the object is achieved with the scarf ^¬ processing arrangement and the method of the independent claims.

The invention claims a circuit arrangement for generating an X-ray tube voltage with a mains input circuit for generating a DC link voltage, with an inverter circuit for converting the DC link voltage into a high-frequency AC voltage and with a high voltage generator, which converts the high-frequency AC voltage into a high voltage for the X-ray tube, wherein the high voltage generator is a transformer and a high-voltage capacitor connected in parallel with the secondary winding of the transformer, which together with the in productivity of the secondary winding forms a resonant circuit, which has its resonance frequency in the frequency range between 10 kHz and 50 kHz. The invention offers the advantage that the existing parasitic winding capacitance of the transformer is optionally increased by an additional capacitor to the extent that it can be used as a useful component for increasing the voltage of a high voltage source. This allows the inverter to be designed for smaller currents. Also, the transmission power between the inverter and transformer are relieved.

In one embodiment of the invention, the capacitance of the high-voltage capacitor can be selected such that at a predeterminable operating point of the X-ray tube at the resonance ^¬ frequency of the AC voltage, the voltage at the X-ray tube at least doubles.

The invention also claims a circuit arrangement for generating an X-ray tube voltage with a mains input circuit for generating a DC link voltage, an inverter circuit for converting the DC link voltage into a high-frequency AC voltage and a high voltage generator, which converts the high-frequency AC voltage into a high voltage for the X-ray tube, wherein the high voltage generator comprises a transformer and one to the primary winding of the transformer connected in parallel resonant circuit capacitor and one to the primary winding and the

Resonant circuit capacitor connected in series Schwingkreisspu ^¬ le, which forms a resonant circuit, which has its resonant frequency in the frequency ^¬ range between 10 kHz and 500 kHz.

In a further disclosed embodiment, the capacitance of the resonant circuit capacitor and the inductance of the resonant ^¬ circuit coil may be chosen such that the voltage at the X-ray tube at least doubled for a predeterminable operating point of the X-ray tube at the resonant frequency of the AC voltage. The invention also claims an X-ray generator with a circuit arrangement according to the invention.

The invention also claims an X-ray device with an X-ray generator according to the invention.

The invention also claims a method of generating an X-ray tube voltage in which an intermediate circuit voltage is generated from a mains input voltage and a high-frequency alternating voltage is generated from the intermediate circuit voltage, which is converted into a high voltage for the X-ray tube by means of a high voltage generator with a transformer Secondary winding of the transformer pa ^¬ rallel switched high voltage capacitor is brought together with the inductance of the secondary winding in the frequency range between 10 kHz and 500 kHz in resonance.

The invention further claims a method for generating an X-ray tube voltage in which generates a DC link voltage from a mains input voltage and from the DC link voltage, a high-frequency AC voltage is converted with a high voltage generator with a transformer in a high voltage for the X-ray tube, wherein a Primary winding of Trans ^¬ formator connected in parallel resonant circuit capacitor together with a primary winding and the resonant circuit capacitor connected in series resonant circuit coil in the frequency range between 10 kHz and 500 kHz are brought into resonance.

In a further disclosed embodiment, the method of the X-ray tube in the Reso can ^¬ nanzfrequenz the voltage at the X-ray tube be at least doubled at a predeterminable operating point. Other features and advantages of the invention will become apparent from the following explanations of several embodiments with reference to schematic drawings.

Show it:

Figure 1: a block diagram of a circuit arrangement for

Generation of a high voltage according to the prior art,

Figure 2 is a block diagram of a circuit arrangement for

Generation of a high voltage with a secondary-side high-voltage capacitor,

FIG. 3 shows a block diagram of a circuit arrangement for

Generation of a high voltage with a primary-side resonant circuit capacitor and a primary-side resonant circuit coil,

FIG. 4 shows a diagram of the tube voltage as a function of the inverter frequency for different tube currents,

Figure 5 is a block diagram of a high voltage generator and

6 shows a block diagram of another high-voltage ^¬ creator.

1 shows indicated in accordance with the prior art, such as in DE 10227841 Al typical Comp ^¬ components and their interconnection of a high-frequency X-ray generator for generating the high voltage for an X-ray tube in a block diagram.

For this purpose, the network input side includes a network input circuit 1, which generates a rectified intermediate circuit voltage U _dC from the two- or three-phase input voltage. This rectified intermediate circuit voltage U _DC is then applied to the input of an inverter circuit 2 that converts the intermediate circuit voltage U _DC into a high-frequency AC voltage clamping ^¬. In the embodiment shown in Figure 1, a rectangular inverter is shown. Instead of egg nes such rectangle inverter are often used Schwing ^¬ circular inverters.

The present at the output of the inverter circuit 2, high-frequency alternating voltage is then forwarded to a high voltage generator 6, which consists essentially of a transformer 3 and the transformer 3 on the secondary side rectifying rectified and smoothing device 4. The rectifying and smoothing device 4 is often designed as a doubler circuit. The applied at the output of the high voltage ^generator 6, rectified Hochspan ^¬ voltage U _h v is then applied to the X-ray tube 5.

A scheme is usually carried out such that the U _h v as actual ^¬ value to a regulator (not shown) is fed, is compared there with a predetermined by the operator of the x-ray device voltage setpoint and, accordingly, a correction value ^¬ 5 generates value applied to the high voltage at the X-ray tube is given, for example, as a control variable to the inverter circuit, so that there according to the frequency and thus ultimately the high voltage is changed in the desired manner.

The transformer must be selected so in its ratio u that at a the highest Shaped ^¬-made tube voltage U _h v is accomplished by the predetermined ultimately from the network intermediate circuit voltage U _DC. If the equal ^¬ straightening and smoothing means 4 is formed as a doubler circuit, the necessary ratio u by the aforementioned equation (1) is given.

In the following calculation example it is assumed that the power supply of the X-ray tube 5 over a voltage range between 40 and 160 kV must provide a constant power of 40 kW. At 40 kV then the maximum current I _{t m &} x, which must be available at the X-ray tube 1 A. Is also assumed that as a rectified intermediate circuit voltage U _DC = 500 V are available, obtained from Equation (1) for the required transla ^¬ reduction ratio ü of the transformer 3:

^{1 60kV} , 60 (3)

(2 x 500V)

Only with this ratio u the maximum X-ray tube voltage of 160 kV can be achieved in the gegebe ^¬ NEN input voltage.

According to equation (2) arises in the transmission behaves ^¬ nis ü = and at 160 a maximum current I _TMX = 1 A at the X-ray tube for the maximum current I _{avg WR} on the primary side of the transformer and the inverter: wR max = It max · 2 · Ü = 1 A · 2 · 160 = 320 A

Equation (4) shows that at the maximum tube current of the inverter circuit 2, a very high current must be taken. In order to reduce the maximum Stormbedarf, therefore, the transmission ratio ü must be reduced. This ge ^¬ lingt shown by the inventive arrangement as shown in FIG. 2

FIG. 2 shows a block diagram as described in FIG. In addition, in the high voltage generator 6 to the secondary winding of the transformer 3, a high-voltage capacitor 7 is connected in parallel and in series with the primary winding of a resonant circuit capacitor 8. The high-voltage capacitor 7 and the resonant circuit capacitor 8 form a series resonant circuit with the stray inductance of the transformer 3. The capacity of the high voltage capacitor 7 is selected such that the re ^¬ sonanzfrequenz the oscillating rice for tube currents between 0.5 and 1 A is in the range 10 kHz to 500 kHz. Alternatively, the parasitic capacitance of the transformer 3 can be increased by construction ^¬ market measures. If the series resonant circuit operated at or near its Reso ^¬ nanzfrequenz, it behaves like a constant-power source. By appropriate dimensioning of the resonant rice, the tube voltage U _hV may be higher than the secondary voltage of the transformer ^¬ Se. 3 This can now be used to achieve a higher tube voltage U _h v at lower tube currents. This can be selected via a smaller ^¬ gear ratio ü of the transformer 3, where ^¬ significantly reduced by the current in the inverter circuit. 2 As can be read from Figure 4, a ^¬ Ver doubling of the voltage can be achieved whereby the transla- subscription ratio u can be halved. This means according to equation (4) a halving of the maximum current load l _a v _g WR of the inverter 2. The required capacity of the high-voltage capacitor is about 100 pF. It is an ever-present stray capacitance of the transformer 3 connected paral ^¬ lel.

Figure 3 shows a block diagram of an alternative embodiment to Figure 2. Instead of the connected in parallel to the secondary winding of the transformer 3 Hochspannungskondensa ^¬ gate 7 in Figure 2, a resonant circuit is formed on the primary side of the transformer 3, which its resonant frequency for tube currents of between 0.5 A and 1 A in the range 10 kHz to 500 kHz. For this purpose, a resonant circuit capacitor 8 is connected in parallel with the primary winding of the transformer 3. Zusätz ^¬ Lich is inserted a resonant circuit coil 9 in series with the primary winding and the resonant circuit capacitor. 8 This embodiment achieves the same effect according to the invention as the embodiment according to FIG. 2.

FIG. 4 shows, in the form of a diagram, the voltage overshoot caused by the resonant circuit according to the invention in the circuits according to FIGS. 2 and 3 as a function of the AC frequency f (in kHz) of the inverter for three different operating points (tube currents). The size of the Röh ^¬ renstroms is conces- by the cathode X-ray tubes led heating power determined. In the y-direction, the ratio s of the tube voltage to the secondary voltage of the transformer is plotted in FIG.

The load characteristic A shows the voltage ratio s for a tube current of 0.5 A. The resonant frequency of the resonant circuit damped by the tube resistance is about 35 kHz. The voltage overshoot at the resonant frequency is more than twice. Via a variation of the drive frequency of the inverter, the tube voltage along the load characteristic A can be set to the desired value. It is also possible to control the inverter with the resonance frequency and to realize the voltage regulation via a pulse width modulation or phase shift.

The load curve B in FIG. 4 shows the profile of the voltage ratio s for a tube current of 0.75 A and the load characteristic C the course for 1 A tube current.

Figure 5 shows another embodiment of a high voltage generator 6 ^¬ similar to the circuit arrangement in Figure 2, except that no primary side Schwingkreiskapa ^¬ capacity is available.

FIG. 6 shows a further ^exemplary embodiment of a high-voltage ^generator 6 similar to the circuit arrangement in FIG. 3, wherein the series connection of the primary-side coil and capacitor has been replaced by a parallel circuit of a resonant circuit capacitor 8 and a resonant circuit coil 9.

The invention is preferably used in X-ray generators and Rönt ^¬ geneinrichtungen. Reference sign list

1 power input circuit

2 inverter circuit

3 transformer

4 rectification and smoothing device

5 x-ray tube

6 high voltage generators

7 high voltage capacitor

8 resonant circuit capacitor

9 oscillating circuit coil

A load characteristic

B load characteristic

C load characteristic

f AC frequency

s voltage is available

U _ac high-frequency AC voltage

Udc DC link voltage

Uhv tube voltage

Claims

claims

1. Circuit arrangement for generating an X-ray tube voltage (Uhv) with

a network input circuit (1) for generating an intermediate circuit voltage (Ud _C ),

an inverter circuit (2) for converting the intermediate circuit voltage (Udc) into a high-frequency alternating ^¬ voltage (U _ac),

and a high-voltage generator (6) which converts the high-frequency AC voltage (U _ac ) into a high voltage (Uhv) for the X-ray tube (5),

characterized,

that the high-voltage generator (6) comprises a transformer (3) and a to the secondary winding of the transformer (3) parallel-connected high-voltage capacitor (7) which forms a resonant circuit together with the inductance of the secondary winding, wherein the capacitance of the high voltage ^¬ capacitor (7) in such a way is chosen that the resonant circuit in the frequency range between 10 kHz and 500 kHz has its resonance frequency.

2. Circuit arrangement according to claim 1,

characterized,

the capacity of the high-voltage capacitor (7) is such that at a predeterminable operating point of the x-ray tube (5) at the resonant frequency of the alternating voltage, the voltage (Uhv) at the x-ray tube (5) at least doubles.

3. Circuit arrangement for generating an X-ray tube voltage (Uhv) with

a network input circuit (1) for generating an intermediate circuit voltage (Udc) ι

an inverter circuit (2) for converting the intermediate circuit voltage (Udc) into a high-frequency alternating ^¬ voltage (U _ac), and a high-voltage generator (6) which converts the high-frequency AC voltage (U _ac ) into a high voltage (U _h v) for the X-ray tube (5),

characterized,

in that the high-voltage generator (6) has a transformer (3) and a resonant circuit capacitor (8) connected in parallel with the primary winding of the transformer (3) and a resonant circuit coil (9) connected in series with the primary winding and the resonant circuit capacitor (8) and forming a resonant circuit forms, wherein the capacity of the Schwingkreiskondensa ^¬ sector (8) and the inductance of the oscillating circuit coil (9) are ^{¬ the type} chosen that the resonant circuit in the frequency range between 10 kHz and 500 kHz has its resonant frequency.

4. Circuit arrangement according to claim 3,

characterized,

in that the capacitance of the resonant circuit capacitor (8) and the inductance of the resonant circuit coil (9) are such that at a predeterminable operating point of the x-ray tube (5) at the resonant frequency of the AC voltage, the voltage (U _h v) at the x-ray tube (5) at least doubles ,

5. X-ray generator with a circuit arrangement according to one of claims 1 to 4.

6. X-ray device with an X-ray generator according to claim 5.

7. Method for generating an x-ray tube voltage (U _h v) _/ in which a DC link voltage (Udc) is generated from a mains input voltage and a high-frequency AC voltage (U _ac ) is generated from the intermediate circuit voltage (Udc) which is connected to a high-voltage generator (6) with a transformer (3) into a high voltage (U _h v) for the x-ray tube (5) is converted,

characterized,

that the capacitance of the secondary winding of transformers ^¬ gate (3) parallel-connected high-voltage capacitor (7) is chosen such that a resonant circuit formed from the Hochspannungskondensa ^¬ tor and the inductance of the secondary winding in the frequency range between 10 kHz and 500 kHz is brought into resonance.

8. A method for generating an X-ray tube voltage (Uhv) r in which a DC link voltage (UDC) is generated from a mains input voltage and from the intermediate circuit voltage (UDC) a high-frequency AC voltage (U _ac ) is generated with a high voltage generator (6) with a transformer

(3) in a high voltage (UHV) for the X-ray tube (5) is converted ^¬ converts,

characterized,

that of a to the primary winding of the transformer (3) pa ^¬ rallel switched resonant circuit capacitor (8) and the primary winding and the resonant circuit capacitor (8) connected in series resonant circuit coil (9), a resonant circuit is formed, wherein the capacitance of the resonant circuit capacitor (8) and the Inductance of the oscillating circuit coil (9) are chosen such that the resonant circuit in the frequency range between 10 kHz and 500 kHz has its resonant frequency.

9. The method according to claim 7 or 8,

characterized,

that at a predeterminable operating point of the X-ray tube (5) at the resonance frequency, the voltage (Uhv) at the X-ray ^¬ tube (5) is at least doubled.