DE102019130602A1 - Island network power supply for a CT scanner - Google Patents

Abstract

A power supply for X-ray tubes of a CT scanner comprises an inverter circuit and a filter circuit. The inverter circuit comprises four semiconductors that form a full bridge. The filter circuit comprises two series coils of the first filter stage, a parallel capacitor of a first filter stage and a suction circuit comprising a series resonance circuit of a coil and a capacitor. The filter further comprises a first common mode choke and an output filter.

Description

Technical field

The invention relates to computed tomography scanners (CT scanners) and a power supply for such CT scanners. X-ray tubes with a comparatively high output are used in CT scanners. An improved power supply provides a supply voltage to such X-ray tubes.

State of the art

A rotatable transformer for CT scanners is in the US 7,717,619 B2 disclosed. An isolating transformer is provided between an inverter and a rotatable transformer. Such an isolating transformer has a comparatively high mass, requires installation space and increases costs.

Presentation of the invention

The invention has for its object to provide a power supply for CT scanners with an inverter to feed a load such as an X-ray tube, but without the need for an isolating transformer.

Solutions to the problem are described in the independent claims. The dependent claims relate to further improvements of the invention.

Most inverters provide a pulse width modulated (PWM) signal. Such a PWM signal has higher frequency components that can cause electromagnetic interference and are therefore undesirable in a CT scanner environment. The removal of these high frequency components requires filtering. A wide range of inverters are available in the motor control application market. A standard electric motor has a comparatively high inductance, which blocks high-frequency currents. Therefore, in most motor control applications, a simple inverter can be connected directly to a motor without an additional filter.

A standard X-ray tube power supply, such as that used in a CT scanner, does not provide as high an inductance as a motor. Therefore, the power supply is unable to suppress and / or filter currents at higher frequencies. Furthermore, there can be electrical lines between the inverter and the power supply, which can radiate RF signals. Accordingly, additional filtering at the output of the inverter may be necessary. This filtering can be done with standard filters called sine filters. These filters filter the voltage between the phase lines of the inverter, but a high frequency voltage can remain between the phases and the protective earth. An isolating transformer can be used to separate and / or suppress this higher frequency voltage signal. This isolating transformer can have a mass of up to 15 kilograms for CT scanner applications. There can be losses causing the transformer to heat up and it is expensive.

In one embodiment, a power supply circuit and a filter are provided that do not require an isolation transformer. An inverter circuit, which comprises a plurality of semiconductor switches, generates a pulse-width-modulated output signal. There can be two, four, six, or any other suitable number of semiconductor switches that can be connected in a two-quadrant or four-quadrant bridge circuit, or a three-phase bridge circuit. The semiconductor switches can be power MOSFETs or IGBTs. The semiconductor switches are the core of the inverter, also called the frequency converter stage. They are supplied with direct current, which can be generated from an alternating current source by a rectifier, which can be a bridge rectifier. Alternatively, a DC power source can be provided. Such a DC power source can be an AC power line connected to a rectifier, which can be a bridge rectifier or a three-phase bridge rectifier. At least one smoothing capacitor is preferably provided on the power supply lines connected to the semiconductor switches. There may be further filter capacitors for filtering the RF signal components, which can either be connected to the semiconductor switches between the input current lines or to a protective earth from the input current lines. The input power lines may include a positive power line and a negative power line. Protective earth is also provided, which is connected to the chassis or the housing of the CT scanner. The semiconductor switches can be operated by a driver circuit which can be connected to the gates of the individual semiconductor switches and which can control the switches for switching on and off. The driver circuit may include a control circuit, which may further include a closed loop, for controlling at least one of the output frequency, output voltage, and output current of the inverter circuit or the power supply. The driver circuit can also include a pulse width modulator that forms PWM control signals for the semiconductor switches.

The output of the inverter circuit, which is also the output of the semiconductor switch, is connected to a filter circuit, which is also connected to a load circuit. At the input of the filter circuit, first coils of the first filter stage can be series coils to the AC lines from the inverter circuit. These coils of the first filter stage can be followed by a parallel capacitor of the first filter stage. This can be followed by a suction circuit that connects the AC lines. This suction circuit can comprise a series connection of an inductor and a capacitor, which can be set to the switching frequency of the inverter. It can form a short circuit for undesired high-frequency components.

The suction circuit is followed by a first common mode choke that includes two windings on the same magnetic core that are wound in directions so that a differential current, which may be a current that flows from the first AC line and back into the second AC line, that compensated for magnetic fields within the core. Accordingly, the inductance of the differential signals is low, while the inductance of the common mode signals is high. Therefore, the first common mode choke has a high filtering effect on common mode signals. The first common mode choke may include a magnetic core made of ferrite material. Ordinary common mode chokes typically use lossy material to increase losses at higher frequencies. In one embodiment of the first common mode choke, a broadband power ferrite material can be used, which can be dimensioned taking into account the voltage-time ranges of the signal.

The first common mode choke may be followed by a second common mode choke that has the same basic properties. In one embodiment, the first common mode choke is configured to filter low frequency components, while the second common mode choke is configured to filter high frequency components. Low frequency components can be components from the PMW modulation frequency, while high frequency components can be from the PWM signal edges. The high frequency components can be in a frequency range that is 10 times higher than the low frequency components.

Either the negative power line or the positive power line is connected to the protective ground at a point near the AC or DC power source. There can be only one connection between the negative power line or the positive power line with the protective earth.

Figure list

• 1 zeigt ein Schaltungsdiagramm einer ersten Ausführungsform.

The invention is described below by way of example without limitation of the general inventive concept using exemplary embodiments with reference to the drawings.

• 1 shows a circuit diagram of a first embodiment.

In 1 A first embodiment is shown as a circuit diagram. A power supply for a CT scanner can be an inverter circuit 200 followed by a filter circuit 300 include. The power supply can come from a DC power source 100 can be fed and its output current to a load circuit 400 which may include or be part of an X-ray tube power supply.

The inverter circuit 200 may include a variety of semiconductor switches.

In one embodiment, four are semiconductor switches 241 , 242 , 243 , 244 which form a full bridge or H-bridge. A first semiconductor switch 241 can be between a positive supply node 291 and a first AC line 201 be connected. A second semiconductor switch 242 can be between the first AC line 201 and a negative supply node 292 be connected. A third semiconductor switch 243 can be between the positive supply node 291 and the second AC line 202 be connected. A fourth semiconductor switch 244 can be between the second AC line 202 and the negative supply node 292 be connected. The bridge thus has inputs from the positive supply node 291 and negative supply nodes 292 . The outputs are on the first AC line 201 and second AC line 202 .

The switches can normally be operated in groups, just like the switches in a first state 241 and 244 can be closed while switches 242 and 243 are open. In a second state, the switches 242 and 243 be closed while 241 and 244 are open. Between the positive supply node 291 and the negative supply node 292 can be a smoothing capacitor 230 be provided. The capacitor can be an electrolytic capacitor and can have a comparatively high capacitance.

Furthermore, a ground capacitor 231 from the negative supply node 292 to protective earth 103 be provided. The inverter circuit 200 can have an input with a positive power line 101 and a negative power line 102 which have an input bridge rectifier, the four diodes 221 , 222 , 223 , 224 includes, with the positive supply node 291 and the negative supply node 292 can be coupled. In some cases, the positive power line 101 directly with the positive supply node 291 be connected and the negative power line 102 can go directly to the negative supply node 292 be connected. A bridge rectifier can ensure greater flexibility because it allows the inverter circuit to be fed with DC signals of any polarity or even AC signals. At the input of the inverter circuit, in front of the bridge rectifier, there can be at least one input filter capacitor. A first input filter capacitor 211 can between the positive power line 101 and the protective earth 103 be coupled. A second input filter capacitor 201 can between the negative power line 102 and the protective earth 103 be connected.

A DC or AC source 100 can provide direct current or alternating current into the inverter circuit 200 through the positive power line 101 and the negative power line 102 is coupled. In one embodiment, the DC or AC source 100 a direct DC power supply or a battery, or the rectified output of an inverter circuit, or the output of a power line connected to the rectifier. In the latter case, the rectifier can be a simple bridge rectifier or a three-phase rectifier. Alternatively, there can also be a direct current source, such as a 50 Hz power line, which can be connected to the inverter circuit.

A filter circuit 300 can through the first AC line 201 and the second AC line 202 with the inverter circuit 200 be connected. The filter circuit comprises several stages. The first filter stage may include a pair of filter coils as series inductors. A coil of the first filter stage 311 in series with the first DC line 201 is with the first filter node 301 connected and a coil of the first filter stage 312 in series with the second DC line 202 is with the second filter node 302 connected. A capacitor of the first filter stage 313 can be between the first filter node 301 and the second filter node 302 be connected.

The next filter level, between the first filter node 301 and the second filter node 302 connected can include a suction circuit. This can be a series resonance circuit of a coil 321 and a capacitor 322 (which are connected in series), wherein the series resonance frequency can be adapted to the switching frequency of the inverter circuit. This suction circuit creates a short circuit for higher frequency components, which are generated by PWM circuit of the inverter circuit.

The suction circuit can be followed by a first common mode choke. The input is at the first filter node 301 and at the second filter node 302 while the output is on the third filter node 303 and at the fourth filter node 304 is. This first common mode choke comprises a first thread 331 , which forms a first coil and a second thread 332 that has a second coil on a common magnetic core 333 forms. The first common mode choke comprises two windings on the same magnetic core, which are the coils 331 , 332 are and are wound in directions such that a differential current, which may be a current, through the first winding from the first filter node 301 in the third filter node 301 flows and through the second winding from the fourth filter node 304 in the second filter node 302 flows back, a compensation of magnetic fields and thus a magnetic field of zero field strength within the magnetic core of the common mode choke 333 caused. Accordingly, the inductance of the differential signals is low, and the inductance of the common mode signals is high. The inductance for common mode signals can be higher than the inductance for differential signals. Accordingly, the common mode choke has a higher filter effect on current compensated signals. The first common mode choke may include a magnetic core made of ferrite material. Typically, first common mode chokes use lossy material to increase losses at higher frequencies. In this embodiment of a common mode choke, a broadband power ferrite material can be used which has low losses and which can be dimensioned in terms of voltage-time ranges of the signal. The first coil A of the common mode choke 331 is with the first filter node 301 connected and the first coil B of the common mode choke 332 is with the second filter node 302 connected. The other ends of the coils of the first common mode choke are connected to the first filter node 303 and the second filter node 304 connected.

An output filter is through the components that make up the third filter node 303 and the fourth filter node 304 connect, formed. A first output filter capacitor A 341 is between the third filter node 303 and the positive supply node 291 connected. Another first output filter capacitor B 342 is between the fourth filter node 304 and the positive supply node 291 connected. Another first output filter capacitor C 343 is between the third filter node 303 and the filter node 304 connected. Another first output filter capacitor D 344 is between the third filter node 304 and one Protective earth 103 connected. Another first output filter capacitor E 345 is between the fourth filter node 304 and a protective earth 103 connected.

The first common mode choke can be followed by a second common mode choke, which has the same basic properties. A coil A of the second common mode choke 351 and a coil B of the second common mode choke 352 which together with the core of the second common mode choke 353 form a second common mode choke are with the nodes 303 and 304 connected. These coils are also connected to the filter outputs 305 and 306 connected. There are also second filter output capacitors 361 and 362 from the first filter outlet 305 and second filter output 306 to protective earth 103 connected.

The power shift 400 is with the first filter output 305 and second filter output 306 connected. The load circuit can be a load input filter capacitor 410 comprise, which is connected in parallel between the first filter output and the second filter output. It can further comprise a load bridge rectifier, which has four diodes 421 , 422 , 423 , 424 in a bridge rectifier circuit that can include a positive load line 401 and a negative load line 402 feeds. Between the positive load line 401 and the negative load line 402 can be a load filter capacitor 430 be. Weight 440 Which can be part of an x-ray tube power supply and / or inverter circuit can be connected in parallel to the load filter capacitor.

In one embodiment, the protective earth is 103 either with the positive load line 401 or the negative load line 402 connected, preferably close to the direct current or alternating current source 100 . In one embodiment, the capacitors 341 and 342 with the positive power line 101 and the capacitors 231 , 244 , 245 , 248 , 249 refer to the protective earth wire 103 . In another embodiment, the protective earth 103 with the positive power line 101 be connected while capacitor 231 between the positive power line 101 and the protective earth 103 is connected, and capacitors 344 , 345 , 361 , and 362 are also connected to the protective earth wire 103 connected. The capacitors 342 and 341 are with the negative power line 102 connected.

Reference symbol list

101

DC or AC power source

101

positive power line

102

negative power line

103

Protective earth

200

Inverter circuit

201

first AC line

202

second AC line

211

first input filter capacitor

212

second input filter capacitor

221-224

Input bridge rectifier

230

Smoothing capacitor

231

Ground capacitor

241-244

Semiconductor switch

291

positive supply node

292

negative supply node

300

Filter circuit

301

first filter node

302

second filter node

303

third filter node

304

fourth filter node

305

first filter output

306

second filter output

311, 312

Coils of the first filter stage

313

First filter stage capacitor

321

Suction circuit coil

322

Suction circuit condenser

331

Coil A of the first common mode choke

332

Coil B of the first common mode choke

333

magnetic core of the first common mode choke

341

first output filter capacitor A

342

first output filter capacitor B

343

first output filter capacitor C

344

first output filter capacitor D

345

first output filter capacitor E

351

Coil A of the second common mode choke

352

Coil B of the second common mode choke

353

magnetic core of the second common mode choke

361

second output filter capacitor A

362

second output filter capacitor B

400

Load switching

401

positive load line

402

negative load line

410

Load input filter capacitor

421-424

Load bridge rectifier

430

Load filter capacitor

440

Power circuit (X-ray tube power supply / inverter)

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 7717619 B2 [0002]

Claims (17)

A power supply for CT scanner x-ray tubes comprising an inverter circuit (200) and a filter circuit (300), the inverter circuit (200) comprising four semiconductor switches (241, 242, 243, 244) which have a full bridge with inputs of a positive supply node (291 ) and a negative supply node (292) and outputs to a first AC line (201) and a second AC line (202), the filter circuit (300) comprising: a coil of the first filter stage (311) between the first AC line (201) and a first filter node (301), and a further coil of the first filter stage (312) between the second AC line (202) and a second filter node (302), a capacitor of the first filter stage (313), which is connected between the first filter node (301) and the second filter node (302), a suction circuit comprising a series resonance circuit of a coil (321) and a capacitor (322) which is connected between the first filter node (301) and the second filter node (302), - a first common mode choke comprising a coil A of the first common mode choke (331), which is connected between the first filter node (301) and a third filter node (303), and a coil B of the first common mode choke (332), which is connected between the second filter node (332) 302) and a fourth filter node (304), the coil A of the first common mode choke (331) and the coil B of the first common mode choke (332) comprising a common magnetic core (333), - a second common mode choke comprising a coil A of the second common mode choke (351), which is connected between the third filter node (303) and the first filter output (305), and a coil B of the second common mode choke (352), which is connected between the fourth filter node (352) 304) and the second filter output (306), the coil A of the second common mode choke (351) and the coil B of the second common mode choke (352) comprising a common magnetic core (353), a first output filter capacitor A (341), which is connected between the third filter node (303) and the positive supply node (291), a first output filter capacitor B (342) which is connected between the fourth filter node (304) and the positive supply node (291), a first output filter capacitor D (344) which is connected between the third filter node (303) and a protective earth (103), a first output filter capacitor E (345) which is connected between the fourth filter node (304) and the protective earth (103), a second output filter capacitor A (361) which is connected between the first filter output (305) and the protective earth (103), - A second output filter capacitor B (362) which is connected between the second filter output (306) and the protective earth (103). Power supply after Claim 1 , characterized in that the semiconductor switches (241, 242, 243, 244) are configured to generate a PWM signal. Power supply according to one of the preceding claims, characterized in that the semiconductor switches (241, 242, 243, 244) are operated by a driver circuit which can be connected to the gates of individual semiconductor switches and which can control the switches for switching on and off, to generate a PWM signal. Power supply according to one of the preceding claims, characterized in that the series resonance frequency of the suction circuit (321, 322) is adapted to the switching frequency of the inverter circuit. Power supply according to one of the preceding claims, characterized in that the semiconductor switches (241, 242, 243, 244) comprise current MOSFETs or IGBTs. Power supply according to one of the preceding claims, characterized in that the magnetic core (333) of the first common mode choke comprises a broadband power ferrite material which may have losses. Power supply according to one of the preceding claims, characterized in that the first common mode choke comprises a first winding which is the coil A of the first common mode choke (331) and a second winding which is the coil B of the first common mode choke (332), the the first winding and the second winding are on the same magnetic core of the first common mode choke (333). Power supply after Claim 7 , characterized in that the first winding and the second winding are wound in directions so that a differential current, which may be a current, flows through the first winding from the first filter node (301) into the third filter node (303) and which flows back through the second winding from the fourth filter node (304) into the second filter node (302), causes a magnetic field with zero field strength within the magnetic core of the first common mode choke (333). Power supply according to one of the preceding claims, characterized in that the first common mode choke (331, 332, 333) and / or second common mode choke (351, 352, 353) provide a low inductance for differential signals and a high inductance for common mode signals. Power supply according to one of the preceding claims, characterized in that the first common mode choke (331, 332, 333) is configured for filtering low-frequency components, while the second common mode choke (351, 352, 353) is configured for filtering high-frequency components. Power supply after Claim 10 and one of the Claims 2 to 9 , characterized in that low-frequency components can be components of the PWM modulation frequency, and high-frequency components can be from the PMW signal edges. Power supply according to one of the preceding claims, characterized in that a first output filter capacitor C (343) is connected between the third filter node (303) and the fourth filter node (304). Power supply according to one of the preceding claims, characterized in that the positive supply node (291) and the negative supply node (292) are connected to a direct current source. Power supply according to one of the preceding claims, characterized in that the inverter circuit comprises: - a first input filter capacitor (211) which is connected between a positive power line (101) and the protective earth (103), - a second input filter capacitor (212) which is connected between a negative current line (101) and the protective earth (103), - an input bridge rectifier comprising four diodes (221, 222, 223, 224) in a bridge rectifier circuit, which is connected to the positive current line (101) and the negative current line (102) and feeds the positive supply node (291) and the negative supply node (292), - a smoothing capacitor (230) which is connected to the supply node (291) and the negative supply node (292). Power supply according to one of the preceding claims, characterized in that the negative power line (102) or the positive power line (101) is connected to the protective earth (103). A computed tomography scanner comprising a power supply according to one of the preceding claims and a load circuit (400) connected to the first filter output (305) and second filter output (306), the load circuit (400) further comprising: a load input filter capacitor (410) which is connected to the first filter output (305) and the second filter output (306), a load bridge rectifier comprising four diodes (421, 422, 423, 424) in a bridge rectifier circuit which is connected to the first filter output (305) and the second filter output (306) and feeds: - A load filter capacitor (4360) in parallel - a load (400). A computed tomography scanner after Claim 16 , characterized in that an AC or DC power supply (100) is connected to the positive power line (101) and the negative power line (102).

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