WO2011024137A1 - Appareil inverseur multiniveau et procédé d'inversion - Google Patents

Appareil inverseur multiniveau et procédé d'inversion Download PDF

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Publication number
WO2011024137A1
WO2011024137A1 PCT/IB2010/053840 IB2010053840W WO2011024137A1 WO 2011024137 A1 WO2011024137 A1 WO 2011024137A1 IB 2010053840 W IB2010053840 W IB 2010053840W WO 2011024137 A1 WO2011024137 A1 WO 2011024137A1
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WIPO (PCT)
Prior art keywords
voltage
voltages
inverter
output
input
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PCT/IB2010/053840
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English (en)
Inventor
Christoph Loef
Peter Luerkens
Oliver Woywode
Frank Johnen
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Koninklijke Philips Electronics N.V.
Philips Intellectual Property & Standards Gmbh
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Publication of WO2011024137A1 publication Critical patent/WO2011024137A1/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/0515—Magnetic particle imaging
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current

Definitions

  • the present invention relates to a multi-level inverter apparatus and a corresponding method for converting a DC input voltage into an AC output voltage.
  • the present invention relates further to a power supply circuit for supplying an AC load voltage to a load, in particular to a Magnetic Particle Imaging (MPI) device for influencing and/or detecting magnetic particles in a field of view, wherein the field of view comprises an object of interest containing magnetic particles.
  • MPI Magnetic Particle Imaging
  • Magnetic Particle Imaging is an emerging medical imaging modality.
  • the first versions of MPI were two-dimensional in that they produced two-dimensional images. Future versions will be three-dimensional (3D).
  • a time-dependent, or 4D, image of a non-static object can be created by combining a temporal sequence of 3D images to a movie, provided the object does not significantly change during the data acquisition for a single 3D image.
  • MPI is a reconstructive imaging method, like Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). Accordingly, an MP image of an object's volume of interest is generated in two steps.
  • the first step referred to as data acquisition, is performed using an MPI scanner.
  • the MPI scanner has means to generate a static magnetic gradient field, called “selection field”, which has a single field free point (FFP) at the isocenter of the scanner.
  • selection field which has a single field free point (FFP) at the isocenter of the scanner.
  • FFP single field free point
  • the scanner has means to generate a time-dependent, spatially nearly homogeneous magnetic field. Actually, this field is obtained by superposing a rapidly changing field with small amplitude, called “drive field”, and a slowly varying field with large amplitude, called “focus field”.
  • the FFP may be moved along a predetermined FFP trajectory throughout a volume of scanning surrounding the isocenter.
  • the scanner also has an arrangement of one or more, e.g. three, receive coils and can record any voltages induced in these coils.
  • the object to be imaged is placed in the scanner such that the object's volume of interest is enclosed by the scanner's field of view, which is a subset of the volume of scanning.
  • the object must contain magnetic nanoparticles; if the object is an animal or a human, a contrast agent containing such particles is administered to the animal or human prior to the scan.
  • the MPI scanner steers the FFP along a deliberately chosen trajectory that traces out the volume of scanning, or at least the field of view.
  • the magnetic nanoparticles within the object experience a changing magnetic field and respond by changing their magnetization. Only those, which are in the field free point, exhibit a change. All other particles do not respond, because of being saturated by the selection field.
  • the changing magnetization of the nanoparticles induces a time dependent voltage in each of the receive coils. This voltage is sampled in a receiver associated with the receive coil. The samples output by the receivers are recorded and constitute the acquired data.
  • the parameters that control the details of the data acquisition make up the scan protocol.
  • the image is computed, or reconstructed, from the data acquired in the first step.
  • the image is a discrete 3D array of data that represents a sampled approximation to the position-dependent concentration of the magnetic nanoparticles in the field of view.
  • the reconstruction is generally performed by a computer, which executes a suitable computer program. Computer and computer program realize a reconstruction algorithm.
  • the reconstruction algorithm is based on a mathematical model of the data acquisition. As with all reconstructive imaging methods, this model is an integral operator that acts on the acquired data; the reconstruction algorithm tries to undo, to the extent possible, the action of the model.
  • Such an MPI apparatus and method have the advantage that they can be used to examine arbitrary examination objects - e. g. human bodies - in a non-destructive manner and without causing any damage and with a high spatial resolution, both close to the surface and deep in the body of the examination object.
  • arbitrary examination objects e. g. human bodies - in a non-destructive manner and without causing any damage and with a high spatial resolution, both close to the surface and deep in the body of the examination object.
  • Such an arrangement and method are generally known and are first described in DE 101 51 778 Al and in Gleich, B. and
  • a high quality sinusoidal input current is required to supply the drive field coil inside a scanner for MPI. Since the spatial resolution depends on the quality of the drive field coil current, a high quality signal is required.
  • the drive field coil can be treated electrically as an inductance with low parasitic resistance. The coil will cause very high reactive power, when supplied with a desired AC-current. The reactive power flow can be reduced by means of paralleling capacitances either in a tapped or non-tapped outline to the coil. Additionally, a filter can be placed between the supply unit and the drive field coil.
  • the supply unit is realized by means of analogue amplifiers. Due to the high demand of reactive power, an analogue amplifier solution is not a favorable solution. The losses of this solution equals at least the amount of apparent power times 4/ ⁇ . On a clinical scale, the power requirements are huge and lead to enormous energy consumption and cost.
  • switched amplifier will provide a higher efficiency and will be able to cope with the high reactive power demand.
  • known switched amplifiers would cause higher harmonic contents at the inverter output, when operating with a Pulse Width Modulation (PWM) control. It would require a very high switching frequency and an enormous resolution in time to fulfill the typical precision requirements of the application.
  • Standard multi-level converters (sometimes also called multistep converters) tend to become extremely complex if a sufficient fine stepping of voltage levels has to be achieved.
  • nonlinear signal distortion is prevalent in switched amplifiers because of imperfections of the implemented semiconductor switches that have current dependent voltage drop and even more relevant current dependent delay effects. This can be mitigated by either increasing the number of stages and so levels in multi-level converter to very high numbers, or use a switching frequency at the PWM converters that is substantially higher than the frequency range, which is relevant for the application.
  • the second is known from
  • US 5,757,633 discloses a multi-level inverter using multiple inverter H- bridges connected in series to piecewise approximate a sine wave.
  • the inverter H-bridges are bypassed or switched into service as required for sine wave synthesis. After a step is switched in, it creates its portion of the sine wave.
  • Each step is further smoothed using pulse width modulation which leads to a smoother sine wave with the consequent advantages of lower distortion, smaller and lighter filtering circuits, and lower conversion losses during transistor switching.
  • a third problem is that a feed- forward scheme for compensation of unwanted signal components require an enormous precision of the compensation signal if a relevant suppression of the noise shall be achieved.
  • a multi-level inverter apparatus that comprises
  • inverter circuits coupled to one of said DC input terminals, each receiving a DC input voltage or a supply voltage derived therefrom and generating an AC intermediate voltage
  • connection means coupled to said plurality of inverter circuits for connecting the AC intermediate voltages in series
  • control means for controlling said inverter circuits to convert the one or more DC input voltages into predetermined AC intermediate voltages.
  • the invention is based on the idea to use a stacked configuration of several digital amplifiers, which produce voltage levels in the manner of a numbering system, for instance based on the radix 5, and to achieve an optimal trade-off between quantization and required maximum switching frequency.
  • a large number of different voltage levels with a rather limited number of individual inverters are obtained by an optimized scaling of the voltage levels of the individual stages. This results into easy to fulfill requirements of precision and power dimensioning of the individual stages, within the technical constraints of the components, e.g. with regard to the required switching frequency.
  • the invention thus provides a solution both for the high power requirements of linear amplifiers and the harmonics problem of conventional switched amplifier solutions.
  • the switched amplifier and control method according to the present invention enable the supply of high power demanding field coils for magnetic particle imaging applications, and also a fine stepping of the output voltage levels is achieved leading to low signal distortion and noise, with a relatively simple configuration.
  • Another advantage is that the system control is not obliged anymore to take care of a proper balancing of the loading of the different inverter stages. As these are coupled over a common DC supply, they will all have the same voltage, and differences in the individual load are balanced automatically.
  • At least two, in particular all, inverter circuits are adapted for converting the one or more DC input voltages into AC intermediate voltages having different voltage levels.
  • said pair of output terminals is coupled to the end terminals of said aid series connection of AC intermediate voltages.
  • one or more additional AC output terminals coupled to interconnections between said series connection of AC intermediate voltages, i.e. not only the total voltage from the end terminals of said series connection of AC intermediate voltages.
  • At least two of said AC intermediate voltages produce different sets of voltage levels, wherein the different sets of voltage level preferably follow a rule of 1 :n:n 2 :n 3 etc.. Further, the different AC intermediate voltages are obtained by different DC supply voltages of the inverters.
  • connection means comprises a transformer circuit having a plurality of transformers, each comprising a primary winding coupled to the output of an associated inverter circuit for receiving an AC intermediate voltage, and a secondary winding, wherein said secondary windings are coupled in series and wherein said transformer circuit generates an AC output voltage from said AC intermediate voltages.
  • At least two, in particular all, transformers have a different turn ratio.
  • the output voltages of the various transformers, in particular at the various secondary windings of the transformers are thus different. This enables to selectively "compose" the desired voltage level of the AC output voltage, in particular by appropriate control of the individual inverter circuits (in the apparatus according to the first aspect) or of the individual secondary inverter circuits (in the apparatus according to the second aspect), e.g. by switching the switching elements comprised in the individual (secondary) inverter circuits on or off as desired.
  • the transformer having the highest turn ratio provides the smallest voltage level and, thus, is used for enabling the smallest changes in the AC output voltage.
  • the smallest changes in the AC output voltage which is preferably a sinusoidal function, show the highest frequency, caused by a plurality of small voltage portions during short switching intervals of the respective inverter).
  • connection means comprises a series connection of said inverter circuits, and the DC supply voltages or DC input voltages of the individual inverter circuits are galvanically isolated. This generally requires less hardware.
  • the multilevel inverter apparatus further comprises
  • a primary inverter circuit coupled to said DC input terminals for converting said DC voltage into an AC primary transformer input voltage
  • a primary transformer circuit having a plurality of primary transformers each comprising a primary winding and a secondary winding, wherein said primary windings are connected in parallel to the output of said primary inverter circuit for providing said AC primary transformer input voltage to said parallel connection, said transformer circuit generating AC primary transformer output voltages from said AC primary transformer input voltage,
  • the at least two, in particular all, primary transformers preferably have a different turn ratio leading to the same advantages as mentioned above for the transformers. .
  • the corresponding inverter has the lowest current in switching elements of the respective control means. This is advantageous for the operation of these inverters, which can be operated at a higher frequency with reduced current or voltage, which in turn reduces the losses in the switching elements of the control means.
  • Each inverter preferably comprises two pairs of switching elements forming a H-bridge.
  • the switching elements of a first pair are connected in series, forming three independent terminals.
  • a first terminal is connected to the positive input voltage terminal of the respective inverter, a second terminal is connected to the negative input voltage terminal of the inverter, and the third terminal is forming an alternating output voltage terminal.
  • the second pair is connected the same way, thereby forming a second output voltage terminal of the inverter.
  • Each switching element can preferably be switched on and off individually such that two serially coupled switching elements are never in a switched on state at the same and that the voltage difference at the output voltage terminals of the inverter is zero, equal to the input voltage of the inverter, or equal to the input voltage multiplied by minus 1.
  • a balance of the losses in the switches of the inverter circuits, particularly if the power supply is to deliver output voltages with small amplitude or with zero output voltage level, can be achieved according to a further embodiment according to which said control means is adapted for controlling said inverter circuits such that an equal current distribution is obtained in the switching elements over a predetermined time period by changing the switching configuration depending on whether a reference signal changes sign.
  • control means is adapted for changing the freewheeling path of an inverter circuit synchronized with a zero crossing of the output current of said inverter circuit or synchronized to a predetermined, in particular first, switching state of the sign of the output current of said inverter circuit.
  • the switching configuration is changed depending on whether a reference signal changes sign.
  • the reference signal is preferably an input signal to the modulator.
  • the modulator maps the desired output voltage to the appropriate switching configuration of the inverter circuits. This embodiment thus ensures that the change of a switching configuration no longer depends on the previous state of the switching configuration. This way the stress on the switches may be balanced even if output voltages with small amplitudes are required.
  • the switching frequency is several times higher than the fundamental operating frequency, and the conduction loss distribution is averaged over half cycles or cycles, in particular one or two cycles, of the fundamental operating frequency.
  • the multi-level inverter apparatus is preferably applied in a power supply circuit.
  • a power supply circuit for supplying a load with an AC voltage signal comprising: a multi-level inverter apparatus according to the present invention for converting a DC input voltage provided by a DC voltage source into an AC output voltage, and
  • a filter circuit coupled to the output of said multi-level inverter apparatus for filtering said AC output voltage signal into said AC voltage signal.
  • said (active or passive) filter circuit comprises a control loop including:
  • a loop control circuit for receiving the difference between said AC voltage signal and a reference signal and for generating a loop control signal
  • the multi-level inverter apparatus and the inversion method as well as the power supply circuit can be used in various applications.
  • a preferred use is in the field of medical application in devices for medical imaging, such as Magnetic Resonance Imaging (MRI) devices or, preferably, Magnetic Particle Imaging (MPI) devices as described above.
  • MRI Magnetic Resonance Imaging
  • MPI Magnetic Particle Imaging
  • an imaging device for imaging an object, in particular a patient, comprising imaging means and one or more power supply circuits as described above for supplying power to said imaging means.
  • said imaging means comprises an X-ray unit or a magnetic resonance unit, wherein said power supply unit is, for instance, adapted to supply power to the cathode of an X-ray generator, to provide the voltage between the cathode and the anode, or to provide the supply power to the control grid of a grid-controlled X-ray generator.
  • the multilevel inverter apparatus may, for instance, be used in the power supply units for supplying power or control voltages to the gradient coils.
  • an MPI device comprising:
  • selection means comprising a selection field signal generator unit and selection field elements for generating a magnetic selection field having a pattern in space of its magnetic field strength such that a first sub-zone having a low magnetic field strength where the magnetization of the magnetic particles is not saturated and a second sub-zone having a higher magnetic field strength where the magnetization of the magnetic particles is saturated are formed in the field of view,
  • drive means comprising drive field signal generator units and drive field coils for changing the position in space of the two sub-zones in the field of view by means of a magnetic drive field so that the magnetization of the magnetic material changes locally, wherein said drive field signal generator units comprises one or more power supply circuit according to the present invention.
  • said MPI device Dependent on the kind of application of said MPI device, e.g. whether it is desired to be used for imaging (a small or large area), heating a certain area in the object and/or moving an object, it might comprise further means, such as focus coils, receive coils, image processing means, control means etc., which are generally all known in the art of MPI devices.
  • transformer circuit having a plurality of transformers each comprising a primary winding, to which an AC intermediate voltage is applied, and a secondary winding, wherein said secondary windings are coupled in series and wherein said transformer circuit generates an AC output voltage from said AC intermediate voltages,
  • control means for controlling said inverter circuits to convert the DC input voltage into predetermined AC intermediate voltages.
  • a pair of DC input terminals for receiving a DC input voltage
  • a primary inverter circuit coupled to said DC input terminals for converting the DC input voltage into an AC transformer input voltage
  • transformer circuit having a plurality of transformers each comprising a primary winding and a secondary winding, wherein said primary windings are connected in parallel, which parallel connection being coupled to the output of said primary inverter circuit for providing said AC transformer input voltage to said parallel connection, said transformer circuit generating AC transformer output voltages from said AC transformer input voltage, a plurality of rectifier circuits coupled to said secondary windings for converting said AC transformer output voltages into DC intermediate voltages,
  • Fig. 1 shows a block diagram of the general layout of a system, in which the present invention can be used
  • Fig. 2 shows a diagram illustrating a PWM modulated output voltage
  • Fig. 3 shows a diagram illustrating a piecewise approximated inverter output voltage
  • Fig. 4 shows a block diagram of a first embodiment of a multi-level inverter apparatus according to the present invention
  • Fig. 5 shows a diagram illustrating the number of addressable output voltages vs. the number of inverter stages using identical inverter supply voltages
  • Fig. 6 shows a diagram illustrating the number of addressable output voltages vs. the number of inverter stages using inverter supply voltages that are halved at each additional inverter
  • Fig. 7 shows a diagram illustrating the number of addressable output voltages vs. the number of inverter stages having two pairs of inverters with a stepping of 1 :5 between the pairs
  • Fig. 8 shows a block diagram of a second embodiment of a multi-level inverter apparatus according to the present invention
  • Fig. 9 shows a block diagram of an embodiment of a power supply circuit according to the present invention.
  • Fig. 10 shows a block diagram of the power supply circuit shown in Fig. 9 in more detail
  • Fig. 11 shows a first embodiment of an MPI device in which the power supply circuit according to the present invention can be used
  • Fig. 12 shows an example of the selection field pattern produced by a device as shown in Fig. 11,
  • Fig. 13 shows a block diagram of an MPI device according to the present invention
  • Fig. 14 shows a block diagram of a control unit according to a further embodiment of the present invention.
  • Fig. 15 shows diagrams illustrating a first embodiment of the control method applied by the control unit shown in Fig. 14,
  • Fig. 16 shows diagrams illustrating a second embodiment of the control method applied by the control unit shown in Fig. 14, and
  • Fig. 17 shows a block diagram of a third embodiment of a multi-level inverter apparatus according to the present invention.
  • Fig. 1 shows a block diagram of the general layout of a system in which the present invention can be used.
  • a DC power source 1 with an output voltage Udc is used to supply the amplifier 2.
  • the amplifier 2 can either be of linear mode of operation or digital switching.
  • the output Ua of the amplifier 2 is connected to a filter 3 which interfaces the output of the amplifier 2 to a load 4, e.g. a field coil of a MPI device, as AC load voltage Uload.
  • the amplifier 2 and the filter 3 thus form a power supply circuit 5 for supplying the load with the AC load voltage Uload.
  • a digital operating amplifier offers the option of reduced losses, especially with respect to the high amount of reactive power flow.
  • the output amplitude of the switched amplifier 2 can be set by means of a pulse width modulation.
  • Fig. 2 shows an example for a sinusoidally modulated output voltage.
  • Um denotes the modulated output voltage
  • Us denotes the fundamental voltage component.
  • the difference between both the traces denotes the amount of filtering which is required. In applications which need a high quality output voltage and/or current a large filter is required. However, a highly effective filter setup implies a large amount of reactive power at the inverter.
  • the first embodiment of the present invention described herein applies a piecewise approximated output voltage Ua.
  • the piecewise steps are arranged in a way which provides the lowest possible harmonic content of the output voltage Ua.
  • the amount of filtering can be reduced.
  • Fig. 3 an example of the piecewise approximated inverter output voltage Ua described above is shown. Higher numbers of different output voltage steps will lower the output voltage harmonic content.
  • the mentioned discrete output voltage steps can be realized by means of series connected H-bridge inverters as used in a first embodiment of a multi-level inverter apparatus 6 according to the present invention as shown in Fig. 4.
  • the multi-level inverter apparatus 6 shown in Fig. 4 comprises a pair of DC input terminals 61 for receiving a DC input voltage Udc from the DC voltage source 1.
  • a primary inverter circuit 62 is coupled to said DC input terminals 61 for converting the DC input voltage Udc into an AC transformer input voltage UtI, which is provided to a transformer circuit 63 having a plurality of transformers 63a-63d (here four transformers) comprising a plurality of primary windings (e.g. primary winding 64a for transformer 63a) connected in parallel, which parallel connection being coupled to the output of said primary inverter circuit 62 for providing said AC transformer input voltage UtI to said parallel connection.
  • Said transformer circuit 63a further comprises a plurality of secondary windings (e.g. secondary winding 65a for transformer 63a).
  • the transformers 63a-63d thus generate a plurality of AC transformer output voltages Ut2a-Ut2d from said AC transformer input voltage UtI.
  • the multi-level inverter apparatus 6 further comprises a plurality 66 of rectifier circuits 66a-66d coupled to said secondary windings of the transformers 63a-63d for converting said AC transformer output voltages Ut2a-Ut2d into DC intermediate voltages Udcl-Udc4. Coupled to the output of said rectifier circuits 66a-66d is a plurality 67 of secondary inverter circuits 67a-67d for converting said DC intermediate voltages Udcl-Udc4 into a plurality of AC intermediate voltages Ual-Ua4. In this embodiment the secondary inverter circuits 67a-67d are coupled in series.
  • a pair of AC output terminals 68 is coupled to said secondary inverter circuits, in this embodiment the first output terminal of the first secondary inverter circuit 67a and the last output terminal of the last secondary inverter circuit 67d, so that a maximum AC output voltage Uout is provided as the sum of the AC intermediate voltagesUal-Ua4 at said AC output terminals 68.
  • a control means 69 is coupled to the plurality 67 of secondary inverter circuits 67a-67d, in particular comprising a control line to each secondary inverter circuits 67a-67d, for controlling said secondary inverter circuits 67a-67d to convert the DC input voltagesUdcl-Udc4 into predetermined AC intermediate (galvanically insulated) voltages UaI -Ua4, wherein at least two, in particular all, secondary inverter circuits 67a-67d are adapted for converting the respective DC input voltage Udcl-Udc4 into AC intermediate voltages UaI -Ua4 having different voltage levels.
  • the AC output voltage Uout is provided to a (passive or active) filter circuit 3, at the output of which the load 4 is coupled, which is provided with the load voltage Uload.
  • the multi-level inverter circuit can be used to provide several levels of output voltages.
  • the number of secondary inverter circuits 67 denotes the number of output voltage levels, which can be addressed.
  • the output voltages addressable are depicted in the diagram shown in Fig. 5, which particularly shows the number Nv of addressable output voltages versus the number Ni of secondary inverter circuits.
  • the contributions of the secondary inverter circuits 67a-67d are non-equal, i.e. that the AC intermediate voltages UaI -Ua4 are non-equal.
  • This can be achieved by having different secondary inverter circuits 67a-67d and/or by providing different DC input voltages Udcl-Udc4 to the (equal or non-equal secondary inverter circuits 67a-67d), the latter being achievable by using transformers 63a-63c having primary and/or secondary windings 64a-64d or 65a-65d having different numbers of windings.
  • each of the secondary inverter circuits 67a-67d will operate at different switching frequencies.
  • Another embodiment of the present invention has a semi- linear distribution for the DC input voltages Udcl-Udc4.
  • DC input voltage levels with exemplarily a rating of 5:2 an optimum of output levels and switching frequency range can be achieved.
  • a further embodiment of the present invention described herein has pairs of inverters exemplarily having identical level of DC input voltages Udcl-Udc4 and a stepping of the DC input voltage between the pairs by 5:lFor such an embodiment the number Nv of addressable output voltages versus the number Ni of secondary inverter circuits is depicted in Fig. 7.
  • Each pair effectively forms a five-level inverter as could be read from the diagram shown in Fig. 5.
  • the stepping of 5:1 between the two pairs avoids the overlapping of states in the finest quantization level and thus achieves almost the same number of levels as in Fig. 6. Yet, switching frequency of the high resolution steps is only 5 times higher than the fundamental.
  • a further embodiment of the invention described herein provides the operation of inverter circuits from one identical intermediate DC input voltage.
  • a block diagram of a multi-level inverter apparatus 8 according to such an embodiment is shown in Fig. 8.
  • the apparatus 8 shown in Fig. 8 comprises a pair of DC input terminals 81 for receiving a DC input voltage Udc provided by the DC voltage supply 1.
  • a plurality 82 of inverter circuits 82a-82d is coupled in parallel to said DC input terminals 81 for converting the DC input voltage Udc into a plurality of AC intermediate voltages UaI -Ua4.
  • a transformer circuit 83 having a plurality of transformers 83a-83d comprising a plurality of primary windings 84a- 84d, to which said AC intermediate voltages Ual-Ua4 are applied, and a plurality of secondary windings 85a-85d coupled in series.
  • the transformer circuit 83 thus generates the AC output voltage Uout from said AC intermediate voltages UaI -Ua4, provided at a pair of AC output terminals 86 coupled to said transformer circuit 83, in particular the first contact of the first secondary winding 85a and the last contact of the last secondary winding 85d.
  • a control unit 87 is finally provided for controlling said inverter circuits 82a-82d to convert the DC input voltage Udc into predetermined AC intermediate voltages Ual-Ua4.
  • each branch needs an isolated DC voltage, which is implemented by the primary inverter and the arrangement of primary transformers.
  • the embodiment described in Fig. 8 uses a common DC rail for all the inverter circuits 67a-67d.
  • the isolation is realized with the four transformers 83a-83d, which may have different turn ratios to address different output voltage steps.
  • the non- identical voltage steps can be realized.
  • the advantage here is that the system control is not obliged anymore taking care for a proper balancing of the loading of the different inverter stages. As these are coupled over a common DC supply, they will all have the same voltage, and differences in the individual load are balanced automatically.
  • one or more additional AC output terminals 88 coupled to interconnections between said series connection of AC intermediate voltages are provided. This enables, if needed, a further refinement of the output voltage Uout, if the output voltage is taken from one or more of the end terminals 86 or additional output terminals 88.
  • another control means is provided for controlling from which terminals the output voltage Uout is taken.
  • Fig. 9 shows a block diagram of an embodiment of a power supply circuit according to the present invention. It comprises a multi-level inverter apparatus 9 according to the present invention, e.g. as shown in Fig. 4 or 8, and an active filter circuit 3 coupled in series to the multi-level inverter apparatus 9. Further, a modulator 10 is coupled to the input of the multi-level inverter apparatus 9. A control loop is provided that receives the difference between the final output voltage Utot and the desired output voltage Uref and feeds the active filter 3, comprising a control element 31 and a linear amplifier 32, with a control signal, which leads to minimized difference between the two.
  • the multi-level inverter apparatus 9 which is similar to the multi-level inverter apparatus 8 shown in Fig. 8 comprises several inverter circuits 9a, 9b, 9c, 9d, each comprising, for example, a full bridge circuit (H-bride circuit) 11a, 1 Ib, l ie, 1 Id with a transformer 12.
  • a number of four inverter circuits 9a, 9b, 9c, 9d are shown, which are grouped in two pairs, i.e. the pair of inverter circuits 9a, 9b and the pair of inverter circuits 9c, 9d. In each pair the inverter circuits produce the same output voltage.
  • the first pair 9a, 9b produces a voltage quantity "5", which leads to five different output voltages for this pair, namely -10,-5, 0, 5, and 10, depending on the switching state of the individual inverter circuits 9a, 9b.
  • the inverter circuits produce a voltage quantity of only "1", leading to output voltages of -2, -1, 0, 1, and 2.
  • the modulator 10 maps the input voltage Uref to the appropriate switching states of the inverter apparatus 9, for example in the manner of a nearest sample method.
  • the desired input voltage (reference voltage) Uref ist a predetermined (analog or digital) voltage prescribing the desired form of the effective output voltage Utot.
  • the inverter circuits preferably each comprise two pairs of switching elements 13, 14, 15, 16 forming a H-bridge.
  • the switching elements 13, 14 and 15, 16 of each pair are coupled in series, and the pairs are coupled in parallel.
  • the switching elements 13-16 can preferably be switched on and off individually such that two serially coupled switching elements 13, 14 and 15, 16 are never in a switched on state at the same time and that at the output of the inverter circuit 11 a voltage UaI is zero, equal to the input voltage of the inverter, or equal to the input voltage multiplied by minus 1.
  • the active filter 3 is shown in the lower part of Fig. 9. It is effectively connected in series with the multi-level inverter apparatus 9. As such multi-level inverters 10 are typically voltage sources, the output impedance of the multi-level inverter 9 has little or even no influence on the effect of the active filter 3. It is therefore relatively easy to design a stable control function G(s) with a high gain to eliminate any differences in the effective output signal Utot.
  • the maximum voltage that has to be produced by the active filter 3 is exactly the quantization error of +/-4%, in the given exemplary configuration. This is widely not affected by the waveform of the output current and corresponds also to the power dimensioning and the potential losses of the presumably linear amplifier 32 in the active filter 3. It is now much easier to design a linear amplifier 32 for only 4% of the power level rather than 100%.
  • the power dimensioning of the active filter 3 may be even further reduced by increasing the number of different levels of the multi-level inverter apparatus 9, either by adding further digit level (e.g. 0.2, which multiplies the number of levels by 5) or by changing to a higher order numbering system, e.g. by adding one more full-bridge circuit per level and ending up with a radix of 7, producing 49 steps.
  • further digit level e.g. 0.2, which multiplies the number of levels by 5
  • a higher order numbering system e.g. by adding one more full-bridge circuit per level and ending up with a radix of 7, producing 49 steps.
  • the present invention is usable to provide an output voltage with low harmonic content. It is particularly useful to supply a field coil in a magnetic particle imaging apparatus, e.g. for use as a drive coil amplifier in a magnetic particle imaging apparatus where extremely high quality power signals are required in combination with a high flexibility in respect to the waveform within a defined frequency window.
  • the embodiment 200 of the MPI scanner shown in Fig. 11 has three prominent pairs 212, 214, 216 of coaxial parallel circular coils, each pair being arranged as illustrated in Fig. 11. These coil pairs 212, 214, 216 serve to generate the drive and, optionally, the focus fields.
  • the axes 218, 220, 222 of the three coil pairs 212, 214, 216 are mutually orthogonal and meet in a single point, designated the isocenter 224 of the MPI scanner 200.
  • the scanner 200 can be set to direct a predetermined, time dependent electric current through each of these coils 212, 214, 216, and in either direction (polarity). If the current flows clockwise around a coil when seen along this coil's axis, it will be taken as positive, otherwise as negative. To generate the static selection field, a constant positive current I s is made to flow through the z + -coil, and the current - I s is made to flow through the z -coil. The z-coil pair 216 then acts as an anti-parallel circular coil pair.
  • the magnetic selection field which is generally a gradient magnetic field is represented in Fig. 12 by the field lines 250. It has a substantially constant gradient in the direction of the (e.g. horizontal) z-axis 222 of the z-coil pair 216 generating the selection field and reaches the value zero in the isocenter 224 on this axis 222. Starting from this field- free point (not individually shown in Fig. 12), the field strength of the magnetic selection field 250 increases in all three spatial directions as the distance increases from the field-free point.
  • first sub-zone or region 252 which is denoted by a dashed line around the isocenter 224 the field strength is so small that the magnetization of particles present in that first sub- zone 252 is not saturated, whereas the magnetization of particles present in a second sub- zone 254 (outside the region 252) is in a state of saturation.
  • the field- free point or first sub- zone 252 of the scanner's field of view 228 is preferably a spatially coherent area; it may also be a punctiform area, a line or a flat area.
  • the magnetic field strength of the selection field is sufficiently strong to keep the magnetic particles in a state of saturation.
  • the (overall) magnetization in the field of view 228 changes.
  • magnetization information about the spatial distribution of the magnetic particles in the field of view 228 can be obtained.
  • further magnetic fields i.e. the magnetic drive field, and, if applicable, the magnetic focus field, are superposed to the selection field 250 in the field of view 228 or at least in a part of the field of view 228.
  • a time dependent current I°i is made to flow through both x-coils 212, a time dependent current I D 2 through both y-coils 214, and a time dependent current I D 3 through both z-coils 216.
  • each of the three coil pairs acts as a parallel circular coil pair.
  • a time dependent current I F i is made to flow through both x-coils 212, a current I F 2 through both y-coils 14, and a current I F 3 through both z-coils 216.
  • the embodiment 200 of the MPI scanner has at least one further pair, preferably three further pairs, of parallel circular coils, again oriented along the x-, y-, and z- axes.
  • These coil pairs which are not shown in Fig. 11, serve as receive coils.
  • the magnetic field generated by a constant current flowing through one of these receive coil pairs is spatially nearly homogeneous within the field of view and parallel to the axis of the respective coil pair.
  • the receive coils are supposed to be well decoupled.
  • the time dependent voltage induced in a receive coil is amplified and sampled by a receiver attached to this coil. More precisely, to cope with the enormous dynamic range of this signal, the receiver samples the difference between the received signal and a reference signal.
  • the transfer function of the receiver is non-zero from DC up to the point where the expected signal level drops below the noise level.
  • the embodiment 200 of the MPI scanner shown in Fig. 11 has a cylindrical bore 226 along the z-axis 222, i.e. along the axis of the selection field. All coils are placed outside this bore 226.
  • the patient (or object) to be imaged (or treated) is placed in the bore 226 such that the patient's volume of interest - that volume of the patient (or object) that shall be imaged (or treated) - is enclosed by the scanner's field of view 228 - that volume of the scanner whose contents the scanner can image.
  • the patient (or object) is, for instance, placed on a patient table.
  • the field of view 228 is a geometrically simple, isocentric volume in the interior of the bore 226, such as a cube, a ball, or a cylinder.
  • a cubical field of view 228 is illustrated in Fig. 11.
  • the patient's volume of interest is supposed to contain magnetic nanoparticles.
  • the magnetic particles are positioned in the volume of interest, e.g. by means of a liquid comprising the magnetic particles which is injected into the body of the patient (object) or otherwise administered, e.g. orally, to the patient.
  • An embodiment of magnetic particles comprises, for example, a spherical substrate, for example, of glass which is provided with a soft-magnetic layer which has a thickness of, for example, 5 nm and consists, for example, of an iron-nickel alloy (for example, Permalloy).
  • This layer may be covered, for example, by means of a coating layer which protects the particle against chemically and/or physically aggressive environments, e.g. acids.
  • the magnetic field strength of the magnetic selection field 250 required for the saturation of the magnetization of such particles is dependent on various parameters, e.g. the diameter of the particles, the used magnetic material for the magnetic layer and other parameters.
  • a magnetic field of approximately 800 A/m (corresponding approximately to a flux density of 1 mT) is then required, whereas in the case of a diameter of 100 ⁇ m a magnetic field of 80 A/m suffices.
  • Magnetic particles that can generally be used are available on the market under the trade name Resovist.
  • the data acquisition starts at time t s and ends at time t e .
  • the x-, y-, and z-coil pairs 212, 214, 216 generate a position- and time dependent magnetic field, the applied field. This is achieved by directing suitable currents through the coils.
  • the drive and focus fields push the selection field around such that the FFP moves along a preselected FFP trajectory that traces out the volume of scanning - a superset of the field of view.
  • the applied field orientates the magnetic nanoparticles in the patient.
  • the resulting magnetization changes too, though it responds nonlinearly to the applied field.
  • the sum of the changing applied field and the changing magnetization induces a time dependent voltage Vk across the terminals of receive coil pair along the Xk-axis.
  • the associated receiver converts this voltage to a signal Sk(t), which it samples and outputs.
  • Fig. 11 is, of course, only an example of such an MPI apparatus. Further embodiments are known and can be envisaged. As shown in the above embodiment the various magnetic fields can be generated by coils of the same coils pairs and by providing these coils with appropriately generated currents. However, and especially for the purpose of a signal interpretation with a higher signal to noise ratio, it may be advantageous when the temporally constant (or quasi constant) selection field and the temporally variable drive field and focus field are generated by separate coil pairs. Generally, coil pairs of the Helmholtz type can be used for these coils, which are generally known, e.g.
  • permanent magnets (not shown) can be used. In the space between two poles of such a selection field, permanent magnets (not shown) can be used. In the space between two poles of such a selection field, permanent magnets (not shown) can be used. In the space between two poles of such a selection field, permanent magnets (not shown) can be used. In the space between two poles of such a selection field, permanent magnets (not shown) can be used. In the space between two poles of such
  • Fig. 13 shows a general block diagram of an MPI apparatus 100 according to the present invention. The general principles of magnetic particle imaging and of magnetic resonance imaging explained above are valid and applicable to this embodiment as well, unless otherwise specified.
  • the embodiment of the apparatus 100 shown in Fig. 13 comprises a set of various coils for generating the desired magnetic fields. First, the coils and their functions in a MPI mode shall be explained.
  • selection means comprising a set of selection field (SF) coils 116, preferably comprising at least one pair of coil elements.
  • the selection means further comprises a selection field signal generator unit 110.
  • a separate generator subunit is provided for each coil element (or each pair of coil elements) of the set 116 of selection field coils.
  • Said selection field signal generator unit 110 comprises a controllable selection field current source 112 (generally including an amplifier) and a filter unit 114 which provide the respective section field coil element with the selection field current to individually set the gradient strength of the selection field in the desired direction.
  • a DC current is provided. If the selection field coil elements are arranged as opposed coils, e.g. on opposite sides of the field of view, the selection field currents of opposed coils are preferably oppositely oriented.
  • the selection field signal generator unit 110 is controlled by a control unit
  • the selection field current generation 110 which preferably controls the selection field current generation 110 such that the sum of the field strength and the sum of the gradient strength of all spatial fractions of the selection field is maintained at a predefined level.
  • the apparatus 100 further comprises focus means comprising a set of focus field (FF) coils, preferably comprising three pairs
  • focus means comprising a set of focus field (FF) coils, preferably comprising three pairs
  • Said magnetic focus field is generally used for changing the position in space of the region of action.
  • the focus field coils are controlled by a focus field signal generator unit 120, preferably comprising a separate focus field signal generation subunit for each coil element (or at least each pair of coil elements) of said set of focus field coils.
  • Said focus field signal generator unit 120 comprises a focus field current source 122 (preferably comprising a current amplifier) and a filter unit 124 for providing a focus field current to the respective coil of said subset of coils 126a, 126b, 126c which shall be used for generating the magnetic focus field.
  • the focus field current unit 120 is also controlled by the control unit 150.
  • the apparatus 100 further comprises drive means comprising a subset of drive field (DF) coils, preferably comprising three pairs 136a, 136b, 136c of oppositely arranged drive field coil elements.
  • the drive field coils are controlled by a drive field signal generator unit 130, preferably comprising a separate drive field signal generation subunit for each coil element (or at least each pair of coil elements) of said set of drive field coils.
  • Said drive field signal generator unit 130 comprises a drive field current source 132 (preferably including a current amplifier) and a filter unit 134 for providing a drive field current to the respective drive field coil.
  • the drive field current source 132 is adapted for generating an AC current and is also controlled by the control unit 150.
  • Said signal receiving unit 140 comprises a filter unit 142 for filtering the received detection signals.
  • the aim of this filtering is to separate measured values, which are caused by the magnetization in the examination area which is influenced by the change in position of the two part-regions (252, 254), from other, interfering signals.
  • the filter unit 142 may be designed for example such that signals which have temporal frequencies that are smaller than the temporal frequencies with which the receiving coil 148 is operated, or smaller than twice these temporal frequencies, do not pass the filter unit 142.
  • the signals are then transmitted via an amplifier unit 144 to an analog/digital converter 146 (ADC).
  • ADC analog/digital converter
  • the digitalized signals produced by the analog/digital converter 146 are fed to an image processing unit (also called reconstruction means) 152, which reconstructs the spatial distribution of the magnetic particles from these signals and the respective position which the first part-region 252 of the first magnetic field in the examination area assumed during receipt of the respective signal and which the image processing unit 152 obtains from the control unit 150.
  • the reconstructed spatial distribution of the magnetic particles is finally transmitted via the control means 150 to a computer 154, which displays it on a monitor 156.
  • a computer 154 which displays it on a monitor 156.
  • an input unit 158 is provided, for example a keyboard.
  • a user is therefore able to set the desired direction of the highest resolution and in turn receives the respective image of the region of action on the monitor 156. If the critical direction, in which the highest resolution is needed, deviates from the direction set first by the user, the user can still vary the direction manually in order to produce a further image with an improved imaging resolution.
  • This resolution improvement process can also be operated automatically by the control unit 150 and the computer 154.
  • the control unit 150 in this embodiment sets the gradient field in a first direction which is automatically estimated or set as start value by the user.
  • the direction of the gradient field is then varied stepwise until the resolution of the thereby received images, which are compared by the computer 154, is maximal, respectively not improved anymore.
  • the most critical direction can therefore be found respectively adapted automatically in order to receive the highest possible resolution.
  • the above described power supply circuits e.g. comprising a multi-level inverter apparatus as, for instance, shown in Figs. 4 or 8, can be used in such an MPI apparatus 100 as said drive field signal generator unit 130.
  • each single inverter circuit e.g. each single H-bridge module, is able to generate output voltages of level: -1, 0, +1.
  • Zero output voltage of each individual inverter or zero state may be realized by either turning on both low-side or both high-side switches of a single inverter circuit.
  • FIG. 10 shows four inverter circuits 9a, 9b, 9c, 9d each including a H-bridge (full bridge) circuit l la, 1 Ib, l ie, 1 Id connected in series by means of an isolating output transformer 12.
  • H-bridge full bridge circuit
  • a first embodiment for achieving equally distributed conducting losses in all the switches 13-16 employed in a full bridge circuit l la changes the path of freewheeling, i.e. when the output of the inverter is zero, synchronic to each period of the applied pulse pattern.
  • Fig. 14 shows a schematic diagram of a control circuit 20 for generate control signals for the switches 13-16 of a full bridge circuit l la.
  • "equally distributed conducting losses” means that the current distribution in the switches 13, 15, which are connected to +Udc, is equal to the current coverage in the switches 14, 16, which are connected to -Udc.
  • the control circuit 20 may be a separate element coupled between the modulator 10 and the inverters 9, but it may also be implemented within the modulator 10, e.g. in the form of software or dedicated hardware (e.g. EPLD).
  • Exemplarily two input control signals Cl, C2 are provided, e.g. by means of a microprocessor (not shown), in particular by means of the modulator 10.
  • the first input control signal Cl sets the output voltage Uout either to the positive or negative supply rail voltage.
  • the second input control signal C2 enables the output voltage Uout to be set.
  • the switching pattern for the switching control signals T13-T16 for controlling the switching of the switches 13-16 is generated with respect to the desired output voltage level and shape.
  • the control circuit 20 e.g. a programmable logic device (PLD), extracts the switching control signals T13-T16 to turn on and off each the power switches 13-16 of the full bridge circuit l la.
  • PLD programmable logic device
  • a freewheel control signal FWD is provided as input to the control circuit 20, e.g. by means of the above mentioned microprocessor (not shown), in particular by means of the modulator 10, which preferably generates said signal from the control signals Cl, C2. Said freewheel control signal FWD indicates whether the
  • said signals Cl, C2, FWD are determined in another superior unit (not shown), wherein said sequences are calculated in advance.
  • the modulator 10 or the above mentioned
  • Fig. 15 shows signal diagram of the inverter output voltage Uinv and the inverter output current Iinv. In the case shown, both the output voltage Uinv and current Iinv are in phase.
  • the currents 113, 114, 115, 116 in the switches 13-16 are shown in the lower part of Fig. 15. As it can be seen from the traces, the current distribution (over the first or second four half periods) is not equal in all the switches 13-16. leading to the disadvantage that the switches 13-16 are subjected to different stress.
  • Fig. 15 particularly shows the switching of the freewheeling path together with the resulting current distributions in the switches 13-16. As is shown, an identical current distribution is achieved in all switches 13-16. The switching of the freewheeling path is made in the zero crossing of the current Iinv.
  • the switching pattern will be varied in the control circuit 20 in such a manner that the currents in the switches 13-16 are identical over two periods.
  • Fig. 16 the inverter output voltage Uinv and the inverter output current Iinv are depicted with respect to the described switching scheme.
  • the average over two full periods of the current I in each individual switchl3-16 shows equal current coverage.
  • the switching manner shown enables a current load averaging over two half cycles.
  • Fig. 16 the switching of the freewheeling path is thus depicted together with the resulting current distributions in the switches 13-16. As is shown, an identical current distribution is achieved in all switches 13-16. The switching of the freewheeling path is made in the the first switching process of a half phase of the basic oscillation.
  • the averaging timer can be set over one, three or more half cycles by varying the FWD signal which controls the freewheeling.
  • FIG. 15 Another embodiment of a multi-level inverter apparatus, in which equal distributed conducting losses are achieved in all the switches 13-16 focuses on the synchronization of the freewheeling signal FWD.
  • the current and the first harmonic content of the output voltage Uinv is in phase with each other.
  • the change of the freewheeling path can be done according to a further improvement by changing the freewheeling path at the first switching instance after the current changes its sign. This is illustrated in the corresponding signals shown in Fig. 16.
  • the freewheeling signal FWD switches from high level to low level at an earlier moment in time with respect to the reference signal Uref.
  • the zero vector i.e. output voltage zero
  • the switching can selectively be made in the zero crossing of the current (as shown in Fig. 15) or at another moment. It is, however, important that the duration of the single freewheeling paths always n times ⁇ .
  • a special embodiment is shown in Fig. 16, since the switching of the freewheeling path is made with the first switching operation after the zero crossing.
  • Still another embodiment focuses on the condition, if not all full bridge inverters are operating. If a lower output voltage is required, exemplarily only one or two full bridge inverters of a set of a plurality of inverters are operated. The remaining inverters are turned into a zero state and the output of those inverters is zero. This is realized by turning on the switches T13 and T 15. Other combinations are possible also to set the output voltage actively to zero and thus to short-circuit the output. The switches, which short-circuit the output voltage, are changed to achieve the current load averaging over all switches in the inverters.
  • the freewheeling path will be changed in a full bridge inverter according to the above described embodiment.
  • the change of the freewheeling path will change synchronously with the zero crossing of the load current (as shown in Fig. 15) or synchronously with the first switching state after the change of the load current sign, (as shown in Fig. 16).
  • control method explained above with reference to Figs. 14 to 16 is does not require that a common DC input voltage is used and that the outputs of the inverter are coupled in series or in parallel via transformers. Further, it is also not required, that individual, isolated DC voltages are used and that the outputs of the inverters are coupled in series.
  • this control method may also be used in an embodiment of a multi-level inverter apparatus according to the present invention shown in Fig. 17, where two (or more) inverters 11a', 1 Ib' are arranged as a cascaded H-bridge inverter circuit.
  • each inverter 11a', 1 Ib' is provided at its own input terminals 61a', 61b' with its own DC input voltage Udcl ', Udc2'.
  • These DC input voltage Udcl', Udc2' can be equal or different and may be provided from a common voltage source or separate voltage sources, e.g. may be derived from a DC voltage supplied from a single voltage source.
  • the switching control signals for the various switches of the inverters 1 Ia', 1 Ib' are provided from the control unit 20 which derives them from the control signals Cl, C2 and FWD as explained above.
  • the current distribution in all switching elements is equal, wherein the average of the current in the switches of the inverters over one, two or more half periods of a periodic current signal is identical to achieve an equal load of the switches.
  • an inverter within a cascaded embodiment does not make a change of the output voltage, i.e. if the output voltage has the value zero over a longer period of time
  • said method provides that at predetermined moments in time a change of the switching states in the respective inverter is performed. Said change is done such that the desired value of the output voltage is maintained, but the load on the switches is equally distributed.
  • Tis can also be achieved with a cascaded embodiment of inverters, and the output voltage can also have the value zero over multiple periods.
  • this control method can be applied in various applications.
  • One application is in an MPI apparatus as explained above, but this control method can also be applied in an MRI apparatus or an X-ray apparatus.
  • the power supplied to the gradient coils of an MRI apparatus, or the power supplied to the cathode and/or a control grid of an X-ray apparatus can be generated as proposed according to the present invention.
  • the number of inverter circuits in the above described embodiments has been selected to be four. In principle, however, any number of modules may be chosen. Further, the transformers turns ratio can be freely selected as needed, i.e. they may or may not be equal.

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Abstract

La présente invention concerne un appareil inverseur multiniveau et un procédé d'inversion multiniveau pour convertir une tension d'entrée CC en une tension de sortie CA. L'appareil comprend une ou plusieurs paires de bornes d'entrée CC (61; 81; 61a', 61b') destinées à recevoir une ou plusieurs tensions d'entrée CC (Udc; Udc1', Udc2'), plusieurs circuits inverseurs (67a-67d; 82a-82d; 11a-11d; 11a', 11b'), couplés à une desdites bornes d'entrée CC, chacune recevant une tension d'entrée CC (Udc; Udc1', Udc2') ou une tension d'alimentation (Udc1-Udc4) dérivée de cette dernière et générant une tension intermédiaire CA (Ua1-Ua4), un moyen de connexion (83) couplé à ladite pluralité de circuits inverseurs (67a-67d; 82a-82d) pour relier les tensions intermédiaires CA en série, une paire de bornes de sortie CA (68; 86) couplée aux bornes d'extrémité de la connexion série de tensions intermédiaires CA (Ua1-Ua4), et un moyen de commande (69; 87; 10, 20) pour commander lesdits circuits inverseurs (67a-67d; 82a-82d; 11a-11d; 11a', 1b') afin de convertir la ou les tensions d'entrée CC (Udc; Udc1', Udc2') en tensions intermédiaires CA prédéfinies (Ua1-Ua4).
PCT/IB2010/053840 2009-08-31 2010-08-26 Appareil inverseur multiniveau et procédé d'inversion WO2011024137A1 (fr)

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WO2016075076A1 (fr) * 2014-11-11 2016-05-19 Koninklijke Philips N.V. Système d'amplificateur de gradient dans un système irm et procédé pour fournir du courant à l'aide de ce système
US9759789B2 (en) 2011-12-02 2017-09-12 Koninklijke Philips N.V. Coil arrangement for MPI
CN107205682A (zh) * 2014-12-29 2017-09-26 皇家飞利浦有限公司 线缆布置结构、线圈设备和用于影响和/或检测磁性粒子的设备
EP2506416A3 (fr) * 2011-03-30 2017-11-15 General Electric Company Système et procédé pour conversion de puissance
EP3266100A1 (fr) * 2014-12-16 2018-01-10 John Wood Coupleur de puissance
US9927466B2 (en) 2012-07-06 2018-03-27 General Electric Company System and method for controlling dynamic output impedance of an inverter
US10338172B2 (en) 2014-12-18 2019-07-02 Koninklijke Philips N.V. Power device and method for driving a load
WO2024028982A1 (fr) * 2022-08-02 2024-02-08 三菱電機株式会社 Dispositif de conversion de puissance

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