CN214337770U - Current transformer circuit with constant switching frequency and magnetic resonance tomography device - Google Patents

Current transformer circuit with constant switching frequency and magnetic resonance tomography device Download PDF

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Publication number
CN214337770U
CN214337770U CN202022095248.4U CN202022095248U CN214337770U CN 214337770 U CN214337770 U CN 214337770U CN 202022095248 U CN202022095248 U CN 202022095248U CN 214337770 U CN214337770 U CN 214337770U
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circuit
auxiliary
switching element
converter
converter circuit
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G.西格勒
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Siemens Healthcare GmbH
Siemens Healthineers AG
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Siemens Healthineers AG
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    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Dc-Dc Converters (AREA)

Abstract

A converter circuit (1) with a constant switching frequency has an input circuit (2) for obtaining an input signal, and an output circuit (3) for outputting an output signal. The main switching element (4) is arranged and configured for connecting the input circuit (2) with the energy source (5) or disconnecting the input circuit from the energy source. The auxiliary circuit (6) is connected to the input circuit (2) and to the output circuit (3). The auxiliary switching element (7) is arranged and configured for selectively connecting or disconnecting the auxiliary circuit (6) to or from the energy source (5). The control unit (8) is configured to switch the main switching element (4) currentless at a predetermined load-independent frequency and the auxiliary switching element (7) currentless at the frequency and at a load-dependent duty cycle. Furthermore, the invention relates to a magnetic resonance tomography apparatus with such a converter circuit.

Description

Current transformer circuit with constant switching frequency and magnetic resonance tomography device
Technical Field
The utility model relates to a converter circuit with constant switching frequency, which is provided with an input circuit for obtaining an input signal; an output circuit for outputting an output signal dependent on an input signal; and a main switching element arranged and configured for selectively connecting or disconnecting the input circuit to/from the electrical energy source. Furthermore, the invention relates to a magnetic resonance tomography apparatus with such a converter circuit.
Background
When using a device that utilizes a particular characteristic frequency, it may be desirable that the frequency not be disturbed by electrical circuitry, such as current transformer circuitry, in the vicinity of the device.
For example, in a shielded room (so-called magnet room) for performing examinations by means of magnetic resonance tomography MRI, current transformers, in particular direct current voltage converters (i.e., DC/DC converters), are used in order to provide a supply voltage or a supply current for the MRI apparatus or other electrical apparatuses. In this case, it may be particularly important that no interference or only slight interference is caused in the range of the reception frequency of the MRI device, i.e. in the larmor frequency range, since these interferences may have a negative effect on the examination.
For example, a frequency corresponding to a predetermined fundamental frequency in the range of several MHz or corresponding to a multiple of the fundamental frequency may remain unoccupied for a corresponding MRI reception frequency, so that a clock signal from a CPU, FPGA or switching converter having this frequency may be used without interfering with the reception of the MRI signal.
Therefore, switching converters or other converters with constant, unchanging switching frequency must be used in such applications.
Switching converters which are hard-switched, i.e. which operate switching elements during the current flow through them, are known from the prior art. Such a switching converter can be operated at a constant frequency and load fluctuations can be adjusted by pulse width modulation of the switching elements or switching transistors.
However, these hard-switching converters have the disadvantage of large switching losses, which can account for a large fraction of the total losses. This is especially true at relatively high switching frequencies of a few MHz. Furthermore, hard-switching converters (e.g., buck converters) have circuit nodes on which the voltage changes rapidly (i.e., high values of dU/dt occur), which may cause interference that only decreases slowly as the frequency becomes larger, i.e., at typical larmor frequencies of 63MHz (1.5T) or 123MHz (3T), significant interference may still be caused.
In addition to switching converters which perform hard switching, switching converters with resonant switching elements are also known from the prior art, in which switching elements can be switched flexibly, i.e. both without voltage and without current. At low load currents, known switching converters which perform voltage-free switching have high losses. In order to adjust the load fluctuations, known switching converters which perform currentless switching are operated at variable frequencies, which is, however, not acceptable in the application fields outlined above. Furthermore, such resonant switching converters generally provide only a very limited range for load regulation.
SUMMERY OF THE UTILITY MODEL
Against this background, the object of the present invention is therefore to provide an improved design for converting electrical signals in which it is not necessary to change the switching frequency in order to compensate for load fluctuations, and which at the same time leads to low switching losses, thus overcoming the disadvantages of the switching converters known from the prior art.
According to the utility model discloses, above-mentioned technical problem passes through the utility model discloses a corresponding theme is solved. Advantageous embodiments and preferred embodiments are the subject matter of the present invention.
The improved design is based on the following ideas: in addition to the main switching element, which is switched currentless at a predetermined frequency that is independent of the load, the auxiliary switching element is also switched currentless at the same frequency, but at a duty cycle that is dependent on the load, in order to be able to compensate for load variations.
According to a separate aspect of the improved design, a converter circuit, in particular a dc voltage converter, with a constant switching frequency is proposed. The converter circuit has an input circuit in order to obtain an input signal, in particular from an electrical energy source. The converter circuit has an output circuit for outputting an output signal dependent on the input signal. The converter circuit has a main switching element which is arranged and configured for optionally connecting or disconnecting the input circuit, and in particular the output circuit therefore, with or from the electrical energy source in order to in particular generate the output signal. The converter circuit has an auxiliary circuit connected with the input circuit and with the output circuit at a node of the converter circuit, and an auxiliary switching element arranged and configured for selectively connecting or disconnecting the auxiliary circuit with or from the energy source. The converter circuit has a control unit which is configured to switch the main switching element at a predetermined, in particular constant, load-independent frequency in a currentless manner and to switch the auxiliary switching element at the same predetermined load-independent frequency and at a load-dependent duty cycle in a currentless manner.
In particular, the term "converter" can be understood here to include electrical devices or electronic circuits for converting a fed voltage or a fed current from one type to another, i.e. from a direct current or a direct voltage to an alternating current or an alternating voltage or vice versa, respectively. The converter also comprises an electrical device or an electronic circuit for changing a characteristic electrical parameter, such as the voltage or the frequency of the fed voltage or the fed current.
In particular, the converter can be designed as a converter, a rectifier, an inverter or as a switching regulator or a switching converter, in particular as a dc voltage converter.
Accordingly, the input signal may be a direct voltage signal or a direct current signal (as in the case of a direct voltage converter, a switching regulator, a switching converter or an inverter) or an alternating voltage signal or an alternating current signal (as in the case of a converter and a rectifier). Accordingly, the output signal may be a direct voltage signal or a direct current signal (as in the case of a direct voltage converter, a switching regulator, a switching converter or a rectifier) or an alternating voltage signal or an alternating current signal (as in the case of a converter or an inverter).
Here and below, the circuits, i.e. the input circuit, the output circuit and the auxiliary circuit, can be understood as corresponding electrical or electronic circuits.
In particular, a node is a node of the converter circuit at which the output circuit and the input circuit are connected to each other.
In particular, the separation of (e.g. the input circuit or the auxiliary circuit) from the energy source may be understood as separating at least one electrical connection between a pole of the energy source and the respective circuit (i.e. the input circuit or the auxiliary circuit).
In particular, the energy source can be designed as a current source or as a voltage source.
Here and in the following, "currentless switching" may be understood as the operation of a corresponding switching element in order to switch it from an off state to an on state and vice versa, wherein the current flowing through the switching element is equal to zero or substantially zero during the switching process, in particular at the beginning of the switching process. This may be the case, for example, when the current crosses zero or during a time period in which the current flowing through the respective switching element is equal to zero or substantially zero.
A currentless switch may also be referred to as a Zero Current Switching (ZCS).
In particular, the converter circuit may be based on a resonant circuit or on an electrical oscillator, i.e. comprise such a resonant circuit or electrical oscillator.
The term "switching at a frequency" is understood to mean that the switching-on and switching-off processes of the respective switching element are carried out periodically, wherein the period duration for switching on and/or the period duration for switching off is given by the frequency.
Here, turning on corresponds to switching the respective switching element into an on-state, and turning off corresponds to switching the switching element into an off-state.
The input circuit is in particular connected to or disconnected from the energy source by switching the main switching element by means of the control unit. Correspondingly, the auxiliary circuit is disconnected from or connected to the energy source by switching the auxiliary switching element.
Here and below, "independent of the load" or "dependent on the load" may be understood as an amount that is independent of or dependent on the output signal and/or the further output signal and/or the load. For example, a resistance value or an impedance value of a load, which is located at an output of the output circuit and at which the output signal is output, may be understood as a quantity of the load.
The converter circuit may have a main circuit, for example, which contains or is formed by an input circuit and an output circuit.
According to an improved design, the main circuit or the input circuit generates the necessary current and voltage profiles, so that the main switching element and also the auxiliary switching element can be switched currentless.
By means of the load-dependent operation of the auxiliary circuit, i.e. by means of the load-dependent duty cycle with which the auxiliary switching element is switched, the output signal can be provided, in particular, at a higher power or output power, as a result of which fluctuations in the load or in the load current can be compensated without having to change the switching frequency of the switching element.
Since the frequency with which the main switching element and the auxiliary switching element are switched is load-independent and constant, i.e. in particular a converter circuit with a constant switching frequency is proposed, interference of further frequencies in the surroundings of the converter circuit can be avoided.
In addition, in the converter circuit according to the improved design, only very low or no switching losses are accumulated, since the auxiliary switching element and the main switching element are each switched currentless, i.e. in particular flexibly.
Thus, with a converter according to the improved design, the advantages of the known hard-switching device and the known switching frequency-dependent device can be combined without their respective disadvantages.
In particular, the control unit is configured to switch the main switching element with a duty cycle that is independent of the load.
Here and below, the ratio of the on-time to the period duration for switching the corresponding switching element can be understood as the duty cycle. The Duty Cycle may also be referred to as a modulation degree (austerergrad) or a Duty Cycle (Duty Cycle).
Accordingly, the duty cycle may in principle take a value from zero to one.
However, the load-independent duty cycle with which the main switching element is switched is in particular greater than zero. The load dependent duty cycle with which the auxiliary switching element is switched may be equal to zero or greater than zero.
According to at least one embodiment of the converter circuit according to the improved design, the input circuit is designed as a resonant circuit or as a circuit with resonant switching elements and/or as an oscillating circuit.
Accordingly, switching in the currentless state can be achieved by the corresponding current flowing through the input circuit automatically returning to zero.
According to at least one embodiment, the main switching element and/or the auxiliary switching element each comprise a transistor, in particular a power transistor, for example a bipolar transistor IGBT with an insulated gate electrode. This also applies correspondingly to the additional auxiliary switching elements which are optionally introduced below.
In particular, the control unit is connected to a control terminal, for example a gate terminal, of the transistor in order to apply a corresponding control signal to the transistor. The transistor can be switched to an on state or an off state in accordance with the control signal.
According to at least one embodiment, the input circuit and the output circuit are galvanically coupled or connected. In other words, the input circuit and the output circuit are not galvanically separated from each other. In particular, the converter circuit is not designed with a transformer which inductively couples the input circuit to the output circuit and which is galvanically separated from the input circuit and the output circuit.
This has the following advantages: it is not necessary to provide a transformer with a magnetic or ferromagnetic core, which may possibly enter saturation in the surroundings of the MRI device due to the high stray field strengths and thus may limit the functionality of the converter circuit.
According to at least one embodiment, in particular for switching the main switching element and the auxiliary switching element, the control unit is configured to disconnect the main switching element and the auxiliary switching element from the energy source simultaneously.
In other words, the control unit periodically turns on and off the auxiliary switching element and the main switching element, respectively, wherein the turning off of the auxiliary switching element is performed simultaneously with the turning off of the main switching element.
This may simplify the control of the switching element by the control unit.
In particular, the respective control signals for controlling the main switching element and the auxiliary switching element can be synchronized such that the mentioned turn-off time points or the respective falling signal edges coincide, respectively.
The input circuit specifies, for example by means of a resonance condition, when the current flowing through the main switching element is equal to zero. If this is the case, the control unit may for example switch off the main switching element. At this point in time, the current flowing through the auxiliary switching element is then also equal to zero, so that it is advantageous to switch both switching elements simultaneously.
Thereby, advantageously, there is no need to individually adjust the turn-off time point of the auxiliary switching element.
According to at least one embodiment, the control unit is configured for controlling or adjusting the turn-on point in time of the auxiliary switching element (i.e. the point in time at which the auxiliary switching element is connected to the energy source) in dependence on the load, in order to switch the auxiliary switching element with a duty cycle which is dependent on the load.
In particular, pulse width modulation can be used for load-dependent control or regulation of the auxiliary switching element.
In particular, the control or regulation of the auxiliary switching element can be carried out as a function of the output signal or of a further output signal.
By adjusting the on-time point of the auxiliary switching element, the occurring load variations can be compensated without having to change the frequency.
According to at least one embodiment, the input circuit comprises an inductive element, in particular a coil, and a capacitive element, in particular a capacitor. The node is arranged between the inductive element and the capacitive element. The auxiliary circuit is arranged between the node and the energy source.
In particular, the input circuit has an oscillating circuit with an inductive element and a capacitive element.
In particular, the resonant frequency of the circuit is greater than or equal to the frequency at which the main switching element is switched. Thus, for example, even at zero crossings of the current or, for example, in the case of using a diode in the input circuit, the switching of the main switching element can be carried out after a zero crossing or after a current value of zero has been reached. In particular, arranging the auxiliary circuit between the node and the energy source may be understood as an auxiliary circuit being connected with the node, and in particular being connectable with the energy source via an auxiliary switching element.
The resonant circuit is responsible for nulling the current flowing through the main switching element and thus also through the auxiliary switching element in order to achieve the condition for currentless switching.
According to at least one embodiment, the inductive element comprises an air coil.
The use of an air-core coil is advantageous because the ferromagnetic core can thus be omitted. Such a ferromagnetic core may for example go into saturation in the MRI stray field and no longer work as normally as required.
According to at least one embodiment, the auxiliary circuit has a rectifying element, for example a diode, which is connected in series with the auxiliary switching element.
The current through the auxiliary switching element can thus only assume one sign or equal to zero. Accordingly, the available duration during which the auxiliary switching element can be switched currentless is increased.
According to at least one embodiment, the input circuit has a rectifying element, for example a diode, which is connected in series with the main switching element.
According to at least one embodiment, the auxiliary circuit has an inductive auxiliary element, in particular by means of the control unit, which can be switched in parallel with the inductive element of the input circuit by means of the auxiliary switching element.
Thereby, when the duty cycle for switching the auxiliary switching element is larger than zero, further power may be provided by the inductive auxiliary element to be able to serve a higher load at the output of the output circuit.
According to at least one embodiment, the inductive auxiliary element comprises a coil, in particular an air coil.
According to at least one embodiment, the inductance of the inductive auxiliary element is different from the inductance of the inductive element of the input circuit and is, for example, smaller than the inductance of the inductive element of the input circuit.
According to at least one embodiment, the converter circuit has a further auxiliary circuit connected with the input circuit and the output circuit, and a further auxiliary switching element arranged and configured for optionally connecting the further auxiliary circuit with the energy source or disconnecting it from the energy source. The control unit is configured for currentless switching of the further auxiliary switching element at the frequency and at a further load-dependent duty cycle.
By using additional auxiliary circuits, a larger load range can be compensated or adjusted, or a coarse adjustment and a fine adjustment can be achieved.
According to at least one embodiment, the control unit is configured for simultaneously decoupling the main switching element and the further auxiliary switching element from the energy source.
According to at least one embodiment, the control unit is configured for controlling or adjusting the on-time point of the further auxiliary switching element in dependence on the load, in order to switch the further auxiliary switching element with a further load-dependent duty cycle.
According to at least one embodiment, the further auxiliary circuit has a further inductive auxiliary element which can be switched in parallel with the inductive switching element of the input circuit by means of a further auxiliary switching element.
In particular, the further inductive auxiliary element comprises a coil, for example an air coil.
Further embodiments of the converter circuit are obtained by further auxiliary circuits which are arranged between the energy source and the node in a manner similar to the auxiliary circuits and the further auxiliary circuits.
According to at least one embodiment, the converter circuit is designed as a dc voltage converter, in particular as a buck converter.
Such an embodiment is particularly suitable for application in a magnet room in which an MRI device is operated. Such magnet housings usually have shielding or filtering means for shielding the magnet housing magnetically or electromagnetically from the surroundings. If a relatively small voltage is required inside the magnet chamber and this voltage would be supplied directly through the shielding or filtering means, a relatively large loss would thus be created. It is therefore advantageous to conduct a relatively large voltage into the magnet chamber and to convert it to the required relatively small voltage inside the magnet chamber by means of a step-down converter.
According to a further independent aspect of the improved design, an MRI apparatus with an energy supply device is proposed, wherein the energy supply device comprises a converter circuit according to the improved design.
Thereby, interference of the frequency used for performing MRI, i.e. the receiving frequency of the MRI receiving coil, can be advantageously avoided. For this purpose, in particular, the switching frequency of the main switching element and the auxiliary switching element for switching the converter circuit is selected to be different from the reception frequency of the magnetic resonance tomography apparatus.
According to at least one embodiment, the frequency with which the main and auxiliary switching elements are switched is of the order of a few MHz, for example between 1MH and 5 MHz.
According to a further independent aspect of the improved design, it is proposed to use the converter circuit according to the improved design for the electrical energy supply of a device inside a shielded room, in particular an electromagnetically shielded room.
The improved design may be applied in a method for converting an electrical input signal into an electrical output signal. Here, the input signal is provided by an electrical energy source. In particular, the control unit connects or disconnects the input circuit, in particular the input circuit of the converter circuit, to or from the energy source at a predetermined frequency independent of the load without current. In particular, the control unit connects or disconnects the auxiliary circuit, in particular of the converter circuit, to or from the energy source at a predetermined frequency and with a duty cycle that is dependent on the load in a currentless manner. The output signal is output (in particular generated and output) as a function of the input signal by means of an output circuit, in particular an output circuit of a converter circuit.
In particular, the currentless switching of the main switching element makes it possible to connect or disconnect the input circuit to or from the energy source currentless.
In particular, the currentless switching of the auxiliary switching element enables the auxiliary circuit to be connected to the energy source or to be disconnected from the energy source.
Here, the auxiliary circuit and the input circuit may be separated from the energy source at the same time.
In particular, this is done periodically at a predetermined frequency.
In this case, it is conceivable to control or regulate, in particular by means of the control unit, the switch-on time point at which the auxiliary circuit is connected to the energy source in a load-dependent manner, in order to connect or disconnect the auxiliary circuit from the energy source with a load-dependent duty cycle.
According to at least one embodiment, the input signal is provided as an input dc voltage and the output signal is output as an output dc voltage, wherein in particular the output dc voltage has a smaller absolute value than the input dc voltage.
The features and feature combinations mentioned in the foregoing description and those mentioned in the following description of the drawings and/or shown in the drawings individually may be used not only in the respectively indicated combination but also in further combinations without departing from the scope of the invention. Embodiments and combinations of features not having all of the features of the invention originally developed and/or which exceed or deviate from the combinations of features set forth in the subsequent citations of the invention are also considered disclosed.
Drawings
The invention will be explained in more detail below on the basis of specific embodiments and associated schematic drawings. In the drawings, identical or functionally identical elements may have the same reference numeral. The description of identical or functionally identical elements does not have to be repeated, if necessary, with respect to different figures.
In the drawings:
fig. 1 shows a block diagram of an exemplary embodiment of a converter circuit according to an improved design;
fig. 2 shows a schematic diagram of a further exemplary embodiment of a converter circuit according to an improved design;
fig. 3 shows a schematic diagram of the signal profile in a further exemplary embodiment of a converter circuit according to an improved design; and
fig. 4 shows a schematic diagram of a converter circuit according to the improved design and the use of an MRI apparatus according to the improved design.
Detailed Description
A block diagram of an exemplary embodiment of a converter circuit 1 according to an improved design is shown in fig. 1. The converter circuit 1 can be designed, for example, as a dc voltage converter, in particular as a buck converter.
The converter circuit 1 has two input contacts 26, 26', between which a voltage source 5 can be connected, which can supply an input signal, in particular an input voltage V of the converter circuit 1E. The converter circuit 1 furthermore has two output contacts 27, 27', between which a load 9, in particular a load resistor, can be connected. During operation, an output voltage V which drops across the load 9 is present between the output contacts 27, 27A. Output voltage VARepresenting the output signal of the converter circuit 1.
The converter circuit 1 is configured for converting an input voltage VEConverted to an output voltage VA。
In particular, the converter circuit 1 is designed as a switching converter, also referred to as a switching regulator.
The converter circuit 1 has an input circuit 2 arranged between the input contacts 26, 26'. Furthermore, the converter circuit 1 has an output circuit 3 arranged between the output contacts 27, 27'. The input circuit 2 is connected, in particular galvanically connected, to the output circuit 3.
Accordingly, the input circuit 2 can obtain an input signal, i.e. an input voltage VEAnd the output circuit 3 can output an output signal, i.e., an output voltage VA。
Furthermore, the converter circuit 1 has a main switching element 4 which is arranged between the input circuit 2 and the first input contact 26 such that the input circuit 2 is disconnected from the voltage source 5 when the switching element 4 is open, i.e. when the switching element 4 is switched off, and the input circuit 2 is connected to the voltage source 5 when the main switching element 4 is closed, i.e. when the main switching element 4 is switched on.
In this case, the main switching element 4 can be designed in particular as a transistor, for example as an IGBT. Then, by applying a corresponding control voltage or a corresponding control signal to the control terminal or the gate terminal of the main switching element 4, opening and closing of the main switching element 4, or turning off and on of the main switching element is performed.
Furthermore, the converter circuit 1 has a control unit 8, which is configured to control the main switching element 4, i.e. in particular to open and close, i.e. to turn off and on, the main switching element. For this purpose, the control unit 8 is connected to the control connection of the main switching element 4 in order to apply a corresponding control signal.
Furthermore, the converter circuit 1 has an auxiliary circuit 6 connected to a node 14, wherein the input circuit 2 and the output circuit 3 are likewise connected to one another at the node 14. Furthermore, the converter circuit 1 has an auxiliary switching element 7, which is arranged between the auxiliary circuit 6 and the input contact 26.
The auxiliary switching element 7 can also be designed as a transistor, in particular as an IGBT, and can be controlled by the control unit 8 as described in connection with the main switching element.
According to the improved design, controlThe unit 8 is configured for being used for setting a predetermined voltage, in particular independently of the load 9 and the output voltage VAThe main switching element 4 is turned on and off, and the auxiliary switching element 7 is turned on and off at the same frequency.
Here, the on-time and the off-time are selected by the control unit 8 such that both the switching on and off of the main switching element 4 and the switching on and off of the auxiliary switching element 7 are performed, respectively, without current (i.e. at the time point when no current flows through the main switching element 4 or the auxiliary switching element 7).
The control unit 8 switches the main switching element 4, for example, with a constant duty cycle, in particular independently of the load. Conversely, the control unit 8 switches the auxiliary switching element 7 with a duty cycle that depends on the load. Here, the duty ratio depending on the load may have a value from 0 to 1.
By periodically switching the main switching element 4, a corresponding current and voltage profile is provided, which is necessary in order to be able to switch the auxiliary switching element 7 also in a currentless manner. The auxiliary switching element 7 then switches on the auxiliary circuit 6 in dependence on the load 9 in order to provide additional power at the output 27, 27'.
This makes it possible to use the frequency at which the switching elements 4, 7 are switched to remain constant and nevertheless to compensate for load fluctuations, in particular fluctuations in the load resistance, when switching is always carried out currentless.
Fig. 2 shows a schematic diagram of a further exemplary embodiment of a converter circuit 1 according to an improved design, which is based on the converter circuit 1 from fig. 1.
The converter circuit 1 of fig. 2 is designed as a buck converter.
In particular, the converter circuit 1 of fig. 2 is designed as a resonant circuit or as a resonant switching converter, also referred to as a switching converter with resonant components.
This means in particular that the input circuit 2 has an oscillating circuit, i.e. a coil 10 and a capacitor 15. Here, the coil 10 is arranged between the first input contact 26 and the node 14, and the capacitor 15 is arranged, for example, between the node 14 and the second input contact 26'. In this case, in particular, the second input contact 26 'can be connected directly to the second output contact 27'.
Furthermore, the input circuit 2 may have a diode 12, which is connected in series with the coil 10, for example, between the first input contact 26 and the node 14. For example, the anode of the diode 12 is coupled to the first input contact 26 and the cathode of the diode 12 is coupled to the coil 10.
In particular, the output circuit 3 has a coil 17 arranged between the node 14 and the first output contact 27, as well as a capacitor 18 and a diode 16. The diode 16 and the capacitor 18 are connected in parallel with each other and with the output contacts 27, 27'. For example, the anode of the diode 16 is coupled with the second input contact 26 'and with the second output contact 27', and the cathode of the diode 16 is coupled with the first input contact 27. The coil 17 of the output circuit 3 is arranged between the diode 16 and the capacitor 18, in particular between a first contact of the capacitor 18 and the cathode of the diode 16.
A signal diagram relating to the converter circuit 1 from fig. 2 is shown in fig. 3.
In this case, fig. a) shows a control signal S for controlling the main switching element 44The time course of (c). For example, at the main switch-on point in time t0The main switching element 4 is switched on and at the off-time t2The main switching element is turned off.
The current i flowing through the coil 10 of the input circuit 2 is shown in diagram d) of fig. 310Corresponding current trend. The resonance of the resonant circuit of the input circuit 2, i.e. in particular the resonance of the coil 10 and the capacitor 15, results in a current i10At the switch-off time t2Time or turn-off point in time t2Previously returned to 0 from itself, the current i10And also to the current flowing through the main switching element 4. The diode 12 ensures that the current flowing through the main switching element 4 at the off time t2Again remaining at zero.
The voltage U formed at the node 14 is shown in the diagram c)14I.e. in particular at node 14 with the second output contact 27' or the second input contactThe voltage between the points 26', i.e. in particular the voltage dropped across the capacitor 15 of the input circuit 2.
Voltage U14From the point of time t1(the time point is, for example, at time point t0Thereafter) rises, in particular until the voltage has assumed the input voltage VETwice the corresponding value.
As shown in fig. 2, the auxiliary circuit 6 likewise has a coil 11, which is arranged between the node 14 and the auxiliary switching element 7. The auxiliary circuit 6 also has, for example, a diode 13 connected in series with the coil 11 and having, for example, an anode coupled to the first input contact 26 and a cathode coupled to the coil 11.
The control signal S for controlling the auxiliary switching element 7 is shown in diagram b) of fig. 37. By the control unit 8, in particular at the auxiliary switch-on time t0' turn on the auxiliary switching element 7. In particular, at the main switch-on time t, due to the load 9, in particular the load resistance or the output voltage VA or the associated output current0And an auxiliary switch-on time t0There is an on-time difference Δ t between'.
In particular, depending on the duty cycle of the auxiliary switching element 7, the auxiliary turn-on point in time t0' may be located at the main switch-on time point t0Before or after.
As shown in the example of fig. 3, for example, it is possible to switch off at the same time t as the main switching element 42The auxiliary switching element 7 is turned off. Control can be simplified by simultaneous turn-off.
However, the turn-off time points of the main switching element 4 and the auxiliary switching element 7 are not necessarily made to coincide. In particular, a time window is provided for each of the two switching elements 4, 7, during which the switching element can be switched off without current. The time window for the main switching element 4 is, for example, the current i flowing through the coil 1010Point in time t becoming zero4Is started and at U14Lower than the input voltage VEAt a time point t5And (6) ending. Correspondingly, the time window for the auxiliary switching element 7 is the current i flowing through the coil 1111Point in time t becoming zero4' onFirst, and also at a point in time t5And (6) ending.
For example, the current profile i at the coil 11 and thus at the auxiliary switching element 7 is given11As it is shown in fig. e) of fig. 3. Current i11From the auxiliary switch-on point of time t0' rises and returns to zero before turning off the auxiliary switching element 7. In particular, i here10Whether or not in i11The preceding or following zero return depends on the inductance of the coils 10 and 11 and on the switch-on time t0、t0'。
At a time point t which may be, for example, at switch-off2After a time t3Voltage U14Eventually returning to zero as well.
By means of the described switching of the switching elements 4, 7, when no current flows through the switching elements 4, 7, for example at the switch-off time t2The switching element is turned off. On the one hand, the described operating principle results in a certain charge quantity flowing into the capacitor 18 of the output circuit 3 during each switching-on of the main switching element 4. By the described circuit of the auxiliary switching element 7, the fluctuations of the load current can be regulated without having to change the switching frequency. In particular, the input circuit 2 specifies a minimum load current and generates the voltage U required for currentless switching14The curved shape of (2). Correspondingly, the auxiliary switching element 7 is switched off simultaneously with the main switching element 4, so that the advantage of current-free switching is obtained.
Auxiliary turn-on time t when the load current increases0' for example, further forward, i.e. in particular to an earlier point in time, in order to transfer a higher charge amount through the coil 11 into the capacitor 18 per switching cycle. Thus, the fluctuating load current can be adjusted by varying the on-time of the auxiliary switching element 7 without losing the advantage of switching in the currentless state. In particular, switching off is performed in the currentless state and switching on is performed at a current rise speed limited to a moderate value due to the coil 11.
Optionally, the converter circuit 1 has a further auxiliary circuit 6 'comprising a coil 11' arranged between the node 14 and the first input contact 26. In this case, the converter circuit 1 also has a further auxiliary switching element 7 'and, for example, a further diode 13' which is arranged between the further auxiliary switching element 7 'and the further coil 11'.
The control unit 8 may generate a further control signal S7', in order to open or close the auxiliary switching element 7'.
The further auxiliary switching circuit 6' then operates in a manner similar to the described operation of the auxiliary switching circuit 6. Thereby, a larger regulation range for the load current can be achieved. With different inductances of the coils 11, 11', different auxiliary circuits 6, 6' can be designed for fine or coarse adjustment of the load current. In a similar manner, additional further auxiliary circuits may also be provided.
Furthermore, the converter circuit 1 according to the improved design has the following advantages: the converter circuit does not have a mesh with a rapidly changing current and also does not require a node with a voltage that rises particularly quickly. This is particularly advantageous in terms of high frequency EMC (electromagnetic compatibility) interference, which should be very small especially when used in the surroundings of MRI equipment.
The use of a converter circuit 1 according to a modified design is schematically shown in fig. 4.
An MRI device 21 is shown, for example, with a control device 22 or other electronics 22, which are arranged in the magnet room 20 like the MRI device 21. The magnet chamber 20 is electromagnetically shielded to a large extent by means of a shielding or filtering device 25, so that the alternating electromagnetic field generated by the MRI apparatus 21 is attenuated to a particularly great extent. A control or technical room 19 is located in the immediate surroundings of the magnet room 20, from which, for example, an MRI device 21 can be operated.
To operate, the device 22 and/or the MRI device 21 require a relatively low dc voltage. If this relatively low dc voltage is provided, for example, in the technical space 19 and is conducted directly through the shielding 25 into the magnet space 20, this can lead to high losses if necessary.
It is therefore advantageous to arrange the voltage source 5 in the technical room and to arrange the energy supply 23 with the converter circuit 1 according to the improved design in the magnet room 20. Thus, a relatively high dc voltage from the voltage source 5 can be provided as the input voltage V by means of the insulating sleeve 24 or the like of the converter circuit 1EFrom the converter circuit, the input voltage can be converted into a lower output voltage V as described aboveAAnd may then be provided to the device 22 and/or the MRI device 21.
By means of the load-independent constant frequency with which the converter circuit 1 is operated, it is possible to dispense with the frequency range used by the MRI device 21, in particular around the receiving frequency of the coil of the MRI device 21. As a result, disturbances which can possibly influence the function of the MRI device 21 as a result of the operation of the converter circuit 1 can be avoided.
According to the improved design, it is achieved, as described, that the converter circuit is operated at a constant, load-independent frequency for currentless switching and correspondingly low switching losses. For this purpose, the input circuit of the converter circuit is provided with one or more further phases, which may be referred to as auxiliary circuits, in order to regulate the load fluctuations, for example by changing the corresponding pulse width in accordance with PWM at a constant switching frequency.
In additional phases or auxiliary circuits, different inductance values of the corresponding coils may be used in order to cover different power ranges. It is therefore possible in particular for the input circuit to have a coil with a relatively high inductance in order to generate predominantly the temporal course of the current and voltage with low power, i.e. low output current, which is required for the other phases in order to be able to switch without current. The auxiliary circuit then has a coil with the same or a different inductance in order to cover a certain range of output current regulation. The further auxiliary circuit may have, for example, a coil with an inductance which is significantly smaller than the inductance of the input circuit, for example by a factor of ten, in order to allow a coarse adjustment even for high output currents.

Claims (11)

1. A converter circuit with constant switching frequency has
An input circuit (2) for obtaining an input signal;
an output circuit (3) for outputting an output signal dependent on the input signal; and
a main switching element (4) arranged and configured for selectively connecting or disconnecting the input circuit (2) with/from an electrical energy source (5),
it is characterized in that the preparation method is characterized in that,
an auxiliary circuit (6) connected at a node (14) with the input circuit (2) and with the output circuit (3);
an auxiliary switching element (7) arranged and configured for selectively connecting the auxiliary circuit (6) with the energy source (5) or disconnecting the auxiliary circuit from the energy source; and
a control unit (8) which is configured to switch the main switching element (4) at a predetermined load-independent frequency and to switch the auxiliary switching element (7) at the frequency and at a load-dependent duty cycle in a current-free manner.
2. The converter circuit with constant switching frequency of claim 1,
it is characterized in that the preparation method is characterized in that,
the control unit (8) is configured for simultaneously disconnecting the main switching element (4) and the auxiliary switching element (7) from the energy source (5).
3. The converter circuit with constant switching frequency of claim 1,
it is characterized in that the preparation method is characterized in that,
the control unit (8) is configured to control or adjust a switch-on time point of the auxiliary switching element (7) in dependence on the load, in order to switch the auxiliary switching element (7) with a duty cycle which is dependent on the load.
4. The converter circuit with constant switching frequency according to one of claims 1 to 3,
it is characterized in that the preparation method is characterized in that,
the input circuit (2) comprises an inductive element (10) and a capacitive element (15);
the node (14) is arranged between the inductive element (10) and the capacitive element (15); and
the auxiliary circuit (6) is arranged between the node (14) and the energy source (5).
5. The converter circuit with constant switching frequency of claim 4,
it is characterized in that the preparation method is characterized in that,
the auxiliary circuit (6) has an inductive auxiliary element (11) which can be switched in parallel with the inductive element (10) of the input circuit (2) by means of the auxiliary switching element (7).
6. The converter circuit with constant switching frequency according to one of claims 1 to 3,
it is characterized in that the preparation method is characterized in that,
the converter circuit (1) has a further auxiliary circuit (6') connected to the input circuit (2) and the output circuit (3), and a further auxiliary switching element (7') arranged and configured for selectively connecting the further auxiliary circuit (6') to the energy source (5) or disconnecting the further auxiliary circuit from the energy source; and
the control unit (8) is configured for currentless switching of the further auxiliary switching element (7') at the frequency and at a further load-dependent duty cycle.
7. The converter circuit with constant switching frequency of claim 6,
it is characterized in that the preparation method is characterized in that,
the further auxiliary circuit (6') is arranged between the node (14) and the energy source (5).
8. The converter circuit with constant switching frequency of claim 7,
it is characterized in that the preparation method is characterized in that,
the further auxiliary circuit (6') has a further inductive auxiliary element (11') which can be switched in parallel with the inductive element (10) of the input circuit (2) by means of the further auxiliary switching element (7 ').
9. The converter circuit with constant switching frequency according to one of claims 1 to 3,
it is characterized in that the preparation method is characterized in that,
the converter circuit (1) is designed as a DC voltage converter.
10. The converter circuit with constant switching frequency according to one of claims 1 to 3,
it is characterized in that the preparation method is characterized in that,
the converter circuit (1) is designed as a buck converter.
11. A magnetic resonance tomography apparatus has an energy supply device (23),
it is characterized in that the preparation method is characterized in that,
the energy supply device comprises a converter circuit (1) with a constant switching frequency according to any one of claims 1 to 10.
CN202022095248.4U 2019-09-25 2020-09-22 Current transformer circuit with constant switching frequency and magnetic resonance tomography device Active CN214337770U (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5663635A (en) * 1995-05-24 1997-09-02 Vlt Corporation Reverse energy transfer in zero-current switching power conversion
US8520413B2 (en) * 2011-08-17 2013-08-27 Mks Instruments, Inc. Adjustable resonant buck converter
WO2019170781A1 (en) * 2018-03-06 2019-09-12 Npc Tech Aps A resonant power converter

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