DE102016105897A1 - Apparatus and method for impressing an electric current - Google Patents

Abstract

It is a device for impressing an electric current on a current path, on which a DC potential (Vdc) is applied, disclosed. The device comprises: a first capacitor (10) and a second capacitor (20), the current path (PI) connecting the first capacitor (10) and the second capacitor (20); and generating means (30) configured to generate an AC injection voltage (Vac) at a switching frequency (f) between the first capacitor (10) and the second capacitor (20). The first capacitor (10) and the second capacitor (20) electrically disconnect the DC potential (Vdc) from the generating means (30) and capacitively impress the impressing AC voltage (Vac) on the current path (PI).

Description

The present invention relates to an apparatus and method for impressing an electric current, and more particularly to a capacitive power transfer for high current injection of direct current (DC) to a high DC potential.

background

The DC transmission at high DC potential is increasingly important. For example, with a DC transmission line, high power can be transmitted over long distances with relatively small losses. In addition, it is possible in DC transmissions to lay the cables underground, which can no longer be carried out at AC voltages above a certain voltage level at acceptable costs and / or losses.

In order to test devices for this application, there is a need to test and test the lines and / or the corresponding components and equipment at a high DC voltage potential with high current DC currents. In this case, the high-voltage potential can be, for example, up to ± 600 kV or more in terms of amount. For testing such lines should be energized, for example, with a current of up to 5000 A or even more. In order to permanently energize a line with such a high direct current potential at high direct current, a current source is required which can deliver high powers (for example in the three-digit kilowatt range) permanently.

In conventional solutions, current is supplied by means of an alternating current, which can be inductively coupled into the appropriate device under test (i.e., the component or line under test) by means of a high current transformer. At least a portion of the device under test may be a high voltage cable that forms a winding through the high current transformer, for example, for the inductive coupling.

However, such a coupling is not possible when using direct current.

Therefore, there is a need for alternative solutions to impart current to a current path (e.g., through the device under test) that is at DC potential.

Summary

The above object is achieved by an apparatus according to claim 1 and a method according to claim 14. The dependent claims relate to advantageous developments of the device according to claim 1 or the method according to claim 14.

The present invention relates to a device for impressing an electric current on a current path (or a load circuit), on which a DC potential is applied. The device comprises a first capacitor and a second capacitor, wherein the current path connects the first capacitor and the second capacitor. The apparatus further comprises a generating means configured to generate an impressing AC voltage having a switching frequency between the first capacitor and the second capacitor. The first capacitor and the second capacitor electrically separate the DC potential from the generating means and capacitively impress the impressed AC voltage on the current path. Optionally, a rectifier may also be present, which generates a DC current which is impressed on the current path (PI) from the impressing AC voltage.

For example, the first capacitor and the second capacitor each include a first terminal and a second terminal, wherein the two first terminals of the two capacitors are at the DC potential. The two second terminals of the two capacitors are, for example, connected to the generating device, for example, to ground potential, so that the impressed alternating voltage can be applied between the two second terminals. The two capacitors thus isolate and disconnect the DC potential, e.g. may be more than 100 kV, from the impressing AC voltage generating means, e.g. may be less than 20 kV.

The term "imprinting" (or impressing on) a voltage is to be understood as meaning that the corresponding voltage is transmitted to the current path, so that in addition to the direct voltage potential an added or impressed electrical voltage is added, so that the corresponding voltage value increases or reduced.

Embodiments of the present invention thus allow, in particular, a high-current injection at a DC potential of, for example, 600 kV (or in a range between 100 kV and 1000 kV), the impressed DC current having a current intensity of For example, 5000 A (or in a range between 1000 A and 8000 A) may have. The embossing can be effected, for example, by a voltage drop along the current path, wherein the voltage drop results from the resistance of the test object and can be, for example, 25 V (or in a range between 10 V and 100 V).

In order to achieve this, embodiments need in particular no isolation transformers or machine sets or generators located at high potential, which are used in conventional systems and would be very complicated and expensive. Embodiments also need no generator sets with insulating waves that would have to withstand high mechanical loads.

Embodiments solve the above-mentioned technical task instead by the fact that the power for DC excitation by means of high-frequency AC voltage via capacitors are transferred to the DC potential.

In further exemplary embodiments, the generating device comprises a DC voltage source for providing a first DC voltage and a converter device which generates a first AC voltage with the switching frequency from the first DC voltage. An advantage of the DC voltage source in combination with a converter is that a frequency and a voltage curve of the AC voltage can be flexibly selected or adapted to the specific circumstances.

In further embodiments, the DC voltage source comprises a connection to an AC supply voltage (for example a mains connection with, for example, 50 Hz or 60 Hz) and a rectifier, wherein the rectifier is designed to generate the first DC voltage from the AC supply voltage. An advantage of this approach is that the device can be connected to an existing normal supply voltage source, which is first rectified and then flexibly an AC voltage with the desired parameters can be generated.

In other embodiments, the mains connection can be controlled via a variable transformer, so as to control the amplitude of the mains voltage and thus the available power.

In further embodiments, the conversion device is designed to generate the first alternating voltage with an adjustable switching frequency and / or with an adjustable peak value for the alternating voltage and / or with an adjustable average current strength. For example, the converter is designed to adjust the switching frequency controllable. This can be done for example by the generation of rectangular pulses having an adjustable pulse width, and are generated at a predetermined repetition frequency. The rectangular pulses can only be positive voltage pulses or have positive and negative voltage pulses. Thus, it is possible to flexibly adjust the frequency of the AC voltage (e.g., the repetition frequency of the voltage pulses) and / or the transmitted power or the average current over the pulse width of the plurality of voltage pulses.

In further embodiments, the generating means further comprises a matching transformer configured to generate the impressing AC voltage by a voltage adjustment from the first AC voltage.

In further embodiments, the matching transformer has a center tap, so that the connection to both capacitors can be made symmetrical. Likewise, the matching transformer can be designed as autotransformer to make the solution cheaper.

In further embodiments, the conversion device comprises a plurality of converters and the matching transformer, a plurality of transformer units, wherein each one of the inverter together with one of the transformer units each form a Umrichtmodul. Each of the converter modules formed in this way can receive the first DC voltage in parallel and generate their own AC voltage, the own AC voltages being added together via serial interconnection in order to generate the first AC voltage. The resulting AC voltage can be adjusted with other transformers both directly in front of the capacitors and after the capacitors in the voltage level. Therefore, each inverter module provides a voltage share of the total AC voltage. Advantageously, however, each transformer unit can isolate the full voltage.

The modularization of the converters offers the advantage that relatively low voltages are present during the generation of the alternating voltage in the individual modules. Therefore, standard components can be used and no separate precautions for high voltage / high current protection are required.

In further embodiments, the generating means further comprises a compensation inductor for reducing a reactive power upon transfer of the impressing AC voltage to the current path. This will make it possible, the operate capacitive coupling together with the compensation reactor and the matching transformer in a resonant mode, so as to keep the reactive power as low as possible.

In further embodiments, the device further comprises (e.g., at DC potential) at least one high current transformer and at least one further rectifier. The at least one further rectifier is configured to rectify and generate a desired DC voltage drop along the current path based on the AC load voltage. A primary side of the high current transformer may be coupled between the first capacitor and the second capacitor and at the DC potential. The high current transformer may have a center tap to realize a symmetrical split. A secondary side of the high current transformer may couple to the further rectifier to adjust an AC level between the first capacitor and the second capacitor so as to achieve the desired DC voltage drop along the current paths.

By setting the DC voltage drop, it is possible to set the current to be impressed along the current path. For this purpose, the desired DC voltage drop can be adjusted as a function of a given resistance value along the current path so as to achieve a desired current flow through the current path.

In further embodiments, the apparatus further includes a plurality of current injection modules and optionally a plurality of matching transformers. Each of the embossment modules may include a high current transformer, another rectifier, two input terminals coupling to the primary side of the high current transformer, and two output terminals. The plurality of current injection modules may be serially connected with their respective input terminals between the first capacitor and the second capacitor on the high voltage side or behind a matching transformer connected between both capacitors and connected in parallel with the current path with their respective two output terminals. The modularization of the current injection has the advantage that relatively low voltages and currents are present during the generation of the desired DC voltage drop in the individual modules. Therefore, standard components can be used and there are no separate precautions for the high voltage / high current protection required (for example, increased copper use, higher insulation voltage, etc.).

In further embodiments, the switching frequency and / or a capacitance of the first and / or the second capacitor and / or an inductance of the compensation inductor and / or the matching transformer is selected to minimize (or at least minimize) reactive power during energy transfer from the AC supply voltage to the current path to reduce).

In further embodiments, the capacitance of the first capacitor and / or the capacitance of the second capacitor and / or the inductance in dependence on the switching frequency is / are selected such that the impressed AC voltage is less than a predetermined proportion (eg 50% or 10%) of the DC potential is. This restriction is intended to ensure that the rated voltage value of the DC voltage remains substantially the same, for example, because a device under test with a certain rated voltage value is to be tested.

In further embodiments, the first capacitor and / or the second capacitor each comprise parallel and / or series-connected capacitors. Resistors may be provided in parallel and / or in series with the capacitors (eg for potential control). An advantage of this approach is that standard components can be used and thus can be worked cost-effectively. Furthermore, in further embodiments, one or more resistors can be connected in parallel with the series-connected capacitors. An advantage of this procedure is that a voltage drop across the capacitors is distributed accordingly, so that the high-voltage potential is divided symmetrically across all capacitors and thus all components are charged equally.

In further embodiments, the at least one further rectifier comprises a synchronous rectifier. In this type of rectifier, no components are used which inherently allow current to flow in only one direction (eg, diodes). Instead, for example, field-effect transistors (for example MOS-FETs) are used, which are controlled by drive electronics in such a way that they act like a semiconductor diode with a very low forward voltage. This method has the advantage that lower heat losses in the rectifier arise at DC potential and, if necessary, can be dispensed with cooling units.

The present invention also relates to a method for impressing an electric current on a current path on which a DC potential is applied. The method comprises the following steps: generating an impressing alternating voltage with a switching frequency in one Circuit portion that is electrically isolated from the DC potential (eg, ground potential) and capacitive transfer of the impressed AC voltage to the current path. For example, a direct connection of the impressing AC voltage on the current path can take place.

In further embodiments, the method also includes rectifying the capacitive impressed AC voltage so as to form a desired DC voltage drop on the current path.

Advantages of the embodiments are that a very compact and lightweight construction is possible. Since no novel components or techniques are required, a very favorable power transmission is possible. In addition, the high voltage capacitors decouple the DC potential (eg, high voltage) from the components that produce the AC component.

In the context of the present invention, the terms "connect" and "switch" should refer in particular to electrical connections and electrical interconnections and be restrictive only insofar as a current path can be formed between the connected / connected components (if corresponding voltages are present). An electrical connection does not necessarily have to include a direct electrical connection. Therefore, in the context of the present invention, an electrical connection is to be understood to mean the formation of a current path which allows a flow or a movement (for example in the case of alternating currents) of electric charge carriers between the components. The term "couple" should be interpreted to include any connection through which energy can be transported (including wireless).

Brief description of the figures

The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the different embodiments, which should not be construed as limiting the disclosure to the specific embodiments, but for explanation and understanding only.

1 shows a schematic representation of the device according to an embodiment of the present invention.

2 shows further details of the device according to further embodiments.

3 shows an exemplary alternating voltage curve which can be generated according to embodiments of the generating device.

4 FIG. 10 is a flowchart of a method of applying an electric current according to embodiments of the present invention. FIG.

Detailed description

1 shows a device which is adapted to impose an electric current on a current path on which a DC potential Vdc is applied. The device comprises: a first capacitor 10 and a second capacitor 20 , where the current path PI is the first capacitor 10 and the second capacitor 20 combines. The device also comprises a generating device 30 , which is designed to be an impressed AC voltage Vac with a switching frequency f between the first capacitor 10 and the second capacitor 20 to create. The first capacitor 10 and the second capacitor 20 disconnect the DC potential Vdc from the generator 30 electrically from each other and impress the imprinting AC voltage Vac capacitively on the current path PI, wherein along the current path PI other components such as a rectifier may be present.

Optionally, the following further components can be formed in the device: a power rectifier with converter for a frequency range for the impressing alternating voltage between 20 kHz and 200 kHz (or between 5 kHz and 1000 kHz), a compensation coil and a high-current transformer, which can comprise a synchronous rectifier.

2 shows an embodiment of a possible interconnection of the other optional components. In the embodiment shown, the first capacitor separates 10 and the second capacitor 20 a low voltage side from a high voltage side, wherein the high voltage side in the illustrated embodiment of 2 on the right side of the line 400 and the low voltage side is on the left side of the line 300 located. For example, the low voltage side may be at a ground potential (ground), while the high voltage side may be at more than 1000V.

On the low voltage side 300 is the generating device 30 for generating a Einprägenwechselspannung Vac through the dashed box and is represented by a supply AC voltage connection 311 for example, supplied with a mains voltage. The device 30 includes a rectifier 315 , a conversion device 320 , a matching transformer 340 and a choke coil 350 ,

The rectifier 315 includes two connectors connected to the AC supply voltage connection 311 are connected, and is adapted to generate from the AC supply voltage, a first DC voltage Vdc1. Thus, the rectifier provides 315 together with the connected AC voltage source, a DC voltage source 310 Optionally, the rectifier 315 also make an adjustment of the voltage value for the first DC voltage Vdc1.

At the output of the rectifier 315 is the inverter device 320 arranged, which receives the first DC voltage Vdc1 and generates therefrom the first AC voltage Vac1. For example, the inverter device 320 generate a first AC voltage Vac1 with a frequency between 20 kHz and 200 kHz, wherein the first AC voltage Vac1 can represent, for example, a rectangular pulse train. Optionally, the inverter device 320 a plurality of field effect transistors or IGBT full bridges, which are used to generate the desired first AC voltage Vac1.

At the output of the inverter 320 is the matching transformer 340 arranged. The matching transformer 340 includes, for example, a primary coil and a secondary coil, wherein the primary coil through the inverter 320 generated first AC voltage Vac1 receives. The secondary side of the matching transformer 340 is between the first capacitor 10 and the second capacitor 20 connected. For example, a center contact of the secondary coil of the matching transformer 340 be placed on a ground potential. Optional is also a choke coil 350 formed along the current path of the first capacitor 10 to the secondary coil of the matching transformer 340 towards the second capacitor 20 can be switched.

On the high voltage side 400 is between the current path PI and the first capacitor 10 and the second capacitor 20 a high current transformer 40 and another rectifier 50 (For example, a synchronous rectifier) is formed.

The high current transformer 40 again comprises a secondary coil and a primary coil, the primary coil between the first capacitor 10 and the second capacitor 20 is formed, and opposite to the coupling of the matching transformer 340 , The secondary coil of the high current transformer 40 generates a second AC voltage Vac2 from the AC signal, which is between the first capacitor 10 and the second capacitor 20 is applied and outputs the second AC voltage Vac2 to the other rectifier 50 further.

The further rectifier 50 is designed to generate from the second AC voltage Vac2 a DC voltage drop ΔVdc along the current path PI. Optionally, it is also possible that the additional rectifier 50 is a synchronous rectifier, which offers the advantage that less heat is generated compared to other conventional rectifier devices.

Optionally, it is possible that the high current transformer 40 and the other rectifier 50 are formed several times. For example, on the high voltage side 400 a plurality of Einprägemodulen be serially formed between the first capacitor 10 and the second capacitor 20 are switched. Each of the plurality of embossing modules includes, for example, a high current transformer unit 40 and another rectifier unit 50 and impresses a DC component on the current path PI. This makes it possible for each of the plurality of imprint modules to generate a comparatively small current (eg less than 100 A) and that the superimposition of all the currents generated by the impressing module leads to the entire current which is to be impressed on the current path PI (which for example has more than 1000 A). Thus, the plurality of Einprägemodulen can be formed parallel to the current path PI.

It is also possible that the Umrichteinrichtung 320 includes a plurality of inverters, each to a primary coil of the matching transformer 340 couple. An advantage, in turn, is that the voltages generated are smaller for each inverter than for just one inverter 320 , because only on the secondary side of the matching transformer or the matching transformers 340 the voltages generated are added together and add up to the total voltage drop Vac.

3 shows an exemplary voltage waveform for the first AC voltage Vac1 passing through the one or more inverter devices 320 is produced. For example, the first AC voltage Vac1 can be generated as a pulse train as described in US Pat 3 you can see. Positive voltage pulses with a voltage peak value Vr follow negative voltage pulses with a negative voltage peak value -Vr, followed by a positive voltage pulse. For example, a first voltage pulse P1 is generated at time t1 and has a Pulse width t2 - t1. There is no voltage output between the second time t2 and the third time t3 (ie, the ground potential is applied, for example). At time t3, a negative voltage pulse P2 is generated with a negative voltage peak -Vr, which stops until time t4. No voltage value is output between time t4 and t5, and at time t5 a positive voltage pulse P3 is again generated, which stops until time t6. Optionally, it is also possible that alternately positive and negative voltage pulses are generated, but that only positive voltage pulses are generated. The pulse widths (t2 - t1 or t4 - t3 or t6 - t5) are, for example, by the inverter 320 specifically adjustable. The frequency refers to the inverse time between two pulses (eg t3 - t1 or t5 - t3 or t5 - t1) and can also be adjustable. For example, the transmitted power or the forwarded current intensity can be regulated over the pulse widths. Optionally, it is also possible that the amplitude of the pulses is regulated to control the transmitted power. Optionally, other pulse shapes are conceivable in addition to rectangular pulses. For example, sinusoidal waveforms can be generated by overlapping pulses.

4 shows a flowchart of a method for impressing an electric current on a current path, which is applied to a DC potential. The method comprises the steps of generating S110 an impressed AC voltage Vac at a switching frequency f in a circuit portion (eg, the low voltage range 300 from the 2 ) electrically isolated from the DC potential Vdc; and capacitively transmitting S120 the impressed AC voltage Vac to the DC potential Vdc on the current path PI. A rectifier can optionally be used to impress a direct current on the current path PI.

In further embodiments, the functions described above with the device are implemented as further optional method steps in the method.

Aspects of the present invention may be summarized as follows:
Embodiments may be used to test components or components that are at a very high DC potential (where a high DC potential is, for example, 500 kV), with the DC components completely decoupled by capacitors. If the power is transmitted at very high frequencies (eg 20 kHz to 200 kHz), despite a possibly small capacitance of the coupling capacitors 10 . 20 (For example, less than 10 nF or in a range of 0.5 nF to 100 nF) and very high power - compared to the DC potential only small AC components of the coupling capacitors 10 . 20 , There is therefore no significant dielectric stress on the capacitors due to the impressed AC voltage. To minimize the losses of these components, a compensation reactor 350 to be built in. The compensation choke forms with the capacitors 10 . 20 an electrical resonant circuit. For example, arise in the case of resonance in the circle relatively low ohmic transmission losses. Only the very low dielectric losses in the capacitors and the ohmic losses in the lines and the coil reduce the efficiency of the circuit. The majority of the power is thereby converted into the current path PI.

The switching frequency of the inverter 320 For example, it is possible to set such that the sum capacity of the two coupling capacitors 10 . 20 from the coil 350 be compensated. The capacity of the capacitors 10 . 20 For example, it can be chosen so that at the set frequency and the current required to transmit the power, the AC component is less than 10% of the DC component. The useful AC voltage is for example in a range of 10 kV at a frequency of about 50 kHz and a current of about 13 A. This results in 10 nF as the capacitance for the coupling capacitors, a peak value of the AC component of about 5.8 kV, ie about 1 % of DC component.

As coupling capacitors 10 . 20 For example, polypropylene foil capacitors connected in series can be used which have a dielectric strength of up to 1.2 kV and each have a separate DC resistance of approximately 2 MOhm for voltage division and discharge.

The inverter 320 may also have a fixed frequency, which may be adjustable or even works in resonance mode. The former offers the advantage that in the event of a fault (for example due to destruction of components in the electrical oscillating circuit), the power output drops. However, this approach is unsuitable for the use of highly voltage- and / or temperature-dependent capacitors, such as ceramic capacitors. In this case, the frequency may need to be adjusted to change the capacitance and inductance of the components.

In further embodiments it is possible to increase the power up to 30 (or more) smaller inverters 321 . 322 , ..., where each inverter has its own matching transformer 341 . 342 , ..., which provides a secondary example of 1/30 of the voltage, but can isolate the full voltage. This means that all secondary windings can be connected in series, which ensures an exact distribution of the power across all inverters.

Likewise, the secondary Stromeinprägung example, by 100 Single modules take place, which in turn can be primarily connected in series and are connected in parallel on the high-current side in order to obtain the same current distribution.

To the waste heat in the high current modules 40 . 50 To reduce, a synchronous rectifier may be formed with field effect transistors (eg MOSFETs). The exemplary MOSFETs operate from about 8 V secondary voltages. At very low voltages (and thus also small currents) the rectifier works 50 via the specially provided parallel diodes of the MOSFETs passive.

A critical component in the power transmission chain is the capacitors 10 . 20 , These capacitors 10 . 20 are loaded on the one hand with a high DC voltage, as well as a very small, high-frequency (<10%) AC voltage and also exposed to a very high alternating current high frequency. For this reason, the thermal losses in the lines of the capacitors dominate 10 . 20 , The dielectric losses are low. The load on the capacitors 10 . 20 depends on the DC component, the alternating current and the frequency of the alternating current. The amount of AC voltage that is transferred plays for the load on the capacitors 10 . 20 only a minor role, because of the capacitors 10 . 20 only the part due to the current and impedance drops. In order to reduce the current through the capacitors, however, an increased voltage level is preferred for the impressed alternating voltage (eg 10 kV at 15 A for the transmission of 150 kVA power).

The device can also be used according to embodiments for the following parameters. The DC potential may be, for example, 60 kV (or between 5 kV and 200 kV). The AC current can be effectively 10 A (or between 1 A and 50 A). For example, at the output of the high-voltage side, 18 V may be present at 45 A. The overall efficiency is about 85%, without the losses in the high voltage circuit due to possibly built-in control resistors.

The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention either individually or in any combination.

LIST OF REFERENCE NUMBERS

10

first capacitor

20

second capacitor

30

generator

40

High Voltage Transformer

50

another rectifier

310

DC voltage source

311

AC supply voltage

315

rectifier

320

Umrichteinrichtung

340

matching transformer

350

Shunt Reactors

Vdc

DC potential

Vdc1

first DC voltage

Vac

Aufprägewechselspannung

Vac1

first alternating voltage

ΔVdc

impressed voltage drop

Vr

Voltage peak

f

switching frequency

PI

current path

Claims (15)

Device for impressing an electric current on a current path (PI) on which a DC potential (Vdc) is applied, comprising: a first capacitor (PI) 10 ) and a second capacitor ( 20 ), where the current path (PI) is the first capacitor (PI) 10 ) and the second capacitor ( 20 ) connects; and a generating device ( 30 ) which is designed to generate an impressing alternating voltage (Vac) with a switching frequency (f) between the first capacitor ( 10 ) and the second capacitor ( 20 ), the first capacitor ( 10 ) and the second capacitor ( 20 ) the DC potential (Vdc) from the generator ( 30 ) electrically and transfer the impressed AC voltage (Vac) capacitively. Apparatus according to claim 1, wherein the generating means ( 30 ) Comprises: a DC voltage source ( 310 ) for providing a first DC voltage (Vdc1); and a conversion device ( 320 ) for generating a first AC voltage (Vac1) with the switching frequency (f) from the first DC voltage (Vdc1). Apparatus according to claim 2, wherein the DC voltage source ( 310 ) a connection ( 311 ) to an AC supply voltage and a rectifier ( 315 ), wherein the rectifier ( 315 ) is configured to generate the first DC voltage (Vdc1) from the AC supply voltage. Apparatus according to claim 2 or claim 3, wherein the conversion device ( 320 ) is formed to the first AC voltage (Vac1) with a adjustable switching frequency (f) and / or with an adjustable peak value (Vr) for the voltage and / or with an adjustable average current to produce. Apparatus according to claim 4, wherein said generating means ( 30 ) further a matching transformer ( 340 ) adapted to generate the impressing AC voltage (Vac) by a voltage adjustment from the first AC voltage (Vac1). Apparatus according to claim 5, wherein the conversion device ( 320 ) a large number of converters ( 331 . 332 , ...) and the matching transformer ( 340 ) a plurality of transformer units ( 341 . 342 , ...), whereby in each case one of the converters ( 331 . 332 , ...) together with one of the transformer units ( 341 . 342 , ...) each form a Umrichtmodul, and wherein each of the Umrichtmodule thus formed receive the first DC voltage (Vdc1) and each generate their own AC voltage to generate by serial addition of their own AC voltages, the first AC voltage (Vac1). Device according to one of the preceding claims, wherein the generating device ( 30 ) a compensation choke ( 350 ) to reduce a reactive power in a transmission of the impressed AC voltage (Vac) on the current path (PI). Device according to one of the preceding claims, further comprising at least one high-current transformer ( 40 ) and at least one further rectifier ( 50 ), wherein the at least one further rectifier ( 50 ) is configured to generate a desired DC voltage drop (ΔVdc) along the current path (PI) based on the impressed AC voltage (Vac), and wherein a primary side of the at least one high current transformer (Vac) 40 ) between the first capacitor ( 10 ) and the second capacitor ( 20 ) and is at the DC potential (Vdc) and a secondary side of the at least one high-current transformer ( 40 ) to the further rectifier ( 50 ) is coupled to an AC level between the first capacitor ( 10 ) and the second capacitor ( 20 ) to achieve the desired DC voltage drop (ΔVdc) along the current paths (PI). Apparatus according to claim 8, wherein the at least one further rectifier ( 50 ) comprises a synchronous rectifier. Apparatus according to claim 8 or claim 9, comprising a plurality of current impressing modules, each of the embossing modules comprising a high current transformer (10). 40 ), which is at the DC potential (Vdc), another rectifier ( 50 ), two input terminals connected to the primary side of the high current transformer ( 40 ), and having two output terminals, and the plurality of current injection modules connected in series with their respective input terminals between the first capacitor (12) and 10 ) and the second capacitor ( 20 ) and their respective two output terminals are connected in parallel with the current path (PI). Device according to one of the preceding claims, wherein the switching frequency (f) and / or a capacitance of the first and / or the second capacitor ( 10 . 20 ) and / or an inductance of the compensation reactor ( 350 ) and / or the matching transformer ( 340 ) are selected to minimize reactive power in energy transfer from the AC supply voltage to the current path (PI) and / or to produce a desired current along the current path (PI). Device according to one of the preceding claims, wherein the capacitance of the first capacitor ( 10 ), the capacity of the second capacitor ( 20 ) and the inductance (L) are selected as a function of the switching frequency (f), so that the impressing AC voltage (Vac) is less than a predetermined proportion of the DC potential (Vdc). Device according to one of the preceding claims, wherein the first capacitor ( 10 ) and / or the second capacitor ( 20 ) in each case in series and / or parallel-connected capacitors.  Method for applying an electric current to a current path (PI) on which a direct voltage potential (Vdc) is applied, comprising the following steps: Generating (S110) an impressed AC voltage (Vac) having a switching frequency (f) in a circuit portion electrically disconnected from the DC potential (Vdc); and capacitively transmitting (S120) the impressed AC voltage (Vac) to the DC potential (Vdc) on the current path (PI).  The method of claim 14, further comprising rectifying the capacitive impressed AC voltage (Vac) so as to form a desired DC voltage drop (ΔVdc) on the current path (PI).

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