WO2013189525A1

WO2013189525A1 - High-voltage direct current transmission comprising a plurality of taps

Info

Publication number: WO2013189525A1
Application number: PCT/EP2012/061729
Authority: WO
Inventors: Hans-Joachim Knaak
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-06-19
Filing date: 2012-06-19
Publication date: 2013-12-27
Also published as: EP2850713A1

Abstract

The invention relates to a serial and a parallel tapping for a high-voltage direct current transmission path, such that electrical power can be provided to an alternating current network along the high-voltage direct current transmission line or electrical power can be fed into the high-voltage direct current transmission path from the alternating current network. Thus it is possible to take power from or feed power into the high-voltage direct current transmission path in a flexible manner. Voltage compensation may take place simultaneously. In particular a longitudinal voltage which is favourable for the high-voltage direct current transmission path can be flexibly coupled in.

Description

description

HIGH VOLTAGE DC TRANSMISSION WITH SEVERAL

taps

The invention relates to a high-voltage direct-current transmission line (HVDC link), a device for an HVDC link, and a method for transferring electrical power from or to an HVDC link.

If energy is transmitted by means of three-phase current, it is relatively easy to decouple or couple energy along the transmission path by means of a transformer. This is especially inte ^¬ esting when long-distance transmissions pass through sparsely populated, less developed area and ei ^¬ ne supply from the long-distance transmission to be provided there punctually.

In contrast, has a high-voltage DC transmission ^¬ distance (hereinafter also referred to as "DC About ^¬ transmission" or "DC transmission") have the disadvantage that extending or couplings of electrical energy are relatively complex on the track. This is especially true for electrical services that are low in terms of transmitted power.

A branch from the DC transmission or a tapping of the same is also referred to as "tapping". Hereinafter, the term tapping is used synonymously with the term tapping.

In a so-called serial tapping a tapping device is arranged in a line branch, the tapping device (in particular the power electronics) is traversed by the entire main stream of the transmission line.

On the other hand, in a so-called parallel tapping, the tapping device is connected, for example, to both lines of the transmission path, ie parallel to the source or Valley arranged. In this case, the tapping device must be designed for the entire voltage of the transmission ^link . For high-voltage direct current (HVDC) transmission, so-called modular multilevel inverters (MMC: modular multi-level converters) are increasingly being used, the basic building block of which is usually a so-called half bridge of IGBTs and diodes. This basic module is also called a submodule (also: converter module). It is known to connect a large number of such submodules in series in order to achieve high-voltage stability.

Fig.l shows an example of such an arrangement, wherein an AC network 101 is connected via a transformer 102 with an MMC 103 and thus with a DC voltage network (with terminals 105 and 106). The MMC 103 comprises ei ^¬ ne plurality of submodules 104, wherein the construction of a submodule 104 is shown as an example: An electronic switch Tl is connected in series with a second electronic switch T2, each electronic switch Tl, T2 a diode Dl, D2 in opposite directions is connected in parallel. Parallel to the series connection of the electronic switches Tl and T2, a capacitor C is arranged. The electronic switches may be transistors, eg bipolar transistors, in particular IGBTs. The submodule 104 represents a two-terminal, which is connected on the one hand with a Mittenab ^{¬ grip} between the switches Tl, T2 and on the other hand to a pole of the capacitor C.

By a corresponding control of the electronic

Switches of the submodules can be an efficient conversion of the alternating current into a direct current or vice versa. WO2010 / 115453A1 proposes voltage compensation in DC transmission networks. There, longitudinal voltage sources are inserted in DC transmission lines in order to reduce the voltage in DC grids at all points in a permissible gene range. By inserting the longitudinal voltage source, the DC system is unavoidably supplied or removed with energy at this point. According to WO2010 / 115453 this energy is taken from an existing three-phase network or by means of an additional device from the direct current line itself.

The object of the invention to provide an efficient Mög ^¬ friendliness for removal or for feed of electrical energy from or in a HVDC transmission line.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

To solve the problem, a device for a high-voltage direct-current transmission line (HVDC ^link ) is given ^¬

with a serial tap adapted for serial connection in a line of the high-voltage direct-current transmission link,

with a parallel tap, which is directed towards the parallel connection between the two lines or poles of the high-voltage ^direct -current transmission path,

- Wherein the serial and the parallel tap je ^¬ Weils or in combination with each other provide electrical power for an AC network or an electrical power from the AC mains in the high voltage DC power transmission line can be fed.

The tap may be a means for serial or parallel connection to or with the transmission link. Thus, it is possible to flexibly extract power from the HVDC route or feed it into it. At the same time, a voltage compensation can take place. In particular, a longitudinal voltage which is favorable for the HVDC route can be flexibly coupled in.

The statements concerning the device apply to the HVDC line or the method accordingly. A further development is that the device has a further serial tap in another line of the high-voltage direct current transmission path.

Thus, a serial tap can be provided in each DC line (branch) of the HVDC line.

Another development of the device according to the invention is that the serial tap has at least one controllable longitudinal voltage source.

In particular, by the serial tap (also) a controllable source of longitudinal voltage can be realized.

In particular, it is a development that an adjustment of the power, the current and / or the voltage based on the at least one controllable source of longitudinal voltage is feasible.

The power, the voltage and / or the current are tapped or fed quantities.

For example, the longitudinal voltage source may adjust the current indi ^¬ rectly on the voltage. It is also possible that the longitudinal voltage source allows the clamping voltage ^¬ adjustment between two DC networks. The energy required for this can be achieved with the shunt arm and / or an AC network be replaced. For this purpose, the longitudinal voltage source is arranged, for example, between two DC networks.

It is also a development that the serial and / or the parallel tap has / have submodules.

In the context of an additional development, the submodule has a half-bridge circuit. It is also a development that the submodule has a full ^¬ bridge circuit.

A next development is that the serial and / or parallel tap has a grid-controlled inverter.

An embodiment is that the serial tap and the parallel tap are coupled or connected to an AC mains.

In particular, such a feedback through a transformative ^¬ gate, if necessary, be realized with galvanic isolation. It is also possible that the parallel tap and / or the se ^¬ rielle tap generates a three-phase AC signal, for example, fed via the transformer in the AC mains (or in the opposite direction, the three-phase AC signal via the transformer and the multilevel inverters are fed into the HVDC link). An alternative embodiment is that a

Power supply of the serial tap by means of the transmission path is feasible.

Thus, the serial tap can be powered by the DC line of the transmission line itself.

A next embodiment is that - The serial tap provides the electrical power for the AC mains or feeds the electrical power from the AC mains in the high voltage DC power transmission line, - wherein an energy from the parallel tap ent ^{¬ is} acceptable or fed back into this.

Thus, the respective energy can be taken as power from the parallel tap or (in this) fed back.

It is also an embodiment that the serial tap and the parallel tap for symmetrizing voltages and currents can be used. This applies in particular to bipolar systems. It can be effected in ^¬ example, a simultaneous balancing of voltages and currents in the positive and in the negative system. The above object is also achieved by a high-voltage direct-current transmission path

with a serial tap in a line of the high voltage DC link,

- with a parallel tap between the two lines or poles of the high voltage direct current

Transmission link,

- Wherein the serial and the parallel tap je ^¬ Weils or in combination with each other provide electrical power for an AC mains or feed electrical power from the AC mains in the high-voltage DC transmission line.

Also, a method is proposed to solve the problem for the transfer of electrical power in a high-voltage ^direct -current transmission path or from a high-voltage ^¬ DC transmission path, in which, by means of a serial tap, the electrical power is supplied to an AC network or fed into the high-voltage DC transmission link (eg from the AC network),

- In which an energy is taken from a parallel tap or fed back into this.

Accordingly, the statements made above on the device or on the HVDC route also apply to the method.

A development consists in that based on the serial tap and / or the parallel tap voltage compensation, in particular a longitudinal voltage compensation, the high-voltage direct current transmission path is performed.

It should be noted here that the longitudinal voltage source is connected to a DC network via a respective terminal and thus a voltage adaptation between two DC networks is different

Tension is possible. The longitudinal voltage source can allow men ^¬ together with the transverse branch or the AC terminal a controlled exchange of energy between two DC networks, regardless of their rated voltage or the currently existing voltage.

In a development of the invention, a control unit is provided for controlling the multilevel inverters, so that a corresponding adaptation of the powers can be achieved.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of exemplary embodiments, which will be described in more detail in conjunction with the drawings. The same or equivalent elements can be provided with the same Bezugszei ^{¬ Chen} for clarity. Show it:

2 shows an exemplary schematic diagram with a serial tap and with a parallel tap of a HVDC link;

3 shows an example of a serial tap under Ver ^¬ application of two AC side coupled multilevel inverter per tap.

It is a high-voltage dc transmission line (HVDC line) is proposed which has a serial tap and a parallel tap along the transmission link up, the serial tap and the parallel Anzap ^¬ Fung are preferably locates together, eg in a ge ^¬ common device are executed. The serial tap is connected in series with a line of the HVDC link or forms part of the line of the HVDC link. The parallel tap is connected to the two lines of the HVDC link.

Accordingly, a device is proposed, which is connectable to a HVDC link and a parallel and a serial tap for any HVDC ^link has on ^¬ . In particular, the device may have two connection terminals for connection to the HVDC route. The taps, for example, are each a two-pole. The device may have at least one parallel and / or at least one serial tap.

It should be noted that the HVDC route can have one or more lines. It is advantageous that the serial and the parallel An ^¬ tap in each case or in combination with each other can provide an electrical power for an AC power network or that an electric power from the AC mains can be fed ^¬ in the high-voltage DC transmission line.

2 shows an exemplary schematic diagram with a serial tap 207 and with a parallel tap 206.

A DC network 201 (may also consist of an HVDC station, for example) is connected to a DC network 204 via an additional (long) DC line 202 and an additional (long) DC line 203. The DC network 204 may also be an HVDC station.

Between the DC lines 202 and 203, the serial tap 207 and the parallel tap 206 are located, wherein the serial tap 207 by way of example Zvi ^¬ rule is the lines of the HVDC transmission line in the top line of the transmission path and the parallel tap 206th Through the serial tap 207, a current I _{DC of} the transmission path flows and at her falls from a voltage U _se r. The serial tap 207 provides in particular a three-phase AC ^¬ with a power P _ser a Lei tung ^¬ 209 to an AC power grid 205 (also referred to as AC power). For example, the coupling or connection to the AC network (also referred to as AC coupling) is designed as a three-phase system with a grid frequency; In principle, other phase numbers and / or other frequencies are possible.

Through the parallel tap 206, a current flows I _par and it drops the voltage U _D c from it. The parallel tap 206 provides a three-phase alternating current signal with a Leis ^¬ tung P _par via a line 208 to the AC power 205th

Thus, the AC network 205 is provided by the parallel tap 206 and the serial tap 207 in total a power P _ne tz. The serial tap 207 and the tap 206 preferably have parallel multi-level inverter, which may be implemented as a half-bridge or full-bridge ^¬ and via a transformer (possibly several transformers) are coupled to the AC power 205th

Preferably, the parallel tap 206 and the seriel ^¬ le tap 207 are located together, for example, housed in a common device and there connected to the AC network 205.

Furthermore, in accordance with the above explanations, a coupling of electrical power from the AC network 205 into the HVDC transmission path can also take place.

The two DC lines 202 and 203 are optional, and the DC networks 201 and 204 may also be coupled via only one of the DC lines 202 or 203 or directly to each other.

The taps can be used simultaneously for energy extraction and voltage compensation. This advantageously takes advantage of the required components twice and leads to greater economic attractiveness. Furthermore, it is possible for the DC grid 201 and the DC grid 204 to each be an HVDC station, and thus also for a DC point-to-point connection to be realized.

Optionally, the power supply to the desired serial tap 207 may be via the DC line itself.

One advantage is that combining both serial and parallel taps in a common device allows both energy and energy to be extracted. It is also possible to couple in an advantageous for the DC network longitudinal ^¬ voltage. These two functions can be fulfilled completely independent from each other: the power P _ser resulting entspre ^¬ accordingly sign and magnitude of the desired longitudinal voltage U r _se and the main current I _DC on the line; The power P _ne tz can be freely adjusted accordingly:

- Thus, the power P _ne tz has a positive sign, if, for example, a remote region with electrical energy from the passed line to be supplied.

- The power P _ne tz can also have a negative sign, if, for example, energy from a nearby wind farm is to be fed into the DC line.

The respective energy corresponds to a power difference IP _S er-Pnetz I and is taken as power P _par from the parallel An ^¬ tapping 206 or fed back.

FIG. 2 was based, for example, on a DC transmission with two poles or lines. The explanations also apply accordingly to multi-pole DC transmission. One or two parallel taps can be used, connected between each one pole and the earth. Serial taps can be installed in one or both DC lines.

In bipolar systems advantageous serial and paral ^¬ lele taps can be used in positive and negative system as required simultaneously for symmetry parameterization of voltages and / or currents. For instance, accordingly symmetrically serial and parallel taps can be seen ^¬ which are controllable such that adjustment of the symmetric voltages and / or currents in the positive and negative system. 3 shows an example of a serial tap of a device according to the invention. The described serial tap may be coupled to a parallel tap as described above via connecting means. A DC line 301 is symbolically interruptible by means of a switch Sl, so that the serial Anzap ^¬ tion shown in Figure 3 with the DC line 301 is functionally connected in series.

Each multi-level inverter of the serial tap shown in Figure 3 has a DC voltage connection 302 be ^¬ relationship as 314. The DC terminal 302 is connected with three phase modules 303-305, having a series circuit of submodules 306-311. Each phase module is equipped with an AC voltage connection, which is also referred to here as a tap. A tap in the respective series circuit 303 to 305 provides a phase for a three-phase AC current and is correspondingly connected via a transformer 312 to an AC network 313 (consumer network).

The same applies to the DC input terminal 314 on the opposite side of the switch Sl: The DC terminal 314 is connected to three parallel phase modules 315-317 from each of a plurality of series Submo ^¬ dulen 318-323. A tap in the respective series circuit 315 to 317 supplies a phase for the three-phase AC signal and is correspondingly connected via the transformer 312 to the AC network 313 (consumer network).

Furthermore, the opposite direct voltage terminal 324 of the parallel phase modules 303-305 with the AGAINST YOU berliegenden DC voltage terminal 325 is parallel Pha ^¬ senmodule 315-317 connected to the.

At the parallel phase modules 303 to 305, a voltage Ul drops and at the parallel phase modules 315 to 317 a voltage U2 drops. For example, the paral ^¬ Lele arrangement of the phase modules represent 303-305 a first tap station and the parallel arrangement of the phase modules 315-317, a second tap station. The DC terminals 302 and 314 are below ^¬ schiedlichem DC potential. The transformer connection is preferably designed to be galvanically isolated. This can be achieved by a 3-winding transformer or by the use of individual transformers for both taps. A tapping may be a tapping station. Also, a tapping station may have one or more taps.

In the exemplary embodiment shown in FIG. 3, the submodules are designed with half bridges.

Alternatively, the submodules can be designed as full bridge modules. For multilevel inverters with full bridges, a reversing circuit can be omitted

If full bridges are used in the submodules shown in FIG. 3, then the converter comprising the phase modules 303 to 305 and the converter with the phase modules 315 to 317 can be used redundantly; Accordingly, the falling voltage between the two converters (different) can be divided or adjusted. Such a full bridge inverter can generate voltages in different polarities between zero and a maximum voltage.

On the other hand, if the submodules in FIG. 3 are half-bridges, the polarization of the voltages through the two inverters can be used to set a drawn or fed-in power. For example, the

Half-bridge circuits of the inverter also be switched against each other so that the decoupled power is zero. Such a half-bridge converter can generate voltages between a minimum and a maximum voltage; the polarity of the generated voltage results from the mounting direction of the half bridges. For example, the minimum voltage is determined by a rectified mains voltage. The proposed solution allows (regardless of the game adhere at ^¬ realization according to Figure 3) an adjustment of different voltages (for example between networks). In particular, an energy flow control or an energy exchange can be achieved. The taps can act as a DC-DC converter and transfer energy between networks.

With half-bridge modules, it is not possible to limit the short-circuit current flowing through the freewheeling diodes. For this purpose, AC or DC side arranged power switch ^¬ to be provided for interrupting the fault current and open in this scenario.

In contrast, when using full bridge modules, a current flowing from the AC to DC side fault current can be completely blo ^¬ ckiert. Therefore, when using the full-bridge modules, no additional AC or DC-side switching operations or the switching devices required for this purpose are required.

In the event of a fault in the tap converter or in the connected mains, the inverter can be disabled and the power switch will be opened in this case. ^¬ the main current continues to flow, so the serial tap is bridged to protect the components from an overload.

One embodiment is to carry out the taps symmetrically and to insert in each case one subsystem in the positive pole and one subsystem in the negative pole of the HVDC route.

The taps according to FIG. 3 can be made relatively small for the extraction or coupling of services. In a first approximation can be - starting from a maximum permissible for the modules used RMS _RMS and the DC operating _current I _dc the transmission - the DC voltage Ul (according to Figure 3: for the tap 1: Ul, for the tap 2: U2) of the taps and thus estimate their size as follows:

With

AC operating current of the inverter

permissible RMS current of the modules of the converter

DC operating current of the transmission

Total power of the converters of both taps

Voltage control of the inverters (ratio of amplitude AC phase-to-ground voltage to half DC voltage Ul) Despite the boundary condition of a restricted setting range for the voltages Ul and U2 and an impressed, uncontrollable transmission current (this must flow via the DC terminals of the two multilevel inverters ) results in no restriction of the decoupled power of the consumer network shown in Figure 3, since the DC side in the two partial converter on or applied power can always be compensated on the AC side.

Em advantage of the circuit according to Figure 3 is the low, adaptable to the output power output in the converters of the two taps. The power converter does not have to be adapted to the voltage of the HVDC transmission with its series switching capacity. The circuit can be executed not only with multilevel inverters but also with other inverter topologies. The converters can be self-or network-controlled. Although the invention in detail by a ge ^¬ showed embodiment has been illustrated and described in detail at least, so the invention is not limited to this and other variations can be derived therefrom by the skilled artisan without departing from the scope of the invention.

Reference sign list

101 AC mains

102 transformer

103 MMC (multilevel inverter)

104 submodule

105, 106 DC power connection

D1, D2 diode

T1, T2 electronic switch (e.g., IGBT)

201 DC grid (DC grid)

202, 203 optional (long) DC line

204 DC network (DC network)

205 AC grid (AC mains), e.g. consumer network

206 parallel tapping

207 serial tap

208, 209 line

301 DC line (line of the DC network)

302 knots (DC voltage connection)

303 series connection of several submodules 306 to 307 (also referred to as phase module)

304 Series connection of several submodules 308 to 309 (also referred to as phase module)

305 series connection of several submodules 310 to 311 (also referred to as phase module)

306-311 submodule

312 transformer

313 AC network (eg consumer network)

314 nodes (DC voltage connection)

315 Series connection of several submodules 318 to 319 (also referred to as phase module)

316 series connection of several submodules 320 to 321 (also referred to as phase module)

317 Series connection of several submodules 322 to 323 (also referred to as phase module)

318-323 submodule

324, 325 knots (DC voltage connection)

Claims

Patent claims

Device for a high-voltage direct current transmission line

- with a serial tap (207), which is set up for serial connection in a line of the high ^- voltage direct current transmission path,

- with a parallel tap (206), which is set up for a parallel connection between the two lines or poles of the high-voltage direct current transmission path,

- wherein the serial tap (207) and the parallel tap (206) each or in combination with one another provide electrical power for an alternating current network (205) or an electrical ^power can be fed from the alternating current network (205) into the high-voltage direct current transmission path.

Device according to claim 1, with a further serial tap which is provided for serial connection in another line of the high-voltage direct current transmission path.

Device according to one of the preceding claims, in which the serial tap has at least one controllable longitudinal voltage source.

Device according to claim 3, in which an adjustment of the power, the current and / or the voltage ^can be carried out using the at least one controllable longitudinal voltage source.

5. Device according to one of the preceding claims, in which the serial and / or the parallel tap has / have submodules.

6. Device according to claim 5, in which the submodule has a half-bridge circuit.

7. The device according to claim 5, wherein the submodule has a full bridge circuit.

8. Device according to one of the preceding claims, in which the serial and / or parallel tap has a mains-controlled converter.

9. Device according to one of the preceding claims, in which the serial tap and the parallel tap are coupled or connected to an AC network.

10. Device according to one of the preceding claims, in which a power supply to the serial tap

Means can be carried out using the transmission route.

11. Device according to one of the preceding claims,

- in which the serial tap provides the electrical power for the AC network or ^feeds the electrical power from the AC network into the high-voltage direct current transmission path,

- where energy can be taken from the parallel tap or fed back into it.

12. Device according to one of the preceding claims, in which the serial tap and the parallel tap can be used to balance voltages and currents.

13. High voltage direct current transmission line

- with a serial tap (207) in a line of the high-voltage direct current transmission path, - with a parallel tap (206) between the

both lines or poles of the high-voltage direct current transmission line, - wherein the serial tap (207) and the parallel tap (206) each or in combination with one another provide electrical power for an alternating current network (205) or feed electrical ^power from the alternating current network (205) into the high-voltage direct current transmission path.

14. Method for transferring electrical power into a high-voltage direct current transmission path or from a high-voltage direct current transmission path,

- in which the electrical power is provided for an alternating current network (205) or fed into the high-voltage direct current transmission path using a serial tap (207),

- in which an energy difference is taken from a parallel tap (206) or fed back into it.

15. The method according to claim 14, in which a voltage compensation, in particular a longitudinal voltage compensation, of the high-voltage direct current transmission path is carried out using the serial tap and / or the parallel tap.