WO2019101305A1

WO2019101305A1 - Converter and operation thereof

Info

Publication number: WO2019101305A1
Application number: PCT/EP2017/080104
Authority: WO
Inventors: Nicolas Söllner; Johann Messner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2017-11-22
Filing date: 2017-11-22
Publication date: 2019-05-31
Also published as: EP3698458A1

Abstract

The invention relates to a converter station (1) having two line-commutated converters (4, 5), and to a method for operating the converter station (1). The two converters (4, 5) are electrically connected in an anti-parallel circuit at the same voltage polarity of a bipolar high-voltage direct current transmission line (30). One of the converters (4, 5) is operated as a rectifier in an AC network (27) and the other converter (4) is operated as an inverter in the AC network (27). A station reactive power (Q1) exchanged between the converter station (1) and the AC network (27) is controlled by an active power specification for converter active powers (P1) that is identical for both converters (4, 5), each of these converter active powers being exchanged between the converters (4, 5) and the AC network (27).

Description

description

Converter station and its operation

The invention relates to a converter station with two line-commutated converters and a method for their

Business .

Electrical energy is often transmitted between AC networks over long distances with high DC voltage

Because the transmission of energy with DC voltage over long distances compared to an energy transfer with AC voltage loss less and cheaper. This type of energy transfer is referred to as high voltage direct current (HVDC) transmission. The

Energy transmission can take place via a monopolar or a bipolar high-voltage direct current transmission link (HVDC link). A monopolar HVDC link has only one high-voltage line, at which a high voltage is applied to a ground potential. A bipolar HVDC line has two high-voltage lines, where at one

High voltage line one against a ground potential positive high voltage is applied and on the other

High voltage line against the earth potential negative high voltage is applied. The parts of an HVDC track which are assigned to the same voltage polarity are referred to below as poles of the HVDC track. A monopolar HVDC link thus has one pole, a bipolar HVDC link has two poles.

In order to connect an HVDC line to an AC grid, a converter station is arranged between the AC grid and one end of the HVDC link, in which the

Conversion between AC and AC voltage of the AC mains in DC and DC voltage of the HVDC takes place. Converter stations have for each connected to her pole of the HVDC track on a power converter, which is often used as a line-commutated power converter (LCC = Line Commutated Converter) is performed on a thyristor basis. Unlike a self-commutated power converter (VSC = Voltage Sourced Converter) requires a mains-powered

Power converter to its operation reactive power from the

AC mains. The reactive power exchanged by a grid-commutated power converter with the AC grid is inherently in accordance with a reactive power with the

Active power in relation to the set characteristic of the

Active power transmitted by the power converter. Blind and active power can therefore at a

Mains-controlled power converters can not be set independently of each other without further ado. In particular, line-commutated power converters can therefore be used without changing the

Use active power flow only very limited to a reactive power compensation in the AC network.

The invention is based on the object, in particular with regard to the reactive power exchange with a

AC power system to provide improved converter station on a bipolar high-voltage DC transmission line and an improved reactive power exchange method for the operation of such a converter station.

The object is achieved by a method having the features of claim 1 and by a converter station with the features of claim 5.

Advantageous embodiments of the invention are the subject of the dependent claims.

In the inventive method for operating a

Converter station with two line-commutated converters, the two converters in an anti-parallel circuit with the same voltage polarity of a bipolar

High voltage DC transmission link electrically connected. One of the converters is operated as a rectifier on an AC mains, the other power converters is operated as an inverter to the AC mains and one between the converter station and the

AC mains replaced station blind power is identical for both converters

Effective power specification for converter performance

controlled, which are each exchanged between a power converter and the AC mains.

The invention thus provides monopolar operation of the two power converters of the converter station in an anti-parallel circuit, that is, on the same voltage polarity of a bipolar HVDC route. One of the converters is operated as a rectifier to the AC mains, that is, this converter takes active power from the

AC mains. The other power converter is called

Inverter operated on the AC mains, that is, this converter transmits active power in the

AC mains. In this case, the station reactive power exchanged by the converter station with the alternating current network is identical to that for both converters

Active power specification controlled for their converter active power, that is, both converters are operated with the same converter active power.

The invention makes use of the fact that the station active power, which exchanges the converter station with the AC network, is the difference between the converter converter outputs of the two

Power converter is because one of the power converters is operated as a rectifier and the other power converter is operated as an inverter, while the station reactive power is the sum of the converter reactive power. Since the power converters are operated with the same power conversion efficiency, the converter efficiencies cancel each other out neglecting the losses, so that the

Station active power, which is exchanged between the converter station and the AC network, disappears. In addition, since each converter reactive power depends on a characteristic curve of the respective converter active power, the Stations reactive power by changing the

Active power specification for the converter performance can be controlled. For example, the

Station blindness can be increased by the

Power converter efficiencies for rectifier and inverter are increased by the same amount.

The invention thus enables in addition to the conventional

Operating mode of the converter station in which the

line-commutated converters both as equal or as

Inverter and are operated at different poles of the HVDC line, another mode of operation in which no station active power is exchanged between the converter station and the AC mains, but with the converter station a network system service

Reactive power compensation is provided, similar to self-commutated power converters or a

Reactive Power Compensator (SVC = Static Var Compensator).

An embodiment of the invention provides that a

Reactive power setpoint for the station reactive power

is given and by the active power specification, a sum of converter reactive power, which are exchanged by the converters with the AC mains, on the

Reactive power setpoint is set. This allows the station blind power through the active power specification for the converter output of the power converter to a

Set value.

A further embodiment of the invention provides that an offset of a reactive power exchange between the

Converter station and the AC network is changed by connecting or disconnecting at least one AC filter to a grid connection of the converter station to the AC mains. In this case, a reactive power jump of the reactive power exchange between the converter station and the AC network caused by a connection or disconnection of at least one AC filter can be achieved by a the reactive power jump counteracting change in

Active power input for the converter performance can be reduced at the time of connecting or disconnecting the at least one AC filter. As a result, the reactive power exchange between the converter station and the AC network can be additionally controlled by switching AC filters on or off. Without further action causes the switching on and off of

AC filters, however, a reactive power jump of the reactive power exchange between the converter station and the AC network. This reactive power jump can be caused by a change in the converter efficiency

Advantageously reduced at the time of connection or disconnection. This embodiment of the invention makes use of the fact that the opposite operation of the power converters makes it possible for the station blind power through the

To influence converter performance.

A power converter station according to the invention comprises two line-commutated power converters, each optionally as a rectifier or as an inverter on a

AC network operable and with the same

Voltage polarity of a bipolar high voltage DC transmission link are electrically connected, and a control unit, which is set up between the

Converter station and the AC network replaced station blind power by an identical for both converters active power input for

Power converter active power, each between a

Inverters and the AC mains are exchanged to control, if both power converters in one

Antiparallelschaltung are connected to the same voltage polarity of the high voltage DC transmission link.

A converter station according to the invention makes it possible to carry out the method according to the invention with the advantages mentioned above. Compared to a conventional one

Converter station with line-commutated converters only a circuit that allows the anti-parallelization of the two converters, and a control unit, the control of the invention

Converter output of the antiparallel switched converter is set up needed. If necessary, already existing switching devices of a converter station can be used for the circuit, wherein

if necessary, an isolation level of this

Switching devices must be increased to a high voltage potential. The device of the control unit can

be realized for example by appropriate programming. Therefore, the additional hardware costs for a converter station according to the invention compared to a conventional converter station with mains-driven

Power converters relatively low. The invention may therefore also be used to upgrade existing bipolar converter stations with line-commutated converters.

A further embodiment of the invention provides that the AC network is three-phase. In this case, each power converter may, for example twelve in one of two

Six-pulse bridge circuits existing twelve-pulse bridge circuit arranged valve units, each valve unit may in particular comprise at least one thyristor. Furthermore, each power converter can be connected by a transformer unit with the AC power, the one for each phase of the AC power supply

Primary winding, a first secondary winding and a second secondary winding, wherein the primary windings are connected by a star connection, the first secondary windings are connected by a delta connection and the second secondary windings are connected by a star connection. At a

such design of the power converter, preferably, each winding end of each first secondary winding is connected to a first six-pulse bridge circuit of a power converter and / or one of a star point of the star connection remote winding end of each second secondary winding is connected to a second six-pulse bridge circuit of

Power converter connected. The aforementioned embodiments of the invention relate to the prevalent design of HVDC links between three-phase AC networks. In these cases, in particular converter stations have proven with twelve-pulse converters and the other aforementioned properties, which therefore also advantageous

Represent embodiments of the present invention. It should be emphasized, however, that the invention is not limited to three-phase

AC grids and / or power converters of the aforementioned type is limited, but for example, for single-phase AC grids and / or six-pulse converters

is applicable.

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

Related to the following description of

Embodiments associated with the

Drawings are explained in more detail. Showing:

1 shows a circuit diagram of a converter station according to the prior art,

2 shows schematically two converter stations, which are connected via an HVDC route,

3 shows a network connection of a converter station to an AC network,

4 shows a first embodiment of a

AC filter,

5 shows a second embodiment of a

AC filter, 6 shows a third embodiment of a

AC filter.

Corresponding parts are provided in the figures with the same reference numerals.

1 shows a circuit diagram of a converter station 1 according to the prior art for energy transmission via a bipolar HVDC path 30. The converter station 1 comprises two line-commutated power converters 4, 5 (LCC = Line

Commutated Converter), each as an optional

Rectifier or as an inverter on one

three-phase AC mains 27, 28 are operable.

Each power converter 4, 5 has twelve valve units 7 which are arranged in a twelve-pulse bridge circuit 26 consisting of two six-pulse bridge circuits 26.2, 26.2. Each valve unit 7 has one or more thyristors connected in series or in parallel. For each valve unit 7, a surge arrester 9 is connected in parallel.

Each power converter 4, 5 is connected by a

Transformer unit 11 with the AC power 27th

connected, which has a primary winding 13, a first secondary winding 15 and a second secondary winding 17 for each phase of the AC network 27. The primary windings 11 of each transformer unit 11 are connected to each other by a star connection, the first secondary windings 15 are connected to each other by a delta connection and the second secondary windings 17 are connected to each other by a star connection.

Each winding end of each first secondary winding 15 is connected to one of six valve units 7

Six-pulse bridge circuit 26.1 connected. A winding end of each second secondary winding 17 facing away from a star point 19 of the star connection is connected to one of the other six valve units 7 of the respective

Power converters 4, 5 formed second six-pulse bridge circuit 26.2 connected.

A first power converter 4 is connected to a first pole 21 of the HVDC track 30. For this purpose, the second six-pulse bridge circuit 26.2 of the first power converter 4 is connected to the first pole 21 of the HVDC track 30. The second

Power converter 5 is connected to the second pole 23 of the HVDC track 30. For this, the second six-pulse

Bridge circuit 26.2 of the second power converter 5 connected to the second pole 23 of the HVDC track 30. Further, the two power converters 4, 5 via a medium voltage

designed power converter connection line 25 connected to each other. For this purpose, the first six-pulse bridge circuits 26.1 of both power converters 4, 5 are connected to the power converter connection line 25.

FIG. 2 schematically shows two converter stations 1, 2 which are connected to one another via a HVDC link 30 on the DC side. AC side is a first

Converter station 1 is connected to a first AC mains 27, and the second converter station 2 is connected to a second AC network 28.

The HVDC path 30 is formed bipolar with a first pole 21 and a second pole 23 and high voltage lines 32, 34 between the two converter stations 1, 2.

Each converter station 1, 2 is like that in FIG. 1

formed converter station 1, wherein each connected to one pole 21, 23 outputs each

Converter station 1, 2 via a pole connecting line 36 are connected to each other. The outputs of a converter station 1, 2 which are each connected to a pole 21, 23 can also be connected, for example, via (not shown).

Polwendeschaltungen be connected to each other. The

Pole connection line 36 of each converter station 1, 2 is further via a reconfiguration switch 40 with the

Power converter connection line 25 of the converter station 1,

2 connectable and has between its connection to the reconfiguration switch 40 and each power converter 4, 5 of the converter station 1, 2 an interruption switch 42. The power converter connection lines 25 of the

Converter stations 1, 2 are over a

Medium voltage line 44 connected to each other. each

Converter station 1, 2, 3 has a control unit 46, through which the valve units 7 of their power converters 4, 5 are driven.

In the case shown in FIG. 2, both become

Converter stations 1, 2 according to the invention

Operated method. In this case, the two power converters 4,

5 each converter station 1, 2 in one

Antiparallelschaltung connected to the same voltage polarity of the HVDC track 30, wherein the pole-side outputs of each converter station 1, 2 via the

Pole connection line 36 connected to each other and separated from the HVDC route 30. Alternatively, the

pole-side outputs of each converter station 1, 2

be connected to each other for example via a Polwendeschaltung. The converter stations 1, 2 are thus each monopolar and in a stand-alone operation, that is, at the same Spannungspolarität and decoupled from the HVDC line 30, operated.

Further, one of the power converters 4, 5 will be any

Converter station 1, 2 operated as an inverter, that is, it transmits a converter active power PI, P2 in the AC network connected to him 27, 28. The other power converter 5 of the converter station 1, 2 is called

Rectifier operated, that is, he takes the

Power converter active power PI, P2 from the respective

AC power 27, 28. Here are the two

Power converter 4, 5 each converter station 1, 2 with

the same power converter PI, P2 operated. Thereby the power converter efficiencies PI, P2 of the

Power converter 4, 5 each converter station 1, 2 below

Neglecting the losses on each other, so that the station active power of each converter station 1, 2

disappears .

In the example shown in Figure 2, the first

Power converter 4 a first converter station 1 as

Inverter operated, that is, he transmits the

Converter active power PI in the first AC mains 27. The second converter 5 of the first converter station 1 is operated as a rectifier, that is, it takes the converter active power PI from the first

AC power 27.

The first power converter 4 of the second power converter station 2 is operated as a rectifier, that is, it takes the power converter active power P2 from the second

AC power network 28. The second power converter 5 of the second power converter station 2 is operated as an inverter, that is to say it transmits the power converter active power P2 into the second AC power network 28.

Each converter station 1, 2 exchanges with the

AC network 27, 28, to which it is connected, a station blind power Ql, Q2, where Ql the

Station blind power of the first converter station 1 and Q2 denotes the station blind power of the second

Converter station 2 called. The station blind power Ql of the first converter station 1 is the sum of

Converter power ratings Qll, Q12, which are respectively exchanged between the converters 4, 5 of the first converter station 1 and the first AC network 27.

Accordingly, the station blind power Q2 of the second converter station 2 is the sum of

Converter power ratings Q21, Q22, which are respectively exchanged between the power converters 4, 5 of the second converter station 2 and the second AC network 28. The Direction of each active and reactive power flow is shown in Figure 2 by an arrow. If the two

Power converters 4, 5 of each converter station 1, 2 are formed identically, applies Qll = Q12 and Q21 = Q22.

The converter active power PI, P2 of the power converters 4, 5 of a converter station 1, 2 are by means of

Control unit 46 of the converter station 1, 2 controlled by an identical for both converters 4, 5 active power specification for the converter active power PI, P2. Because the

Converter reactive power Qll to Q22 of a power converter 4,

5 depends on a characteristic of the converter active power PI, P2 of the power converter 4, 5, the

Stationsblindleistung Ql, Q2 a converter station 1, 2 by the active power setting for the

Power converter active power PI, P2 of the power converters 4, 5 of the converter station 1, 2 are controlled. For example, the station blind power Ql, Q2 can be increased by increasing the power converter efficiencies PI, P2.

According to the invention, a reactive power setpoint of

Stationsblindleistung Ql, Q2 given and the

Station blind power Ql, Q2 is determined by the

Effective power specification for the converter output PI,

P2 of the converter station 1, 2 on the

Reactive power setpoint set. The method according to the invention therefore makes it possible, with a converter station 1,

2 for an AC mains 27, 28 a

Power supply system to provide reactive power compensation, similar to self-commutated converters or a reactive power compensator (SVC = Static Var

Compensator).

Instead of providing such a network system service of reactive power compensation with both converter stations 1, 2, the network system service can of course also be provided with only one of the converter stations 1, 2 for the AC network 27, 28 connected to it, the other converter station 1, 2 being switched off, for example is or exchanges electrical power with another (not shown) converter station via a HVDC line.

A further embodiment of the method according to the invention relates to the connection or disconnection of

AC filters 54 at a power terminal 50 a

Converter station 1, 2 to an AC network 27, 28th

FIG. 3 shows an embodiment of a

Power supply 50 a converter station 1 to a

AC power network 27. The power converter station 1 is like one of the power converter stations 1, 2 shown in FIG

educated. The power connection 50 has several

Busbars 52, busbar outlets 53 and

AC filter 54 on each other through

Circuit breaker 56 are interconnected. By switching on and off of AC filters 54, an offset of the reactive power exchange between the converter station 1 and the AC network 27 is changed. It can be provided that a reactive power jump of

Station blind power Ql, by switching on or

Switching off at least one AC filter 54 is caused by the reactive power jump counteracting change in the converter performance PI of the converters 4, 5 of the converter station 1 at the time of switching on or off the at least one AC filter 54 is reduced. In other words, the

Station blind power Ql of the converter station 1 to the

Time of connection or disconnection of the at least one AC filter 54 by a change of

Power converter active power PI changed so that this change compensates for the reactive power jump at least partially.

Figures 4 to 6 show circuit diagrams of various

Embodiments of AC filters 54 that may be used on a power supply 50. FIG. 4 shows an AC filter 54 with a capacitor 60 and a parallel connection of a coil 62 and a capacitor connected in series with the capacitor 60

Resistor 64. AC filter 54 also includes a grounded filter surge arrester 66.

FIG. 5 shows an AC filter 54, which differs from the AC filter 54 shown in FIG. 4 only in that a series connection of a coil 62 and a resonant circuit 68 runs parallel to the resistor 64

is switched.

FIG. 6 shows an AC filter 54, which differs from the AC filter 54 shown in FIG. 4 only in that a series connection of a coil 62 and two oscillating circuits 68 runs parallel to the resistor 64

is switched.

Although the invention in detail by preferred

While embodiments have been further illustrated and described, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the present invention

To leave invention.

LIST OF REFERENCE NUMBERS

1, 2 power converter station

4, 5 power converters

7 valve unit

9 surge arresters

11 transformer unit

13 primary winding

15, 17 secondary winding

19 secondary-side star point

21, 23 pol

25 power converter connection line

26 twelve-pulse bridge circuit

26.1, 26.2 six-pulse bridge circuit

27 to 29 AC mains

30 high-voltage DC transmission line

32, 34 power transmission line

36 pole connection line

40 reconfiguration switch

42 interruption switch

44 medium voltage line

46 control unit

50 power connection

52 busbar

53 busbar outlet

54 AC filter

56 power switch

60 capacitor

62 coil

64 resistance

66 filter surge arresters

68 resonant circuit

PI, P2 converter active power Ql, Q2 Stations reactive power

Qll to Q22 converter reactive power

Claims

claims

1. A method for operating a converter station (1) with two line-commutated converters (4, 5), wherein

- The two power converters (4, 5) in one

Anti-parallel circuit are electrically connected to the same voltage polarity of a high-voltage bipolar DC transmission link (30),

- One of the power converters (4, 5) is operated as a rectifier on an AC network (27),

- The other power converter (4, 5) is operated as an inverter to the AC mains (27) and

- one between the converter station (1) and the

AC mains (27) replaced

Station blind power (Ql) by one for both

Power converter (4, 5) identical effective power specification for converter active power (PI), each between a power converter (4, 5) and the AC power network (27)

be exchanged, controlled.

2. The method according to claim 1,

characterized in that a reactive power setpoint for the station blind power (Ql) is specified and by the active power setting a sum of

Converter power ratings (Qll, Q12) between the converters (4, 5) and the AC mains (27)

be replaced, to the reactive power setpoint

is set.

3. The method according to any one of the preceding claims, characterized in that an offset of a

Reactive power exchange between the

Converter station (1) and the AC mains (27) by connecting or disconnecting at least one

AC filter (54) at a mains connection (50) of the converter station (1) to the AC network (27)

is changed.

4. The method according to claim 3,

characterized in that a by switching on or off at least one AC filter (54)

caused reactive power jump of the

Reactive power exchange between the

Converter station (1) and the AC network (27) by a reactive power jump counteracting change in the active power specification for the converter active power (Pli, P12) at the time of switching on or off the at least one AC filter (54) is reduced.

5. converter station (1) comprising

- two line-commutated power converters (4, 5), each

optionally operable as a rectifier or as an inverter on an AC mains (27) and electrically connectable to the same voltage polarity of a bipolar high voltage DC transmission line (30),

- And a control unit (46) which is arranged, one between the converter station (1) and the

AC mains (27) replaced

Station blind power (Ql) by one for both

Power converter (4, 5) identical active power specification for

Power converter active power (PI), each between a power converter (4, 5) and the AC network (27)

be exchanged, when both converters (4, 5) in an anti-parallel circuit with the same

Voltage polarity of high voltage direct current

transmission link (30) are connected.

6. converter station (1) according to claim 5,

characterized in that the AC mains (27) is three-phase.

7. converter station (1) according to claim 6,

characterized in that each power converter (4, 5) arranged twelve in a twelve-pulse bridge circuit (26) consisting of two six-pulse bridge circuits (26.1, 26.2)

Valve units (7).

8. converter station (1) according to claim 7,

characterized in that each valve unit (7)

has at least one thyristor.

9. converter station (1) according to one of claims 6 to 8, characterized in that each power converter (4, 5) by a transformer unit (11) to the AC network (27) is connected, for each phase of the AC network (27) Primary winding (13), a first secondary winding (15) and a second secondary winding (17), wherein the primary windings (13) are interconnected by a star connection, the first secondary windings (15) are interconnected by a delta connection and the second secondary windings ( 17) are interconnected by a star connection.

10. converter station (1) according to claim 9,

characterized in that each winding end of each first secondary winding (15) is connected to a first six-pulse bridge circuit (26.1) of a power converter (4, 5).

11. converter station (1) according to claim 9 or 10,

characterized in that one of a star point (19) of the star connection remote winding end of each second secondary winding (17) with a second six-pulse bridge circuit (26.2) of a power converter (4, 5) is connected.