AU2014395431A1

AU2014395431A1 - Modular converter system for an electric supply network

Info

Publication number: AU2014395431A1
Application number: AU2014395431A
Authority: AU
Inventors: Markus Pfeifer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2014-05-26
Filing date: 2014-05-26
Publication date: 2016-11-24
Anticipated expiration: 2034-05-26
Also published as: CN106416043B; EP3123607A1; WO2015180751A1; EP3123607B1; AU2014395431B2; KR20160149255A; KR101898975B1; CN106416043A

Abstract

The invention relates to a converter system (1) for an electric supply network, comprising - a first and at least one second converter device (2), each of the converter devices (2) comprising - a voltage source (3) for providing an electric voltage (U

Description

PCT/EP2014/060827 2014P08112WOAU 1

Description

Modular converter system for an electric supply network

The present invention relates to a converter system for an electric supply network according to patent claim 1. Electric supply networks are used to distribute electric energy inside the power network. At present, interest is aimed at medium-voltage networks, in particular. Such medium-voltage networks are usually used to transmit energy over distances of up to 100 kilometers. In this case, electric AC voltages of 10 kV or higher are transmitted.

Converter systems comprising, for example, a low-voltage converter and a transformer are used, for example, to feed current into the medium-voltage network or draw it from the latter. Very large and extremely heavy transformers are usually required here. In this context, there is the problem that the transportation of transformers throughout the world and even in Europe can entail serious problems which result in some projects being able to be carried out only with a delay or with a large amount of effort. For example, road construction work, bridge construction work or the like must be carried out in order to transport the heavy transformers, during which work corresponding reinforcements of the road are necessary so that transport vehicles can travel on them.

In principle, it is possible to design a converter system in such a manner that it does not require a transformer and can nevertheless feed into the medium-voltage network. In this case, however, the costs are very high on account of the required design of the components of the converter for the medium-voltage network. Furthermore, these converters are usually very restricted by their dynamic response. Depending on the requirements, the transformers and the converters for proj ects

PCT/EP2014/060827 2014P08112WOAU are generally

PCT/EP2014/060827 2014P08112WOAU 2 usually produced separately and are possibly oversized.

The object of the present invention is to show a solution of how a converter system of the type mentioned at the outset can be provided in a more cost-effective manner and with less effort.

This object is achieved by means of a converter system having the features of patent claim 1. The dependent claims, the description and the figures relate to advantageous developments of the present invention.

The converter system according to the invention for an electric supply network comprises a first and at least one second converter apparatus, each of the converter apparatuses comprising a voltage source for providing an electric voltage, an inverter device for providing an AC voltage from the electric voltage provided by the voltage source, and a transformer device for transforming the AC voltage provided by the inverter and applied to a primary coil into a transformed AC voltage which is applied to the secondary coil, the secondary coils of the first and the at least one second converter apparatus being electrically connected in series, and a medium voltage formed by the series circuit of the secondary coils being applied to an output of the converter system.

The invention therefore provides a modular converter system comprising at least two converter apparatuses which, in combination, can feed current into the electric supply network and can draw it from the latter. The electric supply network may be a low-voltage network or a high-voltage network. In particular, the electric supply network is a medium-voltage network. In this case, the converter apparatuses are preferably structurally identical. The converter apparatuses may also

PCT/EP2014/060827 2014P08112WOAU 3 be different. Each of the converter apparatuses comprises a voltage source which can be used to provide an electric voltage. The voltage source is electrically connected to an inverter device which is designed to convert the electric voltage provided by the voltage source into an AC voltage. The inverter device is in turn electrically connected to a transformer device or to be precise to a primary coil of the transformer device. The AC voltage is therefore applied to the primary coil of the transformer device. This AC voltage is converted by means of the transformer device, with the result that a transformed AC voltage is applied to the secondary coil.

The secondary coils of the converter apparatuses are electrically connected in series. In addition, the secondary coils are electrically connected to an output of the converter system or to a connection. DC isolation with respect to the voltage source or with respect to the inverter device can be provided by transformer devices of the converter apparatuses. The transformed AC voltages from the individual converter apparatuses which are applied to the secondary coils are therefore added to the medium voltage. The medium voltage can be adapted for the respective application by means of the number of converter apparatuses used in the converter system and their respectively provided electric voltage. In addition, the transportation of the converter system can be simplified as a result of the modular configuration of the converter system.

The inverter device of the first converter apparatus preferably has a measuring unit for measuring the AC voltage provided using the inverter device of the at least one second converter apparatus. Provision may also be made for each of the converter apparatuses to have a corresponding measuring unit which can be used to record the AC voltage provided by at least one inverter device

PCT/EP2014/060827 2014P08112WOAU 4 of another converter apparatus. The measuring unit may be designed, for example, to record an amplitude and/or a phase of the AC voltage. One converter apparatus can therefore be used to check whether the other converter apparatus is functional.

In one embodiment, the inverter device of the first converter apparatus is designed to adapt an amplitude and/or a phase of the AC voltage provided using the inverter device of the first converter apparatus on the basis of the measured AC voltage from the inverter device of the at least one second converter apparatus. For example, the measuring unit of the inverter device of the first converter apparatus can be used to measure the AC voltage provided using the inverter device of the second converter apparatus. On the basis of this, the amplitude and/or the phase of the inverter device of the first converter apparatus can be adapted. In this case, provision may also be made for the amplitude of the AC voltage from the inverter device of the first converter apparatus to be increased if the inverter device of the second converter apparatus is defective.

It has also been shown to be advantageous if the inverter device of the first converter apparatus is designed to adapt the AC voltage provided using the inverter device of the first converter apparatus in such a manner that the medium voltage has a substantially sinusoidal profile. The measuring unit of the inverter device of the first converter apparatus can be used to measure the amplitude and/or the phase of the AC voltage provided using the inverter device of the second converter apparatus. If the signal waveform of the AC voltage differs from a sinusoidal profile, the amplitude and/or phase of the AC voltage provided using the inverter device of the first converter apparatus can be adapted in such a manner

PCT/EP2014/060827 2014P08112WOAU 5 that a sum voltage of the transformed AC voltages from the converter apparatuses, which forms the medium voltage, has a substantially sinusoidal profile. This makes it possible to provide a sinusoidal AC voltage at the output of the converter system.

In another configuration, the converter system has a control device for controlling the inverter devices of the first and the at least one second converter apparatus. The control device can be used to output appropriate control signals to the inverter devices. The inverter devices may also be designed to adapt the amplitude and/or phase of the AC voltage provided using them on the basis of the control signal. The control device can control the inverter devices in such a manner that it is possible to uniformly utilize the individual converter apparatuses. For example, a first group of converter apparatuses can be operated for a first predetermined period and a second group of converter apparatuses can be operated in a subsequent, second predetermined period of time. It is therefore possible to prevent individual converter apparatuses or a plurality of converter apparatuses from being operated continuously and therefore to prevent overloading or premature aging of these converter apparatuses, for example.

The first and/or the at least one second converter apparatus preferably has/have a communication device connected to the control device for the purpose of communicating data. The respective communication device may be connected to the measuring unit, for example. Alternatively, the communication device itself may be designed to record an amplitude and/or a phase of the AC voltage from the respective inverter devices and to transmit it/them to the control device. Therefore, it is possible to reliably monitor the instantaneous operating state of the individual converter apparatuses, for example.

PCT/EP2014/060827 2014P08112WOAU 6

In another configuration, the respective voltage source of the first and the at least one second converter apparatus is designed to output a DC voltage as the electric voltage. In other words, the voltage source of the respective converter apparatus may be in the form of a DC voltage source. The respective voltage source may comprise, for example, a battery or a rechargeable battery. The respective voltage source may also be part of a photovoltaic installation. For example, electric energy can be produced by means of a photovoltaic installation and can be directly fed into the medium-voltage network by means of the converter system. A number of turns of the primary coil preferably corresponds to a number of turns of the secondary coil in the respective transformer device of the first and the at least one second converter apparatus. The transformer device therefore has a transfer factor having the value of 1, for example. Such a transformer device can therefore be produced in a simple and cost-effective manner.

In another embodiment, the respective inverter device of the first and the at least one second converter apparatus is designed to output a first AC voltage and at least one second AC voltage which is phase-shifted with respect to the first AC voltage. The respective inverter devices can therefore have a multiphase design. For example, it is possible to output a three-phase AC voltage with three AC voltages which are phase-shifted through 120 degrees. This makes it possible to also use the converter system for medium-voltage networks which are in the form of a multiphase three-phase system.

It has also been shown to be advantageous if the respective transformer device of the first and the at least one second converter apparatus comprises at least two partial transformers

PCT/EP2014/060827 2014P08112WOAU 7 with a primary side and a secondary side, the first AC voltage being applied to the primary side of the first of the at least two partial transformers and the second AC voltage being applied to the primary side of a second of the at least two partial transformers. The transformer device may therefore comprise a plurality of partial transformers. These may be in the form of separate components. Alternatively, the partial transformers of the transformer device may have a common core, for example.

The secondary sides of the first partial transformers and the secondary sides of the second partial transformers of the first and the at least one second converter apparatus are preferably each electrically connected in series. The secondary sides of the first and second partial transformers may also each be connected to a corresponding connection. A multiphase electric voltage for the medium-voltage network can therefore be provided at the connections.

In another embodiment, the converter system is designed to transform a medium voltage applied to the connection by means of the respective transformer device of the first and the at least one second converter apparatus and to convert it by means of the respective inverters of the first and the at least one second converter apparatus. In other words, the converter system is designed to draw an electric current from the medium-voltage network and to transmit it to the respective voltage sources. The respective voltage sources may be in the form of an electric energy store, for example, or may comprise such an electric energy store. This energy store can be charged using the electric voltage from the medium-voltage network, for example .

Further features of the invention emerge from the claims, the figure and the description of the figure. All of the features and combinations of features mentioned above in the description PCT/EP2014/060827 2014P08112WOAU and the features and combinations of features mentioned below in the description of the figure and/or shown solely in the figure can be used not only in the respective stated combination but also in other combinations or else alone.

The invention is now explained in more detail using a preferred exemplary embodiment and with reference to the accompanying drawing. In this case, the figure shows a schematic illustration of a converter system for a medium-voltage network.

The figure shows a modular converter system 1 which can be electrically connected to a medium-voltage network. The converter system 1 comprises at least two converter apparatuses. In the present exemplary embodiment, the converter system 1 comprises three converter apparatuses 2. Each of the converter apparatuses 2 comprises a voltage source 3 which is in the form of a DC voltage source in the present exemplary embodiment. Each of the voltage sources 3 is used to provide an electric voltage UG. Instead of the embodiment shown here, the respective voltage sources 3 can also be used to provide an AC voltage, for example.

In addition, each of the converter apparatuses 2 comprises an inverter 4. The inverter 4 is electrically connected to the voltage source 3. The inverter 4 is designed to convert the electric voltage UG provided using the voltage source 3 into an AC voltage. In the present case, the respective inverter devices 4 are set up to provide three AC voltages Ui, U2 and U3 which are each phase-shifted through 120° with respect to one another.

In addition, each of the converter apparatuses 2 comprises a transformer device 5. In the present exemplary embodiment, each of the transformer devices 5 comprises three partial transformers ΤΙ, T2 and T3. The first partial transformer T1

PCT/EP2014/060827 2014P08112WOAU 9 has a first primary side PI and a first secondary side SI, the second partial transformer T2 has a second primary side P2 and a second secondary side S2 and the third partial transformer T3 has a third primary side P3 and a third secondary side S3. The first AC voltage Ui is provided on the first primary side PI, the second AC voltage U2 is provided on the second primary side P2 and the third AC voltage U3 is provided on the third primary side P3.

The three partial transformers ΤΙ, T2 and T3 preferably have a transfer factor of 1. The first AC voltage is converted using the first partial transformer Tl, with the result that a first transformed AC voltage UTi is applied to the first secondary side. The second electric voltage U2 is converted using the second partial transformer T2 such that the second transformed AC voltage UT2 is applied to the second secondary side S2. The third AC voltage U3 is transformed using the third partial transformer T3 such that a third transformed AC voltage UT3 is applied to the third secondary side S3.

The respective secondary sides SI or secondary coils of the first partial transformers Tl of each of the converter apparatuses 2 are electrically connected in series. In addition, the second secondary sides S2 of the second partial transformers T2 of the respective converter apparatuses 2 are electrically connected in series. Finally, the third secondary sides S3 of the third partial transformers T3 of the respective converter apparatuses 2 are electrically connected in series. The series circuit of the first secondary sides Si is electrically connected to a first connection A1 on a first side and is electrically connected to a star point P on a second side. The series circuit of the second secondary sides S2 is connected to the second connection A2 on a first side and is connected to the star point P on a second side. The series circuit of the third secondary sides S3 is

PCT/EP2014/060827 2014P08112WOAU 10 connected to the third connection A3 on a first side and is connected to the star point P on a second side.

During operation of the converter system 1, the respective inverter devices 4 provide the three sinusoidal electric AC voltages Ui, U2 and U3. The AC voltages Ui, U2 and U3 may have, for example, a root mean square voltage of 230 volts, for example. Since the respective partial transformers ΤΙ, T2 and T3 ideally have a transfer factor of 1, an electric AC voltage having a root mean square value of 230 volts, for example, is respectively applied to the respective secondary sides SI, S2 and S3. The respective first transformed AC voltages Ui are added, with the result that a sum voltage of the transformed first AC voltages UTi is applied to the first connection A1. A sum voltage of the second transformed AC voltages UT2 is applied to the second connection A2. Finally, a sum voltage of the third transformed AC voltages UT3 is applied to the third connection.

The first connection A1 can be connected to a first phase LI of the medium voltage, the second connection A2 can be connected to a second phase L2 of the medium voltage and the third connection A3 can be connected to a third phase L3 of the medium voltage. The star point P can be connected to a neutral conductor N of the medium-voltage network. A three-phase system which is electrically connected to the medium-voltage network can be provided at the connections Al, A2 and A3.

In this case, provision may also be made for the respective AC voltages Ui, U2 and U3 provided using the respective inverter devices 4 to be respectively adapted. For example, the AC voltages Ui, U2 and/or U3 output using one inverter device 4 can be adapted to the respective AC voltages Ui, U2 and/or U3 output using a different inverter device 4. For this purpose,

PCT/EP2014/060827 2014P08112WOAU 11 a measuring unit may be provided, for example, in each of the inverter devices 4 and can be used to measure the AC voltages Ui, U2 and/or U3 from the other inverter devices 4. Alternatively or additionally, the respective inverter devices 4 may comprise a communication device or a communication port which is connected to a central control device. This means that, for example, the respective AC voltages Ui, U2 and/or U3 are adapted in such a manner that a respective sinusoidal sum voltage is produced at the respective outputs Al, A2 and/or A3.

The respective transformed AC voltages UTi, Ut2 and Ut3 are added at the respective outputs Al, A2 and A3. The respective medium voltage can be adapted using the number of converter apparatuses 2 and the transformed AC voltages UTi, UT2 and UT3 applied to the respective partial transformers ΤΙ, T2 and T3.

It is therefore possible to provide a modular converter system 1 which can be easily transported, for example. In addition, a standard mass product can be used to provide the respective converter apparatuses 2, with the result that the respective converter apparatuses 2 can be produced in a cost-effective manner. If one of the converter apparatuses 2 fails, the remaining converter apparatuses 2 can be controlled in such a manner that the missing electric voltage is compensated for. In addition, a corresponding fault message can be output via the communication device or the control device. Furthermore, no network filters are required since the individual converter apparatuses 2 produce a sinusoidal output voltage. This also makes it possible to use long connection lines. The form of the output voltage or the current can be influenced by individually controlling the inverter devices 4. In addition, it is possible to use favorable standard

PCT/EP2014/060827 2014P08112WOAU 12 inverter components which can be designed for low voltages, for example .

Furthermore, an inverter device 4 which fails during operation can be replaced in a simple manner since it is DC-isolated from the medium voltage. This also makes it possible to switch off the installation in a simple and favorable manner since the individual converter apparatuses 2 can individually isolate the flow of energy. There is no need to use any corresponding load interrupters for the medium-voltage network, for example. The power losses are very low on account of the comparatively high electric voltages or AC voltages Ui, U2 and U3 on the respective primary sides PI, P2 and P3. In addition, the cross section of the lines of the partial transformers ΤΙ, T2 and T3 can therefore also be reduced. Finally, it can be expected that the efficiency of the converter system 1 is very high since no downstream transformer and corresponding filters are required. PCT/EP2014/060827 - 13 - 2014P08112WOAU List of reference symbols 1 Converter system 2 Converter apparatus 3 Voltage source 4 Inverter device 5 Transformer device Al, A2, A3 Connection P Star point PI, P2, P3 Primary side SI, S2, S3 Secondary side Tl, T2, T3 Partial transformer uG Electric voltage Ui, U2, U3 AC voltage Uti, Ut2, Ut3 Transformed AC voltage

Claims

Patent claims

1. A converter system (1) for an electric supply network, comprising - a first and at least one second converter apparatus (2), each of the converter apparatuses (2) comprising - a voltage source (3) for providing an electric voltage (UG) , - an inverter device (4) for providing an AC voltage (Ui, U2, U3) from the electric voltage (UG) provided by the voltage source (3), and - a transformer device (5) for transforming the AC voltage (Ui, U2, U3) provided by the inverter (4) and applied to a primary coil into a transformed AC voltage (UTi, Ut2, the) which is applied to a secondary coil, - the secondary coils of the first and the at least one second converter apparatus (2) being electrically connected in series, - and a medium voltage formed by the series circuit of the secondary coils being applied to an output (Al, A2, A3) of the converter system (1).
2. The converter system (1) as claimed in claim 1, the inverter device (4) of the first converter apparatus (2) having a measuring unit for measuring the AC voltage provided using the inverter device (4) of the at least one second converter apparatus (2).
3. The converter system (1) as claimed in claim 1, the inverter device (4) of the first converter apparatus (2) being designed to adapt an amplitude and/or a phase of the AC voltage (Ui, U2, U3) provided using the inverter device (4) of the first converter apparatus (2) on the basis of the measured AC voltage from the inverter device (4) of the at least one second converter apparatus (2) .
4. The converter system (1) as claimed in claim 3, the inverter device (4) of the first converter apparatus (2) being designed to adapt the AC voltage (Ui, U2, U3) provided using the inverter device (4) of the first converter apparatus (2) in such a manner that the medium voltage has a substantially sinusoidal profile.
5. The converter system (1) as claimed in one of the preceding claims, the converter system (1) having a control device for controlling the inverter device (4) of the first and the at least one second converter apparatus (2).
6. The converter system (1) as claimed in claim 5, the first and/or the at least one second converter apparatus (2) having a communication device connected to the control device for the purpose of communicating data.
7. The converter system (1) as claimed in one of the preceding claims, the respective voltage source (3) of the first and the at least one second converter apparatus (2) being designed to output a DC voltage as the electric voltage (UG) .
8. The converter system (1) as claimed in one of the preceding claims, a number of turns of the primary coil corresponding to a number of turns of the secondary coil in the respective transformer device (5) of the first and the at least one second converter apparatus (2).
9. The converter system (1) as claimed in one of the preceding claims, the respective inverter device (4) of the first and the at least one second converter apparatus (2) being designed to output a first AC voltage (Ui) and at least one second AC voltage (U2) which is phase-shifted with respect to the first AC voltage (Ui) .
10. The converter system (1) as claimed in claim 9, the respective transformer device (5) of the first and the at least one second converter apparatus (2) comprising at least two partial transformers (Tl, T2, T3) with a respective primary side (PI, P2, P3) and a respective secondary side (SI, S2, S3), the first AC voltage (Ui) being applied to the primary side (PI) of a first of the at least two partial transformers (Tl) and the second AC voltage (U2) being applied to the primary side (P2) of a second of the at least two partial transformers (T2) .
11. The converter system (1) as claimed in claim 10, secondary sides (SI, S2, S3) of the first partial transformers (Tl) and the secondary sides (SI, S2, S3) of the second partial transformers (T 2) of the first and the at least one second converter apparatus (2) each being electrically connected in series .
12. The converter system (1) as claimed in one of the preceding claims, the converter system (1) being designed to transform a medium voltage applied to the connection by means of the respective transformer device (5) of the first and the at least one second converter apparatus (2) and to convert it by means of the respective inverter device (4) of the first and the at least one second converter apparatus (2).