WO2012098107A2

WO2012098107A2 - Converter circuit with a charging unit

Info

Publication number: WO2012098107A2
Application number: PCT/EP2012/050626
Authority: WO
Inventors: Marc Pellerin; Joseph DURON; Philippe Haeberlin; Philippe Stefanutti; Silvia LEWDENI-SCHMID; Toufann Chaudhuri
Original assignee: Abb Technology Ag
Priority date: 2011-01-17
Filing date: 2012-01-17
Publication date: 2012-07-26
Also published as: WO2012098107A3

Abstract

In a rail vehicle, a converter circuit comprises a housing 56 for enclosing a fluid in which housing at least a part 52, 54 of a charging unit 50 for charging an energy storage of the converter circuit is accommodated. The housing 56 comprises a fluid 58 for cooling and/or isolating the part 52, 54 of the charging unit 50. A transformer 28 or generally an inductor 28 may be accommodated in the housing 56.

Description

DESCRIPTION

CONVERTER CIRCUIT WITH A CHARGING UNIT

FIELD OF THE INVENTION

The invention relates to the field of supplying vehicles with electrical power from a power grid. In particular, the invention relates to a converter circuit, a use of a converter circuit and a rail vehicle.

BACKGROUND OF THE INVENTION

To be supplied with power, many electrically driven rail vehicles are connected over a rail catenary to a power grid.

Usually, such a rail vehicle comprises a converter with a converter circuit that is adapted for converting the AC voltage from the power grid into an AC voltage of different voltage and frequency to be supplied to the motor of the rail vehicle. For example, the converter circuit comprises a rectifier and an inverter electrically connected over a DC link with an energy storage, for example a capacitor.

There are different ways to charge up the DC link capacitor of the voltage converter. The energy required to charge the capacitors may be taken from the power grid feeding the converter. For example, a resistor may be connected in series with the capacitors during the charging up phase to limit the current inrush and to damp oscillations that may be caused by resonant phenomena between the capacitors and further inductors of the converter circuit. When the capacitors are charged, the resistor may be by-passed by using a switch. In the case of a medium voltage converter, the resistor and the switch may be chosen such they withstand a medium voltage, in the case of rail vehicle normally 15kV nominal (75kV BIL). There may be also 25kV applications (with 95 or even 125kV BIL).

The resistor and the switch may be seen as components of a charging unit of the converter circuit. In known applications, the charging unit is connected via a step down transformer with the power grid. Usually, the voltage level after the step down transformer is low enough so that standard component such as a contactor and a wound resistor may be used for the charging unit. In this case, the insulation distances required in air may be still acceptable.

In EP 1750360 Al, in particular in Fig. l a multilevel power converter topology of a traction transformer arrangement of a railway vehicle is disclosed. A plurality of converters is connected in series on the input side over line impedance and direct to the railway current collector. The converter topology works without energy storage on converter side. Therefore no charging unit to charge the energy storage is needed. In Fig. 2A fluid cooling circuit to cool the transformer and the converters is further proposed. In Fig.1 of "Main traction converter with medium-frequency transformer: Control of converters around MF transformer"; International symposium on Power Electronics, Electrical Drives, Automation and Motion, 2008; SPEED AM 2008., IEEE, Piscataway, NJ, USA; 11 June 2008 (2008-06-11), pages 1194-1198, XP031293362, ISBN: 978-1- 4244-1663-9; by Komrska. et al a traction converter topology with a medium frequency transformer is diclosed. An energy storage in form of a capacity is interconnected between the primary voltage rectifiers and the primary voltage inverters and can be charged via an line impedance over a resistor and a switch form the grid. Resistor and switch are connected in parallel and forming the charging unit which is directly connected to the grid. A system for cooling parts or the entire topology is not proposed.

In Fig. l of "Power electronics traction transformer", 2007 European Conference on Power Electronics and Applications, 1 January 2007, (2007-01-01), pages 1-10, XP55008025, DOI: 10.1109/EPE.2007.4417649; a multilevel converter topology connected to the catenary through a choke inductor is proposed for railway applications. Sixteen direct current converters (cycloconverters) are connected in series and deliver a medium voltage to the medium frequency transformer. The converter topology works without energy storage on cycloconverter side (as illustrated in Fig. l) and therefore no charging unit is needed. In Fig.5 the cooling principle is shown in which the converters and the medium frequency transformer are cooled with circulating oil.

DESCRIPTION OF THE INVENTION

It may be an object of the invention to simplify the construction of a converter for a rail vehicle and to simplify the maintenance of a rail vehicle.

This objective is achieved by the subject-matter of the independent claims. Further embodiments are evident from the dependent claims and the following description. A first aspect to the invention relates to a converter circuit, for example for a rail vehicle.

According to an embodiment of the invention, the converter circuit comprises a converter subsystem, a charging unit and a housing. The converter subsystem comprises at least a first converter unit, a DC-link with an energy storage and a second converter unit.

The charging unit is adapted for charging the energy storage. The energy storage may comprise a medium voltage capacitor. A charging unit may be defined as a unit that permits to charge capacitors.

On an AC side, the first converter unit is connected to the charging unit on a DC side to the DC link. The first converter unit may be adapted to convert an AC voltage from the power grid into a DC voltage for the DC link. On a DC side, the second converter unit is connected to the DC link. The second converter unit may be adapted to convert the DC voltage from the DC link to an AC voltage with a different frequency.

In other words, the rail vehicle may comprise a converter with a converter circuit that is adapted for converting a first current of a first voltage and/or a first frequency from the power grid into a second current of a second voltage and/or a second frequency for further components of the converter. These components may comprise a transformer and an electrical motor for driving the rail vehicle.

According to an embodiment of the invention, at least a part of the charging unit is accommodated in the housing for enclosing a fluid, and the housing comprises a fluid for cooling and/or isolating the part of the charging unit. The housing may comprise a tank or is a tank which accommodates the at least one part of the charging unit. As a rule, the fluid is oil, but also gas may be possible for the fluid. The dielectric properties of the fluid may be used for the isolation of the at least one part of the charging unit and/or for the transport of heat, i. e. for the cooling of the at least one part of the charging unit.

In general, there are other setups possible for a converter circuit in which the charging unit may be used. For example, the converter circuit may comprise a direct converter connected on the one side to the charging unit and on the other side to the transformer, which is connected to a further converter with a DC link. In this case this DC link may be charged by the charging unit.

According to an embodiment of the invention, the charging unit is electrically connected with the power grid, i. e. the charging unit is not galvanically isolated from the power grid. In such a way, standard components such as a contactor and a wound resistor may not be used for the charging unit, since they may not withstand the voltage of the power grid. The required insulation distances in air would become very large and the charging unit may have to withstand the high voltage. The use of oil, or in general a fluid, as a dielectric makes it possible to reduce these distances. It may also be possible to use a solid for isolating the parts inside the housing.

According to an embodiment of the invention, the first converter unit may be connected over the charging unit to a power grid. It may also be possible that the first converter unit is connected over the charging unit to the ground, i. e. to an earthing. The converter circuit may comprise more than one charging unit. Additionally and/or alternatively it may be possible that the charging unit is connected on the secondary side, i.e. after the converters.

According to an embodiment of the invention, the charging unit may be placed on the low voltage side of the power supply, for example, the low voltage side of the converter circuit.

According to an embodiment of the invention, the converter circuit comprises an inductor that is accommodated in the housing. For example, the inductor may be an inductor of a transformer (the primary or secondary windings) or it may be a smoothing inductor. This inductor may be isolated and cooled by the fluid in the housing.

According to an embodiment of the invention, the converter circuit comprises a transformer. On an AC side, the second converter unit is connected to the transformer. The transformer may be adapted for transforming the AC voltage from the second converter unit into a lower AC voltage.

The transformer may be accommodated in the housing. In such a way, all the inductors of the transformer may be cooled and isolated by the fluid in the housing. For example, the whole charging unit may be located in an enclosure (i. e. the housing) containing one or more transformers, and/or one or more inductors. The enclosure can be filled with a dielectric fluid or solid.

If a tank already is necessary for other components, it may be advantageous to use the same tank for the charging unit. This may also permit to save weight and space.

If the tank is filled with a dielectric fluid or dielectric solid, it may reduce the clearance and/or creepage distance of the charging unit.

It may be an aspect of the invention, that standard medium voltage components may be used to build the charging unit, i. e. the at least one part of the convert unit may be a medium voltage component. These components may be located inside the tank of the transformer or the smoothing inductor and may be surrounded by oil. Better dielectric properties of the oil compared to air may reduce the clearance and creepage distances.

According to an embodiment of the invention, a smoothing inductor is accommodated in the housing. For example, the charging unit may be electrically connected over the smoothing inductor to the power grid, i. e. the charging unit is galvanically connected to the power grid. The smoothing inductor may be used for smoothing resonances caused by capacitors and/or inductors of the converter circuit. Since the smoothing inductor may not be galvanically isolated from the grid, for example since it is not connected via a transformer to the grid, it also has to withstand the same voltages as the charging unit. Thus, the fluid or solid in the housing may be used for isolating the smoothing inductor, too.

According to an embodiment of the invention, the converter circuit comprises a further converter subsystem connected in series with the (first) converter subsystem. In other words, the above mentioned converter subsystem may be a first converter subsystem and the converter circuit may have a plurality of converter subsystems connected in series.

The further converter subsystem may comprise the same components as the first converter subsystem (except the charging unit). In such a way the charging unit may be used for charging both converter subsystems. The charging unit may be a charging unit for a multilevel converter that is directly (not through a step down transformer) connected to a medium voltage grid.

According to an embodiment of the invention, the charging unit (or an additional charging unit) may be connected between two converter subsystems, for example between the first and the second converter subsystem.

All the embodiments may be applicable to a charging unit for a converter (multi-level included) comprising at least one capacitor. The charging unit may be connected to the main power supply of the converter, for example the rail catenary. In the case of a converter comprising more than one capacitor, connecting the charging unit to the main power supply allows to use only one charging unit.

The charging unit may be seen as a capacitors charging unit for a multilevel voltage source converter that is connected to a railway catenary. Using such a charging unit may enable to charge the DC link capacitor of the multilevel converter in a controlled manner, avoiding current peaks on the catenary line and also resonances. According to an embodiment of the invention, the charging unit comprises a charging resistor and a switch connected in parallel. The charging resistor may be a medium voltage resistor, i. e. a resistor adapted for a voltage between 1 kV and 15 or even 20 kV. Also applications with 25 kV and higher may be possible. The resistor may be seen as a surge energy resistor. The resistor may be selected for its high surge capability required to charge the capacitor.

According to an embodiment of the invention, the switch is a vacuum switch. The switch may be a medium voltage switch. For example, a vacuum bottle may be used as switch. It may be the same kind of switch that may be used in switchgear applications such as a circuit breaker. The switch may be opened and/or closed using a magnetic actuator (a mechanical actuator could also be used) controlled by a dedicated electronic board, for example by the controller of the converter circuit.

For charging the energy storage, the switch may be opened and the energy storage may be connected to the power grid over the resistor.

The medium voltage switch and the medium voltage resistor may be directly connected with the medium voltage powering line, i. e. the rail catenary. They may be situated in oil (or in gas) to reduce insulating distances. The tank of the transformer may be used for housing the medium voltage switch and the medium voltage resistor.

According to an embodiment of the invention, the charging resistor and/or the switch are integrated into the housing. The charging resistor or the switch may be the at least one part of the charging unit. The resistor and the switch may be located in the tank or in the housing.

According to an embodiment of the invention, an actuator of the switch is arranged outside of the housing. The actuator and the control board (i. e. the controller) may be located outside of the tank or outside of the housing to enable easy maintenance (easy in the sense that the actuator and the control board may be dismounted without having to open the tank of the transformer.

According to an embodiment of the invention, the actuator may be positioned on the switch in a slot of the housing. The switch and/or the resistor may be accessible from the upper side of the housing, such that the switch and/or the resistor are adapted for being dismounted from the housing without discharging the fluid from the housing. In such a way, if maintenance is necessary, it can be done without having to empty the tank or the housing fully or at least partially. According to an embodiment of the invention, the power grid is a medium voltage grid, the converter subsystem is a medium voltage system, and/ or the transformer is a medium voltage transformer. In other words, these components are all adapted for operating with a medium voltage and may be adapted for withstanding a medium voltage. A medium voltage may be a voltage between 1 kV and 15kV, 20 kV or 25kV.

Further aspects of the invention relate to a use of a converter circuit as described in the above and in the following and to a rail vehicle with a converter circuit as described in the above and in the following.

If technically possible but not explicitly mentioned, also combinations of embodiments of the invention described in the above and in the following may be embodiments of the converter circuit and the rail vehicle.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

Fig. 1 schematically shows a rail vehicle according to an embodiment of the invention.

Fig. 2 schematically shows a converter circuit according to an embodiment of the invention.

Fig. 3 schematically shows a housing according to an embodiment of the invention.

Fig. 4 schematically shows a housing according to a further embodiment of the invention.

Fig. 5 schematically shows a housing according to a further embodiment of the invention.

Fig. 6 schematically shows a converter circuit according to a further embodiment of the invention.

Fig. 7 schematically shows a converter circuit according to a further embodiment of the invention.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. l shows a rail vehicle 10 on rails 12 with a current collector 14 connecting the rail vehicle 10 to a power grid 16. For example, the power grid 16 may provide a voltage of 15 kV at 16.7 Hz.

The rail vehicle 10 has an electrical motor 18 that is supplied by a converter circuit 20 connected to the current collector 14. In such a way, the rail vehicle 10 is driven by electrical power from the power grid 16. The electrical vehicle 10 further has a controller 22 for controlling the converter circuit 20 and the motor 18.

Fig. 2 shows the converter circuit 20 in more detail. The converter circuit 20 comprises a plurality of converter subsystems 24 connected in series on the input side. Each converter subsystem comprises a first part 26 for generating a voltage with a higher frequency as the frequency of the power grid 16, a transformer 28 for transforming the voltage with the higher frequency to a lower voltage level and a second part 30 for rectifying the lower voltage.

Each first part 26 of the converter subsystem comprises a first converter unit 32 and second converter unit 34 connected over a DC link 36. The first converter unit 32 is a rectifier for rectifying the AC voltage from the power grid 14 into a DC voltage; the second converter unit 34 is an inverter for generating an AC voltage from the DC voltage. The DC link 36 comprises an energy storage 38 in the form of a capacitor 38.

The converter subsystems 24 are connected in parallel on the output side. The rectified lower voltages of the second parts 30 of the converter subsystems 24 are supplied to a further DC link 40 and after that to one or more further inverters 42, which generate the supply voltages for the one or more electrical motors 18.

On the input side, the first converter subsystem 24 is connected to the current collector 14, the last converter subsystem is connected to an earthing 44, for example the rails 12.

Between the current collector 14 and the first converter subsystem 24, the converter circuit 20 further comprises a main switch 46, a smoothing inductor 48 and a charging unit 50 connected in series. The charging unit 50 comprises a bypass switch 54 and a resistor 52 connected in parallel.

Additionally or alternatively, a charging unit 50a with a bypass switch 54a and a resistor 52a may be connected between the earthing 44 and the last converter subsystem 24. Further additional or alternative charging units 50b (with a bypass switch 54b and a resistor 52b) may be connected between the converter subsystems 24. In general one or more charging units 50, 52a, 52b may be connected into the series of converter subsystems 24.

When the rail vehicle 10 is switched off, the main switch 46 is opened, thus completely disconnecting the converter circuit 20 from the power grid 16.

For starting the operation of the converter circuit 20, the switch 54 (and/or the switches 54a, 54b) is opened (by an actuator 62, see Fig. 3 to 5) and after that the main switch 46 closed. In such a way, the energy storages 38 are electrically connected via the first charging units 26 and via the resistor 52 (and or the resistors 52a, 52b) to the power grid 14. With this switch position, the energy storages 38 may be charged until a certain charging level has been reached.

When the energy storages 38 are charged, the switch 54 is closed and the converter subsystem are directly connected to the power grid 16. The normal operation of the converter circuit may start.

The switches 46, 54, 54a, 54b and in particular the actuator 62 are controlled by the controller 22.

Fig. 3 schematically shows a housing 56 accommodating the transformers 28, the smoothing inductor 48 and the charging unit 50. The transformers 28, the inductors 48 and the charging unit 50 are situated in oil 58 for isolating and cooling the components 28, 48 and 50. The housing 56 may comprise a tank for the oil 58or the housing may be a tank for the oil 58.

The housing has a slot 60 on its upper side for receiving an actuator 62 for actuating, i. e. opening and closing the switch 54. Due to the slot, the arrangement of housing and actuator may be very compact. Without the slot it may be possible that the actuator may be removed from the housing without emptying the housing at all.

It makes it easier for maintenance not to have any slot.

For better maintaining the components inside the housing 56 and in particular the charging unit 50, the actuator 62 may be removed from the slot 60. When the actuator 62 is removed, the switch 54 and the resistor 52 may be accessed via the opening 60. It is not necessary to remove all of the oil 58 from the housing 56 for exchanging the switch 54 or the resistor 56. With the slot, only just enough oil may have to be removed such that the oil does not spill out into the slot. When there is no slot, then (almost) no oil needs to be removed. In practice however, a small quantity may be removed to avoid it spilling out. It may be important that the other components in the tank remain covered fully in oil such they are not exposed to humidity.

Fig. 4 schematically shows a further embodiment of a housing 56. Only the inductor 48 and the charging unit 50 are accommodated in the housing 56 for enclosing the fluid 58. This configuration may be useful, when using dry transformers 28 that do not need to be situated in oil 58.

Fig. 5 schematically shows a third embodiment of a housing 56 in which only the charging unit 50 is accommodated in the housing 56 for enclosing the fluid 58. In this case, for example, the inductor 28 and the transformers 28 may have a housing or tank of its own.

Fig. 6 shows a further embodiment of a converter circuit 20a. In the embodiment of Fig.

6, the converter circuit 20a has a transformer 28a with multiple primary windings and one secondary winding. The transformer 28a has one single core. Each second converter unit 34 of the converter subsystems 24 are connected to one of the primary windings. The secondary winding is connected to one second part (rectifier) 30 of the converter circuit 20a, wherein the rectifier 39 over a further DC link 40 and a further inverter 42 is connected to a motor 18. The primary windings and/or secondary winding of the transformer 28b may be accommodated in the housing 56.

Fig. 7 shows a further embodiment of a converter circuit 20b. In the embodiment of Fig.

7, the converter circuit 20b has two (or a multiple of) transformers 28b with multiple primary windings and one secondary winding. Each second converter unit 34 of the converter subsystems 24 are connected to one of the primary windings of one of the transformers 28b. The secondary winding of the transformer 28b is connected to a second part (rectifier) 30 of the converter circuit 20b. Each rectifier 30 is connected over a further DC link 40 and a further inverter 42 to a motor 18. The primary windings and/or secondary windings of the transformers 28b may be accommodated in the housing 56.

It has to be understood that the charging unit 50 of the embodiments of Fig. 6 and Fig. 7 may be situated at the other positions 50a, 50b indicated in Fig. 2. Also, the embodiments of Fig. 6 and Fig. 7 may comprise more than one charging unit 50, 50a, 50b as indicated in Fig. 2.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference symbol in the claims should not be construed as limiting the scope.

LIST OF REFERENCE SYMBOLS

10 rail vehicle

12 rail

14 current collector

16 power grid

18 motor

20, 20a, 20b converter circuit

22 controller

24 converter subsystem

26 first part of converter subsystem

28, 28a, 28b transformer

30 second part of converter subsystem

32 first converter unit

34 second converter unit

36 DC link

38 energy storage, capacitor

40 further DC link

42 further inverter

44 earthing

46 main switch

48 smoothing inductor

50, 50a, 50b charging unit

52, 52a, 52b resistor

54, 54a, 54b bypass switch

56 housing

58 oil

60 slot

Claims

A converter circuit (20), comprising:

a converter subsystem (24),

a charging unit (50),

wherein the converter subsystem (24) comprises at least a first converter unit (32), a DC-link (36) with an energy storage (38) and a second converter unit (34), wherein the charging unit (50) is adapted for charging the energy storage (38), wherein the first converter unit (32) on an AC side is connected to the charging unit (50) and on a DC side is connected to the DC-link (36),

wherein the second converter unit (34) on an DC side is connected to the DC link (36),

characterized in that a housing (56) for enclosing a fluid is provided and in that at least a part (52, 52a, 52b, 54, 54a, 54b) of the charging unit (50) is accommodated in the housing (56), and

in that the housing (56) comprises a fluid (58) for cooling and/or isolating the part (552, 52a, 52b, 54, 54a, 54b) of the charging unit (50).

The converter circuit (20) of claim 1, further comprising:

a transformer (28),

wherein the second converter unit (34) on an AC side is connected to the transformer (28), wherein the transformer (28) is accommodated in the housing (56).

The converter circuit (20) of claim 1 or 2, further comprising:

a smoothing inductor (48) accommodated in the housing (56).

4. The converter circuit (20) of claim 3,

wherein the charging unit (50) is electrically connected over the smoothing inductor (48) to a power grid (16).

5. The converter circuit (20) of one of the preceding claims, further comprising:

a further converter subsystem (24) connected in series with the first converter subsystem (24).

6. The converter circuit (20) of one of the preceding claims,

wherein the charging unit (50) comprises a charging resistor (52, 52a, 52b) and a switch (54, 54a, 54b) connected in parallel.

7. The converter circuit (20) of claim 6,

wherein the charging resistor (52) and/or the switch (54) is integrated into the housing.

8. The converter circuit (20) of one of the claims 6 and 7,

wherein the switch (54) is a vacuum switch.

9. The converter circuit (20) of one of the claims 6 to 8,

wherein an actuator (62) of the switch (54) is arranged outside of the housing (56).

10. The converter circuit (20) of claim 9,

wherein the actuator (62) is positioned on the switch (54) in a slot (60) of the housing (56).

11. The converter circuit (20) of one of the claims 6 to 10,

wherein the switch (54) and/or the resistor (52) are accessible from the upper side of the housing (56) , such that the switch (54) and/or the resistor (52) are adapted for being dismounted from the housing (56) without discharging the fluid (58) from the housing (56).

12. The converter circuit (20) of one of the preceding claims,

wherein the energy storage (38) comprises a capacitor.

13. The converter circuit (20) of one of the preceding claims,

wherein the converter circuit is connected to a medium voltage power grid (16), wherein the subsystem (24) is a medium voltage system,

wherein the transformer (28) is a medium voltage transformer.

14. A use of a converter circuit (20) according to one of the claims 1 to 13 in a rail vehicle (10).

15. A rail vehicle (10) with a converter circuit (20) according to one of the claims 1 to