WO2006021414A1

WO2006021414A1 - Transferring electric energy between converters

Info

Publication number: WO2006021414A1
Application number: PCT/EP2005/009070
Authority: WO
Inventors: Peter Mellberg
Original assignee: Bombardier Transportation Gmbh
Priority date: 2004-08-24
Filing date: 2005-08-23
Publication date: 2006-03-02
Also published as: GB0418857D0; GB2417622A

Abstract

The invention relates to an arrangement for transferring electric energy, in particular for high-power applications. The arrangement comprises a first converter (1) for converting an electric current, at least one second converter (4) for converting an electric current, and a direct current connection line (5b), which connects the first converter (1) with the at least one second converter (4). The direct current connection line (5b) is electromagnetically coupled to a secondary side inductance so that an impedance of the direct current connection line (5b) is influenced by the secondary side inductance.

Description

Transferring Electric Energy Between Converters

Description

The invention relates to an arrangement and a method for transferring electric energy. More particularly, the invention relates to the field of high-power applications, for example providing electric energy for a driving motor of a railroad traction vehicle.

In order to provide electric energy for propulsion of railroad vehicles, converters are used. A line converter may be connected to a single-phase alternating current network in order to convert the alternating current to a direct current. The line converter is connected to at least one motor converter via a direct current intermediate circuit. The motor converter inverts the direct current to a three-phase alternating current in order to provide a driving motor with electric energy. However, the invention is not limited to this specific arrangement. Rather, other types of converters (such as a three-phase line converter for industrial applications and/or a DC-DC converter) may be used in connection with the invention.

In many cases, the line converter and the motor converter are closely located to each other. This means that the direct current connection line between the converters is short and can be adapted to have a small inductance. However, one might wish to locate the line converter and the motor converter far away from each other, for some applications. For example, it might be desirable to locate the motor converter in the middle section of a railroad train and to locate the line converter at the front of the railroad train. As a result, the parasitic inductance of the direct current connection

CONFIRMATION OQPY line may cause adverse effects, such as oscillations at unknown resonance frequencies.

One way to handle the cable inductance is to introduce an inductor between the converters in the direct current connection line. Then, the cable inductance is negligible and the inductor or inductors determine the overall inductance. However, this may cause resonant oscillations during operation of the converters. In order to deal with this problem, a DC (direct current) resistor may be connected in series with the inductor. The DC resistor will damp the oscillations, but will also result in significant losses of electric energy. For example, if a DC resistor of 0.4 Ohm is used carrying a current of 500 A, electric energy is dissipated into heat at a power of 100 kW.

It is an object of the present invention to provide an arrangement and a method for transferring electric energy between a first converter and a second converter via a direct current connection line which make it possible to operate the converters at long distances to each other, wherein the operation is resistant to resonant oscillations and wherein the energy losses in the direct current connection line are moderate.

According to an aspect of the present invention it is proposed to electromagnetically couple the direct current connection line to a secondary side, wherein the secondary side comprises an inductance and a DC resistance. The secondary side is electrically insulated against the direct current connection line (the primary side). The arrangement is adapted so that the secondary side significantly determine^~s the effective impedance of the primary side. In particular, the secondary side may comprise a closed-loop electric circuit having an inductor and a DC resistor which are connected in series to each other.

More generally, the following is proposed: a first converter for converting an electric current, at least one second converter for converting an electric current, a direct current connection line, which connects the first converter with the at least one second converter, wherein the direct current connection line is electromagnetically coupled to a secondary side inductance so that an'impedance of the direct current connection line is influenced by the secondary side inductance.

Furthermore, it is proposed that the direct current connection line comprises a primary side inductor which is electromagnetically coupled to the secondary side inductance. In particular, the electromagnetic coupling may be realised by arranging the primary side inductor and a secondary side inductor (which secondary side inductor forms at least a part of the inductance) in a corresponding manner. For example, the primary side inductor and the secondary side inductor may be arranged like the primary coil and the secondary coil of a transformer.

The direct current connection line may be a first DC line of a DC intermediate circuit which connects the first converter with the second converter and only one of the direct current connection lines may comprise a (primary side) inductor which is electromagnetically coupled to the secondary side. This measure is sufficient to damp oscillations in the intermediate circuit, in particular severe oscillations due to fact that the DC intermediate circuit comprises long connection lines.

According to a preferred embodiment, the primary side inductor comprises a first coil of a first electrically conductive line, wherein the first electrically conductive line is electrically connected to the direct current connection line or is part of the direct current connection line. The secondary side inductance is at least partially formed by a second coil of a second electrically conductive line. At least a part of the first electrically conductive line and at least a part of the second electrically conductive line are wound around a common kernel area. As a result, the common kernel area is an area inside the first coil and inside the second coil. For example, the primary side inductor and the secondary side inductor may be integrated in the same electric part. In a specific embodiment, the second electrically conductive line may be wound around the coil of an inductor (the first coil) to produce the second coil. The first coil is electrically insulated against the second coil. The first electrically conductive line may comprise a smaller specific (per length) DC-resistance than the second electrically conductive line, for example due to a larger cross sectional area of a wire, in order to carry high electric currents. Furthermore, the second electrically conductive line may be wound around the first electrically conductive line on the outer side of the first coil.

It is an advantage of this embodiment that the electromagnetic coupling between the first coil and the second coil is very good and that second coils with different values of the inductance can be produced easily.

In a specific embodiment, the secondary side inductance is at least partially formed by a secondary side inductor, wherein the secondary side inductor and a direct current resistor are connected in series to each other. For example, the secondary side inductor and the direct current resistor may be part of a single-loop electric circuit.

it is an advantage of the present invention that it is possible to place the converters in any part of a railroad train, wherein resonant oscillations at the direct current connection line can be damped or can be avoided. For example, the first converter may be located in a first carriage of a railroad train and the second converter or at least one of the second converters may be located in a second carriage of the railroad train. In this case, the direct current connection line electrically connects the converters in the different carriages. The terms "first" and "second" in "first carriage" and "second carriage" do not necessarily denote the numbers of the carriages in their consecutive order. Furthermore, at least one of the carriages may be a railroad traction vehicle, such as a locomotive. The term "carriage" is not limited to a conventional carriage of the train which has at least two bogies. Rather, a carriage may be an element of a railroad train which can be separated from other elements.

Furthermore, the invention covers a propulsion system for a railroad train comprising the arrangement according to any embodiment described in this description.

In addition, a method for transferring electric energy (in particular for high-power applications) from a first converter via a direct current connection line to at least one second converter and/or vice versa is proposed: A secondary side inductance is used to damp electric oscillations on the direct current connection line, wherein the secondary side inductance is electromagnetically coupled to the direct current connection line and wherein the direct current connection line and the secondary side are electrically insulated against each' other.

According to a further aspect of the invention, a method for transferring electric energy, in particular for high-power applications, is proposed wherein a first converter for converting an electric current is provided, at least one second converter for converting an electric current is provided, the first converter and the at least one second converter are connected to each other via a direct current connection line, the direct current connection line is electromagnetically coupled to a secondary side inductance, the direct current connection line and the secondary side are electrically insulated against each other.

The invention is not restricted to the case of two converters which are connected via the direct current line. For example a line converter may be connect via the line with a plurality of second converters (e.g. a plurality of motor converters in a railroad train).

In the following, the invention will be described in more detail by way of example and with reference to the accompanying drawings. However, the invention is not limited to the example, which corresponds to the presently known best mode of the invention. The figures of the drawing show:

Fig. 1 an arrangement with a line converter and a motor converter;

Fig. 2 a two-dimensional diagram illustrating the resistive (real) part of an impedance as a function of a frequency of the current carried by the direct current connection line;

Fig. 3 a two-dimensional diagram illustrating the reactance (the imaginary part) as a function of the frequency; Fig. 4 a two-dimensional diagram illustrating the amplitude of an oscillation as a function of the frequency for a conventional arrangement; and

Fig. 5 a two-dimensional diagram illustrating the amplitude of an oscillation as a function of the frequency for an arrangement according to the present invention.

Figure 1 shows a line converter 1 which may be connected to a single-phase alternating current energy supply network via connection contacts 2a, 2b. Furthermore, the arrangement comprises a second converter 4 which may be, for example, a three-phase motor converter for providing electric energy via three phases of an alternating current connection (not shown in Figure 1 ) to a motor.

The line converter 1 and the second converter 4 are connected to each other via a direct current intermediate circuit 3 having two DC lines 5a, 5b. Figure 1 is a schematic drawing and the arrangement may comprise further parts and/or components, such as capacitors which are arranged so as to connect the two DC lines 5a, 5b.

A closed-loop circuit 14 is electromagnetically coupled to the DC line 5b of the direct current intermediate circuit 3. The DC line 5b constitutes a primary side of the electromagnetic coupling. The ^"closed-loop circuit 14 constitutes the secondary side of the coupling; The electromagnetic coupling is realised by a primary side inductor 6, which comprises a part of the DC line 5b, and by a secondary side inductor ^"8. During operation of the arrangement, an Increase or decrease of the electric current carried by the DC line 5b causes an electromagnetic field which induces a corresponding electric current in the secondary side inductor 8, due to the electromagnetic coupling between the primary side inductor 6 and the secondary side inductor 8.

The internal (ohmic) resistances of the primary side inductor 6 and of the secondary side inductor 8 are symbolised (in the manner of an equivalent circuit diagram) by resistors 10 and 12 which are connected in series with the respective inductor 6, 8. However, the closed-loop circuit 14 comprises an additional resistor 13 which is connected in series with the secondary side inductor 8. Terminal points at opposite ends of the primary side inductor 6 are denoted with letters A and B.

The effective impedance z_AB across the terminal points A and B is

AB

equation (1-1), wherein z, denotes the impedance of the primary side O₁ being the internal resistance of the primary side inductor 6 and L_x being the inductance of the primary side inductor 6), wherein z₂ denotes the impedance of the secondary side (r₂ being the internal resistance of the secondary side inductor 8 and L₂ being the inductance of the primary side inductor 8), wherein z₂ is the impedance z₂ of the secondary side referred to the primary side, wherein R denotes the resistance of the resistor 13, wherein ω = 2π - f denotes the frequency of an alternating current carried by the DC line 5b and wherein j denotes the square root of -1. Furthermore,

M denotes the mutual inductance defined as, \M\ = Jc^L₁L₂ , wherein A: is a coupling factor which describes the electromagnetic coupling between the primary side and the secondary side.

It can be derived from equation (1-1 ) that the real part of the transferred secondary impedance is larger than zero. Hence, the total resistance on the primary side js increased compared to the case without electromagnetic coupling of the primary side inductor. However, the transferred imaginary part is negative and the total reactance is therefore reduced compared to the case without electromagnetic coupling of the primary side inductor.

If we introduce the coupling factor k according to the definition given above, equation (1-1) can be written as follows, wherein the real part and the imaginary part are separate terms,

^Z-

For example, the coupling factor k may be equal to 0.9, the inductance L₁ of the primary side may be equal to 1 mH, the inductance L₂ of the secondary side may be equal to 1 mH, the internal resistance r_x of the primary side inductor 6 may be equal to 10 mΩ, the internal resistance r₂ of the secondary side inductor 8 may be equal to 20 mΩ and the resistance of the resistor 13 in the closed-loop circuit 14 may be equal to 0.6 Ω.

Figure 2 and Figure 3 show the corresponding values of the real part B and of the imaginary part S in Ω as a function of the frequency f. In Figure 3, the upper curve (which is merely a straight line) corresponds to the case of an inductor having an inductance I₁ of 1 mH without electromagnetic coupling to a secondary side. This confirms the conclusion given above that the electromagnetic coupling reduces the imaginary part S.

Figure 4 and Figure 5 show the result of an experiment, wherein an electric current of 10 A is input at the second converter 4 as a ripple current having a frequency f. The amplitude of the voltage response in the direct current intermediate circuit 3 at the second converter 4 and at the line converter 1 is show in Figure 4 for the case without a secondary circuit (or coupling factor zero) and is a shown in Figure 5 for the above given example with a secondary circuit and a coupling factor of 0.9.

It can clearly be seen that the resonant oscillations (in this. example at a frequency of 50 Hz) are significantly damped in the case with a secondary circuit. However; this result is achieved without a resistor which is connected in series with the primary side inductor. Consequently, the ohmic energy losses due to the remaining DC- resistance in a direct current connection line between the converters are small. This makes it is possible to arrange the two converters at significant distances to each other. In particular, the line converter may be placed in the middle section of a railroad train and the motor converter may be placed in the front of the train, or vice versa.

Claims

1. An arrangement for transferring electric energy, in particular for high-power applications, wherein the arrangement comprises: a first converter (1 ) for converting an electric current, at least one second converter (4) for converting an electric current, a direct current connection line (5b), which connects the first converter (1) with the at least one second converter (4), wherein the direct current connection line (5b) is electromagnetically coupled to a secondary side inductance so that an impedance of the direct current connection line (5b) is influenced by the secondary side inductance.

2. The arrangement of the preceding claim, wherein the direct current connection line (5b) is a first direct current connection line of a direct current intermediate circuit which connects the first converter (1) with the second converter (4) and wherein only one of the direct current connection lines (5a, 5b) comprises a primary side inductor (6) which is electromagnetically coupled to the secondary side.

3. The arrangement of one of the preceding claims, wherein the direct current connection line (5b) comprises a primary side inductor (6) which is electromagnetically coupled to the secondary side inductance.

4. The arrangement of the preceding claim, wherein the primary side inductor (6) comprises a first coil of a first electrically conductive line, wherein the first electrically conductive line is electrically connected to the direct current connection line or is part of the direct current connection line, wherein the secondary side inductance is at least partially formed by a second coil of a second electrically conductive line and wherein at least a part of the first electrically conductive line and at least a part of the second electrically conductive line are wound around a common kernel area.

5. The arrangement of any one of the preceding claims, wherein the secondary side inductance is at least partially formed by a secondary side inductor (8) and wherein the secondary side inductor (8) and a direct current resistor (13) are connected in series to each other.

6. The arrangement of any one of the preceding claims, wherein the first converter (1 ) is located in a first carriage of a railroad train and wherein the second converter (4) or at least one of the second converters is located in a second carriage of the railroad train.

7. A propulsion system for a railroad train comprising the arrangement of any one of the preceding claims.

8. A method for transferring electric energy, in particular for high-power applications, from a first converter (1 ) via a direct current connection line (5b) to at least one second converter (4) and/or vice versa, wherein a secondary side inductance is used to damp electric oscillations on the direct current connection line (5b), wherein the secondary side inductance is electromagnetically coupled to the direct current connection line and wherein the direct current connection line (5b) and the secondary side are electrically insulated against each other.

9. A method for transferring electric energy, in particular for high-power applications, wherein a first converter (1 ) for converting an electric current is provided, at least one second converter (4) for converting an electric current is provided, the first converter (1 ) and the at least one second converter (4) are connected to each other via a direct current connection line (5b), the direct current connection line (5b) is electromagnetically coupled to a secondary side inductance, the direct current connection line (5b) and the secondary side are electrically insulated against each other.