CH719226A2 - converter. - Google Patents

Abstract

An electrical converter according to the invention is provided for exchanging energy between a single-phase AC voltage input of a given frequency and amplitude and a three-phase three-phase voltage output of variable amplitude and frequency. An input connection (38) is connected to a first output connection (37) of the converter directly or via an output inductance (34a). A switching unit (100) is designed to feed a second and a third output connection (35, 36) of the converter with different AC voltages based on at least one input voltage of the single-phase AC voltage system, so that together with the voltage at the first output connection (37) of the Inverter results in a required three-phase system of voltages.

Description

The invention relates to the field of power electronic circuit technology and in particular to a topology of an electrical converter with a single-phase AC voltage input of a given frequency and amplitude and a three-phase three-phase voltage output of variable amplitude and frequency, this variation also including a DC voltage.

STATE OF THE ART

[0002] In order to minimize electrical conduction losses, high-power electrical systems are usually supplied with energy by means of high and/or medium-voltage lines. In the case of railway systems, for example, single-phase AC systems with 15 kV and 16.67 Hz are widely used in Switzerland. By comparison, electric machines (e.g. electric train motors) are generally operated in three phases with relatively low voltages and relatively high currents. In order to avoid the need for complex mechanical gearing, it is also advantageous to be able to operate these electrical machines with voltages (and currents) of variable frequency and amplitude.

In order to make this possible, an electrical converter is used, which converts an input-side, single-phase AC voltage with a given frequency and amplitude into an output-side, three-phase AC voltage (and current) with variable frequency (including zero frequency) and variable amplitude. The converter used is also able to exchange approximately pure active power with the grid and to provide the voltages and currents required on the output side. In addition, there are further requirements for the converter such as bidirectional power flow, e.g. for the recuperation of braking energy, high efficiency, low complexity, compact design, low weight, low maintenance effort, low acquisition and maintenance costs, etc.

In addition, corresponding converters can be used in the generation of the single-phase AC voltage system with 16.67 Hz, which is fed by the national three-phase 50 Hz transmission network

Fig. 1 shows a converter topology that is widely used today, with a mains transformer 103 and a DC intermediate circuit 105. A possible flow of energy leads from a single-phase voltage source 25 via input terminals 31, 32 and an optional mains impedance 33, via the mains transformer 103, to a rectifier 107, DC intermediate circuit with optional center tap 105, inverter 108, and optional rotary system impedances 34 to terminals 35, 36 and 37 of a rotary system, ie a multi-phase AC voltage system. In particular, this topology enables bi-directional power flow and variable output amplitude and frequency, while virtually no reactive power is exchanged with the grid. Since there are currently no power semiconductors that can switch high or medium voltages directly, the voltage on the input side is first reduced to a level that is compatible with power semiconductors using a mains-frequency transformer. Since the mains or supply voltage frequency fgoft is relatively low (16.67 Hz - 50Hz), the volume V and thus also the weight of this transformer are correspondingly large for a given apparent power S (approximately V ∝ (S/fg)<3⁄4> ), while the efficiency is in the range of 87%-97%, see e.g. "ABB breakthrough transformer for trains improves efficiency and safety significantly" published by ABB as a press release on 09/18/2018.

[0006] As shown in FIG. 1 also shows that the mains-frequency transformer is connected on the secondary side by a suitable rectifier circuit or power semiconductor with a DC intermediate circuit. which can have a center tap connected. The intermediate circuit is then connected to one or more three-phase voltage systems on the output side via one or more inverter circuits. The DC intermediate circuit decouples the input-frequency side of the converter from the output-frequency side. In this way, among other things, beats between the voltages and/or currents at the input frequency and the voltages and/or currents at the output side can be avoided. Only when the output is operated at very low frequencies, e.g. when starting a motor, do additional measures have to be taken to enable the conversion of the DC intermediate circuit voltage(s) into low-frequency or zero-frequency (DC) output voltages and currents.

Several concepts have been presented that try to replace the mains-frequency transformer with modular topologies with one or more medium-frequency transformers, e.g. in "MVDC Railway Traction Power Systems; State-of-the Art, Opportunities, and Challenges” by P. Simiyu and I.E. Davidson, published in Energies, vol. 14, no. 14, p. 4156, Jul. 2021, and "Solid-State Transformers in Locomotives Fed through AC Lines: A Review and Future Developments," by S. Farnesi, M. Marchesoni, M. Passalacqua, and L. Vaccaro, published in Energies, vol. 12, no. 24, p. 4711, Dec. 2019, among other things to reduce the converter volume and weight and potentially increase the efficiency. However, the complexity of these systems is significantly higher, which has a direct impact on reliability. For example, several DC intermediate circuits are used, each of which must be supplied by an upstream rectifier circuit and a downstream inverter circuit, both bidirectional. The number of semiconductors required increases accordingly and with it the statistical probability of defects. In addition, the number and complexity of the associated regulation and control systems are increasing, which further reduces the statistical reliability of the overall system.

PRESENTATION OF THE INVENTION

It is therefore a possible object of the invention to create an electrical converter for the exchange of energy between a single-phase AC voltage input of a given frequency and amplitude and a three-phase three-phase voltage output of variable amplitude and frequency, which has a simplified hardware structure compared to known solutions.

Another possible object of the invention is to provide an alternative to existing solutions.

At least one of these tasks is solved by an electrical converter according to patent claim 1.

The input voltage system is a single-phase AC voltage system with an input frequency and an input amplitude. The output voltage system is a three-phase AC voltage system with an output frequency and an output amplitude.

The single-phase AC voltage system typically has a frequency that can be selected but is fixed during operation of the converter. This can also be zero, corresponding to a direct current (DC). The three-phase AC system has an output frequency and output amplitude that are typically variable and controllable. In particular, they can be changed when the converter is in operation. The output frequency can also be zero, corresponding to a DC voltage.

The voltages between all three output terminals of the converter form the three-phase system with a certain frequency and amplitude.

The main function of the converter is performed by a unit, which is called the core unit in the following. The converter and core unit have corresponding input and output connections, i.e. each input connection (or output connection) of the converter is assigned to exactly one corresponding input connection (or output connection) of the core unit. In embodiments, mutually corresponding input and output connections of core unit and converter are directly connected to each other. In other embodiments, they are connected to one another via input or output inductances and/or connected to one another via energy equalization circuits.

[0015] A switching unit can be defined as a hierarchical intermediate level between the converter and the core unit. This also has input and output connections, which are respectively connected to the input. Output terminals of the converter and the core unit correspond.

The switching unit has at least two input connections, which are each connected to a corresponding input connection of the converter either directly or via a corresponding input inductance.

Furthermore, the input terminals of the switching unit are connected to input terminals of the core unit either directly or via an input-side power balancing circuit.

The switching unit has three output terminals which are each connected to a corresponding output terminal of the converter either directly or via a corresponding output inductance.

Furthermore, the output terminals of the switching unit are connected to the output terminals of the core unit either directly or via an output-side power balancing circuit.

If there are no input and output inductances, the converter is identical to the switching unit. In the absence of power balancing circuits, the switching unit is identical to the core unit.

The topology can do without a mains-frequency transformer and DC intermediate circuits and, depending on the design, can also do without AC intermediate circuits or medium-frequency transformers. Possible applications of the invention are the supply of three-phase railway machines through the single-phase railway network and the recuperation of braking energy from such a machine, since the ratio of output voltage level and input voltage level and the output frequency can be varied and bidirectional power flow is possible with a relatively simple and compact electrical and mechanical design at the same time .

BRIEF DESCRIPTION OF THE DRAWINGS

The subject of the invention is explained in more detail below with reference to preferred exemplary embodiments which are illustrated in the accompanying drawings. The following are shown schematically in each case: FIG. 1 shows a known structure of a rail converter; FIG. 2-3 converter topologies according to the invention; FIG. 4 shows a basic converter design; FIG. 5 shows the embodiment from FIG. 4 with extensions for energy equalization; FIG. 6 shows an alternative basic converter design; FIG. 7 shows the embodiment from FIG. 6 with extensions for energy equalization; FIG. 8 shows a switching module; Figure 9 shows a switching unit; and FIGS. 10-12 further embodiments of converters.

In principle, identical or identically acting parts are provided with the same reference symbols in the figures.

WAYS TO CARRY OUT THE INVENTION

shows a first topology of the converter for unidirectional or bidirectional feeding of a three-phase voltage system of variable amplitude and frequency (including zero frequency) at output terminals 35.36.37 of the converter by a single-phase voltage system of variable amplitude and frequency (including zero frequency) 25 with optional flexible intermediate tap 38 by fixing the potential of a first phase of the three-phase voltage system in relation to the single-phase voltage system and varying the potentials of the other two phases of the three-phase voltage system. Line impedances or input inductances 33a, 33b or rotary system impedances or output inductances 34a, 34b, 34c can optionally be present in series with the output connections or input connections. An input-side voltage supply of the converter is shown combined by two voltage sources 25 . The voltage sources are part of the same single-phase system, i.e. they have the same phase position and typically also the same amplitude. In embodiments they have different amplitudes. The two voltage sources can, for example, be realized by a transformer with a center tap.

There is a switching unit 100 which is arranged to feed a second output connection 35 and a third output connection 36 of the three output connections 35, 36, 37 of the converter. The switching unit 100 itself is to be fed through at least one second input connection 31 of the at least two Input terminals 31, 32 of the converter arranged.

Switching unit 100 is designed to switch the second and third output terminals 35, 36 of the converter with different to feed AC voltages. The feeding occurs in such a way that the voltages between all three output connections 35, 36, 37 of the converter form a required three-phase system with a specific frequency and amplitude.

FIG. 3 shows a second topology as a special case of the first topology, in the event that one of the two voltage sources 25 in FIG. 2 has an amplitude of zero or is not present. In other words, the single-phase intermediate tap can be eliminated by moving it all the way to one side.

As a result, two of the input terminals 32, 38 of the converter coincide. A lower mains impedance 33a and upper mains impedance 33b from FIG. 2 act in series and can thus be combined in a single mains impedance, e.g. as upper mains impedance 33b.

4 shows a first embodiment of the switching unit 100. It contains controllable impedances, hereinafter switching modules 20, which can be in the form of modular elements. The switching modules form an H-bridge, i.e. a bridge circuit with two branches. A first input terminal 38 of the converter, which can be considered as a first input terminal 138 of the switching unit 100, is directly connected to a first output terminal 137 of the switching unit, which is connected to a first output terminal 37 of the converter via an optional first output inductor 34a.

A first bridge arm and a second bridge arm, each with two switching modules and a center tap, are connected between a second input connection 131 and a third input connection 132 of the switching unit and via their respective center tap and a respective output inductance 34 to the second output connection 35 or third output connection 36 of the converter switched.

The bridge circuit of the switching modules 20 allows the voltage at the second and third output connection 35, 36 of the converter to be varied such that the required three-phase system of voltages results together with the voltage at the first output connection 37 of the converter.

The input and output inductances can also be omitted if the input or the output of the converter has a sufficiently current-impressing character and/or the switching modules 20 already have sufficiently large inductances to represent, for example, rudimentary overvoltage protection.

FIG. 5 shows an expansion of the circuit from FIG. 4 with energy equalization circuits 41, 42, 43, 44, 45. Each unit framed in dashed lines can be used on its own. That is, either the units with the reference numbers 41, 42 or 43 (inclusive 41&42) on the input side and/or 44 or 45 (inclusive 44). With the help of the energy equalization circuits, energy stored in the individual switching modules 20 can be shifted between them and thus evenly distributed over them. This can prevent individual switching modules from being overloaded in certain states, for example with DC voltage at the input or output, or when starting up. The energy equalization circuits thus expand the degrees of freedom in the converter and/or a possible operating range.

shows a second embodiment of the switching unit 100, also used with controllable impedances or switching modules 20, which can be present as modular elements. As shown in FIG. 4, the first input connection 38 of the converter is also connected to the first output connection 37 of the converter via an optional first output inductor 34a. A first switching module 20 is connected as a shunt between the second input connection 131 and the third connection 132 switching unit 100 . Three further switching modules 20 are connected to one another in series in parallel with the first switching module. The second and third output connections 35, 36 of the converter are connected at two taps between these three switching modules and via a respective output inductance 34.

The three switching modules 20 connected in series allow the voltage at the second and third output connection 35, 36 of the converter to be varied such that the required three-phase system of voltages results together with the voltage at the first output connection 37 of the converter.

FIG. 7 shows an expansion of the circuit from FIG. 6 with energy equalization circuits. Each dashed boxed unit can be used on its own. I.e. either the units with the reference number 61 or 62 (including 61) and independently of this 63.

8 shows an embodiment of a switching module 20 or a controllable impedance. It has a series connection of an arm inductance 23, one or more switching units 10 and optionally an arm capacitance 24, which are connected between switching module connections 21, 22. By means of the switching module connections 21, 22, such switching modules 20, as shown in the other figures, can be used at various points in a converter according to the invention. If the voltages expected during operation across a switching module 20 are sufficiently small, a switching module 20 can also be implemented by a simple 2-quadrant or 4-quadrant switch in embodiments.

9 shows an embodiment of a switching unit 10 as a full-bridge module with a DC capacitor as the module capacitance 14 and four power switches 13, for example transistors with freewheeling diodes connected in antiparallel, as well as module connections 11, 12. The module capacitance 14 is in operation on an approximately maintained constant tension. If the selected operating mode permits, half-bridge modules can also be used instead of the full-bridge modules.

10 shows an expansion of the circuit according to FIG. Four further controllable impedances are arranged in a bridge circuit in front of the energy equalization circuits 44, 45 on the output side. These can also be thought of as an energy balancing circuit. For example, an AC intermediate circuit with a variable frequency can be implemented. The extensions with the reference numerals 41, 42, 43 can optionally be present as already shown above.

11 shows a possible input-side extension. A transformer 71 with an intermediate tap 38 on the secondary side forms the single-phase voltage sources 25. A circuit 70 on the primary side of the transformer is used to convert a single-phase mains voltage without an intermediate tap at connection terminals 75, 76 into a single-phase AC voltage with an intermediate tap. A capacitance circuit 73 with input capacitances 72 is optional.

The converter can also be expanded here (not shown) by energy equalization circuits 41-45 on the input and/or output side.

On the secondary side, the switching unit 100 can be realized, for example, with a basic structure according to FIG. 4 or according to FIG. 6, and possibly with the corresponding optional energy equalization circuits. This is illustrated by FIG.12.

The current flowing through the first output terminal 37 of the converter in the resulting configuration does not cause any magnetic flux in the transformer 71 if it is divided equally between the upper and lower transformer windings. In order to define the electrical potential of the rotary system side, the center tap on the secondary side of the transformer 71 can be connected to connection 38 and thus brought to ground potential, for example.

Compared to previously known topologies, the invention can on the one hand dispense with a mains or low-frequency transformer and on the other hand allows a significant reduction in complexity and the number of modular components by providing a three-phase voltage or three-phase system of variable amplitude and frequency and on DC -Intermediate circuits omitted. From a statistical point of view, this increases the reliability of the overall system. In order to increase the degree of freedom of the converter and/or the possible operating range, versions with an AC intermediate circuit and optionally with a center tap, and versions with a medium-frequency transformer, also optionally with a center tap, are possible. In embodiments with an AC intermediate circuit, the medium-frequency intermediate circuit voltages and currents are potentially converted directly, ie without a DC intermediate circuit, to the variable output voltages and currents.

Claims (10)

An electric converter for exchanging electric energy between an input voltage system and an output voltage system, wherein the input voltage system is a single-phase AC voltage system and the output voltage system is a three-phase AC voltage system, and wherein the converter has at least two input terminals (31, 32, 38) for connection to the input voltage system and three output terminals (35, 36, 37) for connection to the output voltage system, wherein a first output terminal (37) of the three output terminals (35, 36, 37) of the converter is connected via an optional first output inductance (34a) to a first input terminal (38) of the at least two input terminals (31, 32) of the converter, and a switching unit (100) for feeding a second output terminal (35) and a third output terminal (36) of the three output terminals (35, 36, 37) of the converter is arranged, and the switching unit (100) itself for feeding through at least one second input terminal ( 31) the at least two input connections (31, 32) of the converter are arranged, wherein the switching unit (100) is designed to switch the second and third output connection (35, 36) during operation of the converter on the basis of at least one voltage of the single-phase AC voltage system which is present at the at least two input connections (31, 32, 38) of the converter of the converter with different AC voltages. 2. Electrical converter according to claim 1, comprising a switching unit (100) and a core unit. each input connection (31, 32, 38) of the converter being assigned exactly one corresponding input connection (131, 132, 138) of the switching unit (100) and a corresponding input connection (231, 232, 238) of the core unit, and each output connection (35, 36, 37) of the converter being exactly one corresponding output connection ( 135, 136, 137) of the switching unit (100) and a corresponding output port (235, 236, 237) of the core unit. 3. Electrical converter according to claim 2, wherein input inductances (33a, 33b) are connected between input connections (31, 32, 38) of the converter and corresponding input connections (131, 132, 138) of the switching unit and/or wherein in each case between output connections (35 , 36, 37) of the converter and corresponding output connections (135, 136, 137) of the switching unit output inductances (34a, 34b, 34c) are connected. The electric converter according to claim 2 or 3, wherein an input-side energy equalization circuit (43) is connected between the input terminals (131, 132, 138) of the switching unit and the input terminals (231, 232, 238) of the core unit and/or wherein between the output terminals (135, 136, 137) of the switching unit and the output terminals (245, 236, 237) of the core unit, an output-side power equalization circuit (45) is connected. 5. Electrical converter according to claim 4, wherein an input-side energy equalization circuit (43) is present, and this • an input-side parallel balancing circuit (41) with a switching module (20) connected between the second (131) and the third (132) input connection of the switching unit and or • an input-side serial balancing circuit (42) with a switching module (20) connected between the second input connection (131) of the switching unit (100) and the second input connection (231) of the core unit having. 6. Electrical converter according to claim 4 or 5, wherein an output-side energy equalization circuit (45, 62) is present, and this • an output-side parallel balancing circuit with a switching module (20) connected between the second (135) and the third (136) output connection of the switching unit and optional • an output-side serial balancing circuit (44, 61) with a switching module (20) connected between the second output connection (135) of the switching unit (100) and the second output connection (235) of the core unit and with a switching module (20) connected between the third output connection (136). switching unit (100) and the third output port (236) of the core unit switched switching module (20) having. 7. Electrical converter according to one of claims 2 to 6, wherein the core unit has a bridge circuit made up of four switching modules (20), which each implement a controllable impedance, with • a switching module (20) between the second core unit input port (231) and the second core unit output port (235), • a switching module (20) between the third core unit input port (232) and the second core unit output port (235), • a switching module (20) between the second core unit input port (231) and the third core unit output port (236), • a switching module (20) between the third core unit input port (232) and the third core unit output port (236). 8. Electrical converter according to one of claims 2 to 6, wherein the core unit has a voltage divider circuit made up of four switching modules (20), which each implement a controllable impedance, with • a switching module (20) between the second core unit input port (231) and the second core unit output port (235), • a switching module (20) between the second core unit output port (235) and the third core unit output port (236), • a switching module (20) between the third core unit output port (236) and the third core unit input port (232), • a switching module (20) between the second core unit input port (231) and the third core unit input port (232). 9. Electrical converter according to claim 1, wherein the switching modules (20) each implement controlled impedances, in particular by a series connection of an arm inductance (23), at least one switching unit (10) and optionally an arm capacitance (24). 10. Electrical converter according to claim 1, wherein the switching units (10) of the switching modules (20) each have two switching module connections (11, 12) and a module capacitance (14) and a bridge circuit, and the bridge circuit for selectively charging or discharging the module capacitance is arranged by the switching module connections (11, 12).