Power supply system for bidirectional energy flow

Abstract

The present invention relates to a power supply system (10), in particular a power supply system (10) for bidirectional energy flow between a medium voltage power grid (11) and a low voltage power consumption site (60). The system (10) comprises a feeding system (25), which is configured to convert an AC medium voltage power signal from the medium voltage power grid (11) into a low voltage power signal (29) for feeding power to the power consumption site (60). In addition, the system (10) comprises: a low voltage multiphase converter (40), which is configured to convert a low voltage signal (41, 42) into a low voltage multiphase signal (49), wherein the multiphase converter (40) is arranged in anti-parallel with the feeding system (25); and an LV / MV multiphase transformer (50), which is configured to convert the low voltage multiphase signal (49) into an output signal (59) that conforms to the AC medium voltage power signal (11).

Description

Technical Field

[0001] The invention relates to the field of power supplies, for example for electric vehicles, in particular for bidirectional energy flow between a medium voltage grid and a low voltage power consumption station. The invention also relates to a method and use of a power supply. Background Art

[0002] Power supplies, such as charging systems for electric vehicles (EV) and other low voltage (LV) power stations, require high power levels. Therefore, in many cases, a medium voltage grid (MV grid) is used as the basis for the power supply. In addition, for many systems, legal conditions and / or other requirements of the MV grid standards need to be met. In addition, in some cases, it is also required to feed solar panels and other energy sources available on the LV side of the charging station into the MV grid. Therefore, it is necessary to support at least partially bidirectional power flow of these power sources. This may result in a bulky system front end for feeding the charging pole. Summary of the invention

[0003] It is therefore an object of the present invention to provide an improved power supply for low voltage utility points, such as electric vehicles.

[0004] One aspect relates to a power supply system for bidirectional energy flow between a medium-voltage power grid and a low-voltage power consumption site. The power supply system includes a feeding system, which is configured to convert an AC medium-voltage power signal from the medium-voltage power grid into a low-voltage power signal for feeding power to the power consumption site. In addition, the power supply system includes: a low-voltage multiphase converter, configured to convert a second low-voltage signal based on a first low-voltage signal from the power consumption site into a low-voltage multiphase signal, wherein the multiphase converter is arranged in anti-parallel with the feeding system; and an LV / MV multiphase transformer, configured to convert the low-voltage multiphase signal into an output signal that conforms to the AC medium-voltage power signal.

[0005] Bidirectional energy flow is used to support energy transfer from a medium voltage (MV) power source to a low voltage (LV) sink and from a LV power source to a MV sink. The energy flow of energy may be asymmetric, for example, the energy flow from the LV power source to the MV sink is lower than that from the MV power source to the LV sink, and may even be much lower. The MV power source and sink can be, for example, an MV grid having a frequency of 50 Hz or 60 Hz and a voltage of about 10 kV to 30 kV. The LV power source and sink can be a bidirectional low voltage power consumption site, such as an electric vehicle charging system, configured to feed energy such as batteries, solar panels and other power sources available at the low voltage power consumption site to the MV site, such as into the MV grid. In some cases, the batteries at the LV site can be used for grid stabilization.

[0006] The feed system uses MV power and delivers LV DC voltage or LV AC voltage, which may be LV HF-AC (high frequency alternating current) voltage with a frequency of about 5kHz–100kHz. The low voltage power signal at the LV power station can be fixed and have a voltage range of about 400V to 1000V, or about 230V or about 110V. The LV power station can include other modules, such as for converting the LV signal to a standardized signal for the EV station, possibly to a variable and / or controlled voltage.

[0007] The type of low voltage multiphase converter from the LV power source depends on the type of signal delivered by the LV power source. For example, the LV power source may be a battery that delivers a DC voltage as a first low voltage signal that is fed directly to the input of the multiphase converter as a second low voltage signal. As another example, the LV power source may be HF-AC as a first low voltage signal and may be converted by an AC / DC converter to a DC signal as a second low voltage signal. Additionally or alternatively, the LV power source may be any type of excess energy that the system allows to be fed to the MV grid.

[0008] The multiphase converter may generate, for example, a 3-phase 50 Hz signal. This signal may depend on the type of signal in the MV grid. The multiphase converter may further act as an active filter, thereby meeting MV grid standards in a flexible manner. The LV / MV multiphase transformer may convert the low voltage multiphase output signal into an output signal that complies with the AC medium voltage power signal. Conformity may be established by a combination of a multiphase converter and a LV / MV multiphase transformer. Conformity may mean, for example, having the same phase as the MV grid and meeting other MV grid requirements, such as regarding current harmonic limits and / or other requirements determined by IEEE 519 and / or IEC 61000-3-6.

[0009] Thus, the characteristics of the power supply system advantageously result in a system that controls bidirectional power flow with low distortion. The clear concept further results in a highly flexible system, e.g. with respect to the number of LV power supplies. Furthermore, the size of the system components is small (e.g. compared to conventional 50 Hz transformers) and / or the manufacturing and / or maintenance costs of the system are low.

[0010] In various embodiments, the feeding system includes a line phase transformer LIT. The feeding system can be implemented as a rectifier based on the line phase transformer LIT. The line phase transformer LIT can be a multi-pulse line phase transformer LIT with a pulse number of 12, 18, 24 or more than 24. Therefore, due to the multi-pulse line phase transformer LIT, the harmonics of the passive main rectifier may be very small. In addition, the active filter can be designed to be only a small part of the full station power. This may help to use a very small 50Hz active filter transformer and may result in reduced cost and / or small no-load losses.

[0011] In various embodiments, the low voltage multiphase converter is an active filter that injects current based on the signal of the MV grid. In particular, the multiphase converter injects current to reduce current harmonics greater than or equal to 2 in the MV grid. This advantageously helps not only to compensate for distortion of the current "backward" fed to the MV grid, but also to compensate for distortion of the entire power supply system, thereby further improving its consistency with the AC medium voltage power signal.

[0012] In various embodiments, the system further comprises a first inductor arranged between the AC medium voltage power signal and the feed system and between the AC medium voltage power signal and the LV / MV multiphase transformer. Thus, the inductor connecting the MV grid and the rectifier, for example based on a line interphase transformer LIT, is designed to reduce distortion factors and / or current harmonics that may affect the MV grid. In at least some countries, this may be a legal and / or standard requirement, for example, in compliance with relevant MV grid standards, for example in compliance with IEEE 519 or IEC 61000-3-6. Advantageously, the requirements can be met without the need for a complex and expensive MV grid active front end, resulting in a simpler design, lower manufacturing costs and / or reduced maintenance workload.

[0013] In various embodiments, the LV multiphase DC / AC converter includes a multiphase switch subsystem and a second inductor, which is arranged between the multiphase switch subsystem and the LV / MV multiphase transformer. The second inductor can be integrated into the LV / MV multiphase transformer. This arrangement can help to further reduce the distortion factor forwarded to the MV grid.

[0014] In various embodiments, the power supply system further comprises a converter configured to convert a first low voltage signal from the power consumption site (60) into a DC low voltage signal. The converter may be a DC / AC converter, an AC / AC converter and / or an AC / DC converter having a DC / AC converter. The type of converter may depend on the LV power supply, for example whether the power supply is a DC power supply or an AC power supply, and / or the frequency of the AC power supply. Thus, the converter may adapt the voltage and / or frequency of the LV power supply to the input of the low voltage multiphase DC / AC converter. This advantageously allows the use of a variety of LV power supplies to feed back their energy.

[0015] One aspect relates to a method for supporting bidirectional energy flow between a medium voltage power grid and a low voltage power consumption site. The method comprises the following steps:

[0016] Converting AC medium-voltage power signals from the medium-voltage power grid into low-voltage power signals for power stations through the feeding system;

[0017] Outputting a first low-voltage signal from the power consumption site;

[0018] feeding a second low voltage signal based on the first low voltage signal into a low voltage multiphase DC / AC converter, the low voltage multiphase DC / AC converter being arranged in anti-parallel with the feed system;

[0019] forwarding the low voltage multiphase signal from the output of the low voltage multiphase DC / AC converter to the LV / MV multiphase transformer; and

[0020] The low voltage multi-phase output signal is converted into an output signal that conforms to the AC medium voltage power signal through the LV / MV multi-phase transformer.

[0021] In various embodiments, the feed system comprises a line phase transformer LIT. The line phase transformer LIT may be a multi-pulse line phase transformer LIT with a pulse number of 12, 18, 24 or more.

[0022] In various embodiments, conversion of a DC medium voltage power signal into a low voltage power signal for a point of use power station is achieved by a modular DC / DC converter with a large step-down gain and a medium frequency transformer for galvanic isolation.

[0023] In various embodiments, the method further comprises the step of filtering the AC medium voltage power signal from the feed system and the AC medium voltage power signal from the LV / MV multiphase transformer by a first inductor.

[0024] One aspect relates to a bidirectional power supply system as described above and / or below for transmitting energy from a medium voltage grid to a low voltage consumer and from a low voltage consumer to a medium voltage grid.

[0025] One aspect relates to the use of a bidirectional power supply system as described above and / or below for delivering energy from a medium voltage grid to a low voltage power consumption site (LV site) and from a LV site to a medium voltage grid. The low voltage power consumption site can be a charging box and / or charging pole for charging electric vehicles, data centers and / or multiple low voltage drives, and is configured to deliver energy from batteries, solar panels and / or other energy production equipment. As another example, a manufacturing site with power consumption equipment (such as an electric motor) and multiple solar panels (e.g., mounted on a roof) can be a LV site.

[0026] For further clarity of explanation, the present invention is described by the embodiments shown in the drawings. These embodiments are only considered as examples and not as limitations. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Schematic description:

[0028] Figure 1a , Figure 1b , Figure 1c Schematically, various designs of parts of a power supply system according to an embodiment;

[0029] Figure 2a , Figure 2b Schematically, various designs of parts of a power supply system according to other embodiments;

[0030] Figure 3 Schematically a power supply system according to an embodiment;

[0031] Figure 4 Schematically, a method according to an embodiment;

[0032] Figure 5 Indicatively Figure 3 Examples of systems that

[0033] Figure 6 Indicatively Figure 3 Another example of a system of;

[0034] Figure 7 Indicatively Figure 3 Another example of a system of;

[0035] Figure 8 Schematically, Figure 5 Similar simulation examples;

[0036] Figure 9a to Fig.9e Schematically, a simulation of the MV grid behavior of a power supply system according to an embodiment is shown. DETAILED DESCRIPTION

[0037] Figure 1aA power supply system 10 is shown with a 50 Hz MV / LV transformer 12 for insulation from a medium voltage AC grid 11 or an AC medium voltage power signal. The 50 Hz low voltage signal is transformed by a 50 Hz LV / LV transformer 14. The LV / LV transformer 14 galvanically separates a plurality of charging poles 19 from each other. The two conversion stages of the low frequency transformer may result in a large footprint and size of the system. An AC / DC transformer and a DC / DC transformer are arranged between each LV / LV transformer 14 and the respective charging pole 19.

[0038] Figure 1b The diagram shows a power supply system 10 with a multi-winding 50 Hz transformer 13. This is a system with one conversion stage, so that both MV is converted into LV and multiple charging poles 19 are provided to each other. Figure 1c A power supply system 10 is shown with a first conversion stage of a 50 Hz MV / LV transformer 12. As a second conversion stage, the system 10 has a low voltage medium frequency transformer LV / LV-MFT 17, the higher frequency of which is provided by a DC / AC transformer.

[0039] Figure 2a The power supply system 10 is shown with an MV MFT 14 for galvanic separation from a medium voltage AC grid 11. It also has an LV / LV MFT 17 for galvanic separation of charging poles 19 from one another.

[0040] Figure 2b The power supply system 10 is shown with a first conversion stage MV / LV-MFT 15 which is fed by a MV-DC / AC converter HF-AC for high frequencies. The second conversion stage is a LV / LV MFT 17 for galvanically isolating charging poles 19 from one another.

[0041] Figure 3 A schematic diagram of a power supply system 10 is shown. The power supply system 10 has a feeding system 25 in its "forward branch". The feeding system 25 is configured to convert an AC medium voltage power signal from a medium voltage AC grid (MV grid) 11 into a low voltage power signal (LV signal) 29. The LV signal 29 can feed power to multiple power consumption sites (LV sites) 60. The LV site can have other modules for controlling and / or distributing power, for example. Examples can include charging systems for electric vehicles. At least some LV sites 60 can have a bidirectional energy flow, i.e., some LV sites can be configured to deliver energy in a forward direction, some LV sites deliver energy in a reverse direction and / or some LV sites deliver energy in both directions.

[0042] In the "reverse branch" (i.e., arranged in anti-parallel with the feeding system 25), the feeding system 10 has a low-voltage multiphase DC / AC converter 40. The low-voltage multiphase DC / AC converter 40 is configured to convert a second DC low-voltage signal 41, 42 based on a first low-voltage signal 68, 69 from a power consumption site 60 into a low-voltage multiphase signal 49. For example, in the case where the LV site 60 transmits a DC power signal as a first low-voltage signal 68, 69, the multiphase converter 40 can be directly connected to one or more LV sites 60. The low-voltage multiphase DC / AC converter 40 can be connected to one or more LV sites 60 through a converter 30. The converter 30 can be configured to convert a first low-voltage signal 68, 69 from a power consumption site 60 into a second DC low-voltage signal 41, 42. The converter 30 is a DC / AC converter, an AC / AC converter, and / or an AC / DC converter with a DC / AC converter. This may depend on the type of the first low-voltage signal 68, 69 of the power transmission site 60. The converter 30 may be integrated with the low voltage multiphase DC / AC converter 40, for example, as a hardware part thereof. The converter 30 may be a separate component or integrated with one or more LV stations 60. The low voltage multiphase DC / AC converter 40 may deliver, for example, a 3-phase signal at its output. The low voltage multiphase signal 49 is forwarded to the LV / MV multiphase transformer 50. The LV / MV multiphase transformer 50 converts the low voltage multiphase signal 49 into an MV output signal 59 that is consistent with the AC medium voltage power signal of the medium voltage AC grid 11. Consistency may mean, for example, having the same phase as the MV grid and meeting other MV grid requirements, for example regarding current harmonic limits and / or other requirements determined by IEEE 519 and / or IEC 61000-3-6.

[0043] Figure 4 A flowchart 70 of a method according to an embodiment is schematically shown. The flowchart 70 depicts a method for supporting a medium voltage AC grid 11 (see e.g. Figure 3) and a low-voltage power consumption site 60. In step 71, the AC medium-voltage power signal from the medium-voltage AC power grid 11 is converted into a low-voltage power signal 29 for the power consumption site 60 by the feeding system 25. In step 72, the first low-voltage signals 68, 69 are output from the power consumption site 60. In step 73, the second DC low-voltage signals 41, 42 based on the first low-voltage signals 68, 69 are fed into the low-voltage multi-phase DC / AC converter 40, which is arranged in anti-parallel with the feeding system 25. In step 74, the low-voltage multi-phase signal 49 is forwarded from the output of the low-voltage multi-phase DC / AC converter 40 to the LV / MV multi-phase transformer 50. In step 75, the low-voltage multi-phase signal 49 is converted into an output signal 59 that conforms to the AC medium-voltage power signal by the LV / MV multi-phase transformer 50. Steps 72 to 75 can be performed in parallel with step 71.

[0044] Figure 5 Schematically shows Figure 3 This embodiment of the power supply system 10 comprises a line phase transformer LIT based rectifier having a 12-pulse line phase transformer LIT 23. Each input 22a, 22b, 22c of the line phase transformer LIT 23 is connected to each phase 11a, 11b, 11c of the medium voltage AC grid 11 through an inductor 20a, 20b, 20c. The line phase transformer LIT based rectifier generates a LV power signal 29 for feeding a plurality of power consumption sites 60. The first component of the line phase transformer LIT based rectifier is a 12-pulse line phase transformer LIT 32, whose output 35 is fed to a multi-pulse diode rectifier 37. Figure 5 (And similarly, Figure 6 ) describes the magnetic core of the inductive component of the coupled line phase transformer LIT as a line coupled by magnetic resistance (the small rectangular box is an equivalent circuit diagram).

[0045] In the "reverse direction", at least some of the LV stations 60 can transmit first LV power signals 68, 69 of different types (i.e., DC and / or AC of possibly different and / or variable voltages, different frequencies (possibly 50 Hz, 60 Hz)) at a fixed or variable frequency in the range of about 5 kHz-20 kHz and / or other frequencies. Depending on the type of LV power supply, the converter 30 is arranged in the "reverse branch" of the power supply system 10. The converter 30 feeds the second DC low voltage signal 41, 42 to the low voltage multiphase DC / AC converter 40. The low voltage multiphase DC / AC converter 40 generates a low voltage multiphase signal 49 that is fed to the LV / MV multiphase transformer 50. The low voltage multiphase DC / AC converter 40 includes a multiphase switch subsystem 44 and a second inductor 46. The second inductor 46 is arranged between the multiphase switch subsystem 44 and the LV / MV multiphase transformer 50. Alternatively, the second inductor 46 can be part of the LV / MV multiphase transformer 50. The LV / MV multiphase transformer 50 converts the low voltage multiphase signal 49 into an output signal 59, and feeds the output signal 59 to the medium voltage AC grid 11 through the output signal 59 and the inductors 20a, 20b, 20c of each phase of the medium voltage AC grid 11. The output signal 59 consistent with the AC medium voltage power signal and its distortion factor are further reduced by the inductors 20a, 20b, 20c. The inductance of the inductors 20a, 20b, 20c can be very small; for the illustrated embodiment with a 12-pulse line phase transformer LIT, an example can be about 34mH.

[0046] Figure 6 Schematically shows Figure 3 Another example of a system. This embodiment of the power supply system 10 includes a rectifier based on a line phase transformer LIT with an 18-pulse line phase transformer LIT 23. A higher number of pulses may advantageously result in a smaller distortion factor, thereby further reducing the inductors 20a, 20b, 20c. In other aspects, Figure 6 Examples and Figure 5 In particular, the same reference numerals denote the same or similar components.

[0047] Figure 7 Schematically shows Figure 3 Another example of a system. This embodiment of the power supply system 10 includes a simple diode bridge in the feed system 25. In other aspects, Figure 6 Examples and Figure 5 In particular, the same reference numerals denote the same or similar components.

[0048] Figure 8 Schematically shows the Figure 5A similar simulation example of a power supply system 10. The feeding system 25 is based on U DC =12.4kV voltage to deliver a maximum power of 2MW to multiple LV sites 60. LV site 60 delivers 246kVA power, voltage U DC,AF =1kV. The LV / MV multiphase transformer 50 converts it into a voltage of 10kV. The simulation results are shown in Figures 9a to Figure 9d shown.

[0049] Figure 9a shows the simulated waveforms of the MV grid voltage (upper figure) and the 12-pulse input current of the rectifier based on the line phase transformer LIT (lower figure), with a rectified current of I=124A. Figure 9b shows the effect of the active filter arranged in the "reverse branch". In the upper figure, the straight line shows the rectifier input current based on the line phase transformer LIT. In the lower figure, the curve shows the "correction" current injected by the active filter. The effect can be seen from the dotted curve in the upper figure: the dotted curve shows a very smooth curve with low distortion. This is in Figure 9c to Figure 9e This can also be seen in the chart. Fig.9c Shows Figure 8 The 11th and 13th current harmonics generated by the rectifier based on the line interphase transformer LIT. Figure 9d The results of the active filter injection current are shown. It is clear that the distortion energy is significantly reduced. Fig.9e shows what the injected current looks like in this example.

[0050] Reference numerals

[0051] 10 Power supply system

[0052] 11 Medium Voltage AC Grid (MV Grid)

[0053] 11a,11b,11c Phase of MV grid

[0054] 12 MV / LV Transformer

[0055] 13 Transformer

[0056] 14 MV / LV Transformer

[0057] 15 MV / LV-MFT

[0058] 17 LV / LV-MFT

[0059] 19 Charging pole

[0060] 20 First inductor 20a, 20b, 20c

[0061] 22a, 22b, 22c Input of line phase transformer LIT

[0062] 23 Line phase transformer LIT

[0063] 25 Feeding system

[0064] 29 LV power signal

[0065] 30 Converter

[0066] 40 Low voltage multiphase DC / AC converter

[0067] 41,42 Second DC low voltage signal

[0068] 44 Switch Subsystem

[0069] 46 Second Inductor

[0070] 49 Low voltage multiphase signal

[0071] 50 Multiphase Transformer

[0072] 59 MV output signal

[0073] 60 Low Voltage Sites (LV Sites)

[0074] 68,69 Low voltage power signal

[0075] 70 Flowchart

[0076] Steps 71-75

Claims

1. A power supply system (10) for bidirectional energy flow between an AC medium voltage power grid (11) and a low voltage power consumption station (60), the system (10) comprising: A power feeding system (25) configured to convert an AC medium voltage power signal from the AC medium voltage power grid (11) into a low voltage power signal (29) for feeding power to the power consumption site (60); The feeding system (25) comprises a line interphase transformer LIT (23); as well as A reverse branch is configured to feed energy from the power consumption site (60) to the AC medium voltage power grid (11), the reverse branch comprising: A low voltage multiphase DC / AC converter (40) configured to convert a second DC low voltage signal (41, 42) based on a first low voltage signal (68, 69) from the power consumption site (60) into a low voltage multiphase signal (49), wherein the low voltage multiphase DC / AC converter (40) is an active filter based on the signal injection current of the AC medium voltage grid (11); as well as An LV / MV multiphase transformer (50) is configured to convert the low voltage multiphase signal (49) into an output signal (59) that conforms to the AC medium voltage power signal.

2. The power supply system (10) according to claim 1, The line phase transformer LIT (23) is a multi-pulse line phase transformer LIT with a pulse number of 12, 18, 24 or more.

3. The power supply system (10) according to claim 1 or 2, Also included is a first inductor (20), which is arranged between the AC medium voltage power signal and the feed system (25) and between the AC medium voltage power signal and the LV / MV multiphase transformer (50).

4. The power supply system (10) according to claim 1 or 2, The low voltage multiphase DC / AC converter (40) includes a multiphase switch subsystem (44) and a second inductor (46), wherein the second inductor (46) is arranged between the multiphase switch subsystem (44) and the LV / MV multiphase transformer (50).

5. The power supply system (10) according to claim 1 or 2, The utility model also comprises a converter (30) configured to convert the first low voltage signal (68, 69) from the power consumption site (60) into a second DC low voltage signal (41, 42).

6. A method for supporting a bidirectional energy flow between an AC medium voltage grid (11) and a low voltage power consumption site (60), the method comprising the following steps: Converting an AC medium voltage power signal from the AC medium voltage power grid into a low voltage power signal (29) for the power consumption site (60) by means of a feeding system (25); wherein the feeding system (25) comprises a line phase transformer LIT (23); Outputting a first low-voltage signal (68, 69) from the power consumption site (60); Feeding a second DC low-voltage signal (41, 42) based on the first low-voltage signal (68, 69) into a low-voltage multiphase DC / AC converter (40), the low-voltage multiphase DC / AC converter (40) being arranged in anti-parallel with the feeding system (25); forwarding a low voltage multiphase signal (49) from the output of the low voltage multiphase DC / AC converter (40) to a LV / MV multiphase transformer (50); and The low voltage multi-phase signal (49) is converted into an output signal (59) conforming to the AC medium voltage power signal by means of the LV / MV multi-phase transformer (50).

7. The method according to claim 6, The line phase transformer LIT (23) is a multi-pulse line phase transformer LIT with a pulse number of 12, 18, 24 or more.

8. The method according to claim 6 or 7, further comprising the following steps: The AC medium voltage power signal from the feed system (25) and the AC medium voltage power signal from the LV / MV multiphase transformer (50) are filtered by means of a first inductor (20).

9. A bidirectional power supply system (10), according to any one of claims 1 to 5, for transmitting energy from an AC medium-voltage power grid to a low-voltage power consumption site (60) and transmitting energy from the low-voltage power consumption site (60) to the AC medium-voltage power grid.

10. Use of the bidirectional power supply system (10) according to claim 9, for transmitting energy from an AC medium voltage power grid to a low voltage power consumption site (60) and transmitting energy from the low voltage power consumption site (60) to the AC medium voltage power grid, The low-voltage electricity consumption site (60) is a charging box and / or charging pole for charging electric vehicles, data centers and / or electric motors, and is configured to deliver energy from energy production equipment.

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