3-phase PV inverter with 2-phase isolated operation in the event of a network fault

Patent metadata

Field	Value
Publication number	US-12199440-B2
Application number	US-202217985243-A
Country	US
Kind code	B2
Filing date	Nov 11, 2022
Priority date	May 11, 2020
Publication date	Jan 14, 2025
Grant date	Jan 14, 2025

Abstract

The disclosure relates to an inverter including a first bridge branch with a first phase output, a second bridge branch with a second phase output, a third bridge branch with a third phase output, wherein the phase outputs of the bridge branches can each be connected to a phase conductor of a three-phase power distribution network. The inverter is configured, in a normal operating mode of the three-phase power distribution network and/or of a higher-level power supply network connected thereto, to connect the phase outputs to the relevant phase conductor and, in the event of a fault in the three-phase power distribution network and/or in the higher-level power supply network connected thereto, to disconnect the three-phase power distribution network from the higher-level power supply network via a network disconnector, to disconnect the first phase output from the first phase conductor by means of a switching unit and to connect same to a neutral conductor of the three-phase power distribution network, and to establish a neutral potential for the neutral conductor via the first bridge branch. The disclosure further relates to a method for operating an inverter of this kind.

First claim

What is claimed is:

1. An inverter, comprising
a first bridge branch comprising a first phase output,
a second bridge branch comprising a second phase output,
a third bridge branch comprising a third phase output,
wherein the first, second and third phase outputs of the first, second and third bridge branches are each configured to be connected to a respective first, second and third phase conductor of a three-phase power distribution network,
wherein the inverter is configured:
in a normal operating mode of the three-phase power distribution network and/or of a higher-level power supply network connected thereto, to connect the first, second and third phase outputs to the respective first, second and third phase conductor, and
in the case of a fault in the three-phase power distribution network and/or in the higher-level power supply network connected thereto, to disconnect the three-phase power distribution network from the higher-level power supply network using a network disconnector, to disconnect the first phase output from the first phase conductor using a switching unit and to connect the first phase output to a neutral conductor of the three-phase power distribution network, to establish a neutral potential for the neutral conductor via the first bridge branch, and to control the second bridge branch and the third bridge branch after the network disconnection so that voltages between the second and third phase outputs and the neutral conductor in each case have a different phase position in relation to one another.

2. The inverter according to claim 1 , further comprising a DC voltage intermediate circuit coupled in parallel with each of the first, second and third bridge branches, wherein the inverter is further configured to control the first bridge branch such that a middle potential of a voltage of the DC voltage intermediate circuit is established at the first phase output.

3. The inverter according to claim 1 , wherein the three-phase power distribution network has the higher-level power supply network connected thereto, wherein the inverter is further configured to disconnect all poles of the three-phase power distribution network from the higher-level power supply network using the network disconnector in the event of a fault in the three-phase power distribution network and/or in the higher-level power supply network connected thereto.

4. The inverter according to claim 1 , which is further configured to control the second and third bridge branches after the network disconnection such that a phase shift of voltages between the second and third phase outputs and the neutral conductor in each case, relative to one another, deviates from 120°.

5. The inverter according to claim 4 , which is further configured to control, in a transition operating mode, the second and third bridge branches such that, after the network disconnection, voltages with a phase shift of 120° relative to one another are initially output at the second and third phase outputs, and the phase shift of the voltages between the second and third phase outputs and the neutral conductor in each case is subsequently changed to a value deviating from 120°.

6. The inverter according to claim 5 , wherein the transition operating mode lasts fewer than 5 network periods.

7. The inverter according to claim 1 , wherein the first, second and third bridge branches comprise a 2-level B6 or 3-level NPC, BSNPC, ANPC, or FLC topology.

8. A method for operating an inverter comprising first, second and third bridge branches and respective first, second and third phase outputs that each configured to connect selectively to a respective first, second and third phase conductor of a three-phase power distribution network comprising:
in a normal operating mode of the three-phase power distribution network and/or of a higher-level power supply network connected thereto, connecting the first, second and third phase outputs to the respective first, second and third phase conductors, and
in the case of a fault in the three-phase power distribution network and/or in the higher-level power supply network connected thereto, disconnecting the three-phase power distribution network from the higher-level power supply network, disconnecting the first phase output from the first phase conductor and connecting it to a neutral conductor of the three-phase power distribution network, establishing a neutral potential for the neutral conductor via the first bridge branch, and controlling the second bridge branch and the third bridge branch after the network disconnection such that voltages between the second and third phase outputs and the neutral conductor in each case have a different phase position with respect to one another.

9. The method according to claim 8 , further comprising controlling the first bridge branch after the disconnection from the first phase conductor, such that a middle potential of a voltage of a DC voltage intermediate circuit, that is coupled in parallel with the first, second and third bridge branches, is established as a neutral potential at the first phase output.

10. The method according to claim 8 , further comprising controlling the first bridge branch after the disconnection from the first phase conductor such that a periodically modulated voltage curve is established as a neutral potential at the first phase output.

11. The method according to claim 8 , further comprising, after a detection of the fault in the three-phase power distribution network and/or in the higher-level power supply network connected thereto, disconnecting the three-phase power distribution network at all poles from the higher-level power supply network.

12. The method according to claim 8 , wherein the inverter comprises a 3-level topology of the first, second and third bridge branches, the method further comprising, after the network disconnection, controlling the second and third bridge branches such that voltages phase-shifted by approximately 180° relative to one another are provided between the neutral conductor in each case and the second and third phase outputs.

13. The method according to claim 12 , further comprising regulating a value of the phase shift via a control loop such that a magnitude of voltage ripples at twice a network frequency of the three-phase power distribution network is minimized in a DC voltage intermediate circuit of the inverter.

14. The method according to claim 8 , wherein the inverter comprises a 2-level topology of the bridge branches, the method further comprising, after the network disconnection, controlling the second and third bridge branches such that voltages phase-shifted by at least 90° and less than 120° are provided between the neutral conductor in each case and the second and third phase outputs.

15. The method according to claim 14 , wherein the phase shift is 90°.

16. The method according to claim 14 , further comprising measuring a maximum current at the first phase output, and reducing the phase shift toward 90° when the maximum current is below a predetermined threshold value and increasing the phase shift toward 120° when the maximum current is above or at the predetermined threshold value.

Assignees

• Sma Solar Technology Ag

Inventors

• Unru Alexander
• Müller Burkard

Classifications

• H02J2101/24

  Photovoltaics · CPC title

• H02M7/53871 Primary

  with automatic control of output voltage or current · CPC title

• H02M7/487

  Neutral point clamped inverters · CPC title

• H02M1/325

  with means for allowing continuous operation despite a fault, i.e. fault tolerant converters · CPC title

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title