Multiphase inverter with series of connected phase legs

• US 6,519,169 B1
• Filed: 12/03/2001
• Issued: 02/11/2003
• Est. Priority Date: 03/29/1999
• Status: Expired due to Term

• Current Assignee: ABB Power Grids Switzerland AG (ABB Limited)
• Original Assignee: ABB AB (ABB Limited)
• Inventors: Asplund, Gunnar, Bijlenga, Bo
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US09/936,988
• Time in Patent Office: 435 Days
• Field of Search: 363/132, 363/137
• US Class Current: 363/132
• CPC Class Codes: H02M 1/0074 Plural converter units whose inputs are connected in series
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: H02M 7/4837 Flying capacitor converters
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters

Abstract

A VSC-converter for converting direct voltage into alternating voltage and conversely has at least two phase legs (1-3) with each at least two current valves (4-9) connected in series, the valves consisting of at least a semiconductor element (10) of turn-off type and a rectifying member (11) connected in anti-parallel therewith. A midpoint (12) of the phase leg between said valves is adapted to form a phase output and be connected to a phase (29) of an alternating voltage network. The phase legs (1-3) of the converter are connected in series, and opposite ends of the series connection formed by an outer end of a respective outer phase leg (1-3) in the series connection are intended to be connected to a pole conductor (19, 20) each of a direct voltage network.

Claims

1. A VSC-converter for converting direct voltage into alternating voltage and conversely and which has at least two phase legs having each at least two current valves connected in series, said valves comprising at least a semiconductor element of turn-off type and a rectifying member connected in anti-parallel therewith, a mid point of the phase leg between said valves being adapted to form a phase output and to be connected to a phase of an alternating voltage network, wherein the phase legs of the converter are connected in series and the opposite ends of the series connection are for connection across a direct voltage network.

2. A converter according to claim 1, wherein a transformer is connected to each phase output between this and the alternating voltage network phase belonging thereto.

3. A converter according to claim 2, wherein one winding of the respective transformers is connected through a first end to the phase output of the phase leg and through a second end to a mid point between two capacitors connected in series in parallel with the current valves of the phase leg.

4. A converter according to claim 2, wherein one winding of the respective transformer is connected through a first end to the phase output of the phase leg and through a second end to a mid point between the two capacitors connected in series in parallel with the current valves of the phase leg.

5. A converter according to claim 2, wherein for each phase leg a winding of the transformer is connected between a first end connected to a mid point between the two current valves of one series connection of the current valves and connected to the mid point between the two current valves of the other series connection of current valves.

6. A converter according to claim 2, wherein at least one inductor and a high pass filter are arranged between the respective current valve and the windings of the transformer for reducing harmonics out towards the alternating voltage network and reducing stresses on the transformer.

7. A converter according to claim 1, wherein each phase leg comprises four current valves connected in series, a point of the phase leg between the two inner valves of said series connection forming said phase output, and said rectifying members are arranged to take a voltage so as to participate in defining a voltage level of the phase output located between the voltage level of the two ends of the phase leg are connected between a point between one outer valve of the series connection and the inner valve next thereto and a point between the other outer valve of the series connection and the inner valve next thereto.

8. A converter according to claim 7, wherein said rectifying members are formed by a flying capacitor connected between said points.

9. A converter according to claim 8, wherein each phase leg comprises 2n current valves, n being an integer≧

3, and further comprising (n−

1) couples of mid points located in corresponding positions with respect to the phase output on opposite sides thereof and connected to each other through a flying capacitor.

10. A converter according to claim 7, wherein said rectifying members are formed by a series connection of two clamping rectifiers directed in the same direction with respect to said series connection as said rectifying members, and that a mid point between the two clamping rectifiers is connected to a zero potential defined by capacitors connected in series and connected in parallel with the phase leg.

11. A converter according to claim 10, wherein the clamping rectifiers each comprise a rectifying diode and a semiconductor element of turn-off type connected in anti-parallel therewith.

12. A converter according to claim 1, wherein each phase leg has two current valves connected in series.

13. A converter according to claim 1, one of said pole conductors is intended to be on high voltage potential, while the other pole conductor is adapted to be on a potential close to earth for monopolar operation of the direct voltage network.

14. A converter according to claim 1, wherein both pole conductors are intended to be on high voltage potential of the same amount but of opposite signs for bipolar operation.

15. A converter according to claim 1, wherein each phase leg is formed by two series connections of two current valves each, said series connections being connected in parallel.

16. A converter according to claim 1, wherein the alternating voltage network has three phases and the number of phase legs connected in series is three.

17. A converter according to claim 1, connected to a direct voltage network for transmitting high voltage direct current (HVDC).

18. A converter according to claim 1, designed to deliver a high voltage within the interval 10-400 kV on the direct voltage network.

19. A converter according to claim 1, wherein said semiconductor elements of turn-off type comprise bipolar transistors having an insulated gate.

20. A converter according to claim 1, the semiconductor elements of turn-off type comprise thyristors of turn-off type.

21. A converter according to claim 1, each current valve comprises a plurality of semiconductor elements of turn-off type connected in series and a plurality of rectifying members connected in series.

22. A converter according to claim 1, designed to deliver a high voltage within the interval 50-400 kV on the direct voltage network.