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Voltage source converter

  • US 8,422,257 B2
  • Filed: 06/09/2008
  • Issued: 04/16/2013
  • Est. Priority Date: 06/09/2008
  • Status: Active Grant
First Claim
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1. A Voltage Source Converter having at least one phase leg connecting to opposite poles of a direct voltage side of the converter and comprising a series connection of M2LC converter valve branch switching cells, each said switching cell having at least two semi-conductor assemblies connected in series, a phase output of the converter being configured to be connected to an alternating voltage side of the converter being formed along said series connection of switching cells, each said switching cell being configured to obtain two switching states by control of said semiconductor devices of each switching cell, namely a first switching state and a second switching state in which the voltage across at least one energy storing capacitor and a zero voltage, respectively, is applied across the terminals of the switching cell, for obtaining a determined alternating voltage on said phase output, wherein one of said opposite poles is a high voltage potential pole connected to a high voltage potential on said direct voltage side and the other of said opposite poles is a neutral potential pole connected to a neutral voltage potential on said direct voltage side and said series connection of switching cells has a first end thereof configured to be connected to said high voltage potential pole and a second end configured to be connected to said phase output, wherein the converter further comprises an arrangement configured to connect said phase output to said neutral position pole and to deliver voltage pulses to said phase output being both positive and negative with respect to said neutral voltage potential, the arrangement comprising:

  • at least one H-bridge comprising two switching elements connected in parallel and each having at least two semiconductor assemblies connected in series and having each a semiconductor device of turn-off type and a free-wheeling diode connected in parallel therewith, said H-bridge also having at least one energy storing capacitor connected in parallel with said switching elements, and a mid point between semiconductor assemblies of a first of said switching elements is connected to said neutral potential and a mid point between semiconductor assemblies of a second of said switching elements is connected to said phase outputand/or at least two of said switching cells connected in series, which switching cells are oppositely directed with respect to the voltage provided by said energy storing capacitor thereof, anda control unit configured to control the converter for obtaining said determined alternating voltage on said phase output having a peak voltage of between ⅓

    to ⅔

    , preferably about ½

    , of the high voltage potential on said high voltage potential pole with respect to ground and controlling the arrangement to deliver said voltage pulses to said phase output varying between maximum peak values with respect to said neutral potential substantially corresponding to a peak value of the alternating voltage to be delivered by the converter on said phase output.

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