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Method for controlling a converter

  • US 20040246746A1
  • Filed: 07/12/2004
  • Published: 12/09/2004
  • Est. Priority Date: 07/16/2001
  • Status: Abandoned Application
First Claim
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1. A method for controlling a VSC converter, which converter comprises a series connection of at least two current valves arranged between two poles a positive and a negative, of a direct voltage side of the converter, each of which current valves comprising a semiconductor element of turn-off type and a rectifying member connected in anti-parallel therewith, an alternating voltage phase line being connected to a midpoint denominated phase output, of the series connection between two current valves while dividing the series connection into two equal parts, an intermediate link arranged on the direct voltage side of the converter, which intermediate link comprises at least one intermediate link capacitor, a resonant circuit comprising at least a capacitive member, an inductor and an auxiliary valve provided with semiconductor components of turn-off type for recharging said capacitive member in connection with commutation of the phase current, a control device for controlling turn-on and turn-off of the semiconductor elements of turn-off type of the current valves and the semiconductor components of turn-off type of the auxiliary valve, and means for measuring the phase current, said turn-on and turn-off being controlled by the control device in dependence on control signals received from a modulator, which signals indicate desired instants for commutation, wherein the control device, in connection with the effectuation of an intended commutation process ordered by the modulator, sends control signals to the current valves and auxiliary valve that are taking part in the commutation process, for turning on or turning off thereof, at instants determined on the basis of a desired commutation instant given by the modulator and a calculation algorithm, which is based upon knowledge about the influence the components included in the converter have on the intended commutation process, said calculation algorithm being elaborated in consideration of the condition that the desired commutation instant is to coincide with an equivalent transition instant for the phase voltage, which equivalent transition instant is given by the condition

  • ttr-tcttr=tc

    up





    h


    (t)




    t
    =0where uph(t) is the phase voltage, ttr is the equivalent transition instant and tc is so chosen that the changing of the phase voltage (uph(t)) has not began at the instant ttr

    tc and has been completed at the instant ttr+tc.

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