Abstract: A device for converting a DC voltage into an AC voltage and vice versa comprises a control system to control the voltage conversion and at least one phase leg (1) with a first (Uvp1) voltage source connected in series between a first DC terminal (4) and a first AC terminal (6) and with a second (Uvn1) voltage source connected in series between the first AC terminal (6) and a second DC terminal (5). Each of the voltage sources comprises at least a first and a second submodule (15) in series-connection, where each submodule (15) comprises at least two power electronic switches (16) connected in parallel with at least one capacitor (17).

Abstract: An apparatus for controlling a voltage source converter with at least two bridges (V1, V2) of semiconducting self commutating elements (11) connected in anti-parallel with a diode (12), comprising means (OPWM) for producing a switching control pulse train (19) to form a fundamental frequency (18), means (C) for effecting a switching order (CP) and means (VCU) for detecting a switching event.

Abstract: An installation for transmission of high-voltage direct current comprises a converter (SR1) which is controlled by a control unit (CU1). The control unit comprises a quotient-forming member, which forms a current order (IO) for the current (Id) in the dc connection of the installation in dependence on the quotient between a power order (PO) and a calculating value (UDF) of the direct voltage (Ud) at the converter, and a low-pass filter with a bandwidth (1/T1, 1/T2) capable of being controlled, which forms the calculating value as a filtered measured value (UD) of the direct voltage. The control unit comprises a signal-forming member which forms a state signal (FC), indicating that a short-circuit fault has occurred. The state signal influences the bandwidth of the low-pass filter such that the bandwidth is temporarily changed from a smaller value (1/T1) to a larger value (1/T2).