An arrangement for exchanging power, in shunt connection, with a three-phase electric power network includes a Voltage Source Converter having at least three phase legs with each a series connection of switching cells. Each switching cell has at least two semiconductor assemblies connected in series and having each a semiconductor device of turn-off- type and a rectifying element connected in anti-parallel therewith and at least one energy storing capacitor. A control unit is configured to control the semiconductor devices of each switching cell and to deliver a voltage across the terminals thereof being zero or U, in which U is the voltage across the capacitor. The control unit is also configured to calculate a value for amplitude and phase position for a second negative sequence-current or a zero-sequence voltage or a value of a dc current.