A voltage source converter having two DC terminals (DC1, DC2) and a number of AC terminals (ACA1, ACA2, ACB1, ACB2, ACC1, ACC2) for providing a number of phases of an AC voltage, the converter comprising: a number of director valves (V1A, V2A, V1B, V2B, V1C, V2C) connected in series between the DC terminals, the director valves being provided in pairs, where each pair forms a valve phase leg comprising an upper and a lower valve phase arm, where the junction between the two valve phase arms of a valve phase leg provides a primary AC terminal (ACA1, ACB1, ACC1) for a corresponding AC phase, a number of multilevel cells connected in series between the DC terminals, the cells being grouped in waveshaper phase legs, where each waveshaper phase leg is connected in parallel with a corresponding valve phase leg and comprises an upper and a lower waveshaper phase arm (WS1A, WS2A, WS1B, WS2B, WS1C, WS2C), where the junction between the upper and lower waveshaper phase arm of a waveshaper phase leg provides a secondary AC terminal (ACA2, ACB2, ACC2) for a corresponding AC phase and linked to the primary AC terminal of the corresponding valve phase leg, where the upper waveshaper phase arm (WS1A, WS1B, WS1C) of a waveshaper phase leg is configured to be operated in conjunction with the upper valve phase arm (V1A, V1B, V1C) of the corresponding valve phase leg and the lower waveshaper phase arm (WS2A, WS2B, WS2C) of a waveshaper phase leg is configured to be operated in conjunction with the lower valve phase arm (V2A, V2B, V2C) of the corresponding valve phase leg, for forming an AC waveform at least during steady state operation, and a control unit configured to control each waveshaper phase leg and valve phase leg for forming a number of phases of an output AC voltage, where the voltage of one phase is formed on the primary and secondary AC terminals of a pair of valve and waveshaper phase legs through alternately operating the valve of the upper valve phase arm and the cells of the corresponding upper waveshaper phase arm with the valve of the lower valve phase arm and cells of the corresponding lower waveshaper phase arm, thereby one waveshaper phase arm in each phase is inactive with regard to waveshaping and thus considered as an available waveshaper phase arm, characterized in that the control unit is further configured to control at least one of the available waveshaper phase arms to decouple the DC voltage from the AC voltage through controlling the at least one of the available waveshaper phase arms towards a target phase arm voltage using a control value (rpai) that is based on a sum of the absolute values of reference voltages (Vrefa, Vrefb, Vrefc) used for waveshaping in the waveshaper phase legs. a number of director valves (V1A, V2A, V1B, V2B, V1C, V2C) connected in series between the DC terminals, the director valves being provided in pairs, where each pair forms a valve phase leg comprising an upper and a lower valve phase arm, where the junction between the two valve phase arms of a valve phase leg provides a primary AC terminal (ACA1, ACB1, ACC1) for a corresponding AC phase, a number of multilevel cells connected in series between the DC terminals, the cells being grouped in waveshaper phase legs, where each waveshaper phase leg is connected in parallel with a corresponding valve phase leg and comprises an upper and a lower waveshaper phase arm (WS1A, WS2A, WS1B, WS2B, WS1C, WS2C), where the junction between the upper and lower waveshaper phase arm of a waveshaper phase leg provides a secondary AC terminal (ACA2, ACB2, ACC2) for a corresponding AC phase and linked to the primary AC terminal of the corresponding valve phase leg, where the upper waveshaper phase arm (WS1A, WS1B, WS1C) of a waveshaper phase leg is configured to be operated in conjunction with the upper valve phase arm (V1A, V1B, V1C) of the corresponding valve phase leg and the lower waveshaper phase arm (WS2A, WS2B, WS2C) of a waveshaper phase leg is configured to be operated in conjunction with the lower valve phase arm (V2A, V2B, V2C) of the corresponding valve phase leg, for forming an AC waveform at least during steady state operation, and a control unit configured to control each waveshaper phase leg and valve phase leg for forming a number of phases of an output AC voltage, where the voltage of one phase is formed on the primary and secondary AC terminals of a pair of valve and waveshaper phase legs through alternately operating the valve of the upper valve phase arm and the cells of the corresponding upper waveshaper phase arm with the valve of the lower valve phase arm and cells of the corresponding lower waveshaper phase arm, thereby one waveshaper phase arm in each phase is inactive with regard to waveshaping and thus considered as an available waveshaper phase arm, characterized in that the control unit is further configured to control at least one of the available waveshaper phase arms to decouple the DC voltage from the AC voltage through controlling the at least one of the available waveshaper phase arms towards a target phase arm voltage using a control value (rpai) that is based on a sum of the absolute values of reference voltages (Vrefa, Vrefb, Vrefc) used for waveshaping in the waveshaper phase legs.