A voltage source converter for connection between power transmission elements (14, 20, 22) related to a power transmission system, and comprising - a group of interconnected phase legs, where each phase leg has a first and a second end point via which said interconnection is achieved, - at least three connection terminals (AC1, AC2, AC3, DC+, DC-) for connecting the phase legs to said power transmission elements, - a first group of cells (C1p1, C2p1, C1n1, C2n1, C1p2, C2p2, C1n2, C2n2, C1p3, C2p3, C1n3, C2n3) included in each phase leg, wherein the cells (C1p1, C2p1, C1n1, C2n1, C1p2, C2p2, C1n2, C2n2, C1p3, C2p3, C1n3, C2n3) in the first group are only capable of providing unipolar voltage contributions to the operation of the converter and also connected in the phase legs for only being capable of such unipolar voltage contributions, and the cells in the first group are dedicated to a basic control function of the converter, and - a control unit arranged to provide control signals to cells in the first group to control the operation of the voltage source converter according to their basic functionality characterized in that the voltage source converter further comprises - a second group of cells (C3p1, C3n1, C3p2, C3n2 C3p3, C3n3), wherein the cells (C3p1, C3n1, C3p2, C3n2 C3p3, C3n3) in the second group are connected to the cells of the first group, the cells in the second group are arranged for being capable of each providing bipolar voltage contributions to the operation of the converter, the cells in the second group are connected in each phase leg, the cells in the second group are dedicated to an additional AC voltage providing functionality, and the control unit is further arranged to provide control signals to the cells in the second group for making these cells provide additional AC voltages for enhancing converter operation according to the additional AC voltage providing functionality. - a group of interconnected phase legs, where each phase leg has a first and a second end point via which said interconnection is achieved, - at least three connection terminals (AC1, AC2, AC3, DC+, DC-) for connecting the phase legs to said power transmission elements, - a first group of cells (C1p1, C2p1, C1n1, C2n1, C1p2, C2p2, C1n2, C2n2, C1p3, C2p3, C1n3, C2n3) included in each phase leg, wherein the cells (C1p1, C2p1, C1n1, C2n1, C1p2, C2p2, C1n2, C2n2, C1p3, C2p3, C1n3, C2n3) in the first group are only capable of providing unipolar voltage contributions to the operation of the converter and also connected in the phase legs for only being capable of such unipolar voltage contributions, and the cells in the first group are dedicated to a basic control function of the converter, and the cells (C1p1, C2p1, C1n1, C2n1, C1p2, C2p2, C1n2, C2n2, C1p3, C2p3, C1n3, C2n3) in the first group are only capable of providing unipolar voltage contributions to the operation of the converter and also connected in the phase legs for only being capable of such unipolar voltage contributions, and the cells in the first group are dedicated to a basic control function of the converter, and - a control unit arranged to provide control signals to cells in the first group to control the operation of the voltage source converter according to their basic functionality - a second group of cells (C3p1, C3n1, C3p2, C3n2 C3p3, C3n3), wherein the cells (C3p1, C3n1, C3p2, C3n2 C3p3, C3n3) in the second group are connected to the cells of the first group, the cells in the second group are arranged for being capable of each providing bipolar voltage contributions to the operation of the converter, the cells in the second group are connected in each phase leg, the cells in the second group are dedicated to an additional AC voltage providing functionality, and the control unit is further arranged to provide control signals to the cells in the second group for making these cells provide additional AC voltages for enhancing converter operation according to the additional AC voltage providing functionality. the cells (C3p1, C3n1, C3p2, C3n2 C3p3, C3n3) in the second group are connected to the cells of the first group, the cells in the second group are arranged for being capable of each providing bipolar voltage contributions to the operation of the converter, the cells in the second group are connected in each phase leg, the cells in the second group are dedicated to an additional AC voltage providing functionality, and the control unit is further arranged to provide control signals to the cells in the second group for making these cells provide additional AC voltages for enhancing converter operation according to the additional AC voltage providing functionality.