A voltage source converter comprising: a plurality of phase limbs connected between high and low DC terminals; wherein each phase limb comprises: a high side director switch (S W1, S W3, S W5) connecting the high DC terminal (DC+) to an AC node (102a-c) for that phase limb; a low side director switch (S W4, S W6, S W2) connecting the AC node to the low DC terminal (DC-); and a chain-link circuit (101a-c), a first end of the chain-link circuit being connected between the high side and low side director switches to be electrically coupled to the AC node; the converter further comprising first and second additional chain-link circuits (301, 302), where first ends of the first and second additional chain-link circuits are connected to the high side DC terminal and low side DC terminals respectively; and a converter controller configured to control the director switches of each phase limb in a power cycle and to control the chain-link circuits of each phase limb in a voltage mode to provide a controlled voltage transition at the AC node during the power cycle, wherein said converter controller is operable to control at least some of said chain-link circuits in a current mode to provide a defined current at times during the power cycle; wherein each chain-link circuit comprises a plurality of series-connected chain-link modules, each of the chain-link modules comprising at least one energy storage element that can be selectively connected in series with the other modules or bypassed; and wherein a second end of the chain-link circuit of each phase limb and a second end of each of the additional chain-link circuits are connected to a common node such that, in use, a current can flow from one phase limb to another via the respective chain-link circuits. a plurality of phase limbs connected between high and low DC terminals; wherein each phase limb comprises: a high side director switch (S W1, S W3, S W5) connecting the high DC terminal (DC+) to an AC node (102a-c) for that phase limb; a low side director switch (S W4, S W6, S W2) connecting the AC node to the low DC terminal (DC-); and a chain-link circuit (101a-c), a first end of the chain-link circuit being connected between the high side and low side director switches to be electrically coupled to the AC node; a high side director switch (S W1, S W3, S W5) connecting the high DC terminal (DC+) to an AC node (102a-c) for that phase limb; a low side director switch (S W4, S W6, S W2) connecting the AC node to the low DC terminal (DC-); and a chain-link circuit (101a-c), a first end of the chain-link circuit being connected between the high side and low side director switches to be electrically coupled to the AC node; the converter further comprising first and second additional chain-link circuits (301, 302), where first ends of the first and second additional chain-link circuits are connected to the high side DC terminal and low side DC terminals respectively; and a converter controller configured to control the director switches of each phase limb in a power cycle and to control the chain-link circuits of each phase limb in a voltage mode to provide a controlled voltage transition at the AC node during the power cycle, wherein said converter controller is operable to control at least some of said chain-link circuits in a current mode to provide a defined current at times during the power cycle; wherein each chain-link circuit comprises a plurality of series-connected chain-link modules, each of the chain-link modules comprising at least one energy storage element that can be selectively connected in series with the other modules or bypassed; and wherein a second end of the chain-link circuit of each phase limb and a second end of each of the additional chain-link circuits are connected to a common node such that, in use, a current can flow from one phase limb to another via the respective chain-link circuits.