An interface arrangement configured to couple an alternating current, AC, power system comprising a plurality of phases with a direct current, DC, power system, the interface arrangement comprising: a plurality of converter modules (104, 105, 106) for conversion of DC power to AC power, or vice versa, electrically connected in series, each converter module corresponding to one of the phases and being configured to provide at least a portion of an AC waveform, and each converter module comprising: at least one multi-level converter cell (141-1,..., 141-N, 142-1,..., 142-N, 143-1,..., 143-N, 144-1,..., 144-N, 145-1,..., 145-N, 146-1,..., 146-N), each multi-level converter cell configured to provide a voltage contribution to the AC waveform based on voltage of the DC power system; and at least one converter valve (151-1,..., 151-N, 152-1,..., 152-N, 153-1,..., 153-N, 154-1,..., 154-N, 155-1,..., 155-N, 156-1,..., 156-N) electrically connected to the at least one multi-level converter cell; wherein the interface arrangement is configured such that the at least one converter valve is controllably switchable between conducting states with a selected current conduction direction and a non-conducting state, wherein the at least one converter valve includes at least two anti-parallel thyristors (194, 195); the interface arrangement further comprising a control unit configured to control operation of the at least one converter valve at least with respect to switching, said control with respect to the switching comprising selectively controlling polarity of any voltage contribution provided by the at least one multi-level converter cell, wherein the control unit is configured to, in response to receiving an indication indicating presence of a fault current in the interface arrangement, control switching of the at least one converter valve so as to route the fault current through the at least one converter valve and bypass at least a portion of the at least one multi-level converter cell. a plurality of converter modules (104, 105, 106) for conversion of DC power to AC power, or vice versa, electrically connected in series, each converter module corresponding to one of the phases and being configured to provide at least a portion of an AC waveform, and each converter module comprising: at least one multi-level converter cell (141-1,..., 141-N, 142-1,..., 142-N, 143-1,..., 143-N, 144-1,..., 144-N, 145-1,..., 145-N, 146-1,..., 146-N), each multi-level converter cell configured to provide a voltage contribution to the AC waveform based on voltage of the DC power system; and at least one converter valve (151-1,..., 151-N, 152-1,..., 152-N, 153-1,..., 153-N, 154-1,..., 154-N, 155-1,..., 155-N, 156-1,..., 156-N) electrically connected to the at least one multi-level converter cell; at least one multi-level converter cell (141-1,..., 141-N, 142-1,..., 142-N, 143-1,..., 143-N, 144-1,..., 144-N, 145-1,..., 145-N, 146-1,..., 146-N), each multi-level converter cell configured to provide a voltage contribution to the AC waveform based on voltage of the DC power system; and at least one converter valve (151-1,..., 151-N, 152-1,..., 152-N, 153-1,..., 153-N, 154-1,..., 154-N, 155-1,..., 155-N, 156-1,..., 156-N) electrically connected to the at least one multi-level converter cell; wherein the interface arrangement is configured such that the at least one converter valve is controllably switchable between conducting states with a selected current conduction direction and a non-conducting state, wherein the at least one converter valve includes at least two anti-parallel thyristors (194, 195); the interface arrangement further comprising a control unit configured to control operation of the at least one converter valve at least with respect to switching, said control with respect to the switching comprising selectively controlling polarity of any voltage contribution provided by the at least one multi-level converter cell, wherein the control unit is configured to, in response to receiving an indication indicating presence of a fault current in the interface arrangement, control switching of the at least one converter valve so as to route the fault current through the at least one converter valve and bypass at least a portion of the at least one multi-level converter cell.