A Modular Multilevel Converter, MMC,, comprising: a control system arranged for controlling the MMC; and a power converter phase leg, the phase leg comprising: a first cell arrangement comprising a plurality of series connected converter cells; a second cell arrangement comprising a plurality of series-connected converter cells; and a breaker arrangement comprising a plurality of breakers (B1, B2, B3) and arranged to enable alternately connecting the first and second cell arrangements in series and in parallel by means of said plurality of breakers; wherein the breaker arrangement comprises three breakers (B1, B2, B3) connected in series along a bus of the phase leg, where the first cell arrangement is connected across the first and second breakers (B1, B2) and the second cell arrangement is connected across the second and third breakers (B2, B3); and wherein the control system comprises processing circuitry and data storage storing instructions executable by said processing circuitry whereby said control system is operative to: obtain current information that a current through the phase leg is above a predetermined current threshold, and based on the obtained current information, by means of the plurality of breakers, connect the first and second cell arrangements in parallel; and obtain voltage information that a voltage across the phase leg is above a predetermined voltage threshold, and based on the obtained voltage information, by means of the plurality of breakers, connect the first and second cell arrangements in series; such that the first and second cell arrangements are alternatingly connected in series, when the voltage across the phase leg is high, and in parallel, when the current through the phase leg is high. a control system arranged for controlling the MMC; and a power converter phase leg, the phase leg comprising: a first cell arrangement comprising a plurality of series connected converter cells; a second cell arrangement comprising a plurality of series-connected converter cells; and a breaker arrangement comprising a plurality of breakers (B1, B2, B3) and arranged to enable alternately connecting the first and second cell arrangements in series and in parallel by means of said plurality of breakers; a first cell arrangement comprising a plurality of series connected converter cells; a second cell arrangement comprising a plurality of series-connected converter cells; and a breaker arrangement comprising a plurality of breakers (B1, B2, B3) and arranged to enable alternately connecting the first and second cell arrangements in series and in parallel by means of said plurality of breakers; wherein the breaker arrangement comprises three breakers (B1, B2, B3) connected in series along a bus of the phase leg, where the first cell arrangement is connected across the first and second breakers (B1, B2) and the second cell arrangement is connected across the second and third breakers (B2, B3); and wherein the control system comprises processing circuitry and data storage storing instructions executable by said processing circuitry whereby said control system is operative to: obtain current information that a current through the phase leg is above a predetermined current threshold, and based on the obtained current information, by means of the plurality of breakers, connect the first and second cell arrangements in parallel; and obtain voltage information that a voltage across the phase leg is above a predetermined voltage threshold, and based on the obtained voltage information, by means of the plurality of breakers, connect the first and second cell arrangements in series; such that the first and second cell arrangements are alternatingly connected in series, when the voltage across the phase leg is high, and in parallel, when the current through the phase leg is high. obtain current information that a current through the phase leg is above a predetermined current threshold, and based on the obtained current information, by means of the plurality of breakers, connect the first and second cell arrangements in parallel; and obtain voltage information that a voltage across the phase leg is above a predetermined voltage threshold, and based on the obtained voltage information, by means of the plurality of breakers, connect the first and second cell arrangements in series; such that the first and second cell arrangements are alternatingly connected in series, when the voltage across the phase leg is high, and in parallel, when the current through the phase leg is high.