Modular multilevel converter having at least one arrangement comprising a module (1_1) of the modular multilevel converter, wherein the module comprises at least two electronic switching elements (202, 206) and an electrical energy storage device, and wherein the arrangement comprises a switch (S1_1) which in its closed switching state electrically bypasses the module (1_1), wherein - the two electronic switching elements (202, 206) of the module are arranged in a half-bridge circuit, or - the module comprises the two electronic switching elements (202, 206) and two additional electronic switching elements (302, 306), wherein the two electronic switching elements (202, 206) and the two additional electronic switching elements (302, 306) are arranged in a full-bridge circuit, wherein the module comprises a switch actuation device inside the module, wherein said switch actuation device is configured to close the switch (S1_1) in the event of a fault in the module (1_1), wherein the arrangement comprises a measuring sensor for measuring a physical variable which arises at the switch (S1_1) and which assumes different values depending on whether the switch (S1_1) is in its open switching state or in its closed switching state, and wherein the modular multilevel converter comprises a control unit, characterized in that - the physical variable is an electrical voltage (Us), and the measuring sensor is a voltage measuring sensor connected in parallel with the switch (S1_1), and the arrangement is designed so that - the physical variable measured is the voltage (Us) arising across the switch (S1_1) forming a switch voltage measurement value (MUs), and the closed switching state is identified when the switch voltage measurement value (MUs) falls below a minimum switch voltage value, and the open switching state is identified when the switch voltage measurement value exceeds the minimum switch voltage value, - the control unit of the multilevel converter reduces an output current of the multilevel converter if, in the case of a faulty module, the respective switch is in its open switching state, and - if the switch (S1_1) is in its closed switching state, switch voltage measurement values (MUs) are repeatedly determined at intervals, and these switch voltage measurement values (MUs) are evaluated to determine whether the ohmic contact resistance of the switch (S1_1) increases. - the two electronic switching elements (202, 206) of the module are arranged in a half-bridge circuit, or - the module comprises the two electronic switching elements (202, 206) and two additional electronic switching elements (302, 306), wherein the two electronic switching elements (202, 206) and the two additional electronic switching elements (302, 306) are arranged in a full-bridge circuit, wherein the module comprises a switch actuation device inside the module, wherein said switch actuation device is configured to close the switch (S1_1) in the event of a fault in the module (1_1), wherein the arrangement comprises a measuring sensor for measuring a physical variable which arises at the switch (S1_1) and which assumes different values depending on whether the switch (S1_1) is in its open switching state or in its closed switching state, and wherein the modular multilevel converter comprises a control unit, characterized in that the arrangement comprises a measuring sensor for measuring a physical variable which arises at the switch (S1_1) and which assumes different values depending on whether the switch (S1_1) is in its open switching state or in its closed switching state, and wherein the modular multilevel converter comprises a control unit, characterized in that - the physical variable is an electrical voltage (Us), and the measuring sensor is a voltage measuring sensor connected in parallel with the switch (S1_1), and the arrangement is designed so that - the physical variable measured is the voltage (Us) arising across the switch (S1_1) forming a switch voltage measurement value (MUs), and the closed switching state is identified when the switch voltage measurement value (MUs) falls below a minimum switch voltage value, and the open switching state is identified when the switch voltage measurement value exceeds the minimum switch voltage value, - the control unit of the multilevel converter reduces an output current of the multilevel converter if, in the case of a faulty module, the respective switch is in its open switching state, and - if the switch (S1_1) is in its closed switching state, switch voltage measurement values (MUs) are repeatedly determined at intervals, and these switch voltage measurement values (MUs) are evaluated to determine whether the ohmic contact resistance of the switch (S1_1) increases.