Method for operating a modular multilevel converter that has at least one converter module (KM1-KM6) comprising electrically series-connected submodules, wherein each submodule comprises in each case at least two switches and an energy store, wherein, in the method, - the voltage on the at least one converter module (KM1-KM6) is ascertained so as to form voltage actual values (Uk), - the voltage actual values (Uk) are compared with voltage setpoint values (Uks) and - at least one of the switches of the submodules is switched over when a voltage deviation value, formed on the basis of the differential values between the voltage actual values (Uk) and the voltage setpoint values (Uks), deviates above a measure defined by a predefined hysteresis band, which is given by an upper hysteresis band threshold (+Hmax) and a lower hysteresis band threshold (-Hmax), - wherein the upper hysteresis band threshold (+Hmax), the lower hysteresis band threshold (-Hmax) or both hysteresis band thresholds are modified regularly or irregularly with a control variable so as to achieve a predefined converter behaviour, - wherein the control variable directly defines the upper hysteresis band threshold (+Hmax) and the lower hysteresis band threshold (-Hmax) corresponds to the control variable with an inverted mathematical sign, characterized in that - the submodule voltages present on the submodules are measured so as to form submodule voltage measured values (Usm), - a voltage auxiliary value (Uh) is ascertained by incorporating an addition of the submodule voltage measured values (Usm) of all submodules of the converter module (KM1-KM6), independently of whether these are activated or deactivated, - a voltage edge variable (Sfg) is formed by calculating an absolute value of the mathematical derivative of the differential values between the voltage actual values (Uk) and the voltage setpoint values (Uks) over time, and - the control variable is formed by calculating a quotient between the square of the voltage auxiliary value (Uh) and a multiple of, in particular 12 times, the voltage edge variable (Sfg), - as a result of which the switching frequency for switching over the submodules is able to be reduced. - the voltage on the at least one converter module (KM1-KM6) is ascertained so as to form voltage actual values (Uk), - the voltage actual values (Uk) are compared with voltage setpoint values (Uks) and - at least one of the switches of the submodules is switched over when a voltage deviation value, formed on the basis of the differential values between the voltage actual values (Uk) and the voltage setpoint values (Uks), deviates above a measure defined by a predefined hysteresis band, which is given by an upper hysteresis band threshold (+Hmax) and a lower hysteresis band threshold (-Hmax), - wherein the upper hysteresis band threshold (+Hmax), the lower hysteresis band threshold (-Hmax) or both hysteresis band thresholds are modified regularly or irregularly with a control variable so as to achieve a predefined converter behaviour, - wherein the control variable directly defines the upper hysteresis band threshold (+Hmax) and the lower hysteresis band threshold (-Hmax) corresponds to the control variable with an inverted mathematical sign, - the submodule voltages present on the submodules are measured so as to form submodule voltage measured values (Usm), - a voltage auxiliary value (Uh) is ascertained by incorporating an addition of the submodule voltage measured values (Usm) of all submodules of the converter module (KM1-KM6), independently of whether these are activated or deactivated, - a voltage edge variable (Sfg) is formed by calculating an absolute value of the mathematical derivative of the differential values between the voltage actual values (Uk) and the voltage setpoint values (Uks) over time, and - the control variable is formed by calculating a quotient between the square of the voltage auxiliary value (Uh) and a multiple of, in particular 12 times, the voltage edge variable (Sfg), - as a result of which the switching frequency for switching over the submodules is able to be reduced.