A method for controlling a modular multilevel power converter which has at least one phase module branch with a series circuit of modules. Each of the modules has an energy storage device and a power semiconductor circuit with electronic switching elements. A duty cycle of the phase module branch is ascertained, wherein the duty cycle describes the ratio between the voltage which is being output by the phase module branch and the voltage which can be maximally output by the phase module branch. The maximum value of the duty cycle during a preselected time period is ascertained, and the maximum value of the duty cycle is controlled to a target value for the maximum value of the duty cycle by a controller.