Protective device for an electric drive system which comprises a power converter which is connected on the input side to an intermediate circuit capacitor, and which is connected on the output side to an electric machine, wherein the protective device comprises the following: a voltage sensor which is configured to sense an electrical voltage across the intermediate circuit capacitor; and a control apparatus which is configured to make available alternately a first actuation signal for the power converter on the basis of a first space vector and a second actuation signal for the power converter on the basis of a second space vector, after an electrical voltage which exceeds a first predetermined threshold value (Umax) has been sensed across the intermediate circuit capacitor by the voltage sensor, wherein the first space vector sets a motor operating mode in the electric drive system and the second space vector sets a generator operating mode in the electric drive system, wherein, in order to reduce the electrical energy in the electric drive system, switching to and fro between the motor operating mode and the generator operating mode is performed repeatedly, characterized in that the control apparatus is configured to make available the first control signal after the electrical voltage across the intermediate circuit capacitor exceeds the first predetermined threshold value, and to make available the second control signal after the electrical voltage across the intermediate circuit capacitor undershoots a second predetermined threshold value (Umin), and to adapt the first predetermined threshold value (Umax) and the second predetermined threshold value (Umin), wherein, after the first predetermined threshold value has been exceeded for the first time and the energy reduction initiated in response thereto, the first predetermined threshold value and the second predetermined threshold value are subsequently lowered. a voltage sensor which is configured to sense an electrical voltage across the intermediate circuit capacitor; and a control apparatus which is configured to make available alternately a first actuation signal for the power converter on the basis of a first space vector and a second actuation signal for the power converter on the basis of a second space vector, after an electrical voltage which exceeds a first predetermined threshold value (Umax) has been sensed across the intermediate circuit capacitor by the voltage sensor, wherein the first space vector sets a motor operating mode in the electric drive system and the second space vector sets a generator operating mode in the electric drive system, wherein, in order to reduce the electrical energy in the electric drive system, switching to and fro between the motor operating mode and the generator operating mode is performed repeatedly, characterized in that the control apparatus is configured to make available the first control signal after the electrical voltage across the intermediate circuit capacitor exceeds the first predetermined threshold value, and to make available the second control signal after the electrical voltage across the intermediate circuit capacitor undershoots a second predetermined threshold value (Umin), and to adapt the first predetermined threshold value (Umax) and the second predetermined threshold value (Umin), wherein, after the first predetermined threshold value has been exceeded for the first time and the energy reduction initiated in response thereto, the first predetermined threshold value and the second predetermined threshold value are subsequently lowered. the first space vector sets a motor operating mode in the electric drive system and the second space vector sets a generator operating mode in the electric drive system, wherein, in order to reduce the electrical energy in the electric drive system, switching to and fro between the motor operating mode and the generator operating mode is performed repeatedly, characterized in that the control apparatus is configured to make available the first control signal after the electrical voltage across the intermediate circuit capacitor exceeds the first predetermined threshold value, and to make available the second control signal after the electrical voltage across the intermediate circuit capacitor undershoots a second predetermined threshold value (Umin), and to adapt the first predetermined threshold value (Umax) and the second predetermined threshold value (Umin), wherein, after the first predetermined threshold value has been exceeded for the first time and the energy reduction initiated in response thereto, the first predetermined threshold value and the second predetermined threshold value are subsequently lowered.