Adaptive hold current for electric motors

A device for generating a blocking moment in a standstill state of an electrically commutated electric motor having at least two windings, wherein, on the electric motor a varying load moment acts from outside in the standstill state, comprising:

• a blocking current generation unit for supplying a blocking current into a terminal of a first winding of the electric motor,
• a motor inductivity detection unit for the detection of a motor inductivity parameter representing a value of a motor inductivity during the standstill state of the electric motor,
• a controller for controlling the blocking current during the standstill state of the electric motor for compensation of the varying load moment acting on the electric motor from the outside, the controller being supplied, as a control deviation, with a difference between a set value for the motor inductivity parameter as a reference variable and an actual value of the motor inductivity parameter as a feedback variable, the actual value of the motor inductivity parameter being a value that occurs due to a value of the blocking current supplied during the standstill state and a value of the load moment acting on the electric motor, and the controller outputting a signal to the blocking current generation unit as a control variable, and
• a control unit for
• controlling, during the standstill state of the electric motor, the blocking current generation unit to supply a maximum blocking current,
• controlling the motor inductivity detection unit to detect the motor inductivity parameter when the electric motor is supplied with the maximum blocking current,
• switching between a first operation mode in which the blocking current generation unit is controlled by the control unit, and a second operating mode in which the blocking current generation unit is controlled by the controller,
• controlling the blocking current generation unit to supply a blocking current which decreases successively starting from the maximum blocking current so as to cause a control deviation at the input of the controller which is greater than a predetermined threshold value, the control of the blocking current generation unit ending at latest when the blocking current has been reduced to a predetermined minimum current, and
• activating a function of the controller for switching the control of the blocking current generation unit from the control unit to the controller if, during the successive reduction of the blocking current, the control deviation exceeds the predetermined threshold value, to control the motor inductivity to the value of the motor inductivity parameter given upon activation of the function of the controller.