A Crane system includes: Siemens inverter Micromaster440 15kW, motor 7.5kW with gearbox; cable, rewinder.

-       Inverter control motor. Motor winds or rewinds cable through gearbox. The distance from ground to rewinder is about 6m. The cables supply power for crane. Cable’s length = 80m, type: triple core, D=185mm. Inverter have breaking resistor.

-       Crane: forward or backward. When it moves forward( leave from origin), cable is wind off. When crane moves backward, cable is wind on (cable isn’t slack)

-       Solution: set Inverter in mode “Sensorless vector torque control” and “braking kinetic enegy”, we can wind on cable but cannot wind off cable ( rewinder rotates 30 degrees and stops, then it continues rotating 30 degrees and stop).

How can we solve this problem?