The sensitivity of the hoist system in crane applications from speed control methods at induction motor

Abstract

Choosing the appropriate control technique in variable speed drive (VSD) is very important to avoid faults on the hoisting system of molten metal. This paper analyzes the sensitivity of the hoist system in crane applications from the three various control techniques of variable speed drives of induction motors: V/f open-loop control, V/f closed-loop control and closed-loop vector control. It is noticed that stoppages of motor run are usually caused by the wrong selection of control technique, by overload (overcurrent and overvoltage) or by both. On the V/f control (open and closed-loop), when the load is 45 t in low output speed (5–6 Hz), the hook is moving without control downward direction, even if the command was given for lifting (upward direction), therefore we cannot use this control technique on the main hoist 50 T Crane. In the closed-loop vector control, the feedback error information determines the exact voltage vector position and norm to produce exactly what is needed to correct the error, as the result of the number of fault/trip on hoist crane applications will be minimal. For different loads, although the output currents change obviously, motor temperature remains constant.