Load sharing in V/F speed controlled multi-motor driven system under mechanical wheel-slippage

In this paper a method is proposed for sharing the torques equally between the wheels of a gantry crane, driven by V/F controller, under wheel slippage. Induction Machines (IM´s) are used for driving the wheels of the gantry crane. These motors are controlled by Volts/Hertz controller. Over time the adhesion between the wheels and the rails decreases because of wear-out. Water or oil spillage, etc. also results in sudden drop in the adhesion. Such a reduction in adhesion causes wheel slippage. If the slippage is unequal for the wheels then the load shared by the wheels will be disturbed with one wheel carrying lesser load and the other motor equivalently overloaded. A novel and simple method is suggested to correct the speed reference of the drives so as to improve the load sharing and to effectively use the machines under these conditions. The control strategy may be readily extended to other similar applications where the coupling between the motors is not rigid and the torque passed onto the load is by the virtue of adhesion.