A Study on Probable Configurations of Cascaded H-Bridge Multilevel Converters for Slip Power Recovery Application in Sugar Industry

In a typical sugar factory, around 3 motors (or 6 if used as twin mechanically-coupled motors), which are in the top range of rating, from 200 kW to 2 MW, used at cane preparation station, are invariably Wound Rotor Induction Motors (WRIMs). The load type of these motor is continuous variable with intermittent impact type load. Conventionally, a slip/buffer resistance is left in the rotor circuit to reduce the effect of impact load. An appreciable amount of power, around 7-10% of total installed power at cane preparation station is estimated to be lost in the form of heat through these buffer resistances. The very application has a scope of implementing Cascaded H-Bridge Multi Level Converters (CHBMLCs) in the rotor circuits to recover the slip power which is otherwise wasted in the slip/buffer resistances. This paper presents different configurations of CHBMLCs in the rotor circuit for slip power recovery for single and twin mechanically-coupled WRIMs for two cutters (chopper and leveller) plus one shredder/fibriser set-up of cane preparation. The cases for three single WRIMs set-up and three twin mechanically-coupled WRIMs set-up is studied. For these cases, both Voltage Source and Current Source CHBMLCs are proposed for slip power recovery application in sugar industry.