Current Concepts in Engineering Research and Technology Vol. 3

Load sharing in conventional V/f-controlled multi-induction motor systems is strongly influenced by parameter mismatch, particularly rotor resistance variation arising from manufacturing tolerances. These variations cause unequal torque distribution among motors operating at a common speed, which may reduce the operational reliability of the drive system. This study proposes a V/f control strategy incorporating a reference speed compensator to improve equal torque sharing between induction motors with mismatched rotor resistances. The method modifies the command frequency and corresponding voltage of the second motor drive according to rotor resistance variation while maintaining constant air-gap flux and the required common operating speed. The proposed approach was evaluated through simulation studies using two-motor load-sharing arrangements with 3-hp and 5-hp induction motors under ±7% rotor resistance variation. Under conventional V/f control, both motors maintained the same speed, but torque sharing remained unequal. In the 3-hp system, the torque contributions were 9 Nm and 7 Nm under a 16 Nm load, whereas the proposed compensator produced equal sharing of 8 Nm each. In the 5-hp system, the torque contributions changed from 19 Nm and 25 Nm under conventional control to 22 Nm each with the compensator under a 44 Nm load. The results indicate that the proposed V/f load-sharing scheme can compensate for rotor resistance mismatch by adjusting the voltage and frequency commands, thereby improving torque sharing without affecting speed synchronisation.