This paper presents a simplified approach for a digital controller of variable frequency three-phase inverter supplied a three-phase induction motor. The performance characteristics with variable frequency supply have been studied and simulated by a computer program. The torque-speed characteristics of the motor varied with variation of the frequency. Torque-speed characteristics at different frequencies are presented. Interesting waveforms of the digital controller have been recorded. Frequency variation covers many industrial applications such as manufacturing rollman belly, water pumps, composers, chiller fans and some home application.