Performance Evaluation of A Developed Variable Frequency Drive: For Speed Control of Asynchronous Machines Use as Induction Generators

Abstract

This paper presents the performance characteristics of a developed variable frequency drive (VFD) adaptable for operation of ac machines speed control. The VFD developed is robust, durable, cheap and have low maintenance cost compared to conventional VFDs. The controlled  asynchronous ac motor was operated to drive another self - excited  induction motor (SEIM) at hyper synchronous speed to generate electricity, a phenomenon of the non constant - speed obtainable in hydro schemes. The drive converts input ac mains to dc followed by dc to ac conversion at any desired frequency from 20HZ-65HZ in this case. A diode full-wave bridge rectifier is used to effect ac to dc conversion, while MOSFET inverter is used to convert the dc to ac. An SG3524 voltage pulse width modulation IC was used to produce the gate pulses required to drive the MOSFET inverter. Digital display of the VFD’s output voltage and frequency was actualised by means of the common anode seven segment displays by
ICL7107 which is a three and half digit analogue to digital converter. The desired speed control is achieved by varying the frequency of the voltage supplied to the motor. The model tested on load was found to work satisfactorily with its operational characteristics.

Keywords: Variable Frequency Drive, Desired Frequency, Speed, Flux, Voltage, Current, Torque Control, PWM Inverter.