Design and Fabrication of Three Phase 1 HP Induction Motor Drive using V/F Control

Abstract

Applications of solid-state converters for Variable Frequency Drives are popular in industrial systems. The ac to dc and dc to ac conversion is frequently used to provide Variable Frequency with Adjustable Voltage for constant torque. The design and fabrication of a Variable Frequency Drive(VFD) based on Sinusoidal Pulse Width Modulation(SPWM) Technique for a three Phase Induction Motor using a 16f877 PIC micro controller. The work involves implementation of an open loop control scheme for an induction motor. The technique is extensively used in industry as it provides the accuracy required at minimum cost. Voltage/frequency(V/f) controlled motors are used to maintain maximum torque up to base speed. The speed of the induction motor need to be varied, there are need to control the frequency with respect to output voltage of the inverter for maintaining V/f ratio to achieve constant flux.To vary the output voltage of the inverter, the modulation index of the carrier signal has to be changed. Amplitude of Carrier signal varies inversely as the three phase output voltage adjust with change in frequency respectively. By changing amplitude of carrier signal and compare with constant amplitude of reference signal output six SPWM pulses carried out through 16f877 PIC micro controller. This pulses are used to trigger the three phase inverter through TLP250 driver IC and thereby speed of the motor can be controlled.The short circuit dc current and ac over current sense through LEM sensor and CT respectively. The fabrication of short circuit current and over current protections with the use of op-amps and merge them to make reliable control of Induction motor. Design and Implementation of Stand-by UPS System with PWM Controller, Automatic Voltage Regulator Section and Charging Section.