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INTRODUCTION An induction motor can run only at its rated speed when it is connected directly to the main supply However many applications need variable speed operations This is felt the most in applications where input power is directly proportional to the cube of motor speed In applications like the induction motor based centrifugal pump a speed reduction of results in an energy savings of approximately Driving and controlling the induction motor efficiently are prime concerns in today's energy conscious world With the advancement in the semiconductor fabrication technology both the size and the price of semiconduc tors have gone down drastically This means that the motor user can replace an energy inefficient mechani cal motor drive and control system with a Variable Frequency Drive VFD The VFD not only controls the motor speed but can improve the motor's dynamic and steady state characteristics as well In addition the VFD can reduce the system's average energy consumption Although various induction motor control techniques are in practice today the most popular control tech nique is by generating variable frequency supply which has constant voltage to frequency ratio This technique is popularly known as VF control Generally used for open loop systems VF control caters to a large num ber of applications where the basic need is to vary the motor speed and control the motor efficiently It is also simple to implement and cost effective The PIC16F7X7 series of microcontrollers have three on chip hardware PWM modules making them suitable for phase motor control applications This application note explains how these microcontrollers

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