Variable Frequency Drive 3 phase Induction Motor using Pic Microcontroller

This project is about variable frequency drive for three phase induction motor using pic microcontroller. In this project  voltage frequency control ( V/F ) method is used to control the speed of three phase induction motor. Induction motors have many industrial and domestic applications.

VFD Introduction

Induction motors are widely used in compressors, washing machines. All induction motors which you buy from the market have rated power and rated speed. When you power the induction motor, it will start running at its rated speed.  But there are many applications where we need variable speed induction motors. So we need a controller which can make induction motor speed controllable. 

There are many methods to design variable speed drive for induction motor for both single-phase and three-phase. But in this project, we have designed a variable frequency drive by voltage frequency control or V/F method. So now let’s start with an introduction of the V/F control method for variable frequency drive.

What is Voltage frequency control method ( V/F)

V/F method is also known as variable voltage and variable frequency. It is a most popular method for speed control of three phase induction motor. It is used in many variable frequency drive applications. We can control the speed of induction motor by applying a variable frequency supply to induction motor.

But if we change the frequency only, it will change the motor flux also. Motor flux is directly proportional to motor torque. So only changing the frequency affects the motor torque also.  So we need to keep the flux constant. To keep flux constant, we need to change the voltage applied to the motor also. Because the voltage applied to an induction motor is directly proportional to the flux and angular speed of the motor. 

So we need to keep the ratio of V/F constant to maintain flux of motor. Only changing the voltage or current may also saturate the core of the induction motor. So V/F ratio should be constant in the operating range of induction motor. In this variable frequency drive project, we have used V/F method to control the speed of the induction motor.

Implementation of Variable Frequency Drive using Pic Microcontroller

To implement variable frequency drive for three phase induction motor, we first converted single phase supply into dc voltage using rectifier circuit. This dc voltage is used to generate variable voltage and frequency using pic microcontroller. This dc voltage is given to a input of three phase H bridge. Software for this project is implemented using pic18f452 microcontroller and spwm signals are given to three phase H bridge. induction motor is connected at the output of three phase H bridge.

You may also like to check my other induction motor related projects:

• Bidirectional rotation of induction motor by Remote control device
• ACPWM control for induction motor using pic microcontroller
• Thyristor controlled power for single phase induction motor
• Soft starter for three phase induction motor using Arduino