Variable Frequency Drive For a Single Phase Induction Motor Using PIC Microcontroller

Project Supervisor:

Sir Hafiz Tahir

Team Members:

Umair Abbas…………………………………….M11-439

Ijaz Ahmed………………………………………M11-424

Muhammad Imran Ishfaq………………………..M11-436

Zeeshan Ali Cheema……………………………..M11-401

Session:

2010-2014

DEPARTMENT OF ELECTRICAL ENGINEERING

COLLEGE OF ENGINEERING & EMERGING TECHNOLOGIES

UNIVERSITY OF THE PUNJAB

LAHORE, PAKISTAN

Variable Frequency Drive For a Single Phase Induction Motor Using PIC MicrocontrollerThis project report is submitted to the Department of Electrical Engineering, University of the Punjab Lahore, Pakistan for the partial fulfillment of requirements for the degree

Of

Bachelor of Science

In

Electrical Engineering

Approved on _________________

Internal Examiner:

Sign: _______________________________

(Project Supervisor) Name:_Hafiz Tahir________

External Examiner: Sign: ________________________________

Name: ________________________________

Session:

2010-2014

DEPARTMENT OF ELECTRICAL ENGINEERING

COLLEGE OF ENGINEERING & EMERGING TECHNOLOGIES

UNIVERSITY OF THE PUNJAB

LAHORE, PAKISTAN

Acknowledgement

We would like to acknowledge the contributions made by our revered teachers in the completion of this project. Without their mentoring and supervision, we would never have been able to fulfill this profoundly critical part of our Engineering Degree.

First of all, we’d like to thank Sir Kamal Shahid, who did a remarkable job at acquainting us with the concepts of Power Electronics. We’ve made a lot of use of the knowledge we gathered from his lectures. We would also like to thank Sir Murad Habib, whose course in Micro-controllers made it possible for us to learn the subtle art of interfacing software with hardware.

No acknowledgement would be complete without taking into account the kindness and availability shown by the Laboratory Attendants at the laboratories of our Department of Electrical Engineering. Not once did we have to worry about Instrumentation and Measurements in the completion of our FYP, all due to the coo-operation of our Laboratory Attendants.

Last, but not least, we’d like to thank our Project Supervisor, Sir Hafiz Tahir who had to put up with a lot of nagging and vexing from our side but never gave up his patience with us and always offered his valuable advice in all matters regarding our FYP.

Dedication

“ To our beloved parents, primarily, because they paid, not only for this project, but also our entire Sixteen Years education. ”

Abstract

CHAPTER 1

INTRODUCTION Final Year Project constitutes the most invaluable part of engineering education. It allows students to practically apply the knowledge gained over the course of their degree program to real life industrial applications. The experienced earned in this exercise helps students become learned and trained Assistant Engineers.

1.1 Project Synopsis

Our project is Variable Frequency Drive for an Induction Motor. According to some estimates, 75% of the power generated in the entire world is consumed by motors. Motors have applications in all types of industries and house-hold appliances. From fans to pumps, lifters, compressors and convener belts, motors are involved everywhere. However, these motors are not always required to run at constant speeds. In fact, motors are, more often than not required to run at variable speeds. Also, increasing load on a motor, decreases its speed. Even in such cases a motors’ speed has to be varied by external means to keep it running at the required speed.

1.2 Scope of Work

All work done in the completion of this project has been done on purely scientific basis. Various scopes of work in this project include:

a) Literature Review on AC Motor Drivesb) Designing a VFD Circuit according to the

requirements of our project.c) Stimulating and troubleshooting the designed

circuit on Proteusd) Assembling the VFD Circuit in hardwaree) Testing the VFD Circuit on a quarter single

phase induction motor.

This projected challenged our effectiveness as engineers as much as our skill and knowledge in the required fields. The projected was privately funded by all the members of our group.

1.2 Project Planning The project was planned along the lines of the popular industrial project planning technique of EPC, namely Engineering, Procurement, Construction.

1.2.1 Engineering: Engineering involves the designing of the project in software. But before that, extensive research was done in regards with this topic. Textbooks on Power Electronics and Micro-controllers were the most helpful in this regard. We took care of the particular industrial requirements of our country in designing our VFD Circuitry. Firstly, the design was sketched on paper, than run on Proteus.

1.2.2 Procurement: In this stage of EPC, all necessary equipments and components were purchased. Components involved PIC Micro-controllers, variable resistors, opto-couplers, current transformer, voltage transformer, power transformer, FETs, various ICs and most importantly, an Induction Motor. Equipment was mostly purchased from Hall Road, Lahore and paid for by ourselves.

1.2.3 Construction: This stage is where the actual work began. It was also the most time consuming and nerve wrecking. The components purchased were assembled on several breadboards and then brought together on a large wooden board.

1.3 Flow Chart

1.4 Gantt Chart

Chapter 2

Literature ReviewAC Drive Evolution

The VFD is used to create a controlled frequency AC wave form to the AC induction motor. By changing the frequency of the AC wave form the speed of the AC motor is changed. It is equally important to control the flux density in the motor to maintain torque producing capabilities throughout the speed range.

VFD technology has improved due to power devices and the microcomputer. Early VFD's used silicon controlled rectifiers (SCRs) or gate tum off thyristors (GTOs) and was either variable voltage inverter (VVI) or current source inverter (CSI) drives. As technology improved the pulse width modulated (PWM) drive was introduced. Originally the PWM drive used Darlington bi-polar transistors as power devices. However, with the introduction of the insulated gated bi-polar transistor (IGBT) in the late 1980's vast improvements in the design of AC VFD's resulted.

Vector controlled drives were also introduced around the time as IGBT's became more readily available. They are similar to the PWM VFD except they use a more sophisticated level of control logic. The basic principal is to model the motor's electrical performance inside the controller. This allows the controller to perfectly match the motor performance to the load requirement. Vector controlled drives provide higher dynamic performance. There are many types today with both direct and indirect methods of control.

Costs of VFD's have come down dramatically primarily from the improved technology of power devices, microcomputer advancements and improved manufacturing techniques. For example, a 10 horsepower drive manufactured in the early 1980's was large and bulky. Today that same drive can be held in the palm of your hand at approximately one third the cost.

Speed Control Methods

a) By changing the applied voltage:

Torque equation of induction motor is 

Rotor resistance R2 is constant and if slip s is small then sX2 is so small that it can be neglected. Therefore, T ∝ sE2

2 where E2 is rotor induced emf and E2 ∝ V And hence T ∝ V2, thus if supplied voltage is decreased, torque decreases and hence the speed decreases.This method is the easiest and cheapest, still rarely used because-1) A large change in supply voltage is required for relatively small change in speed.2) Large change in supply voltage will result in large change in flux density, hence disturbing the magnetic conditions of the motor.

b) By changing the applied frequency

Synchronous speed of the rotating magnetic field of induction motor is given by,

where, f = frequency of the supply and P = number of stator poles. Thus, synchronous speed changes with change in supply

frequency, and thus running speed also changes. However, this method is not widely used. This method is used where, only the induction motor is supplied by a generator (so that frequency can be easily change by changing the speed of prime mover).

c) Changing the number of stator poles

From the above equation, it can be also seen that synchronous speed (and hence, running speed) can be changed by changing the number of stator poles. This method is generally used for squirrel cage induction motors, as squirrel cage rotor adapts itself for any number of stator poles. Change in stator poles is achieved by two or more independent stator windings wound for different number of poles in same slots.For example, a stator is wound with two 3phase windings, one for 4 poles and other for 6 poles. For supply frequency of 50 Hzi) synchronous speed when 4 pole winding is connected, Ns = 120*50/4 = 1500 RPMii) synchronous speed when 6 pole winding is connected, Ns = 120*50/6 = 1000 RPM

d) Phase Control

The SCR phase control works much like the common TRIAC dimmer, but has numerous advantages including increased current capability, robustness and absence of minimum voltage “Snap-On.” A complementary, symmetrical trigger circuit consisting of two PUTs (programmable uni-junction transistors) enables firing of two anti-parallel THYRISTORs (SCRs). The circuit makes up a two terminal power device that is simply inserted between the AC power source and load. Besides controlling the intensity of incandescent lighting, it is

useful in controlling the speed of universal (commutator brush type) AC motors.

Chapter 3

Methodology In our project we divide it in following modules according to

their functions,

Modules of Circuit:

Potential Transformer ModuleCurrent Transformer ModulePower Transformer ModuleRPM Sensor ModuleMotor Power SupplyMeasuring & Controlling ModuleLCD ModuleKeypad ModuleSignal Isolation ModuleVFD Controlling ModuleVFD Module

Potential Transformer Module

Here is a block diagram which describes the function of potential transformer. The supply voltage of motor is measured by this module. First voltages step down from 220v to 12v. a bridge rectifier is used to convert it to DC. We use a

voltage divider consisting on two resistances to further step down the voltages to 5v which is now safe for our controller. These 5v can be changed with respect to supply voltages as they fluctuate.

Current Transformer Module

Here is a block diagram which completely describes the function of current transformer module. Motor current passes through the primary of the transformer from source

to load (motor). This current develops an AC voltage on secondary side. A diode is used to convert this AC voltage to pulsating DC.

A voltage divider is used to drop this voltage according to the requirement of our controller. A capacitor is used as a filter to remove the ripples from DC and fed to controller input.

Power Transformer Module