MICROCONTROLLER BASED SPEED CONTROL OF INDUCTION

MOTOR USING V/F CONTROL

submitted in partial fulfillment of the requirements for the award of

Bachelor of Engineering

In

ELECTRICAL AND ELECTRONICS ENGINEERING

BY

SIDHARTHA SHANKAR RAY

2914233

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

SATHYABAMA UNIVERSITY(Established under Section 3 of UGC Act 1956)

JEPPIAAR NAGAR, OLD MAMALLAPURAM ROAD

CHENNAI 600119

APRIL 2013

SATHYABAMA UNIVERSITY(Established Under section 3 of the UGC Act, 1956)

Accredited with B++ Grade by NAACJEPPIAAR NAGAR, CHENNAI - 600 119

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING BONAFIDE CERTIFICATE

This is to certify that this Project Report is the bonafide work of

Mr. SIDHARTHA SHANKAR RAY ( Reg.No 2914233) who carried out the

project entitled “MICROCONTROLLER BASED SPEED CONTROL OF INDUCTION

MOTOR USING V/F CONTROL” under our supervision from NOVEMBER 2012 to

March 2013.

INTERNAL GUIDE

Mr.S.JAYAPRAKASH

HEAD OF THE DEPARTMENT

Dr.V. SIVACHIDAMBARAMNATHAN

Submitted for Viva voce Examination held on

INTERNAL EXAMINER

EXTERNAL EXAMINER

CONTENTS

CHAPTER-1

1.1

Introduction.....................................................

..............................1

1.1.1

General..........................................................

........................1

1.1.2 Overview Of The

Thesis........................................................1

1.1.3 Objective Of The

Thesis........................................................1

1.1.4 Organisation Of The

Thesis...................................................2

CHAPTER-2

AIM AND SCOPE OF THE PRESENT

INVESTIGATION..................3

2.1

Objective........................................................

...............................3

2.2 Basis Of Im

Control..........................................................

.............3

2.3 Variable Frequency Drives (Vfd)

Basics......................................5

2.3.1 Components Of Vfd’s

Are......................................................5

2.4 Pi

Control..........................................................

............................6

2.4.1 The Process To

Control.........................................................6

2.4.2 Pi Control-

Definition.......................................................

.......7

2.4.3 Simulink Model Of The Pi-

Algorithm......................................9

2.4.4

Output...........................................................

.........................10

2.5 Spm, Based Igbt Power

Module..................................................11

2.6 Fsbb20ch60 - Smart Power

Module.............................................11

2.6.1 General

Description......................................................

.........11

2.7 Time Charts Of Spm Protective

Functions...................................13

2.8 Speed Torque Characteristics Of

Induction.................................14

2.9 V/F Control

Theory...........................................................

............15

2.10 Scalar Control Of Induction

Motor..........................................15

CHAPTER-3

EXPERIMENTAL METHODS AND ALGORITHM

USED......................17

3.1

General..........................................................

..................................17

3.2 Open And Closed Loop

Control....................................................17

3.2.1 Open Loop

Control..........................................................

...17

3.2.1.1 Block Diagram Of Open Loop

Control............................18

3.2.1.2 Execution Of Open Loop

Control.....................................19

3.2.1.3 Simulation Results Of Open

Loop V/F Control.................19

3.2.2 Closed Loop

Control..........................................................

.......21

3.2.2.1 Block Diagram Of Closed Loop

Control.............................22

3.2.2.2 Execution Of Closed Loop

Control.....................................23

3.2.2.3 Simulation Results Of Closed

Loop V/F Control................23

3.3. Hardware

Implementation...................................................

............24

3.3.1 Block Diagram Of Hardware

Implementation............................24

3.3.1.1 Rectifier

Unit.............................................................

...........25

3.3.1.2 Pwm-Voltage Source

Inverter.............................................25

3.3.1.3 Driver

Circuit..........................................................

..............27

3.3.1.4 Voltage Regulation

Circuit...................................................27

3.3.1.5

Microcontroller..................................................

...................27

3.3.2 Hardware Circuit

Diagram..........................................................

...28

3.3.2.1 Layout Diagram Of The

Components Of Hardware................29

3.3.2.2 Driver

Circuit..........................................................

..................30

3.3.2.3 Working Of Driver

Circuit..........................................................

31

3.3.2.3.1 And

Gate.............................................................

.............31

3.3.2.3.2

Optoisolator.....................................................

................31

3.3.2.3.3 Not

Gate.............................................................

.............31

3.3.2.3.4 Pwmis

Signal...........................................................

........31

3.3.2.3.5 Phase

Output...........................................................

........31

3.3 Smart Power Module

Circuit..........................................................

......32

3.3.1 Working Of Smart Power

Module..................................................33

3.3.1.1 Fsbb20ch60

Module...........................................................

.....33

3.3.1.2 Protection

Circuit..........................................................

...........33

3.4 Microcontroller

Circuit..........................................................

................34

3.4.1 Microcontroller Pin

Configuration...................................................3

6

3.5 Functional Circuit Of Flip

Flop............................................................3

8

CHAPTER -4

RESULTS AND DISCUSSION, PERFORMANCE

ANALYSIS..................40

4.1general...................................

..............................................................40

4.2 Open Loop Control

Results..........................................................

.......40

4.2.1 Tabulation For Open Loop

Control..............................................40

4.2.2 Graphs For The Results Of Open Loop

Control...........................41

4.2.3 Simulation Results For Open Loop

Control...................................43

4.3 Results Of Closed Loop

Control.........................................................4

4

4.3.1:Tabulation For Closed Loop

Control............................................44

4.3.2 Graphs For The Results Of Closed

Loop Control........................45

4.3.3 Tabulation For Finding The V/F

Ratio..........................................45

4.3.4 Simulation Results Of Closed Loop

Control.................................47

4.4 Performance

Analysis.........................................................

................48

4.4.1 To Drive The

Motor............................................................

............48

4.4.2 Operation Of The Entire

Hardware...............................................49

4.4.3 Oscilloscope

Results..........................................................

...........51

4.4.4

Hardware.........................................................

............................52

4.5

Advantages.......................................................

................................... 53

4.6

Application......................................................

......................................54

CHAPTER-5

SUMMARY AND

CONCLUSION.......................................................

........55

5.1

Summary..........................................................

...................................55

5.2

Conclusion.......................................................

.....................................56

LIST OF FIGURES

S.NO. DESCRIPTION PAGE NO.

Figure 2.1 Graph Showing V/F Control

4

Figure 2.2 VARIABLE FREQUENCY DRIVE

5

Figure 2.3 House Model With PI-Controller 6

Figure 2.4 BLOCK DIAGRAM OF PI CONTROLLER

8

Figure 2.5 GRAPH OF PI CONTROLLER

8

Figure 2.6 PI-Controller 9

Figure 2.7 Saturation Block To Constrain The Heat Output 9

Figure 2.8 Output 10

Figure 2.9 General View Of Spm Module

11

Figure 2.10 Spm (Top View)

12

Figure 2.11 Spm (Side View)

12

Figure 2.12 Under Voltage-Low Side

13

Figure 2.13 Under Voltage Protection-High Side

13

Figure 2.14. Speed Torque Characteristics Of

Induction Motor 14

Figure 2.15. Speed Torque Characteristics With V/F

Control 15

Figure 3.1 Block Diagram Of Open Loop

18

Figure 3.2 Output Speed Wave Form

19

Figure 3.3 Output Gate Pulses

20

Figure 3.4 Output Line Voltage Waveform

21

Figure.3.5 Block Diagram Of Closed Loop Control

22

Figure 3.6 Output Speed Waveform

23

Figure 3.7 Output Line Voltage Waveform

23

Figure 3.8 Block Diagram Of Hardware

Implementation 24

Figure 3.9 Diagram Of Rectifier Unit

25

Figure 3.10 Circuit Diagram Of PWM-Voltage Source

Inverter Circuit 26

Figure 3.11 Hardware Circuit Diagram

28

Figure 3.12 Layout Diagram Of Component Of Hard

Ware 29

Figure 3.13 Circuit Diagram Of Driver Circuit

30

Figure 3.14: Circuit Diagram Of Smart Power Module

32

Figure 3.15 Pin Configuration Of Microcontroller

34

Figure 3.16 Connection Of Microcontroller Circuit

35

Figure 3.17 Microcontroller DSPIC30F4011

37

Figure 3.18 Diagram Of Functional Circuit Of Flip

Flop 38

Figure 4.1: Frequency Vs. Modulation Index Graph

41

Figure 4.2: Actual Speed Vs Modulation Index Graph

42

Figure 4.3: Actual Speed Vs Frequency Graph

42

Figure 4.4: Open Loop Input Voltage And Time

43

Figure 4.5: Open Loop Input DC Voltage And Current

43

Figure 4.6: Actual Rotor Speed And Time

44

Figure 4.7: Set Speed And Actual Speed Graph

45

Figure 4.8: Voltage Vs Frequency Graph

46

Figure 4.9: Input Voltage Vs. Time

47

Figure 4.10: Set Speed/Voltage Speed Vs. Time Period

47

Figure 4.11 Operational Block Diagram To Drive The

Motor 48

Figure 4.12 Operational Block Diagram Of The

Hardware 49

Figure 4.13 CRO Output Of PWM Pulse.

51

Figure 4.14 CRO Output Of The Dc Voltage Applied To

The Motor 51

Figure 4.15 CRO Output Of The Motor Current

Waveform 52

Figure 4.16 Hardware Model

52

Figure 4.17 Connected Model Of Hardware

53

TABULAR INDEX

SL NO. DESCRIPTION

PAGE NO.

TABLE 2.1 Comparison between proposed and

existing method 16

TABLE 4.1 Tabulation for open loop control

40

TABLE 4.2 Tabulation for closed loop

control 44

TABLE 4.3 Finding the V/F ratio

45

ABSTRACT:

An induction motor can run only at its rated speed when it

is connected directly to the main supply. This is felt the

most in applications where input power is directly

proportional to the cube of motor speed. So we can reduce

the speed of the motor upto 20% and save the power upto

50%. As the semiconductor fabrication technology has

advanced than previous both the size and price have gone

than before. Due to this the usage of motor has already

been reduced where as it can be replaced by VFD(variable

frequency drive). 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.

Generally we use open loop control for controlling the

speed of a motor but for VF controlling we use the

closed loop control. It is also simple to implement and

cost effective. The on-chip hardware PWM modules, making

them on-chip hardware PWM modules, making them suitable

for 3-phase motor control applications.

VF CONTROL:

The base speed of the induction motor is directly

proportional to the supply frequency and the number of

poles of the motor. Since the number of poles is fixed by

design, the best way to vary the speed of the induction

motor is by varying the supply frequency. The torque is

directly proportional to the ratio of the applied voltage

and the frequency. This is exactly what VF control tries

to achieve.

ACKNOWLEDGEMENT

The satisfaction and elation that accompany the

successful completion of any task would be incomplete

without the mention of the people who have made it a

possibility. It is my great privilege to express my

gratitude and respect to all those who have guided me and

inspired me during the course of the project work.

First and foremost, I would express my sincere

gratitude to our beloved Chancellor Col. Dr. JEPPIAAR,

M.A., B.L., Ph.D., and also thanks to our Directors Dr.

MARIE JOHNSON, B.E., M.B.A., M.Phil., Ph.D and

Dr. MARIAZEENA JOHNSON, B.E., M.B.A., M.Phil., Ph.D for

providing me the necessary facilities for the completion of

my project. Also, I acknowledge our Vice Chancellor Dr.

B.SHEELA RANI, M.S (By Research)., Ph.D. for her constant

support and endorsement.

I also like to express my gratitude to Mrs. G. R. P.

LAKSHMI Head of the Department (Administrative and

Research) of Electrical and Electronics Engineering and Dr.

V. SIVACHIDAMBARANATHAN Head of the Department (Academics)

of Electrical and Electronics Engineering, Sathyabama

University for having been a constant source of support and

encouragement for the completion of the project.

I would also like to express my sincere thanks to my

internal guide of the project Mr.S.JAYAPRAKASH for his

constant guidance and supervision during the period of my

project work and for providing me the necessary facilities

for the completion of my project.

DECLARATION

I SIDHARTHA SHANKAR RAY hereby declare that the project titled

“MICROCONTROLLER BASED SPEED CONTROL OF INDUCTION MOTOR USING V/F

CONTROL”was done by me under the guidance of Mr.S.JAYAPRAKASH is

submitted in partial fulfillment of the requirements for the award of

the degree in BACHELOR OF ENGINEERING.

DATE:

PLACE:

SIGNATURE OF THE CANDIDATE

CHAPTER-1

1.1 INTRODUCTION

1.1.1 GENERAL

Industrial drive applications are generally classified into

constant speed and variable speed drives.Traditionally AC

machines have been used in constant speed ap- plications,whereas

DC machines were preferred for variable speed drives. DC machines

have the disadvantages of higher cost and maintenance problems

with commutators and brushes. Commutators and brushes do not

permit a machine to operate in dirty and explosive environment.

An AC machine overcomes the drawback of DC machines. Although

currently, the majority of variable speed drive applications use

DC machines, they are progressively being replaced by AC drives.

While there are different methods of speed control of induction

motor,Variable Voltage Variable Frequency (VVVF) or V/F is the

most common method of speed control. This method is most suitable

for applications without position control requirements or the

need for high accuracy of speed control. Examples of these

applications include heating, air conditioning, fans and blowers.

1.1.2 OVERVIEW OF THE THESIS

First, implementation of open loop and closed loop V/F control of

induction motor has been done using MATLAB Simulink toolbox and

corresponding waveforms are analyzed.

Finally, hardware implementation for open loop V/F control of

three phase induction motor is carried out and waveforms are

analyzed. A comparison is made between software implementation

and hardware implementation.

1.1.3 OBJECTIVE OF THE THESIS

To control the speed of three phase induction motor using V/F

control stregery.

1

1.1.4 ORGANISATION OF THE THESIS

This thesis is organized into five chapters including

introduction, brief description of the thesis and also it deals

with the objective and Organisation of the thesis. Chapter 2

deals with the discussion in detail about basics theory of V/F

control stregery of induction motor. Chapter 3 deals with

simulation and results of V/F control of induction motor.

2

CHAPTER-2

AIM AND SCOPE OF THE PRESENT INVESTIGATION:

2.1 OBJECTIVE:

To control the speed of an induction motor by varying

frequency as well as voltage.

To develop SPWM with V/F Control techniques in dspic

microcontroller (pwm controller).

To develop SPM Based Voltage source inverter Power circuit

(driver).

To develop Bi directional Speed control algorithm , PI

Closed Loop control & braking operation in

microcontroller.

2.2 BASIS OF IM CONTROL :

Synchronous Speed (Ns) = 120 x F/P

F = rated frequency of the motor

P = number of poles in the motor

The base speed of the induction motor is directly proportional to

the supply frequency and the number of poles of the motor. Since

the number of poles is fixed by design, the best way to vary the

speed of the induction motor is by varying the supply frequency.

By varying the supply frequency alone is not suitable for speed

variation efficiently –why-

Stator Voltage (V) ∝ [Stator Flux(φ)] x [Angular Velocity (ω)]

V ∝ φ x 2πf

φ ∝ V/f

3

The torque developed by the motor is directly proportional to the

magnetic fields produced by the stator. So, the voltage applied

to the stator is directly proportional to the product of stator

flux and angular velocity. This makes the flux produced by the

stator proportional to the ratio of applied voltage and frequency

of supply. By varying the frequency, the speed of the motor can

be varied. Therefore, by varying the voltage and frequency by the

same ratio, flux and hence, the torque can be kept constant

throughout the speed range.

Fig

2.1: Graph showing V/F Control

4

2.3 VARIABLE FREQUENCY DRIVES (VFD) BASICS:

2.3.1 Components of VFD’s are :-

1. SPWM Controller

2. Analogue

3. Digital

4. Digital –Re configurable

5. POWER Circuit

6. AC-DC Rectifier

7. DC-AC Inverter

8. Motor

FIG 2.2: VARIABLE FREQUENCY DRIVE

5

2.4 PI CONTROL :

Basic proportional and integral feedback control (PI)

How to tune the PI-controller

2.4.1 THE PROCESS TO CONTROL :

The model used in b) P-control will be used again. The only thing

to be changed, is the content of the controller block i.e. the

block "Controller - PI-controller" see figure 1 below.

Fig 2.3: House model with PI-controller

6

2.4.2 PI CONTROL- DEFINITION:

The definition af proportional feed back control is still

where 

e ="error"

KP = Proportional gain

The definition of the integral feed back is

where KI is the integration gain factor.

In the PI controller we have a combination of P and I control,

ie.:

where

τI ="Integrationtime"[s]

τN = "Reset time" [s]

 NB: There is - in the real life - some confusion in the use of

these two definitions.

7

FIG 2.4: BLOCK DIAGRAM OF PI CONTROLLER

FIG 2.5: GRAPH OF PI CONTROLLER

8

2.4.3 SIMULINK MODEL OF THE PI-ALGORITHM:

Figure 2.6: PI-controller

If the error is negative (t > tset) then u would be negative and

the radiator heat negative! Which is not possible, therefore we

have included a "Saturation" block in the actuator block, see

figure 3. The settings of this block is Max = Q_R and Min = 0.

Figure 2.7: Saturation block to constrain the heat output

9

2.4.4 OUTPUT:

Running the model - with almost arbitrary PI-parameters - gives

this output:

Figure 2.8: Output

This is the the steady-state "off-set" is almost zero!  Which is

the main benefit of the ingetration part of the PI-controller.

10

2.5 SPM, BASED IGBT POWER MODULE:

Specification

FSBB20ch60b

3phase,200v

1.8amp

3 phase source case induction motor

2.6 FSBB20CH60 - Smart Power Module:

2.6.1 General Description:

It is an advanced smart power module (SPMTM) that Fairchildhas

newly developed and designed to provide very compactand high

performance ac motor drives mainly targeting lowpowerinverter-

driven application like air conditioner and washing machine. It

combines optimized circuit protection and drivematched to low-

loss IGBTs. System reliability is furtherenhanced by the

integrated under-voltage lock-out and shortcircuitprotection. The

high speed built-in HVIC provides optocoupler-less single-supply

IGBT gate driving capability that furtherreduce the overall size

of the inverter system design. Eachphase current of inverter can

be monitored separately due tothe divided negative dc terminals.

Fig 2.9 GENERAL VIEW OF SPM MODULE

11

FIG 2.10 SPM (TOP VIEW)

FIG 2.11 SPM (SIDE VIEW)

12

2.7 TIME CHARTS OF SPM PROTECTIVE FUNCTIONS:

FIG.2.12 UNDER VOLTAGE-LOW SIDE

FIG.2

.13 UNDER VOLTAGE PROTECTION-HIGH SIDE

13

2.8 SPEED TORQUE CHARACTERISTICS OF INDUCTION:

Fig 2.14. Speed Torque Characteristics of Induction Motor

The x-axis shows slip speed, the y-axis shows torque and current,

the characteristics shown in Fig 2.1 are drawn with rated voltage

and frequency suppliedto the stator. During startup the motor

typically draws up to seven times the ratedcurrent. This high

current is result losses in the stator and rotor windings, and

lossesin the bearings due to the friction.At startup the motor

delivers 1.5 times the rated torque of the motor. This starting

torque is also called locked rotor torque .As the speed

increases, the currentdrawn by the motor reduces slightly. At the

base speed the motor draws the rated current and delivers the

rated torque .At base speed if the load on the motor shaft is

increased beyond its ratedtorque, the speed starts dropping and

slip increases.

The disadvantages like motor draws high current during start up,

torqueis highly non linear as speed varies. These drawbacks can

be overcome by using V/F control.

14

2.9 V/F CONTROL THEORY:

Fig.2.15. Speed Torque Characteristics With V/F Control

The base speed of the induction motor is directly proportional to

the supply frequency and the number of poles of the motor. Since

the number of poles is fixed by design, the best way to vary the

speed of the induction motor is by varying the supply frequency.

The torque developed by the induction motors is directly

proportional to the ratio of the applied voltage and the

frequency of supply. By varying the voltage and the frequency,

but keeping their ratio constant, throughout the speed range.

This exactly what v/f control tries to achieve.

2.10 SCALAR CONTROL OF INDUCTION MOTOR:

The following are the scalar control techniques of an induction

motor are given.

(1) Voltage/frequency (V/F) control

(2) Stator current and slip frequency control

Scalar control, as the name indicates, is due to magnitude

variation of control variables only and disregards the coupling

effect in the machine. For example, the voltage of a machine can

be controlled to control the flux, and frequency or slip can be

controlled to control the torque. However, flux and torque are

also the function of frequency and voltage, respectively.

15

TABLE 2.1 COMPARISON BETWEEN PROPOSED AND EXISTING METHOD

16

CHAPTER-3

EXPERIMENTAL METHODS AND ALGORITHM USED

3.1 GENERAL:

The V/F is simulated on MATLAB/Simulink

software. The actual system can be simulated with a high degree

of accuracy in this package. It provides a user interactive

platform and wide variety of numerical algorithm. This Chapter

discusses the realization of V/F control using Simulink block.

Matlab (Matrix laboratory) is an interactive software system for

numerical computations and graphics. As the name suggests, Matlab

is especially designed for matrix computations: solving systems

of linear equations, computing eigenvalues and eigenvectors,

factoring matrices, and so forth. Matlab is designed to solve

problems numerically, that is, in finite-precision arithmetic.

3.2 OPEN AND CLOSED LOOP CONTROL:

The experiment is conducted into two main steps.

They are-

1. Open loop control and

2. Closed loop control.

3.2.1 Open loop control:

The open loop control consists of –

a) MOSFET inverter,

b) IGBT module,

c) LCD screen,

d) 3 phase AC motor.

The operation of an ac induction motor is governed by two

principles:

1. Base speed is directly proportional to the frequency of the

alternating current applied to the stator and the number of

poles of the motor.

2. Torque is directly proportional to the ratio of applied

voltage and frequency of the applied

ac current.

The Figure shows the simulation diagram of open loop V/F control

of

three-phase induction motor. It consists DC source, three -phase

PWM inverter and

three phase induction motor. Dc source is connected to the dc

side of the converter.

In this reference speed is set. From that reference speed

frequency is determined

using the formula . V/F function block determines the amplitude

corresponding to that frequency. This frequency and amplitude are

used to update the PWM duty cycle. MOSFET based converter gives

the supply of the induction motor. Connecting the scope through

bus selector shows speed of the induction motor.

3.2.1.1 Block diagram of open loop control:

Fig.3.1: Block diagram of open loop

control

3.2.1.2 Execution of open loop control:

The open loop control is executed into the following steps –

I. The 220V is applied to a MOSFET inverter where the DC

voltage is converted into 3 phase AC voltage.

II. 3 phase AC voltage is applied to the motor through current

sensors.

III. The current input applied to the motor is measured through

the current sensors.

IV. The carrier signal is applied to the IGBT module.

V. The desired modulation index and frequency input is given to

the microcontroller and further applied to PWM module.

VI. Finally the six PWM wave is generated and drive the motor.

3.2.1.3 Simulation results of open loop v/f control:

The Figure shows the simulated speed waveform of open loop V/F

control of three-phase induction motor. Reference speed is set at

1460 RPM. Speed

reaches the steady state at 0.3 second.

Fig.3.2: Output Speed waveform

The Figure shows the gate pulses for PWM inverter consists of

three

legs, one for each phase. The gating signals for the three phase

inverters have a phase difference of 120°. The first pulse is

given to the positive switch of phase A, the pulse is given to

the positive switch of phase B the third to the positive switch

of

phase C.

Fig. 3.3: Output Gate Pulses

Fig. 3.4: Output line

voltage waveform

The Figure shows the simulated line-to-line voltage waveform of

open loop V/F control of three-phase induction motor. It is

observed that the voltage waveform is almost sinusoidal.

3.2.2 Closed loop control:

The closed loop control consists of –

a) MOSFET inverter,

b) IGBT module,

c) PI controller and

d) 3 Phase AC motor.

It consists DC source, three -phase PWM inverter and three phase

induction motor as open loop in addition to that it has PI

controller,limiter. Connecting the scope through bus

selector .Now the simulation circuit is run with closed loop

control shows speed of the induction motor.

3.2.2.1 Block diagram of closed loop control:

Fig.3.5:Block diagram of closed loop

control

3.2.2.2 Execution of closed loop control:

I. The execution of closed loop control is executed very

similar to the open loop control.

II. In extra the PI controller is added here for controlling the

error wave.

3.2.2.3 Simulation results of closed loop v/f control:

The Figure shows the simulated speed waveform of

closed loop V/F

control of three-phase induction motor. Reference speed is set at

1460 RPM. It

reaches the steady state at 0.1 second.

Fig.3.6: Output Speed

waveform

The Figure shows the simulated line-to-line voltage waveform of

closed loop V/F control of three-phase induction motor. It is

observed that the voltage waveform is almost sinusoidal.

Fig. 3.7: Output line

voltage waveform

3.3. HARDWARE IMPLEMENTATION:

The V/F control of three-phase induction motor is

implemented in hardware and the gating pulses for the inverter

fed motor are generated through the DSPIC Microcontroller. The

main controlling unit of the project is the microcontroller.

3.3.1. Block diagram of hardware implementation:

Fig.3.8: Block diagram of hardware implementation

Figure shows the block diagram of hardware implementation. It

consists of voltage source from the rectifier supply, three-phase

inverter and with AC motor load. The rectifier rectifies AC

voltage to DC voltage. In this bridge rectifier is used. This

rectified output DC voltage fed to the three-phase inverter main

circuit. The inverter main circuit consists of six switches.

Gating signals are generated from the PWM. This signals fed to

the MOSFET Gate terminals. Depends upon the Gating signal

inverter operates, this output fed to the AC load or motor.

3.3.1.1 Rectifier Unit:

The single-phase ac supply is given to Diode Bridge. The

output of rectifier is dc. The filter capacitor (1000 μF) is

connected across the rectifier output.

Fig.3.9: Rectifier

Unit

3.3.1.2 PWM-Voltage Source Inverter:

The Fig 5.3 shows PWM-voltage source inverter circuit

diagram.Inverters are employed to get a variable frequency as

supply from a dc supply. For the control of ac motor, voltage

should also be controlled along with frequency.Variation in

output voltage can be achieved by varying the input dc voltage.

Output voltage and current have stepped waveform. Consequently

they have substantial amount of harmonics. Variable frequency and

variable voltage ac is directly obtained from fixed voltage dc

when the inverter is controlled by pulse width modulation the pwm

control also reduces harmonics in the output voltage and also it

eliminates the following draw back of 6-step inverter drives like

the motor losses increases at all speeds causing derating of

motor, torque pulsation at low speeds.

Fig.3.10: Circuit Diagram of PWM-Voltage Source Inverter Circuit Diagram

In this method, several pulses per half cycle are used as in case

of multiple pulse width modulation. Instead of maintaining the

width of all pulses the same as in the case of multiple pulse

modulation, the width of each pulses is varied proportional to

the amplitude of a sine wave evaluated at the center of the same

pulses. By comparing a sinusoidal reference signal with a

triangular carrier wave frequency, fc, the gating signal are

generated.

The PWM control has the following advantages,

(1) The output voltage control can be obtained without any

additional components

(2) With this type of control, lower order harmonics can be

eliminated of minimized along with its output voltage control.

The filtering requirements are minimized

as higher order harmonics can be filtered easily.

3.3.1.3 Driver circuit:

The driver circuit is the circuit which controls

the PWM waves and thereby controls the speed of the motor. The

driver circuits of AND gates, optoisolators, camparators, not

gates, Smart Power Module (SPM), current sensors etc.

3.3.1.4 Voltage regulation circuit or power circuit:

This circuit takes the input

power and gives the required power after regulating this. This

circuit regulates the voltage and gives the output of 5V which is

the operating voltage for the microcontroller.

The another 18V input is regulated

by an another voltage regulation circuit which consists of a

IC7815. It gives the output of 15V which is the operating voltage

of the driver circuit.

3.3.1.5 Microcontroller:

Microcontroller DCPIC30F4011 is used here.

This microcontroller operates at 5V and 10KHZ. An oscillator is

attached with the micro controller to generate 10KHZ. The

microcontroller generates the 6 PWM pulses which directly goes to

the driver circuit.

Below all the driver circuit, Smart Power

Module (SPM) and microcontroller is discussed elaborately with

their full circuit diagram.

3.3.2 Hardware circuit diagram:

Fig.3.11: Hardware Circuit

diagram

This is the full circuit diagram the entire

circuit. Here all the units such as microcontroller, SPM, Driver

circuit, protection circuit connection is shown as the actual

hardware model.

3.3.2.1 Layout diagram of the components of hardware:

Fig. 3.12: Layout diagram of the components of

hardware

3.3.2.2 Driver circuit:

Fig.3.13: Circuit diagram of driver circuit

3.3.2.3 Working of Driver circuit:

3.3.2.3.1 AND gate:

Each PWM pulse is passed through an U1 4081 AND gate. The PWM

signal and the signal C1 (current from the capacitor which is

connected through 5V) is applied to the AND gate and the output

of the AND gate is fed to the optoisolator.

3.3.2.3.2 OPTOISOLATOR:

This isolator isolates the high voltage and low voltage

sides of the driver circuit. It also filters the signals. 6 PWM

pulses are obtained from the 6 isolators as shown in the above

diagram.

3.3.2.3.3 NOT gate:

The output signals of the optocoupler is given to the

NOT gate to invert the signal. Actually when the signal is passed

through the optocoupler it gets inverted. So, again it has to be

inverted which is done by the NOT gate.

3.3.2.3.4 PWMIS signal:

Here an extra PWM i.e. PWMIS is also used to

stimulate all the pulses so that we get a constant flow of PWM

pulses. PWMIS signal stimulates all the PWM waves to keep a

constant value of them.

3.3.2.3.5 Phase output:

Thus from 6 PWM waves we get 3 couples of signal.

They are as RTOP, RBOT, YTOP, YBOT, BTOP and BBOT.

Now these 6 signals goes to the Smart Power Module (SPM)

FSBB20CH60 module.

3.3 Smart Power Module circuit:

Fig.3.14: Circuit diagram of smart power module

3.3.1 Working of smart power module:

3.3.1.1 FSBB20CH60 module:

It is a 27 pin module. All the signals like RTOP,

RBOT, YTOP, YBOT, BTOP, BBOT is given to the module. Finally the

3 phase signal ( R, Y, B) is obtained as output from the module.

This 3 phase signal is then directly fed to the 3 phase induction

motor.

I. All the signals (RTOP, RBOT etc.) are fed to the FSBB20CH60

module.

II. There is a current resistance (IRES) signal which is also

fed to the FSBB20CH60 module.

III. Finally the output (three phase signals- R, Y, B) are

obtained through three INOUT devices.

IV. There are a few diodes and capacitors are connected with the

SPM module for filtering the signal.

V. A protection circuit is also included to process the higher

values without affecting the circuit.

3.3.1.2 Protection circuit:

The protection circuit consists of a comparators which

are used to detects that high voltage is coming. So, the

comparator does not allow the high voltage value through the

circuit.

Each comparator is fed from a 15V source.

When any fluctuation or disturbance is appeared, the

protection circuit responds and protect the main SPM as well

as the driver circuit.

3.4 Microcontroller circuit:

Fig.3.15: Pin configuration of

microcontroller circuit

Fig.3.16: Connection of microcontroller circuit

3.4.1 Microcontroller pin configuration:

PIN 1 -Reset

PIN 2-4 -Analog to digital converter

PIN 11 -Voltage Source

PIN 8-10 -K4,K3,K2 Signal

PIN 12,20 -Gnd

PIN 13,14 - Crystal Oscillator

PIN 17 - K1 signal

PIN 22-30 -LCD

PIN 33-38 -PWM signals.

Here, the pin configuration of the DSPIC

microcontroller has been given. There all the

functions of the pins are internally configured.

There is a crystal oscillator connected with the

microcontroller.

The signal K1 is given to the pin 17.

The signal K2,K3 and K4 is given to the pin 8 to

10.

Fig.3.17: Microcontroller

DSPIC30F4011

3.5 Functional circuit of flip-flop:

Fig.3.18: Diagram of functional circuit of flip flop

The functional circuit is shown in the above diagram. For

protecting the entire hardware a protection circuit is

developed which flip flops and optoisolator and a few

diodes and resistors.

If any sudden high voltage is raised due to any

disturbances in supply voltages then the protection circuit

operates and it doesn’t allow the high voltage to the

circuit. Thus it prevents the circuit.

At normal condition the regular pulse or low current comes

at the pin 7 of the first flip flop.

Then the output Q bar is high and the output signal Q is

given as signal F1.

This output Q bar goes to the optoisolator.

At the optoisolator the high pulse signal is converted to

the low pulse signal SHUTDOWN1.

Then the low pulse signal SHUTDOWN1 is applied to the pin 7

of the second flip-flop.

So, the output Q bar of the second flip-flop is high which

is represented as signal C1 and it is applied to the AND

gate and the other output is given as F2.

When any disturbance or high voltage is appeared as COM1 at

the pin 7 of the first flip- flop.

So, the output Q bar is low which goes to the optoisolator.

After passing though the optoisolator it becomes high pulse

signal. This is referred as SHUTDOWN1.

Now this signal SHUTDOWN1 is applied to the pin7 of the

second flip-flop.

Now the output Q bar is low pulse signal. This gives the

input of the AND gate C1.

As the output Q bar is low C1 applied to AND gate is zero.

So, as per the operation of the AND gate the output is also

zero. So, the driver circuit as well as the motor remains

inactive and the entire hardware is very much safe.

CHAPTER- 4

RESULTS AND DISCUSSION, PERFORMANCE

ANALYSIS

4.1 GENERAL:

To analyze the speeds of the motor and to

control the speeds a few readings are taken both in open loop and

closed loop control. Simulation has become a very powerful tool

on the industry application as well as in academics, nowadays. It

is now essential for an electrical engineer to understand the

concept of simulation and learn its use in various applications.

Simulation is one of the best ways to study the system or circuit

behavior without damaging it .The tools for doing the simulation

in various fields are available in the market for engineering

professionals. Many industries are spending a considerable amount

of time and money in doing simulation before manufacturing their

product. In most of the research and development (R&D) work, the

simulation plays a very important role. Without simulation it is

quiet impossible to proceed further deails.

4.2 OPEN LOOP CONTROL RESULTS:

4.2.1 Tabulation for open loop control:

DC Volt = 200V (constant)

Serial

Number

Modulation

Index

(M.I)

Set

frequency

(HZ)

Actual

Speed

(RPM) 1

0.95

50

1462 2

0.77

40

1186 3

0.57

30

883 4

0.38

20

590 5

0.70

10

305Table 4.1: Tabulation for Open loop control

So, in open loop arrangement the modulation index

is increased gradually from 0 to 1 and the frequency is decreased

from 50 to 10 HZ. So, according to that the speed is varied.

4.2.2 Graphs for the results of open loop control:

Fig 4.1: Frequency vs. Modulation Index graph

The frequency is varied from 0 to 50 HZ and the

modulation index is varied from 0 to 1.

So, here both the frequency and modulation Index is

increased and the graph comes linearly.

Fig 4.2: Actual speed vs Modulation Index graph

When the modulation index is plotted with the

actual speed primarily the graph becomes in a

curve.

At higher values the graph remains almost

linear.

The modulation index is varied from 0 to 1

and the speed is varied upto 1450 rpm

( asynchronous speed).

Fig 4.3: Actual speed vs frequency graph

4.2.3 Simulation results for open loop control:

Fig 4.4:Open loop input voltage and time

Fig 4.5:Open loop input DC voltage and current

Fig 4.6: Actual rotor speed and time

4.3 RESULTS OF CLOSED LOOP CONTROL:

4.3.1:Tabulation for closed loop control:

Kp =0.1, Ki=0.02, DC Volt

= 200V (constant)

Serial

Number

Set Speed

(RPM)

Actual Speed

(RPM) 1 350 350

2 550 550 3 950 950 4 1250 1250 5 1450 1450

Table 4.2: Closed loop control

4.3.2 Graphs for the results of closed loop control:

Fig 4.7: Set speed and Actual speed graph

Here the Kp and Ki value is kept constant. The Kp and Ki values

are 0.1 and 0.02 respectively. The dc voltage is also kept as

constant at 200V.

Here the values of actual speed

are accurately same as the set speed due the operation of closed

loop.

4.3.3 Tabulation for finding the V/F ratio:

Serial

Number

Voltage

(Volt)

Frequency

(HZ) V/F

ratio 1 13.6 10

1.36 2 29 20

1.45 3 42 30

1.40 4 54 40

1.08 5 63 50

1.26

Table 4.3: Finding the V/F ratio

Fig 4.8: Voltage vs Frequency graph

Here the values of the voltages are increased gradually.

Also the frequency values are increased from 0 to 50.Finally the

V/F ratio is determined.

So, the mean value of V/F ratio is –

(1.36+1.45+1.40+1.08+1.26)/5 = 1.31

4.3.4 Simulation results of closed loop control:

Fig 4.9:Input voltage vs. time

Fig 4.10: Set speed/voltage speed vs. time period

4.4 PERFORMANCE ANALYSIS:

4.4.1 To drive the motor:

Fig 4.11 Operational block diagram to drive

the motor

I. To analyze the full operation of the hardware the driving of

the motor must to be understood well first.

II. The above block diagram explains the operation of driving

the motor.

III. The input supply is applied to the autotransformer. The

autotransformer is the device which takes the input supply

and give as the output voltage as the wish of the operator.

So we can vary the output voltage of the autotransformer as

our wish. That is the reason it is called variac otherwise.

IV. Now, we can gradually increase the output voltage of the

autotransformer which is applied to IGBT power module and

thereby goes to the motor.

V. We can keep the output voltage at any values like 100V, 150V

etc. But here we are keeping the output voltage in such a

value that it produces 200V after converted to dc.

VI. The isolation transformer connected with the autotransformer

is used to isolate

VII. The high disturbance from the current.

VIII. The single phase bridge rectifier is connected with the

isolation transformer.

IX. So, the output of the isolation transformer is converted to

DC voltage by the single phase bridge rectifier.

X. Now, the converted voltage is constant 200V. This is applied

to the smart power module which is also consists of the IGBT

devices.

XI. Now, finally the output current from the SPM is applied to

the motor to run the motor and also to control the speed of

the motor.

XII. The current is applied to the motor through the current

sensors for getting the current readings of the current

waves.

XIII. Fig- shows the current waveform which is given to the

motor.

4.4.2 Operation of the entire hardware:

Fig 4.12 Operational block diagram of the hardware

I. The operating voltage of the microcontroller is 5V, which is

supplied from the input voltage source. That voltage is

regulated by a voltage regulation circuit.

II. Here we are using 3 switches for the entire operation.

a) Increment switch,

b) Decrement switch and

c) Reset switch.

III. The increment and decrement switch is for increasing and

decreasing the values of the frequency, modulation index, set

speeds etc.

IV. Now, the microcontroller DSPIC30F4011 is operated at 5V and it

generates 6 PWM pulses.

V. This PWM pulses directly goes to the 3 phase inverter module

(smart power module- SPM) and thereby applied to the motor.

VI. Now, if the modulation index is varied the ON time and OFF

time of the PWM pulses are also varied.

VII. But if the frequency is varied then also the speed of the

motor is varied.

VIII. So, by varying the modulation index and the frequency the PWM

pulses are varied and thereby the speed of the motor is

varied.

IX. A LCD display is given where the inputs and the outputs are

visualized.

X. From table no. 4.1 we can see that in open loop the frequency

can be varied by using the increment or decrement switches and

the DC voltage is kept constant at 200V. So, with that the

modulation index is also varied and as the result the actual

motor speed is varied.

XI. From table no. 4.2 we can see that in closed loop the set

frequency we are giving is the same what we are getting as

motor actual speed.

XII. From table no. 4.3 we can see that by changing both the

voltage and the frequency the speed of the motor is varied.

So, the V/F ratio drives the motor speed. The mean value of

the V/F ratios we taken over the operation is 1.31.

4.4.3 Oscilloscope results:

4.13 CRO output of PWM pulse.

4.14 CRO output of the dc voltage

applied to the motor

4.15 CRO output of the motor current waveform

The PWM wave is obtained by connecting the CRO probes

to optoisolator terminal and supply terminal.

The motor current waveform is obtained by connecting

the CRO probes to the current sensor pins.

4.4.4 Hardware:

Fig 4.16 Hardware model

Fig 4.17 Connected model of Hardware

These are the actual hardware model which we have prepared. The

induction motor whose speed we have to control is connected with

it and the speed control is done by this hardware.

4.5 ADVANTAGES:

Easy programming,

Soft hardware control,

Rugged,

less power required,

Multiple duty cycle generator,

Multiple Conversion Sequencing Options,

Wide operating voltage range (2.5V to 5.5V),

Bidirectional operation.

4.6 APPLICATION:

From small appliances to the largest of mine mill drivers

and compressors

Centrifugal pump

Fixed speed and variable speed electric motor

Global market penetration

Home appliances applications like air conditioner and

washing machine.

Chapter – 5

SUMMARY AND CONCLUSIONS

5.1 SUMMARY:

This chapter describes the hardware implementation of the V/F

control of an induction motor using microcontroller.It includes

the development of hardware for microcontroller circuit, SPWM

pulses generation, optocoupler circuit was explained. For SPWM

pulses, the sine wave is generated from PIC microcontroller

(DSPIC30F4011) and ramp wave is generated through ramp generator

The output of the controller is given to the optocoupler circuit

which is used for protection and isolation purpose, in case of

commutation failure and short circuit due to the improper

trigger. From the optocoupler circuit the pulses are given to the

appropriate switches of the MOSFETs inverter fed induction motor.

The use of a Variable Speed Drive for a speed control

application usually offers an energy efficient and

environmentally friendly solution. The best opportunities for

energy savings, with subsequent economic savings, arise through

the laws which govern the operation of centrifugal fans and

pumps. Simple and straight forward VSD’s, such as the PWM

inverter drives, are available for applications where the speed

control accuracy is not critical. This compact inverter had its

hardware reduced to a minimum through the use of bridge inverter.

The variable speed drive with variable frequency control method

will offer new, low-cost solutions for light commercial and

consumer applications. The frequency range of the constructed

circuit is 10 Hz to 50 Hz at constant voltage for changing the

speed of induction motor between theoretical limits of 300 rpm to

1460 rpm if 50 Hz, single-phase AC

motors are used.

The speed of a 3-phase induction motor in open loop and closed

loop, supply voltage and frequency need to be varied with

constant ratio to each other. A low cost solution

of this control can be implemented in a DSPIC microcontroller.

This requires six PWMs to control a 3-phase inverter bridge. Many

DSPICmicro microcontrollers have two hardware PWMs.

5.2 CONCLUSION:

The speed of three-phase induction motor is being controlled by

varying supply voltage and frequency with constant (V/F) ratio.

It is simple, economic to easier to design and implement in open

loop. But the drawbacks of open loop is it doesn’t correct the

change in output also it doesn’t reach the steady state quickly.

These drawbacks can be overcome by modifying an open loop into a

closed loop system. In this project only open loop was

implemented in hardware.The project can be extended in future to

control the speed of induction motor in closed loop.