Speed Control of Three Phase Induction Motor Using PIC Microcontroller

SPEED CONTROL OF 3-  INDUCTION MOTOR USING PIC MICROCONTROLLER

Session 2007-2011

Project Supervisor PROF. DR. ASGHAR SAQIB

BY Kashif Shehzad (2007-Elect-90) Arslan Fida

(2007-Elect-143)

Ahsan Rashid (2007-Elect-206) Asif Shafiq Khan(2007-Elect-208)

DEPARTMENT OF ELECTRICAL ENGINEERING

UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE.

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SPEED CONTROL OF 3-  INDUCTION MOTOR USING PIC MICROCONTROLLER

This thesis is submitted to the Faculty of Department of Electrical Engineering, University of Engineering and Technology, Lahore in partial fulfillment of the requirements for

Bachelor‘s Degree In

Electrical Engineering

INTERNAL EXAMINER

EXTERNAL EXAMINER

Signature_______________

Signature_______________

DIRECTOR UNDERGRADUATE STUDIES

Signature_______________

































DECLARATION We declare that the work contained in this report is our own, except where explicitly stated otherwise. In addition, this work has not been submitted to obtain another degree or professional qualification.

_____________________

_____________________

Kashif Shahzad

Arslan Fida

_____________________

_____________________

Ahsan Rashid

Asif Shafiq Khan

































ACKNOWLEDGMENTS

First of all we are very thankful to my almighty ―ALLAH‖ WHO gave us the courage and

patience to complete this project. We would like to express our profound gratitude, most sincere appreciation and special thanks to our project supervisor, Prof. Dr. Asghar Saqib for his fabulous suggestions, invaluable advice and continuous encouragement through the completion of this project. We are extremely thankful to the entire staff of Department of Electrical Engineering, U.E.T. Lahore for their co-operation and help.

































Dedicated to our Parents



































































ABSTRACT The electrical machine that converts electrical energy into mechanical energy and vice versa is the workhorse in a drive system, and when the output speed of the motor can be controlled by changing its input frequency ,then the drive is said to be VARIABLE SPEED DRIVE or VARIABLE FREQUENCY DRIVE. Presently, it is just the combination of a motor and a controller. Drives can be classified as, 1) DC Drives 2) AC Drives AC Drives mainly consist of Induction motor drives and Synchronous motor drives. The control of dc motors requires providing a variable dc voltage which can be obtained from dc choppers or controlled rectifiers. These voltage controllers are simple and less expensive. DC motors are relatively expensive and require more maintenance due to brushes and commutators. However, dc drives are used in many industrial applications. As far as AC drives are concerned, their control requires complex control algorithms by microprocessors or by microcomputers commonly known as CONTROLLERS. The AC motors have number of advantages e.g. 1) They are 20% to 40% lighter than equivalent dc motors.

































e) Stator current control f) Voltage, Current and Frequency control In this project we are going to control the speed of induction motor by STATOR VOLTAGE AND FREQUENCY method using microcontrollers.

































LIST OF FIGURES PART-I

Figure 2.1 …………..Typical Squirrel Cage Rotor Figure 2.2…………...Speed-Torque Characteristics of Induction Motor Figure 2.3…………...Typical Name-Plate of Induction Motor

PART-II

Figure 1.1…………...Components of VFD

Figure 1.2…………...PWM and Sine Wave Figure 1.3…………...Speed-Torque Characteristics of Induction Motor with V/F Control Figure 1.4…………...Block Diagram of VFD System

Figure 2.1…………...Half Wave Rectifier Using 2 Diodes Figure 2.2…………...Full Wave Rectifier Using 4 Diodes Figure 2.3…………...3-Phase Full-Wave Bridge Rectifier Circuit Figure 2.4…………...3-Phase Full-Wave Bridge Rectifier Waveform

Figure 3.1…………...VDMOS Structure Showing Source, Drain and Gate Figure 3.2…………...MOSFET Figure 3.3…………...IGBT

































Figure 5.1…………...Pin Diagram of PIC16F877 Figure 5.2…………...Table of Pins Description of PIC16F8X Figure 5.3…………...Table of Pins Description of PIC16F8X

Figure 5.4…………...Key Features of PIC microcontroller Figure 5.5…………...Option Register Figure 5.6…………...Registers Associated with TMR0 Figure 5.7…………...Timer1 Control Register Figure 5.8…………...Registers Associated with Timer1 as a Timer/Counter Figure 5.9…………...Transmit Status and Control Register Figure 5.10………… Receive Status and Control Register Figure 5.11………….Register Associated with Baud Rate Generator

Figure 6.1…………...Principle of Delta PWM Figure 6.2…………...Principle of Sigma-Delta PWM Figure 6.3…………...Generation of PWM using Natural Sampling

PART-III

Figure 4.1…………...Valve Control Figure 4.2…………...VFD Soft-Start System Figure 4.3…………...Under-voltage Fault Indication Figure 4.4…………...Over-Current Fault Indication



































CONTENTS

ABSTRACT ACKNOWLEDGEMENT LIST OF FIGURES

PART-I INTRODUCTION

CHAPTER 1 Introduction…………………………………………………………………………..2 --6

1.1

Statement of Problem……………………………………………………...3

1.2

Aim and Ob jective ……………………………………………………… ………………………………………………………..3 ..3

1.3

Scope of the Project………………………………………………….........3

1.4

Methodology of Research……………………………… Research…………………………………………………4 …………………4

































PART-II (ESSENTIAL BACKGROUND)

CHAPTER 1 VFD (Components and Types)…………………………………………………….18--25 Types)…………………………………………………….18--25

1.1

Introduction…………………………………………………………........18

1.2

Types of VFD………………………… VFD……………………………………………………… …………………………………18 ……18

1.3

Components of VFD……………………………………………………..19 VFD……………………………………………………..19

1.4

Basic Working of VFD……………………….………………………….20 VFD……………………….………………………….20

1.5

V/F control theor y of VFD…………………………… VFD………………………………………………22 …………………22

1.6

Block Diagram………………………… Diagram……………………………………………………… …………………………….......25 .......25

CHAPTER 2 Power Source and Rectifiers………………………………………………………26--33 Rectifiers………………………………………………………26--33

2.1

Power Supply…………………………… Supply………………………………………………………… ……………………………….26 ….26

































CHAPTER 4 Inverter……………………………………………………………………………...43--51 Inverter……………………………………………………………………………... 43--51

4.1

History…………………………………………… History……………………………………………………………………43 ………………………43

4.2

Classification of Inverters……………… Inverters………………………………………… ………………………………..45 ……..45

4.3

Disadvantages of Square or Quasi Wave Inverter……………………….49

4.4

Applications……………………………………………………………...49

CHAPTER 5 PIC Microcontroller………………………………………………………………..52--67 Microcontroller………………………………………………………………..52--67

5.1

Why We Used PIC Microcontroller?……...……….…………...…........52

5.2

Basic Introduction to PIC16F877…...……….………………… PIC16F877…...……….…………………………..52 ………..52

5.3

Resources of PIC16F877 Used……………………………………… Used………………………………………56 56

5.4

Timer1 Module…..………………………… Module…..……………………………………………………… ……………………………59 59

5.5

Addressable USART…………….……………………………………….62

5.6

USART Baud R ate ate Generator……………………… Generator…………………………………………….65 …………………….65

































1.4

ORCAD (PSpice)………………………………………………………...82

1.5

MPLAB……………………………………………………………..........84

CHAPTER 2 Project Code………………………………………………………………….……..85--93 Code………………………………………………………………….……..85--93

2.1

Introduction ………………………… ……………………………………………………… …………………………………...85 ……...85

2.2

Built In Routines Of Micro C Compiler……..……………… Compiler……..…………………………..87 …………..87

2.3

The Source Code……………………………… Code………………………………………………………… …………………………89 89

CHAPTER 3 Project Simulation’s……………………………………………………………....94--104 Simulation’s……………………………………………………………....94--104

3.1

Introduction………………………………………………………………94

3.2

Generation of PWM P WM Signals (PROTEUS)……………………………….95

3.3

VFD Simulation (PROTEUS)…………………… (PROTEUS)…………………………………………...98 ……………………...98

3.4

Variation of Frequency Frequenc y (PROTEUS)………………………………….. (PROTEUS)…………………………………....99



































































CHAPTER 1 INTRODUCTION There are millions of motors in use in industry and offices around the world. They operate sewage and irrigation pumps, milking machines and ski lifts, paper machines and power-plant fans, sawmill conveyors and hospital ventilation systems, to name just a few examples. In fact, more than 65 percent of industrial electrical energy is consumed by motors. Hence, electric industry plays a vital role in the progress of a country because all the other industries are directly or indirectly based on the electrical energy and it becomes b ecomes

































1.1

STATEMENT OF PROBLEM Speed Control of Three Phase Induction Motor Using PIC Microcontroller

1.2

AIM AND OBJECTIVE The aim of the project is to design more intuitive modalities, and to evaluate those modalities. Project was really helpful in understanding the vast applications and use of power electronics at industrial level. We got the knowledge of PIC peripherals, inverter

































We have used sinusoidal PWM in our project so the output waveform closely replicates the Sine wave, hence loads that need pure sine wave for their operation can be connected to the VFD. Besides due to sinusoidal nature the losses are reduced considerably. 1.4

METHODOLOGY OF RESEARCH

The whole report is divided into three sections. The brief overview of the chapters is as follows:

PART 1 gives an introduction of the project and induction motor.

































PART 2 discusses the theory and basic working of different components used in the project.

CHAPTER 1 discusses the basic working of a VFD, V/F control theory and also lists all

components of a VFD system and is shown diagrammatically as well. CHAPTER 2 gives a detailed explanation about various types of power supplies, types

of rectifiers and their working.

































PART 3 constitutes of project softwares and simulations and other useful data

CHAPTER 1 gives basic information about different softwares used in the project. CHAPTER 2 presents the programming code used. CHAPTER 3 includes all the design work, different circuits and simulations carried out

during our project. CHAPTER 4 is about benefits of variable frequency drives, their applications and also



































CHATPER 2 INDUCTION MOTORS



































three-phase AC induction motor is the only type where the rotating magnetic field is created naturally in the stator because of the nature of the supply. DC motors depend either on mechanical or electronic commutation to create rotating magnetic fields. A



































2.3

SPEED OF INDUCTION MOTOR

The magnetic field created in the stator rotates at a synchronous speed (NS).



































Our project is based on the speed control of 3 phase motor so we will discuss only 3 phase motor. Three-phase AC induction motors are widely used in industrial and commercial



































2.4.2

Wound Motor

The slip-ring motor or wound-rotor motor is a variation of the squirrel cage induction motor. While the stator is the same as that of the squirrel cage motor, it has a set of



























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































Line Interactive Inverter

The true LINE INTERACTIVE design is in fact a combination of OFFLINE & ONLINE, in which the inverter plays a dual role of charging the battery when mains supply is present as well as regulating the output voltage and working as a normal inverter in absence of mains supply, so to the user it appears like an ONLINE System.

Online Inverter

An ONLINE UPS is the one in which the inverter always supplies power to the protected load and hence the same quality of power is ensured all the time. When mains supply is present, the inverter derives its power from thee mains supplied rectifier and the backup batteries are also kept in charged state. When the mains fail, the source of DC power for the inverter section shifts to the battery without any breaks whatsoever in the output to the Inverter. It also bears all the vagaries and noise borne out of the mains supply and insulates the secure bus supply from it. An ONLINE UPS is especially useful for sensitive and critical equipments/devices.

































4.2.3

Classification on the Basis of Output Square Wave Inverter

The output of this kind of inverter is square wave which is most easily generated. Half bridge can be used to produce this output with minimal control circuitry. They are the cheapest of inverters. Modified Sine Wave Inverter

This kind of inverter is better than the square wave but worse as compared to pure sine wave inverter because it contains harmonics. Pure Sine Wave Inverters

The output of this kind of inverter is pure sine wave and its free of harmonics

































4.3

DISADVANTAGES OF SQAURE OR QUASI WAVE INVERTER 

Voltage spikes



Over Voltages



Harmonic Distortion

Harmonic distortion is multiples of frequency superimposed on the power waveform, causing excess heating in the wiring and fuses. It is the reason for distortion and causes electro- magnetic interference.

4.4

APPLICATIONS

4.4.1

DC Power Source Utilization

Inverter designed to provide 115 VAC from the 12 VDC source provided in an

































An inverter converts the DC electricity from sources such as batteries, solar panels, or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage. Grid tie inverters can feed energy back into the distribution network because they produce alternating current with the same wave shape and frequency as supplied by the distribution system. They can also switch off automatically in the event of a blackout. 4.4.2

Induction heating

Inverters convert low frequency main AC power to a higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power. 4.4.3

HVDC Power Transmission

With HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a static inverter plant converts the power back to AC. 4.4.4

Variable Frequency Drives

A variable-frequency drive controls the operating speed of an AC motor by controlling the frequency and voltage of the power supplied to the motor. An inverter provides the controlled power. In most cases, the variable-frequency drive includes a rectifier so that DC power for the inverter can be provided from main AC power. Since an inverter is the key component, variable-frequency drives are sometimes called inverter drives or just inverters.

































4.4.5

Electric vehicle drives

Adjustable speed motor control inverters are currently used to power the traction motors in some electric and diesel-electric rail vehicles as well as some battery electric vehicles and hybrid electric highway vehicles such as the Toyota Prius. Various improvements in inverter technology are being developed specifically for electric vehicle applications. In vehicles with regenerative braking, the inverter also takes power from the motor (now acting as a generator) and stores it in the batteries. 4.4.5

Air conditioning

An air conditioner bearing the inverter tag uses a variable-frequency drive to control the speed of the motor and thus the compressor. 4.4.6

The general case

A transformer allows AC power to be converted to any desired voltage, but at the same frequency. Inverters, plus rectifiers for DC, can be designed to convert from any voltage, AC or DC, to any other voltage, also AC or DC, at any desired frequency. The output power can never exceed the input power, but efficiencies can be high, with a small proportion of the power dissipated as waste heat.



































CHAPTER 5

RESOURCES OF PIC16F877 UTILISED IN THE PROJECT This chapter is dedicated to the resources resources of PIC16F877 which we utilized in our project. Only those features are discussed that we employed in our circuitry. The features like timers, interrupts, USART are discussed below and it is explained how to configure these according to our requirement. A little bit of basic introduction of PIC 16F877 is also given.

5.1

WHY WE USED PIC MICROCONTROLLER?

We opted to PIC microcontroller as an obvious choice because of its simplicity and efficiency. The compiler programs like ―MICKRO C‖ contain built in routines for

programming different modules of PIC. That makes its programming very easy and simple. PICs are powerful microcontrollers. Common alternatives are the 8051 architecture or the Atmel AVR architecture. But in my views use of 8051 is getting obsolete and there is not much use of these in industrial applications. PICs are used heavily in the industry. They

































DIP, QFP and PLCC packages. It has very low power consumption and a very long operating voltage range : 2.0-5.0V. pin configuration and other features are given below in tabulated form, obtained from microchip data sheet.

































l

Figure 5.2

Legend: I = input O = output ou tput I/O = input/output P = power po wer

































































Figure 5.4 5.3

RESOURCES OF PIC16F877 USED:-

5.3.1

TIMER0 MODULE:-



































Timer mode is selected by clearing bit T0CS(OPTION_REG<5>). In Timer mode, the

Timer0 module will will increment every instruction cycle(without prescaler). If the TMR0 register is written, the increment is inhibited for the following two instruction cycles. The user can work around this by writing an adjusted value to the TMR0 register.

Counter mode is selected by setting bit T0CS(OPTION_REG<5>). In Counter mode,

Timer0 will increment either on every rising, or falling edge of pinRA4/T0CKI. The incrementing

edge

is

determined

by

the

Timer0

Source

Edge

Select

bit,

T0SE(OPTION_REG<4>). Clearing bit T0SE selects the rising edge. The prescaler is mutually exclusively shared between the Timer0 module and the Watchdog Timer. The prescaler is not readable or writable. We have used timer mode in our application.

5.3.2

Timer0 Interrupt:-

The TMR0 interrupt is generated when the TMR0 register overflows from FFh to 00h. This overflow sets bitT0IF (INTCON<2>). The interrupt can be masked by clearing bit

































5.3.4

Register associated with timer0:-

Figure 5.5

bit 7 RBPU bit 6 INTEDG bit 5 T0CS: TMR0 Clock Source Select bit 1 = Transition on T0CKI pin 0 = Internal instruction cycle clock (CLKOUT) bit 4 T0SE: TMR0 Source Edge Select bit 1 = Increment on high-to-low transition on T0CKI T0CK I pin 0 = Increment on low-to-high transition on T0CKI pin p in

































































The operating mode is determined by b y the clock clo ck select bit, b it, TMR1CS (T1CON<1>).

In Timer mode, Timer1 increments every instruction cycle. In Counter mode, it increments on every rising edge of the external clock input.

Timer1

can

be

enabled/disabled

by

setting/clearing

control

bit

TMR1ON

(T1CON<0>)

(Additional information on timer modules is available in the PICmicro™ Mid -Range

MCU Family Reference Manual (DS33023).) T1CON: TIMER1 CONTROL REGISTER (ADDRESS 10h):-

T1CON the register used to control the operation of timer1.it is shown below and each bit explained under:

































bit 2 T1SYNC: Timer1 External Clock Input Synchronization Control bit When TMR1CS = 1: 1 = Do not synchronize external clock input 0 = Synchronize external clock input When TMR1CS = 0: This bit is ignored. Timer1 uses the internal clock when TMR1CS = 0. bit 1 TMR1CS: Timer1 Clock Source Select bit 1 = External clock from pin RC0/T1OSO/T1CKI RC0 /T1OSO/T1CKI (on the rising edge) 0 = Internal clock (FOSC/4) bit 0 TMR1ON: Timer1 On bit 1 = Enables Timer1 0 = Stops Timer1



































5.5

ADDRESSABLE UNIVERSAL SYNCHRONOUS ASYNCHRONOUS RECEIVER TRANSMITTER (USART):-

The Universal Synchronous Asynchronous Receiver Transmitter (USART) module is one of the two serial I/O modules. (USART is also known as a Serial Communications Interface or SCI.) The USART can be configured as a full duplex asynchronous system that can communicate with peripheral devices such as CRT terminals and personal computers, or it can be configured as a half-duplex synchronous system that can communicate with peripheral devices such as A/D or D/A integrated circuits, serial EEPROMs etc. Communication in our project between the control circuit

































Figure 5.9

bit 7 CSRC: Clock Source Select bit Asynchronous mode: Don‘t care

Synchronous mode: 1 = Master mode (clock generated internally from B 0 = Slave mode (clock from external source) bit 6 TX9: 9-bit Transmit Enable bit

































REGISTER 3-2: RCSTA: RECEIVE STATUS AND CONTROL REGISTER (ADDRESS 18h):-

The bitwise operation of the RCSTA register used for serial transmission is given und er

Figure 5.10

































1 = Enables continuous receive until enable bit CREN is cleared (CREN overrides SREN) 0 = Disables continuous receive bit 3 ADDEN: Address Detect Enable bit Asynchronous mode 9-bit (RX9 = 1): 1 = Enables address detection, enables interrupt and load of the receive buffer when RSR<8> is set 0 = Disables address detection, all bytes are received, and ninth bit can be used as parity bit bit 2 FERR: Framing Error bit

































rate error in some cases. Writing a new value to the SPBRG register causes the BRG timer to be reset (or cleared). This ensures the BRG does not wait for a timer overflow before outputting the new baud rate.

5.7

SAMPLING:-

The data on the RC7/RX/DT pin is sampled three times by a majority detect circuit to determine if a high or a low level is present at the RX pin.



































can be disabled through their corresponding enable bits in various registers. Individual interrupt bits are set, of the status of the GIE bit. The GIE bit is cleared on RESET.

The ―return from interrupt‖ interrupt‖ instruction, RETFIE, exits the interrupt routine, as well as



































CHAPTER 6 PULSE WIDTH MODULATION (PWM)



































PWM of a signal or power source involves the modulation of its duty cycle, to either convey information over a communications channel or control the amount of power sent to a load.



































6.2.2

Delta-sigma

In delta-sigma modulation as a PWM control method, m ethod, the output signal is subtracted from a reference signal to form an error signal. This error is integrated, and when the integral



































6.2.4

Sinusoidal PWM

Sinusoidal PWM is a type of "carrier-based" pulse width modulation. Carrier based PWM uses pre-defined modulation signals to determine output voltages. In sinusoidal



























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































can be substantial even when the equipment providing variable speed operation is relatively inefficient. While a throttled pump consumes slightly less power than it would running free, it continues to rotate at the same speed, thus maintaining high velocity in the mechanical seal and bearings, and velocity directly determines bearing and mechanical seal life. Moving the operation of a centrifugal pump equipped with a constant pressure volute (the most common centrifugal pump type) away from BEP alters the hydraulic balance between the volute and impeller. i mpeller. The pump develops ever-increasing radial thrust loads, which increases radial forces that produce high bearing loads and shaft deflection affects mechanical seal alignment and, therefore, reduces bearing and mechanical seal life. In addition to energy savings, operation at reduced pressures can result in longer pump seal life, reduced impeller wear, and less system vibration and n oise. These benefits could provide additional savings over potential energy savings. 4.1.2

Soft Starter Application

The modern petrochemical industry requires large compressors in the high power range. Specifically the polyethylene production is moving towards bigger rated machines that are often large enough to take advantage from soft starting or even impose the utilization of a soft starting solution. The commonly used Direct on Line (DOL) starting method implies in high transients in the power system and the machine. The high current drawn from the grid can cause problems such as voltage drop and in some cases uncontrolled shutdown, reducing process reliability and eventually resulting in production and financial losses. Towards the machine, the high starting current causes additional mechanical stress that may also affect the driven equipment, limiting the number of consecutive starts and reducing equipment‘s lifetime. These disadvantages can be overcome by using a soft start method. One or more of the large drives in a process plant can take advantage of the soft starting providing a more reliable, flexible and safe

































The synchronous machine (SM) with its main excitation and the running circuit breaker (RCB) are the components which are required to operate the load direct on line. The task of the VFD is to accelerate the SM from zero up to nominal speed and synchronize it to the power supply system by closing the RCB, and optionally - after RCB has been opened – to to decelerate the SM from nominal speed to standstill. Its main function is to control the energy exchange between the power system and the motor, which during acceleration and deceleration is operated at variable frequency and voltage. For induction motors, the starting torque is approximately proportional to the square of the starting current drawn from the line. This starting current is proportional to the applied voltage (V). So the torque can also be considered to be approximately proportional to the applied voltage. By adjusting voltage during starting, the current drawn by the motor and the torque produced by the motor can be reduced and controlled. The soft start technology constantly monitors the voltage and current going to the motor. When the voltage and current sine waves diverge, greatly when the phase-lag increased the motor is lightly lightly loaded and operating inefficiently. inefficiently. When this happens the soft start start

































this condition and increases the power to the motor so it does not stall. A Soft Start keeps the motor running at full RPM and reduces the power used by the motor when it is lightly loaded, much like cruise control in cars. Soft-starters are normally air cooled due to their short operation time. For high powers or in case of reduced availability of cooling air, water cooled converters might be preferred. 4.1.3

Other Applications:

When applied properly, the variable frequency drive (VFD) is the most effective motor controller in the industry today. Modern VFDs are affordable and reliable, have flexibility of control, and offer significant electrical energy savings through greatly reduced electric bills. Variable frequency drives are frequently used in many areas because of their energy saving quality and reduced cost. Hence it is almost impossible to list all the applications but few other common areas or equipment where we find a VFD system s ystem are as follows:

Radiator fans of Synchronous Machine



Compressors



Elevators



Ventilation systems



Condensate pumps



Water supply pumps, etc.



Oxygen-generators of steel production



Cement Filling station in Cement Industry



Conveyors



Machine Tools

































4.2

4.2.1

BENEFITS OF VARIABLE FREQUENCY DRIVES 

Smooth and accurate speed control



Optimisation of power



Reduction in cost of controls / switch gear



Improved system efficiency



Energy savings



Low motor starting current



Reduction of thermal and mechanical



Stresses on motors and belts during starts



Simple installation high power factor



Lower KVA



Reduction in maximum Demand.

Low Inrush Motor Starting

It is common for AC induction motors to draw 6 to 8 times their full load amps when they are started across the line. When large amounts of current are drawn on the transformers, a voltage drop can occur, adversely affecting other equipment on the same electrical system. Some voltage sensitive applications may even trip off line. For this reason, many engineers specify a means of reducing the starting current of large AC induction motors. Wye-delta, part winding, autotransformer, and solid-state and VFD starters are often used to reduce inrush during motor starting. A VFD is the ideal soft starter since it provides the lowest inrush of any starter type as shown in Table 9.1

































4.2.2

High Power Factor

Power converted to motion, heat, sound, etc. is called real power and is measured in kilowatts (KW). Power that charges capacitors or builds magnetic fields is called reactive power and is measured in Kilovolts Amps Reactive (KVAR). The vector v ector sum of the KW and the KVAR is the Total Power (energy) and is measured in Kilovolt Amperes (KVA). Power factor is the ratio of KW/KVA. Motors draw reactive current to support their magnetic fields in order to cause rotation. Excessive reactive current is undesirable because it creates additional resistance losses and can require the use of larger transformers and wires. In addition, utilities often penalize owners for low power factor. Decreasing reactive current will increase power factor. Power factor correction capacitors can be added to reduce the reactive current measured upstream of the capacitors and increase the measured power factor. The VFDs include capacitors in the DC Bus that perform the same function and maintain high power factor on the line side of the VFD. This eliminates the need to add power factor correction equipment to the motor or use expensive capacitor banks. In addition, VFDs often result in higher line side power factor values than constant speed motors equipped with correction capacitors.

4.2.3

Easy Installation

Many pieces of equipment are factory shipped with unit mounted VFDs that arrive pre programmed and factory wired. Motor leads, control power for auxiliaries, and communication lines are all factory wired. The VFD cooling lines on unit-mounted chiller VFDs are also factory installed. The installing contractor needs only to connect the line power supply to the VFD.



































4.3

TROUBLESHOOTING VARIABLE FREQUENCY DRIVES

4.3.1

Under-voltage Fault Indication

































































4.3.3

Motor Not Running

































APPENDIX A

A.1

BASIC MECHANICS

Torque is constant at any speed while there is a direct proportional relationship between horsepower and speed; horsepower varies directly with the speed. Therefore, horsepower is motion dependent, torque is not. Torque 

A force applied in a manner that tends to produce rotation, such as a pipe wrench on a shaft. Torque (force) without rotation is termed static torque, since no motion is produced.



Torque is measured in Ib-in or Ib-ft which is the product of the force in pounds (I b) x the distance in inches (in) or feet (ft) from the center of the point of apparent rotation. Figure 16 shows 120 Ib-in (12 inches x 10 Ibs) or 10 Ib/ft torque.



Because

most

power

transmission

is

based

upon

rotating

elements,

torque is important as a measurement of the effort required to produce work (horsepower).

































Three basic factors are involved: Factor

Unit

Distance (Radius)

Foot (or inches)

Force (Push or Pull)

Pounds

Time

One (1) Minute HP =

F (Load in pounds) x Feet per Minute 33,000

Horsepower-Torque, Getting It Together 

Suppose 50 lb load is acting on the 5 inch radius (distance) of the winch, producing a load torque of 250 lb-in (50 lbs x 5 inches) that must be overcome to lift the load. Since the hand crank arm has a 10 inch radius (distance), a minimum force of 25 lbs must be exerted to overcome the load torque (25 lbs x 10" = 250 lb/in). If no motion is involved, the system is in balance. Although torque is being exerted, no work is accomplished and no horsepower is developed.



The winch diameter is 10 inches. Therefore, each revolution of the hand crank will lift the weight 10 inches X



= 31.416 inches (2.618 feet). feet).

If the crank is turned at 10 RPM, 50 Ibs will be lifted a distance of 26.18 feet in

one minute: HP =

50 x 26.18 33,000

= .03966 HP



































APPENDIX B

B.1 IR2136 (INVERTING DRIVER IC)

































































































B.3 IRF740 (MOSFET)



































































REFERENCES 

M.H. Rashid, January 1988, Power Electronics: Circuits, Devices, and Applications, Prentice Hall.



Muhammad Ali Mazidi, Rolin D. McKinaly, Danny Causey, February 2007, PIC Microcontroller And Embedded Systems: Using Assembly and C for Pic18, Prentice Hall.



Stephen J. Chapman, June 2010, Electric Machinery Fundamentals, McGraw-Hill Science Engineering.

Speed Control of Three Phase Induction Motor Using PIC Microcontroller

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