PROJECT 005: POWER QUALITY MONITORING UNIT

Transcription

1 UNIVERSITY OF NAIROBI DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING PROJECT 005: POWER QUALITY MONITORING UNIT AUTHOR: NJOGU SWALEH KAMUTHIERE REG NO: F17/21669/2007 SUPERVISOR: PROF. ELIJAH MWANGI EXAMINER: Mr. S.A. AHMED A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS OF BSc. ELECTRICAL AND ELECTRONIC ENG. OF THE UNIVERSITY OF NAIROBI. MAY, 2016

2 DECLARATION OF ORIGINALITY NAME OF STUDENT: Njogu Swaleh Kamuthiere REGISTRATION NUMBER: F17/21669/2007 COLLEGE: Architecture and Engineering FACULTY/SCHOOL/INSTITUTE: Engineering DEPARTMENT: Electrical and Information Engineering COURSE NAME: Bachelor of Science in Electrical and Electronic Engineering TITLE OF WORK: Microcontroller based power quality measurement 1. I understand what plagiarism is and I am aware of the university policy in this regard. 2. I declare that this project is my original work and has not been submitted elsewhere for examination, award of a degree or publication. Where other peoples work or my own work has been used, this has properly been acknowledged and referenced in accordance with the University Of Nairobi 3. I have not sought or used the services of any professional agencies to produce this work. 4. I have not allowed, and shall not allow anyone to copy my work with the intention of passing it off as his/her own work. 5. I understand that any false claim in respect of this work shall result in disciplinary action, in accordance with University anti-plagiarism policy. Signature:. Date. This report has been submitted to the Department of Electrical and Information Engineering, The University of Nairobi with my approval as supervisor: Signature:.. Name: Prof. E. Mwangi

3 DEDICATION To my dear parents, family and friends for their continuous support and encouragement throughout this course.

4 ACKNOWLEDGEMENT First and foremost, I would like to thank God for giving me the strength and ability and guidance to carry out this project and complete the project successfully. I would also like to thank my supervisor, Prof. E. Mwangi, for being a source of guidance Throughout the duration of the project. The solutions to the cosine function in assembly language was a big help. My sincere gratitude goes out to my classmates for their suggestions, opinions, and help in this project. I would like to thank my family for their support financially.

5 LIST OF FIGURES Fig 2-1 in phase sinusoidal waveforms..5 Fig 2-2 phase relations waveforms 8 Fig 2-3 in phase sinusoidal waveforms 9 Fig degrees out of phase waveforms..10 Fig 2-5 phase difference between a Sine wave and Cosine wave 12 Fig 2-6 PIC16F690 Pin Diagram..20 Fig 2-7 PIC16F690 PIN SUMMARY 21 Fig 2-8 PIC16F690 pin diagram 22 Fig 2-9 memory organization of PIC16f Fig 2-10 above are the PIC16F690 Special Function Registers 26 Fig 2-11 ADC CONVERTER BLOCK DIAGRAM 27 Fig 2-12 results formatting..29 Fig 2-13 above is the capture mode..30 Fig 2-13 LCD Pin diagram and instructions..32 Fig 2-14 initializing by internal reset circuit diagram..35 Fig bit initialization.37 Fig bit initialization.38 Fig 2-17 LCD instruction set.39 Fig 3-1 online LCD images.40 Fig 3-2 simulation circuit op amp.44 Fig 3-3 power supply circuit 45 Fig 3-4current zero crossing detection circuit..46 Fig 3-5 voltage zero crossing detection circuit.46

6 LIST OF TABLES Table 4-1 simulated results..49

7 LIST OF ABBREVIATIONS A/D Analog to digital AC Alternating Current ALU Arithmetic Logic Unit ASCII Arithmetic Standard Code for Information Interchange CISC Complex Instruction Set Computer CPU Control Processing Unit DDRAM Double Data Random Access Memory EPROM Erasable Programmable Read Only Memory HZ Hertz I/O Input/Output KPLC Kenya Power and Lighting Company LCD Liquid Crystal Display PIC Peripheral Interface Controller RAM Random Access Memory RISC Reduced Instruction Set Computer ROM Read Only Memory TMR1 Timer One TMR0 Timer Zero

8 TABLE OF CONTENTS DECLARATION OF ORIGINALITY i DEDICATION.. ii ACKNOWLEDGEMENT iii LIST OF FIGURES. iv LIST OF TABLES v LIST OF ABBREVIATIONS.. vi CHAPTER 1: INTRODUCTION Background study Problem definition Objectives Justification Scope... 3 CHAPTER 2: LITERATURE REVIEW Introduction Waveforms Phase Difference Phase Relationship of a Sinusoidal Waveform MICROCONTROLLER Microcontrollers and Microprocessors Microcontroller types Microcontroller structure Pic architecture PIC16F690 19

9 2.6.1 PIC16F690 pin diagram PIC16F690 pin summary PIC16F690 properties Memory Organization Program Memory Organization Data Memory Organization Analog to Digital Converter Interrupts Capture mode Timers Liquid Crystal Display DDRAM - Display Data RAM CGROM - Character Generator ROM CGRAM - Character Generator RAM BF - Busy Flag Instruction Register (IR) and Data Register (DR) Commands and Instruction set LCD initialization Initializing by Internal Reset Circuit Initialization by Instruction Bit Interface, Initialization by Instruction Bit Interface, Initialization by Instruction LCD instruction set LCD connection 39 CHAPTER 3: DESIGN AND IMPLEMENTATION.40

10 3.1 Introduction Hardware section LCD Operational Amplifier Power Supply Zero Crossing Detection Programming.46 CHAPTER 4: Results and Analysis Simulation results Simulated circuit Practical results 50 CHAPTER 5: Conclusions And Recommendations Conclusions Recommendations..52 REFERENCES 53 APPENDIX A: Assembly Language Code.54 APPENDIX B: Cost Analysis 84

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12 CHAPTER 1: INTRODUCTION 1. BACKGROUND STUDY Power factor is basically due to lag and lead concept of current and voltage. When current waveform lags behinds the voltage by some angle, power factor will be lagging and when current wave form leads the voltage by some angle, power factor will be leading. Inductor causes a lagging power factor and capacitors produces leading power factor. Hence capacitors improve power factor by providing leading VARS or reactive power to system which cancels the lagging power factor effect of inductors. Power factor was measured using a pic microcontroller. To measure power factor it was needed to measure phase angle difference between voltage and current wave form. The cosine of this phase angle is power factor. Power factor is also represented by following formula: Power factor = Cos (θ) Where θ is basically phase angle difference between voltage and current wave form. The phase angle is the lateral difference between two waveforms as per our case. That is voltage and current along a common axis. Low power factor causes increase in current drawn by load. This results in use of larger equipment on distribution systems and also an increase in the amount of greenhouse gases released into the atmosphere. 2. PROBLEM DEFINITION In order to measure the power factor it was required to obtain the phase angle in order to obtain the power factor by calculating the cosine of the phase angle. It is required to measure the power factor accurately because of its importance to the consumer and the supplier. In this project a microcontroller was used to measure the phase angle and calculate the power factor.

13 With the power factor low as mentioned earlier a lot of current is drawn by the consumers or the load connected. The drawing of current leads to more losses being encountered. Which affects the profits in distribution companies. From the resistance equation it can be observed that resistance is inversely proportional to the area of the conductor. Maintaining the voltage in ohms law V=IR ( where V=Voltage, I=Current and R=Resistance) increase in current leads to reduction in the current. As the resistance decreases the area of the conductor must increase according to the resistance equation with the inverse relation between resistance and area of the conductor. Increase in the area of the conductor assuming copper means that more copper will be used thus increasing the distribution cost. It should be noted that KPLC require their consumers to keep thepower factor close to one as possible. 1.3 OBJECTIVES The main objective was to design and implement a system that will measure the phase difference in a single phase supply and compute the power factor. The power factor was to be displayed on an LCD. That is a liquid crystal display. The circuit was supposed to also measure the frequency and the amplitude. Compare two sinusoidal waves ie voltage and current and obtain their phase difference. That is check if they are in phase or not. Calculate the power factor by finding the cos of the phase angle. Compute the frequency of the single phase supply and record. Obtain the amplitude and record.

14 1.4 JUSTIFICATION There are different methods to measure the phase angle. For instance the use of an oscilloscope. But this has limitations like the cost of a modern oscilloscope is very high. And an oscilloscope has errors too which are due to; Present dc offset errors present Reduced precision near certain angles Incorrect solution possibility By obtaining the power factor power factor correction measures can be implemented in order to reduce the phase angle. Large phase angle leads to a lot of power being drawn leading to very high costs which are unnecessary. But first the phase angle must be measured very accurately so that the required corrections xan be made to reduce the costs. Large consumers require very accurate data. Microcontrollers are very efficient and fast. Being fast the power factor will obtained fast and displayed instantly. Other methods of power factor measurement are full of errors and and tiresome. 1.5 SCOPE OF THE PROJECT

15 The project will deal with the problem of power factor measurement by measuring the phase angle from a single phase supply and calculating the power factor by obtaining the the cos of the phase angle. The power factor is to be displayed on an LCD. The power factor will not be displayed as leading or lagging because in the project we wont know which wave form will be leading or lagging. Timers will be employed, in this case we will use TMR1 for the phase measurement. Where the rising edge of the first waveform will be recorded and the timer will be activated. The timer will count until the second rising edge which will stop the timer and this will be considered as sample one. To be accurate five readings will be taken and the average power factor will be obtained, this improves the accuracy of our project. The average phase angle will then be used to compute the power factor which will be displayed on the LCD. For the frequency the rising edge at the zero crossing will be detected and the falling edge will also be detected. This is a quarter of the period of the wave. The timer will record the rising edge time and the falling edge time. Thus obtaining the time difference which will be multiplied by four to obtain the entire period. The frequency will be the reciprocal of the entire period. Which can also be displayed on the LCD.

16 CHAPTER 2:LITERATURE REVIEW 2.1 INTRODUCTION In this chapter, we will describe the various researches that has been carried out from various sources such as the internet, textbooks, online articles. This information is essential to the development of the project. The power quality monitoring unit is made up of the following : PIC16F690 MicrocontrollerThis is the heart of the whole monitoring unit. It is the main device in which the project will be based on. Interfacing the PIC microcontroller with external devices is made possible with the various I/O pins that the PIC microcontroller has. Liquid Crystal Display(LCD)Facilitates the viewing of the power factor, the peak voltage and frequency that is required of this project. OP-AMP 2.2 WAVEFORMS

17 A waveform is the result of plotting values of quantities which vary with time (t). It is in the form of a graph. As for alternating waveforms like in the case of single phase the wave changes direction that is it has positive and negative values as shown in the image above. A period is defined as the time taken by an alternating signal to complete one cycle of the waveform. Usually described by the symbol T. Frequency on the other hand is described as the number of cycles completed in a second. It can also be described as the the reciprocal of the period. In Kenya the frequency of supplied electricity is 50 Hz Phase Difference Sine Wave can be presented graphically in the time domain along an horizontal zero axis, and that sine waves have a positive maximum value at time π/2, a negative maximum value at time 3π/2, with zero values occurring along the baseline at 0, π and 2π. However, not all sinusoidal waveforms will pass exactly through the zero axis point at the same time, but may be shifted to the right or to the left of 0o by some value when compared to another sine wave.

18 Comparing a voltage waveform to that of a current waveform. This then produces an angular shift or Phase Difference between the two sinusoidal waveforms. Any sine wave that does not pass through zero at t = 0 has a phase shift. The phase difference or phase shift as it is also called of a Sinusoidal Waveform is the angle Φ (Greek letter Phi), in degrees or radians that the waveform has shifted from a certain reference point along the horizontal zero axis. In other words phase shift is the lateral difference between two or more waveforms along a common axis and sinusoidal waveforms of the same frequency can have a phase difference. The phase difference, Φ of an alternating waveform can vary from between 0 to its maximum time period, T of the waveform during one complete cycle and this can be anywhere along the horizontal axis between, Φ = 0 to 2π (radians) or Φ = 0 to 360o depending upon the angular units used. Phase Difference Equation Where: Am - is the amplitude of the waveform. ωt - is the angular frequency of the waveform in radian/sec. Φ (phi) - is the phase angle in degrees or radians that the waveform has shifted either left or right from the reference point. If the positive slope of the sinusoidal waveform passes through the horizontal axis before t = 0 then the waveform has shifted to the left so Φ >0, and the phase angle will be positive in nature, +Φ giving a leading phase angle. In other words it appears earlier in time than 0 o producing an anticlockwise rotation of the vector. Likewise, if the positive slope of the sinusoidal waveform passes through the horizontal x-axis some time after t = 0 then the waveform has shifted to the right so Φ <0, and the phase angle

19 will be negative in nature -Φ producing a lagging phase angle as it appears later in time than 0o producing a clockwise rotation of the vector. Both cases are shown below Phase Relationship of a Sinusoidal Waveform Considering that two alternating quantities such as a voltage, v and a current, i have the same frequency ƒ in Hertz. As the frequency of the two quantities is the same the angular velocity, ω must also be the same. So at any instant in time we can say that the phase of voltage, v will be the same as the phase of the current, i. Then the angle of rotation within a particular time period will always be the same and the phase difference between the two quantities of v and i will therefore be zero and Φ = 0. As the frequency of the voltage, v and the current, i are the same they must both reach their maximum positive, negative and zero values during one complete cycle at the same time (although their amplitudes may be different). Then the two alternating quantities, v and i are said to be inphase

20 In phase sinusoidal waveforms Considering that the voltage, v and the current, i have a phase difference between themselves of 30o, so (Φ = 30o or π/6 radians). As both alternating quantities rotate at the same speed, i.e. they have the same frequency, this phase difference will remain constant for all instants in time, then the phase difference of 30o between the two quantities is represented by phi, Φ as shown below. Phase Difference of a Sinusoidal Waveform

21 The voltage waveform above starts at zero along the horizontal reference axis, but at that same instant of time the current waveform is still negative in value and does not cross this reference axis until 30o later. Then there exists a Phase difference between the two waveforms as the current cross the horizontal reference axis reaching its maximum peak and zero values after the voltage waveform. As the two waveforms are no longer in-phase, they must therefore be out-of-phase by an amount determined by phi, Φ and in our example this is 30 o. So we can say that the two waveforms are now 30o out-of phase. The current waveform can also be said to be lagging behind the voltage waveform by the phase angle, Φ. Then in our example above the two waveforms have a Lagging Phase Difference so the expression for both the voltage and current above will be given as.

22 where, i lags v by angle Φ Likewise, if the current, i has a positive value and crosses the reference axis reaching its maximum peak and zero values at some time before the voltage, v then the current waveform will be leading the voltage by some phase angle. Then the two waveforms are said to have a Leading Phase Difference and the expression for both the voltage and the current will be. where, i leads v by angle Φ The phase angle of a sine wave can be used to describe the relationship of one sine wave to another by using the terms Leading and Lagging to indicate the relationship between two sinusoidal waveforms of the same frequency, plotted onto the same reference axis. In our example above the two waveforms are out-of-phase by 30o so we can say that i lags v or v leads i by 30o. The relationship between the two waveforms and the resulting phase angle can be measured anywhere along the horizontal zero axis through which each waveform passes with the same slope direction either positive or negative. In AC power circuits this ability to describe the relationship between a voltage and a current sine wave within the same circuit is very important and forms the bases of AC circuit analysis. Phase Difference between a Sine wave and a Cosine wave

23 Alternatively, we can also say that a sine wave is a cosine wave that has been shifted in the other direction by -90o. Either way when dealing with sine waves or cosine waves with an angle the following rules will always apply. Sine and Cosine Wave Relationships When comparing two sinusoidal waveforms it more common to express their relationship as either a sine or cosine with positive going amplitudes and this is achieved using the following mathematical identities.

24 By using these relationships above we can convert any sinusoidal waveform with or without an angular or phase difference from either a sine wave into a cosine wave or vice versa. In the next tutorial about Phasors we will use a graphical method of representing or comparing the phase difference between two sinusoids by looking at the phasor representation of a single phase AC quantity along with some phasor algebra relating to the mathematical addition of two or more phasors.

25 2.4 Microcontroller A microcontroller is a computer on a chip. It is an electronic device containing: A processor core Memory Input/Output peripherals The input/output peripherals are programmable. They allow the microcontroller to communicate with the outside world. They do not require external components for their applications. They are useful in that they are cheap thus reducing prices and due to their small size they make the end products smaller in size. They are used in development of electronics for instance television sets, dvd machines, phones, personal computers, laptops etc microcontrollers and microprocessors Microcontrollers and microprocessors do differ in functionality. Microprocessor requires other components for example memory or components for receiving and sending data. While the microcontroller already has all that. Microprocessors are also designed to be general purpose. Therefore comparing the two it can be concluded that microcontrollers are definitely smaller. Therefore saving on space.

26 2.4.2 Microcontroller types Microcontrollers are divided into categories according to their memory architecture, bits, and instruction sets. 1. Memory Architecture Harvard Memory Architecture Microcontroller In the Harvard Architecture, the program memory is completely separate from the data memory. All PICs have Harvard Memory Architecture. The CPU fetches the next instruction and loads or stores data simultaneously and independently. This physical separation of instructions and data is the distinguishing feature of Harvard Architecture. The PIC architecture has a two-stage instruction pipeline; however, since the fetch of the current instruction and the execution of the previous one can overlap in time, one complete instruction is fetched and executed at every machine cycle. This is known as instruction pipelining. Princeton Memory Architecture Microcontroller In Princeton Architecture, the program memory is such that it stores both the instructions and data in one memory pool. When the computer needs memory to hold a program, it goes to the memory pool and requests that some memory is allocated for it. When it needs space to hold data it goes to the same pool and asks for memory for data. The disadvantage of this is that if a certain amount of memory is allocated for data, but the program tries to put more data than will fit, it may place the extra data in the next memory location, which could actually contain the program. 2. Bits

27 8 bit microcontrollers-8 bit microcontrollers contain 8 bit internal bus with the ALU performing logic and arithmetic operations. Examples of 8 bit microcontrollers include the Intel 8031/ bit microcontrollers-this executes ALU operations with greater accuracy and performance in contrast to the 8 bit microcontrollers. Example of the 16 bit microcontroller is the Intel bit microcontrollers-this are employed mainly in automatically controlled appliances such as office machines, implantable medical appliances etc. It requires 32 bit instructions to carry out any logical or arithmetic operation. 3. Memory Microcontrollers can be divided into two types in accordance with memory : External Memory Microcontroller- When an embedded structure is built with a microcontroller which does not comprise of all the functioning blocks existing on a chip, then it is named an external memory microcontroller. For illustration, 8031 microcontroller does not have program memory on the chip. Embedded Memory Microcontroller- When an embedded structure is built with a microcontroller which comprises of all the functioning blocks existing on the chip, then it is named an Embedded Memory Microcontroller. For Example the 8051 Microcontroller has all the program and data memory, counters & timers, Interrupts, I/O ports etc. 4. Instruction set This can be categorised into the following;

28 CISC- CISC meaning Complex Instruction Set Computer. It allows the user to apply 1 instruction as an alternative to many simple instructions. The CISC design is based on each low-level instruction performing several operations. Examples of CISC instructions include decrementing a counter register, determining the state of a processor flag, and executing a jump instruction if the flag is set or cleared. The idea of CISC was to provide high level instructions in order to implement the implementation of high level languages[4][6]. RISC- RISC means Reduced Instructions Set Computer. RISC reduces the operation time by shortening the clock cycle per instruction. In contrast to CISC, RISC machine contains fewer instructions and each instruction performs more elementary operations. Consequences of this are a smaller silicon area, faster execution, and reduced program size with fewer accesses to main memory. The PIC designers have followed the RISC route[4][6] Microcontroller structure The basic structure of a microcontroller comprises of: I. Memory- There are two types of memory: Volatile and Non-volatile. Volatile Memory loses its data when its switched off, but can be written by the CPU to store current data e.g. RAM(Random Access Memory). ROM(Read Only Memory)is nonvolatile and retains its data when switched off. The memory in the microcontroller stores all programs and data. The ideal memory should be non-volatile, read and write, fast, large and cheap, but since it does not exist, then the Flash ROM is closest to the ideal memory since its non-volatile and rewritable [1]. II. CPU- This is the brain of the microcontroller. The CPU facilitates the fetching of data, decoding of the same and at the end completing the assigned task successfully. With the help of the CPU all the components of the microcontroller are connected into a single system. A program that is stored in the memory of the microcontroller is fetched by the CPU in sequence and executed. In actual sense the instructions that are stored in the memory locations are copied to an instruction

29 register in the CPU via a data bus. The instructions control the selection of the required operation in the control unit of the CPU[4]. III. Serial Ports-These ports give serial interfaces amid microcontrollers and various other peripherals. The serial communication involved in the PIC microcontroller for example include the EUSART(Enhanced Universal Synchronous Asynchronous Receiver Transmitter), the SPI(Serial peripheral Interface) and the I2C (Inter-Integrated circuit). IV. Input/output ports- Without some means of getting information or signals in and out, then the microcontroller would be of no help to the outside world. Thus the importance of input/output ports. There are two main type of ports: serial and parallel. Parallel ports transfer data in and out 8 bits at a time. While in serial ports it is transmitted 1 bit at a time on a single line. Therefore the I/O ports are employed to interface or drive different external appliances e.g. LCD s, LED s etc.[2]. V. Timers and Counters-A microcontroller may be in-built with one or more timers and counters.[4].they control all timing and counting operations within the microcontroller. The main operations performed by timers are : i. Pulse generations ii. Clock functions iii. Frequency measuring iv. Modulation v. Making oscillations VI. Analog-to-Digital Converters- The peripheral signals that we connect to the microcontroller(usually analogue) are quite different from the ones that the microcontroller comprehends (i.e. one and zero).thus they have to be converted into a pattern which can be understood by the microcontroller. This task is performed by the Analog-to -Digital Converter[2]. VII. Bus - It represents a group of 8, 16, or more wires that have the function of interconnecting the memory and the CPU. They are two types of buses.

30 i. Address bus ii. Data bus The address bus consists of as many lines as the amount of memory we wish to address. On the other hand a data bus will be as wide as the data.it can either be 8 bit or 16 bit. The address is employed to transmit address from CPU memory while the data bus will connect all the internal components of the microcontroller. VIII. Watchdog Timer-It acts a free-run counter where our program needs to write a zero in every time it executes a program correctly. If program counter skips to a memory location where its not supposed to be, this will allow the chip to recover. This means that the zero will not be written on the watchdog timer and it will reset the microcontroller. 2.5 Pic architecture PIC microcontrollers are classified by Microchip into three groups : a) Baseline-This group includes members of the PIC10, PIC12, and PIC16 families. b) Mid-range -The mid-range PIC family includes members of the PIC12 and PIC16 groups. c) High-performance -The high-performance PICs belong to the PIC18 group. 2.6 PIC16F690 This is a 20 pin count microcontroller from microchip technology. It basically contains:

31 Program memory 4096 Flash (words) Data memory SRAM 256 bytes EEPROM 256 bytes I/O 18 pins 10 bit A/D 12 ch Comparators -2 Timers 8 bit 2 16 bit 1 SSP ECCP+ EUSTART PIC16F690 pin diagram

32 2.6.2 PIC16F690 pin summary

33 PIC16F690 Pin diagram (QNF) The PIC16F690 consists of three ports namely : a. PORTA- Pins 19,18,17,4,3,2 b. PORTB- Pins 13,12,11,10. c. PORTC- pins 16,15,14,5,6,7,8,9. A few key observations while looking at the pin out diagram of the above PIC 16F690 are: i. Pins 1 and 20 act as the power supply and ground of the pic microcontroller. ii. Pins 2 and 3 acts as the external oscillator pins.

34 iii. Pin 4 is the Master Clear pin iv. Pins 10 and 12 can be configured as the transmitter and receiver pins respectively. v. Pins 19 and 17 can be configured as the comparator1 input and output respectively vi. Pins 16 and 6 can be configured as the comparator2 input and output respectively vii. Pin 18 can be used as a Voltage reference when using the Analog to Digital Converter PIC16F690 properties 4 x 14 flash memory 256 bytes RAM 256 bytes EEPROM 13 bit 8 level stack Internal oscillator software selectable 8MHz 32MHz V operating voltage 12 channel of 10 bit A/D converter Two channel analog comparator Programmable on chip voltage reference Auto shut down and restart option Maximum current source/sunk in all ports combined in 200 ma Maximum output current sourced/sunk by any input/output pin is 200Ma Temperature range of -40 to 125 degrees celcius

35 2.6.4 Memory Organization Program Memory Organization The PIC16F6690 has a 13-bit program counter capable of addressing an 8K x 14 program memory space. Only the first 4K x 14 (0000h-0FFFh) for the PIC16F690. Accessing a location above these boundaries will cause a wrap around. The Reset vector is at 0000h and the interrupt vector is at 0004h Data Memory Organization

36 The data memory is partitioned into four banks which contain the General Purpose Registers (GPR) and the Special Function Registers (SFR). The Special Function Registers are located in the first 32 locations of each bank. The General Purpose Registers, implemented as static RAM, are located in the last 96 locations of each Bank. Register locations F0h-FFh in Bank 1, 170h-17Fh inbank 2 and 1F0h-1FFh in Bank 3 point to addresses 70h-7Fh in Bank 0. The actual number of General Purpose Resisters (GPR) in each Bank depends on the device. All other RAM is unimplemented and returns 0 when read. RP<1:0> of the STATUS register are the bankselect bits: RP1 RP0 0 0 Bank 0 is selected 0 1 Bank 1 is selected 1 0 Bank 2 is selected 1 1 Bank 3 is selected GENERAL PURPOSE REGISTER FILE The register file is organized as 256 x 8 in the PIC16F690. Each register is accessed, either directly or indirectly, through the File Select Register (FSR) SPECIAL FUNCTION REGISTERS The Special Function Registers are registers used by the CPU and peripheral functions for controlling the desired operation of the device. These registers are static RAM. The special registers can be classified into two sets: o Core

37 o Peripheral

38 Above are the PIC16F690 Special Function Registers

39 2.6.5 Analog to Digital Converter The Analog-to-Digital Converter (ADC) allows conversion of an analog input signal to a 10-bit binary representation of that signal. This device uses analog inputs, which are multiplexed into a single sample and hold circuit. The output of the sample and hold is connected to the input of the converter. The converter generates a 10-bit binary result via successive approximation and stores the conversion result into the ADC result registers (ADRESL and ADRESH).

40 ADC CONVERTER BLOCK DIAGRAM ADC CONFIGURATION The Analogue to Digital Converter need to be configured before being able to operate. The following are the steps that need to be understood first before anything else. These are: i. PORT CONFIGURATION When converting analog signals, the I/O pins should be configured for analog by setting the associated TRIS and ANSEL bits.

41 ii. CHANNEL SELECTION This determines which channel is connected to the sample and hold circuit. iii. ADC VOLTAGE REFERENCE The VCFG bit of the ADCON0 register provides control of the positive voltage reference. The positive voltage reference can be either Vdd or an external voltage source. iv. CONVERSION CLOCK The source of the conversion clock can be selected via the ADCS bit of the ADCON1 register There are seven possible clock options : Fosc/2 Fosc/4 Fosc/8 Fosc/16 Fosc/32 Fosc/64 Frc(dedicated internal oscillator). v. INTERRUPT CONTROL Upon completion of the analog-to-digital converter the ADC module allows for generation of an Interrupt. This interrupt can be generated while the ADC is in operation or while in Sleep. Upon waking from Sleep, the next instruction following the SLEEP instruction is always executed vi. RESULTS FORMATTING The 10-bit A/D conversion result can be supplied in two formats, left justified or right justified. The ADFM bit of the ADCON0 register controls the output format.

42 2.6.6 Interrupts The ADC module allows for the ability to generate an interrupt upon completion of an Analog-to-Digital conversion. The ADC interrupt flag is the ADIF bit in the PIR1 register. The ADC interrupt enable is the ADIE bit in the PIE1 register. The ADIF bit must be cleared in software. This interrupt can be generated while the device is operating or while in Sleep. If the device is in Sleep, the interrupt will wake-up the device. Upon waking from Sleep, the next instruction following the SLEEP instruction is always executed. If the user is attempting to wake-up from Sleep and resume in-line code execution, the global interrupt must be disabled. If the global interrupt is enabled, execution will switch to the interrupt service routine.

43 2.6.7 Capture mode In Capture mode, CCPR1H:CCPR1L captures the 16-bit value of the TMR1 register when an event occurs on pin CCP1. An event is defined as one of the following and is configured by the CCP1M<3:0> bits of the CCP1CON register: Every falling edge Every rising edge Every 4th rising edge Every 16th rising edge When a capture is made, the Interrupt Request Flag bit CCP1IF of the PIR1 register is set. The interrupt flag must be cleared in software. If another capture occurs before the value in the CCPR1H, CCPR1L register pair is read, the old captured value is overwritten by the new captured value.

44 Above is the capture mode Timers Timers are either 8-bit or 16-bit counters with postscalers and prescalers which divide down the input or output of the counter to extend its range. They are used in counter or timer mode and also capture, compare or pulse width modulation. Which was useful in this case. PIC16F690 has 3 hardware timers: o Timer 0 (8-bit timer 0) o Timer 2 (16-bit timer 2) o Timer 1 (8-bit timer 1)

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46 2.7 Liquid Crystal Display HD44780 has 8 bit wide data bus represented by D0-D7. It also has three control lines RS, RW and E. And three power lines VSS, VDD and VEE. It is a small low cost display easy to interface with a micro-controller because of an embedded controller. It can connected to the microcontroller via 11 ports or 7 ports depending on the configuration method chosen. Below is a diagram of the LCD and a table representing the pins.

47 An LCD is an electronic visual display. It uses the light modulating properties of liquid crystals which do not emit light directly. Using electronically modulated optical device made up of any number of segments filled with liquid crystals and arrayed in front of a light source or reflector to produce images in monochrome or color. Data is displayed when the microcontroller sends data to the LCD via the data lines when pin E is enabled DDRAM - Display Data RAM Display data RAM (DDRAM) stores display data represented in 8-bit character codes. Its extended capacity is 80 X 8 bits, or 80 characters. The area in display data RAM (DDRAM) that is not used for display can be used as general data RAM. So whatever you send on the DDRAM is actually displayed on the LCD. For LCDs like 1x16, only 16 characters are visible, so whatever you write after 16 chars is written in DDRAM but is not visible to the user CGROM - Character Generator ROM The character generator ROM generates 5 x 8 dot or 5 x 10 dot character patterns from 8-bit character codes (see Figure 5 and Figure 6 for more details). It can generate x 8 dot character patterns and 32 5 x 10 dot character patterns. Userdefined character patterns are also available by mask-programmed ROM CGRAM - Character Generator RAM CGRAM area is used to create custom characters in LCD. In the character generator RAM, the user can rewrite character patterns by program. For 5 x 8 dots, eight character patterns can be written, and for 5 x 10 dots, four character patterns can be written BF - Busy Flag Busy Flag is an status indicator flag for LCD. When we send a command or data to the LCD for processing, this flag is set (i.e BF =1) and as soon as the instruction is executed successfully this flag is cleared (BF = 0). This is helpful in producing and exact ammount of delay. for the LCD processing. To read Busy Flag, the condition RS = 0 and R/W = 1 must be met and The MSB of the LCD data

48 bus (D7) act as busy flag. When BF = 1 means LCD is busy and will not accept next command or data and BF = 0 means LCD is ready for the next command or data to process Instruction Register (IR) and Data Register (DR) There are two 8-bit registers in HD44780 controller Instruction and Data register. Instruction register corresponds to the register where you send commands to LCD e.g LCD shift command, LCD clear, LCD address etc. and Data register is used for storing data which is to be displayed on LCD. when send the enable signal of the LCD is asserted, the data on the pins is latched in to the data register and data is then moved automatically to the DDRAM and hence is displayed on the LCD. Data Register is not only used for sending data to DDRAM but also for CGRAM, the address where you want to send the data, is decided by the instruction you send to LCD. We will discuss more on LCD instuction set further in this tutorial Commands and Instruction set Only the instruction register (IR) and the data register (DR) of the LCD can be controlled by the MCU. Before starting the internal operation of the LCD, control information is temporarily stored into these registers to allow interfacing with various MCUs, which operate at different speeds, or various peripheral control devices. The internal operation of the LCD is determined by signals sent from the MCU. These signals, which include register selection signal (RS), read/write signal (R/W), and the data bus (DB0 to DB7), make up the LCD instructions (Table 3). There are four categories of instructions that: Designate LCD functions, such as display format, data length, etc. Set internal RAM addresses Perform data transfer with internal RAM Perform miscellaneous functions LCD initialization There are two methods for LCD initialization:

49 Initializing by Internal Reset Circuit Initialization by Instruction Initializing by Internal Reset Circuit This is the datasheet information regarding Initialization of the LCD controller. The 'Internal Reset' technique described above is relied upon by many programmers but, in my opinion, this is not a wise choice. Perhaps they are seduced by the first sentence with the promise of 'automatic' initialization. If you look at the result of this automatic initialization you will see that the controller is configured for a 1-line display when in fact the majority of LCD modules should be configured for a 2-line display. It also leaves the display off. This means that two of the four steps that were automatically performed are going to have to be redone. But that is NOT the main reason that this technique should be avoided. The note at the bottom clearly states that this technique will fail if the power supply does not meet certain specifications, specifications that are buried elsewhere in the datasheet. In cases where the power supply cannot be guaranteed to meet those specification the datasheet recommends using "Initializing by Instruction".

50 Initialization by Instruction It really isn't that hard to use this technique once you decipher the flowcharts that describe the procedure. All of the flowcharts in the various datasheets seem to derive from the same source and they are all equally ambiguous in certain areas. Any differences are probably due to typographical or editing errors and those are easily spotted, providing you compare several different datasheets. There are separate initialization flowcharts for the 8-bit interface and the 4-bit interface, but the actual sequence of instructions sent to the LCD controller is essentially the same in each case. First there are a series of what are technically Function Set instructions whose purpose is to effectively 'reset' the LCD controller. Next, if the 4-bit interface is desired, there is an additional Function Set instruction to change the interface from the default 8-bit configuration. Finally there are four more instructions, the 'real' Function Set, the Display on/off Control, the Clear Display, and the Entry Mode Set. When power is applied to the LCD module the LCD controller always comes up in the 8-bit interface mode. This means that the LCD controller reads all eight of its data pins each time the Enable pin is pulsed. This is fine if an 8-bit data interface is actually being used, but what about the other possibility, where a 4-bit data interface is connected? In this second case there may be indeterminate data on the lower four bits, especially if those pins have not been grounded as recommended. The answer is that the controller has been set up to ignore those lower four bits throughout the early part of the initialization process, until the actual interface has been established by what I called the 'real' Function Set instruction in the previous paragraph. It is important to make sure that the LCD controller has finished executing an instruction before sending it another one, otherwise the second instruction will be ignored. The datasheets give specific times for the delays during the beginning what I call the 'reset' sequence. The datasheets are ambiquious when it comes to the time delay associated with the end of this sequence and with the mode change in the 4-bit initialization. For the final sequence of instructions the datasheets all specify that you must either check the busy flag to see if the LCD

51 controller is finished or wait a sufficient amount of time, a time that is longer than the instruction execution time. Below you will find a detailed explanation of the 8-bit initialization sequence followed by a detailed explanation of the 4-bit initialization sequence Bit Interface, Initialization by Instruction Here's the flowchart as it appears in the Hitachi datasheet.

52 Bit Interface, Initialization by Instruction Here's the flowchart as it appears in the Hitachi datasheet.

53 2.7.8 LCD instruction set

54 2.7.9 LCD connection This depends on number of lines used which is usually four or eight. There is 4-bit LCD mode and 8-bit LCD mode. 4 bit LCD mode uses D4-D7 while 8 bit LCD mode uses data pins D0D7.

55 CHAPTER 3: DESIGN AND IMPLEMENTATION 3.1 Introduction This chapter seeks to explain in depth the process used in the implementation and operation of the power quality monitoring unit which is PIC-microcontroller based. In this chapter the various project segments or breakdowns shall be discussed. The segments are: Hardware section Software section The following flow chart below depicts the sequence of events used in the implementation of the power quality monitoring unit and power factor measuring system.

56 3.2 Hardware section LCD The LCD used uses alphanumeric dot matrix. It is used to display a wide range of characters and Numeric values. The display is on LM016L as seen on the circuit diagram. The LM016L displays sixteen characters on two lines thus the 16 x 2 display. Each character is 8 x 6 pixels making 80 x 16 pixels. The LCD pins are divided into Command pins (RS, E and RW) and data pins (D0-D7). For this project the 4 bit initialization was used instead of the 8 bit initialization. Data pins D4 D7 used and E was enabled. A variable resistor is used to control the LCD brightness. RW is set at 0 thus setting the LCD at write mode.

57 3.2.2 Operational Amplifier The LM358N was used to amplify the generated signal. This is because the signal produced is small and in order to use falling edge as an interrupt detectable. LM358 is a type of operational amplifier that consists of two independent, high gain, frequency compensated operational amplifier designed to operate from a single supply over a wide range of voltages. Operation from split power supplies is also possible and low power supply current drain is independent of the magnitude of the power supply. Application areas include transducer amplifiers, dc gain blocks and all the conventional op-amp circuits which can be easily implemented in single power supply systems. It features: Low power drain. A common mode input voltage range extending to ground/vee Single supply or split supply operation Compatible pinouts They operate at at supply voltages as low as 3.0V or as high as 32V. the common mode input range includes the negative supply thereby eliminating the necessity for external biasing components in many applications. The output voltage range also includes the negative power supply voltage.

58 3.2.4 Power Supply The figure below shows the circuit used to implement the stepping down of 240v(AC) to 5V (DC).The circuit used in supplying the 5 volts was not used due to the cumulative expensive cost of all the components. Instead alternative and cheaper means of providing a constant supply of 5v(dc) was used. A mobile phone charger was used in this case.

59 3.2.5 Zero Crossing Detection To measure the time difference between the voltage and current signals it was needed to get the zero-crossing detection of the two signals. From there the time difference between these two signals was obtained. There are many ways to detect the zero point of the signals, but as we are using PIC micro-controllers we can use the advantage of the micro-controller itself. The micro-controller has a input voltage protection itself, but we can ensure that limit using a Zener diode across the pins those are used to take the signals. The sine wave was rectified by diode (1N4007) and then the signal is fed to the interrupt pin (RB0/INT0; pin # 33) of the micro-controller (PIC16F690). The supply voltage is much more than 5V, but as that voltage is not directly but through a series resistor (R1-100K) and a protection Zener diode so the MCU will get just a clipped 5V signal at its pin. The voltage signal is clipped by the Zener diode and being feed to the micro-controller interrupt pin so that the signal can be used as a falling edge interrupt. The current signal is also converter in to this type of falling edge signal by adding some extra circuitry. As the CT(Current Transformer) generates only a small signal so we need to amplify this signal to a level so that we can use the falling edge as the interrupt detectable. current zero crossing detection circuit

60 voltage zero crossing detection circuit Using the hardware interrupt facilities of the micro-controller and the two signals (voltage and current) were fed and ran. A timer interrupt was used in between these two signals. A timer was started while MCU gets an interrupt signal [hardware interrupt, falling edge]in INT0 [PIN#33] and stop the timer while MCU gets an interrupt signal [hardware interrupt, falling edge] in INT1 [PIN# 34]. In between Timer1 module is used to count a variable. Timer1 interrupt of 10uS timing was used. And counting a variable each time the timer overflows. The variable value is obtained. And from that value the time difference was obtained. At least 200 data was taken and average of these 200 data calculated for accuracy. Multiplying the time difference by (pie) gives the phase difference between current and voltage signals. The cosine inverse of the phase angle gave the power factor. 3.3 Programming Programmer PICKIT2 was used to load the code PIC16F690. The code was written using MPLABX IDE and MIKROC PRO.

61 CHAPTER 4: Results and Analysis The simulation and practical results are displayed in this chapter. 4.2 Simulation results The following table shows the simulation results after the circuit was schemated in the proteus software and loaded with the hex file of the written code. With no supply no power factor was displayed. Supplying the power and adjusting the phase angle gave several results that were saved and displayed in the table below

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63 NO PHASE EXPECTED SIMULATED RESULTS ANGLE POWER SETTING FACTOR

64 CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusion The project was to develop a power quality monitoring unit using PIC16F690 that monitored the power factor and also recorded the frequency and amplitude of a single phase outlet. The experiment objectives were met a seen from the results both simulated and practical. The resulting circuit was constructed and found to be lighter and portable due to the use of the PIC. It wasn t possible to tell whether the power factor found was leading or lagging therefore no comment could be made on the type of load present. There were challenges when it came to the programming but thanks to the supervisor Prof. E Mwangi the required hex code required was generated.