Implementation of Multiquadrant D.C. Drive Using Microcontroller

Transcription

1 Implementation of Multiquadrant D.C. Drive Using Microcontroller Author Seema Telang M.Tech. (IV Sem.) Department of Electrical Engineering Shri Ramdeobaba College of Engineering and Management Abstract The goal of this work is to design and implement D.C drive using PWM technique. The speed control of DC motor is very essential in application where precision and protection is necessary. In this paper implementation of PWM is done with the help of microcontroller for the speed control of DC motor fed by a DC chopper. The chopper is driven at a frequency of 20KHZ controlling the PWM duty cycle is equivalent to controlling the motor speed. This chopper circuit used here is 4 quadrants for the rotation of motor in forward and reverse direction. Keywords:- PMDC motor, speed control, PWM, 4Q chopper. I.INTRODUCTION The purpose of the project is to implement a simple and cost effective process to control the speed of DC motors using the most popular technique four-quadrant chopper method. Here four quadrant choppers are used for obtaining the variable dc voltage to the armature of the dc motor from fixed input dc voltage. With this four quadrant chopper we are able to drive the motor in forward and reverse mode and also we can apply braking in both these modes. The main objective of the project is to develop a speed control system for DC motor using four-quadrant chopper. Using four-quadrant chopper it is possible to demonstrate forward & reverse motoring and braking.dc motors still find a wide range of use in various field where controlling of speed is the foremost requirement. Their fields of application are as follows:-for driving constant speed line, for traction work, for intermittent high torque loads. In earlier times mainly rheostatic control was in practice for controlling the speed of dc motor. But this method has many disadvantages such as heat loss smooth speed control is not possible also regenerative action is also not possible. DC series motor has been the most used solution for the traction of locomotives, trolleybuses, trams and others, characterized by a speed and torque control using additional resistances, which means a low efficiency, electromechanical contactors, high maintenance costs, dynamic braking in resistances. In this paper a novel 4 quadrant full control for DC series motor drive is presented. A prototype was designed using IGBTs. Modes of operation Fig. shows the circuit connection analysis of the Seema Telang IJMEIT Volume 2 Issue 12 December 2014 Page 917

2 proposed drive during the different four quadrant operation modes. The two forward modes (i.e. motoring & regeneration) are obtained if the duty cycle D>50% as the average voltage seen by the field-armature combination is positive; hence the armature current is positive. The other two reverse modes are obtained if D<50% since the average voltage is negative and so is the armature current. In all four modes, the field current is always positive due to the action of the 4-diode bridge rectifier. From figure (2a) it can be seen that supply voltage and current are positive and also field and armature currents are positive. Therefore, the electrical power is transferred from the supply to the motor electrical power in the field and mechanical developed output power from the armature. In figure (2b), I a and I f are positive, hence the torque is in forward direction, while V s is positive and I s is negative, hence the energy is regenerated back to the supply. Same analysis can be seen from figures (2c) and (2d) but since I a is negative direction. II.RELATED WORKS The relevant information about project report is explained in various technical books, research papers which we have referred. Choppers have been classified into five types as Class A, Class B, Class C, Class D and Class E. Class E chopper is a four quadrant chopper. The detail chopper operation, control strategies are presented and the operation of four quadrant chopper in all four quadrants i.e. forward motoring in first quadrant, forward braking in second quadrant, reverse motoring in third quadrant and reverse braking in fourth quadrant. Different types of control strategies i.e. time ratio control and current limit control is studied. Among these PWM method is best suited. Hence, it is being implemented in our project. The description of various ICs such as voltage regulator IC 7805 and, opto-coupler IC 6N137 presented, in our project, we require pulse generation, constant voltage, and electrical isolation. The configurations of these ICs have been included briefly in this project report. The ATmega8L is a low power CMOS 8 bit microcontroller based on the AVR RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega8 achieves throughout approaching 1MIPS per MHz, allowing the system designed to optimize power consumption versus processing speed. III. METHODOLOGY Hardware Design As per the advantages of Armature voltage control as discussed in chapter 4 we are going for Armature voltage control. Also the primitive methods which were used earlier had some disadvantages as per the energy scenario is concerned. The following block diagram gives the complete overview of the project of microcontroller based speed control of a dc motor, and also varying the direction of rotation by utilizing the The ATmega8 is a low-power CMOS 8-bit microcontroller based on the AVR RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega8 achieves throughputs approaching 1 MIPS per MHz, allowing the system designed to optimize power consumption versus processing speed. The AVR core combines a rich instruction set with 32 general purpose working registers. All the Seema Telang IJMEIT Volume 2 Issue 12 December 2014 Page 918

3 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers. The device is manufactured using Atmel s high density nonvolatile memory technology. The Flash Program memory can be reprogrammed.in-system through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-chip boot program running on the AVR core. The boot program can use any interface to download the application program in the Application Flash memory. Software in the Boot Flash Section will continue to run while the Application Flash Section is updated, providing true Read-While- Write operation. By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic chip, the Atmel ATmega8 is a powerful microcontroller that provides a highlyflexible and cost-effective solution to many embedded control applications.the ATmega8 AVR is supported with a full suite of program and system development tools, including C compilers, macro assemblers, program debugger/simulators, In-Circuit Emulators, and evaluation kits. Pin Configuration of ATmega8L Software Design The complete design of software programming is given in the flow chart. START Stack initialise SP Set data directions DDRB, DDRC, DDRD= portb=0, portc=0, portd=0 Timer configuration prescaling, compare value ADC configuration FEATURES 1. 8K bytes of In-System Programmable Flash with Read-While-Write capabilities bytes of EEPROM, 1K byte of SRAM general purpose I/O lines general purpose working registers. 5. Three flexible Timer/Counters with compare modes. 6. Internal and external interrupts. 7. A serial programmable USART. 8. a byte oriented Two-wire Serial Interface. Key scan ADC input If Times out =ADC If Time compare = Time period STOP Run Seema Telang IJMEIT Volume 2 Issue 12 December 2014 Page 919

4 The Idle mode stops the CPU while allowing the SRAM, Timer/Counters, SPI port, and interrupt system to continue functioning. ii. The Power down mode saves the register contents but freezes the Oscillator, disabling all other chip functions until the next Interrupt or Hardware Reset. iii. In Power-save mode, the asynchronous timer continues to run, allowing the user to maintain a timer base while the rest of the device is sleeping. iv. The ADC Noise Reduction mode stops the CPU and all I/O modules except asynchronous timer and ADC, to minimize switching noise during ADC conversions. v.in Standby mode, the crystal/resonator Oscillator is running while the rest of the device is sleeping. This allows very fast start-up combined with low-power consumption. Scheme Applied To H-Bridge Figure showing PWM waves. IV.RESULT & DISCUSSION The most important feature of the project is its satisfactory performance with simple control strategy and circuitry. Hardware that has been used in this project for this drive is very less. The operation of the project has been described in detail. Complete process & component information with ratings of various components has also been provided. In this project speed control of dc motor using four quadrant chopper the ATmega8L microcontroller is used for its special features such as thee flexible timer counter with compare modes, programmable timer with internal oscillator, six channel ADC with 10 bit accuracy. Therefore high speed of operation of about 25 khz is obtained. Also the power consumed by the circuit is very low i.e. about 5 to 10 watts. Also, LED.s has been used which gives the indication of direction i.e. forward or reverse, run, stop, power on, ramp start. Thus, our main aim of economical speed control of dc motor is achieved by controlling the switching of IGBT using microcontroller. In this project, speed can be controlled in both directions but only below the base speed. This is because we are using the armature voltage control only and not the field control In this project armature is excited by a variable dc supply obtained from four-quadrant chopper. The system is provided with various control keys, such as start, stop, reverse motoring, reverse brake, forward motoring, forward brake, increment and decrement. Using these keys, the user can set the motor to run in any one of the following modes, namely forward motoring, reverse motoring, forward braking and reverse braking. The speed can be varied by varying the voltage given to the pwm converter (using keypad). Pfacility i.e., starting the motor without allowing the armature current to exceed the full load current, The Hardware of this system includes uncontrolled rectifier using diodes, chopper using IGBT S, control keys, speed adjust potentiometer and other logical circuits. The microcontroller based control scheme has been developed for the control of dc drives. Experimental results have been obtained and discussed in the result section. It can be concluded that the present control scheme is reliable, flexible and easy to use for any size and type of motor. Thus, it can also be used for protection and power cut off system. V.FUTURE SCOPE In future further modification can be made like instead of using a 8 bit microcontroller we can use higher bit microcontrollers like 16 bit or 32 bit to obtain more smooth speed control. Also by Seema Telang IJMEIT Volume 2 Issue 12 December 2014 Page 920

5 exciting the field separately speed above the base speed can be achieved. By controlling the excitation we can control the speed above the base speed also. By increasing the excitation of the field i.e. by making the field voltage greater than the supply voltage regenerative action can be employed. This will result in further saving of energy. REFERENCES 1) Mohammad H. Rashid, Power Electronics circuits, devices and applications, Prentice Hall Publication, Second Edition, 2003, pp ) Vedam Subramanian, Power Electronics, New Edge International Publication, Third Edition, 1998, pp ) M. S. Berde, Thyristor Engineering, Khanna publication, Eighth Edition, 2006, pp ) Dr. P.S. Bimbhra, Power Electronics, Khanna Publications, New Delhi, 2010, pp ) Ramakanth A. Gaikwad, Op-Amps and Linear Integrated Circuits, Prentice- Hall Publication, Fourth Edition, 2003, pp , ) Thomas L. Floyd and R. P. Jain, Digital Fundamentals, Pearson Publication, Eigth Edition, 2009, pp , ) Deodatta Shingare, Industrial and Power Electronics, Electrotech Publication, Fourth Edition, pp ) V.R. Murthy, Power Electronics, Oxford University Press, Fifth Edition, 2005, pp ) Floyd, Electronics Devices and Circuits, Pearson Education, Ninth Edition 2008, pp ) A. Ahmad, Power Electronics for Technology, Pearson Education, Fourth Edition 2003, pp ) alldatasheet4u.com for various components datasheet 12) file://localhost/j:/tutorial+- +Getting+Started+with+PCB+Design.htm 13) for pcb design software Seema Telang IJMEIT Volume 2 Issue 12 December 2014 Page 921