Hardware Design and Implementation of Unity Power Factor Rectifiers using Microcontrollers BIDYUT MAHATO Dept of Electrical Engineering Research Scholar, ISM Dhanbad
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P.R.THAKURA Dept of Electrical & Electronics Associate Professor, BIT Mesra
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Abstract – In this work, a hardware design of phase controlled rectifier has been implemented in an economical manner in power electronics laboratory using microcontroller. Various observations are recorded in this field in centuries but introducing microcontroller in this arena would be a new phase in this field of research, thus making the process more precise with faster response. Microcontroller is used to generate gate pulses to SCR. Zero Crossing Detector is employed for synchronizing the input with firing pulses in order to have controlled DC output. Detailed description and functioning of individual blocks is explained with the relevant waveforms. All waveforms obtained from 200MHz DSO at different stages are included along with the output waveforms obtained on PSIM Software. Phase controlled rectifiers are better than uncontrolled rectifier in the aspect of harmonics generated as well as controlled DC output. Key Words- Zero Crossing Detector, Rectifiers, Operational Amplifiers, SCR, Microcontroller, Unity Power Factor, Opto-Isolator
I. INTRODUCTION Power electronics is a branch of Electrical Engineering which deals with control conversion and protection of power using high power semi-conductor switches. It process the power from source to the load. Every device needs suitable power for its working [1]-[5]. Power electronics prepares suitable power for each device. Designing firing circuit is a most challenging task in laboratory because of the fact that firing has to start from Zero of input which has to be sensed by zero crossing detector (ZCD)[6]-[8]. SCR ranges from few kilowatts to several megawatts in terms of power and from few hundred to several kilo volts levels in terms of voltage level, thus traditionally used as a switching device in medium and large power levels. MOSFET’S and BJT’S having very fast switching frequency compared to SCR’S are being limited to their uses to
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K.C.JANA Dept of Electrical Engineering Assistant Professor,ISM Dhanbad
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medium power levels at few hundred volts[9]-[11]. Though IGBT’S have more due advantages over MOSFET’S & SCR’S being inability to work at very high voltages and costlier makes SCR’S to be a better choice even today. OVERVIEW OF PAPER This paper is introduced with the working principle and operation of SCR in Section II and design of firing circuit in section III. Simulation results in PSIM platform has been shown in section IV along with hardware results. Results are discussed in section V and is concluded in section VI along with references. II. PRINCIPLE AND OPERATION A Silicon controlled rectifier is a layered solid current controlling device, it is also well known as THYRISTOR. Firing angle α is stated as the number of degrees from the beginning of cycle when SCR is gated. Conduction angle is defined as the number of degrees that SCR’S remain conducting.
Fig. 1. Waveform of single phase converter.
This bridge rectifier have four thyristors. T1, T2, T3, T4 . During positive half cycle of sine wave, TI and T2
are forward biased and T3 and T4 are reversed biased. During negative half cycle of input supply, T3 and T4 are forward biased and T1 and T2 are reversed biased. Hence, the gate pulses should be properly synchronized with a.c power supply.[12].
Fig. 3. Experimental waveform of ZCD Output and input supply voltage.
Microcontroller sense this signal as interrupt and executes the programme and provides the pulses which is further fed to the gate of the thyristors. Zero Crossing Detector is employed for the synchronization of input with firing pulses so as to have controlled DC output[16]. Fig. 2. Block diagram representation of the proposed converter.
The proposed system is represented in two different blocks namely Power circuit and Control circuit represented by dotted lines. In the power circuit, input supply is fed to the rectifier block where thyristors have been used and finally the controlled DC output is fed to the load. In control circuit zero crossing detector (ZCD), Microcontroller, Opto-Isolator plays a vital role. Op-Amp is used as zero crossing detector that senses the Zero crossing of input and providing signal to the microcontroller through input pins. Zero Crossing Detector is employed for the synchronization of input with firing pulses so as to have controlled DC output.[11][12]. The synchronized output pulses from the microcontroller fed to the TLP250 for high voltage isolation. Here, grounding is the other aspect of this hardware and thus TLP250 is employed for novel reason. TLP250 needs DC supply which is provided by isolated grounding transformer (230/12V) described in further section. Finally the pulses fed to the thyristor[13][14].
B. TLP250 as Opto-Isolator TLP250 is used as high voltage isolation also well known as Opto-Isolator. It provides isolation between power circuit and control circuit thus providing gate pulses to the respective thyristors. It has Input threshold current of magnitude 5mA(max.), Supply current of magnitude 11mA(max.), Supply voltage of magnitude 10−35V, Output current in the range of ±1.5A (max), Switching time 1.5μs(max), Isolation voltage of magnitude 2500 Vrms(min)[15]. C. DC Supply used for TLP250 Isolated power supply of 12V, 5mA, having six output tapping has been used as shown in Fig.4 below to provide DC supply for Opto-Isolator.
III. DESIGN OF FIRING CIRCUIT A. Op-Amp as ZCD An operational amplifier is a multistage, negative feedback amplifier with very high gain[5][6]. It uses voltage shunt feedback to provide a stabilized voltage gain. It senses the Zero of crossing of input and provides pulses signal to the microcontroller
Fig. 4. Multi-winding transformer used for TLP250
D. Microcontroller Arduino is an open-source electronics platform based on its flexiblity, easy-to-use hardware as well as software. The code is written in a suitable programming language to generate pulses. In this coding, two pulses being generated after being receiving the signal from Zero Crossing Detector (ZCD) as interrupt. Two generated pulses are 180 phase shift from each other. These pulses are then fed to gate of the thyristors. The features of an Atmel ATmega328 microcontroller with 2 Kb of RAM operating at 5 V, flash memory of 32 Kb for storing programs and 1 Kb of EEPROM for parameter storage. The clock speed is 16 MHz, that translates about executing 300,000 lines of C source code per second. The board has 6 analog input pins 14 digital I/O pins. There is a USB connector and a DC power jack for connecting an external power source.
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(c) Fig . 5. Pulses generated being 1800 phase shifted.
IV. SIMULATION AND HARDWARE RESULTS
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Fig. 6. Simulation results of (a) Synchronized gate pulses to the supply, output voltage and current waveform (a) at α=00 (c) at α=300
A. HARDWARE RESULTS IN OSCILLOSCOPE
Fig. 7. Hardware setup of thyristor controlled rectifier in Power Electronics Laboratory
V . RESULT AND DISCUSSIONS In simulation results, single phase controlled rectifier has been has been done in PSIM Software and load voltage and current is shown at α=0 0 and α=300.The hardware set up shown in Fig.7, comprises of TLP250 circuit used as opto-isolator. ZCD (Zero Crossing Detector) is used for synchronizing the input with firing pulses. Microcontroller is used for providing 1800 shifted pulses to SCR’s dc supply for providing supply to TLP Circuit. Fig. 8a) shows the output voltage with input sinusoidal voltage whereas fig.7b) and fig. 7c) indicates the variation of output voltage with variation of firing pulses provided from the microcontroller after detecting the Zero Crossing of input Sinusoidal wave.
(a)
VI. CONCLUSION Designing analog firing circuit makes circuit complex and requires maintenance. Employing microcontroller instead reduces all its disadvantages being economical. It is easier to design with precision output. It can be used for single phase and three phase fully controlled thyristor rectifier. The paper provides a design for a simple microcontroller based SCR Controlled Unity Power Factor Rectifiers. The design is adequate for many purposes. These improvements have been tested in principle, but some detailed work remains to be done in this area for three phase Supply. VII. REFERENCES (b)
[1] [2] [3] [4]
[5] [6] [7]
[8]
(c) Fig. 8. Experimental results of input voltage and output voltage across R-Load at (a) α=00 (b) α=1000 (c) α=1500
[9]
B.K.Bose, “Modern power electronics and AC Drives”, PHI,2001 . P.C.Sen, “Power Electronics”, Tata McGraw Hill Publishers, 4 th edition, 1987. N.Mohan, T.M.Undeland, W.P.Robbins, “Power Electronics: Converters application and Design”, New York: Wiley, 3 rd edition, 2006. Mohammed E. El-Hawary, “Principles of Electric Machines with Power Electronic Applications”, Wiley India, 2nd edition, 2011. Gayakwad, “Operational Amplifier”, Prentice Hall of India, 2009. General Electric, D.R. Grafham and F.B. Golden, SCR Manual, 6th ed. Englewood Cliffs, NJ: Prentice Hall, 1982. B.K.Bose, “Power Electronics- a technological Review”, Proceedings of the IEEE, Vol.80 pp13031334, Aug 1992. B.K.Bose, “Recent advances and trends in power electronics and drives”, proceedings of NORPIE workshop, Helsinki, pp. 170-182,1998. Mukesh Gupta, Sachin Kumar and Vagicharla Karthik
“Design and Implementation of cosine control firing scheme for single phase fully controlled bridge rectifier”, International Journal of Emerging
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[16]
Trends in Electrical and Electronics, Vol.3, Issue 1 May 2013. Tirtharaj Sen, Pijush kanti Bhattacharjee and Manjima Bhattacharya,“Design and Implementation of Firing Circuit for single phase Converter,” International Journal of Computer and Electrical Engineering, Vol 3,pp 368-374, June 2011. S. B. Dewan and W. G. Dunford, "A microprocessor-based controller for a three phase controlled rectifier bridge," IEEE Trans. Ind. App., vol. LA-19, pp. 113-119, Jan./Feb. 1983. P. C. Tang, S. S. Lu, and Y. C. Wu, "Microprocessor-based design of a firing circuit for three-phase full-wave thyristor dual converter," IEEE Trans. Ind. Electron., vol. IE-29, pp. 67-73, Feb. 1982. J. S. Wade, Jr., and L. G. Aya, "Design for simultaneous pulse triggering of SCRs in three phase bridge configuration," IEEE Trans. Ind. Electron. Contr. Instrum., vol. IECI- 18, no. 3, pp. 104-106, 1971. B. Ilango, R. Krishman, R. Subramanian, and S. Sadasivam, "Firing circuit for three-phase thyristorbridge rectifier," IEEE Trans. Id. Electron. Contr. Instrum., vol. IECI-25, no. 1, pp. 45-49, 1978. L. H. Hoang, "A digitally controlled thyristor trigger circuit," Proc. IEEE, vol. 66, no. 1, pp. 8991, Jan. 1978. T.Izumi, M.Yamazoe, and T. Nakano, "A microprocessor-based control system of thyristor converter fed dc motor drives," IECI '79 Proc., Mar. 1979.
K.C.Jana received his M.Tech and Ph.D degree from NIT Durgapur and Jadavpur University in 2003 and 2013 respectively. He is currently serving as Assistant Professor in Indian School of Mines, Dhanbad from June 2012. He has been working in Birla Institute of Technology, Mesra from July 2003 till May 2012. His research is in area of Modelling and Design of Multilevel Inverter , Real-time control of power electronics devices, Design and Implementation of efficient power converters. Dr. Jana visited the Power electronics and Drives lab of CEDT (IISC, Bangalore) in July 2006, visited Chittaranjan Locomotive Works (CLW), West Bengal for study of different Power Electronics Application on Indian Railways in October 2008, visited Chittaranjan Locomotive Works (CLW) in August 2010, visited Chittaranjan Locomotive Works (CLW) West Bengal for industry collaboration in August 2010, visited VSSC, Trivundrum and IIST Trivundrum for study of different application of control, navigation and guidance of Launch vehicle in January 2011.
B.Mahato received his M.E and B.Tech degree from Birla Institute of Technology, Mesra, Ranchi and Guru Nanak Institute of Technology
VIII. BIOGRAPHIES P.R.Thakura received his Ph.D degree from BIT Mesra, Ranchi and BITS Pilani in 2008 and 1990 respectively. He has been working in BITS Pilani from 1987 to 1994. He joined BIT, Mesra in May 1994and is currently serving as associate professor in Dept of Electrical and Electronics Engg. He is working for Eramus Mundus Programme from September 2009. He was winner of Indo-Italian Young Researchers Fellowship and worked in Hybrid Electric Vehicle in University of Padova, Italy from September 2006 to August 2007. He has more than 30 international and national papers guided more than 70 UG projects and has reviewed many books on power electronics by M.D.Singh and K.B.Khanchandani in July 2013. His research interest include Power Electronics, Variable speed drives, high performance AC Drives, Hybrid Electric Vehicles. Dr. Thakura is permanent member of Indian Society of Technical Education, Delhi and Institution of Engineers, Kolkata.
in 2014 and 2011 respectively. Since 2014, he has been working toward the Ph.D degree in the Indian School of Mines, Dhanbad in the department of Electrical Engineering in the field of Power Electronics. His main research interest includes Phase controlled rectifiers, Multilevel inverters, AC Drives and Hybrid Electric Vehicles.
