International Journal of Engineering Research and Development
e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com
Volume 9...
Development of a MPPT-based Single Phase PWM Solar String Inverter…

Fig.2 (a) Flow chart of hill climbing method and (b) ...
Development of a MPPT-based Single Phase PWM Solar String Inverter…

Fig. 4 Full bridge single phase inverter
The full bri...
Development of a MPPT-based Single Phase PWM Solar String Inverter…

Fig.8 Schematic diagram for inverter circuit

III.

F...
Development of a MPPT-based Single Phase PWM Solar String Inverter…
based systems provide huge computational capability an...
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International Journal of Engineering Research and Development (IJERD)

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International Journal of Engineering Research and Development (IJERD)

  1. 1. International Journal of Engineering Research and Development e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com Volume 9, Issue 4 (December 2013), PP. 25-29 Development of a MPPT-based Single Phase PWM Solar String Inverter for AC output for off grid applications Manisha R. Kandgaonkar1, N.N.Shinde2, P.S.Patil3 1 Department of Energy Technology, Shivaji University, Kolhapur,.Maharashtra, India. Department of Energy Technology, Shivaji University, Kolhapur, Maharashtra, India. 2,3 Abstract: A microcontroller based technique of generating a sine wave from the solar panel output is designed and implemented in this paper using a two-stage topology for a solar string inverter. This paper presents the development of a maximum power point tracking (MPPT) and control circuit for a single phase inverter using a pulse width modulation (PWM) IC. The attractiveness of this configuration is the elimination of a complex circuitry to generate oscillation pulses for transistor switches. The controller IC TL494 is able to generate the necessary waveforms to control the frequency of inverter through proper use of switching pulse. The DC to AC inversion is successfully achieved alongside the switching signals; the circuit produced inverter output of frequency nearly 50 Hz. The main objective of the proposed technique is to design a low cost, low harmonics voltage source inverter essentially focused upon low power electronic appliances using variable solar power as inputs. Keywords: AC solar panels, DC-AC converters, MPPT charge controllers, PWM inverters, solar string inverters. I. INTRODUCTION a) Maximum Power Point Tracking (MPPT) When a solar PV module is used in a system, its operating point is decided by the load to which it is connected. Also, since solar radiation falling on a PV module varies throughout the day, the operating point of the module also changes throughout the day. Ideally under all operating conditions, one would like to transfer maximum power from a PV module to the load. In order to ensure the operation of PV modules for maximum power transfer, a special method called Maximum Power Point Tracking (MPPT) is employed in PV systems where, electronic circuitry is used to ensure that maximum amount of generated power is transferred to the load. The maximum power point tracking mechanism makes use of an algorithm and an electronic circuitry. The mechanism is based on the principle of impedance matching between load and PV module which is necessary for maximum power transfer. This impedance matching is done by using a DC to DC converter by changing the duty cycle (d) of the switch. Fig.1 Block diagram of the MPPT algorithm along with the circuit. 25
  2. 2. Development of a MPPT-based Single Phase PWM Solar String Inverter… Fig.2 (a) Flow chart of hill climbing method and (b) schematic diagram demonstrating how the operating point moves towards the maximum power point(MPP) The power from the solar module is calculated by measuring the voltage and the current. This power is an input to the algorithm, which then adjusts the duty cycle of the switch, resulting in the adjustment of reflected load impedance according to the power output of PV module. For instance, the relation between the input voltage (Vi) and the output voltage (Vo) and impedance of load (RL) reflected at the input side (Ri) of a buck type DC to DC converter can be given as: Vo = Vi x d 𝑅𝐿 Ri = 𝑑2 Where d is the duty cycle. By adjusting the duty cycle, Ri can be varied which should be same as the impedance of solar PV module (RPV) in a given operating condition for maximum power transfer [15,16]. b) Inverter: A power inverter, is an electrical power converter that changes direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching and control circuits. In an inverter, dc power from the PV array is inverted to ac power via a set of solid state switches—MOSFETs or IGBTs—that essentially flip the dc power back and forth, creating ac power. Fig.3 shows basic H-bridge operation in a single-phase inverter. This solid state switching process is known as inversion [6]. Fig.3 An H-bridge circuit performs the basic conversion from dc to ac power. The inverter will receive input of 12 V dc from the controller circuit and it will convert this to 230 V ac. The inverter circuit designed as an H bridge inverter with an IC which incorporates PWM technique and converts, with the help of a 12V/230 V transformer, the obtained 12V dc from MPPT circuit, to the output 230V ac for use. 26
  3. 3. Development of a MPPT-based Single Phase PWM Solar String Inverter… Fig. 4 Full bridge single phase inverter The full bridge (single phase) inverter is built from two half bridges connected to form what is known as a full bridge or H-bridge inverter. Its arrangement is shown in figure 4. It comprises of DC voltage source, 4 power switches (usually bipolar junction transistors-BJTs, metal-oxide semiconductor field effect transistors-MOSFETs, insulated gate bipolar transistors- IGBTs or gate turned on transistors-GTOs) and the load. To create a square-wave output voltage, the device pairs Q1Q3 and Q2Q4 are switched alternatively at a delay of 180 degrees. When Q1 and Q3 are ON with Q2Q4 OFF for a duration t, also with Q2Q4 ON and Q1Q3 OFF at t. Assuming there is a sinusoidal load current, the load will absorb power when Q1Q3 and Q2Q4 pairs are conducting alternatively whereas feed backing occurs when the diode pairs are conducting[22]. II. APPROACH AND METHOD The block diagram for the circuit is as shown. Fig.5 Block diagram for a solar power system MPPT Circuit: The next step is to design and test the MPPT circuit. The voltage and the current output from the panel array have to be measured and the maximum power has to be supplied to the battery. +5V BAT_V U4 +5V LCD1 LCD 16x2 2 R12 3 C4 100uF/25V C22 0.1uF R1 100K R14 C5 0.1uF LCD_RS BATV 1k R13 1K 22K LCD_EN C9 0.1uF LCD_D4 LCD_D5 LCD_D6 LCD_D7 +5V C10 3 C13 0.1uF 2 R25 +5V 0.1uF 8 R24 1K + R42 33E B_C 1 - 1 2 3 4 5 4 R26 +5V J10 CON1 J12 CON1 J13 CON1 J14 CON1 RESET +5V PGD PGC PROG J39 CON2 100K R3 10K D1 1N4148 1 2 R4 Solar_V 1K R9 RESET SW1 SW PUSHBUTTON GND Vcc CNT RS RW EN D0 D1 D2 D3 D4 D5 D6 D7 A C J11 U3A LM358 1K +5V 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 VOUT C2 0.1uF 1 VIN LM7805/TO C1 100uF/25V 1 1 10A FUSE 1 2 BAT 1 BAT_V F1 GND BAT+ J4 100K R11 C25 0.1uF Solar_ADC R10 1K Y1 8MHz XTAL2 22K XTAL1 C23 33PF C8 C24 33PF 0.1uF LOAD+ R43 100K R45 BAT_V Load_ADC U7 Q2 D3 IRF9530 R44 1K 1N5822 D4 RESET BATV B_C Solar_ADC C30 22K D6 0.1uF 1N5408 Solar_V 1N5822 J2 +5V 2 1 SOLAR R19 C12 D5 1000uF/25V 47K R20 10E Q4 R21 BC547 1N5408 R22 R23 XTAL1 XTAL2 PIN8 C_CNTRL LOAD_CNTRL R8 4K7 C_CNTRL 1K 3K3 J6 BAT_V LOAD+ IRF9530 R31 PGD PGC LCD_RS LCD_EN LCD_D4 LCD_D5 LCD_D6 LCD_D7 +5V J9 RX TX C17 0.1uF 1 2 3 4 +5V RX TX CON4 R28 1K CON2 J5 2 1 LED 1 2 J3 1N4148 47K 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 1K D7 R15 MCLR/VPP/RE3 RB7/KB13/PGD RA0/ANO RB6/KB12/PGC RA1/AN1 RB5/KB11/PGM RA2/AN2/VREF-/CVREF RB4/KB10/AN11 RA3/AN3/VREF+ RB3/AN9/CCP2 RA4/TOCKI/C1OUT RB2/INT2/AN8 RA5/AN4SS/HLVDIN/C2OUT RB1/INT1/AN10 RE0/RD/AN5 RB0/INT0/FLT0/AN12 RE1/WR/AN6 VDD RE2/CS/AN7 VSS VDD RD7/PSP7/P1D VSS RD6/PSP6/P16 OSC1/CLKI/RA7 RD5/PSP5/P1B OSC2/CLKO/RA6 RD4/PSP4 RCO/T1OSO/T13CKI RC7/RX/DT RC1/T1OSI/CCP2 RC6/TX/CK RC2/CCP1/P1A RC5/SDO RC3/SCK/SCL RC4/SDI/SDA RD0/PSP0 RD3/PSP3 RD1/PSP1 RD2/PSP2 1 2 Q1 0.1E/1W 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 C7 1uF CON2 R16 LOAD R30 PIN11 PIN11 1 2 Q3 R17 BC547 R32 1K J7 10E 1K Load_CNTRL CON2 1K R18 3K3 Fig.6 Schematic diagram for MPPT circuit Fig.7 MPPT circuit. Inverter Circuit: Next is the circuit for the inverter part. For the inverter the IC TL494 is used. The four MOSFETs IR740 are arranged in a bridge network and will be switched on two at a time alternately by the two switching MOSFETs IRF50N06 so that two will conduct at a time. The timing is set by using RC network and IC TL494 controls the waveform. The transformer will convert the output to 230 V a.c. 27
  4. 4. Development of a MPPT-based Single Phase PWM Solar String Inverter… Fig.8 Schematic diagram for inverter circuit III. Fig.9 Inverter circuit. TESTING The MPPT and Inverter circuit: The circuit of the MPPT is first tested with the help of a D.C. power supply. It is checked whether the voltage is passed to the battery to charge it. Finding it to work as required, it is then tested with solar panels. The regulator is also checked by varying the d.c. voltage. It shows the expected readings on the display. Fig.10 a. Waveform of inverter output. b .Observation of Output on Hyper terminal. The efficiency of the MPPT circuit is tested and found to be around 80%. It increases with the increase in intensity. The efficiency of the inverter is tested and found to be as much as 90%. It increases with increase in load. IV. RESULTS AND ANALYSIS The time required to charge the battery is tested. This is done first using an SMPS and then with the two solar panels. The efficiencies of the MPPT and inverter circuits are found to be around 90% and 79.9% respectively. V. CONCLUSION The experiments and observations shows that MPPT based charge controllers are best suitable for solar systems as they track the maximum power in case of power fluctuations at the input side due to environmental condition variation. Hence it is recommended to use the MPPT based charge controllers. Use of microcontroller 28
  5. 5. Development of a MPPT-based Single Phase PWM Solar String Inverter… based systems provide huge computational capability and reduction in the hardware. Microcontroller is a mini computer and brings much more accuracy in the control of MOSFET and IGBT. It is recommended to use a single phase PWM inverter with H bridge using IRF740B N-channel MOSFETs and the TL494 power supply controller. The TL494 incorporates all the functions required in the construction of a pulse-width-modulation (PWM) control circuit on a single chip. Designed primarily for powersupply control, this device offers the flexibility to tailor the power-supply control circuitry to a specific application. Several outstanding features of the developed Sinusoidal PWM inverter are: fewer harmonic, low cost, simple and compact. REFERENCES [1]. [2]. [3]. [4]. [5]. [6]. [7]. [8]. [9]. [10]. [11]. [12]. [13]. [14]. [15]. [16]. [17]. [18]. [19]. [20]. [21]. [22]. Ministry of New & Renewable Energy, Government of India, Solar Lighting Systems Module, Trainers Textbook. Dr. B.D.Sharma, Performance Of Solar Power Plants In India- Submitted To Central Electricity Regulatory Commission New Delhi-February, 2011. Deepak Kumar, Solar India and JNNSM, 1st November 2010. International Finance Corporation, World Bank Group, ‘Utility Scale Solar Power Plants’, New Delhi (India), February 2012. Fritz Schimpf, Lars E. Norum- Grid connected Converters for Photovoltaic, State of the Art, Ideas for Improvement of Transformerless Inverters- Norwegian University of Science and Technology, NTNU Department of Electrical Power Engineering. James Worden and Michael Zuercher-Martinson, How Inverters Work, SOLARPRO, April/May, 2009. AN2794 Application note Cd00201961.pdf http://en.wikipedia.org/wiki/Wikipedia: CleanupTaskforce/String Inverter. http://www.greenworldinvester.com / /topics/solar-renewable-energy-greeninvest/solar inverters/ (6th July 2011). Avinash H.N. and Palak Timbadiya, Global Energy National Institute, Overview of sustainable renewable energy potential of India, 2010. Dr. B.R. Gupta, Generation of Electrical Energy, S. Chand & Co. Ltd. New Delhi, Reprint 2010. Prof H.P. Garg and Dr. J Prakash, Solar Energy-Fundamentals and applications, Tata McGraw-Hill Publishing Company Limited, New Delhi, Eleventh Reprint, 2009. Prof. Dr. Andrea Vezzini, BFH Bern, Switzerland, Institute for Energy and Mobility Research. Angelina Tomova, TU Sofia, Grid Connected Pv Inverter Topologies An Overview, 07 April 2011, Glasgow, UK Chetan Singh Solanki, Solar Photo voltaics, PHI Learning Private Limited, July 2011. Sachin Jain and Vivek Agarwal, A Single-Stage Grid Connected Inverter Topology Solar PV Systems With Maximum Power Point Tracking, IEEE Transactions On Power Electronics, Vol. 22, No. 5, September 2007. Søren Bækhøj Kjær, Design and Control of an Inverter for Photovoltaic Applications, Aalborg University, DENMARK Institute of Energy Technology, January 2005. A. A. Mamun, 1, M. F. Elahi M. Quamruzzaman, M. U. Tomal Design and Implementation of Single Phase Inverter International Journal of Science and Research (IJSR), India Online ISSN: 2319-7064 Muhammad H. Rashid, Power Electronics, Circuits Devices and Applications, Third Edition, Published by Dorling Kindersley (India) Pvt. Ltd., licensees of Pearson Education in South Asia. Muhammad Ali Mazidi, Janice Gillispie Mazidi, Rolin D. McKinlay, The 8051 Microcontroller and Embedded Systems, Second Edition, Published by Dorling Kindersley (India) Pvt. Ltd., licensees of Pearson Education in South Asia. Dr. Amiya Kumar Rath, Alok Kumar Jagadev and Santosh Kumar Swain, Computer Fundamentals and C programming, Scitech Publications, (India) Pvt. Ltd. Omokere, E. S and Nwokoye, Evaluating the Performance of a Single Phase PWM Inverter Using 3525A PWM IC, International Journal of Engineering Research & Technology (IJERT), Vol. 1 Issue 4, June – 2012 Author profile: Manisha R. Kandgaonkar 29

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