INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &

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1 INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & International Journal of Electrical Engineering and Technology (IJEET), ISSN (Print), ISSN (Online) TECHNOLOGY Volume 3, (IJEET) Issue 2, July- September (2012), IAEME ISSN (Print) ISSN (Online) Volume 3, Issue 2, July September (2012), pp IAEME: Journal Impact Factor (2012): (Calculated by GISI) IJEET I A E M E ANALYSIS AND DESIGN OF GRID CONNECTED PHOTOVOLTAIC SYSTEM Manoj Kumar [1] Dr. F. Ansari [2] Dr. A. K. Jha [3] Gateway Inst. of Engg. & Tech. BIT Sindri Anupam Group of Industries [1] mk5272@gmail.com ABSTRACT This paper presents the analysis of PV cells of 4 pv panels (of 30 W p each) for the optimum performance with grid connected. The hardware implementation and design shows the performance of the output at the end of primary and secondary of the isolated transformer. The design of grid connected photovoltaic system consists of driver, isolated transformer and ADMC 331 (DSP kit). The measured value shows the practical performance of PV panel output at the end of primary and secondary of isolated transformer. Key words:- PV cells, DSP, Hysteresis, Converter, Attenuation. 1. INTRODUCTION In the current scenario, the consumption of fossil fuel also has an environmental impact, in the form of CO 2 and other hazardous gases in to the atmosphere. In the past recent years, scientist, academician are combine involved in research to reduce the CO 2 by using of application of renewable energy resources technology, which are effectively cost competitive with fossil fuels. Different renewable energy likes solar power, wind power, tidal power, bio-mass, and geothermal are being popularly used for the electricity generation, so that they are quickly become very popular and attractive alternate proposition [1]. From the mid 1950 s to the early 1970 s, solar energy (Photo Voltaic) research and development was directed primarily towards space application and satellite 69

2 power. Then in 1973, a greatly increased level of research and development on solar cells was initiated, which caused wide spread concern regarding energy supply. In 1976, the US department of energy (DOE), along with its photovoltaic s program was created. In 1980, total global PV (solar) cell production increased from less than 10MW p /year but in year 2008 PV cell production increased by 1200MW p /year [3]. The total global PV installed capacity is about 3GW p. The peak watt (W p ) rating is the power (in watts) produced by a solar module illuminated under following standard condition: 1000W/m 2 intensity, 25 o C ambient temperature and a spectrum that relates to sunlight that has appeared through atmosphere when the sun is at a 42 o elevation from the horizon. 2. PV CELLS The development of solar cells are made using crystalline structure using single crystal wafers, polycrystalline wafers or thin films. Single crystal wafers are sliced, from a large single crystal ingot which has been grown at around 1400 o C, which is very expensive process. Solar cell consists of two type of materials, often p-type Si and n-type Si. Light of the certain wavelength is able to ionize the atoms in the silicon and internal field produced by the junction separates some of the positive charges (holes) from the negative charges (electrons) within the photovoltaic device. Although these opposite charges are attracted to each other, most of them can only recombine by passing through an external circuit outside the material because of the internal potential energy barrier. For high power at high voltage a number of solar cells are required to connected in series (for high voltage) and in parallel for high current /power[2]. Many solar cells are interconnected to constitute a solar module or PV module and many modules are interconnected to form a PV panel. Certain protocols of interconnection to be followed for optimum performance of PV module are All the cells to be connected in series should have the same short circuit current and same maximum power point current. All the cells to be connected in parallel should have same open circuit voltage and same maximum power point voltage. This paper presents the hybrid system combines PV system with a backup of battery system for grid connected PV system. 70

3 3. SYSTEM DEVELOPMENT Figure (1) Block diagram of Grid Connected Power System Figure (1) shows the block diagram of grid connected power system which is designed in the practical setup. A 120-Watt PV array is paralleled with a 4700µF input capacitor (Ci) so that the PV array acts as a voltage source[4]. The current sensor CS1 senses the PV array current through Rsense1 while the voltage sensor VS1 senses the PV array voltage across Rsense2. Both voltage and current of PV array are monitored by an ADMC331 DSP and then are controlled in order that the PV array always transfers the maximum power to the system. A two-switch forward converter receives the maximum electrical energy from PV array. A 6.5 turn ratio isolated transformer, a part of the converter, amplifies the input voltage so that the output voltage of the converter is larger than grid voltage. The ADMC331 DSP is again utilized to generate a rectified sinusoidal reference waveform, I ref, the magnitude of I ref correlates with the maximum power transferred from PV array. The current sensor C S2 senses the output inductor current Io through R sense3. Hysteresis controller compares Io with Iref and shapes the output inductor current to match Iref at high switching frequency. This rectified sinusoidal current is finally unfold and transferred to the distribute line by a single phase inverter. 3.1 ADMC331 DSP Board ADMC331, a 16-bit digital signal processor (DSP) manufactured by Analog Devices Inc., U.S.A, is chosen to implement the control algorithm in this paper[6]. This thesis needs only three significant functions of ADMC331; which are a fixed-point ADSP-2171 core processor, analog-to-digital converters, and timers. These three DSP functions perform important roles in controlling the system. Control algorithms are well designed and programmed into the DSP. Figure 2 presents the diagram of control algorithms inside the ADMC331. The DSP receives four measured signals from the system, which are the PV array voltage (V pv ), the PV array current (I pv ), the grid voltage (V grid ), and the zerocrossing signal. The DSP receives the zero-crossing signal through an input/output port, PIO1.6; this signal tells DSP the conditions of the grid voltage. These conditions include the frequency of grid voltage and the grid voltage is a positive signal. The DSP always waits for the first zero-crossing signal, PIO interrupt occurs, and then starts executing the control algorithms. At the beginning of the algorithm, the DSP enables PMWSYNC 71

4 interrupt which allows DSP to sample the analog inputs at the sampling frequency of 25 khz. Three of analog signals (V pv, I pv, and V grid ) are digitalized by ADC and stored in three registers (ADC1, ADC2, and ADCAUX respectively). V pv and I pv are inputted to the maximum power point tracking algorithm (MPPT). MPPT calculates the instance power of the PV array and estimates the magnitude of the reference current (K) that will draw the maximum electrical energy from the PV array and transfer this energy to the converter. V grid is then normalized to be I norm. By multiplying I norm with K, the DSP generates the digitalized reference current I ref. TLV5618A, a digital-to-analog converter manufactured by TI, converts the digitalized I ref back to be the analog I ref which is applied by the hystersis controller. In the mean while, the current sink algorithm receives the digitalized V grid, then calculates the death time and finally generates the gate drive commands for the inverter via PIO0.6 and PIO0.7. PIO0.6 is responsible for driving the inverter during the positive V grid. PIO0.7, on the contrary, has the responsibility of driving the inverter during the negative V grid. The islanding algorithm is programmed for the security precaution; it monitors the grid voltage via the zero-crossing signal. In the other words, this algorithm must monitor two fault conditions, which are over/under grid frequency and zero grid voltage. The zero-crossing signal, itself, is generated at every rising edge of the grid voltage. As the consequence, the zero-crossing signal has the exact frequency as the V grid has, and this signal will not be generated if the V grid is equal to zero. Hence, the islanding algorithm uses a DSP timer to monitor the frequency of the zero-crossing signal. If there is no fault condition, the islanding algorithm will allow the program to resume its duties. However, if any fault conditions occur, the algorithm will halt the program and then will use the watchdog timer to reinitiate all parameters and finally will wait for a proper grid condition. 3.2 Experimental observation Figure 2 Diagram of control algorithms inside ADMC Investigating Voltage and Current of the Primary Side of the Isolated Transformer This experiment was set to investigate voltage across the primary side of the isolated transformer (V pri ) and to investigate current flows through the transformer (I pri ). Figure 3 illustrates the positions of the voltage-different probe and the current probe which were connected at the primary side of the transformer[8]. 72

5 Figure 3 Positions of probes which were installed to investigate V pri and I pri of the isolated transformer Figure 4 Voltage and current of the primary side of the isolated transformer Figure 4 illustrates voltage and current of the primary side of the transformer. Whereas: - CH1 = Voltage across the primary side of the isolated transformer. - CH2 = Current flows through the primary side of the isolated transformer. - Voltage-different probe was set to 1:20 attenuation ratio, hence V pri = 20* Scope _ read _ out (V/Div) (1) - Current probe was set to 2 A/Div, hence I pri = 2* Scope _ read _ out/10mv (A/Div) (2) Investigating Voltage and Current of the Secondary Side of the Isolated Transformer In this experiment, the voltage across the secondary side of the isolated transformer (V sec ) and the current flows through the transformer (I sec ) were investigated. Figure 5 illustrates the positions of the voltage-different probe and the current probe which were connected at the secondary side of the transformer[8]. 73

6 Figure 5 Positions of probes installed to investigate V sec and I sec of the transformer Figure 6 Voltage and current of the secondary side of the isolated transformer Figure 6 shows voltage and current of the secondary side of the transformer. Whereas: - CH1 = Voltage across the secondary side of the isolated transformer. - CH2 = Current flows through the secondary side of the isolated transformer. - Voltage-different probe was set to 1:200 attenuation ratio, hence Vsec = 200*Scope _ read _ out (V/Div) (3) - Current probe was set to 0.5A/Div, hence Isec = (0.5* Scope _ read _ out)/10mv (A/Div) (4) 4. CONCLUSION The hardware system implemented shows good reliability, stability, optimum performance and improved efficiency at the end of primary and secondary of isolated transformer compared with stand alone photovoltaic system. 74

7 REFERENCES [1] K.H.Hussein et al., Maximum Photovoltaic Power Tracking: an Algorithm for Rapidly Changing Atmospheric Conditions IEE Proceedings Generation, Transmission and Distribution v. 142, page 59-64, January [2] D.P. Hohm, M. E. Ropp., Comparative Study of Maximum Power Point Tracking Algorithms Progress in Photovoltaic: Research and Applications, page 47-62, November [3] J.H.R.Enslin et al., Integrated Photovoltaic Maximum Power Point Tracking Converter IEEE Transactions on Industrial Electronics, Vol. 44,page , December [4] Hua Chihchiang et al., Implementation of a DSP controlled Photovoltaic System with Peak Power Tracking IEEE Transactions on Industrial Electronics, Vol. 45, No. 1, page , February [5] E.Koutroulis et al., Development of a Microcontroller-Based, Photovoltaic Maximum Power Point Tracking Control System In proc. International Journal on Power Electronics, Vol. 16, No. 1, page 46-54, January [6] Castañer, Luis & Santiago Silvestre Modelling Photovoltaic Systems, Using PSpice John Wiley & Sons Ltd, [7] Abdelmalek Mokeddem et.al., Test and Analysis of a Photovoltaic DC-Motor Pumping System In proc. of ICTON on mediterranean winter conference. pp 1-7,2007 [8] Taufik, Akihiro Oi et.al., Modeling and Simulation of Photovoltaic Water Pumping System IEEE Third Asia International Conference on Modelling & Simulation pp , May [9] Anna Mathew et al., MPPT Based Stand-Alone Water Pumping System International Conference on Computer, Communication & Electrical Technology ICCCET2011,pp , March [10] N. Hamrouni et.al., Measurements and Simulation of a PV Pumping Systems Parameters Using MPPT and PWM Control Strategies In proc. of IEEE Mediterranean conference on Electro technical, pp , May