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International Journal for Research and Development in Engineering (IJRDE) www.ijrde.com ISSN: 2279-0500 Special Issue: pp- 012-016 Design and Implementation of Maximum Power Point Tracking For Super Lift Converter Indu V. R1; V. Chamundeeswari2 1,2 Department of EEE, St. Joseph’s college of engineering, Chennai, India ABSTRACT Photovoltaic (PV) is a technical name in which radiant (photon) energy from the sun is converted to direct current (dc) Electrical Energy. PV power output is still low, continuous efforts are taken to develop the PV converter and controller for maximum power extracting efficiency and reduced cost factor. The maximum power point tracking (MPPT) is a process which tracks one maximum power point from array input, varying the ratio between the voltage and current delivered to get the most power it can. A number of algorithms have been developed for extracting maximum power. This paper details the study of incremental conductance MPPT algorithm with the help of a negative output luo converter. Keywords- PV Module, MPPT, Incremental Conductance (IC) Algorithm, luo converter. I. INTRODUCTION Solar Energy is the ultimate source of energy, which is naturally replenished in a short time period of time, for this reason it is called “Renewable Energy” or “Sustainable Energy”. Due to the severity of the global energy crisis and environmental pollution, the photovoltaic (PV) system has become one kind of important renewable energy source. Solar energy has the advantages of maximum reserve, inexhaustibleness, and is free from geographical restrictions, thus making PV technology a popular research topic. The efficiency of solar cells depends on many factors such as temperature, insolation, spectral characteristics of sunlight, dirt, shadow, and so on. Changes in insolation on panels due to fast climatic changes such as cloudy weather and increase in ambient temperature can reduce the photovoltaic (PV) array output power. In addressing the poor efficiency of PV systems, some methods is proposed, among which is a new concept called “maximum power point tracking” (MPPT). All MPPT methods follow the same goal which is maximizing the PV array output power by tracking the maximum power on every operating condition. In this paper we use incremental conductance algorithm for precise control under rapidly changing atmospheric conditions. II. PV CELL MODELING A PV module consists of number of solar cells connected in series and parallel to obtain desired voltage and current. Each solar cell is basically a p-n diode. As sunlight strikes a solar cell, the incident energy is converted directly into electrical energy without any mechanical effort. Transmitted light is absorbed within the semiconductor by using its energy to excite free electrons from a low energy status to an unoccupied higher energy level [6]. When a solar cell is illuminated, excess electron hole pairs are generated by light throughout the material, hence the p-n junction is electrically shorted and current will flow. The equivalent circuit of a PV cell is as shown in Figure1. Figure1. PV cell modeled as diode circuit The current source represents the cell photo current. Rsh and Rs are the intrinsic shunt and series resistance of the cell respectively. Usually the value of Rsh is very large and that of Rs is very small.Equations of PV Module The Methods Enriching Power and Energy Development (MEPED) 2014 12 | P a g e International Journal for Research and Development in Engineering (IJRDE) www.ijrde.com ISSN: 2279-0500 Special Issue: pp- 012-016 photovoltaic module can be modeled mathematically as given in equations shown below. Module photo current: Iph = [Isc + Ki (Tk - Tref)] * / 1000. (1) Module reverse saturation current: Irs = Iscr/[exp( qV / N kAT ) .1] (2) The module saturation current Io varies with the cell temperature, which is given by Io = Irs(T/Tr )^3 exp((qEg/KA)*(1/Tr-1/T)) Figure 3 I-V characteristics of PV panel. (3) The current output of PV module is : Ipv=Iph- Is*[exp{q(V pv +IpvRs)/Ns AKT}-1] (4) Where Vpv=Voc. Here we consider 36 series connected Pv cells Figure 4 P-V characteristic III. MPPT Figure 2 Simulink model PV system naturally exhibits a nonlinear I-V and P-V characteristics which vary with the radiant intensity and cell temperature. The typical I-V and P-V characteristics of solar cell are shown in figure 3& figure4. MPPT algorithms are necessary in PV applications because the MPP of a solar panel varies with the irradiation and temperature, so the use of MPPT algorithms is required in order to obtain the maximum power from a solar array. Over the past decades many methods to find the MPP have been developed and published. These techniques differ in many aspects such as required sensors, complexity, cost, range of effectiveness, convergence speed, correct tracking when irradiation and or temperature change, hardware needed for the implementation or popularity [1]. Among these techniques, the P&O and the Incremental Conductance algorithms are the most common. These techniques have the advantage of an easy implementation. Other techniques based on different principles are fuzzy logic control, neural network, and fractional open circuit voltage or short circuit current etc .Among different Methods Enriching Power and Energy Development (MEPED) 2014 13 | P a g e International Journal for Research and Development in Engineering (IJRDE) www.ijrde.com ISSN: 2279-0500 Special Issue: pp- 012-016 algorithms, Incremental Conductance method is used here. In this method, the array terminal voltage is always adjusted according to the MPP voltage. It is based on the incremental and instantaneous conductance of the PV module figure given below shows that the slope of the PV array power curve is zero at the MPP, increasing on the left of the MPP and decreasing on the right-hand side of the MPPT .The basic equations of this method are as follows dI/dV= - I/V, at MPP (5) dI/dV> − I/V, left of MPP (6) dI/dV< − I/V, right of MPP (7) Where, I and V are the PV array output current and voltage respectively. The left-hand side of the equations represents the Incremental conductance of the PV module, and the right-hand side represents the instantaneous conductance. From (5)–(7), it is obvious that when the ratio of change in the output conductance is equal to the negative output conductance, the solar array will operate at the MPP. In other words, by comparing the conductance at each sampling time, the MPPT will track the maximum power of the PV module. The accuracy of this method is proven, where it mentions that the Incremental conductance method can track the true MPPs independent of PV array characteristics. The efficiency was observed to be as much as 98.2%, but it is some modifications and reformations were proposed on this method so far, but since this method inherently has a good efficiency, the aforementioned amendments increase the complexity and cost of the system and there was no remarkable change in system efficiency. In this paper, control action is done using a microcontroller. It generates pulse width modulation (PWM) waveform to control the duty cycle of the converter switch according to the Incremental conductance algorithm. Flow chart for the incremental conductance is given below. Figure 5. Incremental conductance algorithms IV. CONVERTER Luo converters were developed from the prototypes using VL technique. These converters perform DC-DC voltage increasing conversion with high power density, high efficiency, and cheap topology in simple structure. They are different from any other DC-DC step up converters and possess many advantages including a high output voltage with small ripples. Therefore, these converters are widely used in computer peripheral equipment and industrial applications, especially for high output voltage projects. This paper introduces negative output super lift technique that implements the output voltage increasing in stage by stage along the geometric progression. Equation (8) shows the input output relationship of luo converter Vo = Vin/(1-k) (8) The NOESLLC provides high voltage transfer gain using Super-lift technique Its topology differs from the conventional circuit as it uses additional capacitor in parallel with the load boosting the output voltage. The Methods Enriching Power and Energy Development (MEPED) 2014 14 | P a g e International Journal for Research and Development in Engineering (IJRDE) www.ijrde.com ISSN: 2279-0500 Special Issue: pp- 012-016 linkage between input and output is alleviated which degrades the output voltage. The above figure shows the circuit diagram of NOESLLC. It consists of a power switch MOSFET M1, Inductor L1, Resistor R1, Diodes D1, D2, Capacitor C1, C2 and load resistance. Figure 8 mode 2 representations V. SIMULATION RESULTS The simulation system consists of PV module; negative output luo converter circuit and MPPT control block as shown in the figure (9). Figure 6 negative output luo converter MODE1 When the switch is closed during the duty interval 0 to ∆T, the supply voltage increases the current through the inductor L1 and the capacitor C1 gets charged. The load current is maintained constant by the discharge of the capacitor C2 during this period Figure 9 simulation system Output power available at the output of the system without MPPT is given in figure 10. By using incremental conductance algorithm, PV panels working point is shifted to the MPP and power output is increased. Figure 7 mode 1 representation MODE 2 During the duty interval ∆T to T the switch is closed where the stored charges in the inductor supplies the load current and the capacitor C1 and C2 produces the boosted voltage across the load Figure 10 PV output power without MPPT Methods Enriching Power and Energy Development (MEPED) 2014 15 | P a g e International Journal for Research and Development in Engineering (IJRDE) www.ijrde.com ISSN: 2279-0500 Special Issue: pp- 012-016 Electrical Energy in the 21st Century, July 20-24, 2008, Pittsburg, USA. Figure 11 Output power with MPPT. VI. CONCLUSION This paper presents the design and simulation for maximum power point tracking (MPPT) for photovoltaic system, which includes a high-efficiency luo converter with incremental conductance algorithm. The converter can draw maximum power from the PV panel for a given solar insolation and temperature by adjusting the duty cycle of the converter. REFERENCES [1] Azadeh Safari And Saadmekhilef, Member, IEEE, (2011) “Simulation And Hardware Implementation Of Incremental Conductance Mppt With Direct Control Method Using Cuk Converter” IEEE Transactions On Industrial Electronics, Vol. 58, No. 4, April 2011 [2] S. Nema, R.K.Nema, and G.Agnihotri, “Matlab / simulink based study of photovoltaic cells / modules / array and their experimental verification,” International Journal of Energy and Environment, pp.487-500, Volume 1, Issue 3, 2010. [3] N. Femia, D. Granozio, G. Petrone, G. Spagnuolo, andM. Vitelli, “Predictive & adaptive MPPT perturb and observe method,” IEEE Trans. Aerosp.Electron. Syst., vol. 43, no. 3, pp. 934–950, Jul. 2007. [4] E. Koutroulis, K. Kalaitzakis, and N. C. Voulgaris, “Development of a microcontroller-based, photovoltaic maximum power point tracking controlsystem,” IEEE Trans. Power Electron., vol. 16, no. 1, pp. 46–54,Jan. 2001. [5] S. Jain and V. Agarwal, “A new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems,” IEEE PowerElectron. Lett., vol. 2, no. 1, pp. 16–19, Mar. 2004. [6] S.Chowdhury, S.P.Chowdhury, G.A.Taylor, and Y.H.Song, “Mathematical Modeling and Performance Evaluation of a StandAlone Polycrystalline PV Plant with MPPT Facility,” IEEE Power and Energy Society General Meeting -Conversion and Delivery of Methods Enriching Power and Energy Development (MEPED) 2014 16 | P a g e