Maximum power point tracking system for photovoltaic systems

maximum power point tracking techniques.

1. MAXIMUM POWER POINT TRACKING SYSTEM FOR PHOTO VOLTAIC SYSTEMS Presented by Guide P.PRIYADARSINI M .MURALI KRISHNA,M.Tech 19MT8405

2. Contents ... OBJECTIVE MATHEMATICAL MODEL WHAT IS MPPT? SYSTEM MODELLING MPPT TECHNIQUES APPLICATIONS CONCLUSION

3. OBJECTIVE Solar Cell A solar cell,or photo voltaic cell,is an electrical device that converts the energy of light directly into electricity by the photo voltaic effect. Efficiency of solar cell is less,it only converts 30-40% of energy incident on it to electrical energy. Need to use solar energy Pollution free Maintenance free Silent operation Long life time Efficiency of solar cell increased by this technique called MPPT,by installing this technique we can get additional 20-30% of efficiency.

4. Mathematical model of solar cell Equivalent circuit of PV cell Current equation I=I L -I D - I sh I -Cell current(A) I L -light generated current(A) I o -Diode saturation current q -Charge of electron =1.6*10^-19( coul ) K - Boltzman constant(j/K) T -Cell temperature(K) Rs,Rsh are cell series and shunt resistance(ohms) V -Cell output voltage(V)

5. V-I and P-V Characteristics of a solar cell

6. Variation of I-V and P-V curves with solar irradiation

7. Variation of I-V curve with temperature

8. Variation of P-V curve with temperature

9. Maximum Power Point Tracking(MPPT) MPPT Maximum power point tracking or sometimes power point tracking is a technique used commonly with wind turbines and PV systems to maximize power extracting under all conditions. Generally MPPT is installed in between PV system&load. Coupling to the load for maximum power transfer may required either providing a higher voltage at lower current or lower voltage at higher current. Maximum power point(MPP) It is an operating point at which maximum power can be extracted from the system,usually represents maximum power point(MPP).

10. System modelling

11. Classification Of MPPT Techniques Offline Technique Open Circuit Voltage Short Circuit Current Online Technique Perturb&Observe Incremental Conductance Intelligent Technique Artificial Neural Network Fuzzy Logic Control

12. Offline Technique The offline technique is commonly called as indirect technique since this algorithm is worked in offline i.e. not on the real time. In this technique, there is a necessity of prior requirement of particular PV panel data such as the mathematical modeling, I-V, P-V curve, etc. The basic indirect techniques of MPPT are open circuit voltage and Short circuit current method. In both the methods, a DC/DC converter with the driver circuit is controlled by the micro controller or DSP operates either in Buck/Boost mode is required. The duty cycle of the switching converter can be varied based on the computation of the open circuit voltage or short circuit current to track the maximum power point (MPP).

13. Open circuit voltage In this technique, the value of Vmpp under different solar insolation and temperature is calculated approximately by the equation: Where Voc -is the open circuit voltage K1 -is the coefficient value ranges from 0.71 to 0.9 depending upon the characteristics of the panel. The value of Vmpp is computed by measuring the value of Voc periodically. Short circuit current In this technique,The peak value of current Impp is computed by the following equation as: Where K2 -is the coefficient value ranges from 0.73 to 0.95 depending on the cell material and characteristics of the PV panel. By computing the values of Impp, at different sampled values of Isc, the duty cycle of the DC/DC converter is increased or decreased so that the output current becomes equal to Impp. Vmpp=K1Voc Impp=K2Isc Offline Techniques

14. Online Technique The online technique is commonly called as direct technique since this algorithm is worked in real time i.e. not on the offline. The popular online techniques used directly for the maximum power point are Perturb and Observe Technique (P&O) and Incremental conductance Technique (INC). In the direct techniques, there will be an online measurement of voltage and measurement of the panel periodically for computing the duty cycle of the converter to track the maximum power point MPPT.

15. Perturb&Observe MPPT Technique In this different MPP for different condition of temperature and irradiation which is tracked by MPPT technique and can be delivered to load. The P&O MPPT technique algorithm calculates the power P(t) by measuring the instant voltage V(t) and current I(t) and then compares it with last calculated power P(t-1). The algorithm continuously perturbs the system if the operating point variation is positive; otherwise the direction of perturbation is changed if the operating point variation is positive. The duty cycle of the DC/DC converter is varied till it reaches the maximum power point. With higher step size of perturbation, system may oscillate around MPP which results into wastage of energy.

16. P&O MPPT Technique Flowchart Yes No strart Measure V(t),I(t) P(t)=V(t)*I(t) ▲ P=P(t)-P(t-1) ▲P>0 ▲V>0 ▲V>0 Decrease voltage Increase voltage Return Increase voltage Decrease voltage

17. Incremental Conductance Technique This is a most popular MPPT algorithm and widely used. The disadvantages of the P&O MPPT algorithm is overcome and eliminated by this INC technique but it is more complex and very difficult to implement. The theory of the incremental conductance is to determine the variation direction of the output terminal voltage of the PV modules by measuring and comparing the incremental conductance and instantaneous conductance of PV modules. If the value of incremental conductance and the instantaneous conductance are equal, then it represents the operating point reaches the MPP maximum power point. Compare to the offline techniques, the online techniques like incremental conductance (INC) algorithms are advantageous under rapidly changing atmospheric conditions but it involves complex calculation which increases the hardware requirement and cost.

18. INC MPPT Technique Flowchart dP/dV=0 at MPP dP/dV>0 left of MPP dP/dV<0 right of MPP dP/dV = d(VI)/d(V)= I + V*dI/dV The dP/dV is defined as Maximum power point identifier factor.By utilizing this factor, the INC method is proposed to effectively track the MPP of PV module.

19. Intelligent Technique Intelligent MPPT controllers are very robust than conventional nonlinear controllers and it is able to effectively improve the dynamic response and steady state performance of the PV systems. The popular intelligent techniques are Artificial Neural Network Fuzzy Logic Control

20. Artificial Neural Network It is a new emerging technology used to solve complex problem. It is best suited for approximation of non-linear system. Input, hidden and output are the three layers of the artificial neural network. Feed forward type of neural network is the simplest one and it passes the information only in forward direction to all the layers. the numbers of nodes are defined by the user and varied based on the requirement.

21. Block Diagram of ANN Input of the neural network for maximum power point tracking PV array parameters such as PV voltage and current, environmental data like irradiance and temperature, or the combination of these. the output layer may be in the form of voltage, duty cycle depending. Input Layer Hidden Layer Output Layer Tr V mpp I r I PV P PV

22. Fuzzy Logic Control For over a decade Fuzzy Logic MPPT is popular and most powerful control method. It works with estimated inputs, ability to handle non-linearity, and have no need of accurate mathematical model; these are the advantages of the fuzzy logic control. FLC consist three state; fuzzification, decision-making and defuzzification. The inputs of the FLC are usually an error E and change error ▲E . To track maximum power point error is computed based on irradiance and temperature or instantaneous values such as power and voltage. The output signal is either the duty cycle itself, or & from which the duty cycle can be generated Fuzzification Decision-making Base Defuzzification E ▲E

23. Fuzzification : The process of converting numerical value into linguistic variable. The interval [-1 1] of membership function are chosen for the inputs. As in PV array for MPPT voltage and power are the two variables used to describing the control rule. Decision making base rule : In this base rule, the system behavior of the input/output variable are derived from the IF – THEN rule. To satisfy different condition rule base tables are obtained which gives several possible combinations of the degree which varying strengths to the corresponding rules. Defuzzification : The numerical variable outputs are obtained by converting linguistic variable. To control the power and derive the operating point to the MPP, analog signals are provided.

24. Applications The high end application like space satellites and Orbital stations, the complexity of the algorithm, costs doesn’t matter, the only requirement is to track the true MPP within a stipulated time period and no need of periodic tuning. In this type of special applications, P&O and INC are more appropriate. In the case of large scale PV power plants, the efficiency of the MPPT method constitutes the most important initial consideration and the hybrid MPPT algorithm one is the best option. In the case of designing the solar vehicles would mostly require the convergence speed to the MPP to be very fast. Fuzzy Logic, Artificial neural network MPPT will be preferred for high speed of convergence to the MPP. Open circuit voltage and Short circuit current algorithms will be sufficient for the PV systems used for street lightning since it does not require any more tight constraints and only easy and cheap implementation is required.

25. Conclusion This presentation reviews the various MPPT algorithm techniques that have been used for Photo voltaic system at changes in irradiance and temperature. The selection of a particular MPPT technique is based on type of application. It can be concluded that the offline and online techniques are working very well only when the solar irradiation is uniform. But it failed to approach the true MPP when it comes under rapidly changing atmospheric and partial shaded conditions. This drawback was overcome by the new MPPT techniques.