Comparative Analysis of Two Well-known Maximum Power Point Tracking Techniques for Photovoltaic Cell

Comparative Analysis of Two Well-known Maximum Power Point Tracking Techniques for Photovoltaic Cell

Keerti Yadav M.Tech. student Department of EEE

Technocrats Institute of Technology Bhopal (M. P.) India

Anuprita Mishra Professor Department of EEE

Technocrats Institute of Technology Bhopal (M. P.) India

AbstractThis paper provides a comparative analysis of widely used maximum power point technique (MPPT) i.e. Perturb and observe MPPT and Incremental Conductance MPPT used in photovoltaic application. A boost converter is used to step-up the voltage of the PV cell to a required DC-link voltage. A complete analysis of the boost converter has been described in this paper.

Keywords PV cell; Boost converter; DC-link; MPPT

1. INTRODUCTION

   Due to the limited resources of fossil fuel, the development of renewable energy sources is rising now days. The main advantages of these renewable energy sources are (a) it is plenty of available in nature, (b) eco-friendly and (c) recyclable. There are many renewable energy sources such as wind energy, solar energy, hydro energy and tidal energy. To harness electrical energy from renewable energy sources, power conditioning unit (PCU) is required. PCU comprises of one or more than one power electronic converter (PEC). DC-micro grids (Figure 1) are one of the most useful techniques where the renewable energy source is connected to the load with the help of a DC- bus [1]. Design of DC-micro grid has been studied in [13].

   incremental conductance. Both MPPT are hill-climbing algorithm and true MPPT. Simulation results are provided to illustrate the functionality of the MPPT techniques.

   This paper is organized as follows. Section II provides the mathematical modeling of PV cell. Section III presents the functionality of different maximum power point tracking algorithms. Section IV presents details of switched mode power converter. Section V provides simulation results. Section VI concludes the paper.

2. MATHEMATICAL MODEL OF PV CELL

   The photovoltaic system converts sunlight directly to electricity without having any disastrous effect on our environment. The basic segment of PV array is PV cell, which is just a simple p-n junction device. Figure 2 shows the electrical equivalent circuit of PV cell.

   The ideal PV cell consists of a constant current source and a diode whereas the practical PV cell consists of additional series Rs and parallel resistance Rp . Modeling of PV cell is

   summarized in [2-4].

   Rs

   Ipv Rp

   Id

   Fig. 2. Circuit diagram of PV cell

   The basic equation which describes the I-V characteristics of an ideal PV cell can be represented as

   Fig. 1. Block diagram of DC-grid

   I I pv Id

   (1)

   Photovoltaic cell is one of the most widely used renewable

   Where

   I pv

   is current of PV cell and Id

   is Shockley diode

   energy. The photovoltaic cell provides electrical energy when

   equation which can be represented as

   solar irradiance is incident on it. To extract maximum power

   I

   qV

   from PV cell, maximum power point tracking technique is used.

   d Io exp akT 1

   (2)

   This paper provides a detailed design and analysis of two well- known MPPT algorithms such as perturb and observe and

   Therefore, I-V characteristics of an ideal PV cell can be represented as

   I I

   qV

   power. Additional power harvested from the modules is then

   pv Io exp akT 1

   (3)

   made available as increased battery charge current. MPPT can

   Where Io the leakage is current of diode, q is electron charge, K is Boltzmann constant and T is temperature of p-n junction (Kelvin)

   In practice, the series and parallel equivalent characteristics of PV cell can be represented as

   be used in conjunction with a mechanical tracking system, but the two systems are completely different. Figure 3 displays the concept of MPPT. Figure 4 shows the classification of MPPT algorithms.

   I I

   qV

   V Rs I

   (4)

   pv Io exp akT 1 R

   p

   Where Rs is series resistance and Rp

   is parallel resistance

   Vt is thermal resistance of PV cell and Ns is number of cells

   connected in series. The thermal resistance of PV cell can be represented as

   V Ns kT t q

   The current of the PV cell is dependent on solar irradiance and temperature. The relation between the PV current and temperature can be represented as

   G

   Fig. 3. The concept of MPPT

   I pv I pv,n KI T

   Gn

   (5)

   where

   I pv,n

   is light generated current at nominal operating

   condition (25°C,1000W/m2),

   r is the difference of

   temperature (Actual and nominal temperature), G is the

   irradiance of the surface and Gn

   is the nominal irradiance The

   relationship of diode saturation current with temperature can be represented as

   T 3 qE 1 1

   I I

   n exp g

   (6)

   o o,n T

   ak T T

   n

   The nominal saturation current can be expressed as

   Io,n

   Isc,n

   V

   (7)

   exp oc,n 1

   aVt ,n

   The modified nominal saturation current can be represented as

   Isc,n KV T

   Fig. 4. Classification of different MPPT Techniques

   A comparative analysis of different MPPT techniques have

   Io,n

   V K

   (8)

   been studied in [5-12].

   exp oc,n I T 1

   aVt

3. MAXIMUM POWER POINT TRACKING Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic system that operates the Photovoltaic

   1. Perturb Observe MPPT

      One of the most widely used MPPT is Perturb and Observe (P&O) MPPT because it is true MPPT, independent of PV panel, can be implemented using both analog and digital circuit and the technique doesnt require periodic tuning. The

      dP

      (PV) modules in a manner that allows the modules to produce all the power they are capable of. MPPT is not a mechanical

      main principle of (P&O) MPPT is the checking of

      dV

      slope.

      tracking system that physically moves the modules to make them point more directly at the sun. MPPT is a fully electronic system that varies the electrical operating point of the modules so that the modules are able to deliver maximum available

      The slope is positive at the left of MPP and the slope is negative

      at the right of MPP [15]. This can be mathematically expressed as

      0 dP 0 dV 0

      V Vmpp V Vmpp V Vmpp

      (9)

      Initially the voltage and current of PV module is measured using respective voltage and current sensors and the power is calculated. Change of power and change of voltage is calculated and if the change of power dP 0 and also dV 0 then the duty cycle increases by a fraction of D and for negative slope the duty cycle decreases by a fraction of D . Figure 5 shows the flow chart of perturb and observe MPPT.

      Fig. 6. Flow chart of classical incremental conductance MPPT

      The efficiency of MPPT technique can be calculated using the following formula

      Ppv

      P

      mppt

      mppt

      100

      (10)

      Fig. 5. Flow chart of classical perturb-observe MPPT

   2. Incremental Conductance MPPT

   Figure 6 shows the flow chart of incremental conductance MPPT. The Incremental conductance method eliminates the drawbacks of thePerturb and Observe method. It uses the advantage that the derivate of the power with respect to the voltage at the maximum power point is zero. The incremental conductance can determine that the MPPT has reached the MPP and stop perturbing the operating point. If this condition is not met, the direction in which the MPPT operating point must be perturbed can be calculated.

4. POWER ELECTRONIC INTERFACE FOR PV MODULE Power electronic interface for PV module is illustrated in Figure

   1. PEI comprises of sensors, MPPT algorithms, PWM module, DC-DC converter and resistive load.

      Fig. 7. Block diagram of PEI for PV based generation

      The circuit diagram of DC-DC boost converter is shown in Fig.

   2. DC-DC boost converter is a non-minimum phase system which means the output voltage to duty cycle transfer function of boost converter has a zero in right half of S-plane. This characteristic makes the controller design more complicated.

   D

   rL L

   rC

   R

   Vdc S

   C

   400

   Power (W)

   300

   200

   100

   0

   0 20 40 60 80 100 120

   Voltage (V)

   5

   Current (A)

   4

   3

   Fig. 8. Circuit diagram of boost converter

   2

   The transfer function of boost converter can be represented as 1

   L

   1 sr C 1 s

   0

   0 20 40 60 80 100 120

   Voltage (V)

   v s V c 1 D2 R r

   G s o

   in l

   boost

   d s 1 D2

   1 s

   RrLC R rc L

   s2 LCR

   Fig. 9. P-V and V-I plot for PV cell

   R r r 1 D2 R r 1 D2 R

   c L L TABLE I: SPECIFICATION OF SPR-305-WHT PM MODULE

   Parameters	Variable	Value
   Number of cells per module	Nc	96
   Number of series connected module	Ns	4
   Number of parallel strings	Np	1
   Open-circuit voltage	Voc	64.2V
   Short-circuit current	Isc	5.96 A
   Maximum Power	Pmp	305W
   Series resistance	Rs	0.037998
   Parallel resistance	Rp	993.5
   Saturation current	Isat	1.1753e-8A
   Photovoltaic current	Iph	5.9602A

   The resonant frequency of the LC circuit of the converter can

   1 D

   be represented as o

   LC

   The right-half-zero frequency of the converter can be

   represented as

   R2 1 D 2

   rc rL

   RHP

   R rc L L

   There are different methods to eliminate the RHPZ characteristics. One such method is injected absorbed current method. The transfer function of boost converter using IAC method can be represented as

   V 1

   2

   1 2 L DT

   in

   1 s

   s Ts .

   p

   V 1 D

   G s

   1 D R 2

   Module type: SunPower SPR-305-WHT

   IAC

   1 kW/	m2
   0.75 k	W/m2
   0.5 k	W/m2 2
   0.25 k	W/m

   2 T

   1 s

   1

   L s

   s2

   LC 6

   1 D R 2 2

   Current (A)

   1 D 4

5. SIMULATION RESULTS

   Figure 9 represents the P-V curve of the PV module under consideration. Form the Figure it can deduce that power in PV system is increased at certain point with the voltage. After a certain value of V, the power of the PV system started to fall. This paper considers a SPR-305-WHT PV module. This is manufactured by Sun Power. P-V and V-I characteristics of SPR-305-WHT module with varying solar irradiance is shown in Fig. 10. When 66 parallel strings and 5 series module of the said scheme is connected, the V-I and P-V characteristics of the solar module is shown in Fig. 11. The electrical response of the PV module changes with change in ambient temperature. Fig. 12 shows the P-V and V-I characteristics of the solar module with varying temperature.

   2

   0

   0 10 20 30 40 50 60 70

   Voltage (V)

   Power (W)

   						/m2
   					0.75	kW/m2
   					0.5 k	W/m2
   					0.25	kW/m2

   300 1 kW

   200

   100

   0

   0 10 20 30 40 50 60 70

   Voltage (V)

   Fig. 10. P-V and V-I characterisitics of SPR-305-WHT module

   400

   Current (A)

   300

   200

   100

   0

   Array type: SunPower SPR-305-WHT; 5 series modules; 66 parallel strings

   1 kW/	m2
   0.75 k	W/m2
   0.5 k	W/m2
   0.25 k	W/m2

   0 50 100 150 200 250 300 350

   Voltage (V)

6. CONCLUSION

This paper provides a detailed analysis and comparative analysis of two well-known MPPT algorithms for PV cell. A 300W PV module is considered and a DC-micro grid has been designed. Detailed simulation results have been provided. The electrical voltage of PV cell gets changed due to change in solar irradiance and ambient temperature. The comparative analysis of two MPPT algorithms are shown using simulation.

REFERENCES

1. A. T. Elsayed, A. A. Mohamed, and O. A. Mohammed, Dc microgrids and distribution systems: An overview, Electric

   4

   					1 kW 0.75	kW/m2
   					0.5 k 0.25	kW/m2

   x 10

   Power (W)

   10

   5

   0

   /m2 W/m2

   Power Systems Research, vol. 119, pp. 407417, 2015.

2. M. G. Villalva, J. R. Gazoli et al., Comprehensive approach to modeling and simulation of photovoltaic arrays, IEEE Trans. Power Electron., vol. 24, no. 5, pp. 11981208, 2009.

3. S. A. Rahman, R. Varma, and T. Vanderheide, Generalised model of

   a photovoltaic panel, IET Renewable Power Generation, vol. 8, no. 3, pp. 217229, 2014.

4. G. Bhuvaneswari and R. Annamalai, Development of a solar cell

   0 50 100 150 200 250 300 350

   Voltage (V)

   Fig. 11. V-I characterisitics of SPR-305-WHT 5 series module and 66 parallel strings

   I-V charateristics

   	25C T 35C T 45C T 5C T 65C T

   5

   4

   I (A)

   3

   pv

   2

   1

   0

   0 5 10 15 20

   Vpv (V)

   P-V charateristics

   60 25C T

   Ppv (W)

   35C T

   40 45C T

   55C T

   20 65C T

   0

   0 5 10 15 20

   Vpv (V)

   Parameters	P&O	IC
   Control variable	V,I	V,I
   Tracking accuracy	Medium	High
   Periodic Tuning	No	No
   Ability to track true maxima	Yes	Yes
   Sensitivity	Medium	Medium
   Efficiency	Medium	High

   Fig. 12. P-V and V-I plot of PV cell with varing temperature TABLE II: COMPARISON OF MPPT TECHNIQUES

   model in matlab for pv based generation system, in Proc. IEEE India

   Conference (INDICON), 2011, pp. 15.

5. B. Subudhi and R. Pradhan, A comparative study on maximum power point tracking techniques for photovoltaic power systems, IEEE Trans. Sustain. Energy, vol. 4, no. 1, pp. 8998, 2013.

6. P.-C. Chen, P.-Y. Chen, Y.-H. Liu, J.-H. Chen, and Y.-F. Luo, A comparative study on maximum power point tracking techniques for

   photovoltaic generation systems operating under fast changing environments, Solar Energy, vol. 119, pp. 261276, 2015.

7. M. Berrera, A. Dolara, R. Faranda, and S. Leva, Experimental test

   of seven widely-adopted mppt algorithms, in Proc. IEEE PowerTech, 2009, pp. 18.

8. V. Salas, E. Olias, A. Barrado, and A. Lazaro, Review of the maximum power point tracking algorithms for stand-alone photovoltaic systems, Solar energy materials and solar cells, vol. 90, no. 11, pp. 15551578, 2006.

9. T. Esram, P. L. Chapman et al., Comparison of photovoltaic array maximum power point tracking techniques, IEEE Trans. Energy Convers., vol. 22, no. 2, p. 439, 2007.

10. A. Anurag, S. Bal, S. Sourav, and M. Nanda, A review of maximum

    power-point tracking techniques for photovoltaic systems,

    International Journal of Sustainable Energy, pp. 124, 2014.

11. S. Bal and B. C. Babu, Comparative study between p&o and current

    compensation method for mppt of pv energy system, in Proc. Students Conference on Engineering and Systems, 2012, pp. 16.

12. Ankit Gupta, Yogesh K. Chauhan, Rupendra Kumar Pachauri, A comparative investigation of maximum power point tracking methods for solar PV systems, Solar Energy, 136, 2016, pp. 236- 253.

13. Ganesh Baliram Ingale, Subhransu Padhee, and Umesh Chandra Pati, "Design of stand-alone PV system for DC micro grid" in Proc. 2016 Int. Conf. Energy Efficient Technologies for Sustainability, Apr. 2016, pp. 775780.