Hardware Realization of Conventional MPPT Techniques

Hardware Realization of Conventional MPPT Techniques

Abstract:This paper presents a comparative study on the conventional MPPT techniques used in the solar photovoltaic system. These techniques have been implemented in a hardware environment and their performance has been studied for variations in environmental conditions. It can be observed from analysing of PV array that, the P-V & I-V characteristics are highly influenced by the environmental factors leading to low conversion efficiency. Thus, the significance of maximum power point tracking controller is very high. The analysis and comparison of various existing technique has to perform to aid in selecting the appropriate method for implementation hardware results are being analysed to examine the feasibility, cost and efficiency obtained for the existing techniques. The MPPT technique included for study are perturb & observer algorithm (P&O), incremental conductance algorithm (INC), constant voltage method (CVM) the simulation studies were carried out in the MATLAB/Simulink environment. The DSPIC30F4011 has been used to implement the MPPT control.

Keywords:MPPT (Maximum Power Point Tracking), P&O (Perturb & Observe), INC(IncrementalConductance), CV(Constant Voltage).

I.INTRODUCTION

Owing to the unavailability of appropriate resources to meet the power demand in developing countries like India, the quest for finding suitable ways of harnessing power from renewable sources of energy is intensifying. The prime energy sources stand out to be solar energy and wind energy. The abundance of solar energy and the intermittent nature of wind energy makes solar energy receive higher importance. The advantage of solar power generating units is that it can be used as a standalone or even a grid connected system based on the availability of grid. The drawback of using solar energy power system is that the solar cell efficiency is low and it is also effected due to fast climatic changes and wide variations in the ambient temperature. Power electronic conditioners have helped in tracking the problem of low efficiency by helping the PV panel to operate at its maximum power. The MPPT controller makes the power output of the solar panel maximum by matching the Thevenin impedance of the system to the load impedance.

The entrenched technique for MPPT are:-

1. Perturb & Observe algorithm

2. Incremental conductance algorithm

3. Constant voltage method

   These algorithms force the PV panel to operate at the maximum power point under corresponding irradiation and temperature conditions. It has been observed from the papers archived in the literature that the implementation of the MPPT techniques in mundane. Thus, it is very important to select the appropriate controller for hardware implementation. The setup can be further utilized for integration to standalone and grid connected PV system.

   1. SYSTEM DESCRIPTION

      The figure 1 shows the block diagram of the solar photovoltaic system incorporating MPPT control. It consists of PV panel connected to the load through a boost converter. The firing pulses to the boost converter are given by the MPPT controller. The switch is operated such that the PV panel delivers maximum power.

      PV PANE L

      BOOST CONVER TER

      LOAD

      MPPT CONTROLLER

      Figure 1.Block diagram of overall system

      1. Modelling of PV panel:-

         Conversion of light energy to electrical energy is the basic function of the photo voltaic cell. The PV panel needs to be modelled mathematically to analyse the characteristics. The PV cells can be realized as a current source in parallel to a diode as in figure 2. The internal resistance is represented by a series resistance Rs in the equivalent circuit. The mathematical equations of the PV panel can be in equation [1-3]

         =

         Where,

         +

         1

         +

         (1)

         Io,stc= normal saturation current under standard test conditions (STC)

         TSTC= temperature under standard test conditions

         Ipv= photo voltaic current Io=saturation current of the diode q=electron charge in coulombs

         =1.602*10-19C

         K=Boltzmann constant

         =1.380*10-23J/K

         a=diode ideality factor Rs=series resistance Rp=parallel resistance T=Temperature in kelvin

         Figure 2.Equivalent Circuit PV cell

         The photo voltaic current Ipv is a function of the irradiance

         (G) and is formulated as:

         Eg= band gap energy of the semiconductor

         SPECIFICATIONS	PARAMETERS
         MAXIMUM POWER	100W
         VOLTAGE AT MAX	17.5V
         CURRENT AT MAX	5.71A
         OPEN CIRCUIT VOLTAGE	21.50V
         SHORT CIRCUIT CURRENT	6.28A

         Figure 3.PV characteristics of panel TABLE 1.PANEL SPECIFICATIONS

      2. Boost Converter:-

      = _ +

      (2)

      Where;

      IPV_STC=light generated current under standard test conditions (STC)

      T= T-TSTC (in kelvin)

      G= surface irradiance of cell (W/m2) GSTC=1000W/m2

      Irradiance under STC

      Ki= short circuit current coefficient

      Figure 4.Circuit Diagram of Boost Converter

      The function of a boost converter in a solar photovoltaic system aided with MPPT is to step up the voltage required by

      The diode saturation current Io

      is given as:

      the load. By stepping up the voltage, the maximum power from the PV panel is extracted. The source side impedance can be matched with the load side impedance.

      =

      3

      1 1 (3)

      Mode1:-

      Where;

      Boost Converter Specifications:-

      TABLE 2.BOOST CONVERTER SPECIFICATION

      SPECIFICATIONS	PARAMETERS
      CAPACITOR C1	50e-6
      CAPACITOR C2	22e-6
      INDUCTOR L	410e-6

      Figure 5.Boost converter Mode1 operation

      di (t)

   2. MPPT Techniques

      The conventional MPPT technique employed to the PV system under uniform insolation conditions are:

      (1)Perturb & Observe Method (2)Incremental Conductance Method

      L l

      0 1 i (t) 1 V

      (t)

      1. Constant Voltage Method

         dt

         1 l g

         (4)

         The growing prominence of these methods is the economic

         C dV (t)

         1

         V (t)

         0 0

         feasibility, easy installation etc…

         dt R

         y 1 0 il (t) y 1 0 il (t) (5)

         V (t) V (t)

         Mode2:-

         1. Perturb & Observe Method:-

            The Perturb & Observe Method is a very popular method due to its simple implementation, few measured parameters and low cost. The location of maximum power point is found by erturbing the voltage of panel as the duty cycle of the boost converter. The basic idea of the algorithm is to periodically perturb the duty cycle of the converter and measure the module current and voltage to determine the power. Based on the difference of the present & past values of voltage, the direction of perturbation is decided. The flow chart of the Perturb & Observer method is shown is that, the system oscillate around the MPP due to perturbations. This leads to a significant loss in power. When there is a change in the uniform insolating the operating voltage cannot change immediately and thus it takes time for the system to converge to the MPP.

            Figure 6.Boost converter Mode2 operation

            L dil (t) 0 0

            dt

            il (t) 1 Vg (t) (6)

            1 V (t) 0 0

            C dV (t)

            1

            dt R

            y 1 0 il (t) y 1 0 il (t) (7)

            V (t) V (t)

            Figure 7.Flowchart of Perturb and Observe Technique

         2. Incremental Conductance Method:-

            The basic principle for formation of the incremental conductance algorithm is the fact that the slop of the PV array curve is zero at the peak, negative on the right side and positive on the left side.

            Figure 8.Flow Chart of Incremental Conductance Method

            The advantage of the incremental conductance MPPT over

            P V * I

            (8)

            the P&O algorithm is that, there are less number of steady

            dP d (V * I ) (9)

            dV dV

            dV * I V * dI 0 (10)

            dV dV

            state oscillations. In the Perturb & Observe algorithm, varying the perturbation size is not very feasible. But, in the INC, the step size can be selected for faster dynamics and reduction in steady state oscillations.

         3. Constant Voltage Method:-

      I V * dI

      dV

      0 (11)

      The idea behind the constant voltage tracking method is that, for a fixed temperature & irradiation conditions the voltage is

      dI I

      at MPP (12)

      fixed to a close value. If the MPPT controller operates such

      dV V

      it can be concluded that

      that the voltage is fixed to that maximum value, maximum power can always be extracted from a PV array. It can be observed from the I-V characteristics that the ratio of the maximum power point voltage to the open circuit voltage is

      dP dI I

      0

      at MPP

      approximately constant and less than 1.

      dV dV V

      dP dI I

      0

      at left side of MPP

      =k

      dV dV V

      The value of K is noted be between 0.8 & 0.9 for majority

      dP dI I

      0

      at right side of MPP

      cases

      dV dV V

      Figure 9.Flowchart of Constant Voltage Control

      The advantage of the method is the simplicity in the algorithm, reduction in the number of sensors etc. But this method holds a huge drawback of low accuracy especially in varying environmental conditions. Due to the varying environmental conditions, significant effect is observed on the characteristics and voltage of the PV array. Simulation and hardware results have been analysed to choose the appropriate algorithm.

   3. SIMULATION RESULTS

      1. Perturb & Observe:-

         Figure 10.Output Power of Perturb & Observer Technique

      2. Incremental Conductance Technique:-

         Figure 11.Output Power of Incremental Conductance Technique

      3. Constant Voltage Method:-

      Figure 12.Output Power of Constant Voltage Method

      From the results obtaining the following comparison table can be drawn

      SPECIFICA TIONS	P&O	INC	CVC
      Efficiency	Medium About 95% depending on how method is optimized	High About 98% depending on how method is optimized	Low About 90%
      Complexity	Easy but complex when site conditions vary	Difficult	Very simple but very difficult to get optimal K1
      Realization	Easy to implement as few measured parameters	More complex hence microcontroller/ DSP is needed	Easy to implement with Analog hardware
      Cost	Relatively lower	Involving higher cost	Relatively lower

      TABLE 3.COMPARISON OF VARIOUS MPPT TECHNIQUES

   4. HARDWARE IMPLEMENTATION & RESULTS

      The hardware implementation of the system shown in figure 13

      Figure 13.Blockdiagram of the Hardware Setup

      The Hardware prototype of the system is shown in figure 14

      Figure 14.Hardware Implementation

      The parameters of the system for hardware implementation are given in the following table

      PARAMETERS	SPECIFICATIONS
      C1	1000F, 63V
      C2	4700F, 50V
      C3	470F, 450V
      DIODE	IN540
      L	1mh

      TABLE 4.HARDWARE SPECIFICATIONS

      The following results were noted during experimental validations of the conventional technique

      Perturb & Observe:-

      TABLE 5.TABULATED OUTPUTS OF P&O

      WITH OUT MPPT			WITH MPPT
      TIME	VOC	ISC	VMP	IMP	VO	IO	PMAX
      10 AM	17.5	3.36	17.54	3.03	23.05	2.30	53.1
      11 AM	17.5	4.92	17.22	4.47	27.8	2.78	77.3
      1 PM	17.5	5.32	17.44	4.84	29.06	2.90	84.4
      2:30 PM	17.5	4.67	17.43	4.25	27.23	2.72	74.1
      3 PM	17.5	4.01	17.8	3.63	25.45	2.54	64.8
      5 PM	17.5	3.00	17.5	2.73	21.87	2.18	47.8

      Incremental Conductance Technique:-

      17.5

      WITH OUT MPPT			WITH MPPT
      TIME	VOC	ISC	VMP	IMP	VO	IO	PMAX
      10 AM	17.5	3.36	17.3	3.07	23.07	2.30	53.2
      11 AM	17.5	4.92	17.52	4.41	27.77	2.77	77.1
      1 PM	17.5	5.32	17.12	4.91	29.07	2.90	85.5
      2:30 PM	17.5	4.67	17.13	4.31	27.33	2.72	74.1
      3 PM	17.5	4.01	17.56	3.68	25.42	2.54	64.6
      5 PM	3.00	17.3	2.77	21.99	2.19	47.9

      TABLE 6.TABULATED OUTPUTS OF INC

      Constant Voltage Control:-

      TABLE 7.TABULATED OUTPUTS OF CVC

      TIME	VOLTAGE (V)	POWER(P)
      10 AM	8	18
      11.30 AM	12	40.2
      1 PM	19	67
      2.30 PM	14	55.5
      3 PM	11	29.7
      5 PM	7	13.65

      Figure 15.Duty cycle to boost converter

   5. CONCLUSION

It can be noted that the incremental conductance method gives the most satisfactory results when compared with the other two techniques. The constant voltage method needs a reference voltage to be set based on the open circuit voltage of the panel. The method is highly inefficient and doesnt give satisfactory results under varying environmental conditions. The perturb and observer method gives oscillation leads to significant loss in the system

REFERENCES

1. Bhuvaneswari, G.; Annamalai, R., "Development of a solar cell model in MATLAB for PV based generation system," India Conference (INDICON), 2011 Annual IEEE , vol., no., pp.1,5, 16-18 Dec. 2011

2. Yuncong Jiang; Qahouq, J.A.A.; Batarseh, I., "Improved solar PV cell Matlab simulation model and comparison," Circuits and Systems (ISCAS), Proceedings of 2010 IEEE International Symposium on, vol., no., pp.2770,2773, May 30 2010-June 2 2010

3. Garg, R.; Singh, A.; Gupta, S., "PV cell models and dynamic simulation of MPPT trackers in MATLAB," Computing for Sustainable Global Development (INDIACom), 2014 International Conference on , vol., no., pp.6,12, 5-7 March 2014

4. Newlin, D.J.S.; Ramalakshmi, R.; Rajasekaran, S., "A performance comparison of interleaved boost converter and conventional boost converter for renewable energy application," Green High Performance Computing (ICGHPC), 2013 IEEE International Conference on , vol., no., pp.1,6, 14-15 March 2013

5. Anzicek, J.; Thompson, M., "DC-DC boost converter design for Kettering Universitys GEM fuel cell vehicle," Electrical Insulation Conference and Electrical Manufacturing Expo, 2005. Proceedings , vol., no., pp.307,316, 26-26 Oct. 2005

6. Reddy, G.N.; Guna-Shekhar, D.; Choudhari, S.; Ademola, M., "A statistical analysis package for DC-DC boost-converter design," Circuits and Systems (MWSCAS), 2011 IEEE 54th International Midwest Symposium on , vol., no., pp.1,4, 7-10 Aug. 2011

7. Kollimalla, S.K.; Mishra, M.K., "Adaptive perturb & observe MPPT algorithm for photovoltaic system," Power and Energy Conference at Illinois (PECI), 2013 IEEE , vol., no., pp.42,47, 22-23 Feb. 2013

8. Durgadevi, A.; Arulselvi, S.; Natarajan, S.P., "Study and implementation of Maximum Power Point Tracking (MPPT) algorithm for Photovoltaic systems," Electrical Energy Systems (ICEES), 2011 1st International Conference on , vol., no., pp.240,245, 3-5 Jan. 2011

9. Femia, N.; Petrone, G.; Spagnuolo, G.; Vitelli, M., "Optimization of perturb and observe maximum power point tracking method," Power Electronics, IEEE Transactions on , vol.20, no.4, pp.963,973, July 2005

10. Montoya, D.G.; Paja, C.A.R.; Petrone, G., "Design method of the perturb and observe controller parameters for photovoltaic applications," Circuits and Systems (CWCAS), 2012 IEEE 4th Colombian Workshop on , vol., no., pp.1,6, 1-2 Nov. 2012

11. Sera, D.; Mathe, L.; Kerekes, T.; Spataru, S.V.; Teodorescu, R., "On the Perturb-and-Observe and Incremental Conductance MPPT Methods for PV Systems," Photovoltaics, IEEE Journal of , vol.3, no.3, pp.1070,1078, July 2013

12. Banu, I.V.; Beniuga, R.; Istrate, M., "Comparative analysis of the perturb-and-observe and incremental conductance MPPT methods," Advanced Topics in Electrical Engineering (ATEE), 2013 8th International Symposium on , vol., no., pp.1,4, 23-25 May 2013

13. Safari, A.; Mekhilef, S., "Incremental conductance MPPT method for PV systems," Electrical and Computer Engineering (CCECE), 2011 24th Canadian Conference on , vol., no., pp.000345,000347, 8-11 May 2011

14. Bangyin Liu; Shanxu Duan; Fei Liu; Pengwei Xu, "Analysis and Improvement of Maximum Power Point Tracking Algorithm Based on Incremental Conductance Method for Photovoltaic Array," Power Electronics and Drive Systems, 2007. PEDS '07. 7th International Conference on , vol., no., pp.637,641, 27-30 Nov. 2007

15. Suwannatrai, P.; Liutanakul, P.; Wipasuramonton, P., "Maximum power point tracking by incremental conductance method for photovoltaic systems with phase shifted full-bridge dc-dc converter," Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON), 2011 8th International Conference on , vol., no., pp.637,640, 17-19 May 2011

16. Kumar, H.; Tripathi, R.K., "Simulation of variable incremental conductance method with direct control method using boost converter," Engineering and Systems (SCES), 2012 Students Conference on , vol., no., pp.1,5, 16-18 March 2012

17. Zhou Xuesong; Song Daichun; Ma Youjie; Cheng Deshu, "The simulation and design for MPPT of PV system Based on Incremental Conductance Method," Information Engineering (ICIE), 2010 WASE International Conference on , vol.2, no., pp.314,317, 14-15 Aug. 2010

18. Yuansheng Xiong; Suxiang Qian; Jianming Xu, "Research on Constant Voltage with Incremental Conductance MPPT Method," Power and Energy Engineering Conference (APPEEC), 2012 Asia-

    Pacific , vol., no., pp.1,4, 27-29 March 2012

19. Leedy, A.W.; Liping Guo; Aganah, K.A., "A constant voltage MPPT method for a solar powered boost converter with DC motor load," Southeastcon, 2012 Proceedings of IEEE , vol., no., pp.1,6, 15-18 March 2012

20. Ye ZhiHao; Wu Xiaobo, "Compensation Loop Design of a Photovoltaic System Based on Constant Voltage MPPT," Power and Energy Engineering Conference, 2009. APPEEC 2009. Asia-Pacific , vol., no., pp.1,4, 27-31 March 2009

21. Nagayoshi, H.; Kajikawa, T.; Sugiyama, T., "Comparison of maximum power point control methods for thermoelectric power generator," Thermoelectrics, 2002. Proceedings ICT '02. Twenty-First International Conference on , vol., no., pp.450,453, 25-29 Aug. 2002