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SOFT SWITCHING DC-DC CONVERTERS FOR PHOTOVOLTAIC MODULESWITH MPPT

NAME OF THE PROJECTEE D.Shankar

MT10PED019.

NAME OF PROJECT GUIDE Dr. P.S.KULKARNI

ELECTRICAL ENGG.DEPT. , VNIT.

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WHY SOLAR ENERGY?

Solar energy is the most readily available source of energy.

It is free. It is also the most important of the non-conventional

sources of energy because it is non-polluting.

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OUTLINE Aims and Objectives. Motivation. Introduction. Modeling Of PV Module. Maximum Power Point Tracking. Soft-switching DC-DC Converter. PV Systems With MPPT. Perturb and Observe (P & O) MPPT Algorithm. Conclusions. Future work. References. Publications.

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AIMS AND OBJECTIVES

To achieve maximum Efficiency from the dc-dc converter by using soft switching techniques.

Study the effect of radiation and temperature on the solar module out put.

To track maximum available power from the solar PV Module.

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MOTIVATION Jawaharlal Nehru National Solar mission of MNRE.

Keeping in view power losses in India everyone is keen to adopt it.

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INTRODUCTION A MPPT system has been consisting of a soft switching

BOOST/BUCK-type dc/dc converter, irrespective of the temperature and irradiation conditions and of the load electrical characteristics.

It overcomes the problem of mismatch between the solar arrays and the given load.

The conventional Boost/Buck converter decreases the efficiency because of hard switching, which generates losses when the switches are turned on/off.

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PROPOSED SYSTEM

A DC-DC converter (step up/step down), serves the purpose of transferring maximum power from the PV module to the load and acts as an interface between the load and the module.

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 STAND-ALONE PV SYSTEM WITH MPPT

The input DC–DC converter part is formed by the PV array and the output section by the batteries and load. The role of the MPPT is to ensure the operation of the PV module at its MPP, extracting the maximum available power.

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MODELING OF PV MODULE A PV module consists of a number of solar cells

connected in series and parallel to obtain the desired voltage and current output levels.

Each solar cell is basically a p-n diode.

The basic equation that describes the current output of PV module of the single diode model is given by

1expc

SP

s

ssPphp AKT

IRN

IRNVq

ININI

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SOLAR CELLS CHARACTERISTICS The solar cell has nonlinear V –I and P–V characteristics,

which depend on the irradiance, the operating temperature and load condition of the cell.

The Current‐Voltage relationship & The Power - voltage relationship curve of a solar PV module is given by

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WHAT IS A MAXIMUM POWER POINT TRACKER?

Maximum Power Point Tracking (MPPT): Technique used in power electronics systems to obtain the

maximum possible energy from PV arrays. Its use is desired to compensate for the effect of

temperature, variations in solar radiation, and load condition in a PV system.

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PV ARRAY CURRENT-VOLTAGE CURVES & POWER-VOLTAGE CURVES

Mismatch between resistive load and PV Source; current–voltage curves & power–voltage curves

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MAXIMUM POWER POINT TRACKING (MPPT) METHODS

These are the some widely used MPPT algorithms can be broadly classified as:

1) Perturbation and Observation (P&O) Method (a) Conventional P&O Method (b) Incremental Conductance Method

2) Linearity-based Methods: (a) Short-circuit current method (b) Open Circuit Voltage Method

3) Ripple Correlation Control Method

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MAXIMUM POWER POINT TRACKING

Incremental Conductance Method These method is based on the fact that the slope dP/dV of the panel P-V curve is positive on the left side of the MPP, zero at the MPP and negative on the right side of the MPP.

The incremental and conductance algorithm makes use of the Following eq:

at MPP.

at the left of the MPP.

at the right of MPP.

0dVdP

0dVdP

0dVdP

dV

IVddVdP .

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MAXIMUM POWER POINT TRACKING

Open Circuit Voltage MethodA linear dependency exists between “cell voltages corresponding toMaximum power and “cell open circuit voltage”.VMP=MV.VOC

Where MV is the voltage factor is equal to 0.74

The optimum operating current for the maximum output power is proportionalTo the short circuit current under various condition of radiation .Iop=k.Isc

Where k is the proportional constant.

Short-circuit current method

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BASIC PERTURB AND OBSERVE

Reference voltage control. Direct duty ratio control.

System performance is affected by: Step Size Perturbation Frequency MPPTf

REFVDor

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Begin P&O algorithm

Measure Vo(K),Io(K)

Po(K)=Vo(K)*Io(K)∆Po= Po(K)- Po(K-1)

∆Po >0

D (K)- D(K-1)>0D (K)- D(K-1)<0

Update History Po(K-1)=Po(K)

Decrease duty cycle

Decrease duty cycle

Increase duty cycle

Increase duty cycle

Perturb and Observe MPPT

Algorithm

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CONTD.. Implemented through a DC/DC converter LOGIC

1. Change duty cycle

2. Observe consequences on power output

3. Decide direction of next change in duty cycle

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SOFT-SWITCHING DC-DC CONVERTER

The dc–dc converter for a PV system has to control the variation of the maximum power point of the solar cell output.

The analysis, design and modelling processes of hard-switched converters are mature, where the switching frequency was limited to a few 10’s of kHz.

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BASIC CONCEPTS ON HARD-SWITCHING Hard-switching

The process of power semiconductor device hard-switching

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THE CONCEPT OF SOFT-SWITCHING

Soft-switching

The process of power semiconductor device soft-switching

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TWO TYPES OF SOFT-SWITCHING

Is to shape the voltage or the current waveform by creating a resonant condition to:

Force the voltage across the switching device to drop to zero before turning it ON Zero-Voltage Switching (ZVS)

Force the current through the switching device to drop to zero before turning it OFF Zero-Current Switching (ZCS)

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WHY SOFT-SWITCHING? Reduce switching losses especially at high switching

frequencies.

Increase the power density, since the size and weight of the magnetic components is decreased by increasing the operating frequency.

Reduce the Electromagnetic Interference (EMI).

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SOFT-SWITCHING BOOST CONVERTER

Values of resonant inductor and resonant capacitor are calculated by

minmaxmin22 IiTDVTVDL Lfwor

oo

r

rr V

TDIVLI

LTDC 2

minmin22

2min

2

22min 8.0404.0

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THEORETICAL WAVEFORMS

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SOFT-SWITCHING BUCK CONVERTER

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THEORETICAL WAVEFORMS

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BUCK CONVERTER PARAMETERS The design procedure of the battery charger with ZCS buck converter

for a 12-V 48-Ah lead acid battery is summarized as follows. The normalized switching frequency fns = 0.7 was set based on the

normalized voltage gain M=Vo/Vs = 14/17 =0.8.

= 14/6 = 2.33 Ω.The characteristic impedance is determined by substitutingRo= 2.33 Ω and Q = 1 into

The necessary resonant frequency is derived from fr=fs/fns= 16 kHz/0.7 = 22.25 kHz.

From above eq..Wo/Z0=1/Lr

Cr=1/WoZ0

Lo=100Lr

Co=100Cr

O

OO I

VR

LrCrWO

1

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MPPT LIMITATION The maximum power transfer occurs when the source impedance

equal to load impedance. i.e. The input impedance is given by The converter output voltage & current is given by

The relation between & is given by

Similarly for buck converter is given by, the converter output voltage & current is given by

The relation between & is given by

in

inin I

VR

DV

V SO

1)1( DII SO

LOADO

O

S

Sin RD

IV

DIV

R 22 11 LOAD

in

RR

D 1

inR loadR

DVV SODI

I SO

inR loadR

LOADO

O

S

Sin R

DIV

DIV

R 22

11

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RESULTS

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BOOST, BUCK CONVERTER & PV MODULE PARAMETERS

Maximum Power(Po,

max )74Wp(optional)

Switching frequency( fs)

20 kHz

PV Module Voltage (Vi)

15-17.5V

Output Voltage (Vo) 25V

Main Inductor( L) 280µH

Resonant Inductor( Lr)

150µH

Input Filter Inductor (Lf)

50µH

Output Capacitor(Co) 1000µF

Resonant Capacitor(Cr)

20nF

Table I. Boost Converter Parameters

Open circuit voltage(Voc) 22.42V

Short circuit current(Isc) 4.2A

Maximum voltage(Vmpp) 18.83V

Maximum current(Impp) 3.93A

Maximum power at STC(Pmax)

74WP

Maximum system voltage

600V

Table II. PV Module Parameters

Maximum Power(Po,

max )74Wp(optional)

Switching frequency( fs)

16kHz

PV Module Voltage (Vi)

15-17.5V

Output Voltage (Vo) 14V

Resonant Capacitor(Cr )

2.98µH

Resonant Inductor( Lr)

16.96µH

Output Inductor (Lo) 160µH

Output Capacitor(Co) 300µF

Table III. Buck Converter Parameters

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MATLAB/SIMULATION &RESULTS

SOLAR PV PANEL

MPPT CONTROLLER

ZVS BOOST/BUCK CONVERTER

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V-I & P-V CHARACTERISTICS UNDER DIFFERENT

RADIATION(MATLAB/SIMULATION RESULTS)

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SERIES AND PARALLEL CONNECTION OF PV MODULE

Connection of 3 panel in parallelConnection of 3 Panel in series

Connection of 3 Panel in parallel

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PV MODULE UNDER DIFFERENT TEMPERATURE

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PV MODULE UNDER PARTIAL SHADING CONDITION

0 5 10 15 20 25 300

100200300400500600700800900

1000

Time(hour)

21/05/2012 variation of solar radiation in VNIT

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BOOST CONVERTER(MATLAB/SIMULATION)

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Fig..1 Represent Waveform of Main Inductor Current and gate pulse.

Fig.2. Voltage and current waveform across main switch.

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Fig.3. Voltage across resonant capacitor and resonant inductor current

Fig.4. Voltage across diode.

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BUCK CONVERTER (MATLAB/SIMULATION)

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FIG.1. WAVEFORMS OF THE TRIGGER SIGNAL VG AND THE CONTROL SIGNAL VGA .

Fig. 2. Waveforms of the freewheeling diode voltage Vdm and the resonant capacitor voltage Vcr .

Main switch

Auxiliary switch

Time(sec)

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Fig.3.The resonant inductor current Ilr .Time(sec)

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CONVERTER OUT PUT VOLTAGES

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For boost converter 35V

Time(sec)

Time(sec)

For buck converter 12.2V

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MPPT P&O METHOD10/29/2012

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PV MODULE POWER, VOLTAGE, AND CURRENT(WITH MPPT

With out MPPT

At 25oC &1000W/m2

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PV MODULE POWER, VOLTAGE, AND CURRENT(WITH STEP INCREASES IN RADIATION)

Time(sec)

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PV MODULE POWER, AND DUTY CYCLE VARIATION(STEP SIZE ΔD =0.005)

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PV MODULE POWER, AND DUTY CYCLE VARIATION(WITH STEP INCREASES IN RADIATION)

Time(s)

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CONCLUSIONS The P&O MPPT algorithm is a simple algorithm that

does not require previous knowledge of the PV generator characteristics or the measurement of solar intensity and cell temperature.

Direct duty ratio control offers better stability characteristics and higher energy utilization efficiency at a slower transient response and worse performance at rapidly changing irradiance.

Noise has significant impact on the algorithm performance, especially with low step sizes where the system response to noise is comparable to that of MPPT perturbations.

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FUTURE WORK Development of a MPPT system has been consisting of a

soft switching boost/buck-type dc-dc converter, irrespective of the temperature and irradiation conditions for home lighting system and battery charging.

Improvement in maximum power point tracking algorithm (MPPT).

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[1] Chetan Singh Solanki, “Solar Photovoltaic's- fundamentals, technologies and application”, PHI learning private Ltd,2012.

[2] A. K. Mukerjee, Nivedita Takur, “Photovoltaic Systems- Analysis and Design”, PHI learning private Ltd,2011.

[3] Trishan Esram, and Patrick L. Chapman, “Comparison of Photovoltaic Array Maximum Power Point Tracking techniques”, IEEE Transactions On Energy Conversion, Vol. 22, No. 2, June 2007.

[4] Sang-Hoon Park, Gil-Ro Cha, Yong-Chae Jung, and Chung-Yuen Won, “Design and Application for PV Generation System Using a Soft-Switching Boost Converter With SARC”, IEEE Transactions On Industrial Electronics, Vol. 57, No. 2, February 2010.

[5] Eftichios Koutroulis, Kostas Kalaitzakis, and Nicholas C. Voulgaris “Development of a Microcontroller-Based Photovoltaic Maximum Power Point Tracking Control System., IEEE Transactions On Power Electronics, Vol. 16, No. 1, January 2001.

REFERENCES

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CONTD.. [6] Weidong Xiao, Nathan Ozogand William G. Dunford,” Topology

Study of Photovoltaic Interface for Maximum Power Point Tracking”, IEEE Transactions On Industrial Electronics, Vol. 54, No. 3, June 2007.

[7] Rahul S. Sable, A. S. Werulkar and P. S. Kulkarni , "Microcontroller Based Soft Switching Buck Converter for Solar Home Lighting System.”, National conference on (ETREEE-201 ) pp.(167-173), February 25-26,2012.

[8] R. Gules, J. De Pellegrin Pacheco, H. L. Hey, and J. Rnhoff, “A maximum power point tracking system with parallel connection for PV stand-alone applications,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2674–2683, Jul. 2008.

[9] Ying-Chun Chuang, “High-Efficiency ZCS Buck Converter for Rechargeable Batteries” , IEEE Transactions On Industrial Electronics, Vol. 57, No. 7, July 2010.

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PAPER PUBLICATION

[1] D.Shankar, A.S. Werulkar, P.S. Kulkarni “Simulation Of Soft Switching Boost Converter With MPPT For Solar Home Lighting System” All India Seminar (with International Participation) On Clean Energy & Energy Conservation 2012, Pp.(100-106), 13th-14th October 2012.

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THANK YOU!! D.Shankar

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