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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.
10/29/2012
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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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