mppt algorith

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Control Of Solar Power Conversion By Dr. Allon Guez Professor ,ECE dept. Drexel University Mr. Harshad Tadas Graduate Student , ECE Dept. Drexel University

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Page 1: mppt algorith

Control Of Solar Power Conversion

By Dr. Allon Guez

Professor ,ECE dept. Drexel University

Mr. Harshad Tadas Graduate Student , ECE Dept. Drexel University

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We have reviewed the Photovoltaic cell Model and

state of the art power control techniques

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OUTLINE

1.A Simple Model of solar cell

2.MATLAB simulation of Solar cell driving RLC load

3.Review of Different MPPT algorithm

4.References

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Due to depletion of non renewable energy sources

Solar Power is Need of the Day.

Solar Power is clean, renewable and less maintenance

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1. MODELING OF THE PV CELLS

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The expression of the I-V curve

where

Voltage equation for PV Cell

where

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Simulation of solar panel ASE 30-DG-UT (32W) manufactured by ASE Americas

Panel specifications: Maximum Output power: PMPP = 32W Short circuit current: Isc = 0.6A Open circuit voltage: Voc=95V Voltage at maximum power: VMPP=68V Current at maximum power: IMPP=0.47A

IV Curve PV curve

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2. MATLAB simulation of Solar cell driving RLC load

Circuit for simulation

S1,S2 and S3,S4 are switched according to duty cycle and switching frequency

Differential Equations governing the simulation

2 2 12

dx dx xL Rx

dt dt C

12

dxx

dt 2 2 1

2

dx dx xL Rx

dt dt C

1x2x

Where = Charge= current

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Main Loopx1(1)=0; %Initial conditionsx2(1)=0; FS=11000Hz; Ts=1/FS;% switching period DC=.7;% Duty CycleR=200; % ResistanceL=.04; %inductanceC=.2*10^-6; %capacitanceNP=700; % # periods of simulation NSP=10; % # sampls per period dt=Ts/NSP; %sampling period for j=1:NP for k=1:NSP i= NSP*(j-1)+k; flag(i)=1; if k*dt>DC*Ts flag(i)=-1; end v(i)=flag(i)*scvtg(x2(i)); p(i)=(v(i)*x2(i))^2; % inst power x1(i+1)=x1(i)+dt*x2(i); x2(i+1)=x2(i)+(dt/L)*(v(i)-R*x2(i)-(x1(i)/(C))); endend

function [v]=scvtg(X)Pmpp= 32;Voc= 95;Isc=0.6;Vmpp=68;Impp=0.47;B=((Impp/(Isc-Impp))+log((Isc-Impp)/Isc))/(((2*Vmpp)/Voc)-1);Rs=(Pmpp/(Impp^2))-((Voc/B)*(1/(Isc-Impp)));v=(Voc*(((log((Isc-X)/Isc))/B)+1))-(Rs*X);

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Challenges:

•Photovoltaic generation output characteristic is unstable due to the changes in solar radiation and temperature.

•Solar cell conversion efficiency is less ie. only about 40% efficiency

•Initial setup is very costly.

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To Minimize power losses

•Operate PV source in Maximum power region during different environmental condition

•DC DC converters called Maximum Power Point Trackers are used.

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3. Review of Different MPPT algorithms

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The Concept Of MPPT

MMPT has a task to virtually change the slope of load line to make it intersect at ‘M’

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Block Diagram of PV system with Components of MPPT

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Various MPPT Algorithms

•The Perturb and Observe (P&O)

•Incremental Conductance (INCC)

•Constant Voltage Method

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1.1 Voltage Based P&O

•P1 is calculated at V1 and Changed by dV (Const)•P2 is calculated at V2 •If ΔP=P2-P1 is +ve, V is increased till it reaches Pm.•Voltage is varied using PWM•Any further increase in V willdecrease P • Thus this algorithm oscillates between pt. A &B

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Voltage Based P&O algorithm require 2 loops •For changing Voltage using PWM •For Changing Power by changing Voltage

And thus Sampling Loop and algorithm coding length increases

This can be removed by tracking the power versus Duty Cycle

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1.2 Duty Cycle Based P&O

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Drawback of P&O algorithm

Tendency of Tracking in Wrong Direction due to change in atmosphere

When power is oscillating between A and B if solar radiation starts increasing , duty cycle change moves operating point to C because power level has increased .

But C is away from MPP and thus P&O fails to track MPP

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2. Incremental Conductance

Slope in P-V curve is Either positive negative or zero on the left , right and peak point respectively

Hence Operating point is at MPP ifThis implies

At MPP

Left and right side of PV curve

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•INCC does not calculate power and only voltage and current value carry on tracking.

•Since this algorithm observes which side of curve the operating Point is working on,Thus this is a eminent Drift Free Tracking .

•Since INCC has a division operation hardware and software implementation is relatively complex .

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3. Constant voltage method

•This method makes use of the fact that the ratio of maximum power point voltage and the open circuit voltage is 0.76.

•First the open circuit voltage Voc is calculated and then Vmpp is easily obtained.

•The operating point is forced to reach optimal value

•This technique is often used in cheaper instrument like solar lantern

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Drawbacks

•The current from the photovoltaic array must be set to zero momentarily to measure the open circuit voltage and then afterwards set to 76% of the measured voltage.

•Energy is wasted during the time the current is set to zero.

•The approximation setting the voltage to 76% of the measured voltage is not accurate.

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4. References

•Photovoltaic systems: Analysis and DesignBy A. K. Mukerjee and Nivedita Thakur

•MODELLING AND SIMULATION OF PHOTOVOLTAIC CELLS By Dorin PETREUŞ, Cristian FĂRCAŞ, Ionuţ CIOCAN’

•Evaluation of Micro Controller Based Maximum PowerPoint Tracking Methods Using dSPACE Platform By Yen-Jung Mark Tung , Dr. Aiguo Patrick Hu