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Boost Control: MPPT Continued• A Simple Method:

Perturb andObserve (P&O)

 – “Climbing” the V-ICharacteristic

 – Vary duty ratiobased on past andpresent power

input – Requires current

and voltage sensing

Source: http://www.iet.aau.dk/~des/papers/PID253435-1_EPE-PEMC2006.pdf

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The Maximum Power Point Tracker (MPPT) optimizes the amount of power

obtained from the photovoltaic array used to charge the electrical power supply

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Important because the voltage and current produced

from the solar panel is variable depending on the

amount of sun exposure to the solar panel.

- The battery charges most efficiently 12V and 3 A.

- purpose is to obtain the largest amount of voltage

vs. current from a solar array.

-voltage from solar panel goes to dc/dc converterwhich is parallel to MCU and battery

-MCU chooses the maximum point at which the

voltage and current will create the maximum power

output as depicted by the equation P = IV.

-Our goal: MPPT is to obtain efficiency of 90%

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0 5 10 15 200

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Panel Voltage (V)

   P  a  n  e   l   C  u  r  r  e  n   t   (   A   )

I-V characteristics for varying irradiance conditions

 

S = 300 W/m2

S = 500 W/m2

S = 800 W/m2

S = 1000 W/m2

0 5 10 15 200

10

20

30

40

50

60

Panel Voltage (V)

   P  a  n  e   l   P  o  w  e  r   (   W   )

P-V characteristics for varying irradiance conditions

 

S = 300 W/m2

S = 500 W/m2

S = 800 W/m2

S = 1000 W/m2

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  Maximum Power Point Tracker (or MPPT) for SPV 

• A maximum power point tracker (or MPPT) is a high efficiency DC to DC converter 

which functions as an optimal electrical load for a photovoltaic (PV) cell, most

commonly for a solar panel or array, and converts the power to a voltage or

current level which is more suitable to whatever load the system is designed to

drive.

•

PV cells have a single operating point where the values of the current (I) andVoltage (V) of the cell result in a maximum power output. These values correspond

to a particular resistance, which is equal to V/I as specified by Ohm's Law. A PV cell

has an exponential relationship between current and voltage, and the maximum

power point (MPP) occurs at the knee of the curve, where the resistance is equal

to the negative of the differential resistance (V/I = -dV/dI). Maximum power point

trackers utilize some type of control circuit or logic to search for this point and thusto allow the converter circuit to extract the maximum power available from a cell.

• Battery-less grid-tied PV inverters utilize MPPTs to extract the maximum power

from a PV array, convert this to alternating current (AC) and sell excess energy back

to the operators of the power grid.

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• Off-grid power systems also use MPPT charge controllers to extract the maximum

power from a PV array. When the immediate power requirements for other

devices plugged into the power system are less than the power currently available,

the MPPT stores the "extra" energy – energy that is not immediately consumed

during the day – in batteries. When other devices plugged into the power system

require more power than is currently available from the PV array, the MPPT drains

energy from those batteries in order to make up the lack. MPPT charge controllers

are quickly becoming more affordable and are more common in use now than ever

before.

• The benefits of MPPT regulators are greatest during cold weather, on cloudy or

hazy days or when the battery is deeply discharged. Solar MPPTs can also be used

to drive motors directly from solar panels. The benefits seen are huge, especially if

the motor load is continuously changing. This is due to the fact that the AC

impedance across the motor is related to the motor's speed. The MPPT will switchthe power to match the varying resistance

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V-I Characteristics of

a PV module

V-P Characteristics

of a PV module