Group 211 Maximum Power Point Tracker

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Group 211Maximum Power Point Tracker

• Scott Harms
• Kelly Ebeling
• Advisor Professor Yuvarajan

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Introduction

• Project Description
• Requirements
• Block Diagram
• Options Considered
• Schematics
• Budget
• Timeline

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Project Description

• The goal of this project is to maximize the power
  transfer between a solar array and load.

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What is a maximum power point tracker?

• A maximum power point tracker optimizes the match
  between the solar array and the battery bank
• Maximum power point trackers are used to correct
  for the variations in the current-voltage
  characteristics of the solar cells

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Why use a maximum power point tracker?

• The current-voltage curve will move and deform
  depending upon such things as temperature and
  illumination
• For the array to be able to put out the maximum
  possible amount of power, either the operating
  voltage or current needs to be controlled

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Why use a maximum power point tracker?

• The power point quickly moves as lighting
  conditions and temperature change, therefore a
  device is needed that finds the maximum power
  point and converts that voltage to a voltage
  equal to the system voltage

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Solar Array

• BP MSX 120
• Pmax120W
• Vmp33.7V
• Imp3.56A
• Minimum Pmax114W
• Isc3.87A
• Voc42.1V

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Our I-V Curve
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Typical I-V Curve
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Current Products

• Outback MX60
• 60A _at_ 125V Max
• Programmable Output
• around 500
• Trace C60
• 35A _at_ 60V Max
• 12/24 V output
• around 150

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Why are we building a MPPT?

• Current devices on the market are expensive
• Devices on the market did not meet our
  specifications

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Requirements

• Input 170 Volt Array, 600 Watts
• Output utilized for charging 24 Volt battery
  system
• Concentration on maximum power extraction

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Block Diagram
Solar Array
Current Measuring
Voltage Measuring
DC Supply
Buck Converter
Microprocessor
Load
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Buck Converter
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Buck-Boost Converter
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Po Pn
General Algorithm Perturbation method
Chosen. Consequences The output power
will Oscillate about the MPP. Advantages Not
specific to a particular Array model.
Read V,I
Calc Pn
Pogt Pn
K -1
No
Yes
K 1
DD K
Limit D
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A possible minimization for the Buck converter

• P V I
• Vout D Vin
• If Vout is a constant K, then
• P I K/D
• Normalizing K
• P a I/D

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Microprocessor Selection

• F876 (Banned by HR)
• 10 bit A/D PWM
• 8K Flash
• EEPROM Memory
• F76
• 8 bit A/D PWM
• 8K Flash
• F73
• 4K Flash

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• 8 Bit Conversion still allows
• 39 mA Resolution for Current.
• 660 mV Resolution for Voltage.
• In Power terms
• A 26 mW resolution.

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DC Supply

• Controller powered from Array.
• Supply source could exceed 170VDC.
• Power dissipation an issue with linear
  regulation.
• Options
• Linear regulation
• Build Switchmode DC-DC (supply issues again)
• COTS converter.

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Preliminary Schematics
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Budget

• Operational Amplifiers 10
• Microprocessor 6
• Analog Components 10
• Power Components 25
• DC Supply 20
• PCB 100
• 2 Free Engineers Priceless

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Timeline
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Questions?