Maximum Power Point Tracking System for Solar Racing Team Andrew Matteson Ingrid Rodriguez Travis Seagert Giancarlo Valentin School of Electrical and Computer Engineering GT Solar Jackets March 14, 2011 Georgia Institute of Technology

Project Overview Customized smart switching power system to charge car batteries with solar energy Intended for use by the Solar Jackets in the World Solar Challenge 2011 Estimated material cost: $194 per unit

Prior Work: Fall 2010 Initial design adaptable to varying sunlight variations Designed for different battery and array specifications Contained one power switching circuit per board

Design Objectives: Spring 2011 Minimized PCB layout area Efficiency > 90% Implement RS-485 communication interface Comply with solar challenge regulations

Design Overview

Maximum Power Extraction Solar Cell I-V Characteristic Maximum Power Point P = IV

Smart Power Switching Circuit

P&O Tradeoffs Advantages: Simple to implement Popular algorithm; open-source code available Highly adaptive Disadvantages: Inevitable oscillation around the maximum power point May interpret local maximum as the absolute maximum

RS-485 Protocol Implementation This standard defines a physical layer The protocol will be defined by the team This standard will be responsible for communication between other electrical systems in the car

Operational Safety Precautions Gradual shutdown by intentionally deviating from maximum power point Maximum voltage Input: 18V Output: 105V Maximum current Input: 8.5A Output: 3.5A

Safety Precautions: Fuses and Connectors Over-current/voltage protection  Automotive fuse at input  Cylindrical fuse at output Touch-safe connectors Courtesy of Fall 2010 Solar Power Array Management Group.

Safety Precautions: Zener Diodes The Zener diodes provide paths for current to flow in the event of an abrupt disconnection.

Efficiency: Synchronous Rectifier Circuit efficiency can be improved by replacing standard components with more efficient alternatives The standard diode can be replaced by a synchronous rectifier The current design will accommodate both alternatives in the following way: Losses ~ I 2 R DS(ON) Losses ~ V F I

Design Challenges and Tradeoffs Georgia Tech PCB Machine Dimensions (10.5 in x 7.5 in ) This constraint dictates how many MPPT circuits can fit onto a single board (currently two) Using a different machine would introduce significant additional costs.

Design Challenges and Tradeoffs Bounding Simulation Parameters Exhaustive circuit simulations cannot be performed for the full range of variable parameters As a result, the circuit’s values are only approximations of the ideal optimal components

Product Delivery Scheduled delivery for Monday April 25, 2011 Fully tested reproducible boards Preprogrammed with microcontroller code Include mechanical switches for easy control

Future Work Schedule March 18, 2011 – First Prototype April 01, 2011 – Design Tests for Prototype April 15, 2011 – PCB Re-Design April 20, 2011 – Final Build April 22, 2011 – Final Design Tests April 25, 2011 – Deliver Completed Board

RS-485 Demonstration

Questions