Smart ENergy Delivery (SEND)

Preliminary Design ReviewOctober 16, 2012

Christopher Corey, Josh Crowley, John Fischer, Tim Myers, Neil Severson,

Kristine Thompson

SEND Mission

Design and implement smart microgrid energy delivery system

Combine multiple/varied energy sources in most efficient use of resources possible

Utilize advantages and address drawbacks of each source

SEND Mission

Intelligently match energy collection to load requirement

Design system to be as grid-independent as possible

Team Motivations

Develop innovative system that has ability to combine sources and pursues intelligent management of sources and loads

Team is varied in skill sets and fields of interests Reflected in requirements and functional

roles of project

Project Motivation

Rwandan Orphans Project Catch-Up School Kigali, Rwanda Provide education for 200-300 orphans

and local community children Unreliable grid Primary Goals

Cheap operation Robust Simple

Microgrid Background

Rise of renewable energy sources has increased the popularity and practicality of localized, grid-independent, and highly efficient power systems

Flexible power solutions to meet needs in many settings, including developing countries

Societal Impacts

Increase the effectiveness and efficiency of small scale power systems

System concept able to supply steady power to facilities such as schools, medical facilities, and community centers in areas of expensive and/or unreliable grid connection

SEND System

Basic System Goals

Convert solar and grid power to single homogeneous energy carrier (DC bus)

Store energy in battery system for use when resources are unavailable

Delivery energy to both DC and AC loads

Monitor load usage and display to user through web interface

Ability to isolate system components for protection

Reach Goals

Predictive load profiling System mode control by the user Optimum power point tracking for solar Weather solar resource prediction Add scalability

Allow for multiple source possibilities System architecture may be followed for

higher power applications Load prioritization and control

Functional Decomposition

Functional Decomposition

Power Inputs

• Two control signals

• Variable DC output to bus/battery voltage

• AC constant voltage output to bus

• 2 Charge Controllers

• Bridge Rectifier

• Charge Controller

Controller

• 3 control signal outputs, one control input from Linux Server

• Load data output to Linux Server

• Current and voltage measurements from AC Rectifier, solar converter

• State of charge and load monitoring input for decision making

Load Monitoring

• Separate in-line SCRs for load control

• Monitoring hardware with output to controller

• Spec’d for max draw of 55W and up to 4 loads

PV Array and Battery

PV Array

Monocrystalline Most efficient Most expensive

Polycrystalline Less efficient than mono Less expensive

Thin Film Lowest efficiency and density Least expensive Potentially available from University

Battery

Lead-acid for best emulation of large scale implementation

AGM deep-cycle Maximum safety Low self-discharge Low hydrogen emission High charge rate Maintenance free Deliverable by UPS

Input Power Electronics

Solar Energy Power Electronics

Responsible for drawing and converting power from the solar panel, outputting to power bus without overcharging battery

Solar Panel

Solar Converte

r / Charge

Controller

Battery

Variable DC

Power Bus

Battery Voltage DC

Battery Voltage DC

Solar Energy Converter

Implemented as DC-DC switching converter Buck/boost to be determined by solar panel

voltages

Output voltage is controlled by the power bus Set by the battery voltage

This, duty cycle from controller, and converter M(D) set the PV operating point

Solar Energy Charge Controller Prevent overcharging of battery with

charge controller

Solar panel may be producing power even though battery is at max capacity

Must also prevent power from flowing back into panel during times of no insolation

Grid Energy Rectifier

Responsible for drawing energy from grid when deemed necessary, outputting to power bus without overcharging battery

AC GridGrid

Rectifier

Battery

120V 60Hz AC

Power Bus

Battery Voltage DC

Battery Voltage DC

Grid Energy Rectifier

Implemented using a full-wave rectifier and switching (buck) regulator

Will receive an input from the controller dictating whether it is in operation

Grid Energy Charge Controller

The grid rectifier must also make sure to not overcharge the battery using a charge controller

Design will be similar to the solar energy charge controller

Charge Controller Implementation

System control should prevent excess power to battery, but a safety backup is needed

The two charge controllers must also make sure to not exceed the maximum charge rate of the battery with their combined output currents

Testability

Design will keep testability in mind Allow for subcomponents to be tested on

their own

Ex: Converter will be capable of being tested without solar panel input or charge controller output for proper DC-DC conversion Verify small pieces of functionality

individually

Part Tolerance

Design somewhat hinges on choice of solar panel Operating voltage range dictates

converter type

Currently some of most difficult / high risk components

Project hinges on success of this subsystem

Controller

Required functionality

Brain of operation Central controller

Controls the inputs to provide appropriate power to the loads and battery

Inputs

Current and voltage measurements from the solar panel

Current readings from the grid connection

State of charge of the battery User inputs Web interface settings and readings Load monitoring measurements

Outputs

Load control – on/off

Data to the web interface

Solar panel / converter control

Rectifier control (on/off)

Basic Functionality

Calculating available power from input sources

Power point tracking (PPT) for solar panel(s)

Calculating required power to be delivered Controlling external hardware

AC grid connection Solar converter / power point tracking Includes turning off inputs with insufficient

power Reporting data to the web interface

Goal Functionality

Change of operation based on user mode Load priority control Use predictive models as an input for a

higher efficiency system If it is going to be sunny all day, don’t use the

grid to charge the battery the night before If the grid is unreliable on Tuesdays, charge

the battery in advance Enable optimum power point tracking

when appropriate

Control Logic Flow

Options for implementation

GPIC – General Purpose Inverter Controller National Instruments power controller

board

Microcontroller and custom PCB

GPIC-General

General Purpose Inverter Controller

Robust device for controlling grid tied and high power systems

Built in FPGA

Real time operating system

Power protocol support

GPIC- Advantages/Disadvantages

Advantage Simplifies a lot of implementation

Disadvantage No design experience with a

microcontroller Far more robust than our product needs Unit cost would be high since the GPIC is

expensive

Microcontroller - Analysis

Advantages More design experience▪ Board design▪ High power considerations▪ Choosing the right microcontroller

Much more cost effective implementation▪ Options we don’t need can be eliminated

Disadvantages Large added effort to the system design

and implementation

Testability

Testing will be divided into each subsystem of control Example: power point tracking can be

tested by testing a closed loop converter circuit with bench top power supply

Part Tolerance

There are no required parts for initial design

After PCB fabrication, packages must remain the same for easy integration

Web Monitoring / Load Management

Web Monitoring

Web interface does not require specialized software for access

Enables monitoring of load power consumption

Load Management (On / Off)

Load profiles, for automatic power management

Load Management

Solid State Relays

Non-invasive current sensing

Web Server

Beagle Bone

Arm Cortex A8

Has a webserver pre-installed, running on the Angstrom Linux distribution.

Serial UART, I2C, SPI

Schedule Sept 25

Initial Requirements Specification and Use Case Models

Oct 16 Preliminary Design Review Present Functional Decomposition Level 0 and 1

Oct 23        Functional Decomposition Complete Functional Decomposition to Level 3

Nov 6         Proof-of-Concept Bench Testing Power Point Tracking- Optimum and Peak Switching - Converter Manipulation Apache Server for Web Interface Current Monitoring

Nov 15       Demonstration of major hardware and software

components and subsystems critical to major functions.

Web Interface Power Point Tracking Inverter, Converters, Rectifier

Dec 6 Critical Design Review (CDR)

Dec 13 Proof-of-Concept Open Lab Symposium

Jan 17 Final Architecture and Requirements Specification

Complete

Jan. 24 Detailed Design Draft Software Implementation design Order PCBs / Complete BOM

Feb  7  Bench Testing of Prototype Whole System

(Hardware and Software) Feb 21

Complete test analysis and report results Mar 7

Develop initial integration test plan Mar 14

Final integration test plan complete Mar 21

Complete integration testing Apr  11        

Final Demonstration (EXPO) Testing Apr 25

EXPO -   Demonstration for Public. May 2

Complete all technical documents 

Division of LaborTask Primary Secondary

Network Interface John Fischer Kit Corey

Load Monitoring Christopher Corey None

Controller H/W Kristine Thompson John Fischer

Solar Charge Controller Josh Crowley Kristine Thompson

Rectifier Charge Controller Tim Myers Neil Severson

Peak Power Point Tracking Tim Myers Josh Crowley

Controller S/W Architecture

Neil Severson Christopher Corey

Appendix II: Division of Labor

Budget

Item Item Total

Implement Solar 660

Load Measure and Monitor 300

Controller Implementation 568

Rectifier, Converters, and Inverter Implementation (Each) 1236

Energy Storage 230

Web Interface Implementation 120

User Interface 390

Margin 300

Total 3804

Risks and ContingenciesArea of Risk Contingency Plan

Controller processor not robust enough to handle software scheduling requirements

Controller selection will be based on robust software specification, code will be written with efficiency in mind

Five boards to be developed:• Scheduling constraints for

system integration• High cost of error

Extensive prototyping combined with major development focus will ensure efficacy

Subsystem implementation could prove to be infeasible

These could be implemented with retail products if absolutely necessary

Smart control algorithm development requires working implementation of hardware; can only be tested late in development cycle

High level algorithm development is easy to scale for implementation, modeling will allow code development to begin prior to full hardware completion

Safety

High currents and voltages in use throughout design

Each board will use over-current protection

System will use “breaker box” to ensure modularity, provide additional protection

Safe usage practices will protect group members

Additional Considerations

Component redundancy for critical blocks Batteries Solar panels

Efficiency of individual parts determines overall system efficiency Not critical for basic goals Critical for reach goals, overall system

efficacy

Sustainability

Efficiency makes up for cost of implementation in time

System components will eventually fail

Boards can be re-spun– no relying on manufacturer supply availability

Disposability always a problem for PCBs and semiconductor materials

System Overview

Fully utilize heterogeneous energy sources

Store energy intelligently Supply power to variable loads Smart control to increase total

system efficiency Adaptable to loss of individual power

sources User monitoring and control

Project Overview

Most systems of this type cannot deal with multiple power sources simultaneously

A new and more effective implementation of popular technology

Energy independence with reliability Scalability and adaptability Use in developing countries

Questions