Smart ENergy Delivery (SEND)

Critical Design ReviewDecember 11, 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

Design system to be as grid-independent as possible

SEND System

Basic System Goals Detect real time power availability and load

demand

Convert sources to single DC bus and deliver required energy to loads

Store energy in battery system for use when resources are unavailable

Monitor load usage and display to user through web interface

Reach Goals

Predictive load profiling Weather solar resource prediction System mode control by the user Load prioritization and control Add scalability

Allow for multiple source possibilities System architecture may be followed for

higher power applications

Functional Decomposition

Subsystems Design

Hardware Subsystems

Power electronics Buck DC-DC converter

▪ Gate Driver▪ Current Control

Full-wave rectifier Current and voltage sensing

AC DC

Battery Charging/Monitoring Interface with control architecture

PV Power Stage Schematic

DC-DC Switching Converter Step down PV/rectified grid voltage

to DC bus efficiently Design elements to minimize losses

Conduction Switching Size for power level used

Control current draw and power point on PV panel using feedback loop References provided by central

controller

Buck Converter

Buck Converter Design

fs = 100kHz

∆iL = 0.3*IL

Keep out of DCM

L = = 180μF C = 3.3 mF

Cutoff above switching

frequency

Current Programmed Controller

Current Programmed Controller

Current Programmed Controller In contrast with a voltage

comparator To set duty cycle Ideal for implementing a charge

controller Necessary for OPPT Since current is being measured and

compared, most accurate Not ordinarily stable at duty cycles >

50% Therefore add a slope compensator

Current Programmed Controller

Artificial ramp stabilizes circuit

Buffer creates a signal appropriate for the MOSFET

Clock sets the output high at the beginning of the period

When comparator is triggered output drops low, setting the duty cycle

Current Programmed ControllerClock sets the output high

Comparator condition met, output set low

Inductor current

Slope compensation and reference current

Current Programmed Controller Choosing a chip to match our

requirements: Large duty cycles 100kHz frequency 12V operation Current sense/ mode control Good documentation

UC3843

OscillatorInput filter

Slope compensator for stability

Current Transformer forisolation and efficiency

Gate Driver

Gate Driver

However the duty cycle output is 5V Not sufficient to drive the MOSFET

Vgs = Gate, Source Voltage

Minimum 12V

Gate Driver The gate driver takes the 5V duty

cycle and converts it to a signal for the MOSFET

Represented by the buffer on the output

Gate Driver

MOSFET Driver

Step downtransformer

BleedResistor

Charge Capacitor

Voltage Limit

DampeningResistor

12V

-12V

12V

0V

From CPC

Rectifier

Rectifier

Rectifier

Smoothing capacitor for DC voltage

Full bridge rectifier

Rectifier Converter

Necessary to match the changing battery voltage

Steps down input voltage Requires current programmed

controller and gate driver Signal from main controller

Microcontroller Hardware

MSP430 Connections

3.3V UART Beaglebone

SPI AC Current/Voltage Sensing

ADC DC Current/Voltage Sensing

PWM Current Reference

MSP430

ADE7753 Power Meter IC

ADE7753 Optoisolation

ADE7753 5V TTL Logic

MSP430 3.3v ADE7753

connected to high voltages, such as 120V RMS on the grid connection.

Software Subsystems

MSP430 Drivers

To minimize code refactoring, we isolated hardware dependent code in driver software modules.

Minimized changes when transitioning from MSP430f636 to MSP430f6333

Software Overview

Software State

Software state determined by battery state of charge.

State 0 – Initialization State 1 – Low Battery State 2 – Sufficient Battery State 3 – Maximum Battery

State 0 – Initialization

State 1 – Low Battery

State 2 – Sufficient Battery

State 3 – Maximum Battery

Beaglebone Software

Web Interface

BeagleBone Data Flow Diagram

BeagleBone

Python Serial Interface Weather Forecasting Database Connection (Write)

Mysql Single Database Multiple Tables

Lighttpd Single site send.int.colorado.edu

PHP Database Connection (Read)

Prototyping & Results in Software

Load Monitoring Prototype

Progress in Software Development Software Drivers developed and

tested on the MSP430 F6736 series Serial Analog to Digital Conversion

Load Monitoring Prototype Open-Loop Toroid

User Interface Minimizing use of the BeagleBone

MSP430 Status

Testing and Prototyping done on F6736 series

Sampling Times ¼ second per 1000 samples

Considering a move to F433x series given an increase in hardware ADCs F433x series provides 12 ADCs at up to

12bit precision Drivers would need to be ported

Load Monitoring Prototype

1 2 3 4 5 6 7 80

0.10.20.30.40.50.60.70.80.9

1

Current Sense Accuracy

Kill A WattCurrent Transformer

Sample Number

Current Measured[Amps]

Sample Number Load Type1 Complex Small Laptop2 Resistive Fan Low

3Complex Small Laptop +Fan(Low)

4 Resistive Fan High

5Complex Single Laptop +Fan(High)

6 Complex Two Laptops

7Complex Large Laptop +Fan Low

8Complex Large Laptop +Fan High

Resistive loads should be more accurate indicating incorrect calibration constant

Non-Linear Differences when adding/removing loads

Mitigate using Energy Sense IC with <0.1% error

User Interface

Energy Data Real-time updating graphs of load usage

Weather Prediction Solar radiance prediction using cloud

cover data from weatherunderground.com

Javascript + Highcharts Fast rendering

PHP Development Future of the User Interface

send.int.colorado.edu

Prototyping & Results in Hardware

Buck Converter Prototype A perf-board prototype was created

to test the buck converter design

Components sized to possible power output of solar panel

Tested with power supply at a range of voltages

Buck Converter Prototype

Buck Converter Prototype

Buck Converter Results

Buck Converter Results

0 5 10 15 20 25 30 35 400.5

0.550.6

0.650.7

0.750.8

0.850.9

0.951

Efficiency at 30, 50, 70% Duty Cycle

30%50%70%

V in

Effici

ency

Buck Converter Simulation A Simulink model was also created

for the buck converter using the Simscape (circuit elements) library

Useful for higher system level modeling

Simulink Model

Step Response

Peak Power Point Tracking Modeling Matlab Simulink model created to

test peak power tracking algorithm

Changes value of a resistor connected to a solar panel to draw max power

Simulink Model

Response to Changing Insolation

Solar Panel

Have received a solar panel to use from the department

Rated for 80 W

Thin film chemistry createsslightly different IV curve

Solar Panel I-V Characterization

Solar Panel P-V Characterization

Risk Analysis and Administration

Primary Risks

Battery usage Measurement accuracy Microcontroller usage System integration

Battery Usage

Accurate estimation of SOC Errors reduce life cycle of battery Adding temperature measurement

Overcharging protection Overcharging harmful to AGM batteries Conservative calculations

Measurement Accuracy

AC current measurement Using energy sense IC provides optimal

accuracy

DC current measurement Current transformer

▪ Available for controller from hardware in converter and rectifier

Sense resistor amplification▪ Battery current measurement

Measurement Accuracy

PV power measurements .2% error on PV Watt output with 10-bit ADCs Determined to be acceptable for PPT

algorithms

Battery SOC calculations Need accurate voltage set-points 10-bit ADC produces ~12mV step size 12-bit ADC produces ~3mV step size 12-bit preferable for charge control algorithm

Microcontroller Usage

Controller I/O MSP430 model has required ADC, UART,

and SPI channels Computation timing

Algorithms: PPT, Charge control, SOC System failure

Controlled boot-cycle reduces hardware fail-safe usage

System Integration Power electronics

Loading, noise, harmonics, interference Up to three board revisions planned and

budgeted Boot sequence

Power controller regardless of battery SOC Hardware will be connected directly to

battery Failsafe mechanisms

Overcurrent Protection on each board

S.E.N.D. Cart

Enables outdoors testing

Easy board mounting Solar panel

adjustment

Budget

Received funds from UROP and EEF

Total funds: $3200

Obtained some parts for free, some

on loan

BudgetCategory New Expected SpentSolar 60 0Load Monitoring 300 10Controller 370 0Rectifier 210 0Converter 310 20Inverter/Converter for Loads

120 0

Energy Storage 60 60User Interface 40 0Web Interface 20 0Loads 260 0Total 1750 90

Division of LaborTask Primary Secondary

Network Interface John Kit

Load Monitoring Kit None

Controller H/W Kristine John

Solar Converter Josh Kristine

Grid Rectifier Tim Neil

Power Point Tracking Tim Josh

Controller S/W Neil Kit

Battery Management Neil None

Schedule

Acknowledgements

Dragan Maksimovic Robert Erickson Trojan Battery Advanced Circuits

Questions