SEPTEMBER 25, 2008

Power MelderMidterm Presentation

About Us

ChristopherHarperEE

Power conversion electronics

Tina McGlastonCPE

Isolation/ADC/Human-interfacing

Daniel WilsonCPE

Firmware/Human-interfacing

Tyler PettitEE

Power-factor correction

Overview

Current ProblemSolutionConstraints

Practical Constraints Technical Constraints

Approach and Trade-off Analysis Power-Factor Correction DC-DC Converter External ADC Opto-coupler Microprocessor

ProgressTimelineQuestions

Current Problem

Small generators cannot power large loads.

Solution

Parallel power generation

Current Solutions

Honda EU1000iA 1 kW generator, may be paralleled Input generators must be identical (same output

power) Must be Honda generators

System Overview

Power Melder System

DC-DC Converte

r

DC-DC Converte

r

LCD

Keypad

μC

Output power busGenerator

Generator

System Overview

Bridge rectifi

er

Power factor

correction

μC

Shunt resisto

r

Fromgenerator

Outputbus

ADC

DC-DC convert

er

Master/Slave bus

DC-DC Converter Subsystem

Yamaha 2500 Watt Generator

with Inverter Technology

$1500

Mitsubishi 2500 Watt Generator

$825

Subaru 1400 Watt Generator with Inverter Technology

$1000

Practical Constraint: Economic

The Power Melder must cost less than a typical consumergenerator with similar capacity.

[1]

Power Melder

• Adds the extra benefit of an inverter

• Must cost no more than typical generators with an inverter

•$1000-$1500

Practical Constraint: Safety

Input IsolationFusesConductor Separation

[2]

Voltage Between Conductors ( AC Peaks or DC Volts ) Minimum Bare Board Spacing

  B1 B2 B3 B4

… … … … …

301-5000.25mm (.01

in.)2.5mm (.1 in.) 12.5mm (.492 in.) 0.8mm (.0315 in.)

… … … … …

B1 - Internal ConductorsB2 - External Conductors, uncoated, Sea level to 3050m ( 10K ft.)B3 - External Conductors, uncoated, over 3050m ( 10K Ft.)B4 - External Conductors, coated with permanent polymer coating

Technical Constraints

Name Description

Input Power Must accept 90-300V DC or AC 50-200Hz

Output Power Must provide a single output DC bus between 12V and 14.5V for use with an AC inverter

Output Stability Must be stable to within 10% of nominal value with a maximum of 10% ripple

Accuracy Measured power draw and power limiting must be accurate to within 10W

Power Capability Must be capable of drawing 150W from any acceptable power source

Power Factor Correction

Bridge Rectifier AC to DC Current pulses at voltage

peaks Poor power factor

Current spikes stress generator

Power Factor Correction

Passive Power Factor Correction Inductor used to shape

current Large inductor

required for high power applications

Increased weight Increased cost

Active Power Factor Correction IC used to shape

current Low cost Compact and

lightweight More accurate current

shaping

Power Factor Correction

Applicable Constraints Input Power: Must accept 90-300V DC or AC 50-

200Hz Power Capability: Must be capable of drawing

150W from any acceptable power source

LT1249 Power Factor Controller Built-in peak current limiting

and over-voltage protection 100kHz switching frequency

DC-DC Converter Topology

Applicable Constraints Output Power: Must provide a single output DC

bus between 12V and 14.5V for use with an AC inverter

Power Capability: Must be capable of drawing 150W from any acceptable power source

Output Stability: Must be stable to within 10% of nominal value with a maximum of 10% ripple

Cost: The Power Melder must cost less than a typical consumer generator with similar capacity.

DC-DC Converter Topology

* Cost for high output power, low volume; more stars means cheaper

Analog to Digital Converter

Used to sense input voltage of the generators

Applicable Constraints:• Measured power draw and power limiting must be

accurate to within 10W

LTC2309

12 bit resolution I2C compatible Low power: 1.5mW at 1ksps Fast Conversion Time: 1.3µs

Opto-Coupler

Components of the Opto-Coupler

•LED•Phototransistor

Opto-coupler

•Isolates two circuits•Passes signals without allowing electrons to move between circuits

[3]

Microcontroller

Microchip PIC24HJ32GP202

[4]

Progress: MCU Firmware (Converter)

Copy ADC value into memory

Reset ADC

ADC Interrupt

Wait for serial

command

Process command

Return any requested

data

Serial comm task Timer Interrupt

Main frozen?

Init frozen?

Signal init semaphore

Signal main semaphore

no

no

yes

Wait on semaphore

Init PWM duty cycle and start PWM

Unfreeze main task and freeze init task

Init task

Progress: MCU Firmware(Converter cont’d)

Main task

Wait on semaphore

Calculate input voltage from ADC value

Voltage too low?

Turn off PWM

Calculate output voltage from ADC value

Voltage too high?

Increase PWM duty cycle

Decrease PWM duty cycle

Voltage too high?

Voltage too low?

Send message to master

Freeze main task

yes

yes

no

no

no

no

yes

yes

Progress: MCU Firmware (Master)

Read voltage of ouput bus

Voltage too high?

Send increase command to all

Send decrease command to all

Voltage too low?

Query current

contributions

Contr. correct?

Send correctional commands

Wait on semaphore

yes

yes

yes

no

no

no

Main task

Progress: Power Factor Correction

Power Melder PFC Stage

Progress: Power Factor Correction

LT1249 Current ShapingInput Voltage = 177VAC, 60Hz

Progress: DC-DC Converter

Timeline

September October November

Hardware Design

Prototype Boards

Single Unit Testing

System Testing

Software

References

[1] http://www.stmicroelectronics.com/stonline/books/pdf/docs/3721.pdf

[2] http://pcbwizards.com/[3] http://www.mech.uwa.edu.au/[4] PIC24HJ32GP202 datasheet.

http://www.microchip.com/

Questions?