SEPTEMBER 25, 2008 Power Melder Midterm Presentation

About Us Christopher Harper EE Power conversion electronics Tina McGlaston CPE Isolation/ADC /Human- interfacing Daniel Wilson CPE Firmware/Hu man- interfacing Tyler Pettit EE Power-factor correction

Overview Current Problem Solution Constraints  Practical Constraints  Technical Constraints Approach and Trade-off Analysis  Power-Factor Correction  DC-DC Converter  External ADC  Opto-coupler  Microprocessor Progress Timeline Questions

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 Converter LCD Keypad μC Output power bus Generator

System Overview Bridge rectifier Power factor correction μC Shunt resistor From generator Output bus ADC DC-DC converter 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 consumer generator 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 Isolation Fuses Conductor Separation [2] Voltage Between Conductors ( AC Peaks or DC Volts ) Minimum Bare Board Spacing B1B2B3B4 …………… mm (.01 in.)2.5mm (.1 in.)12.5mm (.492 in.)0.8mm (.0315 in.) …………… B1 - Internal Conductors B2 - 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 NameDescription Input PowerMust accept V DC or AC Hz Output PowerMust provide a single output DC bus between 12V and 14.5V for use with an AC inverter Output StabilityMust be stable to within 10% of nominal value with a maximum of 10% ripple AccuracyMeasured power draw and power limiting must be accurate to within 10W Power CapabilityMust 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 V DC or AC Hz  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 TopologyCost*Output Power RippleFault Protection Flyback Half-Bridge Full Bridge Forward Forward (double switch) * 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 LTC 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 taskTimer Interrupt Main frozen? Init frozen? Signal init semaphore Signal main semaphore 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 no 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 no Main task

Progress: Power Factor Correction Power Melder PFC Stage

Progress: Power Factor Correction LT1249 Current Shaping Input Voltage = 177VAC, 60Hz

Progress: DC-DC Converter

Timeline SeptemberOctoberNovember Hardware Design Prototype Boards Single Unit Testing System Testing Software

References [1] books/pdf/docs/3721.pdf [2] [3] [4] PIC24HJ32GP202 datasheet.

Questions?