SEPTEMBER 25, 2008 Power Melder Midterm Presentation

About Us Christopher Harper EE Tina McGlaston CPE Daniel Wilson CPE Tyler Pettit EE

Overview Current Problem Solution Constraints Approach  Power Hardware  Microprocessor Progress Questions

Current Problem Small generators can not 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

Mitsubishi 2500 Watt Generator $825 Subaru 1400 Watt Generator with Inverter Technology $1000 Economic Yamaha 2500 Watt Generator with Inverter Technology $1500 The Power Melder must cost less than a typical consumer generator with similar capacity. Images, Prices from:

Safety Input Isolation Fuses Conductor Separation Table from Voltage Between Conductors ( AC Peaks or DC Volts ) Minimum Bare Board Spacing B1B2B3B mm (.002 in.)0.1mm (.004in.) 0.05mm (.002 in.) mm (.004 in.)0.6mm (.024in.) 0.13mm (.005) mm (.004 in.)0.6mm (.024 in.)1.5mm (.06 in.)0.13mm (.005) mm (.008 in.)0.6mm (.024 in.)3.2mm (.126 in.)0.4mm (.016 in.) mm (.008 in.)1.25mm (.05 in.)3.2mm (.126 in.)0.4mm (.016 in.) mm (.008 in.)1.25mm (.05 in.)6.4mm (.252 in.)0.4mm (.016 in.) mm (.008 in.)1.25mm (.05 in.)12.5mm (.492 in.)0.4mm (.016 in.) mm (.01 in.)2.5mm (.1 in.)12.5mm (.492 in.)0.8mm (.0315 in.) >500 add ---> mm/volt(.0001in.) 0.005mm/volt(.0002 in.) 0.025mm/volt(.001 in.) mm/volt( 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

System Overview Generator #1 Generator #2 Power Melder PFC DC-DC Converter Master uC Inverter

Power Factor Correction Power Factor  Ratio of real power to apparent power  Ideal situation  Unity power factor  Current replicates voltage (phase and shape)  Load appears purely resistive  No reactive power drawn

Power Factor Correction Bridge Rectifier  AC to DC  Non-linear current pulses  Poor power factor  More line current to produce same output voltage

Power Factor Correction Passive Power Factor Correction  Inductor used to shape input current  Large inductor required for high power applications  Increased weight  Increased cost  Unregulated output voltage  Requires switch for multiple input voltages Active Power Factor Correction  IC used to shape input current  Low cost  Convenient size  Stable output voltage with small ripple  Over-voltage protection  Input current limiting

Power Factor Correction Active PFC Passive PFC No PFC Image from:

Power Factor Correction LT1249 Power Factor Controller  Peak current limiting  Over-voltage protection  100kHz switching frequency  Low start-up current  No switch required for multiple input voltages

Power Factor Correction Power Melder PFC Stage

Power Factor Correction LT1249 Input Voltage/Current and Output Voltage/Current Input Voltage = 177VAC, 60Hz

Power Electronics Flyback topology.  Simple, Commonly used  Low parts count  High Ripple  Requires relatively large transformer Image from: DC/converter.shtm

Power Electronics Half-Bridge topology.  Relatively high power  Efficient  Large capacitor currents  Requires complex control circuitry Image from: net.com/electron/smps.htm

Power Electronics Full-Bridge topology.  Extremely high power  Very Efficient Image from: net.com/electron/smps.htm –Highest parts count –Requires complex control circuitry –No control circuitry fault tolerance

Power Electronics Double-switch forward topology.  Isolated (safe)  Efficient  Cost-effective Image from: df –Medium power –Very uncommon

Isolation Digital Control Lines OPTO-COUPLER (OPTO-ISOLATOR) Uses a beam of light to transmit the signals or data across an electrical barrier High speed Low power Small size Achieves excellent isolation GALVANIC ISOLATION Isolating functional sections of electric systems Low speed High power Communication between multiple

Opto-Coupler Components of the Opto-Coupler light emitting device light sensitive device

Analog to Digital Converter Used to sense input voltage of the generators LTC bit resolution I2C compatible Low power: 1.5mW at 1ksps Fast Conversion Time: 1.3µs

Microcontroller Microchip PIC24HJ32GP202

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

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

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

Questions?