ARISSat-1 Critical Design Review Orlando, Feb 15, 2010 Maximum Peak Power Point Tracker (MPPT) John Charais / Jerry Zdenek

Feb 15, 2010ARISSat-1 CDR2 Introduction MPPT Extracts the most possible energy from the solar panel for use by the satellite Scope –Requirements –Design –Safety Considerations –Verification –Operations –Status

Feb 15, 2010ARISSat-1 CDR3 Requirements Convert Power from a solar panel to a output capable of charging a 28V Silver-Zinc Battery –Panel Input 51Volts Open Circuit, 0.5A Short Circuit –Battery max Charge Voltage 35.8V Provide Telemetry Data –PPT and Solar Panel Temperatures –Solar Panel Voltage and Current –Communicate back via RS485 Powered off Solar Panel so system can restart in case of battery failure

Feb 15, 2010ARISSat-1 CDR4 MPPT Design PIC16F690 RS485 To PSU UART

Feb 15, 2010ARISSat-1 CDR5 PCB Assembly

Feb 15, 2010ARISSat-1 CDR6 MPPT SEPIC Converter and Oscillator S.P.- S.P.+ Current Amp - + C1 Vout Rhysteresis Rsense Rsource Vosc_ref

Feb 15, 2010ARISSat-1 CDR7 SEPIC Converter SEPIC – Single Ended Primary Inductor Converter –Any input voltage can be any output voltage –Comparator 1 within the Microcontroller controls the frequency of oscillation (relaxation oscillator) –Oscillator is current controlled off return to Solar panel –Voltages expected on components Max voltage across the FET:Vin Max voltage across SEPIC cap: Vin Max voltage across diode:Vout + Vin

Feb 15, 2010ARISSat-1 CDR8 MPPT Over Voltage Protection Rhysteresis Rsource Vosc_ref C1 - + Vout C2 - + Vint_ref Vcurrent_sense

Feb 15, 2010ARISSat-1 CDR9 Over Voltage Protection Over voltage condition forces oscillator off Once condition is removed, oscillator starts again

Feb 15, 2010ARISSat-1 CDR10 MPPT Safety Considerations Hardware –Oscillator is hardware controlled After initialization no software is needed to run the oscillator or over voltage protection –SEPIC output is capacitively coupled: oscillator halts and no power is delivered to the output –Hardware current limit to oscillator Failure conditions –SEPIC FET stuck on Current is limited by Solar Panel Failure mode to over heating is an open –Self powered: if stuck in a bad state a clean reboot happens each orbit or rotation of satellite

Feb 15, 2010ARISSat-1 CDR11 MPPT Safety Considerations Software –Comparators are re-initialize in main loop –WDT is enabled –If microprocessor is in a bad state, the power conversion is just less efficient Self corrects due to rotation in and out of sunlight

Feb 15, 2010ARISSat-1 CDR12 Verification Testing with multiple power sources –Simulated panel –Actual panel with Earth illumination –Multiple non space grade panels

Feb 15, 2010ARISSat-1 CDR13 Operations A Day in the Life of… How will it really work… How will it appear in telemetry…

Feb 15, 2010ARISSat-1 CDR14 Status What remains and how long will it take. Don’t be shy. Bring up issues. End on a positive note.