Augmentation of a nano-satellite electronic power system using a field-programmable-gate-array.
Cupido, Stephen William John
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The CubeSat standard has various engineering challenges due to its small size and surface area. The challenge is to incorporate a large amount of technology into a form factor no bigger than 10cm3. This research project investigates the space environment, solar cells, secondary sources of power, and Field-Programmable-Gate-Array (FPGA) technology in order to address the size, weight and power challenges presented by the CubeSat standard. As FPGAs have not yet been utilised in this particular sub-system as the main controller, this research investigates whether or not the implementation of an FPGA-based electronic power supply sub-system will optimise its functionality by overcoming these size weight and power challenges. The SmartFusion FPGA was chosen due to its analogue front end which can reduce the number of peripheral components required by such complex systems. Various maximum power point tracking algorithms were studied and it was determined that the perturb-and-observe maximum power point tracking algorithm best suits the design constraints, as it only requires the measurement of either solar cell voltage or solar cell current, thus further decreasing the component count. The SmartFusion FPGA analogue compute engine allows for increased performance of the perturb-and-observe algorithm implemented on the microcontroller sub-system as it allows for the offloading of many repetitive calculations. A VHDL implementation of the pulse-width-modulator was developed in order to produce the various changes in duty cycle produced by the perturb-and-observe algorithm. The aim of this research project was achieved through the development and testing of a nano-satellite power system prototype using the SmartFusion FPGA from Microsemi with a decreased number of peripheral circuits. Maximum power point was achieved in 347ms at worst case with a 55% decrease in power consumption from the estimated 330mW as indicated in the power budget. The SmartFusion FPGA consumes only a worst case of 148.93mW. It was found that the unique features of the SmartFusion FPGA do in fact address the size weight and power constraints of the CubeSat standard within this sub-system.