Galvanically isolated transmission of analog control signals and study of commercial state of the art technology for satellites and launchers

Examensarbete för masterexamen
Master Thesis
Electric power engineering (MPEPO), MSc
Johansson, Lars
Space, the unknown place where satellites operate on our behalf. In space, the only known renewable energy comes from the sun, where the energy is captured by solar cells that supply all electronics on-board the satellite via rechargeable batteries. With an environment surrounded by vacuum and radiation, electronics need to be protected and constructed to manage the harsh conditions. Today, a DC/DC converter unit is available at RUAG Space to supply electronics with different voltages and power requirements. It consists of a galvanically isolated flyback topology with a feedback path and is currently operational in space, but there exists potential for improvements of the feedback path and therefore this thesis has been created. The current feedback (the IC-unit UC1901) use amplitude modulation to transfer a voltage error back to a PWM-circuit that adjust the pulse width and thereby regulate the secondary output voltages. A state of the art technology study was performed to investigate other potential feedback solutions on the market. It concluded in some radiation qualified digital solutions, but these were rejected due to high costs. A few commercial products were found too, which might have potential in future development. No directly new concept guaranteed a radiation tolerance alternative except in one case, where the costs were too high, so a decision of improving the original feedback was made. Three new alternative solutions were evaluated in the form of simulations with a base of synchronization: a load design, an improved UC1901 design and a delta sigma design, where the two first alternatives were planned to be constructed on a PCB. But due to high manufacturing cost of the PCB, consequence led to that only the load alternative was constructed on a stripboard. The load feedback uses a three winding transformer, where one winding is pulsed with a square carrier signal. The secondary side act as a load which includes the voltage error in the carrier and couple the signal to the PWM-circuit via the other primary winding. Implementation of the load feedback to the original converter was made and resulted in a stable operation as in the original feedback. Due to some issues with the optimization of the load feedback, the thesis resulted in an operational load feedback with limited performance. A major advantage with the new load feedback compared to the original is the use of simple radiation hardened components. In addition, an alternative symmetric load variant was simulated and showed promising result for further development. Future work would be a closer analysis and optimization of the load alternatives after a PCB implementation, but also evaluation and testing of the other alternatives.
Elkraftteknik , Electric power engineering
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