Fault-Tolerant Design and Implementation for Non-Isolated Reconfigurable DC/DC Converters

Abstract

This thesis mainly focuses on improving the conventional DC-DC converter topology by utilizing the redundancy concept (N+1) and fault-tolerant design to maintain an uninterrupted output operation even on primary switch failure. The proposed fault-tolerant converter (FTC) involves merging three configurations namely buck, boost and buck-boost to derive a new converter structure along with bidirectional capabilities. The proposed FTC is equipped with a single redundant switch and shared with one coupled inductor and one capacitor (1L-1C) to be capable of achieving the step-up and step-down operation. The major faults of the converter system are highly related to the power switching devices, which can be categorized as open circuit fault (OCF), and short circuit fault (SCF). The proposed fault diagnosis scheme is able to detect the OCF and SCF in less than half of the switching period by sampling the rising and failing edge of the pulsating signal to identify the switch fault behavior. Therefore, remedial action of the proposed FTC can be associated with the fault detection unit to anticipate the moment when the converter requires the activation of the redundant switches by providing a back-up operation. However, any reconfigurable decision is necessary to electrically isolate the faulty component in order to avoid the subsequent fault current within the circuit loop. The proposed method of isolation design adopts the joule-integral principle for selecting an appropriate rating between fuse and MOSFET pair. It provides the satisfactory result for protecting the proposed FTC. Finally, a converter reliability model is carried out based on Markov chain theory to formulate the mean time to failure (MTTF) profile for the proposed FTC. The reliability analysis shows that the proposed FTC can surpass the reliability performance of the conventional DC-DC converter through optimization of the circuit topology.