A FAULT TOLERANT CONTROL STRATEGY FOR ELECTRONIC CONVERTERS

Abstract

In this thesis, a proposed fault tolerant control has been explained for the three-phase AC-DC voltage source converters utilizing the hysteresis current controller based space vector modulation technique. The upper switches fault for a certain phase affects the negative half cycle of the phase current while lower switches fault affects the positive half cycle. Each half cycle includes six-half sectors. During the open switch fault, these half sectors are affected by the zero vector. In addition, the two half sectors at the start and end of the half cycle are affected by zero and active vectors. For double switches fault, it includes three cases and each case is divided into one or more regions. The proposed fault tolerant control is based on switching tables for different types of these faults. For the different cases of two switches fault, the switching tables are derived from the superposition of the switching tables of the single open-switch fault at each switch. The simulation results reveal the reduced switching times and hence the reduced switching losses capabilities of the proposed fault tolerant control for different types of open-switch faults. Moreover, a second fault tolerant control based on SMC is presented. SMC is a discontinuous control used to control non-linear systems especially variable structure systems like power converters. The proposed SMC utilizes two inputs to control phase currents depending on the fact that current summation is equal to zero. The third input represents an extra degree of freedom that is used to control the neutral voltage to reduce the switching losses. If an open switch fault occurs in one of the two legs that control current, then the proposed fault tolerant control replaces the faulty leg that controls current with a healthy one, and the faulty leg is assigned to control the neutral voltage. This modification results in currents waveform with reduced total harmonic distorsion and lower switching losses than if the faulty leg is not assigned to control the neutral voltage.

5.2 FUTURE WORK The followings are recommended topics for future work:  Study the utilization of the proposed scheme for non-sinusoidal PWM rectifiers used in power quality conditioners.  Implementation of experimental setup to verify the effectiveness of the proposed technique