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This thesis was focused on the research in the matrix converters domain and, particularly, in direct matrix converters. The 3-leg direct matrix converter consists of 18 power transistors and 18 power diodes and is used for the conversion of a three-phase AC voltage to a three-phase AC voltage of variable amplitude and variable frequency. This topology is also capable of modulating the input current and adjusting the input power factor, whereas bidirectional power flow is allowed. This conversion is achieved in one stage with the direct connection of the input phases with the output phases, without using an intermediate DC link stage, resulting in elimination of the use of large capacitors and large inductors. The use of the matrix topology in power converters results in high efficiency, high power density and very high power-to-mass ratio, whereas the harmonic distortion of the output voltage and the input current is low. The complexity of the matrix converters is high resulting in sig ...
This thesis was focused on the research in the matrix converters domain and, particularly, in direct matrix converters. The 3-leg direct matrix converter consists of 18 power transistors and 18 power diodes and is used for the conversion of a three-phase AC voltage to a three-phase AC voltage of variable amplitude and variable frequency. This topology is also capable of modulating the input current and adjusting the input power factor, whereas bidirectional power flow is allowed. This conversion is achieved in one stage with the direct connection of the input phases with the output phases, without using an intermediate DC link stage, resulting in elimination of the use of large capacitors and large inductors. The use of the matrix topology in power converters results in high efficiency, high power density and very high power-to-mass ratio, whereas the harmonic distortion of the output voltage and the input current is low. The complexity of the matrix converters is high resulting in significant implementation effort.In this thesis, the research in direct matrix converters was focused mainly on the development of diagnosis methods for open-circuit faults that arise in the matrix topology, as well as the development of carrier-based modulation methods for the normal and remedial operation of these converters.This thesis contains eight chapters, the content of which is described below.In Chapter 1 an introduction and a brief description of the aims and the structure of this thesis are provided.In Chapter 2 an introduction to the AC-AC power converters used for the modulation of an output voltage of variable amplitude and variable frequency is provided. A description and a comparison of various matrix converter topologies, a description of the conventional topologies used for the same voltage conversion and a comparison of the latter with the two most popular matrix topologies are included in this chapter.In Chapter 3 the methods required for the control of the direct matrix converter are presented. In detail, various modulation methods are described and compared and the most significant commutation methods are presented. In this chapter a novel carrier-based modulation method that was proposed in this work is also described which results in reduced switching losses for use in cases that the required voltage transfer ratio is up to 50%.In Chapter 4 the direct matrix converter that was designed and constructed in this work is presented and other parts of the experimental setup are described. Additionally, some experimental results related to the operation of matrix converter parts are provided.In Chapter 5 a brief description of the studied system‘s model that was created using the Matlab/Simulink software is provided, the value of various parameters of this model is given and simulation results of the normal (healthy) operation of the matrix converter are presented and commented. Additionally, a vector control method for the speed control of an induction machine fed by a matrix converter is described and simulation results of its operation are demonstrated. Finally, experimental results of the normal operation of the matrix converter are presented and commented.In Chapter 6 the possible faults in direct matrix converters are studied and the methods to detect open-circuit faults and the open-circuited transistors localization method that were developed in this work are presented. Additionally, a description of signal processing methods and the basic theory of fuzzy inference systems, which are used by the proposed diagnosis methods, are included.In Chapter 7 topologies and modulation methods used for the remedial operation of the direct matrix converter after the occurrence of a fault are presented. In this chapter two carrier-based modulation methods for the remedial operation of the direct matrix converter after an open-circuit fault occurrence that were developed in this work are also described, one for the case of using a redundant (fourth) leg and one for the case of not using any redundant switches.In Chapter 8 the contribution of this thesis to the research in the matrix converters domain is highlighted, its additional results are noted and subjects of possible future work are provided.This thesis was conducted under scholarship received by the State Scholarship Foundation of Greece (I.K.Y.) under Grant 4449/2007.
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