Date of Award
1-1-2012
Thesis Type
phd
Document Type
Thesis
Divisions
science
Department
Faculty of Science
Institution
University of Malaya
Abstract
This thesis aims to provide additional contributions to control of multiphase machine, with a focus on asymmetrical six-phase induction machine (machine with two three-phase windings spatially displaced by 30°). Using the VSD approach, the machine’s six phase variables can be transformed into six decoupled variables, namely α-β, x-y and two zero sequence variables. For machine with distributed windings, only the α-β components provide useful electro-mechanical energy conversion, while the other components merely produce losses. The studies presented in this thesis are based on this VSD approach, and are separated into three main parts: x-y current control methods, operation with series-connected converters and post-fault control. The first part of this research work looks into the x-y current control methods of the machine using PI controllers. It was found that the x-y currents can be physically interpreted as the circulating current between the two three-phase windings. Depending on the type of asymmetry, x-y currents can appear as positive sequence component, negative sequence component or a combination of both. Hence, performance of PI controller implemented under different reference frame is compared and discussed. In this part of the study, a dead time compensator implemented using resonant controller for x-y currents is also presented. The second part of this work investigates the operation of the six-phase machine with series-connected machine-side converters. Under this topology, the two three-phase windings are supplied by two separate two-level voltage source converters (VSCs) with their dc-link cascaded in series. The series-topology elevates dc-link voltage which gives a reduction in dc-link current and cable size. However, the additional dc-link voltage balancing control is needed to ensure equal voltage sharing. __________________________________________________________________________________________________________ iv This is accomplished by controlling x-y currents, which is a new concept introduced in this work. The final part of the research work deals with post-fault control of six-phase induction machine for a single open-circuit fault. Post-fault control is based on the full order decoupling transformation, to minimise reconfiguration of the controller. Effect of the single open-circuit fault on the machine is discussed. Here, the leg-to-phase voltage relation is identified as an important issue that needs to be addressed when using PI controllers for post-fault operation. Different modes of post-fault operation are analysed and compared. The study considers both the cases where the six-phase machine is configured with single as well as with two isolated neutrals, such that a unified comparison is achieved. In conclusion, this thesis provides insights on the control of x-y currents in six-phase machine based on PI controllers in different reference frame. Two interesting uses of these currents, i.e. for dead time compensation and dc-link voltage balancing have also been presented. In terms of alternative converter topology, the operation of six-phase machine with series-connected machine-side converter is detailed, addressing the merits and demerits of the topology. Lastly, the operation of six-phase induction machine under different modes of post-fault control is studied and compared. All studies are based on simulation in Matlab/Simulink environment and are further verified on a 1.1 kW prototype asymmetrical six-phase induction machine.
Note
Thesis (Ph.D.) – Faculty of Science, University of Malaya, 2012.
Recommended Citation
Che, Hang Seng, "Contributions to control of an asymmetrical six-phase indcution machine / Che Hang Seng" (2012). Student Works (2010-2019). 1358.
https://knova.um.edu.my/student_works_2010s/1358