چكيده به لاتين
According to the previous technical literatures, although Linear Induction Motors (LIMs) are widely utilized in many industrial applications such as electrical railway industry and in spite of superior advantages of induction motors with more than three phases, until now considerable investigations have not been reported in case of multiphase LIMs. To cover the mentioned lack of research, in this thesis an effort is made to present a comprehensive study of multiphase LIMs. Furthermore, this makes it possible to benefit from the privileges achieved by the combination of LIMs and multiphase induction motors such as simultaneous and independent control of multiple multiphase LIMs through a single voltage source inverter (VSI) in the industries.
Accordingly, in the first stage of this thesis the dynamic model of the multiphase LIM considering the end effect is extracted which can be utilized in study and simulation of multiphase LIMs especially in vector control applications. Then, a comprehensive study of multiphase VSIs have been carried out as the main supply systems in multiphase LIM drives and new equations have been derived for harmonic analysis of seven-phase inverter voltages and also for its harmonic losses calculation. Moreover, a comparative evaluation of different modulation strategies of CHB multilevel VSI have been performed and also their influences on the distortion of inverter output voltage and the input current at power grid side have been carried out. In order to complete this investigation and to verify the theoretical results, an experimental set up has been designed and constructed. As well, the obtained results are compared with the theoretical and simulation results. In the next stage of this research, the equations which are required in vector control of multiphase LIMs considering the end effect is extracted. Then the vector control of a seven-phase LIM prototype has been studied and simulated. In order to improve the dynamic response of the drive, the PI controller optimized using both genetic algorithm and fuzzy logic controller have been applied. In addition, to investigate the harmonic distortion of the seven-phase LIM drive, a five-level CHB inverter has been utilized to supply the drive and its effect on the improved THD index has been compared with the traditional two-level VSI. In addition, in this thesis the principles of simultaneous control of multiple multiphase LIMs supplied through a single VSI have been investigated. As an instance the independent vector control of three seven-phase LIMs fed through a single VSI has been studied. In order to decrease the unwanted forces imposed to the rigid conjunctions between the LIMs, fuzzy logic controller has been successfully applied. Furthermore, to complete the consequences of this work and to validate the attained theoretical results, three prototypes including three-phase, five-phase, and seven-phase LIM have been constructed in the experimental laboratory. Finally, because of extensive application of LIMs in high-speed electrical railway industry, a comprehensive study have been performed in the case of vector control of LIMs above the nominal speed and in the flux weakening region considering the end effect. In this regard, new equations have been extracted for determining the reference flux in the constant force region, partial flux weakening region and full flux weakening region and also for calculation of the base and critical speed in the vector control diagram of LIM drives.
