Thesis supervisor: András Dán
co-supervisor: István Varjasi
Location of studies (in Hungarian): Villamos Energetika Tanszék Abbreviation of location of studies: VET
Description of the research topic:
Usage of conventional bridge type rectifiers for obtaining DC power from AC grid results in injection of unwanted current harmonics into the grid. Due to standards such as IEEE 519-1992 which limit the amount of harmonic injection into the mains, the bridge type rectifiers are being replaced by improved power quality converters which have reduced harmonic injection into the mains along with a host of other advantages. This project deals with the hardware development and control of a 3-phase, 3 switch 3-level UPF rectifier which is a variant of an improved power quality converter named VIENNA rectifier working with one cycle control based technique. The 3-phase, 3 Switch, 3-level rectifier is characterized by its input currents being almost sinusoidal, reduced input current ripple, controllable output DC voltage, high power density and UPF operation. Further, reduced losses and a lesser component count of the 3-phase, 3 Switch, 3-level rectifier compared to the VIENNA rectifier indicate a greater scope for employing the one cycle based carrier control technique.
In the present day scenario of the power systems the role of power electronics is drastically increasing and its presence is very prominently being felt. The applications maybe power conversion like ac to dc or dc to ac or power enhancement and compensation using FACTS devices or CPD(custom power devices) like STATCOM , DVR or D-STATCOM etc or cyclo-converters, choppers etc. However as useful as power electronics might seem, the major drawback is that power electronic devices when used with any system induce a considerable amount of harmonic content back into the system. It is observed that the control strategy techniques like Pulse Width Modulation (PWM) and Space Vector Modulation (SVM) had been successful in lowering the harmonic content by a little amount. But still the remaining harmonic content in the system is sufficient to cause distortion in the load voltage and current and probable malfunction of the system parameters. For this purpose the One Cycle Control technique is proposed. In this proposed method the harmonic content is comparatively lowered by 2 to 5% which results in better functioning of the system which is clearly observed by the FFT analysis of the output voltage and current quantities of the considered system while using conventional techniques (PWM, SVM) and also OCC technique.
The available control strategies are PWM (Pulse Width Modulation), Space Vector Modulation (SVM), OCC (One-cycle control) etc. PWM and SVM are linear control techniques but OCC is a non-linear control technique. These methods have their own
merits and demerits. The performance of a Three Phase Three Switch Three Level (VIENNA) rectifier working with SVM based carried control technique is analyzed by simulating a model of the same in MATLAB-SIMULINK and various performance indices like THD (Total Harmonic Distortion), CD (Current Distortion) are observed in each case and is found that OCC (One-Cycle Control) technique gives the best performance when compared with the same model while working under SVM based carrier control technique under same parameters. The advantages of this control technique are it avoids the badness of voltage instantaneous feed-back PI control and also it has very quick dynamic response and tracing performance. The harmonic content is also reduced in the output voltage and current waveforms.
Overall, this research work involves the building of the 3-phase, 3 Switch, 3-level rectifier setup, design of the controller parameters, validation of the proposed carrier based control strategy both in simulation/hardware and comparison of the proposed control strategy with an originally existing SVM based control strategy .A working type prototype model will be developed to check for the feasibility of the theoretical and practical results. Based on the results obtained from simulation and hardware implementation, a comparison has been done between the VIENNA rectifier operating while employing the already existing SVM based control strategy and the proposed one cycle control strategy.
The modeling of the grid side system and other system is carried out in MATLAB-SIMULINK. A SIMULINK model is developed for the basic analysis of the system. A working prototype for this model would require the necessary hardware components and sufficient financial support for the same purpose. The power rating for the system under consideration is 25KW system.
However a lot of systems which are being used today are digital in nature which calls for the need of developing an OCC techniques which also holds good when applied to the discrete time systems. Further OCC control technique is discretized using DSP or FPGA technique and employed as a control strategy for VIENNA rectifier topology employed in interconnecting renewable sources like solar or wind energy with grid connected systems in order to obtain a better control strategy for converters involved in grid interconnection and also PFC (Power factor control).
Required language skills: english Number of students who can be accepted: 1
Deadline for application: 2017-06-26
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
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