Browsing by Author "Sajadian, Sally"

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    Energy conversion unit with optimized waveform generation
    (2014) Sajadian, Sally; Santos Jr., Euzeli C. dos; Rizkalla, Maher E.; Rovnyak, Steven; King, Brian
    The substantial increase demand for electrical energy requires high efficient apparatus dealing with energy conversion. Several technologies have been suggested to implement power supplies with higher efficiency, such as multilevel and interleaved converters. This thesis proposes an energy conversion unit with an optimized number of output voltage levels per number of switches nL=nS. The proposed five-level four-switch per phase converter has nL=nS=5/4 which is by far the best relationship among the converters presented in technical literature. A comprehensive literature review on existing five-level converter topologies is done to compare the proposed topology with conventional multilevel converters. The most important characteristics of the proposed configuration are: (i) reduced number of semiconductor devices, while keeping a high number of levels at the output converter side, (ii) only one DC source without any need to balance capacitor voltages, (iii) high efficiency, (iv) there is no dead-time requirement for the converters operation, (v) leg isolation procedure with lower stress for the DC-link capacitor. Single-phase and three-phase version of the proposed converter is presented in this thesis. Details regarding the operation of the configuration and modulation strategy are presented, as well as the comparison between the proposed converter and the conventional ones. Simulated results are presented to validate the theoretical expectations. In addition a fault tolerant converter based on proposed topology for micro-grid systems is presented. A hybrid pulse-width-modulation for the pre-fault operation and transition from the pre-fault to post-fault operation will be discussed. Selected steady-state and transient results are demonstrated to validate the theoretical modeling.
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    Energy Conversion Unit with Optimized Waveform Generation
    (Office of the Vice Chancellor for Research, 2013-04-05) Sajadian, Sally; dos Santos, Euzeli C., Jr.
    The ever-increasing demand for electrical energy has put pressure on identifying and implementing ways to increase the efficiency of the devices dealing with energy conversion. The power supplies devices able to generate ac voltage from dc one is crucial in automotive and computing industries. Different technologies have been developed to implement power supplies with higher efficiency, such as multilevel and interleaved converters. This paper proposes an energy conversion unit constituted by a single-phase DC-AC converter with five levels at the output converter side. The proposed converter has an optimized relationship between the numbers of levels per number of switches (nL/nS). The proposed five-level four-switch converter has nL/nS=5/4, which is by far the best relationship among the converters proposed in the technical literature. The most important characteristics of the proposed configuration are: (i) reduced number of semiconductor devices, while keeping the high number of levels at the output converter side, (ii) only one DC source without any need to balance capacitor voltages, and (iii) high efficiency. Details regarding the operation of the configuration and modulation strategy are presented, as well as the comparison between the proposed converter and the conventional ones. Simulated results are presented to validate the theoretical expectations.
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    HYDRAULIC WIND POWER DROOP ANALYSIS
    (Office of the Vice Chancellor for Research, 2012-04-13) Sajadian, Sally; Pusha, Ayana; Izadian, Afshin
    The power transferred from the wind turbine to the generator is im-portant to keep the systems active, power balance and droop frequency con-trol when connected to a network. This is important to ensure maximum power output obtained from wind velocity. When there is a change present in the real power demand at a point in the network, it is reflected throughout the system by fluctuation in frequency. If a drop in frequency occurs the generator will decelerate at a rate determined by the moment of inertia plus all the masses connected to its shaft. This results in the conversion of kinet-ic energy of the generator to electrical energy thus giving a power surge. If there is an increase in the system frequency, the inverse is true. Hydraulic wind power provides opportunities for multiple wind turbine energy collection and central generation. The system has many benefits over direct driver counterparts including simple structure and opportunities for energy storage units. However, as the system relies on hydraulic connection of wind turbine and generators, it exhibits a nonlinear power and speed characteristics. This poster will analyze the effect of increasing the hydraulic wind turbines on the droop characteristics of the system. Several wind speeds and loading conditions have determined that adding wind turbines to the hydraulic energy transfer system will increase the frequency stability of the system. Some of the hydraulic prime mover characteristics will be identi-fied through experimental results from our prototype in Dr. Izadian’s labora-tory. This research was supported by IUPUI Solution Center.