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Voltage and FrequencyC Ontrol of an Electronically-Coupled Distributed Generation Unit

Nejati, Afsoon | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41795 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Karimi, Houshang; Nobakhti, Amin
  7. Abstract:
  8. The use of distributed generation (DG) units provides several advantages for the utility distribution grid. Mostly power electronics converter is used as an interface to connect a DG unit to a utility grid. A DG unit normally operates in a grid-connected mode. In this mode, the host grid dominantly dictates the voltage amplitude and frequency of the local load at the point of common coupling (PCC) and the DG unit controls its real/reactive power components. Separation of the DG unit and its dedicated load from the host grid is called islanding. Subsequent to the formation of an island, due to the lack of control over the voltage magnitude and frequency, the islanded DG system becomes unstable. Therefore, control strategies to regulate the voltage magnitude and frequency are required. This thesis presents a control strategy to control the voltage magnitude and frequency in the closed loop manner for the islanded operation of a DG unit. After linearizing the dynamical model of the islanded DG, the obtained model is represented by a multivariable LTI system with high degree of interaction between its channels. In this thesis, the Nyquist array method is used to design a multivariable controller. First, by using self-adaptive Differential Evolution algorithms (DE), a precompensated is designed which is able to highly reduce system interactions. The precompensated system is almost decoupled so, based on the classic control methods, a SISO controller for each channel is designed. In the second part of the thesis, it's assumed that the load resistance can vary in a relatively large interval. In such a case, an LPV controller is designed to meet all control objectives for the closed loop controlled system with respect to changes in load resistance. Finally at the end of each part, effectiveness of each controllers is verified according to some simulation case studies of the nonlinear system.
  9. Keywords:
  10. Islanding Operation ; Dispersed Generation ; Diagonal Dominance ; Self Adaptive Differential Evolution (DE)Algorithm ; LTI Multivariable Controller ; Linear Parameter Varying (LPV)Controller

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