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Power Flow Control and Power Quality Enhancement in Grid-Connected Microgrid with Back-to-Back Converter

Sekhavatmanesh, Hossein | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47288 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Mokhtari, Hossein
  7. Abstract:
  8. A microgrid system consists of some distributed generators (DGs) and local loads which can operate in both grid-connected and islanded modes of operation. An islanded mode of operation is required when the grid voltage deteriorates and its power quality drops. This islanding operation can be attained by opening grid-side switches or by using back-to-back (b-to-b) converters. Due to the increase of highly sensitive loads and to have better power control and higher power quality, the use of back-to-back converters has recently attracted interests among researchers. However, the major drawback of this solution is the cost of a b-to-b converter. Therefore the aim of this project is to gain some other benefits by adding some control facilities to this converter in order to justify its use as an interface between a microgrid and a utility grid. As the first step in this project, the lower layer control of the b-to-b converter is accurately designed. In contrast to the former papers, in this project, the DC voltage control system with an LCL filter is precisely modeled, without any simplifying assumption, based on which the edge of stability margin is derived. Then, the controllers are modified to compensate the unbalanced and harmonic loads at the point of connection between the main grid and the microgrid. In this manner, the inter-link converter acts like a DG active filter. Majority of the outstanding features of the proposed converter are revealed when it is considered along with the DG units in the microgrid. In the first years of a microgrid operation, the inter-link converter is controlled such that the DGs operate at their maximum capability. In this mode, the extra power generated by the DGs is fed into the main grid. In the following years, the droop control and the PQ control strategies are defined for the b-to-b converter to facilitate the economic dispatch for the microgrid during grid-connected mode of operation. With the application of these strategies, there is no need to change the operating mode of the DGs during islanding or reconnection processes. In the end, the proposed strategies are simulated on a sample microgrid system using MATLAB/SIMULINK software
  9. Keywords:
  10. Back-to-Back Converter ; Microgrid ; Distributed Generation ; Harmonic Loading ; Unbalance Loads ; Droop Method ; Power Quality ; Direct Current Voltage ; Payback Period

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