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Robust Control of an Islanded Microgrid Based on Droop Strategy

Emamian, Sepehr | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43184 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Karimi, Hoshang
  7. Abstract:
  8. Nowadays, the use of distributed generation (DG) units and microgrid systems is mainly limited to their operation in the grid-connected mode. In the grid-connected mode, a microgrid including its loads and DG units is connected to the main grid at the point of common coupling (PCC). In this case, the main grid provides fixed voltage and frequency for the microgird and each DG unit regulates its power components based on the conventional dqcurrent control strategy. Autonomous (islanded) operation of a microgrid, however, is not as straightforward as its operation in the grid-connected mode, i.e., control and power management of an islanded microgrid is very difficult due to the stochastic nature of the renewable energy sources that act as the prime movers for the DG units. A robust control strategy is presented for the general case of unknown load model, i.e., the load is assumed to be parametrically and topologically unknown. Therefore, there are unmodeled dynamics in the microgrid model. To regulate the reference voltage, two control strategy are presented. One of these controllers has PR structure and the optimal parameters of this controller are obtained using of PSO algorithm. The second one is characterized by a one-degree-of-freedom (1DOF) control system consisting of feedback and feedforward signals.The optimal solution of the control strategy is obtained using the linear matrix inequalities (LMIs). Simulation case studies carried out in PSCAD/EMTDC show that the proposed controllers scheme are highly robust against the uncertainties in the load dynamics.
    Finaly, new droop-characteristics are presented to improve the performance of the microgrid in terms of power sharing, voltage regulation, dynamic and transient responses, reduces the reactive power sharing dependency on real power and system parameters, and smoothes the system’s dynamic and transient responses. This work has developed the modeling, control parameters design, and power-sharing control starting from a simplified small signal model of a single voltage source inverter to a number of interconnected DG units forming a flexible microgrid. Simulation results are provided to demonstrate the effectiveness of the proposed control scheme
  9. Keywords:
  10. Microgrid ; Dispersed Generation ; Particles Swarm Optimization (PSO) ; Linear Matrix Inequality (LMI) ; Droop Method ; Proportional-Resonance (PR)Controller

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