Universal Control and Management Strategies for Micro-Grid-Based Smart Grids Using Synchronous Converters

• Author / Creator

  Ashabani, Seyed Mahdi

• The energy sector is moving into the era of distributed generation (DG) and micro-grids (MGs). This research focuses on development of a new family of control and management strategies for integration of micro-grids with numerous voltage source converters and synchronous generators in smart power grids by introducing the new concepts of Synchronous Converters and Synchronous-VSC. The stability and operation aspects of converter-dominated MGs are faced by many challenges. Important among these are: 1) the absence of physical inertia; 2) power quality issues due to permanent frequency offset and voltage and current regulation; 3) mutual interactions among synchronous generators and voltage source converters; 4) transitions to islanding and its detection delays; 5) large sudden disturbances associated with grid restoration, transition to islanding and DG out-of-phase re-closing; and 6) development of high impedance weak MGs because of installation of renewable energy resources in areas which are geographically remote from the load centers.
  This dissertation presents a new family of comprehensive control and management strategies for MGs in smart distribution grids. The thesis also provides a general and computationally-efficient framework for the modeling and analysis of the management strategies in a multiple-DG MGs; the framework facilities MG dynamic studies and controller parameters in large micro-grids with multiple DG units. Three different approaches for real and reactive power management are proposed. The controllers offer the following advantages: 1) the proposed topologies can be applied to both voltage-controlled (VC) and current controlled (CC) voltage source converters (VSCs). 2) The controllers are universal and realize requirements of both grid-connected and islanded modes, i.e. share real and reactive power during islanding and act as grid supporting VSCs in grid connected mode. 3) The controller emulates the behaviour of conventional synchronous generators (SGs) which in turn results in better integration of electronically-interfaced DG units into the power system and prevents instabilities due to interaction of fast response DGs and SGs. 4) The controllers realize seamless and robust transition to islanding mode. 5) The controllers are equipped with a nonlinear supplementary controller to mitigate large power angle swings associated with large-signal disturbances. 6) The controllers can be easily adapted to conventional synchronous machines. 7) The controller provides seamless self-synchronization operation under out-of-phase reclosing. 8) The controllers provide stable operation and superior current decoupling in very weak grids and MGs.

• Subjects / Keywords

  • Micro-grid
  • Smart grid
  • Smart grid
  • microgrid
  • control topology
  • management
  • nonlinear control
  • weak grid
  • self-synchronization

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R35X25K62

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.