Power system restoration using DFIG-based wind farms and VSC-HVDC links

Open Access
Author:
Moradi Farsani, Pooyan
Graduate Program:
Electrical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 14, 2018
Committee Members:
  • Nilanjan Ray Chaudhuri, Thesis Advisor
  • Mehdi Kiani, Committee Member
Keywords:
  • Restoration
  • Black-start
  • DFIG-based wind farm
  • VSC-HVDC
  • Hybrid simulation
Abstract:
Application of Voltage Sourced Converter High Voltage DC (VSC-HVDC) links in power system restoration has been demonstrated in literature through detailed Electromagnetic Transient (EMT)-type models of very small-scale systems. However, studying restoration of large power systems using such detailed models is computationally prohibitive. In this thesis, a hybrid simulation platform is proposed for such studies in which a significant portion of the system, for which developing a detailed three phase model is not necessary, is modelled in a phasor framework and is co-simulated with a detailed EMT-type model of a smaller portion containing VSC-HVDC link. Moreover, in this thesis an innovative restoration strategy is proposed using Doubly-Fed Induction Generator-based wind farms. The strategy involves retention of charge in the DC bus following a blackout, thereby avoiding the need for energy storage, and ‘Hot-Swapping’ between direct flux control mode and conventional grid-connected mode, which does not require resetting of any controller dynamic states. An autonomous synchronization mechanism enabled by remote synchrophasors is also proposed. In this black-start strategy a wind farm and a VSC-HVDC connected to a network unaffected by blackout, conduct line and transformer charging and load pickup for two separate parts of a blacked out area. The proposed ‘Hot-Swapping’ and synchronization approach are applied to connect the two parts of the grid and switch the wind farm to grid connected mode of operation. This approach is verified using the aforementioned hybrid co-simulation platform for a test system. One shortcoming of DC bus charge retention method is that the DC bus capacitors gradually discharge and hence, the restoration process has to begin within a reasonable time frame. In the last part of this thesis it is shown that a DFIG-based wind farm operating in isolated flux control mode, can keep its DC-bus charged even with an open terminal.