Electromechanical Performance Comparison of Low-voltage Ride-through Methods for Variable Speed Wind Turbines

  • Author / Creator
    Zhou, Andrew
  • The increasing penetration of the renewable wind energy systems and the decommissioning of the traditional fuel systems has resulted in an increasingly strict grid codes to circumvent issues with the grid’s stability and reliability. The low-voltage ride-through (LVRT) requirement is one of the most commonly enforced grid codes for variable speed wind turbines. The LVRT grid code requires wind turbines to be grid-connected during a fault to provide reactive power ancillary services and offer fast system restart once the fault is cleared. Today, the two most predominant variable speed wind turbines are the type 3 doubly-fed induction generator (DFIG) and the type 4 permanent magnet synchronous generator (PMSG). The DFIG is very popular in the industry because of its reduced converter rating, which results in higher efficiency and decreased converter costs. The PMSG is now growing in popularity because of its fully rated converter, which can decouple the machine dynamics from the grid. Because of the differences in the structure of these two types of wind turbine generators, they will respond differently to LVRT. For the PMSG, the main concern of LVRT is the charging of the DC-link because the grid power is significantly reduced, while the generator power remains almost unchanged. For the DFIG, the stator winding is directly connected to the grid; this means that when the grid voltage is suddenly reduced, the DFIG will experience severe transients because of its electrical dynamics resulting in large stator and rotor fault currents.
    There are many LVRT solutions proposed for the PMSG and the DFIG, many of which will impact the mechanical drivetrain system resulting in additional stress. The main contribution of this research is the evaluation of the damage and the stress-life impact of these LVRT solutions. Operational and maintenance cost covers a significant portion of the capital investment of the wind turbine, so the additional stress resulting from LVRT may procure additional maintenance cost for the entire wind farm. Therefore, it essential to analyze the lifetime effects that may result from LVRT, so that wind turbine manufacturers and wind farm owners can make a more informed financial decision when selecting the type of wind turbine to purchase and the LVRT method to implement to meet the grid code.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • 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.