Control Strategies for Power Grid Interface of Large Scale Wind Farms

Abstract

Low voltage ride through (LVRT) of fixed speed wind turbines (FSWT) is performed by means of either blade pitch angle control or using external flexible alternating current transmission system FACTS devices. Deployed FACTS solution can be either series or shunt connected. Reactive power injection from shunt FACTS such as the SVC and the static synchronous compensator (STATCOM) are dependent on the connection point voltage. These shunt FACTS have limited reactive power contribution during fault and consequently a limited impact on the WTG terminal voltage. Additionally they have limited ability to help the WTG evacuating its active power in order to limit the rotor acceleration. As LVRT solutions series FACTS are able to boost the WTG voltage and thus advantageous over the shunt FACTS. Among the series FACTS proposed to allow the LVRT of FSWT are the static series synchronous compensator (SSSC) and the series dynamic braking resistor (SDBR). The aim of this thesis is to propose, develop and analyze a low voltage ride through (LVRT) solution for fixed speed wind turbines (FSWT). A continuously variable series braking resistor (CVSBR) is proposed in this work as a successful means for LVRT of FSWTs. The proposed CVSBR is compared to other potential series FACTS. The CVSBR shows a good performance as a solution to enhance the LVRT capability of the FSWT.