978-1-6654-4421-7/21/$31.00 ©2021 IEEE Propagation of Voltage Dips in a Mixed DFIG-PMSG Wind Power Plant Rafael Boeira, Renata Ribeiro, Roberto Chouhy Leborgne Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil rafael.boeira@ufrgs.br renatakfribeiro@hotmail.com roberto.leborgne@ufrgs.br Roger Alves de Oliveira Electric Power Engineering group Luleå University of Technology Skellefteå, Sweden roger.oliveira@ltu.se Abstract— This work assesses the propagation of voltage dips caused by electrical faults in a mixed DFIG-PMSG wind power plant by considering distinct collection transformer connections. Several transmission system operators have required the operation of the wind power plants even during voltage dips. The electronic converters might be affected during the voltage dips. Most of the works which assess this impact applied voltage dips directly to wind turbine terminals. However, the voltage dips which reach the wind turbine terminals are distinct in type of the ones from the transmission level. The reason for this distinction is related to the winding connections of the wind turbines and collection grid transformers. The winding connection of the collection grid varies country by country, i.e some countries apply Yg-Yg and other Yg - Δ. Faced with this, the consideration of the winding connections might possibly lead to distinct operation of the wind turbines during the voltage dip. Besides, the operation during dips also differs depending on the converter technology. This way, this works aims to analyze how the low-voltage ride-through requirements and the behavior of the wind turbines changes in terms of the collection grid transformer for two technologies of wind turbines: PMSG and DFIG. Index Terms — Power Quality, Voltage Dip, LVRT, Wind Power, DFIG, PMSG I. INTRODUCTION In recent years, wind power generation has experienced a huge growth in installed capacity around the world. As a result, transmission system operators (TSO’s) have implemented regulations and standards to ensure the electric grid system’s stability and reliability. One of these regulations is related to the operation of wind turbines (WTs) during voltage dips, the so- called Low Voltage Ride-Through (LVRT) requirements. Before the LVRT requirements, the wind power plants could be disconnected from the main grid during voltage dips [1]. The purpose of the LVRT requirements is to ensure the operation of wind power plants (WPP) when subjected to voltage dips to not compromise the operational safety and stability of an entire power system [2]. Although the WTs can inject an amount of active power proportional to the voltage dips magnitude, the power electronic converters are affected by the dips. The voltage dips that reach the WTs terminals are mainly caused by electrical faults in the transmission grid [3]. The type of dips in the WTs terminals are distinct to the ones in the transmission level due to the winding connections of the wind turbines and collection grid transformers. The Yg – Δ is the most common winding design for a turbine transformer [4]. The winding connections for the collection grid transformer can be Yg - Yg or Yg - Δ. The Yg -Yg wind connection is often used in North America, while the Yg – Δ is more applied in Europe [4]. The main difference between the Yg - Yg and Yg – Δ connections is related to the propagation of asymmetrical voltage dips. An overview of the expected types of voltage dip at the WTs terminals is presented in [3],[4]. Previous works [5-8] have analyzed the dynamic behavior of WTs during voltage dips. The impact of balanced and unbalanced voltage dips on the Doubly Fed Induction Generator (DFIG) is presented in [5-6]. The impact on the Permanent Magnet Synchronous Generator (PMSG) technology is analyzed in [7-8]. Although the works from [5-8] have brought important knowledge about the performance of WPP when subjected to voltage dips, they were applied directly on the terminals of WTs. In other words, the propagation of voltage dips was not considered from the transmission level to the WT terminals in [5- 8]. The winding transformer connection is a key element to analyze the propagation, and depending on them, some voltage dips types will never reach the WT terminals. Besides, the consideration of faults at the WT terminals is not related to the LVRT requirement, but to the protection of the WPP. This way, this works aims to analyze how the low-voltage ride-through and the behavior of the wind turbines changes in terms of the collection grid transformer for two technologies of wind turbines: PMSG and DFIG. A case study of an existing WPP was modelled to conduct the analysis. Equivalent models of a transmission system and a wind power plant were considered to simulate different types of dips and to access the behavior of the WT during these events.