Small-signal Modeling and Modal Analysis of a PMSG-based Wind Power System

Abstract

A unified small-signal model of a wind power system is developed in this paper to study the small-signal stability of permanent magnet synchronous generator (PMSG)-based wind turbines connected to the power grid. The model is composed of both mechanical system and electrical system. A two-mass shaft model for the mechanical system is provided to analyze the dynamic and steady state behaviors. Meanwhile, PMSG, converter system and transmission line of the electrical system are modeled separately to build a unified small-signal model of the PMSG-based wind power system. Then, based on the unified small-signal model, eigenvalue analysis for the whole system is presented, which helps discover the relation between different modes and state variables. Cases involving various series compensation degrees, length of transmission lines and the stiffness of shafts are carried out to study how the modes are influenced by relevant variables specifically. The relatively independent modules of the unified small-signal model allow for easy expansion and modification for various research purposes. The simulation results show that the mechanical and electrical systems of PMSG-based wind turbines are independent to some degree with the implementation of a full-scale converter system.