Chapter 2 - Small-signal model for grid-connected wind turbines

Abstract

The system connecting the wind turbine to the grid can be completely described by the state equation and analyzed by the small-signal method. In this chapter, small-signal models of a doubly-fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG) are established. The DFIG small-signal model includes the mechanical system, induction motor, and control system models. In the PMSG model, the motor model adopts the synchronous motor model. Its full-power converter uses three methods: an uncontrolled rectification boost converter, a “back-to-back” converter with P-Q control, and direct torque control. After the abovementioned connection between the generator and the system is processed by coordinate transformation, the established small-signal model of the wind turbine realizes a connection with the power grid. The composition of this chapter is as follows: 2.1 briefly explains the basic principles of the small-signal analysis method, 2.2 introduces the multimass mechanical system model; 2.3 and 2.4, respectively, deduce the DFIG and PMSG equations, including the converter; and 2.5 derives the line equation to realize the connection between the wind turbine and grid.