Nonlinear Control of a Doubly Fed Generator Supplied by a Current Source Inverter

Abstract

Nowadays, wind turbines based on a doubly fed induction generator (DFIG) are a commonly used solution in the wind industry. The standard converter topology used in these systems is the voltage source inverter (VSI). The use of reverse-blocking insulated gate bipolar transistor (RB-IGBT) in the current source inverter topology (CSI), which is an alternative topology, opens new possibilities of control methods. This paper presents a novel power control system for a DFIG supplied by a CSI. The authors propose to use multi-scalar DFIG state variables. A nonlinear control method realized by feedback linearization was used to control the active and reactive powers of the generator. In the feedback linearization controls, the nonlinear DFIG model was taken into account. In the control system structure, classical proportional−integral controllers were used. The control variables were the output current vector components of the CSI. Such approach was named the “current control”. The proposed control method is characterized by good dynamic properties which, combined with the inverter properties in the rotor circuit, allow to increase the quality of the energy transferred to the grid by the generator. In the simulation tests, the correctness of the decoupling of the active and reactive power control loops, the dynamics of controlled power changes, and the change of the machine operating range resulting from the increase of the rotational speed of the generator shaft were controlled. The simulation studies also evaluated the impact of changes in the value of the passive elements of the system on the operation of the generator system. Characteristic operating states of the generator system were analyzed using computer simulations.

Keywords

• doubly fed induction generator (GFIG)
• current source inverter (CSI)
• nonlinear control