Modelling and Simulation of DFIG Based Standalone Wind Energy System with Battery Backup

Abstract

The DFIG based wind energy generation systems with PWM converter is most popular as a standalone system. Mathematical modeling of the conventional standalone DFIG with IGBT based two back-to-back connected PWM converter is presented. Closed loop control of standalone variable speed constant frequency (VSCF) system is explained in detail. Dynamics of dc-link voltage build up mode, controller design of rotor side converter (RSC) and stator side converter (SSC) is described. The synchronously rotating frame stator flux oriented frame vector control scheme is considered to control the standalone DFIG system. The main objective is to maintain the constant voltage and frequency at the stator terminals of a standalone DFIG irrespective of the wind speed variations and load variations. To achieve this quadrature axis rotor current is used to control the power balance of the system. Any imbalance in the power between mechanical input and load is reflected as a dip in the dc-link voltage which in turn affects the q-axis rotor current.
As this is a standalone system, initial dc-link voltage and dump load are required. Instead of wasting the generated power in dump load now a day’s battery energy storage system is preferred. The control of standalone DFIG based VSCF system with battery backup is analyzed in detail. The analysis of the proposed system is carried out in stator flux oriented synchronously rotating reference frame. The reference q-axis rotor current commands the injection of active power. The reactive power required for the generator is commanded by a closed loop control of the output voltage. A PI controller is used to generate the reactive current set-point d-axis reference rotor current. The system simulation is carried out in MATLAB/SIMULINK and the results are discussed in detail.