Design of DFIG Converters to Overcome Grid Faults Using Improved Stator Flux Based Field Oriented Control and STATCOM Controller

Abstract

The doublyfed induction generator based wind energy conversion system is attracting the energy production market for the last decade. It is due to the facts like large rating single unit, withstand to grid disturbances, independent real and reactive power flow control and mainly low power converter ratings. However, under severe short circuit faults, the doubly fed induction generator (DFIG) is constrained to be in synchronism with the grid as is posed by the modern grid codes. For this, dynamic and transient response of DFIG converter unit control needs to be modified for sustainability and reliability. The article will show that DFIG will follow better grid code requirements using proposed improved stator flux based field oriented control scheme in Rotor Side Converter. Further, a three levels STATCOM controller is externally placed near the grid point to further increase its capability under transients. This can be achieved by minimizing DC offset currents to zero by controlling stator flux decay during transients. The stator d and q axis flux wave is circular during steady state and also deviate its shape and characteristics during transients. This feature is restored using proposed FOC technique and helps in maintaining a minimum voltage and current in rotor and stator circuit. This technique not only improves LVRT but also ensures a longer lifetime of the machine during major disturbances.