Implementation of a three phase grid synchronization for doubly-fed induction generators in wind energy system

This paper implements of a three phase grid synchronization for doubly-fed induction generators (DFIG) in wind generation system. A stator flux oriented vector is used to control the variable speed DFIG for the utility grid synchronization, active power and reactive power. Before synchronization, the stator voltage is adjusted equal to the amplitude of the grid voltage by controlling the d-axis rotor current. The frequency of stator voltage is synchronized with the grid by controlling the rotor flux angle equal to the difference between the rotor angle (mechanical speed in electrical degree) and the grid angle. The phase shift between stator voltage and the grid voltage is compensated by comparing the d-axis stator voltage and the grid voltage to generate a compensation angle. After the synchronization is achieved, the active power and reactive power are controlled to extract the optimum energy capture and fulfilled with the standard of utility grid requirements for wind turbine. The q-axis and d-axis rotor current are used to control the active and reactive power respectively. The implementation was conducted on a 1 kW conventional induction wound rotor controlled the digital signal controller board. The experimentation results confirm that the DFIG can be synchronized to the utility grid and the active power and the reactive power can be independently controlled.