Improved Voltage Harmonics Compensation Strategy for a Stand-Alone DFIG Operating under Unbalanced and Nonlinear Load Conditions
The study presents an improved control and operation for a stand-alone Doubly-Fed Induction Generator (DFIG) energy system under unbalanced and nonlinear load conditions. This type of loads results in unbalance and distorted stator voltage and current at the Point of Common Coupling (PCC), with subsequent power quality degradation and electromagnetic torque pulsations of DFIG. A new and simple control strategy based Proportional-Resonant Controllers (PRCs) in the stationary reference frame is applied in the Load-Side Converter (LSC) for fully compensate the unbalance and harmonic distortion in the PCC and avoid the torque pulsations of DFIG. As a result, symmetrical and sinusoidal AC voltage is applied to the PCC, which indicates that the Rotor-Side Converter (RSC) can be still controlled with the traditional vector control strategy, to adjust the generator torque and to balance active power. This strategy is conceptually simple, it does not require for rotating coordinate transformation and the sequence decomposition process, in addition no current sensors need to be installed at load or stator side, so that the number of current sensors employed is reduced. Simulation results using MatLab/Simulink are given and show the effectiveness and validity of the proposed control scheme to eliminate the harmonics in the PCC and torque pulsations of DFIG.