Multi-Objective Control Strategy for Power Quality Improvement in Wind-Solar Distributed Generation System Under Harmonically Distorted Grid

 Abstract

Grid-interactive wind-solar distributed generation system (DGS) experiences substantial power quality (PQ) challenges pertaining to incessant voltage distortions in the utility gridand nonlinear loads at the point of common intersection. Such system non-idealities cause distortions in grid currents and infuse ripples in grid active and reactive powers. The effect of harmonically distorted voltages on DGS is further intensified in case of wind generation by means of a doubly-fed induction generator (DFIG), as its stator is directly coupled to the grid. Significant performance degradation with regard to distortions in DFIG currents, and ripples in stator power as well asDFIG torque, are observed. In this context, a control strategy, based on multiresonant higher order generalized integrator for harmonic estimation (MRHGI-HE) and a ε-normalized sign regressor least mean fourth (ε-NSRLMF) algorithm, for DGS employing solar photovoltaic array and DFIG based wind generator, is presented in this article. Based on selected objective, the control approach puts-forth a feasible solution for alleviating the aforementioned PQ challenges. The MRHGI-HE provides improved harmonics estimation and superior disturbance rejection, than its conventional counterpart. Besides, ε-NSRLMF algorithm exhibits enhanced system dynamics, as compared with least mean fourth algorithm. The multi objective control strategy is corroborated through extensive simulation and experimental studies, and results demonstrate the PQ improvements in the DGS.

Index Terms—Distorted grid voltages, distributed generation system (DGS), doubly-fed induction generator (DFIG), power quality (PQ), solar photovoltaic (SPV) array.

Block Diagram:

Fig. 1. Block diagram representation for wind-solar DGS.

Expected Simulation Results:

Fig. 2. MPT operation and UPF operation of wind-solar DGS.

Fig. 3. System responses showing distorted grid voltage (vga), rotor current (ira), and stator current (isa) with DFIG-side control objectives DDobj and ADobj-I.

CONCLUSION

A multi objective control strategy to alleviate the PQ problems associated with distorted grid voltage and distorted load currents in a wind-solar DGS has been presented in this article. The multi objective control strategy derives its reference currents from the MRHGI–HE and the ε–NSRLMF algorithms. The MRHGI–HE provides superior dc-offset and harmonics estimation as compared with the conventional MSOGI, while the ε–NSRLMF algorithm outperforms the LMF by displaying better dynamic response amidst sudden system variations. Based on MRHGI– HE and ε–NSRLMF algorithm, appropriate reference currents for four distinct DFIG-side and three separate grid-side control objectives have been estimated. The computational burden for control implementation has been minimized through utilizing the HCC structure in RSC as well as GSC control. Test results have portrayed effective system performance at the corresponding control objectives. Moreover, a comprehensive assessment has revealed ADobj-I (DFIG-side) and DGobj (grid-side), as the optimal control objectives for overall PQ improvement at distorted grid voltages and distorted load currents conditions.

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