الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Microgrids (MGs) gain higher potential and play a key role in grid infrastructure upgrade. It is considered one of the most feasible structures that accommodate the increased penetration of intermittent renewable distributed energy sources. Enabling MGs with renewable energy sources is crucial to meet the environmental concerns, increase economic benefits, support system reliability, and delay the bulk generation expansion. Although MG has many benefits, its performance operation is still facing challenges which need more attentive investigations. In this thesis, comprehensive investigation and characterization of MG performance under different loading conditions and penetration levels have been conducted. The MG under study includes a synchronous diesel generator, inverter-based distribution generation (DG), and a combined load comprising static RLC load, non-linear load, and induction motor (IM) load. This study addresses different inverter control strategies and schemes at normal and fault provoked islanding incidents. The impacts of the inverter control scheme and MG local load type, particularly IM loads, are evaluated and objectively compared.
Comparative simulation results show that the control techniques of the inverter-based DG are highly affecting the MG stability. Further, the MG may lose its stable operation owing to some load type characteristics and DGs penetration levels. Three techniques are presented in this thesis to enhance the MG dynamic performance after fault provoked islanding conditions. First technique is based on developing appropriate inverter control scheme for fault ride through (FRT) capability, known as transient management strategy (TMS). This scheme is designed to support the grid voltage during faults by maximizing the reactive current injection of the inverter-based DG. Second technique is enhancing the MG stability and the quality of voltage waveform, using a low-cost switched modulated power filter compensator (MPFC) which is a new distribution flexible AC transmission system (D-FACTS) device. Hence, employing the MPFC along with the inverter based DG achieves adequate method to overcome the shortcomings of the inverter DG unit. Third technique presented in this thesis, is proposing a hybrid technique based on mixing TMS with MPFC which gives effective solution to enhance the MG dynamic performance. Simulation results prove that the proposed techniques are positively contributing the enhancement of the MG stability and power quality.
Abstract
Integrating doubly fed induction generator (DFIG) based wind turbine in MG is very attractive but it raises even more challenges due to the wind speed variability. This attitude is worse for cases which wind energy supplies a significant part of the load. Hence, in such cases the ability of other generators to balance the demand may be limited subsequently wind power variations may lead to undesirable voltage and frequency oscillations
The operation of MG with DFIG gets worse with fault provoked islanding incident due to the weak behavior of the standard DFIG during faults. So that adequate techniques should be used with DFIG to support the MG voltage and frequency. A new structure of incorporating wind energy in MG along with MPFC is proposed. The MPFC performance enhancement with wind energy intermittence and their impact on stability and power quality are addressed.
In conclusion, this work presents a comprehensive analysis of MG performance. The proposed MG structure with the MPFC can withstand longer fault durations and gives better stability performance. Moreover, the MG equipped with the MPFC has the ability to minimize the voltage THD. In addition, superior features can be obtained by mixing the inverter control strategy based on TMS with MPFC as hybrid solution for enhancing the MG performance