Renewable energy resources are becoming the dominating element in power systems. Along with de-carbonization, they transform power systems into a more distributed, autonomous, bottom-up style one. We speak of Smart Grid and Microgrid when distributed energy resources take over. While being a means to improve technical and financial efficiency, planning, operations, and carbon footprint, it is these new technologies that also introduce new challenges. Reliability is one of them, deserving a new way of describing and assessing system and component reliability. This paper introduces a new reliability framework that covers these new elements in modern power systems. It can be seen that reliability assessment of modern power systems also requires introducing local reliability concepts as well as incorporating different electro-magnetic/mechanical stability issues.

Reliability prediction in power electronic converters is of paramount importance for converter manufacturers and operators. Conventional approaches employ generic data provided in handbooks for random chance failure probability prediction within useful lifetime. However, the wear-out failures affect the long-term performance of the converters. Therefore, this article proposes a comprehensive approach for estimating the converter reliability within useful lifetime and wear-out period. Moreover, this article proposes a wear-out failure prediction approach based on a structural reliability concept. The proposed approach can quickly predict the converter wear-out behavior unlike conventional Monte Carlo-based techniques. Hence, it facilitates reliability modeling and evaluation in large-scale power electronic-based power systems with huge number of components. The proposed comprehensive failure function over the useful lifetime and wear-out phase can be used for optimal design and manufacturing by identifying the failure prone components and end-of-life prediction. Moreover, the proposed reliability model can be used for optimal decision-making in design, planning, operation, and maintenance of modern power electronic-based power systems. The proposed methodology is exemplified for a photovoltaic inverter by predicting its failure characteristics.

Applying conventional dc-voltage based droop approaches for hybrid ac/dc microgrids interconnected by a single interlinking converter (IC) can properly manage the power flow among ac and dc subgrids. However, due to the effect of line resistances, these approaches may create a circulating power as well as overstressing the ICs in the case of employing multiple ICs for interconnecting the ac and dc subgrids. This paper proposes an autonomous power sharing approach for hybrid microgrids interconnected through multiple ICs by introducing a superimposed frequency in the dc subgrid. Hence, a suitable droop approach is presented to manage the power among the dc and ac sources as well as ICs. The outcomes are proportional power sharing, preventing circulating power and overstressing the ICs as well as acceptable dc voltage regulation. Furthermore, the maximum transferred power by the ICs can be improved by employing the proposed approach. The effectiveness of the proposed approach is evaluated by simulation.

This paper aims to incorporate the reliability model of power electronic converters into power system reliability analysis. The converter reliability has widely been explored in device- and converter-levels according to physics of failure analysis. However, optimal decision-makings for design, planning, operation and maintenance of power electronic converters require system-level reliability modeling of power electronic-based power systems. Therefore, this paper proposes a procedure to evaluate the reliability of power electronic based power systems from the device-level up to the system-level. Furthermore, the impact of converter failure rates including random chance and wear-out failures on power system performance in different applications such as wind turbine and electronic transmission lines is illustrated. Moreover, due to a high calculation burden raised by the physics of failure analysis for large scale power electronic systems, this paper explores the required accuracy for reliability modeling of converters in different applications. Numerical case studies are provided employing modified versions of the Roy Billinton Test System (RBTS). The analysis shows the converter failures may affect the overall system performance depending on its application. Therefore, an accurate converter reliability model is, in some cases, required for reliability assessment and management in modern power systems.

This paper proposes a new control scheme to eliminate the $3^{\text{rd}}$ harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical $3^{\text{rd}}$ harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a $3^{\text{rd}}$ harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup.

The reliable design, planning, and operation of power systems are of paramount importance for providing reliable services to customers. This article reviews the different aspects of power system reliability, ranging from planning to operation. Standard benchmarks employed for power system studies are reviewed according to nearly 2,500 IEEE journal papers from 1986 to early 2019. Our overview provides the pros and cons of existing test systems, implying the lack of appropriate benchmarks for future power system studies, including renewable resources and modern technologies. Furthermore, this article presents requirements for updating and modifying the benchmarks for modern power systems analysis.