Multilevel inverters (MLIs) have remained a promising contribution to research in the modern era, especially in the area of energy conversion. Their popularity, nominal and optimal operations have merged them into low, medium, and high-power applications. Their use in advanced and wide range of applications have proved them as innovative solutions to many issues. Advanced MLIs structure tackle high-profile total harmonic distortion (THD) issues, maximum switching losses, low fault tolerance, low-quality output voltage, high rating of devices, low switching frequency, and frequency interfacing. Such factors classify them into various categories, which specify their operations in multiple applications. The existing literature lacks proper control strategies, design mechanisms, mathematical and application analysis. The aforementioned strategies help to investigate switching losses, configuration complexity, cost analysis, load management, input and output voltage categorization and many other prominent features of MLIs. Therefore, this paper provides a detailed review study and investigates various MLI topologies based on their structure, synthesis, mathematical explanations, control strategies, design mechanisms and utilization in various applications. The evolution of MLIs their classification, advantages, disadvantages, design mechanisms, control strategies, load vs input voltage interfacing and applications based utilization are tabulated to highlight their importance in various sectors. The proposed review study is compared with other prominent review studies and have covered a wide range of MLI topologies based on their evolutional development, mathematical representations, generic utilization and design methodologies.

The concept of smart grids has enabled the addition of renewable energy resources in the utility grids. This integration is possible after energy conversion and energy conversion causes the degradation in the quality of electric power. The power quality can be enhanced by reducing the total harmonic distortion (THD) in energy conversion. In this paper, we have presented an improved artificial neural network (ANN) based approach that can be useful to reduce the THD levels in a cascaded H-bridge (CHB) multilevel inverter (MLI). The proposed ANN architecture consists of only one hidden layer with ten neurons and can generate accurate results in both overfitting and underfitting conditions. Due to a smaller number of neurons, the proposed architecture is less complex and can produce results relatively faster as compared to other ANN architectures available in the literature. The proposed ANN architecture is tested on an asymmetrical CHB MLI, and the results are compared with the recent state-of-the-art (SOTA) techniques. The CHB MLI under test had three DC voltage sources with 1:2:4 and inductive loads. The simulations are performed in MATLAB and Simulink environment and the switching angles are optimized by using the ANN architecture. The results have shown a 71.95% improvement in current THDs and a 13.91% improvement in voltage THDs as compared to the SOTA technique. The proposed configuration is 89.6% efficient on inductive load and uses a smaller number of switches. Finally, an experimental setup is created, and the simulation results are validated through various experiments.

In this review paper, the anti-surge control (ASC) of the compressors and fault-tolerant control (FTC) systems are described from the perspective of integration for reliability enhancement against faults in the system components. It explains the phenomenon of a surge in the compressors, surge precursors, and the potential damage caused by this surge. The explanation of surge avoidance methods in compressors incorporated with modern surge control systems is described along with their applications. The sizing of the system components and valves, particularly methodologies for appropriately estimating acceptable upstream pipe sizes, are elaborated. The existing surge protection techniques for compressors are analyzed to highlight the advantages and disadvantages and from a future perspective, new approaches for detecting system changes and surges, are included. In the end, the concept of fault tolerance and its advanced applications concerning the anti-surge control for compressors are explained. This study contributes to the young researchers in the field of anti-surge control systems for compressors with the integration of fault tolerance to increase the reliability of the system.