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High-power converters for regenerative drives and distributed generation need a network-friendly operation, low harmonic conductive electromagnetic emission for low electromagnetic interference and high electromagnetic compatibility reaching high reliability and performance. Nevertheless, the converters must be controlled with low switching frequency in order to reduce the commutation losses. These two requirements can be satisfied if an optimal modulation strategy is used. The selective harmonic elimination (SHE) is one of the low-switching-frequency strategies most used today. However, this strategy only eliminates a reduced set of harmonic components from the input current. This paper presents a novel optimal modulation strategy whose objective is to reduce the total harmonic distortion of the input current. Six- and twelve-pulse three-level neutral-point-clamped pulsewidth modulation rectifiers are used in order to implement both modulation techniques. The results confirm the advantages of the proposed strategy, namely, less input current distortion and remarkable reduction of higher order harmonics compared with the SHE method, while keeping a low-switching behavior. Index Terms--Electromagnetic compatibility, low switching commutation, optimal control, power conversion harmonics, pulsewidth modulation (PWM), selective harmonic elimination (SHE).

The analysis of a multicell topology that is implemented with single-phase nonregenerative cells under an unbalanced ac mains is presented. The study shows that the topology naturally compensates most of the voltage unbalance; for instance, for a 100% voltage unbalance in the ac mains, just 32% reaches the load. For critical applications, a feedforward control technique is proposed in order to compensate the remaining unbalance at the load side. The resulting topology, in combination with the proposed strategy, reduces near to zero the load fundamental voltage unbalance, while the input current unbalance and distortion are also improved. A theoretical analysis that is based on symmetrical components and the experimental results confirm the theoretical considerations. Index Terms--AC-AC power conversion, insulated-gate bipolar transistor, multicell single-phase topology, multilevel system, power electronics, variable-speed drives.

This paper presents the different technologies used in the generation of large controlled currents, in the kiloamperes range. After a brief review of processes requiring large currents, the paper discusses the working principles of thyristor phase-controlled rectifiers commonly used in these applications. Chopper-rectifiers using high-current insulated gate bipolar transistors are introduced as an alternative being considered in recent projects. The pulsewidth-modulated current-source rectifier, currently used in medium-voltage motor drives, is also analyzed as a future alternative for rectification in industrial processes. In addition, this paper presents the most important requirements and specifications to be considered in the applications of these high-power units. A system comparison is developed between thyristor and chopper-rectifiers in terms of quality of control, harmonics, power factor, losses, and efficiency. Index Terms--AC-DC power conversion, chopper-rectifiers, electrochemical processes, phase control, rectifiers, thyristors.

Grinding mill drives play an important role in the mining industry. Almost 60% of the electrical energy consumed by modern concentrator plants goes to grinding mill drives. Different technologies are used in grinding systems presenting special characteristics from the electrical and process points of view. This paper presents a technical evaluation and practical experience of two different technologies used in high-power grinding mill drives. The analysis is focused on the static power converter and associated control scheme required to drive the motor. Cycloconverters and load-commutated inverters are analyzed in terms of power grid interaction, motor interaction, and the required control scheme. The evaluation is supported with practical results obtained in different concentrator plant facilities. Index Terms--Cycloconverters, gearless motor drives, load-commutated inverter.

This paper presents the application of high-power three-level active-front-end rectifiers to regenerate energy in a downhill conveyor system. The selective harmonic elimination method is used to eliminate harmonics 11 and 13, working with very low switching frequency, where six-pulse harmonic orders 6k [+ or -] 1 are eliminated by the delta-wye connection of the transformer. In this way, the input current at the mains is highly sinusoidal with small harmonics starting at frequencies of order 23 and 25. Resonances have been detected, originated mainly by the capacitances of feeding cables and noneliminated harmonics, which produce high-voltage distortion. Theoretical and field measurements present the problem and the solution by using a specially designed high-pass power filter. Index Terms--Active rectifiers, conveyors, pulsewidth modulation (PWM), selective harmonic elimination (SHE).

Multicell power circuit topologies have proved to be an effective alternative to medium-voltage ac drives. The main advantage is the improved power quality at both the ac system and the motor sides. However, several drawbacks are present in these configurations, such as a lack of sustained regenerative operating mode, uncontrolled input reactive power, and a large second current harmonic that is injected by the load into the dc link of each cell, which leads to a bulky electrolytic capacitor. This paper proposes to replace the input diode-based front-end rectifier with an active front-end rectifier in all cells of the topology and a novel control strategy in order to overcome the aforementioned drawbacks. In fact, the active front-end rectifier allows the topology to regenerate and the control strategy handles the reactive input power and reduces the large second current harmonic from the dc-link capacitor, thus reducing its size. These features are achieved without any penalties in the quality of both the ac input current and the motor voltage waveforms. Experimental results confirm the theoretical considerations. Index Terms--Energy storage reduction, multilevel converter, regenerative cell.

New regulations impose more stringent limits on current harmonics injected by power converters that are achieved with pulsewidth-modulated (PWM) rectifiers. In addition, several applications demand the capability of power regeneration to the power supply. This paper presents the state of the art in the field of regenerative rectifiers with reduced input harmonics and improved power factor. Regenerative rectifiers are able to deliver energy back from the dc side to the ac power supply. Topologies for single- and three-phase power supplies are considered with their corresponding control strategies. Special attention is given to the application of voltage- and current-source PWM rectifiers in different processes with a power range from a few kilowatts up to several megawatts. This paper shows that PWM regenerative rectifiers are a highly developed and mature technology with a wide industrial acceptance. Index Terms--High power factor, power electronics, rectifier, regeneration.

Currently available anti-viral drugs may be somewhat useful in reducing the viral load, but are not providing the necessary physiological effects to combat the SARS-CoV-2 complications efficiently. Treatments that will provide better clinical outcomes are urgently needed. Vitamin C, (Ascorbic Acid, AA), is a nutrient with many biological roles that has been proven to play an important part in immune function, serve as an antioxidant, anti-viral, and exert anti-thrombotic effects among many other physiological benefits. Research has proven that AA at pharmacological doses can be beneficial to patients with Acute Respiratory Distress Syndrome (ARDS), and other respiratory illnesses, including sepsis. In addition, High Dose Intravenous Vitamin C (HDIVC) has proven to be effective in patients with different viral diseases such as influenza, chikungunya, sika and dengue. Moreover, HDIVC has been demonstrated to be very safe. Regarding COVID-19, vitamin C can suppress the cytokine storm, reduce thrombotic complications, and diminish alveolar and vascular damage, among other benefits. Due to these reasons, the use of HDIVC should be seriously considered in complicated COVID-19 patients. In this article, we will focus on vitamin C's role in the most prominent pathophysiological processes presented by the COVID-19 disease. [ABSTRACT FROM AUTHOR]

Two predictive space-vector control strategies for direct-frequency converter (DISC) structures are presented. Both algorithms require output-current feedback in order to decide the next best state of the converter. The performance of the control techniques is compared with a high-performance fictitious-link DFC. Computer simulation using Microsim PSpice 5.3 is used to examine the operation of the DFC converter algorithms. The evaluation is done for a wide-operational output frequency and includes input/output-voltage ratio, commutation frequency, input-current balance, input-current total harmonic distortion (THD), and input power factor. From these results, the high performance exhibited by the proposed algorithms is verified.

The article focuses on Vitamin C is an essential micronutrient for humans with an array of pleiotropic physiological functions has related to its ability to donate electrons. Topics include the cofactor for numerous biosynthetic and gene regulatory enzymes, Vitamin C is involved in numerous metabolic processes, and Vitamin C contributes to the immune system by supporting various cellular functions of both the innate and adaptive immune system.