Electric grid codes are expected to change in near future to accommodate an increased number of distributed generation units in the distribution power system without impairing its power quality. It is desired that the generators remain connected during voltage sags and provide ancillary services, such as voltage and reactive power control, ensuring the operational stability of the power system. This paper explores how the existing strategies for active and reactive power injection impact the operation of grid-tied inverters in terms of required power, current flowing and reduction of active power delivery during the voltage sags. Such inputs are relevant to properly size converters for operation under fault events. In addition, this paper contributes to devise ${1}$ ) constant peak current control, ${2}$ ) constant active current control and ${3}$ ) constant average active power control strategies for three-phase four-wire grid-tied inverters considering the natural (abc) reference frame. The design and implementation of the investigated power injection strategies are discussed, and their effectiveness and technical viability are analyzed through dynamic computational simulations under symmetrical/asymmetrical voltage sags, and variation of the short-circuit ratio.

The application of cascaded multilevel converters in large-scale photovoltaic plants connected to the utility grid has many advantages, such as the absence of sinusoidal filters and line-frequency transformers. Improved overall performance under partial shading conditions is possible due to the distribution of arrays among a large number of maximum power point trackers. In this situation, although the cells operate at different power levels, the three-phase currents injected into the point of common coupling must be balanced. A suitable control technique is required to achieve this goal. This paper presents a complete algorithm to handle three-phase power balance and single-phase power harvesting simultaneously. Simulation results assuming a medium-voltage system connected to a typical utility grid illustrate the dynamic and steady-state performance capability of the proposed strategy. Experimental results of a low-voltage, solid-state transformer-based, three-cell prototype are also included.

Power Electronics demand appropriate heat dissipation to secure life span, reliability, and power density. Among several cooling methods, oil immersion is an efficient and cost effective one. Natural convection is the most reliable considering the lack of pumps and fans compared to others practical ways of immersion cooling. This paper brings a case study of a power electronics device submerged in an oil tank, the same one used for power transformers. Using computational fluid dynamics (CFD) simulations and an experimental setup, the natural convection process is demonstrated as well as the better heat flow dissipation of oil immersion cooling.

This paper presents two hybrid filter topologies applied to a hot strip mill electrical system with cycloconverters, to evaluate the harmonic compensation and damping of harmonic resonance. In addition, an evaluation of the performance of hybrid filters in reducing the current rating of the passive filter is also presented. The most relevant waveforms of the system and its harmonic spectrum are analyzed, to assess the performance of each filtering structure in improving the power quality. The results obtained through digital simulation show that a series hybrid filter provides harmonic damping and allows enhancing the harmonic compensation characteristics of the passive filtering system, using an active filter of lower rated power compared to a parallel hybrid filter. However, the series hybrid filter does not present good filtering characteristics in the high frequency range, what can be performed by a parallel hybrid filter with a higher rating.

Steel production worldwide continues to grow and, consequently, also the energy consumption of the steel sector. With the applications of the electric arc furnace route in the steelmaking process, the concern with aspects of power quality and overload of the transmission grid lines increases. This work presents the zero harmonic distortion (ZHD) converter static synchronous compensator (STATCOM), which makes it possible to increase the displacement power factor of an electric arc furnace (EAF) application from 0.88 to 0.98 with total demand distortion in the grid around 1.44% with the ZHD prototype operation, this being accomplished without using high-order sinusoidal filters and with consolidated components in the industry.

Large charging cranes are used to introduce hot metal into the basic oxygen furnace through the use of induction motor drives for the main and auxiliary hoist. These motor drives shall have the capability of dealing with bidirectional power flow due to the action of lifting (motoring) or lowering (regenerating) the load. The use of the active rectifier increases the energy efficiency since the braking energy is not lost in heat. This article proposes a true unit power factor converter with a common dc bus and compares it to an existent solution. Theoretical analysis, simulation results, and losses calculation show the advantages of the proposal in terms of power quality, energy efficiency, and reliability. Hardware-in-the-loop results show the proper work of the developed control system.