Luis Fernando Correa Monteiro

The modular multilevel converter (MMC) is a keystone of modern energy transmission systems. Consequently, there is an ongoing pursue for mathematical models to represent it under different configurations and control approaches. In short, this paper introduces an analytical Thévenin-equivalent model for representing the MMC when it is controlled with inner current- and an outer voltage-loop altogether. The model is based on a linearized representation of the converter and conveys the dynamics of passive components, such as submodule capacitors and arm reactors, as well as both control loops. Besides that, the proposed model is divided into a close-loop transfer matrix and the equivalent impedance matrix, both of which represent the relationships between the ac-side dq voltages and currents. We also propose a framework for implementing electromagnetic–transient simulations using the impedance model of this power electronic converter. The framework reduces a multi-bus power grid to a multi-input multi-output (MIMO) feedback system where impedance/admittance matrices of the MMC and other grid elements compose its loops. For validation purposes, it is considered a three-bus power grid comprising one MMC and another two grid-connected VSC. The proposed model was validated by comparing its results with a switching-level PSCAD model of the system.

This paper aims at improving the Enhanced-PLL (E-PLL) to mitigate the transient low-frequency oscillations, which is inherent to single-phase circuits. These improvements resulted in a new PLL configuration, designated here as the Double-Frequency Mitigation SOGI-EPLL, or simply DFM-SOGiEPLL. We integrate the EPLL with a Second-Order Generalized Integrator (SOGI), by modifying the computation of the internal error signals of the phase-and-frequency loop and the amplitude loop. Thus, the proposed DFM-SOGiEPLL is able to extinguish transient low-frequency oscillations, in a short time period, in comparison to the conventional EPLL. A dynamic model approach of both EPLLs, including four different test-cases, was implemented through numerical simulations and hardware experiments to verify the better performance of the proposed one.

Nowadays, new challenges arise relating to the compensation of power quality problems, where the introduction of innovative solutions based on power electronics is of paramount importance. The evolution from conventional electrical power grids to smart grids requires the use of a large number of power electronics converters, indispensable for the integration of key technologies, such as renewable energies, electric mobility and energy storage systems, which adds importance to power quality issues. Addressing these topics, this paper presents an extensive review on power electronics technologies applied to power quality improvement, highlighting, and explaining the main phenomena associated with the occurrence of power quality problems in smart grids, their cause and effects for different activity sectors, and the main power electronics topologies for each technological solution. More specifically, the paper presents a review and classification of the main power quality problems and the respective context with the standards, a review of power quality problems related to the power production from renewables, the contextualization with solid-state transformers, electric mobility and electrical railway systems, a review of power electronics solutions to compensate the main power quality problems, as well as power electronics solutions to guarantee high levels of power quality. Relevant experimental results and exemplificative developed power electronics prototypes are also presented throughout the paper.

Electrical power grids are rapidly evolving into smart grids, with smart homes also making an important contribution to this. In fact, the well-known and emerging technologies of renewables, energy storage systems and electric mobility are each time more distributed throughout the power grid and included in smart homes. In such circumstances, since these technologies are natively operating in DC, it is predictable for a revolution in the electrical grid craving a convergence to DC grids. Nevertheless, traditional loads natively operating in AC will continue to be used, highlighting the importance of hybrid AC/DC grids. Considering this new paradigm, this paper has as main innovation points the proposed control algorithms regarding the role of front-end AC/DC converters in hybrid AC/DC smart homes, demonstrating their importance for providing unipolar or bipolar DC grids for interfacing native DC technologies, such as renewables and electric mobility, including concerns regarding the power quality from a smart grid point of view. Furthermore, the paper presents a clear description of the proposed control algorithms, aligned with distinct possibilities of complementary operation of front-end AC/DC converters in the perspective of smart homes framed within smart grids, e.g., enabling the control of smart homes in a coordinated way. The analysis and experimental results confirmed the suitability of the proposed innovative operation modes for hybrid AC/DC smart homes, based on two different AC/DC converters in the experimental validation.

This paper exploits the performance of the particle swarm optimization (PSO) algorithm for a photovoltaic system under partial shading condition (PSC). Essentially our main contribution consists on analyzing the hyper-parameters adjustment of the PSO algorithm to determine the minimum particle numbers, such that the assertiveness to identify the Global Maximum Power Point (GMPP) be higher than 99%. The database was obtained throughout 5760 simulations based on different test cases. From these test cases, the PSC was applied in 2880 simulations. In the previous work, it was shown the best results based on 5 particles. In this update version, it is also shown the best results for 3, 7 and 9 particles, together with a comparison among them. Furthermore, this paper also presents the simulation results to evaluate the performance of the developed algorithm under transient- and steady-state conditions.

An experimental evaluation of a digital control system based on a dual Digital Signal Processor (DSP) architecture is proposed for a three phase Unified Power Quality Conditioner (UPQC). A classical UQPC is constituted by two power conditioners, connected in series and shunted with the power grid, and sharing a common DC-link. In a smart grid scenario of operation, a UPQC will be fundamental for compensating power quality problems, also contributing to improving the efficiency of the electrical grids from a global perspective. The UPQC operation requires a bidirectional energy transfer between the two power conditioners, however, respecting some constraints, they can be controlled independently. In order to take advantage of this characteristic, the control algorithms can be executed on two independent DSPs, without any communication between them and maintaining the operational characteristics of the UPQC. Comparing with the classical control architecture based on a single DSP, with the proposed dual DSP architecture, the computational effort of each DSP is decreased of about 35%, allowing to increase the sampling rate. Therefore, the main advantages of the proposed approach are the minimization of delays caused by the processing time, which are very common in digital control systems, as well as the increment of the UPQC performance. Along the paper, detailed analysis of the processing speed and memory requirements to implement the UPQC control algorithms in both DSPs is presented. The paper also presents a set of detailed experimental results, obtained with a developed 5 kVA laboratory prototype of UPQC, which was used to evaluate the performance of the proposed dual DSP architecture.