Search Results (61)

Today’s power grids are being modernized with the integration of new technologies, making them increasingly efficient, secure, and flexible. One of these technologies, which is beginning to make great contributions to distribution systems, is solid-state transformers (SSTs), motivating the present technical and economic study of local level 2 distribution systems in Colombia. Taking into account Resolution 015 of 2018 issued by the Energy and Gas Regulatory Commission (CREG), which establishes the economic and quality parameters for the remuneration of electricity operators, the possibility of using these new technologies in electricity networks, particularly distribution networks, was studied. The methodology for developing this study consisted of creating a reference framework describing the topologies implemented in local distribution systems (LDSs), followed by a technical and economic evaluation based on demand management and asset remuneration through special construction units, providing alternatives for the digitization and modernization of the Colombian electricity market. The research revealed the advantages of SST technologies, such as reactive power compensation, surge protection, bidirectional flow, voltage drops, harmonic mitigation, voltage regulation, size reduction, and decreased short-circuit currents. These benefits can be leveraged by distribution network operators to properly manage these types of technologies, allowing them to be better prepared for the transition to smart grids. Full article

Laser surface treatment (LST) has been employed on ductile cast iron (DCI) parts to obtain a good performance and a long service life. There is a need to understand the laser surface-treated microstructure and hardening ability of DCIs with different matrix structures to facilitate the scientific selection of DCI for specific applications. In this study, a Laserline-LDF3000 fiber-coupled semiconductor laser with a rectangular spot was used to harden the surface of ductile cast irons (DCIs) with different pearlite contents. The hardened surface layer having been solid state transformed (SST) and with or without being melted–solidified (MS) was obtained under various process parameters. The microstructure, hardened layer depth, hardness and hardening ability were analyzed and compared as functions of pearlite contents and laser processing parameters. The results show that the MS layers on the DCIs with varied pearlite contents have similar microstructures consisting of fine transformed ledeburite, martensite and residual austenite. The microstructure of the SST layer includes martensite, residual austenite and ferrite, whose contents vary with the pearlite content of DCI. In the pearlite DCI, martensite and residual austenite are found, while in ferrite DCI, there is only a small amount of martensite around the graphite nodule, with a large amount of unaltered ferrite remaining. There exists no significant difference in the hardness of MS layers among DCIs with different pearlite contents. Within the SST layer, the variation in the hardness value in the pearlite DCI is relatively small, but it gradually decreases along the depth in the ferrite DCI. In the transition region between the SST layer and the base metal (BM), there is a steep decrease in hardness in the pearlite DCI, but it decreases gently in the ferrite DCI. The depth of the hardened layer increases slightly with the increase in the pearlite content in the DCI; however, the effective hardened depth and the hardening ability increase significantly. When the pearlite content of DCI increases from 10% to 95%, its hardening ability increases by 1.1 times. Full article

Solid-State Transformers (SSTs) enable significant improvements in size and functionality compared to conventional power transformers. However, one of the key challenges in Solid-State Transformer design is achieving reliable insulation between the high-voltage and low-voltage sections. This proposal presents the design and optimization of a high-insulation Medium-Frequency Transformer (MFT) for 66 kV grids operating at 50 kHz and delivering up to 75 kW for SST applications using Inductive Power Transfer (IPT) technology. A fixed 50 mm gap between the primary and secondary windings is filled with dielectric oil to enhance insulation. The proposed IPT system employs a double-D coil design developed through iterative 2D and 3D finite element method simulations to optimize the magnetic circuit, thereby significantly reducing stray flux and losses. Notably, the double-D configuration reduces enclosure losses from 269.6 W, observed in a rectangular coil design, to 4.38 W, resulting in an overall system loss reduction of 42.4% while maintaining the electrical parameters required for zero-voltage switching operation. These advancements address the critical limitations in conventional Medium-Frequency Transformers by providing enhanced insulation and improved thermal management. The proposed IPT-based design offers a low-loss solution with easy thermal management for solid-state transformer applications in high-voltage grids. Full article

The increasing penetration of renewable energy sources (RESs) into medium-voltage (MV) and low-voltage (LV) power systems presents significant challenges in ensuring power grid stability and energy sustainability. Advanced power conversion technologies are essential to mitigate voltage and frequency fluctuations while meeting stringent power quality standards. RES-based generation systems typically employ multistage power electronics to achieve: (i) maximum power point tracking; (ii) galvanic isolation and voltage transformation; (iii) high-quality power injection into the power grid. In this context, this paper provides a comprehensive review of up-to-date isolated DC–DC converter topologies tailored for the integration of RES. As a contribution to support this topic, recent advancements in solid-state transformers (SSTs) are explored, with particular emphasis on the adoption of wide bandgap (WBG) semiconductors technologies, such as silicon carbide (SiC) and gallium nitride (GaN). These devices have revolutionized modern power systems by enabling operation at a higher switching frequency, enhanced efficiency, and increased power density. By consolidating state-of-the-art advancements and identifying technical challenges, this review offers insights into the suitability of power converter topologies in light of future trends, serving as a valuable resource for optimizing grid-connected RES-based sustainable power systems. Full article

This paper explores the use of a solid state transformer (SST) to mitigate the $E_{3A}$ component of a high-altitude electromagnetic pulse (HEMP) insult using external energy storage optimal control techniques. In lieu of conventional passive blocking devices or feedback-controlled energy storage devices, a novel implementation of Hamiltonian error tracking is utilized to develop a feedback control law for the variable converter ratio in an SST. The findings of the simulations performed in this paper suggest that additional energy storage is not necessary to protect an individual load from a HEMP insult. The simulations performed examine the response of a single-phase SST connected to a single voltage source on a long transmission line on the one side and a single linear resistor on the other. The control law is specifically developed for the late-time, low-frequency portion of a HEMP insult, namely the $E_{3A}$ components. The Hamiltonian error-based converter ratio control law is compared with nonlinear optimal feedforward controls to show that the HSSPFC is an external energy storage optimal controller. Full article

This study presents a novel structure proposal of a variable inductance high-frequency transformer for enhancement power level of a dual-active-bridge (DAB) converter. The DAB converter is a solid-state transformer (SST) that requires high efficiency, power density, flexibility, and stability. Variable inductance facilitates achieving and extending maximum power levels. The proposed method adjusts the inductance based on the core insertion conditions of the transformer used in the DAB converter without requiring an additional inductor. The method was verified by analyzing the variable inductance characteristics of the transformer based on core insertion conditions via finite element analysis (FEA) and simulation and experiments within the variable inductance range. Full article

Solid State Transformers (SSTs) represent an emerging technology that seeks to improve upon traditional Low-Frequency Transformers (LFTs) with Medium-Frequency Transformers (MFTs) of reduced core size while incorporating modular converter structures as their input and output stages. In addition to magnetic circuit reduction, SSTs provide enhanced functionalities such as power factor correction, voltage regulation, and the capability to interface with various sources and loads. However, owing to the novelty of SSTs and the various proposed implementations, a general review would difficult to follow and might not be able to adequately analyze each aspect of SST structures. This complexity underscores the need for a new division of information and classification based on the number of conversion stages, which is the main contribution of this study. Converter functionalities are derived based on the number of stages. Utilizing these functionalities along with existing and proposed implementations, converter topologies are identified and then detailed in terms of their respective functionalities, advantages, disadvantages, and control schemes. The subsequent chapters provide a comparative analysis of the different topologies and present existing SST implementations. For this analysis, metrics such as the number of SST stages, power flow, voltage control, power quality, and component count are used. Based on the resulting analysis, single-stage SSTs are a promising solution that emphasize economy and high power density, while multi-stage SSTs are also a viable solution thanks to their ease of control and flexible design. This paper constitutes the first part of a two-part review. The second part will focus on the degrees of design freedom (such as multilevel structures/cells) and provide a generalized approach to modularity within SST systems. Full article

The Solid-State Transformer (SST) is a complex conversion device that intends to replace the Low-Frequency Transformers (LFTs) used in various power applications with Medium- or High-Frequency Transformers (MFTs/HFTs) that integrate modular converter structures as their input and output stages. The purpose is to obtain additional capabilities, such as power factor correction, voltage control, and interconnection of distributed supplies, among others, while reducing the overall volume. Given the expansive research conducted in this area in the past years, the volume of information available is large, so the main contribution of this paper is a new method of classification based on the modular construction of the SST derived from its applications and available constructive degrees of freedom. This paper can be considered the second part of a broader review in which the first part presented the fundamental converter roles and topologies. As a continuation, this paper aims to expand the definition of modularity to the entire SST structure and analyze how the converters can be combined in order to achieve the desired SST functionality. Three areas of interest are chosen: partitioning of power, phase modularity, and port configuration. The partitioning of power analyzes the fundamental switching cells and the arrangement of the converters across stages. Phase modularity details the construction of multiphase-system SSTs. Finally, the types of input/output ports, their placements, and roles are discussed. These characteristics are presented together with the applications in which they were suggested to give a broader context. Full article

The integration of hybrid alternating current (AC) and direct current (DC) networks has gained relevance due to the growing demand for more flexible, efficient, and reliable electrical systems. A key aspect of this integration is the parallelization of power converters, which presents several technical challenges, such as current sharing imbalances, circulating currents, and control complexity. This paper proposes a distributed control architecture for parallel resonant CLLC dual active bridge (DAB) converters to address these issues in hybrid AC–DC networks and microgrids. The approach includes a master voltage controller to regulate the output voltage and distributed local current controllers to ensure load balance. The approach minimizes the difference between the output and input voltages, allowing for independent control of power flow. Simulation and experimental results show significant improvements. The system stability has been demonstrated experimentally. Transient response has been improved with response time 80% lower using the feed-forward term. The system maintained stability with current sharing deviations below 3% under full and low load conditions. Finally, scalability is ensured by the proposed distributed controller because the central power controller is not affected by the number of units in parallel used in the application. This solution is suitable for advanced hybrid networks and microgrid applications. Full article

Polyamides’ properties are greatly influenced by the polymerization process and the type of feedstock used. The solid forms of nylon salts play a significant role in determining the final characteristics of the material. This study focuses on the long-chain bio-nylon 512. Firstly, we systematically investigated the possible solid forms of the nylon 512 salt, including crystal forms and morphologies, by massive experimental screening, single-crystal X-ray diffraction, Hirshfeld surface analysis, and TG-DSC measurements. The regulation and control of the various solid forms were achieved through solid-state transformations (SSTs) and solution-mediated phase transformations (SMPTs). Our findings shows that the nylon 512 salt exists in two crystal forms (anhydrate and dihydrate) and four morphologies (needle-like, plate-like, rod-like, and massive block crystal). Many factors will influence the formation of these solid forms, such as water activity, temperature, solvent, and ultrasonic physical fields. We can choose the right factors to regulate this as needed. On this basis, we studied the effects of different solid forms (crystal forms and morphologies) on the properties of the resulting polyamides prepared using direct solid-state polymerization (DSSP). The solid form of the salt had many effects on the polymer, including its structure, melting point, and mechanical properties. The polyamide obtained through DSSP of the anhydrate salt exhibited a higher melting point (204.22 °C) and greater elastic modulus (3.366 GPa) compared to that of the dihydrate salt, especially for the anhydrate salt of plate-like crystals. Full article

This paper presents the control and hardware design for a Hybrid Solid-State Transformer (HSST) applied to modern distribution systems. The HSST combines the advantages of conventional transformers, such as high efficiency and low cost, with those of Solid-State Transformers (SST), such as multifunctionality and fast dynamic response. Real-time simulation using a Typhoon HIL404 device is performed to validate the proposed multifunctional control strategy. The corresponding results validate the HSST’s capability to provide, while only processing partial system power, a regulated output voltage with grid voltage harmonic suppression and, at the same time, current load reactive and harmonic compensation to ensure a high-power factor and improved power quality to the grid. Full article

The large size of the sub-module (SM) capacitor is a typical problem in traditional modular multilevel converter-type solid-state transformers (MMC-SSTs). The MMC-SST based on high-frequency link interconnection is an effective solution for achieving lightweight capacitance. This structure can help to eliminate the symmetric SM fluctuating power, thereby reducing the SM capacitance. In a three-phase interconnected MMC-SST with low capacitance, potential risks may arise during transient processes, especially in cases of three-phase voltage asymmetry, such as large fluctuations in the SM voltage and unstable DC bus voltage. Aiming to solve this problem, this article re-analyzes the internal power characteristics of the MMC-SST under asymmetric operation and re-derives the SM capacitance constraint suitable for different degrees of three-phase voltage asymmetry. The new SM capacitance constraint enhances the asymmetric voltage ride-through capability of the MMC-SST. The new capacitance constraint is higher than that in symmetric operation, but it still has significant advantages in capacitance compared with the traditional MMC-SST. Full article

In this paper, a new linear-based closed-loop control method for a Solid-State Transformer (SST) has been proposed. In this new control method, individual current and voltage loops for each of the power conversion stages (AC-DC, DC-DC, DC-AC) are implemented. The feedback between the input and output control signals for each loop is achieved through the voltage on the DC link capacitors and the current transferred between the converters. This enables the SST to be controlled easily in a linear-based closed-loop manner without the need for complex computations. In order to evaluate the performance analysis of the proposed control system, a simulation of an SST with approximately 10 kVA apparent power was performed. Based on the obtained simulation results, the response time of the proposed control method for dynamic load variations was proved to be in the range of 40 milliseconds, and it has been observed that this method allows electrical power to be transferred from the load to the grid. The power factor value of SST under inductive load is measured to be approximately 99%, and the overall system efficiency is 96% and above, indicating that this proposed new control method has very high performance. Full article

Medium-voltage DC (MVDC) technology has gained increasing attention in recent years. Power electronics devices dominate these grids. Accurate simulation of such a grid, with detailed models of switching semiconductors, can quickly became very time-consuming, according to the number of connected devices to be simulated. A simulation approach based on interactions on a continuous time model can be very interesting, especially for developing a system-level control model of such a modern MVDC distribution grid. The aim of this paper is to present all the steps required for obtaining a continuous time modelling of a +/−10 kV MVDC grid case study, including a solid-state transformer (SST)- and modular multilevel converter (MMC)-based active front end (AFE). An additional aim of this paper is to supply educational content about the use of the continuous time simulation approach, thanks to a detailed description of the various devices modelled into the presented MVDC grid. The results of a certain number of simulation scenarios are eventually presented. Full article

During the energy transition, new types of electrical equipment, especially power electronic devices, are proposed to increase the flexibility of electricity distribution grids. One type is the solid-state transformer (SST), which offers excellent possibilities to improve the voltage quality in electricity distribution grids and integrate hybrid AC/DC grids. This paper compares SST to conventional copper-based power transformers (CPT) with and without an on-load tap changer (OLTC) and with additional downstream converters. For this purpose, a corresponding electricity distribution grid is set up in the power system analysis tool DIgSILENT PowerFactory 2022. A DC generator like a photovoltaic system, a DC load like an electric vehicle fast charging station, and an AC load are connected. Based on load flow simulations, the four power transformers are compared concerning voltage stability during a generator-based and a load-based scenario. The results of load flow simulations show that SSTs are most valuable when additional generators and loads are to be connected to the infrastructure, which would overload the existing grid equipment. The efficiency of using SSTs also depends on the parameters of the electrical grid, especially the lengths of the low-voltage (LV) lines. In addition, a flowchart-based decision process is proposed to support the decision-making process for the appropriate power transformer from an electrical perspective. Beyond these electrical properties, an evaluation matrix lists other relevant criteria like characteristics of the installation site, noise level, expected lifetime, and economic criteria that must be considered. Full article