Design of High-Power Solid-State Transformers with Grain-Oriented Electrical Steel Cores

There is no doubt that society will not turn back: most thermal vehicles will switch to electric ones, not only for cars but also for bigger vehicles. Fast chargers will become more and more essential parts of the global system, they will provide a charge control of batteries and galvanic insulation from the grid. At the present times, compact realizations are based on Solid-State Transformers (SSTs) operating at high frequencies with their well-known advantages and disadvantages, including power limits and reasonably high costs. The authors propose a medium-frequency transformer (MFT) structure using Grain Oriented Electrical Steel (GOES) wound cores and aluminum foil windings. Thanks to this solution, the cost of the device can be reduced. GOES has losses that increase with frequency but decrease with temperature; therefore, the authors propose a transformer structure allowing a hot core inside coils at usual temperatures. This idea is applied to a 400-kW compact battery charger connected to a DC smart grid.

A Solid-State Transformer as Enabling Technology for Microgrids for Integration into the Power Distribution System: An Overview

Recently, medium voltage SiC devices have been developed which can be used for grid tie applications at medium voltage. Two such devices - 15 kV SiC IGBT and 10 kV SiC MOSFET have opened up the possibility of looking into different converter topologies for medium voltage distribution grid interface. These can be used in medium voltage drives, active filter applications or as the active front end converter for Solid State Transformers (SST). Transformer-less Intelligent Power Substation (TIPS) is one such application for these devices. TIPS is proposed as a 3-phase SST interconnecting 13.8 kV distribution grid with 480 V utility grid. The Front End Converter (FEC) of TIPS is made up of 15 kV SiC IGBTs. This paper focuses on the advantages, design considerations and challenges associated with the operation of converters using these devices keeping TIPS as the topology of reference.

Core Loss Reduction of Tubular Flux-Switching Permanent Magnet Machine with Hybrid Magnetic Core

This paper studies the material-saving effect of transformer with 3-D wound core based on comparison and analysis of material- and energy-saving features of 3-D wound core and laminated core. After geometrically decomposing the two iron cores under the condition of the same baseline dimension, we conclude that the 3-D wound core has two advantages, the silicon steel is saved by 23%, and the no-load loss is lowered by 18%~28%.Under the condition of the same loss, the transformer with 3-D wound core can reduce the copper and iron consumption amount by taking advantage of low no-load loss in the optimized design scheme and its feature of material-saving and high filling rate of the iron core. The copper and silicon steel consumption amount are reduced by about 27% and 24% respectively, and the total product cost is lowered by about 24%. Through research and analysis, we find that transformer with 3-D wound core is featured by material- and energy-saving capabilities with low loss.

The efficiency of motor can be increased by optimizing stator, rotor slot design and using more materials, but there is limit within the narrow space of motor frame. Because of limited dimension, high quality material can be adapted, such as copper bar instead of aluminum bar, or low core loss Si-steel. However, adapting low core loss electrical steel does not always mean reduction of core loss. Because of non-linearity of B-H and B-Loss data, applying high grade material could unintentionally increase losses. It is important to consider magnetic flux density and harmonic core loss when applying low core loss electrical steel. In this paper, losses of motor are analyzed with respect to the various electrical steel. Using the finite element analysis (FEA), core loss and stray load loss are calculated with B-H, B-Loss data of electrical steel. Also, test results of 440V, 4pole, 15/30kW induction motor are also provided.

Distribution systems have traditionally received the least attention in the bulk picture of power systems; they are yet the most "critical component" as they directly impact customers’ perception and utilities’ reputation. While transmission systems have seen abundant literature, innovations, and applications of power electronic-based devices to optimize their performance, distribution systems still require more attention toward a flexible and dynamic scheme to cope with volatile energy consumption and production. As a replacement or enhancement of the traditional ones, Solid-State Transformers can play a central role in the energy management of distribution systems towards this goal, in addition to the mere voltage conversion. This manuscript, developed within the IEEE Task Force on Solid-State Transformer integration in distribution grids, offers a critical review of the Solid-State Transformer potential, services, and technical challenges for its integration in distribution systems. Particular attention is given to scientific trends and open points in the current research that must be addressed before utilities extensively integrate the Solid-State Transformer in distribution systems.

The large-scale integration of renewable energy sources (RESs) and the increasing number of energy -storage (FS) systems connected to the grid will create a big challenge for power flow management at the distribution level. In this new scenario, a solid-state transformer (SST) will be a highly efficient key element for providing highly efficient and controllable power flow in distribution grids. SSTs not only mimic the operation of conventional transformers, which scale the voltage level between primary and secondary terminals, but they also control bidirectional power flow, stabilize voltage, facilitate direct integration of ES, and mitigate harmonics and transients, which can cause the power quality of the grid voltage to deteriorate. This article surveys several proposed structures for SSTs in the literature based on different ways of interconnecting power converter topologies.

This study presents a design and optimization methodology to enhance the power density and efficiency of wound field synchronous machines (WFSMs) by selectively applying grain-oriented electrical steel (GOES). Unlike conventional non-grain-oriented electrical steel (NOES), GOES exhibits significantly lower core loss along its rolling direction, making it suitable for regions with predominantly alternating magnetic fields. Based on magnetic field analysis, four machine configurations were investigated, differing in the placement of GOES within stator and rotor teeth. Finite element analysis (FEA) was employed to compare electromagnetic performance across the configurations. Subsequently, a multi-objective optimization was conducted using Latin Hypercube Sampling, meta-modeling, and a genetic algorithm to maximize power density and efficiency while minimizing torque ripple. The optimized WFSM achieved a 13.97% increase in power density and a 1.0% improvement in efficiency compared to the baseline NOES model. These results demonstrate the feasibility of applying GOES in rotating machines to reduce core loss and improve overall performance, offering a viable alternative to rare-earth permanent magnet machines in xEV applications.

The growing demand for the ultra-fast DC charging stations needs the direct connection to the medium-voltage (MV) distribution grid, which can be achieved through the solid-state transformers (SST) as opposed to solutions using line frequency transformers (LFT). By using the MV high current silicon carbide (SiC) modules, which are becoming more available than before, the architecture of SST can be significantly simplified with much less number of series-parallel modular cells. In this work, we investigate the feasibility and present the development of a 3.3 kV SiC based full bridge building block. Then a MV dual active bridge (DAB) with 2 kV DC input and 800 V DC output, which is an essential unit in the MV DC charger, is prototyped using the developed building block. Compared to the use of modules rated at 1.7 kV or lower, the presented DAB can reduce the number of series cells in half, since the DC bus voltage for each cell can be raised from 1 kV to 2 kV. Extensive characterizations, e.g., switching tests, thermal tests, and etc., have been carried out for the 3.3 kV SiC module to extract key information to guide the electro-thermal co-design of the MV DAB system.

Along with the DC grid distribution issue, the Solid State Transformer (SST) is increasingly emerging in the field of electric power electronics, and the Hybrid SST (HSST) study is also emerging between the current AC-based Grid and future DC grid distribution. At present, several SST and HSST studies have discussed ways to implement the same topology in series to create high DC voltages. These cascade-style topologies not only make it difficult to implement controllers and designing gate drivers but also require a lot of elements, which drives up the overall system’s price. Meanwhile, IGBT and MOSFET series connections are actively being studied for high voltage topology, and various techniques are being studied to solve simultaneous turn on/off problems. This paper proposes by altering the PFC circuit used in existing LVs to switch device series-connected base for HSST and SST. In this paper, circuits were constructed using balancing resistance and passive component for voltage balancing of series-connected switches, and validity is verified through proper controller selection and formulas.

Purpose: This paper aims to enhance the design of Solid-State Transformers (SSTs) operating at medium and high frequencies (MF/HF) by optimizing key performance attributes such as efficiency, power density, and thermal management through the use of advanced nanocrystalline materials. Design/Methodology/Approach: An interactive MATLAB-based magnetic characterization tool was utilized to evaluate transformer core losses and efficiencies with various core materials. A hybrid optimization methodology integrating L9 Taguchi design and Response Surface Methodology (RSM) was employed to design a 2 kVA, 20 kHz, 600/60 V shell-type SST. Design parameters such as duty cycle, window utilization factor, insulation material, and core series were optimized across three levels to achieve minimal losses and maximum efficiency. Research Limitations/ Implications: While the study demonstrates promising results, the research is limited to a specific transformer rating and operating frequency, indicating a need for further exploration across varying ratings and frequencies. Practical Implications: The findings contribute to the development of efficient and compact SSTs, benefiting renewable energy systems, electric vehicle charging, grid-connected converters, and compact power supplies by ensuring reduced thermal stress and enhanced durability. Originality/Value: This research highlights the efficacy of integrating advanced nanocrystalline materials and hybrid optimization methodologies in SST design, offering substantial improvements in energy efficiency and operational reliability, thus contributing valuable insights to transformer design and application fields. Major Findings: The optimized Solid-State Transformer (SST) design achieved an impressive efficiency of 99.5832% with core and winding losses of 6.2391 W and 2.2457 W, respectively. The temperature rise was minimized to 11.4541°C, confirming the effectiveness of the hybrid optimization approach. Validation through fuzzy inference systems demonstrated robust alignment with both theoretical and experimental results.

Availability of new high-power semiconductor devices and the desire for developing power systems with higher penetrations of distributed generation have sparked significant research in power electronic converters. The non-sinusoidal nature of the current and voltage waveforms commonly present in power electronic converters makes it difficult to accurately evaluate the copper and core losses of components such as inductors and transformers operating at high and medium frequencies. The evaluation of the core losses for three soft magnetic materials (amorphous, ferrite and nanocrystalline) under different rectangular-voltage waveforms used in solid-state transformers, duty cycles and switching frequencies is the main aim of this work. The test setup comprises a 10 kVA Si IGBT-based three-level full-bridge converter used to generate the rectangular-voltage waveforms exciting the cores. The comparison based on the main material properties establishes criteria for proper core material selection when designing high-and medium-frequency transformers.

Permanent magnet Linear motors are a potential candidate of the mass transportation propulsion systems. In these systems the long secondary or primary core is laid on the track which leads to high amount of core loss. Soft magnetic composite materials have better performance at high frequency in comparison with electrical steel. This paper presents Permanent Magnet Linear Motors (PMLMs) with buried poles thrust force and core losses under both soft magnetic composites (SMC) and Electrical Steel (ES) cores. Calculations are done both by analytical equations and 3D-Finite Element Analysis (FEA) based simulation. A comparison between the results reveals that employment of SMC in the motor structure leads to a reduction in the volume and as a result the core loss per developed unit thrust. Thus it increases the motor efficiency and force density.

The iron loss in the ferromagnetic cores of electrical machines under PWM excitations could be many times higher than the loss under sinusoidal excitation. Therefore, the effects of the PWM waveforms, and their various characteristics (modulation index, switching frequency, and topology, etc.), on the iron loss must be understood and the ability to model these effects in the electrical machine design process is highly desired. In this work, the iron loss is reported for various electrical steels under PWM excitations and the effects of PWM waveform characteristics are studied. The iron loss measurements in a surface mounted permanent magnet motor under PWM excitations are also presented and are in agreement with the measured iron losses in electrical steels. The effect of the iron loss variations on the operating point of the machine is also discussed from the electric vehicle point of view. In the end, a computationally efficient approach based on the static Preisach model is presented to predict the iron loss in electrical steels. The proposed approach can model the effects of changing switching frequency, switching topology and modulation index on the iron loss with a reasonable accuracy.