Transformer Design Optimization Research Articles

Optimal Design and Analysis of High-Frequency Isolation Transformer for Switched-Mode Power Converters

High-frequency (HF) transformers have gained great interest in recent years due to the advent of powerful soft magnetic materials with low core loss in semiconductor power switches. Also, the optimal design of the HF transformer is a significant issue for high-performance energy conversion systems. In this paper, a 40W 50/12.5/25 V universal input and two output discontinuous-conduction mode (DCM) flyback transformer is designed by using mathematical calculations and analyzed via 3D ANSYS/Maxwell simulation including electromagnetic and loss analysis. It is shown that the simulation results accounting for hysteresis losses, eddy current losses, copper losses, and magnetic flux density determine the accuracy of the mathematical model calculation. Analyzes are performed at 100 kHz frequency levels. Results obtained will include core magnetic flux density, core/copper losses, leakage/magnetizing inductances, windings parasitic capacitances, input/output voltage, current values, and all design parameters. Finally, the proposed HF transformer's overall efficiency is calculated and presented. Significantly, the HF transformer achieves 97.8% efficiency thanks to the transformer's core and coil selection, B-H and B-P characteristics, one-to-one dimension design, and mesh operation. The dynamic and mathematical results of the designed transformer demonstrate the design and efficiency success

Multiobjective design optimization of transformers for battery cell balancing converters considering bidirectional power flow

Multiobjective design optimization of transformers for battery cell balancing converters considering bidirectional power flow

A Lightweight Optimization Study for Large Capacity Dry-Type On-board Traction Transformer of EMU Based on CFD and RSM

Using the dry-type on-board traction transformer cooled by train-induced wind is an effective way to realize the lightweight of on-board equipment. However, the existing small capacity fan cooled dry-type on-board traction transformer cannot meet the power requirements of the high-speed electric multiple unit. For the large capacity dry-type on-board traction transformer, the lack of mathematical models that can reflect the relationship between hotspot temperature and design parameters limits its development. This paper aims to propose an optimization method for large capacity dry-type on-board traction transformer. First, the user-defined function based computational fluid dynamics modelling method for dry-type on-board traction transformer is proposed and validated to accurately obtain the winding hotspot temperature. Then, the response surface models of winding hotspot temperature are firstly proposed based on the response surface methodology. Finally, the lightweight optimization of a 6.3 MVA dry-type on-board traction transformer is completed, and the influence of design parameters on the weight reduction is studied. Under the conservative optimization strategy, the total weight of dry-type on-board traction transformer is reduced to 3650.40 kg, which is reduced by 38.55% compared with the oil cooled on-board traction transformer with the same rated capacity. This paper provides an efficient and feasible method and regular guidance for the lightweight optimal design of dry-type on-board traction transformer, and the obtained response surface models can be used for the optimization of similar dry-type on-board traction transformer under different specific needs.

Power Transformer Characterization and Design Optimization Environment

Power Transformers are essential part of all AC Power Grids. This work proposes a characterization and design optimization environment for Power Transformers to increase efficiency while decreasing core volume. It utilizes a Finite-Element State-Space models in conjunction with Artificial Neural Networks and Particle Swarm Optimization. A case study of a 42 MVA, 118/13.8kV distribution power transformer was conducted, and transformer performance characteristics were compared to test data for verification. Next, the optimization environment was used to decrease the transformer volume and improve its efficiency. In addition, the Taguchi orthogonal arrays method was used to reduce computational costs.

Optimal Dielectric Design of Medium Voltage Toroidal Transformer With Electrostatic Shield Under Fast Front Excitation

Accurate calculation of transient overvoltages and dielectric stresses from fast-front excitations is required to obtain an optimal dielectric design of power components subjected to these conditions, which are commonly due to switching and lightning, as well as utilization of power-electronic devices. Toroidal transformers are generally used at the low voltage level. However, recent investigations and developments have explored their use at the medium voltage level. This paper analyzes the model-based improvement of the insulation design of medium voltage toroidal transformers. Lumped and distributed parameter models are used and compared to predict the transient response and dielectric stress along the transformer winding. The parameters of the toroidal transformer are computed using the finite element method considering a three-dimensional geometry. Different strategies for insulation design are proposed by means of optimal insulation thickness and electrostatic shield to reduce transient overvoltage and dielectric stress. The results show that the proposed optimal insulation design based on particle swarm optimization with electrostatic shield can substantially reduce the dielectric stress and dielectric distances. Comparison between simulations and experimental results demonstrates that the frequency domain modeling approach results in accurate calculation of transient overvoltages produced by fast front excitation and can be used effectively for insulation design.

Termination Design Optimization of High-Current PCB-Winding Matrix Transformers

Due to their high power densities and efficiencies, high-frequency resonant converters using printed circuit board (PCB)-based transformers are gaining popularity in applications, such as datacenters and automotive. However, in such high-frequency, high-current applications, the PCB transformer's termination losses may become significant if not designed properly. This article aims to highlight multiple design considerations to minimize the termination losses while designing a PCB-based matrix transformer. Various termination techniques for full-bridge and center-tap secondary-rectifiers are studied, and it is shown that placing the devices and output filter capacitors directly on the secondary windings results in the lowest termination loss. However, this results in the output filter capacitors being split between the two secondary PCB layers, resulting in a long paralleling loop between them. It is demonstrated that the parasitic inductance of this loop undergoes parallel resonance with the filter capacitors, resulting in high circulating currents and, hence, high termination losses. Methods to mitigate this effect at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter's switching frequency are discussed. Improvements of the proposed terminations are demonstrated by modeling and measuring the transformer's ac resistance. Furthermore, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters' efficiency improvements are also showcased with the improved terminations.

Optimal transformer design of DAB converters in solid‐state transformers for maximum power efficiency

AbstractSolid‐state transformers (SST) are a viable solution to replace the conventional low‐frequency transformer in railway vehicles. In the SST, high frequency transformers in dual‐active‐bridge (DAB) converters are essentially used for electrical insulation. Thus, the high‐frequency transformer design becomes so important to increase the high efficiency operation with electrical insulation. Here, an optimal transformer design methodology, which provides a maximum power efficiency operation of the transformer for DAB converters, is proposed. Considering the core loss and copper loss of the transformer, the optimal number of turns for the transformer in a DAB converter N1,op and N2,op can be determined so that the maximum power efficiency for the transformer is achieved at a normal operating point of the DAB converter. To derive the major loss parameters, a finite‐element‐method based simulation was performed for resistive and magnetic loss analysis, which eventually provided the optimal number of turns under the given physical size of ferrite core. The 20 W prototype for a DAB converter with EER2828 and EER3019 of ferrite core shapes were fabricated and verified by simulations and experiments. The results showed that the optimum number of turns N1,op were selected as 12 and 8 turns for two ferrite core models, respectively, which are most highest efficiencies with regard to the different winding turns. To apply the proposed methodology to the SST power level in railway vehicles, 125 kW transformers with inductor set for the SST applications has been fabricated and experimentally verified. As a result, 99.6% of highest efficiency with thermal stable operation was obtained by the proposed transformer design methodology.

Optimal Design of High Frequency Transformer for High Power Density Flyback Converter

This brief presents an optimal design of high power frequency transformer for flyback converter based on E-mode GaN device, which could be used in personal portable chargers. The new generation of wide band gap semiconductor GaN switch is used to improve the switching frequency of the circuit. The high-frequency magnetic core and the winding method of magnetic components are optimized. The leakage inductance of the transformer of magnetic components is greatly reduced. Consequently, the overall power density of the circuit is improved. The feasibility of the design scheme is verified by hardware implementation and experimental results. The test results show that compared with the traditional flyback magnetic element design, the volume of magnetic element is reduced by 30%. Meanwhile, the loss is reduced by 30%, and the peak efficiency of the converter can reach 94.2%. The ratio of leakage inductance of magnetic transformer to excitation inductance decreased from 2.2% to 1%. In addition, power density of the converter reached 20.26W/in3, which is much higher than the existing commercial ones.

"Power Transformer Design Optimization and Productivity Evaluation Using Artificial Intelligence Techniques"

Transformers need to be designed in a way that satisfies not only all international requirements and customer expectations but also that they are effective, economically practical, and satisfy all international criteria. The design of a transformer should ultimately achieve this goal. It is anticipated that the costs of active components, development, and ownership will decrease as the application of AI approaches becomes more widespread. This is expected to occur while maintaining compliance with international standards and constraints. Using the AI technologies that are currently being utilized in Indian manufacturing will not be sufficient to solve TDO issues. The current research is focusing on developing artificial intelligence-based solutions that have the potential to be used to improve the design of distribution transformers. By utilizing this design for the transformer, both the total ownership costs and the expenses associated with its manufacture would be cut in half (TOC). It was demonstrated that when attempting to solve TDO problems using techniques such as GA, PSO, and TLBO, PSO and GA found higher objective feature values than GA. When it comes to percentages, TLBO performs significantly better than both PSO and GA. As a result of the implementation of NSGA II, the TOPSIS technology made it possible for DM to select any solution from among the non-dominated solutions

High-frequency planar transformer optimal design and analysis

High-frequency planar transformer optimal design and analysis

Optimal Design and Performance Analysis of Three-phase Distribution Transformer with Variable Loading

Electrical power passes through several transformers after generation through consumption. The final stage of any power system consists of many small-rating distribution transformers. Since the loads connected to these transformers vary with time, their effective design and operation with variable loading conditions are crucial for the system to operate efficiently and reliably. In most previous works, loads connected to these transformers are treated as constant power and stray losses of the transformers are neglected in the calculations. Neglecting the load variation and stray losses reduces the transformer life span noticeably and impairs grid quality and reliability. In this work, a small-rating distribution transformer is designed and analyzed analytically and numerically. Detailed procedures on the conventional design are presented with the general design issues. The effect of variable loading on the transformer’s power losses, efficiency, temperature rise, voltage regulation, and output voltage variation is analytically and numerically investigated. Results show that the rating and power factor of the load significantly influence the performance characteristics of the transformer.

Assessment of Thermophysical Performance of Ester-Based Nanofluids for Enhanced Insulation Cooling in Transformers

Nanotechnology provides an effective way to upgrade the thermophysical characteristics of dielectric oils and creates optimal transformer design. The properties of insulation materials have a significant effect on the optimal transformer design. Ester-based nanofluids (NF) are introduced as an energy-efficient alternative to conventional mineral oils, prepared by dispersing nanoparticles in the base oil. This study presents the effect of nanoparticles on the thermophysical properties of pure natural ester (NE) and synthetic ester (SE) oils with temperature varied from ambient temperature up to 80 °C. A range of concentrations of graphene oxide (GO) and TiO2 nanoparticles were used in the study to upgrade the thermophysical properties of ester-based oils. The experiments for thermal conductivity and viscosity were performed using a TC-4 apparatus that follows Debby’s concept and a redwood viscometer apparatus that follows the ASTM-D445 experimental standard, respectively. The experimental results show that nanoparticles have a positive effect on the thermal conductivity and viscosity of oils which reduces with an increase in temperature.

OPTIMIZATION OF TRANSFORMERS FOR SOLAR OR BATTERY STORAGE INSTALLATIONS BASED ON A CYCLIC LOADING PATTERN

The popularity of distributed generation forces suppliers to offer more price competitive equipment. This study is aimed at optimization of photovoltaic inverter connected step-up transformers. It also applies to other associated installations, e.g. battery storage. The daily loading patterns in both cases are known. Hence, the effect of this loading would be predicted. The study is for developing a peak load transformer based on the real data collected in a solar farm. The first task is to find out a suitable transformer rating that is equal to average “dissipated” power. The peak generation and the peak loading only occur for a short time during each day. Hence, the equipment does not have to be designed to this maximum capability of the solar panels and the inverter. The transformer rating could be reduced, to reduce the cost of the equipment while keeping the performance and reliability at the highest level. The second aim is to find optimal transformer design, including the most suitable insulation system for handling the expected cyclic loading. The analysed insulation systems included Kraft papers, thermally upgraded papers and the thermally upgraded cellulose paper enhanced with aramid. That last solution appears to be the best option for transformers experiencing repetitive loading cycles.

Optimal Design of a Multiwinding High-Frequency Transformer Using Reluctance Network Modeling and Particle Swarm Optimization Techniques for the Application of PV-Linked Grid-Connected Modular Multilevel Inverters

This article presents an optimal design procedure and development of a multiwinding high-frequency transformer for application in the cascaded modules of a grid-connected modular multilevel inverter. The transformer should be designed for a certain value of inductances and high efficiency because of its effect on the performance of the entire modular structure. To realize such an accurate design procedure with minimum computation effort and design complexity, a three-stage method including initial design using lumped-parameter modeling, optimal design using particle swarm optimization with reluctance network modeling and finite element method is proposed. An amorphous-based toroidal core transformer is designed, developed, and tested under different load conditions and frequency range to validate the design procedure.

Optimal design of minimal footprint high frequency transformer

Transformer design procedure may vary essentially in respect of the transformer type and its operating frequency (ranging between 50/60 Hz and a few megahertz). This paper presents a simple and straightforward method based on the optimal choice of core geometry of a high frequency transformer (HFT) used in Solid State Transformer (SST) applications. The core of SST is the HFT which largely influences its size and overall performance. The proposed design procedure for HFT focuses on optimizing the core geometry coefficient (in cm5) with a constraint inflicted on loss density. The core geometry coefficient has direct impact on the regulation and copper loss and the procedure results in a robust overall design with minimal footprint. Also, the procedure intends to bring all the operating parameters like regulation, losses and temperature rise within permissible limits while retaining desired efficiency. Thus an energy-efficient design is achieved with minimal footprint. The optimization procedure is implemented using recently developed Moth-flame Optimization (MFO) algorithm. The results of the MFO algorithm are compared with the wellestablished PSO technique. An experimental prototype is built to validate the findings.

Design Optimization of Power Electronic Transformers in Traction Applications

Design Optimization of Power Electronic Transformers in Traction Applications

Multiphysics and Multiobjective Design Optimization of High-Frequency Transformers for Solid-State Transformer Applications

This article proposes a multiphysics-based and multiobjective design optimization of high-frequency transformers (HFT) for solid-state transformer (SST) applications. Achieving an efficient SST, regardless of its topology, highly depends on the design optimization of its HFT design parameters. Also, a high-power-density. The proposed algorithm (based on time-harmonic electromagnetic, thermal, and fluid physics model coupling) minimizes the volume of the HFT, total cost as well maximizes its efficiency. A case study of $20 \text{ kW}$ , $10 \text{ kHz}$ is investigated and its Pareto optimal solutions (POS) presented. The simulation results show the various dependencies of the design variables on the proposed objective functions which verifies effectiveness of the proposed algorithm. The Pareto optimal solutions (POSs) show that efficiencies above $99\%$ can be achieved with appropriate selection of the design variables. From the POS, two case studies of the HFTs (referred to as $HFT_1$ and $HFT_2$ using $AMCC-100$ and $AMCC-250$ amorphous cores, respectively) are further investigated based on multiphysics numerical models. An experimental implementation of the optimized HFTs ( $HFT_1$ and $HFT_2$ ) is integrated with a self-tuned dual active bridge converter to validate their performance. The experimental measurements from the HFTs are in very good agreement with the optimization results.

Numerical Study of Electromagnetic Loss and Heat Transfer in an Oil-Immersed Transformer

Transformer is one of the most important pieces of equipment in power system. The insulation aging and lifespan of transformer are significantly affected by hot spot distributions of internal components inside. In the present paper, the electromagnetic losses of different components and heat transfer process in a three-phase forced oil circulation transformer (400 kVA-15 kV/400 V) are numerically studied with finite element method. The leakage magnetic flux and eddy current loss density for metal components and oil tank are carefully analyzed, and the effect of metal components’ electromagnetic loss on hot spot temperature of different components and oil flow in transformer is also studied. It is found that the surface current of metal components is generated by leakage magnetic flux, and surface current density is large when leakage magnetic flux concentrates. The effect caused by relative magnetic permeability of metal components is remarkable on electromagnetic loss of metal components and oil tank, while the effect caused by relative magnetic permeability of transformer tank is relatively small. Due to the mixing of metal components on oil flow, the heat transfer of core is enhanced, its hot spot temperature is lowered, and the hot spot locations of coil and core also change. These results are meaningful for further understanding of heat transfer process in transformer and important for the optimal design of transformer.

A generalized inverse Preisach dynamic hysteresis model of Fe-based amorphous magnetic materials

Fe-based amorphous magnetic materials are attracting more and more attentions in the application of low and medium frequency transformers due to their favorable properties of low core loss and high saturation magnetic flux density. Accurate modelling of their static and dynamic characteristics is required for analysis and design optimization of low and medium frequency transformers. In particular, for numerical analysis using the vectorial magnetic potential, an inverse magnetic hysteresis model is needed to predict the magnetic field strength from the magnetic flux density. When the excitation varies with time, the magnetic hysteresis model must be able to predict the dynamic hysteresis characteristics. This paper presents a generalized inverse Preisach dynamic hysteresis model for dynamic characterization of Fe-based magnetic materials. This model incorporates the reversible magnetization and magnetization dependent hysteresis, as well as all core loss components, including the hysteresis, eddy current, and excess losses. The proposed model can predict accurately the magnetic field strength from the magnetic flux density and hence accurate core losses. The predicted results are verified by experimental measurements.

Optimal Design of High-Power Medium-Frequency Transformer Using Hollow Conductors with Consideration of Multi-Objective Parameters

A power electronic transformer (PET) is applied to the high-speed train for lightweight demand. A 300 kW/5 kHz high-power medium-frequency transformer (HPMFT) using hollow conductors in a power unit of the PET is optimally designed in this paper. The target of the design is to balance the loss, leakage inductance, and weight of the HPMFT. For this purpose, the design parameters of the HPMFT are firstly confirmed according to the system structure and parameters of the PET. Secondly, the design process of HPMFT is developed. Finally, the results of 48 design schemes of core-type and shell-type structures are compared by the comprehensive evaluation standard, which equilibrates the three above objective parameters of the HPMFT. According to the optimal scheme, a prototype is manufactured, whose test results verify the correctness of the optimal design method.