Transformer Topology Research Articles

Power quality improvement of unipolar-input-bipolar-output DC transmission system via load power balancing

In DC transmission and distribution systems, both unipolar and bipolar transmission modes exist, and DC transformers used in these systems are also available in either unipolar or bipolar configurations. In actual systems, due to requirements such as economy, land occupation, and reliability, there is a tendency to use a system with unipolar input and bipolar output. However, the bipolar loads, if unbalanced, will lead to increased equipment costs and voltage imbalance, causing power quality problems. This paper defines the Power Unbalance Factor (PUF) to describe the power quality of the studied DC transmission system and presents an improved DC transformer topology based on a power balancing system. This topology realizes bipolar voltage balance and improves the power quality of the DC transmission system when the load is unbalanced. The influence of the proposed solution on the power design of the DC system is demonstrated through theoretical analysis, and its effectiveness for improving the DC power quality is verified by both simulations in MATLAB/Simulink environment and physical experiments. When the power electronic transformer needs to be overloaded, the proposed topology can reduce the design power of the two branches by using the difference power, which is economical.

Analysis of Power Transmission Characteristics of a Novel Secondary Side LCD Series Forward Converter

A novel secondary-side LCD series forward converter is proposed, and the power transmission characteristics of the excitation inductance of the proposed converter under different modes are analyzed. By analyzing the relationship between the transmission power of forward branch and additional branch and excitation inductance, it is concluded that when the excitation inductance Lm works in CCM (continuous conduction mode), the transmission power of forward branch and additional branch has nothing to do with the value of excitation inductance. When the excitation inductance Lm works in DCM (discontinuous conduction mode), the transmission power of forward branch increases with the increase of excitation inductance, while the transmission power of additional branch decreases with the increase of excitation inductance. At the same time, the influence of power distribution on the efficiency of transformation topology is explored, and the relationship between the transmission power of the forward branch and the current stress of the switching tube was derived, and the parameter design method of magnetic element is put forward. Finally, the circuit model of the novel secondary side LCD series Forward converter is established, and the experimental results verify the correctness of the theoretical analysis and the feasibility of the parameter design method.

Comparative analysis of three‐phase dual active bridge converter with different transformer topology and modern universal control for DC microgrids

AbstractThe presented work discusses issues related to the use of modern multiphase topologies of Dual Active Bridge (DAB)‐type converters. Converters of this type are widely used in most DC microgrid applications. The introduction emphasizes a comparative analysis between single‐phase and multi‐phase DAB topologies within high‐power DC microgrids, delving into their respective advantages, drawbacks, design procedures, and considerations based on the latest knowledge. The publication explores the comparison and selection of viable topologies for deployment in high‐power and high‐efficiency DC microgrids. The unified method of controlling 1‐phase and multi‐phase DAB converters was proposed in this design, simplifying the issues of DC microgrid control. All topologies were tested on the same controller concept. The study performs laboratory investigation of DAB 1‐phase and 3‐phase: Star–Star, and Star–Delta topologies. Attention was paid to maintaining uniform operating conditions of the system, contrary to studies known from the literature, all tests were carried out on the same laboratory stand and the same magnetic components in different configurations. Analytical and laboratory analyses of the Zero Voltage Switching (ZVS) region were performed, accounting for non‐linear phenomena. Based on these findings, an assessment of the system's performance in soft switching was carried out. The presented results were implemented in a simulation model and subsequently validated through tests on a constructed laboratory setup to ensure the proper operation of the system. This work meticulously presents and discusses variations in efficiency, dynamic response, phase current harmonic distribution, phase shift distribution, ZVS switching region, and more among the examined topologies. To ensure a fair comparison, the converter configuration for both simulation and laboratory models utilized identical components across all configurations.

Multi-Mode Control of a Hybrid Transformer for the Coordinated Regulation of Voltage and Reverse Power in Active Distribution Network

The unprecedented growth of distributed renewable generation is changing the distribution network from passive to active, resulting in issues like reverse power flow, voltage violations, malfunction of protection relays, etc. To ensure the reliable and flawless operation of active distribution networks, an electrical device enabling active network management is necessary, and a hybrid distribution transformer offers a promising solution. This study introduces a novel hybrid transformer topology and multi-mode control strategy to achieve coordinated voltage and reverse power regulation in active distribution networks. The proposed hybrid transformer combines conventional transformer windings with a partially rated SiC-MOSFET-based back-to-back converter, reducing additional investment costs and enhancing system reliability. A multi-mode control strategy is proposed to facilitate the concurrent reverse power control and voltage violation mitigation of the presented hybrid transformer, allowing a smooth transition between the P–Q control mode and the V–f control mode. The control mode switching can be activated manually or autonomously in response to voltage violations or reverse power overloading. The effectiveness of the proposed hybrid transformer configuration and its control mode transition mechanism are examined through comprehensive case studies conducted in the PSCAD/EMTDC environment. The proposed HT design has been confirmed to achieve a voltage regulation range of ±20% of the nominal voltage and effectively regulate bidirectional active power flow within a range of −25% to 25% of the rated power.

Automatic Graph Topology-Aware Transformer.

Existing efforts are dedicated to designing many topologies and graph-aware strategies for the graph Transformer, which greatly improve the model's representation capabilities. However, manually determining the suitable Transformer architecture for a specific graph dataset or task requires extensive expert knowledge and laborious trials. This article proposes an evolutionary graph Transformer architecture search (EGTAS) framework to automate the construction of strong graph Transformers. We build a comprehensive graph Transformer search space with the micro-level and macro-level designs. EGTAS evolves graph Transformer topologies at the macro level and graph-aware strategies at the micro level. Furthermore, a surrogate model based on generic architectural coding is proposed to directly predict the performance of graph Transformers, substantially reducing the evaluation cost of evolutionary search. We demonstrate the efficacy of EGTAS across a range of graph-level and node-level tasks, encompassing both small-scale and large-scale graph datasets. Experimental results and ablation studies show that EGTAS can construct high-performance architectures that rival state-of-the-art manual and automated baselines.

Enhancing medical image analysis: A fusion of fully connected neural network classifier with CNN-VIT for improved retinal disease detection

Diseases of the retina continue to be a leading cause of blindness and visual impairment around the world. In the field of medical image analysis, specifically retinal disease identification, deep learning techniques, such as Convolutional Neural Networks (CNNs) and Vision Transformers (ViTs), have showed remarkable potential. In this paper, we present a unique method for detecting retinal diseases by combining the advantages of the Inception-V3, ResNet-50, and Vision Transformer architectures into a single model called a Cascade CNN-ViT. The suggested Cascade CNN-ViT model extracts local features from retinal pictures by leveraging the spatial hierarchy learning capabilities of Inception-V3 and ResNet-50. The Vision Transformer takes these regional characteristics and uses self-attention mechanisms to pick up global context information and long-range interdependence. The model successfully combines fine-grained local information with semantically significant global contextual cues by merging the output representations from the CNNs and Vision Transformer. undertaking comprehensive experiments on a large and varied dataset of multimodal retinal pictures to evaluate the performance of the proposed technique. Cascade CNN-ViT model outperforms standalone CNNs and Vision Transformers, as shown by the experimental findings. The model is also resilient across all classes of retinal diseases and is able to successfully deal with the complications introduced by using multiple picture types. Overall, the power of cascading Inception-V3, ResNet-50, and Vision Transformer topologies for improved retinal illness diagnosis has been demonstrated. Potentially improving the management of retinal illnesses and preserving visual health, the proposed approach could have important consequences for early detection and timely intervention.

Hybrid Isolated Modular Multilevel Converter Based Solid-State Transformer Topology With Simplified Power Conversion Process and Uneven Voltage Ratio

Hybrid Isolated Modular Multilevel Converter Based Solid-State Transformer Topology With Simplified Power Conversion Process and Uneven Voltage Ratio

Comparative Study of Different Topologies of Monolithic On-Chip Planar Transformer for Optical VCSEL Driver

This article presents a comparative study of different topologies of monolithic on-chip planar transformer, operating at high frequencies and suitable for optical VCSEL driver. The vertical cavity surface emitting laser (VCSEL) driver is presented for optical transceiver systems. At the VCSEL driver output stage, the on-chip transformer is used to compensate for large bandwidth and deliver adequate gain. On-chip transformer equivalent circuit model has been proposed and used for simulation and measurement. The eye pattern results show that the VCSEL driver with an on-chip transformer presents good performance. Different topologies of the on-chip transformer are compared and 0,5 µm CMOS technology measurements are considered in the frequency range from 1 GHz to 10 GHz. Square, hexagonal, octagonal, and circular topologies of on-chip transformer have been compared. The circular topology presents a good performance and high-quality factor. The square shape provides a high inductance value and low quality compared to the other topologies.

Magnetic state balance technology of transformer based on magnetic field modulation strategy

The transformer core is easy to saturate in the half cycle under the influence of the remanent magnetism (RM) and the bias magnetism (BM), then the excitation surge current (ESC) and the DC bias will be generated, causing the transformer excitation current (TEC) distort, leading the winding temperature rise and decreasing the transformer insulation. In this paper, one kind of magnetic balance modulation method for the transformer core is proposed. TEC distortion could be improved by adjusting the transformer magnetic field distribution. Firstly, the AC/DC/DC converter was designed and connected to the auxiliary winding according to the hybrid transformer topology. Second, the specific modulated signal for the magnetic field modulation (MFM) was generated and output through the AC/DC/DC. The modulated forward and reverse DC current or the stepped AC current would be injected into the transformer winding to achieve the balance of the transformer magnetic state. Finally, in order to verify the correctness of the design scheme, a 1 kVA/380 V/220 V/38 V transformer experiment platform was built. The results showed that this proposed MFM strategy could effectively solve the impact of the transformer ESC, DC bias and prolong the transformer service life, which provides a novel idea to solve the transformer fault.

A Medium Voltage Input Multiport Isolated Output DC Transformer With Power Self-Balancing and Output Fault Isolation

Medium voltage dc (MVDC) converters with multiple output ports have the challenges of series input module power balancing control and fault isolation between output ports. This paper proposes a new medium voltage input multiport isolated output dc transformer topology. The proposed topology can be extended to up to 2k-1 output ports of different voltages with k modules input connected in series. Moreover, the proposed topology has the voltage self-balancing feature of input modules since they are coupled via the balancing capacitors. Current self-balancing of all MOSFETs is also achieved, as the equivalent impedance of multiple voltage sources discharging to multiple loads is the same under the influence of the split resonant inductor. Besides, the proposed topology can limit the shorted current in the output port automatically without affecting other ports, due to the impedance of the resonant tank of the faulty port being clamped. A 2kV dc input with three output ports of 410V, 380V and 40V prototype is built to verify the feasibility of the proposed topology. The results show that the proposed topology has multiple module power self-balancing feature, and can improve the reliability of the multiport power supply systems. Therefore, it has good prospects for subsea dc power distribution systems and ship electric power distribution systems.

A Novel Solid-State Transformer with Improved Flyback Converter Equipped with Quasi Z-Source Converter for Medium-Voltage Utility Grid

This paper introduces an enhanced solid-state transformer topology for a medium-voltage (MV) utility grid. The main objective of the current study is to develop an improved flyback converter equipped with a quasi z-source converter (qZ_iFC) having a high-voltage conversion capability for the integration of low-input voltage to the DC link of an MV modular multilevel converter (MMC). The system integrates the quasi z-source and flyback converters by operating their existing switches complementary. Furthermore, the high-gain qZ_iFC allows for a reduction in the rated voltage of the input, as well as the use of a high-frequency transformer (HFT) with a unity turns ratio that provides galvanic isolation between the input and the output ports. Thus, using an HFT just for isolation purposes without voltage gain improves the system efficiency. In addition, a controller for (i) qZ_iFC which is regulating complementary switches to prevent the shoot-through current from reaching the HFT resulting in saturation; and (ii) a controller for MMC to produce MV-level AC voltage for loads are suggested. The performance of the proposed system was evaluated for several operating conditions. Results show that the proposed SST smoothly performs the power flow between the ports during steady-state and transient conditions. The power flow capabilities and efficiency values validate the viability and effectiveness of the proposed system.

Inserted-Shunt Integrated Planar Transformer With Low Secondary Leakage Inductance for LLC Resonant Converters

The leakage inductance of an integrated transformer is usually utilized as the series inductor of an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> topology. However, leakage inductance exists on both primary and secondary sides of an integrated transformer and secondary leakage inductance leads the control and design of the converter to difficulty. In this article, a novel topology forinserted-shunt integrated transformers is proposed that has low secondary leakage inductance. The inserted shunt of the proposed topology is not segmental and can be located conveniently within the transformer. In addition, the inserted shunt does not require low permeability core material, simplifying its manufacture. The design and modeling of the proposed transformer topology are presented and verified by finite-element analysis and experimental implementation. The proposed topology is also compared with a recently published inserted-segmental-shunt integrated transformer. It is shown that the proposed transformer provides higher efficiency and lower ac resistance. Finally, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is implemented to examine the performance of the proposed integrated transformer in practice.

Comparing two topology transformer hysteresis models derived from DC hysteresis measurements

PurposeThe purpose of this paper is to investigate the applicability of a direct current (DC) hysteresis measurement on power transformer terminals for the subsequent hysteresis model parametrization in transformer grey box topology models.Design/methodology/approachTwo transformer topology models with two different hysteresis models are used together with a DC hysteresis measurement via the power transformer terminals to parameterize the hysteresis models by means of an optimization. The calculated current waveform with the derived model in the transformer no-load condition is compared to the measured no-load current waveforms to validate the model.FindingsThe proposed DC hysteresis measurement via the power transformer terminals is suitable to parametrize two hysteresis models implemented in transformer topology models to calculate the no-load current waveforms.Originality/valueDifferent approaches for the measurement and utilization of transformer terminal measurements for the hysteresis model parametrization are discussed in literature. The transformer topology models, derived with the presented approach, are able to reproduce the transformer no-load current waveform with acceptable accuracy.

Hybrid Learning of Time-Series Inverse Dynamics Models for Locally Isotropic Robot Motion

Applications of force control and motion planning often rely on an inverse dynamics model to represent the high-dimensional dynamic behavior of robots during motion. The widespread occurrence of low-velocity, small-scale, locally isotropic motion (LIMO) typically complicates the identification of appropriate models due to the exaggeration of dynamic effects and sensory perturbation caused by complex friction and phenomena of hysteresis, e.g., pertaining to joint elasticity. We propose a hybrid model learning base architecture combining a rigid body dynamics model identified by parametric regression and time-series neural network architectures based on multilayer-perceptron, LSTM, and Transformer topologies. Further, we introduce novel joint-wise rotational history encoding, reinforcing temporal information to effectively model dynamic hysteresis. The models are evaluated on a KUKA iiwa 14 during algorithmically generated locally isotropic movements. Together with the rotational encoding, the proposed architectures outperform state-of-the-art baselines by a magnitude of 10$^3$ yielding an RMSE of 0.14 Nm. Leveraging the hybrid structure and time-series encoding capabilities, our approach allows for accurate torque estimation, indicating its applicability in critically force-sensitive applications during motion sequences exceeding the capacity of conventional inverse dynamics models while retaining trainability in face of scarce data and explainability due to the employed physics model prior.

Fully-Integrated Planar Transformer With a Segmental Shunt for LLC Resonant Converters

This article presents two topologies, which provide high leakage inductance in shunt-inserted integrated magnetic transformers. These differ from conventional designs by replacing the low-permeability magnetic shunt of a planar transformer with high-permeability magnetic shunt segments, separated by many small air gaps. This approach results in a shunt with the same bulk permeability as the conventional design, while using lower cost and readily available magnetic materials such as ferrite. A modeling and design approach, which can estimate the leakage and magnetizing inductances precisely is provided for each topology. Theoretical analysis is presented and verified using finite-element analysis and experimental implementation. Ac resistance analysis for both transformer topologies is also presented. In addition, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is built to verify the performance of the proposed fully-integrated magnetic transformers in practice. It is shown that the proposed topologies can integrate all three magnetic components of an isolated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter in a single planar transformer, which reduces the converter's volume and cost.

A Compact, Ultra-Wideband, Transformer-Based Quadrature Signal Generation Network in 45 nm CMOS SOI for 5G Applications

In this article, we present an ultra-wideband, fully-differential quadrature signal generation network for 5G applications. The ultra-wideband network is composed of a passive balun and cascaded transformer-based quadrature hybrid. Passive balun converts a single-ended signal to differential with minimum insertion loss, and transformer-based quadrature hybrids are cascaded to suppress I/Q imbalance over an ultra-wide bandwidth. The coupling coefficient of the transformer-based quadrature hybrid is enhanced by adopting vertically stacked multiturn transformer topology to extend operation bandwidth and reduce passive loss and chip area. A novel layout and signal routings are proposed to reduce passive loss, undesired magnetic coupling and I/Q imbalance, making meander lines for phase matching unnecessary. The proposed ultra-wideband quadrature signal generation network is designed in GlobalFoundries 45 nm CMOS SOI process with a core area of 845 μm × 495 μm. The output I/Q magnitude mismatch is less than 0.5 dB from 16 to 60 GHz, and phase mismatch is less than 2° from 16.5 to 54.7 GHz. The input return loss is lower than −10 dB from 22 to 45 GHz, and signal loss varies from 5.74 to 7.4 dB (including 1:2 power splitting and loss from passive balun). The effective image rejection ratio (IRR) is calculated based on I/Q mismatch and is higher than 40 dB from 21.5 to 53.5 GHz.

Impact of Transformer Topology on Short-Circuit Analysis in Distribution Systems with Inverter-Based Distributed Generations

Distributed energy resources (DERs), recently introduced into distribution systems, are mainly inverter-based distributed generations (IBDGs), which have different short-circuit behaviors from conventional synchronous-based distributed generations (SBDGs). Hence, this study presents a comprehensive analysis of the short-circuit behaviors of distribution systems with IBDGs, based on sequence networks and superposition, from the perspectives of interconnected transformers, and observes the flow of zero-sequence fault currents with different transformer topologies. Moreover, two- and three-winding transformers with various bank connection types and groundings are investigated. It was concluded that the transformer topology and its grounding influence the fault current contribution in zero-sequence networks, and the high penetration of IBDGs alters the fault current magnitude and phase angles.

Research on Triple-Port SST Scheme Based on the Natural Elimination of MMC Submodule Voltage Fluctuation and Imbalance

A triple-port solid-state transformer (TP-SST) topology based on the combination of modular multilevel converter (MMC) and resonant push–pull converter (RP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C) is proposed in this article. For an MMC-based SST, large size capacitor caused by fluctuating power and voltage imbalance of MMC submodules (SMs) are two important problems. Based on a simple open-loop control scheme, the RP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C-based high-frequency links (HFL) are characterized by a voltage source with fixed conversion ratio and low impedance, and then can form a power free-coupling channel between SMs and realize the automatic balance of capacitors voltage. Moreover, the fluctuating power can cancel each other based on their three-phase symmetry, which obviously reduces the capacitance size, and the second-order harmonic circulating current of the arms could be eliminated at the same time, greatly simplifying the control of system. In this article, the working principle of TP-SST is described, and the methods of HFL realizing SM voltage ripple elimination and self-balancing are analyzed in detail. In addition, a comparison with traditional SST in efficiency and cost is presented. Finally, simulation and experimental results verify the correctness and effectiveness of the proposed topology scheme.

AUV Formation Coordination Control Based on Transformed Topology under Time-Varying Delay and Communication Interruption

Aiming at the control problem of autonomous underwater vehicle (AUV) pilot-following formation with communication delay and communication interruption, a controller based on feedback linearization and the PD control method is designed in this paper. Firstly, the nonlinear, strongly coupled vehicle model is transformed into a second-order model via the feedback linearization method, and then the formation coordination controller is designed based on consistency theory and the PD control method. The Markov random jump process is used to simulate the formation topology in the event of communication interruption. The condition of stable convergence of the AUV pilot-following formation is analyzed in the presence of time-varying delay and Markov transformation topology. A Lyapunov–Krasovskii equation is established, and linear matrix inequality (LMI) is used to solve the problem of communication interruption and communication delay. The boundary conditions of error convergence of the control system are obtained. Finally, the effectiveness of the formation coordination controller based on the second-order integral model under the unstable conditions of underwater acoustic communication is verified by simulation.

Design of an ultra-wideband LNA using transformer matching method

A new transformer matching method for ultra-wideband (UWB) low noise amplifier is presented, which effectively extends the bandwidth and has little effect on the circuit noise. Low-frequency gain compression are realized by combining Frlan-style transformer and RC feedback loop topology in the interstage. The output matching network is composed of the Rabjohn-style transformer and LC network after Norton transformation. The power gain is enhanced by using two-stage cascode topology. The proposed UWB LNA is based on a 0.25um GaAs PHEMT process, and the post-layout simulation results show the maximum power gain of 21 dB, minimum NF of 1.6 dB in the frequency range of 4–15 GHz. The input reflection coefficient is less than -7dB. The output reflection coefficient is less than −10dB. The average output 1-dB compression point is 14dBm. The chip size is 0.82 mm2.