Showing papers on "Isolation transformer published in 2023"

Compact MV-Insulated MHz Transformer-Coupled Gate Driver With Staged Turn-Off Scheme for Series-Connected Power Devices in DC Circuit Breaker Applications

Abstract: The short-circuit protection equipment of dc circuit breaker (DCCB) is important for the dc grid. Also, the series-connected power devices are usually employed in the solid-state circuit breaker (SSCB) or hybrid circuit breaker (HCB) to meet the clamping voltage requirement. A simple passive gate driver and power supply solution is a critical component to drive the circuit breakers more cost-effective and reliable. This article proposed a novel compact MV-insulated transformer-coupled gate driver method, which combines the auxiliary power and gate signal together. The proposed high-frequency-modulated multilevel transformer voltage enables both the simultaneous and the staged turn-off schemes. Besides, the cascade high- and low-voltage transformer structures simplify the insulation design and demonstrate better scalability. The common-mode current could be suppressed as well using this structure. The design example of a compact 2-MHz high-voltage planar transformer with >13-kV partial-discharge-free insulation capability is illustrated. Finally, the simulation and experimental results are also given to demonstrate the feasibility of the proposed gate driver method.

A Scalable Electronic-Embedded Transformer (EET), a New Concept toward Ultra-high-frequency High-power Transformer in DC-DC Converters

Abstract: The demand for high-power and high-density isolated dc-dc converter is driven by the rapid development of energy storage system, data center power supplies and transportation electrification. However, designing a high-power and high-frequency transformer presents significant challenges due to the trade-off between thermal management, leakage inductance minimization, and insulation requirements. In order to overcome this trade-off between power rating and operation frequency, a scalable electronic-embedded transformer (EET) is proposed with a low voltage bridge integrated into the transformer windings. The EET addresses the challenge through its simple open-loop control and natural current sharing, enabling easy parallel connection and scaling to different power ratings. Based on this concept, a bi-directional EET-based dc transformer (EET-DCX) is proposed to solve the transformer-level paralleling and resonant point shift issues in traditional LLC-DCX designs. By employing the embedded full bridge, the EET-DCX effectively cancels out the impedance of the leakage inductance, ensuring optimal operation at any frequency. Additionally, the EET-DCX retains the inherent advantages of the LLC-DCX, such as load-independent voltage gain, simple open-loop control, full load range zero voltage switching (ZVS), and low circulating current. Leveraging these advantages, the proposed EET-DCX solution has the potential to push the boundaries of transformer performance to the MHz operation frequency range with hundreds of kilowatts power capability. To validate these merits, a 12 kW 500 kHz EET-DCX with four planar EET units was built. This article is accompanied by two videos demonstrating the dynamic load changing and frequency changing test.

Impact of parallel high voltage transformers with and without earthing transformer

Abstract: The research focuses on the impact of parallel two power transformers with and without earthing transformer based on potential earth fault events. Paralleling two power transformers is recommended in medium voltage substation topology to adopt N-1 criteria and minimize interruption time. However, the paralleling transformers may cause other issues such as increasing the level of fault current and oblige additional protection coordination to isolate the exact transformer during the fault. This research will examine and analyze the benefit and consequence after parallel both transformers with and without earthing transformer. The study focuses on 132/22 kV transformers with star-delta vector group that connected to the diverse topology involving earthing transformer before connected to neutral earth resistor. Based on the investigation, it found that the star-delta transformer without earthing transformer at one side of transformers has a higher potential to cause poor isolation during any event of an earth fault due to insulation design. Moreover, the transformer that connected to earthing transformer has a higher possibility to experience higher fault current which indirectly reduces the life span of that earthing transformer as well as power transformer due to unavailability of the earthing transformer at the other transformer.

Leakage Current Reduction in Four-leg Inverter Utilizing Three-Dimensional Virtual Voltage Vector-based Predictive Control

Abstract: It is possible to connect PV systems to the electrical grid either with a galvanic isolation transformer (transformer) or without one (transformer-less). Galvanic isolation is provided by the low-frequency transformer; nevertheless, this results in an increase in the transformer’s size, cost, and losses. Alternatively, transformer-less PV systems increase leakage current. The leakage current is dependent on a number of characteristics, primarily the topology and switching strategy of the inverter. Since switching scheme change does not require new hardware, it is a cost-effective way to minimize leakage current. Common-mode voltage (CMV) fluctuations in transformer-less systems result in high-frequency harmonics and leakage current flow. This study offers a model predictive current control (MPCC) technique for a three-phase four-leg voltage source inverter using three-dimensional (3-D) virtual voltage vectors (VVVs) or (V ³ ) (VSI). To limit CMV amplitude, leakage current, and overall harmonic distortion of the output current load, only selected vectors are employed. This work presents fresh research into the impact of the suggested method and the use of virtual voltage vectors on leakage current and output current total harmonic distortion (THD) in a two-level, three-phase, four-leg inverter.

Detection of Load Loss of Large Capacity Transformer

Abstract: This paper mainly studies a live monitoring system and scheme for the current loss of power transformer. In the system, the inlet end of the primary side voltage transformer is partially connected with the high temperature side and low temperature side of the power transformer, and its output end is connected with the isolation transformer; The inlet end of the primary side voltage transformer is connected with the terminals of the high temperature side and low temperature side of the power transformer through the jaw, and the output end is connected with the voltage transformers of the two secondary sides; The output end of the isolation transformer is connected with the inlet end of the voltage transformer at the secondary side; The output end of the voltage transformer at the secondary side is connected with the input end of the optocoupler separation module; The output end of the optocoupler module and the output end of the secondary side voltage transformer are connected with the inlet end of the signal acquisition control system, and the output end of the signal acquisition control system is connected with the upper computer control system; The upper computer system is mainly used to extract and analyze the collected pressure and current information, and finally obtains the no-load loss and load loss of power transformer. Therefore, the control system in this paper can accurately evaluate the loss of power transformer, and has the advantages of on-site measurement and live measurement, with high measurement accuracy.

The Study of Materials for Electric Field Protection of Power Transformer Testing

Abstract: This paper proposes the analysis of the material can be protected from transformer testing and presents a mathematical model of the power transformer. In this research, transformers were study in four protective materials, wood, rubber, glass and acrylic that are used in between the electric field measurement and the transformer. By simulating the test results of a transformer with a voltage of 230 kV. Computer-based simulation utilizing the finite element method (FEM) is exploited as a tool for visualizing electric fields distribution volume a power transformer. The simulation results showed that the material with the best protection against the electric field was wood insulation and the best installation location was a distance of 5 m from the transformer.

Low EMI Planar Transformer for an Isolated, Cascaded Buck-LLC Converter

Abstract: A key consideration in spacecraft applications is the conducted and radiated electromagnetic interference (EMI) generated by electronic components. One of the biggest sources of EMI is from the power system, caused by converters rapidly switching large amounts of current and voltage that generates unwanted noise. Without significant engineering considerations of mechanical and electrical layout, EMI can have serious impacts on other spacecraft systems such as communication equipment. Isolated supplies typically use a forward or flyback converter topology with a coil wound toroidal transformer. The transformer can experience a high voltage impulse called an inductive kickback during switching due to its leakage inductance, which contributes to overall power system radiated and conducted emissions. The transformer is a major source of EMI in currently available switching forward topologies, requiring a significant amount of input filtering, snubbing, and shielding. A high efficiency, isolated, cascaded prototype utilizing resonant switching techniques was developed in the form of a Buck-LLC utilizing a traditional wire wound transformer. With the successful testing of a 200W, 1MHz, Buck-LLC converter utilizing gallium nitride (GaN) devices, a planar transformer design was desired for an improvement in overall converter efficiency and EMI performance. In this work, a new transformer winding design is presented for a planar transformer using paired Litz winding interleaving. Ansys finite element analysis (FEA) software is used to verify design parameters. The winding configuration is designed to be compatible with a standard PCB stack-up so that the transformer windings can be directly integrated into the converter PCB even further reducing leakage inductance and increasing power density.

400V-to-48V Transformer-Isolated Stacked Active Bridge Converter with Integrated Magnetics

Abstract: This paper presents a transformer-isolated high step-down dc-dc converter based on a stacked active bridge (SAB) configuration. The isolated SAB (iSAB) converter consists of series-stacked inverter modules and parallel-connected rectifier modules. To achieve galvanic isolation, transformers are inserted between the inverter and rectifier bridges. The nominal step-down conversion ratio is determined by the number of inverter modules and the turns ratio of the transformer. In order to reduce the footprint of the magnetic components, the transformers are coupled on a single core, and the series inductances are realized as controllable leakage inductances within the same magnetic structure using a novel custom core and planar winding arrangement, a solution unique to the iSAB configuration. The approach is verified by experimental results on a 400-to-48 V, 3kW, 400kHz iSAB prototype using low-voltage GaN devices and having 96.7% peak efficiency.

Development of a Turn-to-turn Fault Detection Method in the Three-phase Transformer's Winding

Abstract: Reveal the regularities of turn-to-turn faults influence on to parameters of a three-phase network transformer in the disconnected transformer mode with the supply of control voltages and currents from an external source in the transformer linear operation. To achieve the purpose, experimental studies were carried out on the power transformer (Trihal with a voltage of 20 / 0.4 kV) with an artificially created turn-to-turn fault, mathematical modeling and calculations of the three-phase transformer magnetic system parameters. The influence of the turn-to-turn fault on the magnetic system of the three-phase transformer with the application of voltages and currents of zero and direct sequences is investigated. A mathematical model of three-phase transformer magnetic system has been developed, which makes it possible to determine the change in the parameters of the transformer windings and to establish the relationship between the primary and secondary voltages and currents in conditions of the occurrence of а turn-to-turn fault. An effective method for detecting turn-to-turn faults by measurements with the supply of zero sequence currents is proposed. A simplified model of the three-phase transformer magnetic system has been developed. This model allows us to qualitatively evaluate the changes in the transformer parameters when a turn-to-turn fault occurs.

Exploiting the Depth: Design, Analysis, and Implementation of High-Power-Density High-Frequency Transformers for One Rack Unit CLLC DCX Converters

Abstract: This paper focuses on the analysis and design of different transformer (winding) implementations for bidirectional “DC transformer” (DCX) CLLC resonant DC-DC converters when subjected to a height and width constraint of 1 rack unit (1U = 44.45 mm). Therefore, the depth of the converter must be exploited to increase the converter power rating. On the basis of analytical modeling, the influence of the parasitic parameters of the high-frequency (HF) transformer the design of the DCX CLLC is analyzed. In particular, the energy required to achieve zero-voltage switching (ZVS), i.e. the magnetization energy stored in the air gap of the transformer, is related to the characteristics of the switching devices and to the winding arrangements, to give insight into how the transformer can be scaled into the depth. Moreover, the different trade-offs regarding the design of the HF transformer are discussed, with numerical examples of how the parasitic capacitance scales with different depths of the transformer and different interleaving of its winding. A configuration with proper influence on the energy required for ZVS is selected and different winding implementations have been designed and are presented, namely litz wire, so-called litz PCB, and hybrid (primary in litz wire, secondary in litz PCB). Experimental measurements are reported and the different winding designs are compared in terms of parasitics and AC resistance. In addition, power tests have been carried out in order to evaluate the thermal behavior of the proposed configurations. Ultimately, this work aims at providing insight into the design choices to be considered when trying to efficiently exploit the depth of the converter.

Circuit Configuration and Operation Principle of Electrical Insulation Circuit for AC Fed Transformer-less Electric Vehicles Using High Withstand Voltage Property of SiC Power Module

Abstract: This study aims to develop a power supply system without a traction transformer for weight reduction and downsizing. Transformer-less power supply is expected to realize step-down, rectification, isolation, and motor drive using a high voltage silicon carbide (SiC) power device. The primary challenge of this work is developing a novel circuit that isolates the motor drive circuit from the AC line without using the traction transformer. Accordingly, we devised a flying capacitor circuit to solve the existing problems and aims for capacitive isolation. Subsequently, we devise a nesting capacitor as a short-circuit prevention measure. We report the isolated circuit configuration and operating principle.