Isolation transformer

About: Isolation transformer is a research topic. Over the lifetime, 8145 publications have been published within this topic receiving 72396 citations.

10kV SiC-based isolated DC-DC converter for medium voltage-connected Solid-State Transformers

Abstract: Silicon-carbide semiconductor technology offers the possibility to synthesize power devices with unprecedented blocking voltage capabilities while achieving outstanding switching and conduction performances. Accordingly, this new semiconductor technology is especially interesting for Solid-State Transformer concepts and is utilized in this paper for designing a 25 kW/50 kHz prototype based on 10 kV SiC devices, featuring a 400V DC output. The focus is on the DC-DC converter stage while special attention is placed on the large step-down medium frequency transformer, whereby the impact of the rather high operating frequency and high number of turns with respect to the transformer's resonance frequency is analyzed This leads to useful scaling laws for the resonance frequency of transformers in dependence of the operating frequency and construction parameters. Finally, a transformer prototype and efficiency and power density values for the DC-DC stage are presented.

A New Resonant Modular Multilevel Step-Down DC-DC Converter with Inherent-Balancing

Abstract: Modular multilevel converters (MMCs) have become increasingly interesting in dc-dc applications, as there is a growing demand for dc-dc converters in high-voltage applications. Power electronics transformers can be used for high step-down ratio dc-dc power conversion, with high power rating and efficiency achieved. However, this arrangement requires a large number of high isolation voltage transformers and a complicated balancing control scheme. To provide a simple solution with inherent voltage balancing, this paper presents a new resonant MMC topology for dc-dc conversion. The proposed converter achieves high-voltage step-down ratio depending on the number of submodules. The converter also exhibits simplicity and scalability with no necessary requirement of high-voltage isolation transformers. By using phase-shift control, a much higher converter operating frequency is achieved compared to the switching frequency. Resonant conversion is achieved between the series inductor and submodule capacitors. The operation principle and theoretical analysis are presented in this paper, which have been verified by experimental results based on a bench-scale prototype.

A Three-Phase Step-Up DC–DC Converter With a Three-Phase High-Frequency Transformer for DC Renewable Power Source Applications

Abstract: This paper presents a new three-phase step-up dc-dc converter with a three-phase high-frequency (HF) isolation transformer in an average current-mode controlled closed loop. This converter was developed for industrial applications where the dc input voltage is lower than the output voltage, for instance, in installations fed by battery units, photovoltaic arrays, or fuel cell systems. The converter's main characteristics are reduced input ripple current, step-up voltage, HF transformer, reduced output-voltage ripple due to three-pulse output current, and the presence of only three active switches connected to the same reference, this being a main advantage of this converter. By means of a specific switch modulation, the converter allows two operational regions, each one depending upon the number of switches in overlapping conditions-if there are two switches, it is called R2 region, and if there are three switches, it is called R3 region. An average current-mode control strategy is applied to input-current and output-voltage regulation. Theoretical expressions and experimental results are presented for a 6.8-kW prototype, operating in the R2 region, and for a 3.4-kW prototype, operating in the R3 region, both in continuous conduction mode.

Hybrid Transformer Model for Transient Simulation: Part I - Development and Parameters

Abstract: Summary form only given. A new topologically-correct hybrid transformer model is developed for low- and mid-frequency transient simulations. Power transformers have a conceptually simple design, but behaviors can be very complex. Selection of the most suitable representation for a given behavior depends on the type of transformer to be simulated, the frequency range, and other factors such as the internal design of the transformer and available parameters or design data. Here, a modular model suitable for frequencies up to 3-5 kHz is developed, utilizing a duality-based lumped-parameter saturable core, matrix descriptions of leakage and capacitive effects, and frequency-dependent coil resistance. Implementation and testing of this model was done for 15-kVA 208D-120Y 3-legged and 150 kVA 12, 470Y-208Y 5-legged transformers. The basis and development of the model is presented, along with a discussion of necessary parameters and the approaches for obtaining them.

Electrostatics in Power Transformers

Abstract: In this paper, the streaming electrification in core type forced oil cooled power transformers is investigated, using a full-scale model transformer and various experimental models. It has been clarified that streaming electrification in transformers is influenced mainly by flow rate, oil temperature, surface conditions of insulating materials and characteristics of insulating oil. Electrostatic discharge occurs eventually when the amount of local charge exceeds a certain limit.