D.M. Divan

Bio: D.M. Divan is an academic researcher from General Electric. The author has contributed to research in topics: Eddy current & Magnetic flux leakage. The author has an hindex of 1, co-authored 1 publications receiving 75 citations.

Coaxially wound transformers for high-power high-frequency applications

Abstract: Design considerations for transformers utilized in high-power high-frequency DC/DC converters are addressed. Major areas of concern are core-material selection, minimization of copper losses due to skin and proximity effects, and the realization of controlled leakage inductances. Coreless characteristics for various high-frequency materials are presented, and the influence of various conventional winding arrangements on the copper losses and leakage field is also demonstrated. Coaxial winding techniques (used commonly in high-frequency transformers) are investigated next as a feasible solution for containing the leakage flux within the interwinding space, thus preventing it from permeating the core and resulting in lower core losses and the avoidance of localized heating. Added benefits of this technique are reduced forces within the transformer, lower copper losses, and robust construction. The performances of two experimental single-phase 50 kW, 50 kHz units are reported. A three-phase version of coaxially wound transformers is also presented. >

Performance characterization of a high-power dual active bridge DC-to-DC converter

Abstract: The performance of a high-power, high-power-density DC-to-DC converter based on the single-phase dual active bridge (DAB) topology is described. The dual active bridge converter has been shown to have very attractive features in terms of low device and component stresses, small filter components, low switching losses, high power density and high efficiency, bidirectional power flow, buck-boost operation, and low sensitivity to system parasitics. For high output voltages, on the order of kilovolts, a cascaded output structure is considered. The effects of snubber capacitance and magnetizing inductance on the soft switching region of control are discussed. Various control schemes are outlined. Coaxial transformer design techniques have been utilized to carefully control leakage inductance. The layout and experimental performance of a prototype 50 kW 50 kHz unit operating with an input voltage of 200 V DC and an output voltage of 1600 V DC are presented. >

High-Power Bidirectional DC–DC Converter for Aerospace Applications

Abstract: This paper contributes to the steady-state analysis of the bidirectional dual active bridge (DAB) dc-dc converter by proposing a new model that produces equations for rms and average device currents, and rms and peak inductor/transformer currents. These equations are useful in predicting losses that occur in the devices and passive components and aid in the converter design. An analysis of zero-voltage switching (ZVS) boundaries for buck and boost modes while considering the effect of snubber capacitors on the DAB converter is also presented. The proposed model can be used to predict the converter efficiency at any desired operating point. The new model can serve as an important teaching-cum-research tool for DAB hardware design (devices and passive components selection), soft-switching-operating range estimation, and performance prediction at the design stage. The operation of the DAB dc-dc converter has been verified through extensive simulations. A DAB converter prototype was designed on the basis of the proposed model and was built for an aerospace energy storage application. Experimental results are presented to validate the new model for a 7 kW, 390/180 V, 20 kHz converter operation and the ZVS boundary operation.

Modeling and optimization of bidirectional dual active bridge DC-DC converter topologies

Abstract: This thesis investigates different bidirectional and isolated DC–DC converters with a high voltage port (ranging from 240 V to 450 V), a low voltage port (11V to 16 V), and a rated power of 2 kW. The work starts with an overview on different bidirectional DC–DC converter topologies and investigates their applicability with respect to the given specifications (Chapter 2). Based on the findings of Chapter 2, the singlephase Dual Active Bridge (DAB) converter topology is considered most promising regarding the achievable converter efficiency and the achievable power density. Moreover, due to the wide input and output voltage ranges, two-stage DC–DC converters, i.e. the series connection of an isolated DC–DC converter and a DC–DC converter without galvanic isolation, are expected to facilitate an improved converter efficiency. The subsequent Chapters discuss the single-phase DAB converter in detail. • Chapter 3 explains the working principle of the DAB converter based on 3 different simplified converter models. This includes a lossless model of the DAB, which facilitates basic analytical investigations and allows for a simplified synthesis of optimal modulation schemes (calculated with respect to minimum transformer RMS current). Moreover, two different refinements of the electric DAB converter model are included in order to consider the impacts of the conduction losses and the magnetizing current on the transformer currents. • Chapter 4 discusses a detailed loss model of the DAB, needed in order to parameterize the models developed in Chapter 3 and to develop the efficiency optimized modulation presented in Chapter 5. This loss model is used to calculate the losses in the most relevant converter components. • Chapter 5 presents a systematic investigation of efficiency improvements achievable for the given DAB converter, obtained with the use of optimized modulation schemes. Finally, with the suboptimal modulation schemes discussed in Section 5.2.2, converter operation close to its maximum possible efficiency is achieved (Figure 5.28).

Charge equalization for series connected battery strings

Abstract: A simple technique that provides charge equalization for a series string of battery cells is presented. The advantages of accurate charge equalization are very substantial and include reduced damage to battery cells in the stack, and a dramatic increase in battery life. The basic technique utilizes a simple isolated DC/DC converter with a capacitive output filter along with a multi-winding coaxial winding transformer (CWT). The coaxial winding transformer is known for its low and controlled leakage inductance. The transformer leakage inductance is used as the main driving impedance to control the total charging current for the individual cells. The use of one low-power converter to obtain charge equalization for the entire battery string is very attractive and leads to a low cost implementation. >

Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities

Abstract: In this paper, power electronic transformer (PET)-based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT)-based systems, their pros and cons are summarized. By further reviewing all kinds of PET-based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state of the art, the key challenges and opportunities are identified and discussed. It shows that although PET-based systems are still developing and far from mature, they are already superior to LFT-based systems in terms of system weight, efficiency, and functionalities especially for 15-kV/16.7-Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers, and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.