Comparative Study of a Multi-MW High-Power Density DC Transformer With an Optimized High-Frequency Magnetics in All-DC Offshore Wind Farm

Bahmani, M. A.; Thiringer, Torbjörn; Rabiei, Ali; Abdulahović, Tarik

doi:10.1109/tpwrd.2015.2494883

Cited by 75 publications

(36 citation statements)

References 26 publications

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“…Size reduction at higher frequencies applies to other elements, such as capacitors and inductors. However, this reduction is counterbalanced by core hysteresis and eddy current losses, which increase with frequency [12,16]. Thus, an optimisation approach between size reduction (frequency) and efficiency was explored in [16], and optimum frequencies were determined for different core materials.…”

Section: Introductionmentioning

confidence: 99%

Solid State Transformers Topologies, Controllers, and Applications: State-of-the-Art Literature Review

2018

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With the global trend to produce clean electrical energy, the penetration of renewable energy sources in existing electricity infrastructure is expected to increase significantly within the next few years. The solid state transformer (SST) is expected to play an essential role in future smart grid topologies. Unlike traditional magnetic transformer, SST is flexible enough to be of modular construction, enabling bi-directional power flow and can be employed for AC and DC grids. Moreover, SSTs can control the voltage level and modulate both active and reactive power at the point of common coupling without the need to external flexible AC transmission system device as per the current practice in conventional electricity grids. The rapid advancement in power semiconductors switching speed and power handling capacity will soon allow for the commercialisation of grid-rated SSTs. This paper is aimed at introducing a state-of-the-art review for SST proposed topologies, controllers, and applications. Additionally, strengths, weaknesses, opportunities, and threats (SWOT) analysis along with a brief review of market drivers for prospective commercialisation are elaborated.

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Section: Introductionmentioning

confidence: 99%

Solid State Transformers Topologies, Controllers, and Applications: State-of-the-Art Literature Review

2018

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“…This 500 Hz medium frequency operation would also benefit other passive components' sizing in the converter, such as the internal transformer and arm inductors. Their volume can be decreased to less than 1/3 of that for 50 Hz standard frequency operation [43], [44].…”

Section: Sort and Selectmentioning

confidence: 99%

A Compact Modular Multilevel DC–DC Converter for High Step-Ratio MV and HV Use

Xiang

Zhang

Luth

et al. 2018

IEEE Trans. Ind. Electron.

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In multi-terminal dc networks or future dc grids, there is an important role for high step-ratio dc-dc conversion to interface a high voltage network to lower voltage infeeds or offtakes. The efficiency and controllability of dc-dc conversion will be expected to be similar to modular multi-level ac-dc converters. This paper presents a modular multilevel dc-dc converter with a high step-ratio for medium voltage and high voltage applications. Its topology on high-voltage side is derived from the half-bridge single-phase inverter with stacks of sub-modules replacing each of the switch positions. A near-square-wave current operation is proposed which achieves near-constant instantaneous power for single-phase conversion, leading to reduced stack capacitor and filter volume and also increased the power device utilization. A controller for energy balancing and current tracking is designed. The soft-switching operation on the low-voltage side is demonstrated. The high step-ratio is accomplished by combination of inherent half-bridge ratio, sub-module stack modulation and transformer turns-ratio, which also offers flexibility to satisfy wide-range conversion requirement. The theoretical analysis of this converter is verified by simulation of a full-scale 40MW, 200 kV converter with 146 sub-modules and also through experimental testing of a down-scaled prototype at 4.5 kW, 1.5 kV with 18 sub-modules. Index Terms-Modular multilevel converter, compact volume, high step-ratio, dc grids. NOMENCLATURE Ch Control headroom D Duty-cycle of the near-square-wave ES Sum of the energy stored in all capacitors ETs, EBs Energy stored in the top stack and bottom stack fo, fs Operation frequency, switching frequency fr SM sorting and selection frequency iBac AC component of the bottom stack current Manuscript

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“…In order to evaluate the core losses, the modified expression of the improved generalized Steinmetz equation (IGSE) adapted for non-sinusoidal waveforms has been used as (25) where D and R are equal to 0.5 and 0 respectively for the standard phase shift DAB converter, ρ is the core density and V c , is the core volume corresponding to the investigated sets of free parameters as follows (26) in which H is the window height previously calculated in (19) and G is the core window width calculated from [26] …”

Section: F Core Loss Evaluationmentioning

confidence: 99%

Design Methodology and Optimization of a Medium-Frequency Transformer for High-Power DC–DC Applications

Bahmani

Thiringer

Kharezy³

2016

IEEE Trans. on Ind. Applicat.

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125

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The medium-frequency power transformer (MFPT) is one of the key elements of an isolated, bi-directional DC-DC converters in applications such as future all-DC offshore wind farms, traction and solid state transformers. This paper describes a design methodology taking into account the loss calculation, isolation requirements and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met.

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Comparative Study of a Multi-MW High-Power Density DC Transformer With an Optimized High-Frequency Magnetics in All-DC Offshore Wind Farm

Cited by 75 publications

References 26 publications

Solid State Transformers Topologies, Controllers, and Applications: State-of-the-Art Literature Review

Solid State Transformers Topologies, Controllers, and Applications: State-of-the-Art Literature Review

A Compact Modular Multilevel DC–DC Converter for High Step-Ratio MV and HV Use

Design Methodology and Optimization of a Medium-Frequency Transformer for High-Power DC–DC Applications

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