Medium voltage power distribution architecture with medium frequency isolation transformer for data centers

Hafez, Bahaa; Krishnamoorthy, Harish S.; Enjeti, P.N.; Ahmed, Shehab; Pitel, I.J.

doi:10.1109/apec.2014.6803810

Cited by 34 publications

(5 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In recent years, the need for highly efficient interfaces between the Medium-Voltage (MV) AC grid and the Low-Voltage (LV) DC buses has significantly increased hand in hand with the rapidly growing amount of high-power LV DC loads and sources [1]- [7]. In such a scenario, so-called Solid-State Transformers (SSTs), i.e., galvanically insulated high-power AC/DC, DC/DC, and DC/AC converters, could replace the state-of-the-art technology based on Low-Frequency Transformers (LFTs), due to several benefits such as lower volume and weight [8]- [10].…”

Section: Introductionmentioning

confidence: 99%

Voltage Distribution in the Windings of Medium-Frequency Transformers Operated With Wide Bandgap Devices

Cremasco

Rothmund

Curti

et al. 2022

IEEE J. Emerg. Sel. Topics Power Electron.

View full text Add to dashboard Cite

The short rise time observed in the PWM voltages generated by ultra-fast wide bandgap devices increases the amplitude of voltage harmonics at higher frequencies. These harmonics can excite the resonances of Medium-Frequency Transformers (MFTs), resulting in overvoltages inside the windings during continuous operation. Without further measures, these overvoltages can lead to unexpectedly high electric fields in the insulation material, which can result in partial discharge, accelerated ageing and possible failure of the MFT. To avoid these effects, the mechanism causing the overvoltages has to be understood and quantified during the design process. Based on this, the MFT can be designed in a way that the overvoltages vanish or are tolerable. Therefore, the voltage distribution inside the MFT windings is analysed by a fully-coupled multi-conductor transmission line model, which includes the damping effect of electromagnetic losses in the litz wire and in the core. This method is verified by measuring the transfer functions of the voltage to ground of individual turns and their voltage waveforms during continuous operation. The waveforms indicate repeating overvoltages inside the windings. A guideline for the design verification and a simplified approach to speed-up the modelling process are presented.

show abstract

Section: Introductionmentioning

confidence: 99%

Voltage Distribution in the Windings of Medium-Frequency Transformers Operated With Wide Bandgap Devices

Cremasco

Rothmund

Curti

et al. 2022

IEEE J. Emerg. Sel. Topics Power Electron.

View full text Add to dashboard Cite

show abstract

“…Fuelled by the availability of wide-bandgap (WBG) SiC power semiconductors with blocking voltage ratings of up to 10 kV and beyond, solid-state transformers (SSTs) have been proposed as flexible isolation and voltage-scaling interfaces between medium-voltage (MV) and low-voltage (LV) DC or AC buses. Typical applications include, e.g., hybrid smart grid systems with AC and DC sections [1], [2], grid interfaces for renewable power sources [3], [4], hyperscale data centers [5], [6], high-power electric vehicle (EV) charging stations [7], [8], future ships [9]- [11], and future aircraft with distributed propulsion systems and on-board MVDC grids [12]- [14].…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Performance Limits of 166 kW/7 kV Air- and Magnetic-Core Medium-Voltage Medium-Frequency Transformers for 1:1-DCX Applications

Czyż

Guillod

Zhang

et al. 2022

IEEE J. Emerg. Sel. Topics Power Electron.

View full text Add to dashboard Cite

Solid-state transformers (SSTs) are employing compact high-power medium-voltage (MV) medium-frequency transformers (MFTs) and enable the power transfer between galvanically isolated DC systems. Considering a typical SST isolation stage, i.e., a 166 kW unregulated series-resonant DC-DC converter acting as a DC transformer (DCX) with equal input and output MV DC voltages of 7 kV (1:1-DCX), we derive component-level and system-level performance limits of aircooled realizations with either an air-core transformer (ACT) or with a magnetic-core transformer (MCT). We describe the design of two fully rated MFT prototypes in detail and provide a comprehensive experimental characterization to validate the derived performance limits, including also the dielectric losses and the analysis of stray magnetic fields. The realized ACT and MCT prototypes achieve measured efficiencies of 99.5 % and 99.7 % at gravimetric power densities of 16.5 kW/kg and 6.7 kW/kg, respectively. Considering 10 kV SiC MOSFETs, calculated system-level efficiencies of the ACT-based and MCTbased 1:1-DCX result in 99.0 % and 99.2 % at the nominal operating point, with similar part-load efficiency characteristics. The paper concludes with an application-oriented qualitative evaluation of the two concepts.

show abstract

“…Stringent efficiency requirements for the supply of high-power DC applications such as hyperscale data centers [1][2][3][4] and high-power electric vehicle (EV) charging stations [5][6][7][8] drive the interest in direct power electronic interfaces between a medium-voltage (MV) AC grid and a low-voltage (LV) DC bus. Such flexible isolation and voltage-scaling MVAC-LVDC interfaces are commonly referred to as solid-state transformers (SSTs) [2,3,9,10].…”

Section: Introductionmentioning

confidence: 99%

Load-Independent Voltage Balancing of Multi-Level Flying Capacitor Converters in Quasi-2-Level Operation

et al. 2021

View full text Add to dashboard Cite

Quasi-2-level (Q2L) operation of multi-level bridge-legs, especially of flying-capacitor converters (FCC), is an interesting option for realizing single-cell power conversion in applications whose system voltages exceed the ratings of available power semiconductors. To ensure equal voltage sharing among a Q2L-FCC’s switches, the voltages of a Q2L-FCC’s minimized flying capacitors (FCs) must always be balanced. Thus, we propose a concept for load-independent FC voltage balancing: For non-zero load current, we use a model predictive control (MPC) approach to identify the commutation sequence of the individual switches within a Q2L transition that minimizes the FC or cell voltage errors. In case of zero load current, we employ a novel MPC-based approach using cell multiple switching (CMS), i.e., the insertion of additional zero-current commutations within a Q2L transition, to exchange charge between the FCs via the charging currents of the switches’ parasitic capacitances. Experiments with a 5-level FCC half-bridge demonstrator confirm the validity of the derived models and verify the performance of the proposed load-independent balancing concept.

show abstract

Medium voltage power distribution architecture with medium frequency isolation transformer for data centers

Cited by 34 publications

References 10 publications

Voltage Distribution in the Windings of Medium-Frequency Transformers Operated With Wide Bandgap Devices

Voltage Distribution in the Windings of Medium-Frequency Transformers Operated With Wide Bandgap Devices

Analysis of the Performance Limits of 166 kW/7 kV Air- and Magnetic-Core Medium-Voltage Medium-Frequency Transformers for 1:1-DCX Applications

Load-Independent Voltage Balancing of Multi-Level Flying Capacitor Converters in Quasi-2-Level Operation

Contact Info

Product

Resources

About