As part of its research, SuperGrid Institute studies the phenomena of partial discharge under DC voltage. Environmental issues emphasised in the European project PROMOTioN encourage the exploration for possible replacement of SF6 gas and remains a strong component of the study at SuperGrid Institute.
NPC assessment in insulated DC/DC converter topologies using SiC MOSFETs for Power Electronic Traction Transformer
Power electronic traction transformers (PETT) are multilevel AC/DC on-board converters, studied for railway applications to replace traditional solution with low frequency transformers. This paper focuses on the insulated DC/DC converter in a PETT. Three variants of resonant single active bridges (R-SAB) with 3-level NPC primaries are optimised to maximise the efficiency, under mass and dimension constraints. They are sized and compared for a 2 MW PETT on a 15 kV/16.7 Hz railway infrastructure, using 3.3 kV SiC MOSFETs and nanocrystalline C-core transformers with cast resin insulation and forced air cooling. The highest efficiency at nominal power, 99.17 %, is reached for a configuration with a 3-level full bridge NPC primary, a 2-level full bridge secondary, and a 32.1 L/49.1 kg transformer operating at 6 kHz.
The large-scale integration of renewable electricity generation poses both structural, economic and management challenges. Among the major challenges, one can note the grid integration and the routing of this energy from the production units to the consumption poles. Major issues have to be faced like insufficient transmission capability, inertia reduction, stability margins mitigation. The HVDC is not a new idea but it can provide some interesting answers to these challenges. The keynote will list the locks and how they can be addressed by the HVDC grid. Finally, the underlying scientific issues will be discussed.
This paper evidences the influence of different parameters on the electric field on DC spacers in GIS/GIL and thus their dielectric withstand under S/IMP tests. A notable difference in term of electric field can be observed in function of impulse polarity, load condition (with/without heating current) and insulating material’s properties. For example, an overstress of 0.3pu was obtained on spacer’s surface in case of superimposed impulse test with opposite impulse polarity, high load condition and high leakage current in gas. Contrary to AC system where the simple LI tests were enough, S/IMP tests with both impulse polarity, ZL and HL conditions are mandatory to verify the insulating performance of HVDC GIS/GIL spacer. This paper gives a better understanding of the electric field distribution in HVDC GIS/GIL and helps for the design and tests
Phd Guilherme DANTAS DE FREITAS “Development of a methodology for DC grid protection strategies comparison”
High Voltage Direct Current (HVDC) grids are considered a promising solution for problems faced by nowadays power system such as: lines congestion, integration of large amounts of renewable power and enhancement of AC system stability. Among the challenges in the deployment of a HVDC meshed grid, the protection of these grids is regarded as one of the most critical. The protection of HVDC grid is challenging not only because the swift transients and fault currents without zero-crossing, but also due to the impact a DC faults can have on the AC system. Several propositions for HVDC grids protection strategies can be found in literature...
The article presents a three-phase Medium Frequency Transformer being a part of a 100kW 1.2kV 20kHz Dual Active Bridge DC-DC converter. The transformer design is detailed focusing on winding and core power loss calculation. The high power three-phase MFT prototype is presented. The experimental results include the transformer impedance characteristics, no load test and three-phase DAB full load test waveforms.
Cost-performance framework for the assessment of Modular Multilevel Converter in HVDC transmission applications
This article proposes a methodology of Cost-Performance Assessment (CPA) enabling the efficient cost evaluation required for the Cost-Benefit Analysis (CBA). The proposed method is applied for the Modular Multilevel Converter (MMC) in offshore wind high voltage direct current (HVDC) transmission. Thanks to the developed model, an analysis of submodule voltage rating is performed demonstrating the interest of this methodology in the evaluation of new technologies for HVDC transmission. The analysis shows that increasing the submodule (SM) voltage could lead to savings in the MMC cost and weight.
The number of high voltage direct current (HVDC) links continue to increase over the years, most of them, for offshore applications or bulk power transmission over long distances. The present paper evaluates the possible development of a direct current (dc) grid in Europe given the present, and future, HVDC links. Eight potential cases for the interconnection between close links are suggested as starting scenario for a multiterminal network. The need of a dc-dc converter and its special requirements are evaluated in function of suggested interconnections. As an example, a case study is chosen to evaluate the behavior of an interconnection between line commutated converter (LCC) and voltage source converter (VSC) link using a front-to-front (F2F) isolated converter.
This paper deals with the opportunities to introduce split storage into an MMC. The analysis is focused on the internal energy exchange to maintain the proper function of the converter by using circulating current. Analysis shows that, SM capacitor voltage ripple or semiconductors load are greatly influenced by additional circulating current injection. This study helps to design Embedded ESSs in the converter to provide new function like ancillary services for power system operation. Finally, a simulation of an MMC with ESS confirms analytical calculations.
The thinking caps are on this week at SuperGrid Institute with the “Fête de la Science” event! Over the last few days the institute has welcomed four classes of high school students who learnt about the work that we do through fun, interactive activities. This Saturday afternoon, we are opening our doors to the public to round of the week in style! Come along and see us!