With a growing number of commercial installations around the world, HVDC technology increased its presence and importance in the power systems. Among various converter topologies, the Modular Multilevel Converters (MMCs) are considered as the most suitable one for HVDC application today. Besides its recognised advantages over conventional converters, the MMC has an interesting extra degree of freedom, which is the energy stored in the distributed cell capacitors. Although the amount of this energy is relatively small, it can provide a significant contribution to the DC system stability when properly used. This paper presents experiment results that demonstrate the effectiveness of virtual capacitor control. This control, previously proposed by the authors, makes use of the above additional degree of freedom to attenuate fluctuations of the DC voltage, which tend to be inherently volatile against power disturbances compared to the frequency of conventional AC systems. Under the virtual capacitor control, the MMC behaves as if there were a capacitor on the DC side of the converter whose size is easily adjusted by the control variable and can be even bigger than the physical capacitor actually embedded in the converter. In practice, the emulation of the capacitor dynamics is realised by the auxiliary control which adjusts the exchange of the energy between the stacked cell capacitors and the DC grid during the transient. Thus, no adverse effect is imposed on the AC grid. Furthermore, the system operator can optionally adjust the equivalent capacitance of the system to achieve desired mitigation level of DC voltage fluctuation during the operation. Therefore, this additional degree of freedom can largely extend the operability of the DC systems. The feasibility and effectiveness of the virtual capacitor control is demonstrated by experimental results obtained by using a small-scale MMC prototype.
High voltage direct current (HVDC) technologies are currently emerging to develop new energy transmission networks able to integrate renewable energy sources with remote locations from consumers. Gas Insulated Substations (GIS) have been widely used in alternating current (AC) transmission due to their low footprint and high reliability.
Breakdown Characteristics and Pre-Breakdown Phenomena in Liquid and Boiling Nitrogen with Tape Electrode for r-SCFCL Applications
The rational insulation design of a resistive superconducting fault current limiter (r-SCFCL) requires data gathered from experimental setups relevant for the final apparatus.
This paper presents simulation and calculation results of electric field enhancement due to various cavity shapes carried out on polymeric high voltage direct current (HVDC) cables. Two aspects are considered: partial discharges (PD) in microcavities and field enhancement factor under DC.
This article presents the design, the fabrication, and the test of an isolated DC-DC converter for renewable energy applications. The converter is based on the Dual Active Bridge topology and uses silicon carbide power semiconductors and a medium frequency transformer. The design process covers hardware ranging from the semiconductor die to the complete power converter. For the control, a rapid prototyping approach was used. The experimental validation of the 100 kW prototype is presented.
This paper presents a methodology to optimize the sizing of such power converters in order to compare different topologies for a given application. The proposed procedure maximises the efficiency of the converter under a limited volume.
From 27 to 31 August, SuperGrid Institute participate at the CIGRE Technical Exhibition 2018: the leading Power Systems Event. Posters, workshops, sessions… you will meet many of our SuperGrid Institute experts, and of course at our stand n°243, available to network and discuss.