Reliability and Cost-Oriented Analysis, Comparison and Selection of Multi-Level MVdc Converters

Abstract

DC technology has gained considerable interest in the medium voltage applications due to the benefits over the AC counterpart. However, to utilize the full capacity of this development, the selection of a suitable power electronic converter topology is a key aspect. From the pool of voltage source converters (VSC's), it is unclear which topology is suitable for multi-megawatt applications at medium voltage dc (MVdc) levels. To address this, the paper proposes a selection guideline based on reliability and optimum redundancy levels of VSCs for MVdc applications. This will be combined with other functional factors such as operational efficiency and return-on-investment. Three candidate multi-level topologies namely three-level neutral point clamped converter (3L-NPC), modular multi-level converter (MMC) and cascaded 3L-NPC (which is being used for the first MVdc link in the UK) have been evaluated over two-level-VSC from ±10 kV to ±50 kV. Results show that with the increase of MVdc voltage level MMC shows better performance whereas at low MVdc voltage levels 3L-NPC is the prominent topology.

Reliability and Economic Evaluation of Offshore Wind Power DC Collection Systems

“…The required converter losses with different MVDC voltage levels and power levels were obtained using the PLECS simulations. The work in [49] could be used to calculate these losses.…”

“…The failure and repair rates of different sub-assemblies of typical offshore WT is considered and summarized in Table 5 [54]. The failure rate of the DC/DC converter was obtained using the methodology presented in [49]. Notably, compared to other subassemblies, the failure rates of power converters were relatively higher due to the greater intrinsic failures of semiconductor devices.…”

“…To assess the economies of scale of different candidate DC collection systems, capital and operational costs of each topology were calculated, based on the methodol discussed in Section 3.3. As shown in Figure 13, the capital cost included WT cost, c cost, and converter cost, and the operational losses included cable-and converter-los For this analysis, the average lifetime of the offshore wind farm was considered as 25 y [56] and for electrical energy losses calculations, the energy price of 75 £/MWh [18] wi discount rate of 5% was considered [49]. Among the four topologies, the total cost of SP topology was significantly lower than other topologies, due to the elimination of the centralized DC/DC converter.…”

“…The required converter losses with different MVDC voltage lev levels were obtained using the PLECS simulations. The work in[49] could culate these losses.• Cost of LossesThe total annual energy losses of each DC collection system Eloss can b…”

Analysis and Mitigation of DC Voltage Imbalance for Medium-Voltage Cascaded Three-Level Neutral-Point-Clamped Converters

“…In medium-voltage (MV) applications, since a single two/three level converter cannot withstand the voltage level, multilevel topologies are required. Among them, those using cascaded modular converters are preferred due to their exceptional waveform quality, compact and modular design [9].…”