An Isolated Resonant Mode Modular Converter With Flexible Modulation and Variety of Configurations for MVDC Application

Abstract

The dc tap or dc transformer will play an important role in interfacing different voltages of dc links in dc grids. This paper presents an isolated resonant mode modular converter (RMMC) with flexible modulation and assorted configurations to satisfy a wide variety of interface requirements for medium voltage dc (MVDC) networks. The transformer-less RMMC, as introduced in the literature, implemented a restricted modulation scheme leading to a very limited range of step-ratio and the diode rectifier resulted in unidirectional power flow. Both of these limitations are removed in this proposal and galvanic isolation has also been added. Moreover, this new RMMC approach can serve as a building block for variety of configurations. Two such derived topologies are given, which inherently balance the voltage and current between different constituent circuits and realize the high power rating conversion for very low or very high step-ratio application. The theoretical analysis is validated by a set of full-scale simulations and a down-scaled experimental prototype. The results illustrate that this isolated RMMC and its derivatives have promising features for dc taps or dc transformers in MVDC applications.

Isolated and Nonisolated DC-to-DC Converters for Medium-Voltage DC Networks: A Review

“…Also, this converter can be a base for different configurations to operate as a DC transformer in MVDC networks. However, the high current stress on the switches lets the IRMMC limited in terms of power rating [65].…”

“…The bidirectional power flow capability is another possible feature that converters should have for DC grids interfaces [5], [58]. Required, using FBSMs with non-isolated converters [5], [71], [80], [83] Required, using FBSMs with non-isolated converters [82], [85] Required [86] Unnecessary [92], [93] Required [54], [65], [94] The isolated version of DC-DC converters such as MMC DAB converters is suitable for linking the MVDC to HVDC grids. This topology provides the isolation and the independency of both AC-DC stages.…”

Evolution of the HVDC Link Connecting Offshore Wind Farms to Onshore Power Systems

“…HVAC has the advantage to operate with relatively inexpensive terminals whereas HVDC needs to apply quite costly power converter stations. Moreover, for long distances (like in the case of remote offshore locations), the extra cost of power converters is counterbalanced by cost savings on cheaper DC cables and smaller transmission losses [22]. Additionally, HVDC cables (especially utilizing cross-linked polyethylene as an insulation) have less weight than regular cables.…”

Multi-Port High Voltage Gain Modular Power Converter for Offshore Wind Farms

“…The isolated MMCs in References [21,22] are presented with DC/AC/DC configuration, where medium-frequency high turns-ratio transformers are employed, resulting in a vast volume. Although resonant MMCs [26] achieve galvanic isolation and a small volume of transformers at the same time, its conversion ratio only satisfies MV applications. Alternatively, transformers can be decentralized into multi-module converters, enabling the installation of high-frequency transformers, which reduces the sizes of transformers and reactive components.…”