Review of dc–dc converters for multi‐terminal HVDC transmission networks

Abstract

This paper presents a comprehensive review of high-power dc-dc converters for high-voltage direct current (HVDC) transmission systems, with emphasis on the most promising topologies from established and emerging dc-dc converters.Additionally, it highlights the key challenges of dc-dc converter scalability to HVDC applications, and narrows down the desired features for high-voltage dc-dc converters, considering both device and system perspectives. Attributes and limitations of each dc-dc converter considered in this study are explained in detail and supported by time-domain simulations. It is found that the front-to-front quasi two-level operated modular multilevel converter, transition arm modular converter and controlled transition bridge converter offer the best solutions for high-voltage dc-dc converters that do not compromise galvanic isolation and prevention of dc fault propagation within the dc network. Apart from dc fault response, the MMC dc auto transformer and the transformerless hybrid cascaded two-level converter offer the most efficient solutions for tapping and dc voltage matching of multi-terminal HVDC networks. Key words:High-voltage dc-dc converter; modular multilevel converter; multi-terminal high-voltage dc networks; and prevention of dc faults propagation.I.

Operation Analysis of Thyristor-Based Front-to-Front Active-Forced-Commutated Bridge DC Transformer in LCC and VSC Hybrid HVDC Networks

“…For example, by manipulating the conduction time of the FB-CL and thyristors in the AFC-bridge, the Q3L ac voltage waveform with stepped level transition enables full range modulation index adjustment; thus, black-start capability is guaranteed for the AFC-bridge based converters. Alternatively, if zero-voltage-level is not exploited, a series of selective harmonic elimination (SHE) methods under a quasi-2-level (Q2L) mode can be adopted; but these incur either additional losses or high control complexity on fundamental voltage regulation over a wide range [21,29]. The transformer link in the AFC-bridge dc-dc converter is possible to run with a frequency reasonably higher such as 100Hz (considering the speed of thyristors); in this manner, the overall size and weight of the converter can be reduced [30].…”

“…For satisfying the requirements of HVDC systems, modular multilevel converter (MMC) using half-bridge (HB) chopper cell has been developed to reduce the switching losses and overcome the voltage level limit of using switch series connection as in the two-level VSC [17]; also, several variants of HB-MMC including hybrid topologies have been proposed in literatures, aiming for a compromise between the converter functionality and total energy storage [18][19][20]. These topologies can be configured as F2F dc-dc converters to meet most of the requirements in a MT-HVDC system such as the scalable structure, dc voltage tapping and galvanic isolation [21]. On the other hand, the non-isolated layouts for high voltage dc-dc conversion have also been studied in 3 [22][23][24], which are implemented using MMCs.…”

Geometry optimization and characterization of three-phase medium frequency transformer for 10kVA Isolated DC-DC converter

“…Finally, RMS value of the magnetizing current is ( ) (10) In this case, 10% increase in the value of MMF is considered due to flux concentration at the corners of the window.…”

“…Recently, design considerations of multi-megawatts scale converters haven been studied in [6][7][8][9][10][11]. Especially, [9] introduced a constructed 2.2MVA prototype.…”

Modelling of DC-DC converters based on front-to-front connected MMC for small signal studies

“…A set of high-level requirements for such DC-DC converters was outlined in [3]. Different topologies, that fulfil these requirements for a specific application, have been proposed in literature [5]. This calls for the development of new models for power system studies, such as small signal analysis.…”