An AC–DC Isolated MMC-Based Structure Suitable for MV SST Traction Applications

Abstract

This paper presents the theoretical study and experimental validation of a single-stage bidirectional ac-dc topology for solid-state transformer (SST) applications. This topology is based on the modular multilevel converter (MMC) and employs the concepts of interleaving converters and integrated power stages. A single magnetic element operating at medium frequency is employed to perform galvanic isolation and coupling between the grid-side and load-side converters. The main characteristics of the structure are derived from the aforementioned characteristics, such as passive elements operating with an effective frequency higher than the switching frequency, minimized current ripples at high frequency, as well as reduced volume and weight. Experimental results of the converter are obtained in a small-scale prototype, operating with a switching frequency of 5 kHz, nominal power of 1.5 kW, output voltage of 300 V, and the supply voltage of 165 V at a frequency of 60 Hz. High-power factor of 0.99, low-harmonic distortion of the input current with 3.6%, and efficiency in the 87% were achieved. INDEX TERMS Bidirectional AC-DC converter, modular multilevel converter, power factor correction, medium-frequency isolation, single-stage topologies.

Solid-State Transformers: Fundamentals, Topologies, Applications, and Future Challenges

“…Recently modular multi-level converter technology has emerged as a promising technology. A single-stage SST topology based on modular multi-level converters utilizing the concept of interleaving converters and integrated power stages has been studied and experimentally validated in [74]. It is deemed suitable for traction application with an efficiency of 87%, power factor as high as 0.99, and low harmonic distortion of 3.7% to the input current.…”

Transformador De Estado Sólido Ca-Cc Monofásico 5 Níveis Baseado No Intercalamento De Braços NPC

“…A função de chaveamento nos interruptores do lado secundário do conversor I2NDF1, d ex1 (t), é dada conforme (9).…”

“…Estes equipamentos são apontados como uma alternativa a substituição dos transformadores convencionais (50-60 Hz), sobretudo em aplicações onde peso e volume são aspectos críticos [4]. Posteriormente, diversas estruturas de TES, permitindo flexibilidades adicionais, tais como regulação de tensão, redução da distorção harmônica, controle de reativos foram propostas em várias aplicações, como por exemplo, sistemas de transmissão e distribuição de energia [5]- [7], sistemas de tração [8], [9], interligação de geração distribuída com a rede [10], interface de smart grids [11]- [13], aplicações que envolvem média e alta tensão CC [14], [15] e integração de sistemas de geração de energias renováveis e rede elétrica [16]- [19].…”

Submodule Capacitor Voltage Balancing Through High-Frequency-Side Control for Multiport MMC-Based Solid-State Transformers

“…To overcome this issue, they can be integrated to a medium frequency transformer (MFT), as shown by the structure in Fig. 2(d) [10], [11]. Unlike the other referred topologies, there is only one MFT in the system, which may deteriorate reliability and requires the same power rating as that of the overall system.…”