A Hybrid Modular Multilevel Converter Topology with an Improved Nearest Level Modulation Method

Abstract

In this paper, a hybrid modular multilevel converter (MMC) topology with an improved nearest level modulation method is proposed for medium-voltage high-power applications. The arm of the proposed topology contains N series connected half-bridge submodules (HBSMs), one full-bridge submodule (FBSM) and an inductor. By exploiting the FBSM, half-level voltages are obtained in the arm voltages. Therefore, an output voltage with a 2N+1 level number can be generated. Moreover, the total level number of the inserted submodules (SMs) is a constant. Thus, there is no pulse voltage across the arm inductors, and the SM capacitor voltage is rated. With the proposed voltage balancing method, the capacitor voltage of the HBSM is twice the voltage of the FBSM, and each IGBT of the FBSM has a relatively low switching frequency and an equalized conduction loss. The capacitor voltage balancing methods of the two kinds of SMs are implemented independently. As a result, the switching frequency of the HBSM is not increased compared to the conventional MMC. In addition, according to a theoretical calculation of the total harmonic distortion of the electromotive force (EMF), the voltage quality with the presented method can be significantly enhanced when the SM number is relatively small. Simulation and experimental results obtained with a MMC-based inverter verify the validity of the developed method.

Harmonic minimization of a single-phase asymmetrical TCHB multilevel inverter based on nearest level control method

“…The results show a significantly improved THD, however, the study does not discuss applying the method to a reduced number of levels (less than 21). After a precise review of the literature, it was found that few studies have been conducted on the NLC method applied to the TCHB inverter compared to MMC [22][23][24][25] and asymmetrical CHB MLI [7,21]; Therefore, this paper focuses on applying the NLC method to a 13 level A-TCHB inverter with a DC voltage ratio 1: 2 between two TCHB cells. The method operates at the fundamental frequency and can be extended to any number of levels.…”

An enhanced level-increased nearest level modulation for modular multilevel converter

“…There are lots of high frequency components in arm currents and circulating currents and this will increase the current stress, power loss, and electromagnetic interference of devices. Although the high‐frequency currents generated by pulse voltage can be suppressed by increasing the arm inductance, this will bring other problems such as a large inductor size and circuit dynamic poor performance . A hybrid topology of MMC is able to increase the level number of the output voltage and keeps the total number of inserted SMs unchanged …”

“…Although the high-frequency currents generated by pulse voltage can be suppressed by increasing the arm inductance, this will bring other problems such as a large inductor size and circuit dynamic poor performance. 25 A hybrid topology of MMC is able to increase the level number of the output voltage and keeps the total number of inserted SMs unchanged. 25 However, this makes MMC topology complicated and weakens the modularity of MMC.…”

“…25 A hybrid topology of MMC is able to increase the level number of the output voltage and keeps the total number of inserted SMs unchanged. 25 However, this makes MMC topology complicated and weakens the modularity of MMC. It might be better if modularity, as an important advantage of MMC, can be remained when solving the problems in Hu and Jiang 23 and Lin et al 24 Considering these issues discussed above, this paper proposes an enhanced nearest level modulation (eNLM) method.…”

Modüler çok seviyeli dönüştürücüler için genelleştirilmiş bir kapasitör gerilim dengeleme şeması ve örnekleme frekansı analizi

“…Bu bağlamda, MÇD'ler için faz-kaydırmalı taşıyıcı DGM, UVM ve ESM metotlarının çıkış gerilim ve akım harmonik içerikleri bakımından farklı durum çalışmaları altında hem simülasyon ortamında hem de alanda programlanabilir kapı dizisi (Field Programmable Gate Array-FPGA) kartı kullanılarak gerçek bir platform üzerinde deneysel karşılaştırılmaları yapılmıştır [18]. Yarımköprü ve tam-köprü alt modüllerden oluşan hibrit MÇD topolojisi için iyileştirilmiş ESM stratejisi simülasyon ve deneysel çalışma ile gerçekleştirilerek önerilmiştir [19]. ESM tekniğinin 6-seviyeli MÇD üzerinde uygulanması hem deneysel olarak hem de simülasyon ortamında gösterilmiştir [20].…”