Step-up switched-capacitor multilevel inverter employing multiple inputs with reduced switches

Wang, Yaoqiang,Wang, Zhe,Liu, Wenjun,Zhang, Yun,Wang, Kewen,Liang, Jun The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.7

A large device count, weak boosting capability, and DC voltage imbalance are common issues in conventional multilevel inverters. In this paper, a novel multilevel inverter is presented that can generate the desired number of output levels with reduced devices by using new switched-capacitor circuits (SCCs). The two input sources and capacitors in the SCC can be switched in parallel and series modes. In the parallel mode, the capacitor voltage of the SCC is charged to the DC source voltage, which inherently solves the capacitor voltage imbalance issue without any auxiliary circuits. In the series mode, the capacitor can be used as an alternative source, which helps achieve a high voltage gain. The multiple input sources of the SCC make the proposed topology suitable for application in renewable energy generation systems where several DC sources are available. Instead of an H-bridge module, a structure with two half-bridges and two switches is used as a polarity generation circuit at the load terminal. The input sources of two SCCs can be selected as symmetric and asymmetric patterns, which can result in a great number of output voltage levels. The circuit topology, operational principle, modulation strategy, capacitor analysis, and performance comparisons of the inverter are described in this paper. In addition, experimental results verify the feasibility and validity of the inverter.

Extendable space‑type switched‑capacitor multilevel inverter with fault‑tolerant capability

Yaoqiang Wang,Hengtai Zhang,Jinmu Lai,Kewen Wang,Jun Liang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.6

Low reliability is one of the main concerns in terms of multilevel inverters (MLI) due to the presence of a large number of switches and capacitors. Therefore, the fault-tolerant operation of MLIs has recently gained a great deal of attention. An extendable space-type switched-capacitor MLI topology with fault-tolerant characteristics is proposed in this paper. The proposed inverter employs a single direct-current voltage source and three capacitors to output staircase voltage levels with low distortion. The proposed topology is capable of tolerating open-circuit faults due to the separated charging paths of the inverter. Under pre-fault and post-fault operations, it preserves capacitor voltage balancing, voltage boost capability, as well as the ability to supply inductive loads. Furthermore, the voltage stresses of the switches and the voltage ripples of the capacitors are decreased or remain under post-fault operations. The proposed topology has been validated with a laboratory prototype in both dynamic and steady-state operations.

Bypass arm based DC fault isolation scheme for MMC‑HVDC systems

Yaoqiang Wang,Ruyin Sun,Yanxun Guo,Kewen Wang,Jun Liang 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.8

High voltage direct current transmission based on a modular multilevel converter (MMC-HVDC) is an effective method to solve the grid connection of the new energy. A DC fault is an issue that must be solved for MMC-HVDC. This paper proposes a protection scheme for HVDC converters to quickly suppress DC fault current without increasing the operation loss. By employing a bypass arm in conjunction with a switch-type zero-loss current limiter (SZCL), most of the DC current in the bridge arm fl ows through the bypass arm so the fault current of the power devices is reduced. There are a number of main advantages of this scheme. The fault isolation time can be greatly shortened, the cost of the system is effectively reduced, the steady-state operation loss of the system does not increase, the operation of the AC-grid can be maintained stably when a DC fault occurs, and the overcurrent impulse to the AC-grid is reduced. The proposed scheme is applicable to two-terminal systems and the DC grid, especially for faults at the converter outlet of the DC grid. Simulation results using PSCAD/EMTDC show the superiority of the proposed scheme when compared with other schemes and a comparison of the costs shows the feasibility of the proposed scheme in practical applications.

Mediatory role of K, Cu and Mo over Ru/SiO2 catalysts for glycerol hydrogenolysis

Xiaoyuan Liao,Kewen Li,Xiaomin Xiang,Sheng-Guang Wang,Xichun She,Yulei Zhu,Yongwang Li 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.2

SiO2 supported ruthenium catalysts with and without modifiers were prepared, characterized and tested for glycerol hydrogenation. Addition of K, Cu and Mo affects the reducibility and acidity of the Ru/SiO2catalyst. Characterization data shows that Cu and Mo-modified Ru/SiO2 have stronger acidity. On the contrary, K element on a passive effect on the acidity of Ru based catalyst had been observed. A comparison with the pure Ru/SiO2 indicates the Cu-promoted specimen has better selective to the desired products, acetol, 1,2-propanediol and ethyl glycol, although the reactivity is slightly lower.

vfr, A Global Regulatory Gene, is Required for Pyrrolnitrin but not for Phenazine-1-carboxylic Acid Biosynthesis in Pseudomonas chlororaphis G05

Wu, Xia,Chi, Xiaoyan,Wang, Yanhua,Zhang, Kailu,Kai, Le,He, Qiuning,Tang, Jinxiu,Wang, Kewen,Sun, Longshuo,Hao, Xiuying,Xie, Weihai,Ge, Yihe The Korean Society of Plant Pathology 2019 Plant Pathology Journal Vol.35 No.4

In our previous study, pyrrolnitrin produced in Pseudomonas chlororaphis G05 plays more critical role in suppression of mycelial growth of some fungal pathogens that cause plant diseases in agriculture. Although some regulators for pyrrolnitrin biosynthesis were identified, the pyrrolnitrin regulation pathway was not fully constructed. During our screening novel regulator candidates, we obtained a white conjugant G05W02 while transposon mutagenesis was carried out between a fusion mutant $G05{\Delta}phz{\Delta}prn::lacZ$ and E. coli S17-1 (pUT/mini-Tn5Kan). By cloning and sequencing of the transposon-flanking DNA fragment, we found that a vfr gene in the conjugant G05W02 was disrupted with mini-Tn5Kan. In one other previous study on P. fluorescens, however, it was reported that the deletion of the vfr caused increased production of pyrrolnitrin and other antifungal metabolites. To confirm its regulatory function, we constructed the vfr-knockout mutant $G05{\Delta}vfr$ and $G05{\Delta}phz{\Delta}prn::lacZ{\Delta}vfr$. By quantifying ${\beta}-galactosidase$ activities, we found that deletion of the vfr decreased the prn operon expression dramatically. Meanwhile, by quantifying pyrrolnitrin production in the mutant $G05{\Delta}vfr$, we found that deficiency of the Vfr caused decreased pyrrolnitrin production. However, production of phenazine-1-carboxylic acid was same to that in the wild-type strain G05. Taken together, Vfr is required for pyrrolnitrin but not for phenazine-1-carboxylic acid biosynthesis in P. chlororaphis G05.

vfr, A Global Regulatory Gene, is Required for Pyrrolnitrin but not for Phenazine-1-carboxylic Acid Biosynthesis in Pseudomonas chlororaphis G05

Xia Wu,Xiaoyan Chi,Yanhua Wang,Kailu Zhang,Le Kai,Qiuning He,Jinxiu Tang,Kewen Wang,Longshuo Sun,Xiuying Hao,Weihai Xie,Yihe Ge 한국식물병리학회 2019 Plant Pathology Journal Vol.35 No.4

In our previous study, pyrrolnitrin produced in Pseudomonas chlororaphis G05 plays more critical role in suppression of mycelial growth of some fungal pathogens that cause plant diseases in agriculture. Although some regulators for pyrrolnitrin biosynthesis were identified, the pyrrolnitrin regulation pathway was not fully constructed. During our screening novel regulator candidates, we obtained a white conjugant G05W02 while transposon mutagenesis was carried out between a fusion mutant G05ΔphzΔprn::lacZ and E. coli S17- 1 (pUT/mini-Tn5Kan). By cloning and sequencing of the transposon-flanking DNA fragment, we found that a vfr gene in the conjugant G05W02 was disrupted with mini-Tn5Kan. In one other previous study on P. fluorescens, however, it was reported that the deletion of the vfr caused increased production of pyrrolnitrin and other antifungal metabolites. To confirm its regulatory function, we constructed the vfr-knockout mutant G05Δvfr and G05ΔphzΔprn::lacZΔvfr. By quantifying β-galactosidase activities, we found that deletion of the vfr decreased the prn operon expression dramatically. Meanwhile, by quantifying pyrrolnitrin production in the mutant G05Δvfr, we found that deficiency of the Vfr caused decreased pyrrolnitrin production. However, production of phenazine-1-carboxylic acid was same to that in the wild-type strain G05. Taken together, Vfr is required for pyrrolnitrin but not for phenazine-1-carboxylic acid biosynthesis in P. chlororaphis G05.

LasR Might Act as an Intermediate in Overproduction of Phenazines in the Absence of RpoS in Pseudomonas aeruginosa

( Qiuning He ),( Zhibin Feng ),( Yanhua Wang ),( Kewen Wang ),( Kailu Zhang ),( Le Kai ),( Xiuying Hao ),( Zhifen Yu ),( Lijuan Chen ),( Yihe Ge ) 한국미생물생명공학회(구 한국산업미생물학회) 2019 Journal of microbiology and biotechnology Vol.29 No.8

As an opportunistic bacterial pathogen, Pseudomonas aeruginosa PAO1 contains two phenazineproducing gene operons, phzA1B1C1D1E1F1G1 (phz1) and phzA2B2C2D2E2F2G2 (phz2), each of which is independently capable of encoding all enzymes for biosynthesizing phenazines, including phenazine-1-carboxylic acid and its derivatives. Other previous study reported that the RpoS-deficient mutant SS24 overproduced pyocyanin, a derivative of phenazine-1- carboxylic acid. However, it is not known how RpoS mediates the expression of two phz operons and regulates pyocyanin biosynthesis in detail. In this study, with deletion of the rpoS gene in the PAΔphz1 mutant and the PAΔphz2 mutant respectively, we demonstrated that RpoS exerted opposite regulatory roles on the expression of the phz1and phz2 operons. We also confirmed that the phz1 operon played a critical role and especially biosynthesized much more phenazines than the phz2 operon when the rpoS gene was knocked out in P. aeruginosa. By constructing the translational reporter fusion vector lasR’-’lacZ and the chromosomal fusion mutant PAΔlasR::lacZ, we verified that RpoS deficiency caused increased expression of lasR, a transcription regulator gene in a first quorum sensing system (las) that activates overexpression of the phz1 operon, suggesting that in the absence of RpoS, LasR might act as an intermediate in overproduction of phenazine biosynthesis mediated by the phz1 operon in P. aeruginosa.