A Modified Single-Phase Transformerless Z-Source Photovoltaic Grid-Connected Inverter

Hongpeng Liu,Guihua Liu,Yan Ran,Gaolin Wang,Wei Wang,Dianguo Xu 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

In a grid-connected photovoltaic (PV) system, the traditional Z-source inverter uses a low frequency transformer to ensure galvanic isolation between the grid and the PV system. In order to combine the advantages of both Z-source inverters and transformerless PV inverters, this paper presents a modified single-phase transformerless Z-source PV grid-connected inverter and a corresponding PWM strategy to eliminate the ground leakage current. By utilizing two reversed-biased diodes, the path for the leakage current is blocked during the shoot-through state. Meanwhile, by turning off an additional switch, the PV array is decoupled from the grid during the freewheeling state. In this paper, the operation principle, PWM strategy and common-mode (CM) characteristic of the modified transformerless Z-source inverter are illustrated. Furthermore, the influence of the junction capacitances of the power switches is analyzed in detail. The total losses of the main electrical components are evaluated and compared. Finally, a theoretical analysis is presented and corroborated by experimental results from a 1-kW laboratory prototype.

Droop Control Scheme of a Three-phase Inverter for Grid Voltage Unbalance Compensation

Liu, Hongpeng,Zhou, Jiajie,Wang, Wei,Xu, Dianguo The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.4

The stability of a grid-connected system (GCS) has become a critical issue with the increasing utilization of renewable energy sources. Under grid faults, however, a grid-connected inverter cannot work efficiently by using only the traditional droop control. In addition, the unbalance factor of voltage/current at the common coupling point (PCC) may increase significantly. To ensure the stable operation of a GCS under grid faults, the capability to compensate for grid imbalance should be integrated. To solve the aforementioned problem, an improved voltage-type grid-connected control strategy is proposed in this study. A negative sequence conductance compensation loop based on a positive sequence power droop control is added to maintain PCC voltage balance and reduce grid current imbalance, thereby meeting PCC power quality requirements. Moreover, a stable analysis is presented based on the small signal model. Simulation and experimental results verify the aforementioned expectations, and consequently, the effectiveness of the proposed control scheme.

Droop Control Scheme of a Three-phase Inverter for Grid Voltage Unbalance Compensation

Hongpeng Liu,Jiajie Zhou,Wei Wang,Dianguo Xu 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.4

The stability of a grid-connected system (GCS) has become a critical issue with the increasing utilization of renewable energy sources. Under grid faults, however, a grid-connected inverter cannot work efficiently by using only the traditional droop control. In addition, the unbalance factor of voltage/current at the common coupling point (PCC) may increase significantly. To ensure the stable operation of a GCS under grid faults, the capability to compensate for grid imbalance should be integrated. To solve the aforementioned problem, an improved voltage-type grid-connected control strategy is proposed in this study. A negative sequence conductance compensation loop based on a positive sequence power droop control is added to maintain PCC voltage balance and reduce grid current imbalance, thereby meeting PCC power quality requirements. Moreover, a stable analysis is presented based on the small signal model. Simulation and experimental results verify the aforementioned expectations, and consequently, the effectiveness of the proposed control scheme.

A Modified Single-Phase Transformerless Z-Source Photovoltaic Grid-Connected Inverter

Liu, Hongpeng,Liu, Guihua,Ran, Yan,Wang, Gaolin,Wang, Wei,Xu, Dianguo The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

In a grid-connected photovoltaic (PV) system, the traditional Z-source inverter uses a low frequency transformer to ensure galvanic isolation between the grid and the PV system. In order to combine the advantages of both Z-source inverters and transformerless PV inverters, this paper presents a modified single-phase transformerless Z-source PV grid-connected inverter and a corresponding PWM strategy to eliminate the ground leakage current. By utilizing two reversed-biased diodes, the path for the leakage current is blocked during the shoot-through state. Meanwhile, by turning off an additional switch, the PV array is decoupled from the grid during the freewheeling state. In this paper, the operation principle, PWM strategy and common-mode (CM) characteristic of the modified transformerless Z-source inverter are illustrated. Furthermore, the influence of the junction capacitances of the power switches is analyzed in detail. The total losses of the main electrical components are evaluated and compared. Finally, a theoretical analysis is presented and corroborated by experimental results from a 1-kW laboratory prototype.

Synthesis of (co-)polyethylene with broad molecular weight distribution by the heterogenous Ziegler–Natta catalysts via one-pot strategy

Zhi Liu,Xinli Zhang,Haibing Huang,Jianjun Yi,Wei Liu,Weijiao Liu,Hongpeng Zhen,Kejing Gao,Mingge Zhang,Wantai Yang,Qigu Huang 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.6

A new method was presented for preparing (co-)polyethylene with broad molecular weight distribution (MWD) and high molecular weight employed by the novel heterogeneous Ziegler–Natta catalysts via one-pot strategy. The preparation of these catalysts involved the introduction of alkoxy silane compounds as electron donors. The influences of the electron donors structure, as well as polymerization conditions such as temperature, molar ratio of Al/Ti, ethylene pressure and the concentration of 1-hexene in feed on the polymerization performance for ethylene (co-)polymerization, were investigated. The morphology of the catalyst particles was characterized by SEM and Ti content of these catalysts was characterized by ICP. The GPC results showed that the obtained homopolyethylene and ethylene/1-hexene copolymer had the widest molecular weight distribution up to ca 50 when diethoxy-isopropoxy-(t–butoxy)-silane (ED3) was used as internal electron donor. The 13C NMR and FT-IR analysis indicated that these catalysts efficiently catalyzed the copolymerization of ethylene with 1-hexene.

Dynamic Process Elimination Control Strategy based on Super-Twisting Algorithm for Droop-Controlled Grid-Connected Inverter

Wei Zhang,Hongpeng Liu,Wei Wang,Frede Blaabjerg 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Droop-controlled inverter can operate in both islanded and grid-connected mode without reconfiguring the control structure, which can achieve a seamless transfer between both modes. The traditional double-loop structure based on proportional resonant controller is usually utilized to regulate a drooped voltage across local loads or inject power to the grid, but the dynamic process of load variation and mode transfer can hardly be satisfied. To solve this issue, a based super-twisting algorithm double-loop has been proposed here, which not only improve the dynamic process of mode transfer, but is also robust to the system parameters mismatch. Simulation and experimental results validate the correctness and feasibility of the proposed method.

A Study on the Formation Mechanism and Calculation Method of Surrounding Rock Pressure in Shallow-buried Loess Tunnel Considering the Influence of Vertical Joints

Mingkun Zhao,Hongpeng Lai,Yuyang Liu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.4

Vertical joints have significant effects on the stability of shallow-buried loess tunnel. Due to the presence of vertical joints distributed widely in loess, the formation mechanisms of surrounding rock pressure on shallow-buried loess tunnel and its computational method are far different from those in other types of soil tunnel. In this study, the distribution characteristics of surrounding rock pressure in shallow-buried loess tunnel were investigated, and discrete element software 3DEC was used to analyze the formation mechanism and development process of surrounding rock pressure in loess tunnel under the influence of joints. We correlated the stratum deformation characteristic with the frictional force caused by the mutual dislocation between joints, and revised the semi-empirical method (Chinese Code methods) in China. The results show that the measured data of radial surrounding rock pressure of shallow-buried loess tunnel are generally between 0 − 600 kPa, and 80% in the range of 0 − 200 kPa. The surrounding rock pressure increases with the burial depth, while the distribution of lateral pressure coefficient is relatively discrete. The existence of loess vertical joints (LVJs) aggravates the uneven distribution of the vertical pressure above the tunnel, and the reduction of the lateral earth pressure coefficient at rest under the influence of joints leads to an increase in pressure near the arch shoulder, these two constitute the essence of the joints action on the surrounding rock pressure. The surrounding rock pressure of the shallow-buried loess tunnel reaches the peak stress at about 0.5D from the tunnel face (D is the tunnel span), which is about 1.04 − 1.32 times of the initial stress. After the excavation of the upper step, the stress of the tunnel crown monitoring point decreased to about 60% of the initial stress. Compared with ignoring the influence of joints, the time of reaching the peak stress at the arch shoulder monitoring point is earlier, and the final stress release degree is smaller. The comparison of the analytical results (proposed method) with the numerical results and the field data exhibits good agreement, proving the proposed method's correctness.

Analysis of Power Losses in Z-Source PV Grid-Connected Inverter

Wang Wei,Liu Hongpeng,Zhang Jiawan,Xu Dianguo 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Calculating power losses of the inverter plays an important role for improving system efficiency and power density, designing heat dissipation system and selecting the power devices. Generally, power losses include the main switch losses (conducting losses and switching losses), the drive losses, control circuit losses and losses of inductor. Among them, the losses of semiconductor power switching devices are the largest losses. This paper analyzed the power losses of blocking diode, switching devices of H-bridge, Z-source inductor and filter inductor in detail, combined operating principle with modulation strategy. And the practical formula is deduced. The experimental results verified the proposed method.

Identification of genomic-wide genetic links between cutaneous melanoma and obesity-related physical traits via cFDR

Lin Shen,Shen Runnan,Huang Jingqian,Liu Yanhan,Li Hongpeng,Xu Qingfang 한국유전학회 2023 Genes & Genomics Vol.45 No.12

Background Both epidemiological and clinical studies have suggested the comorbidity between cutaneous melanoma (CM) and obesity-related physical traits. However, it remains unclear about their shared genetic architecture. Objective To determine the shared genetic architecture between CM and obesity-related physical traits through conditional false discovery rate (cFDR) analysis. Method Quantile–quantile plots were firstly built to assess the pleiotropic enrichment of shared single nucleotide polymorphisms between CM and each trait. Then, cFDR and conjunctional cFDR (ccFDR) were used to identify the shared risk loci between CM and each trait. Moreover, the functional evaluation of shared risk genes was carried out through analyses of expression quantitative trait loci (eQTL), Kyoto Encyclopedia of Genes and Genomes and gene ontology, respectively. Finally, single-cell sequence analysis was performed to locate the expression of eQTL-mapped genes in tissues. Results Successive pleiotropic enrichment was found between CM and 5 obesity-related traits or height. 24 shared risk loci were identified between CM and 13 traits except appendicular lean mass using ccFDR analysis, with 17 novel and 4 validated loci. The functions of ccFDR-identified and eQTL-mapped genes were revealed to be mainly involved in cellular senescence, proliferation, meiotic nuclear division, cell cycle, and the metabolism of lipid, cholesterol and glucose. Single-cell sequence analysis showed that keratinocytes contribute to the occurrence and aggressiveness of CM through secreting paracrine cytokines. Conclusion Our findings demonstrate the significant genetic correlation between CM and obesity-related physical traits, which may provide a novel genetical basis for the pathogenesis and treatment of CM.

Response surface analysis of energy balance and optimum condition for torrefaction of corn straw

Shuai Guo,Tiankuo Guo,Deyong Che,Hongpeng Liu,Baizhong Sun 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.5

Corn straw has potential as a biofuel, and is generated in large amounts globally. However, this potentialremains underutilized, and torrefaction is one of the processes that can be implemented to improve the energy grade ofthis biomass. In this study, three process parameters (temperature, heating rate, residence time) were investigated usinga response surface method to optimize the torrefaction process of corn straw. At 242.26 oC, a 60 min residence time,and 6.28 oC/min heating rate, the mass yield and higher heating value (HHV) reached their maximum values. Temperaturewas the most important factor influencing torrefaction, followed by residence time and then heating rate. Thegas and liquid by-products were measured by mass spectrometry and mass spectrometry-gas chromatography, and theheat demand of torrefaction was measured by thermogravimetric analysis-differential scanning calorimetry. The HHVof the by-products changed little before 240 oC but increased considerably as the temperature further increased. TheHHV at 242 oC was 1,273 kJ/kg. When the heat loss was 50%, 242 oC was the critical point of energy balance, and afterthat the torrefaction process was energy self-sufficient. These findings provide data to support the establishment ofsemi-industrial or industrial corn straw torrefaction devices.