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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.
Huifang Wang,Shiping Liang,TaoMa,Qiang Xiao,Panrong Cao,Xuan Chen,Wenquan Qin,Hongpeng Xiong,Zhaohui Sun,XiujunWen,Cai Wang 한국응용곤충학회 2018 Journal of Asia-Pacific Entomology Vol.21 No.2
Ectropis grisescens Warren (Lepidoptera: Geometridae) is an important defoliator pest of the tea plant, Camellia sinensis L. Our previous studies showed that E. grisescens pupae had significantly lower body water content when they pupated in the dry soil (20%-moisture) than those that pupated in the wetter soil (50%- or 80%-moisture). However, it is still unclear whether low-moisture conditions during pupating would further influence the physiological and fitness traits of adults. In the present study, E. grisescens individuals were allowed to pupate in 20%-, 50%- or 80%-moisture soil (silt loam), or in containers without soil (no-substrate conditions) in the laboratory. No significant difference in emergence was detected among different pupating conditions. However, female moths that emerged from 20%-moisture soil had significantly lower body water content compared to 80%-moisture soil, whereas the body water content of males was similar among the four treatments. The paired moths that emerged from 20%-moisture soil laid significantly fewer eggs than those that emerged from 50%- moisture soil. In addition, the number of hatched offerings (larvae) were significantly less when the adults previously pupated in no-soil containers compared to 50%-moisture soil. The longevity of adults was shortest when they emerged from 20%-moisture soil. Our study showed that the no-substrate and low-moisture conditions during pupating adversely affected E. grisescens adults.
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.
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.
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.
Hongpeng Lai,Tengteng Wang,Zuo Kang,Rui Chen,Qiuyang Hong 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7
As an increasing number of metro lines have been planned or executed in urban area, new tunnel undercrossing existing tunnels has been commonly practiced. Construction of the existing tunnel causes disturbance to the surrounding soil and hence affects the operational parameters of undercrossing tunneling especially the chamber pressure of EPB machine. However, very limited research studies this effect. To fill the gap of knowledge, this paper proposed a new method for calculating the chamber pressure of EPB tunneling machine in undercrossing project. First, the effect of existing tunnel on surrounding soil is classified as removal-and-replacement effect, excavation-induced-disturbance effect, and elastic foundation beam effect. Second, based on analysis of the mutual interaction between existing tunnel and the undercrossing tunneling, three zones have been identified to study the chamber pressure of EPB machine. Next, a new method is proposed to calculate the chamber pressure in the process of undercrossing existing tunnel. Finally, the proposed method has been verified with measured data from two engineering cases. The comparison results show that the proposed method is in good agreement with the measured data, indicating that it is reasonable with high accuracy.