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A Virtual Inertia Control Strategy Based on Multi-order lead-lag Compensation
Haizhen Xu,Changzhou Yu,Chun Liu,Qinglong Wang,Xing Zhang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
In view of the contradiction between active power steady-state and dynamic characteristics regulation of VSG based on the existing first-order virtual inertia algorithm operating in grid- connected mode and multiparalleled mode, a virtual inertia control strategy based on multi-stage lead-lag compensation is proposed in this paper. By cascading a multi-stage lead-lag link in the first -order virtual inertia forward channel, the control freedom of VSG grid-connected and paralleled system is increased, so that the zero and poles can be freely configured. Furthermore, a firstorder lead-lag link is taken as an example to analyze its effect on the output active power steady-state and dynamic characteristics of VSG grid-connected system and paralleled systems. Through reasonable configuration of the secondorder virtual inertia parameters, the system damping ratio can be increased and the power oscillation can be eliminated while its steady-state characteristics are not changed under the circumstance of a large inertia. Experimental results verify the effectiveness of the proposed strategy.
Stability Comparison of Paralleled String Inverters and Central Inverters in PV System
Changzhou Yu,Haizhen Xu,Chun Liu,Qinglong Wang,Xing Zhang,Fang Liu,Fei Li 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Mega-scale solar projects are turning to string inverters nowadays. Multi-parallel string inverters are employed as the interface to the utility grid, giving rise to potential unstable problems. Aiming at this issue, the relationship between number of inverters, output power and grid impedance is analyzed. Based on this, according to different topology, control structures and filter parameters, four types of Standard Equivalent Model (SEM) for multiinverters system are established. By analyzing the stability margin of the four SEMs and the sensitivity of their control parameters, the difference of stability between the string inverters and the central inverters is compared. Finally, the established SEM and the comparison results of the string and central inverters are verified by simulation and experimental results.
Rongliang Shi,Xing Zhang,Haizhen Xu,Fang Liu,Wenchao Li,Fubin Mao,Yong Yu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper proposes a novel seamless transfer method for microgrid connected fuel cell inverters (FCIs) between voltage source and current source modes. In order to protect the fuel cell, the FCI output power should be restricted when the microgrid frequency is greatly disturbed. In this sense, the FCI is transfered from voltage source mode to constant current source mode. Meanwhile, the FCI is transfered from constant current source mode to voltage source mode until service can be restored. The proposed method can cooperatively work with well developed virtual synchronous generator (VSG) control algorithm so that these FCIs are able to share load among them as well as subsist under transient events of the system. Theoretical analysis and experimental results validate effectiveness of the proposed method.
Ming Ou,Lin Ma,Limei Xu,Zhuomei Yang,Haizhen Li 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.10
Cobalt-doped MoSe2/nitrogenated graphene composite has been successfully synthesized via a facile hydrothermal route and is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Raman spectrum. The results reveal that Co-doped MoSe2 nanosheets which are characteristic of few layers (2–4 layers) and abundant exposed active edge sites are well anchored on the nitrogen-doped graphene sheets to constitute robust composites. When evaluated as catalysts for HER, the obtained composites demonstrate superior electrocatalytic activities toward HER.
Zuo, Chaohui,Xia, Man,Liu, Jingshi,Qiu, Xiaoxin,Lei, Xiong,Xu, Ruocai,Liu, Hanchun,Li, Jianliang,Li, Yongguo,Li, Qinglong,Xiao, Hua,Hong, Yuan,Wang, Xiaohong,Zhu, Haizhen,Wu, Qunfeng,Burns, Michael,Li Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.1
Objectives: Intrahepatic recurrence is the major cause of death among patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) after curative surgical resection. Several approaches have been reported to decrease the recurrence rate. The objective of our study was to compare the clinical effects of transcatheter arterial chemoembolization (TACE) combined with interferon-alpha (IFN-${\alpha}$) therapy on recurrence after hepatic resection in patients with HBV-related HCC with that of TACE chemotherapy alone. Methods: We retrospectively analyzed the data from 228 patients who were diagnosed with HBV-related HCC and underwent curative resection between January 2001 to December 2008. The patients were divided into TACE (n = 126) and TACE-IFN-${\alpha}$ (n = 102) groups for postoperative chemotherapy. The TACE regimen consisted of 5-fluorouracil (5-FU), cisplatin (DDP), and the emulsion mixed with mitomycin C (MMC) and lipiodol. The recurrence rates, disease-free survival (DFS), overall survival (OS), and risk of recurrence were evaluated. Results: The clinicopathological parameters and adverse effects were similar between the 2 groups (P > 0.05). The median OS for the TACE-IFN-${\alpha}$ group (36.3 months) was significantly longer than that of the TACE group (24.5 months, P < 0.05). The 3-and 5-year OS for the TACE-IFN-${\alpha}$ group were significantly longer than those of the TACE group (P < 0.05) and the recurrence rate was significantly lower (P < 0.05). The TACE and IFN-${\alpha}$ combination therapy, active hepatitis HBV infection, the number of tumor nodules, microvascular invasion, liver cirrhosis, and the BCLC stage were independent predictors of OS and DFS. Conclusions: The use of the TACE and IFN-${\alpha}$ combination chemotherapy after curative hepatic resection safely and effectively improves OS and decreases recurrence in patients with HBV-related HCC who are at high risk. Our findings can serve as a guide for the selection of postoperative adjuvant chemotherapy for patients with HBV-related HCC who are at high risk of recurrence.