LINE SIDE HARMONIC ANALYSIS OF SINGLE-PHASE DIODE BRIDGE RECTIFIER WITH A DC FILTER CAPACITOR

Jinjun Liu,Zhaoan Wang 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-

Single-phase diode bridge rectifiers with dc filter capacitor usually operate in discontinuous mode and generate large amounts of harmonic currents. This paper presents a precise harmonic analysis of the line side current in the case that both the filter inductor and the filter capacitor are not infinite. The analytical expressions of the line side performance parameters associated with harmonics are derived The curves that show the relationship of these parameters as the functions of circuit parameters are illustrated. By simulation the results are verified to be accurate and the conclusion clearly reveals the relations between the line side performance parameters and circuit parameters.

Generalized Stability Criterion for Multi-module Distributed DC System

Liu, Fangcheng,Liu, Jinjun,Zhang, Haodong,Xue, Danhong The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.1

The stability issues of a multi-module distributed DC power system without current-sharing loop are analyzed in this study. The physical understanding of the terminal characteristics of each sub-module is focused on. All the modules are divided into two groups based on the different terminal property types, namely, impedance (Z) and admittance (Y) types. The equivalent circuits of each group are established to analyze the stability issues, and the mathematical equations of the equivalent circuits are derived. A generalized criterion for multi-module distributed systems is proposed based on the stability criterion in a cascade system. The proposed criterion is independent of the power flow direction.

Power Electronics for Electric Utilities and Micro-Grids : A Perspective from China

Jinjun Liu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

On the Control of Active Power Filters

LIU Jinjun,WANG Xiaoyu,YUAN Chang,WANG Zhaoan 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

This paper compares the popular control methods for two dominant types of active power filters (APFs). With the equivalent transformation of their control diagrams, the recently proposed current-source control method for series active power filter (SAPF) is revealed to have the same control structure as the traditional voltage-source control method therefore have same compensation performances. Similarly, two kinds of popular control methods for parallel active power filter (PAPF) are also compared and found to have the similar control structure. The recently proposed PAPF control scheme without harmonics detection is revealed as a reduced version of the traditional control scheme with harmonics detection. Therefore both have same basic control principles regarding load current harmonics compensation. A general expression of the control methods for PAPF is then proposed in the form of both a control diagram and a set of equations based on current detection. With a particular set of filter gains of the three detected currents, each particular control scheme can be specifically identified and described by the general expression. Subsequently the 64 possible sets of filter gains are examined by the proposed necessary conditions to locate practically valid control schemes. Finally 4 valid control schemes come out and among which some are schemes that have never been reported before. With the comprehensive comparison of the control methods and the proposed general expression in this paper, the essential relationships of the control methods are revealed, some misinterpretations from previous publications are clarified, and some new control schemes are obtained.

Unified Control based Seamless Transfer of Microgrids

Zeng Liu,Jinjun Liu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The microgrid must be able to transfer from grid-connected mode into islanding operation mode seamlessly to guarantee the power reliability for the critical local load. In the grid-tied mode, the power exchanged with the main grid should be smoothed to reduce the disturbance to the main grid, while the quality of the bus voltage in the islanding operation mode is significant. This paper presents a unified control strategy for microgrid to achieve above goals, where the microgrid is configured by a master distributed generator (DG) and several slave DGs and the control structures of them are not switched during the transfer of the operation mode. The control strategy is verified by the experimental results.?

A novel droop control strategy to share power equally and limit voltage deviation

Ting Liu,Jinjun Liu,Xuan Zhang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

A novel droop control strategy for controlling parallel inverters is proposed in this paper. In this paper, the reactive power versus PCC voltage droop is introduced, and then output reactive power of the inverters is adjusted to be equal. When load is changed greatly in microgrid, the voltage frequency and amplitude deviate from normal values greatly. By adaptively adjusting the droop position of some large capacity inverters, it can share active and reactive power equally among inverters and limit the frequency and voltage amplitude deviations in a certain margin. The analysis and the design procedure are provided explicitly. Simulation and experiment results validate the proposed control strategy.

Generalized Stability Criterion for Multi-module Distributed DC System

Fangcheng Liu,Jinjun Liu,Haodong Zhang,Danhong Xue 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.1

The stability issues of a multi-module distributed DC power system without current-sharing loop are analyzed in this study. The physical understanding of the terminal characteristics of each sub-module is focused on. All the modules are divided into two groups based on the different terminal property types, namely, impedance (Z) and admittance (Y) types. The equivalent circuits of each group are established to analyze the stability issues, and the mathematical equations of the equivalent circuits are derived. A generalized criterion for multi-module distributed systems is proposed based on the stability criterion in a cascade system. The proposed criterion is independent of the power flow direction.

Culture-Positive Spontaneous Ascitic Infection in Patients with Acute Decompensated Cirrhosis: Multidrug-Resistant Pathogens and Antibiotic Strategies

Jing Liu,Yanhang Gao,Xianbo Wang,Zhiping Qian,Jinjun Chen,Yan Huang,Zhongji Meng,Xiaobo Lu,Guohong Deng,Feng Liu,Zhiguo Zhang,Hai Li,Xin Zheng 연세대학교의과대학 2020 Yonsei medical journal Vol.61 No.2

Purpose: This study investigated multidrug-resistant (MDR) pathogens and antibiotic strategies of culture-positive spontaneousascitic infection (SAI) in patients with acute decompensated cirrhosis. Materials and Methods: We retrospectively analyzed 432 acute decompensated cirrhotic patients with culture-positive SAI from11 teaching hospitals in China (January 2012 to May 2018). A Cox proportional hazards model analysis was conducted to identifyindependent predictors of 28-day mortality. Results: A total of 455 strains were isolated from 432 ascitic culture samples. Gram-negative bacteria (GNB), gram-positive bacteria(GPB), and fungi caused 52.3, 45.5, and 2.2% of all SAI episodes, respectively. Episodes were classified as nosocomial (41.2%), healthcare-related (34.7%), and community-acquired (24.1%). Escherichia coli (13.4%) and Klebsiella pneumoniae (2.4%) were extendedspectrumβ-lactamase producing isolates. The prevalence of methicillin-resistant Staphylococcus aureus was 1.1%. Ceftazidime,cefepime, aztreonam, and amikacin were recommended as first-line antibiotics agents for non-MDR GNB infections; piperacillin/tazobactam and carbapenems for MDR GNB in community-acquired and healthcare-related or nosocomial infections, respectively;and vancomycin or linezolid for GPB infections, regardless of drug-resistance status. Multivariate analysis revealed days ofhospital stay before SAI, upper gastrointestinal bleeding, white blood cell count, alanine aminotransferase, serum creatinine concentration,total bilirubin, and international normalized ratio as key independent predictors of 28-day mortality. Conclusion: MDR pathogens and antibiotic strategies were identified in patients with acute decompensated cirrhosis with culture-positive SAI, which may help optimize therapy and improve clinical outcomes.

Load Power Estimation Based Secondary Control for Microgrids

Teng Wu,Jinjun Liu,Zeng Liu,Shike Wang,Baojin Liu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The well-known active power-frequency and reactive power-voltage amplitude droop control is widely used in the coordinative control of parallel inverters in microgrids. However, this conventional droop method may cause frequency and voltage deviation, which affects the accuracy of power supply. This paper proposes a novel secondary control strategy to compensate this deviation. This strategy mimics the Master-Slave control but requires no communication lines among the parallel inverters. The master inverter adopts conventional droop method (using power to control frequency and voltage amplitude) and is controlled as a voltage source while the slave inverters adopt reversed droop method (using frequency and voltage amplitude to control power) and are controlled as current sources. The droop characteristic bias of slave inverters is designed online based on the estimation of load power demand. Through this method, frequency and voltage deviation can be eliminated and power sharing can be realized among all the slave inverters. Simulation and experimental results are provided to prove the effectiveness of the proposed control strategy.

Active vibration control based on modal controller considering structure-actuator interaction

Jinjun Jiang,Weijin Gao,Liang Wang,Zhaohua Teng,Yongguang Liu 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.8

Active vibration control to suppress structural vibration of the flexible structure is investigated based on a new control strategy considering structure-actuator interaction. The experimental system consists of a clamped-free rectangular plate, a controller based on modal control switching, and a magnetostrictive actuator utilized for suppressing the vibrations induced by external excitation. For the flexible structure, its deformation caused by the external actuator will affect the active control effect. Thus interaction between structure and actuator is considered, and the interaction model based on magnetomechanical coupling is incorporated into the control system. Vibration reduction strategy has been performed resorting to the actuator in optimal position to suppress the specified modes using LQR (linear quadratic regulator) based on modal control switching. The experimental results demonstrate the effectiveness of the proposed methodology. Considering structure-actuator interaction (SAI) is a key procedure in controller design especially for flexible structures.