Phase lag compensation for improving the stability of LCL‑type converters under weak grid condition

Jianfeng Wang,Guobing Pan,Jing Ouyang,Chengyao Liu,Yinghao Zhou,Gong Fei 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.5

LCL-type converters are widely used in the sustainable energy generation system due to their flexible current control strategies and high efficiency. The LCL filter has a resonance peak, which needs to be handled appropriately; otherwise, it causes system instability. Single-loop feedback control strategy is very popular at present; it does not require additional sensors to measure the state variables for active damping. Under weak grid condition, the resonance peak of LCL filter shifts to the left evidently and greatly reduces the stability margin; thus, maintaining the stability of single-loop control is a challenging task. This paper presents an improved grid current feedback (GCF) single-loop control strategy, which is designed to raise the stability margin of system to adapt weak grid condition. Low pass filter controller is used for phase lag compensation. A phase margin design method is proposed to ensure system stability, and the corresponding discrete method in z-domain has been proposed in detail. Experiments performed on a three-phase converter platform are finally presented to verify the effectiveness of the proposed phase lag compensation for GCF control strategy.

RC‑qTPWM method with high DC voltage utilization ratio and power balance for three‑phase CHB inverters

Jianfeng Liu,Renxi Gong,Yuanyuan Zhang 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.3

In this paper, a modified method named reconstructed carrier quasi-trapezoidal pulse width modulation (RC-qTPWM) isproposed to improve the DC voltage utilization ratio, decrease the line voltage total harmonic distortion (THD), and solve thepower imbalance among H-bridge units. The modulation method is based on two steps. In the first step, the quasi-trapezoidal wave obtained by an intercepting sine wave is used as the modulation wave to improve the DC voltage utilization ratio. In the second step, the carrier arrangement of the phase disposition is reconstructed to achieve a power balance among the H-bridge units. Carrier reconstruction is achieved by shifting a single triangular carrier in the horizontal and vertical directions. Through simulation and theoretical analysis, the selection method of the optimal sine coefficient δ and the principle of the carrier reconstruction are expounded, which shows that the optimal sine coefficient δ is 0.58 and that the power balance can be achieved within 3Tc. When compared with conventional TPWM methods, this modulation method has a higher DC voltage utilization ratio, a better efficiency, a smaller line voltage, a reduced current THD, and better power balance performance. Experimental results verify the correctness of the simulation and theoretical analysis, and the feasibility of the RC-qTPWM method.

A Novel Inverter Topology and its Power Balancing Optimization

Xue Bo,Gong Renxi,Liu Jianfeng,Zhang Zhiang 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3

Aiming at the problems of poor quality of the output voltage waveform of the existing multi-level inverters and many switching devices and DC power supplies, a novel cascadable basic unit topology is proposed. The proposed topology consists of three input DC power supplies and eight switches, forming an H half-bridge and an auxiliary bidirectional switch by adding 2 DC power supplies in the traditional H-bridge topology. The advantage of this topology is that it can be used in symmetric and asymmetric voltage source configurations, which can effectively extend the life of the inverters and reduce the production cost. The basic unit topology is cascaded in series to form a multilevel inverter topology to generate higher voltage levels, and its power balance strategy is proposed. The strategy can be described as follows: Firstly, several groups of pulse signals are generated by the traditional LS-PWM modulation strategy in which the modulation wave is compared with several groups of carriers, then a logic operation on the pulse signals is performed to obtain the drive signal of each switch, and the inverter is driven to achieve output power balance. A lot of Simulation and experiments verify the viability of the proposed topology and the effectiveness of the equalization strategy.

Laparoscopic surgery contributes to a decrease in short-term complications in surgical ulcerative colitis patients during 2008–2017: a multicenter retrospective study in China

Zerong Cai,Xiaosheng He,Jianfeng Gong,Peng Du,Wenjian Meng,Wei Zhou,Jinbo Jiang,Bin Wu,Weitang Yuan,Qi Xue,Lianwen Yuan,Jinhai Wang,Jiandong Tai,Jie Liang,Weiming Zhu,Ping Lan,Xiaojian Wu 대한장연구학회 2023 Intestinal Research Vol.21 No.2

Background/Aims: The aim of this study was to analyze the chronological changes in postoperative complications in surgical ulcerative colitis patients over the past decade in China and to investigate the potential parameters that contributed to the changes. Methods: Ulcerative colitis patients who underwent surgery during 2008–2017 were retrospectively enrolled from 13 hospitals in China. Postoperative complications were compared among different operation years. Risk factors for complications were identified by logistic regression analysis. Results: A total of 446 surgical ulcerative colitis patients were analyzed. Fewer short-term complications (24.8% vs. 41.0%, P=0.001) and more laparoscopic surgeries (66.4% vs. 25.0%, P<0.001) were found among patients who received surgery during 2014–2017 than 2008–2013. Logistic regression suggested that independent protective factors against short-term complications were a higher preoperative body mass index (odds ratio [OR], 0.870; 95% confidence interval [CI], 0.785–0.964; P=0.008), laparoscopic surgery (OR, 0.391; 95% CI, 0.217–0.705; P=0.002) and elective surgery (OR, 0.213; 95% CI, 0.067–0.675; P=0.009). The chronological decrease in short-term complications was associated with an increase in laparoscopic surgery. Conclusions: Our data revealed a downward trend of short-term postoperative complications among surgical ulcerative colitis patients in China during the past decade, which may be due to the promotion of minimally invasive techniques among Chinese surgeons.

Intraoperative inspection alone is a reliable guide to the choice of surgical procedure for enteroenteric fistulas in Crohn’s disease

( Zhen Guo ),( Xingchen Cai ),( Ruiqing Liu ),( Jianfeng Gong ),( Yi Li ),( Lei Cao ),( Weiming Zhu ) 대한장연구학회 2018 Intestinal Research Vol.16 No.2

Background/Aims: Resection of the diseased segment and suture of the victim segment is recommended for enteroenteric fistula in Crohn’s disease (CD). The main difficulty in this procedure remains reliable diagnosis of the victim segment, especially for fistulas found intraoperatively and inaccessible on endoscopic examination. We aimed to explore whether intraoperative inspection alone is reliable. Methods: Patients undergoing conservative surgery between 2011 and 2016 for enteroenteric fistulas complicating CD were identified from a prospectively maintained database. Patients were divided according to whether the victim segment was evaluated by preoperative endoscopy + intraoperative inspection (PI group) or by intraoperative inspection alone (I group). Outcomes were compared. Results: Of 65 patients eligible for the study, 37 were in in the PI group and 28 were in the I group. The baseline characteristics were similar between the groups, except for the rate of emergency surgery (0/37 in PI group vs. 5/28 in I group, P=0.012). Fistulas involved more small intestines (4/37 in PI group vs. 15/28 in I group, P< 0.001) and fewer sigmoid colons (17/37 in PI group vs. 4/28 in I group, P=0.008) in I group due to accessibility with endoscopy. No difference was found in postoperative complications, stoma rates, postoperative recurrence, or disease at the repair site between the 2 groups (P >0.05). Conclusions: For fistulas found intraoperatively and inaccessible on endoscopic examination, intraoperative inspection was a reliable guide when choosing between en bloc resection and a conservative procedure. (Intest Res 2018;16:282-287)

Fast-convergence trilinear decomposition algorithm for angle and range estimation in FDA-MIMO radar

Wang, Cheng,Zheng, Wang,Li, Jianfeng,Gong, Pan,Li, Zheng Electronics and Telecommunications Research Instit 2021 ETRI Journal Vol.43 No.1

A frequency diverse array (FDA) multiple-input multiple-output (MIMO) radar employs a small frequency increment across transmit elements to produce an angle-range-dependent beampattern for target angle and range detection. The joint angle and range estimation problem is a trilinear model. The traditional trilinear alternating least square (TALS) algorithm involves high computational load due to excessive iterations. We propose a fast-convergence trilinear decomposition (FC-TD) algorithm to jointly estimate FDA-MIMO radar target angle and range. We first use a propagator method to obtain coarse angle and range estimates in the data domain. Next, the coarse estimates are used as initialized parameters instead of the traditional TALS algorithm random initialization to reduce iterations and accelerate convergence. Finally, fine angle and range estimates are derived and automatically paired. Compared to the traditional TALS algorithm, the proposed FC-TD algorithm has lower computational complexity with no estimation performance degradation. Moreover, Cramer-Rao bounds are presented and simulation results are provided to validate the proposed FC-TD algorithm effectiveness.

Serial Frozen Fecal Microbiota Transplantation in the Treatment of Chronic Intestinal Pseudo-obstruction: A Preliminary Study

( Lili Gu ),( Chao Ding ),( Hongliang Tian ),( Bo Yang ),( Xuelei Zhang ),( Yue Hua ),( Yifan Zhu ),( Jianfeng Gong ),( Weiming Zhu ),( Jieshou Li ),( Ning Li ) 대한소화기기능성질환·운동학회(구 대한소화관운동학회) 2017 Journal of Neurogastroenterology and Motility (JNM Vol.23 No.2

Background/Aims Chronic intestinal pseudo-obstruction (CIPO) is a serious, life-threatening motility disorder that is often related to bacterial overgrowth. Fecal microbiota transplantation (FMT) results in restoration of the normal intestinal microbial community structure. We investigated the efficacy of FMT in the treatment of CIPO patients. Methods Nine patients (age 18-53 years) with CIPO were enrolled in this prospective, open-label study. Patients received FMT for 6 consecutive days through nasojejunal (NJ) tubes and were followed up for 8 weeks after treatment. We evaluated the rate of clinical improvement and remission, feeding tolerance of enteral nutrition, and CT imaging scores of intestinal obstructions. Lactulose hydrogen breath tests were performed before FMT and 8 weeks after FMT to evaluate for the presence small intestinal bacterial overgrowth (SIBO). Results FMT significantly alleviated bloating symptoms, and symptoms of pain were relieved 2 weeks after FMT. Enteral nutrition administered through a NJ tube after FMT was well-tolerated by 66.7% (6/9) of patients. CT scores of intestinal obstructions were significantly reduced after FMT (P = 0.014). SIBO was eliminated in 71.0% (5/7) of patients. Conclusions This pilot study demonstrated the safety of using FMT. FMT may relieve symptoms in selected patients with CIPO. FMT may also improve patient tolerance of enteral nutrition delivered via a NJ tube. (J Neurogastroenterol Motil 2017;23:289-297)