Grid integrated renewable DG systems: A review of power quality challenges and state-of-the-art mitigation techniques

In this paper, the simulation results of using a static synchronous compensator (STATCOM) to achieve damping improvement of an offshore wind farm (OWF) fed to a multi-machine system is presented. The operating performance of the studied OWF is simulated by an equivalent aggregated doubly-fed induction generator (DFIG) driven by an equivalent aggregated wind turbine (WT) through an equivalent gearbox. A PID damping controller and a hybrid PID plus fuzzy logic controller (FLC) of the proposed STATCOM are designed to contribute adequate damping characteristics to the dominant modes of the studied system under various operating conditions. A frequency-domain approach based on a linearized system model using root-loci technique and a time-domain scheme based on a nonlinear system model subject to a three-phase short-circuit fault at the connected bus are systematically performed to examine the effectiveness of the proposed control schemes. It can be concluded from the comparative simulated results that the proposed STATCOM joined with the designed hybrid PID plus FLC is shown to be superior for improving the stability of the studied system subject to a severe disturbance than the PID controller.

Stability Enhancement of DFIG-Based Offshore Wind Farm Fed to a Multi-Machine System Using a STATCOM

This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a $\mathbf{100\;{\rm MW}}$ DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation.

SSR Damping Controller Design and Optimal Placement in Rotor-Side and Grid-Side Converters of Series-Compensated DFIG-Based Wind Farm

India is considering renewable energy resources (RES) like solar and wind as alternative for future energy needs. As on March 31, 2012 the grid interactive power generation from RES is 24914 MW i.e. around 12.1 % of the total installed energy capacity. Further Ministry of New and Renewable Energy (MNRE), Government of India is targeting to achieve 20000 MW grid interactive power through solar and 38500 MW from wind by 2022. However there are various issues related to grid integration of RES keeping in the view of aforesaid trends it becomes necessary to investigate the possible solutions for these issues. Integration of renewable energy sources to utility grid depends on the scale of power generation. Large scale power generations are connected to transmission systems where as small scale distributed power generation is connected to distribution systems. There are certain challenges in the integration of both types of systems directly. This paper presents the some issues and challenges encountered during grid integration of different renewable energy sources with some possible solutions.

Grid integration of renewable energy sources: Challenges, issues and possible solutions

This paper presents a review on grid Integration and power quality issues associated with the integration of renewable energy systems in to grid and Role of power electronic devices and Flexible AC Transmission Systems related to these Issues. In this paper, recent trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented. Classification of various Power Quality Issues used by different researchers has been done and put for reference. Application of various techniques as applied to mitigate the different Power Quality problems is also presented for consideration. Power Electronics interface not only plays a very important role in efficient integration of Wind and Solar energy system but also to its effects on the power-system operation especially where the renewable energy source constitutes a significant part of the total system capacity. However there are various issues related to grid integration of RES keeping in the view of aforesaid trends it becomes necessary to investigate the possible solutions for these issues.

Grid integration and power quality issues of wind and solar energy system: A review

This paper presents a novel control scheme using a variable frequency transformer (VFT) of 100 MW to effectively reduce power fluctuations of an equivalent 80-MW aggregated doubly-fed induction generator (DFIG)-based offshore wind farm (OWF) connected to an onshore 120-kV utility grid. The q-d axis equivalent-circuit model is employed to establish the mathematical models for the VFT and the OWF to derive the complete dynamic equations of the studied system under three-phase balanced conditions. A frequency-domain approach based on a linearized system model using eigen techniques and a time-domain scheme based on a nonlinear system model subject to disturbance conditions are both performed to examine the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed VFT is effective to smooth the fluctuating active power of the OWF injected into the power grid while the damping of the studied OWF can also be improved.

Reduction of Power Fluctuations of a Large-Scale Grid-Connected Offshore Wind Farm Using a Variable Frequency Transformer

Background Colorectal endoscopic submucosal dissection (ESD) is a complex operation. Effective traction is crucial. We have successfully used an orthodontic rubber band (ORB) combined with the clip traction method to assist ESD (ORB-ESD). The aim of this retrospective study is to describe the method and to compare the efficacy and safety of ORB-ESD versus conventional ESD in the treatment of superficial colorectal tumors. Methods We retrospectively analyzed the data of patients with superficial colorectal tumor (with diameter ≥ 20 mm) who received either ORB-ESD (n = 34) or conventional ESD (n = 90) between January 2019 and September 2020. Propensity score matching (PSM) was used to match the clinical data of 31 pairs of patients in each group. Results Operation time was significantly shorter for ORB-ESD than for conventional ESD (34.5 minutes vs. 56 minutes, P ≤ 0.001). In the propensity-matched cohorts, the operation time remained significantly shorter in the ORB-ESD patients (35 minutes vs. 50 minutes, P = 0.001). Postoperative adverse events, en bloc resection rate, and R0 resection rate were comparable between the two groups (P > 0.05), both before and after propensity score matching. In the ORB subgroup analysis, the trainee and expert ESD operation times were similar (37 (26–53) vs. 33.5 (26–37) minutes, respectively; P = 0.274). Conclusion ORB-ESD appears to be an effective technique for ESD of colorectal cancer. Our findings need to be confirmed in large prospective multicenter studies.

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Orthodontic Rubber Band-Assisted Endoscopic Submucosal Dissection: An Efficient Method for Treating Superficial Colorectal Tumors

Abstract Background and aims Effective traction is an important prerequisite for successful endoscopic submucosal dissection (ESD). The combined orthodontic rubber band (ORB) and clip method was effective in colorectal cancer ESD. To date, the method was not reported in gastric ESD. This study aimed to investigate its efficacy and safety for gastric neoplasms ESD. Methods We retrospectively analyzed data of 118 patients with gastric neoplasms treated by ESD from November 2020 to April 2022, 43 by ORB-ESD and 75 by the conventional ESD. The primary outcome measure was the ESD procedure time. Clinical data on efficacy and safety were also collected and analyzed. Propensity score matching (PSM) matched the patients in both groups. Results PSM successfully matched 31 pairs of patients. The ORB-ESD operation time was shorter (median [interquartile range], 35 [30–48] vs. 49 [40–70] min, P &lt; 0.001) and dissection speed was higher (median [interquartile range], 22.6 [14.4–29.3] vs. 13.5 [9.6–17.9] mm 2 /min, P &lt; 0.001) than in the conventional ESD. The groups were similar in muscular injury rate, frequency and time of use of thermal hemostatic forceps, postoperative adverse events, en bloc resection, and R0 resection rate ( P &gt; 0.05). Conclusions Compared to the conventional ESD, ORB-ESD significantly reduced the procedure time and increased the dissection speed, proving beneficial to gastric ESD. 

https://bmcgastroenterol.biomedcentral.com/counter/pdf/10.1186/s12876-022-02606-1

Usefulness of the combined orthodontic rubber band and clip method for gastric endoscopic submucosal dissection

The term “submucosal tumors” generally refers to colorectal uplifted lesions with a complete upper mucosal cortex, including lipomas, stromal tumors, lymphomas, and neuroendocrine tumors [1]. Approximately 13% of gastrointestinal submucosal tumors are malignant. Endoscopic ultrasonography (EUS) is the first choice of modality for the diagnosis of submucosal tumors [2]. Here we report an unusual case of a submucosal fecalith mimicking a submucosal tumor of the appendix. A 74-year-old woman who had been experiencing right lower abdominal pain for more than 3 months was admitted to our hospital for evaluation of a submucosal “tumor” of the appendix that had been identified 1 month previously. It has been difficult to histologically diagnose subepithelial abnormalities of the appendix by means of endoscopic biopsy. However endoscopic ultrasound (EUS) can be used to complete the scanning of appendiceal lesions, and this has been of great significance in the observation of subepithelial appendiceal lesions. A linear-array echoendoscope was placed at the opening of the appendix. By means of the ultrasound-guidedmirror insertion method, a raised lesion was observed in the appendix, with a section size of 14.3×8.9mm, raising the possibility that the appendiceal lesionmight be a submucosal fecalith (▶Fig. 1). Although laparoscopic appendectomy has always been the main treatment option for acute appendicitis caused by appendiceal fecaliths, Salminen et al. showed that the complication rate associated with this surgery could be as high as 20% [3]. With the gradual development of endoscopic technology, endoscopic appendectomy lithotomy has also been occasionally reported [4]. We therefore employed endoscopic submucosal dissection, aided by traction applied using a clip with rubber band, to remove the appendiceal submucosal fecalith. This improved the accuracy of the endoscopic appendectomy in removing the fecalith and avoided damage to the intestinal wall (▶Fig. 2, ▶Video 1). Finally the patient recovered well and was discharged, and showed no abdominal pain during follow-up. Submucosal fecaliths mimicking submucosal tumors of the appendix have been rarely reported in clinical practice. PreE-Videos

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Long-Yi Chen

Papers

Reduction of Power Fluctuations of a Large-Scale Grid-Connected Offshore Wind Farm Using a Variable Frequency Transformer

Orthodontic Rubber Band-Assisted Endoscopic Submucosal Dissection: An Efficient Method for Treating Superficial Colorectal Tumors

Usefulness of the combined orthodontic rubber band and clip method for gastric endoscopic submucosal dissection

Application of rubber band and clip traction for removal of a submucosal fecalith mimicking a submucosal tumor of the appendix under colonoscopy

Antimicrobial prophylaxis in patients undergoing endoscopic mucosal resection for 10- to 20-mm colorectal polyps: A randomized prospective study