Stability Analysis of Fully Power Converter-based Microgrids

Due to rising energy demand and climate crisis, distributed energy generation utilizing the renewable energy resource is constantly evolving. Generation near the electrical loads within a defined boundary forms a microgrid. It can be operated by connecting with utility-grid or as a stand-alone system. Solar and wind energy resources use a power-electronic converter to interface with the load or grid. The fast dynamics of the converter is very different from the inertial dynamics of the grid with large synchronous machines. Furthermore, low short-circuit capacity, more resistive network and unbalanced loading are few inherent characteristics concerning the operational reliability of the microgrid. This thesis aims to present the various issues with fully power converter-based microgrids in terms of stability and protection. High-power converters with LCL-filter are simulated under various operating conditions in typhoon real-time simulator. A relay function is used to detect the unstable operating points. High resistance-to-reactance ratio in the low-voltage line forms active-reactive power coupling, making the conventional droop control inaccurate. For a disturbance, droop control allows a steep voltage or frequency deviations which lead to unnecessary protection tripping. Use of virtual inertia control avoids the steep change in the system variables and preserves the stability. Parallel droop-based converters with non-identical parameters or output impedance induce circulating current or reactive power oscillations. Use of virtual impedance control minimizes the circulating current and enhances power-sharing. Phase-locked loop synchronized with a weak grid (high-impedance grid) is unstable on large-signal disturbances. Current-reference saturation limits the converter current for a three-phase balanced fault condition. For higher fault-impedance, the fault current is nearly equal to the load current, which possibly blinds the microgrid protection

Media Sosial dan Perhubungan Sesama Manusia Menurut Islam

 Tujuan penulisan ini adalah untuk mengkaji kaitan antara media sosial dan perhubungan sesama manusia menurut islam. Dalam era permodenan hari ini, secara langsung atau tidak langsung, setiap individu pasti terlibat dalam penggunaan media sosial. Secara tidak sedar, penggunaan media sosial pun memberikan banyak impak yang positif kepada masyarakat moden harini. Namun dalam kemeriahan meraikan teknologi di hujung jari ini, masyarakat sering lupa akan impak negatifnya. Perhubungan sesama manusia hari ini sangat berkait rapat dengan penggunaan media sosial. Media sosial menjadi perkara yang penting oleh setiap individu. Masyarakat kita pada hari ini menjadikan media sosial sebagai suatu status perhubungan sesama masyarakat. Oleh itu, pengkajian atau penyelidikan berkaitan perhubungan antara suami dan isteri, ibu bapa dan anak, dan juga perhubungan sesame manusia patut dilakukan bagi mengenal pasti punca masalah atau pengaruh media sosial dalam kalangan masyarat demi mencapai suatu keadaan yang harmoni sekali gus melahirkan masyarakat kelas minda pertama

Sacrococcygeal chordoma presenting as a retro rectal tumour

INTRODUCTION: Chordomas are rare, slow growing, locally destructive bone tumours arising from the notochord. PRESENTATION OF CASE: Presenting a case of a 65 year old man, who presented with complaints of swelling on the right lower back for 1 year associated with pain. On, physical examination, a swelling measuring 5 cm × 4 cm was noted in the lower back with posterior wall indentation on per rectal examination. MRI revealed a mass lesion involving the sacrum (s3–s4) and coccyx. FNAC showed features of a chroma. At surgery, we excised a mass from the retrorectal space and biopsy proved it to be a chondroid chordoma, a variant of chordoma. DISCUSSION: Chordomas are solid malignant tumours that arise from vestiges of the foetal notochord. Common locations are the clivus and the sacrococcygeus region. Annual incidence of these tumours is 1 in one million. MRI is the imaging modality of choice. Prognosis improves based on the age, resected margins and postoperative treatment. CONCLUSION: Here, we shall discuss the literature, variants, treatment and prognosis of this rare tumour

PROSPECTIVE OBSERVATIONAL STUDY ON ANTIBIOTIC-PRESCRIBING PATTERN AND MEDICATION ERRORS IN SURGICAL PROPHYLAXIS IN A SPECIALTY HOSPITAL

Objective: The objective was to study the antibiotic-prescribing patterns, identify the medication errors and impact of surgical antimicrobial prophylaxis (SAP) in preventing surgical site infection (SSI), and to understand the prescribers’ adherence to surgical prophylaxis guidelines. Methods: The study was conducted for a period of 6 months in all surgical departments of a specialty hospital. Data were collected from inpatients records. Australian guideline for SAP was used to assess the appropriateness in prescribing pattern. The sample size was calculated using Raosoft sample size calculator. Results: A prospective observational study was carried out among 178 patients. Of which, 100 were male and 78 were female. Four hundred and thirty-three antimicrobials were prescribed as pre- and post-operative surgical prophylaxis, among that 87% prescribed by brand name and 13% by generic. Seventy-one percent received single antimicrobial agent preoperatively, of which 99.5% prescribed as parenteral and 0.5% as oral formulation. Most often prescribed antibiotic was cefoperazone (28%) of cephalosporin group. Only 5.6% of cases had compliance with SAP guidelines. In this study, 11 patients affected with SSI due to inappropriate antibiotic selection and non-adherence to prophylactic antibiotic guidelines. Conclusion: The present study revealed that there is a poor compliance to SAP guidelines in terms of inappropriateness in antibiotic drug selection, dose, duration, and omission of drugs. Inappropriateness and non-compliance are mainly due to unavailability of clinical pharmacist to assist the physicians in the selection and administration of correct choice of prophylactic drug and unavailability of proper national or local guidelines. Hence, there is dire need to make local SAP guidelines to improve SAP-prescribing pattern