Robust dynamic control strategy for standalone photovoltaic system under varying load and environmental conditions

Standalone photovoltaic (PV) systems are widely considered as an alternative source of utility grid due to the notable merits such as inexhaustible solar energy, pollution and noise free power generation, ease of assembly and relatively low costs. However, the major drawbacks of these systems are their environmentally-dependent characteristics and performance degradation due to sudden load variations. In order to address these challenges, two objectives must be met simultaneously for consistent and reliable output of PV system. First, the efficient tracking of maximum power point of the PV array in changing environmental conditions and secondly, the smooth conversion of the direct current (DC) input voltage into the desired level of alternating current (AC) output voltage in the presence of load variations. In this thesis, a standalone PV system with two independent control strategies have been presented. At the first stage, a hybrid non-linear maximum power point (MPPT) technique based on the perturb and observe and integral back-stepping control algorithm is proposed to extract the maximum power from the PV array. The integral action in the MPPT algorithm significantly reduces the oscillations in the PV array output that is fed to the DC-AC inverter at the second stage. Then, at the second stage, a dynamic disturbance rejection strategy based on super twisting sliding mode control (ST-SMC) has been proposed to regulate AC power for a variety of loads at the system output. The PV inverter load parameter disturbances and their effect on the system dynamics are aggregated into a perturbation, which is then estimated online by a newly designed higher-order sliding mode observer. The estimated perturbation is then compensated by the ST-SMC such that a better control performance could be achieved with significant robustness against load disturbances. The proposed control algorithms are evaluated and benchmarked with the existing backstepping controller (BSC) in terms of dynamic response, efficiency, steady-state error and total harmonic distortion (THD) handling capability under varying environmental and load conditions. The designed control strategy reaches the steady-state in 0.005 sec and gives a DC-DC conversion efficiency of 99.85% for the peak solar irradiation level as compared to the 0.008 sec and 99.7% for BSC. The AC-stage steady-state error is minimized to 0.005V compared to 0.51V of BSC whereas, THD is limited to 0.07% and 0.11% for linear and non-linear loads respectively for the proposed algorithm as compared to 0.34% and 2.04% for BSC

Hemodynamic Comparison between modified saddle block and subarachnoid block for Transurethral Resection of Prostate

BACKGROUND:   Spinal anesthesia is often the mode of anesthesia in transurethral resection of prostate (TURP) albeit with risk of hypotension. However, hemodynamic derangement is often less pronounced in saddle block. This study was conducted to compare the mean fall in Mean arterial Pressure (MAP) and Heart rate (HR) between modified saddle block and subarachnoid block for TURP.  OBJECTIVE:   To compare the mean fall in MAP and HR between modified saddle block and subarachnoid block for TURP.  METHODS:   In this randomized controlled trial 120 patients undergoing elective TURP were included and divided into two groups. Group A Patients received subarachnoid block and Group B received modified saddle block. Baseline hemodynamics were recorded before and then at 5 minutes after anesthesia. All the collected data was entered into SPSS version 22 and analyzed. Quantitative data like age, BMI, ASA-PS score, duration of surgery and baseline hemodynamics were presented as means and standard deviations. The fall of mean arterial pressure (MAP) & heart rate (HR) were compared among groups by independent t test and P value < 0.05 was considered as statistically significant.   RESULTS:  Mean fall in MAP was 8.98±1.28 mmHg and 3.13±0.68 mmHg (p<0.001) in group A and B, respectively. Mean fall in HR was 7.17±0.98 and 2.78±0.59 (p<0.001) in group A and group B, respectively.  CONCLUSION:   Modified saddle block resulted in significantly decreased fall in MAP and HR as compared with subarachnoid block for TURP.  KEY WORDS:   Modified Saddle Block; Subarachnoid Block; Mean Arterial Pressure &nbsp

Short-Term Complications of Microscopic Trans Nasal Transsphenoidal Pituitary Adenomectomy

Background/Objective:   The commonest of pituitary gland tumors is pituitary adenoma which may be excised transcranially or trans nasal trans sphenoidal using either microscope or endoscope, in this study, the microscope was used. The objective was to see the short-term outcome of patients after microscopic transnasal trans-sphenoidal pituitary adenomectomy. Material & Methods:  This was a descriptive prospective study carried out from July 2019 to July 2021. 80 cases were included. All patients were investigated by contrast brain MRI, hormonal assay for pituitary gland & visual perimetry. Patients were evaluated for complications at 48 hours and 7 days. Results:  Mean age of the study population was 41.78 ± 11.75 years. There were 61 (76%) men & 19 (24%) women. 55 (68.8%) patients had functioning and 25 (3.3%) patients had nonfunctioning adenoma. Among 33 (41.3%) patients size of the adenoma was < 0.9 cm and 47 (58.8%) patients had adenoma > 1.0 cm. 12 patients had CSF leaks within 48 hours of surgery and 5 had a persistent leak on the 7th day. No statistically significant association was seen between age, gender, and size of adenoma and persistent CSF leak (P > 0.05). Diabetes insipidus was found in 9 patients. 3 had post-operative hematoma, 01 patient had meningitis and 2 patients died. Conclusion:  microscopic transnasal trans-sphenoidal surgery is a safe procedure yet associated with significant complications

Continuous dynamic sliding mode control strategy of PWM based voltage source inverter under load variations

For closed-loop controlled DC-AC inverter system, the performance is highly influenced by load variations and online current measurement. Any variation in the load will introduce unwanted periodic error at the inverter output voltage. In addition, when the current sensor is in faulty condition, the current measurement will be imprecise and the designed feedback control law will be ineffective. In this paper, a sensorless continuous sliding mode control (SMC) scheme has been proposed to address these issues. The chattering effect due to the discontinuous switching nature of SMC has been attenuated by designing a novel boundary-based saturation function where the selection of the thickness of boundary is dependent to the PWM signal generation of the inverter. In order to remove the dependency on the current sensor, a particle swarm optimization(PSO) based modified observer is proposed to estimate the inductor current in which the observer gains are optimized using PSO by reducing the estimation errors cost function. The proposed dynamic smooth SMC algorithm has been simulated in MATLAB Simulink environment for 0.2-kVA DC-AC inverter and the results exhibit rapid dynamic response with a steady-state error of 0.4V peak-to-peak voltage under linear and nonlinear load perturbations. The total harmonic distortion (THD) is also reduced to 0.20% and 1.14% for linear and non-linear loads, respectively

Object Oriented Model for Evaluation of On-Chip Networks

Abstract: The Network on Chip (NoC) paradigm is rapidly replacing bus based System on Chip (SoC) designs due to their inherent disadvantages such as non-scalability, saturation and congestion. Currently very few tools are available for the simulation and evaluation of on-chip architectures. This study proposes a generic object oriented model for performance evaluation of on-chip interconnect architectures and algorithms. The generic nature of the proposed model can help the researchers in evaluation of any kind of on-chip switching networks. The model was applied on 2D-Mesh and 2D-Diagonal-Mesh on-chip switching networks for verification and selection of best out of both the analyzed architectures. The results show the superiority of 2D-Diagonal-Mesh over 2D-Mesh in terms of average packet delay

Čimbenici koji utječu na akademsku uspješnost međunarodnih studenata u Kini: teorija pristupa razumnoga djelovanja

This study aimed to investigate the factors affecting the academic performance of international doctoral students in China. In particular, using insights from the theory of reasoned action, this study analyzed the interplay of academic attitude, subjective norms, knowledge-seeking intention, and academic performance. Data were collected from 415 international doctoral students from six universities in China (61.4 % male, 38.6 % female, 45.5 % Asian, 40 % African, 9.4 % European and 5.1 % American). SPSS (version 23) and AMOS (version 22) were used for data analyses. While academic attitude, subjective norms and knowledge-seeking intentions were found to be positively associated with academic performance, knowledge-seeking intentions mediated the positive relationships of academic attitude and subjective norms with academic performance. The findings suggest that students’ positive attitude toward studies and subjective norms are critical to their academic performance. Implications for theory and practice are discussed.Ovo je istraživanje imalo za cilj istražiti čimbenike koji utječu na akademsku izvedbu međunarodnih doktorskih studija u Kini. Konkretno, koristeći uvide iz teorije razumnoga djelovanja, u ovoj se studiji analiziralo međudjelovanje akademskoga stava, subjektivnih normi, namjere traženja znanja i akademskoga uspjeha. Podatci su prikupljeni od 415 studenata međunarodnnih doktorskih studija sa šest sveučilišta u Kini (muškarci = 61,4 %, žene = 38,6 %; Azijci = 45,5 %, Afrikanci = 40 %, Europljani 9,4 % i Amerikanci 5,1 %). Za analizu podataka korišteni su SPSS (verzija 23) i AMOS (verzija 22). Utvrđeno je da su akademski stav, subjektivne norme i namjere traženja znanja pozitivno povezani s akademskim uspjehom, a namjere traženja znanja posreduju u pozitivnim odnosima akademskoga stava i subjektivnih normi s akademskim uspjehom. Nalazi upućuju na to da su pozitivan stav studentata prema studiju i subjektivne norme ključni za njihov akademski uspjeh. Raspravljaju se implikacije za teoriju i praksu

Modern Breast Cancer Detection: A Technological Review

Breast cancer is a serious threat worldwide and is the number two killer of women in the United States. The key to successful management is screening and early detection. What follows is a description of the state of the art in screening and detection for breast cancer as well as a discussion of new and emerging technologies. This paper aims to serve as a starting point for those who are not acquainted with this growing field

Frequency of hepatitis E and Hepatitis A virus in water sample collected from Faisalabad, Pakistan

Hepatitis E and Hepatitis A virus both are highly prevalent in Pakistan mainly present as a sporadic disease. The aim of the current study is to isolate and characterized the specific genotype of Hepatitis E virus from water bodies of Faisalabad, Pakistan. Drinking and sewage samples were qualitatively analyzed by using RT-PCR. HEV Genotype 1 strain was recovered from sewage water of Faisalabad. Prevalence of HEV and HAV in sewage water propose the possibility of gradual decline in the protection level of the circulated vaccine in the Pakistani population

Augmentation of Fatigue and Tensile Strength of AA-6061 Processed through Equal Channel Angular Pressing

ECAP (Equal Channel Angular Pressing) is a technique used to enhance the strength of material by grain refinement. In this research, an aerospace grade aluminum alloy-6061 is investigated. The specimens were pressed through ECAP die channels, intersecting each other at an angle of 90oC where a shear plane of 45oC was developed, that results grains refinement. Fatigue strengths and CGR (Crack Growth Rate) for the stress ratio R 0.7 and 0.1 are found and compared with the as-received material.It was observed that the CGR is slower at stress ratio R=0.1, as compared to stress ration R=0.7. An electric furnace was embedded with ECAP die to regulate the material flow through this die. The temperature of the die was maintained at 450oC during ECAP pressing and the specimens were also preheated at this temperature using another furnace. The ECAP die consistsof two channels intersecting at 90o provided with safe inner and outer corner radius to avoid scaling.The microstructural observations revealed that the deformation was perfectly plastic. The ECAPed and as-received materials were also characterized by tensile tests, micro-hardness tests, and 3-point bend fatigue tests