Continuous Nonlinear Model Predictive Current Control of PWM AC/DC Rectifier

The present work applies a nonlinear model predictive current control (NLMPCC) approach to ac/dc pulse width modulation (PWM) rectifier. A cascade structure is used to regulate Dc-link voltage and grid currents. The outer loop objective is to regulate the Dc-link voltage to the desired value, providing the level of the required active power to be used with the reactive power to calculate the referencing current for the inner loop. In the inner loop, the proposed approach is considered. After that, the nonlinear model of the converter is developed, based on continuous minimization of predicted tracking errors, the voltage at the terminal of the converter is deduced. After that, a PWM block is used to generate gate signals. Simulation results are performed to illustrate the efficiency of the proposed control la

Evaluation of Reliability Indices for Gas Turbines Based on the Johnson SB Distribution: Towards Practical Development

Recent advancements in computer engineering have provided effective solutions for processing and analyzing complex systems and big data. Consequently, the adjustment and standardization of this data play a crucial role in addressing issues related to the monitoring of industrial systems. In this study, we propose a reliability approach for gas turbines to identify and characterize their degradation using operational data. We introduce a method for adjusting turbine reliability data, which resolves the challenges associated with the nature of these operating data. This enables us to determine a mathematical function that models the relationships between turbine reliability parameters and evaluate the impact of reliability practices in terms of availability. Additionally, we determine the survival function and employ it as a lifespan distribution model by estimating the parameters of the Johnson SB function. Furthermore, we calculate the failure rates and mean time between good operations for this rotating machine under different operating conditions. The obtained results allow us to estimate the parameters of the distribution that best fit the turbine reliability data, which are validated through statistical and graphical tests. We assess the goodness-of-fit using mean square error and reliability tests such as Kolmogorov-Smirnov

Continuous Nonlinear Model Predictive Current Control of PWM AC/DC Rectifier

The present work applies a nonlinear model predictive current control (NLMPCC) approach to ac/dc pulse width modulation (PWM) rectifier. A cascade structure is used to regulate Dc-link voltage and grid currents. The outer loop objective is to regulate the Dc-link voltage to the desired value, providing the level of the required active power to be used with the reactive power to calculate the referencing current for the inner loop. In the inner loop, the proposed approach is considered. After that, the nonlinear model of the converter is developed, based on continuous minimization of predicted tracking errors, the voltage at the terminal of the converter is deduced. After that, a PWM block is used to generate gate signals. Simulation results are performed to illustrate the efficiency of the proposed control law. Keywords: AC/DC PWM rectifier, Active and reactive power, Nonlinear predictive control, Taylor approximation, Continuous minimization

Prevalence of venous sinus stenosis in Pseudotumor cerebri (PTC) using digital subtraction angiography (DSA)

Objectives: To study the prevalence of intracranial venous stenosis in Pseudotumor cerebri patients. Patients and methods: Thirty patients were diagnosed having PTC according to Dandy criteria. All underwent general and neurological assessment. Radiological assessment included CT scan brain ±MRI brain without contrast, MRV. All underwent digital subtraction angiography (DSA) (venous phase) to confirm the validity of filling gaps seen at the level of MRV. Results: MRV brain showed that 24 patients (80%) showed filling gaps. Digital subtraction cerebral angiography (venous phase) showed 9 patients (30%) had stenosis in their dural sinuses. MRV showed to be a good screening tool since it had 100% sensitivity and negative predictive value. However, since it has a moderate specificity (62%) with a positive predictive value (PPV) of only 35%, then lesions detected should be confirmed with digital subtraction cerebral angiography (venous phase) particularly those involving the transverse and sigmoid sinus. Conclusion: Studying the intracranial venous system in patients with PTC is an important step in understanding the pathophysiology of the disease. Detection of venous sinus stenosis opens the way to a novel therapeutic option for refractory patients like venous sinus stenting

A Carrier-Based PWM Techniques Applied to a Three-level Four-Leg Inverter for Use as a Shunt Active Power Filter

International audienc

Power Quality Improvement Using Four-Leg Three-level Inverter and Cross Vector Theory

International audienc

Use of serum leptin and insulin hormones levels as predictors of pregnancy outcome in pregnant women with history of recurrent early pregnancy loss

Aim: To evaluate levels of leptin and insulin in cases of unexplained early RPL in comparison with cases of previous normal pregnancies and suggest these levels as prognostic factors for the continuation of pregnancy beyond the 20th week. Methods: A prospective comparative controlled study was conducted at Obstetrics unit of Tanta University Hospital from Jan to Aug 2014 on 50 pregnant women who were divided into two groups: the study group included 25 cases with history of early RPL, and the control group included 25 cases with previous normal pregnancies. Serum levels of leptin and insulin were measured twice in both groups; at 5–8th and 10–12th week. Results: Leptin levels in ng/ml in the first sample were 9.414 ± 3.183 and 30.559 ± 10.672 in the control and study groups respectively with significant difference. As for the second sample, it was 11.672 ± 2.611 and 29.733 ± 9.133 in the control and study groups respectively with significant difference. Insulin levels in μlU/ml in the first sample were 18.075 ± 5.845 and 32.502 ± 13.057 in the control and study groups respectively with significant difference. In the second sample, on the other hand, it was 20.237 ± 4.944 and 34.128 ± 12.677 in the control and study groups respectively with significant difference. Leptin showed higher accuracy than insulin in prediction of early pregnancy loss. Conclusion: Higher levels of leptin and insulin were found in cases with early RPL especially in the aborted cases. The two hormones could be used as predictors of pregnancy continuation in these cases