Constant Power Generation in Cascaded H-Bridge Inverter-based Photovoltaic Systems Based on Flexible Power Point Tracking

Traditionally, photovoltaic power plants use Maximum Power Point Tracking (MPPT) algorithms to produce maximum electrical energy. However, with the increase of grid-installed photovoltaic power plants, power system operators have faced new challenges such as overload, overvoltage, and proper performance during grid voltage disturbances. As a result, network standards and codes have been updated in the direction of photovoltaic systems that are more controllable and compatible with the network. To provide various grid support functions, such as frequency response and voltage support, the Constant Power Generation (CPG) control algorithm is established by grid codes. For this purpose, MPPT algorithms have been replaced by flexible power point tracking (FPPT) algorithms. This paper proposes an algorithm to control photovoltaic systems based on a multi-level cascaded full-bridge (CHB) inverter to achieve constant power generation control by the FPPT method. The required power reference is distributed among the sub-modules of the CHB converter according to the available power of each sub-module in such a way that, as much as possible, each sub-module is loaded equally. Then, the FPPT algorithm with an adaptive voltage step is used to set the power of each sub-module in its reference value. The voltage step is calculated adaptively based on the observed condition (transient or steady state) so that the tracking performance has fast dynamics. The effectiveness of the proposed algorithm is evaluated by simulating a 500-kW photovoltaic system directly connected to a 4.7 kV grid

Comparing the Effect of Vitamin E and N-Acetylcysteine on Prevention of Contrast-Induced Nephropathy in Diabetic Patients under Coronary Angiography

Introduction:  Considering the incidence of contrast  induced  nephropathy  (CIN) as well as  its  complications  and    costs,  prevention  and  reducing  the  risk  of  CIN  is  an  essential  issue.  The  present  study  aimed  to  evaluate  the  efficacy  of  vitamin  E  and  N-acetylcysteine  (NAC)  on the prevention  of  CIN  in  diabetic  patients  undergoing  coronary  angiography. Materials and Methods:  360  patients  with  diabetes  who  required  angiography,  including  patients  with  stable  angina  susceptible  to  acute  myocardial  infarction  and  patients  with  acute  coronary  syndrome  were  included  and  randomized  into  three  groups .  Group  1  received  serum  therapy  (Normal Saline)  plus  NAC  and  placebo  of  vitamin  E,  group  2  received  serum  therapy  plus  vitamin  E  and  placebo  of  NAC,  and  group  3  only  received  serum  therapy  with  two  placebos  of  NAC  and  vitamin  E.  The groups were compared considering CIN after angiography. Results:  A  total  of  93  patients  were  studied  in  group  1,  94  in  group  2,  and  113  in  group  3.  CIN  occurred  in  4  patients  (4.3%),  4  patients  (4.3%),  and  8  patients  (7.1%)  in  groups  1,  2,  and  3,  respectively  (P=0.58).  There was  a  significant  difference  in  mean  difference  of  creatinine  levels  before  and  after  study  in  groups  1  and  2  (both  P<0.001).  In  the  subgroup  of  patients  with  chronic  kidney  disease,  NAC  significantly  reduced  CIN  (P=0.03). Conclusion:  The results  suggested  efficacy  of  both  interventions,  considering  reduction  of  mean  Serum creatinine ( Scr) after  the  study,  while  lack  of  significant  difference  in  the  incidence  of  CIN  could  be  because  of  the  low  number  of  CIN  in  our  study.  The second  important  finding  of  this  study,  probably the  reduced  risk  of  CIN  in  diabetic  patients  with  chronic  kidney  disease  receiving  NAC,  recommends  the  use  of  NAC  for  prevention  of  CIN,  especially  in  this  subgroup  of  patients  undergoing  angiography

Ultrasound Parameters Changes after Pyeloplasty in Ureteropelvic Junction Obstruction: 6-Month Follow-Up

Background: Ureteropelvic junction obstruction(UPJO) is one of the most common anomalies in children. The gold standard method for follow-up of these patients after pyeloplasty is a nuclear scan, but due to its high cost and limited access, it has recently been replaced with ultrasound. In this study, we want to assess ultrasound parameter changes after pyeloplasty. Methods: In this cross-sectional analytical study, 124 patients from 2006 to 2012 who had undergone open pyeloplasty were enrolled. They were evaluated with ultrasound and nuclear scans before, 3, and 6 months after surgery. We analogized the results of these two methods and described the modifications in ultrasound parameters. Results: Of all 124 patients with a median age of 30 months, according to nuclear scan results, kidney functions have improved by 96.77%. The average AP(anteroposterior) diameter of kidneys before, 3, and 6 months after surgery were 34.28 mm, 18 mm, and 15.19 mm respectively. In patients with successful surgery; PI (percentage improvement) of AP was above 15% after 3 months and above 26% after 6 months, thickness of the cortex raised at least 10 percent, and a reduction of at least 16% and 18% was seen in pelvic/cortex ratio in 3, and 6 months respectively. Conclusions: After pyeloplasty, a reduction in AP diameter, PI of AP, pelvic/cortex ratio, and an expansion in thickness of the cortex have been seen. Ultrasound in 3 months has high sensitivity but low specificity, and in 6 months have high sensitivity and specificity

Maximum Wireless Power Transmission Using Real-Time Single Iteration Adaptive Impedance Matching

Wireless power transfer (WPT) systems’ efficiency is significantly impacted by non-monotonic variations in the coupling coefficient. For very short distances or strong-coupling cases, the WPT efficiency is minimal at the natural resonant frequency, with two peaks around this frequency, known as the frequency splitting phenomenon. On the other hand, WPT capability decreases for long distances or weak coupling cases. Therefore, adaptive matching is required for WPT systems with varying distances, like wireless charging systems for electric vehicles (EVs). This paper first presents a detailed analysis of the frequency splitting phenomenon by studying the root locations of the WPT system’s transfer function. Then, a real-time fixed-frequency adaptive impedance matching (IM) method is proposed, in which the amplitude and phase of the input impedance is estimated using the average active power, the average reactive power, and the amplitude of input voltage. Unlike traditional search-and-find techniques, the proposed method calculates the optimal IM network parameters only in a single iteration, which improves the convergent speed. A scaled-down 20-Watt prototype controlled by the TMSF2812 is fabricated and used to validate the effectiveness of the proposed method over a wide range of coil-to-coil distances

Novel Reduced Switches Single-Phase to Three-Phase On-line Uninterruptible Power Supply

This paper describes design considerations and performance analysis of a novel on-line singlephase to three-phase uninterruptible power supply (UPS) with reduced number of switches. The proposed topology uses only 5 active switches reducing the cost of the system compared to the traditional 10-switch topologies. The proposed UPS consists of a single-phase rectifier/charger, a hvo-leg/three-phase inverter connected to load, battery hank, DC link capacitor and an AC inductor. Detailed circuit operation and analysis as well as simulation results are also presented to verify its feasibility

A Novel Control Strategy for Three-Phase UPS Based on B-Spline Network

This paper is concerned with the control of three-phase Uninterruptible Power Supply (UPS) systems based on a B-spline Network (BSN). A UPS must be able to maintain regulated output voltage in the face of all line/load disturbances. To achieve this, the control system of a UPS must have a fast transient response and a low steady-state error. Fast controllers cannot always maintain the required steady-state accuracy. Therefore, in this paper, a hybrid control solution is proposed. In the proposed method, a fast yet simple controller based on deadbeat (DB) control law is used to achieve the fast transient response required for UPS output voltage control. A B-spline based controller is added to the deadbeat controller to improve steadystate performance of the UPS system. This results in distortion free output voltage along with a fast error convergence. The system modeling and controller design for the proposed structure are presented in this paper. Simulations results are shown for verification of the theoretical analysi