Hemodialysis access has been considered as a support for end-stage renal patients. We measured the hemodynamic changes of the distal part of the upper extremity immediately after providing the AVGs ...in each method mentioned above and then compared the results. This method is a novel one and hasn’t been used in any other studies before. We studied 32 patients referred to the vascular surgery department of Rasht Razi Hospital between 2019-2020 (using the Convenient Sampling method). This study is a case-control study. Out of 32 patients referred to the vascular surgery department of the hospital, 68.8% were male, and their mean age was 53.41±12.75 years, ranging from 28 to 78 years. Changes in distal arterial hemodynamics of the upper limb before and after clamping in dialysis venoarterial loop versus straight grafts are different in studied patients (P<0.05). The mean hemodynamic changes before and after clamping in loop venoarterial grafts (19.5000) are less than straight grafts. In dialysis patients who do not have any superficial vein suitable for venous, arterial fistula, surgical placement of artificial grafts in the upper limb is appropriate. Based on the results of this study, the loop method seems to have lesser ischemic Complications and can be applied to dialysis patients.
Abdominal aortic aneurysm (AAA) is a life-threatening condition. Open surgery and endovascular repair are the options for treating AAA. This study aimed to compare the frequencies of in-hospital ...complications and outcomes in two groups of patients who underwent AAA repair surgery using either an open or an endovascular repair method.
This retrospective study was conducted on the records of 60 patients with AAA undergoing elective surgery repair using endovascular approaches or open surgery at Razi Hospital from 2010 to 2019. Patients' related information, including age, sex, changes in blood pressure, respiratory complications, renal complications, myocardial infarction, paraplegia, cloneischemia, lower limb ischemia, duration of hospital stay in intensive care unit and hospital, the dose of packed RBC, the dose of injectable narcotic analgesics, the need for vasopressor medication, duration of surgery, duration of postoperative oral feeding, and death during hospitalization were assessed.
A total of 60 patients in two groups were studied. The mean age of patients was 72.4 ± 6.28 years, and most were male (86.7%). The incidence of renal complications (3.3%) and respiratory complications (0%), rate of decrease in arterial blood oxygen saturation, length of stay in ICU (median 2 vs. 4) and hospital (median 4.5 vs. 7), the need for vasopressor injection and the dose of packed RBC (median 0.4 vs. 3.33), the dose of narcotic analgesic injection (53.3%), duration of surgery (median 2.5 vs. 3), duration of postoperative oral feeding (median 23 vs. 54), and the incidence of death were significantly lower in the endoscopic surgery group.
Endovascular surgery repairing the rupture of an AAA is associated with fewer postoperative complications and in-hospital death than open surgery.
District energy systems (DESs) and integrated electricity-gas systems (IEGSs) are closely related. The performance of these systems under critical situations, such as faults and equipment outages, ...has not been adequately investigated. The operation of DESs may also be significantly affected by installing central generating systems for gas or electricity sectors. These central generating units may deal with outages and faults. In the literature, there is not a comprehensive model that considers renewables in IEGS, uncertainties of generating systems, mutual connection between electricity and gas sub-grids, ability of exchanging power with upstream grid, centralized storage device for electrical sector, and centralized power supply for gas sector. All these points are considered and modeled in the proposed model. This paper presents several multi-purpose control strategies for DES that are designed and implemented on an IEGS. Electricity and thermal loads are used to model the DES energy needs. In the electricity subsystem, by using several local renewable energy sources (RESs) and a central battery, not only the electric loads are supplied, but also the DES can be connected to the upstream grid and trade the scheduled power in accordance with the electricity market contract in all normal and critical conditions. On the other hand, the gas subsystem is powered by a central fuel cell. Gas and electricity subsystems in the DES region are designed to assist each other during outages and events in order to increase the resilience. All RESs, central battery, and fuel cell are equipped with individual controllers to achieve the above objectives. A centralized control framework is used to manage all these controllers under a variety of operating conditions. Numerical simulations in MATLAB software verify the model ability to control DES and IEGS properly.
•Balancing the unbalanced and time-varying loads under grid-tied and off-grid.•Coordinated single phase control of diesel generator, battery and fuel cell.•Controlling and balancing both the active ...and reactive powers separately.•Improving the voltage profile following faults and events.•Stability improvement and resilient operation under events.
This paper presents an advanced control strategy for balancing the time-varying and unbalanced loads by using the fuel cell and battery under the grid-tied and off-grid operations. In the grid-tied operation, the fuel cell and the battery are coordinately controlled to balance the three-phase unbalanced active and reactive powers of the loads. In this case, the received three-phase active-reactive powers from the grid become completely balanced by the given strategy. In the off-grid, the diesel generator supplies the active-reactive powers of load and the unbalances are handled by coordinated operation of fuel cell and battery. As well, the voltage of off-grid system is improved by injecting adequate reactive power to the system through the fuel cell, battery and diesel generator. The dynamic stability of the system is evaluated under non-linear disturbances like grid outage and single-phase fault. The time-varying unbalanced active-reactive powers are balanced under both off-grid and grid-tied states by implementing the proposed model. The purpose of the proposed control system is to balance the unbalanced load from point of view of the upstream grid at all time periods. In order to realize such function in the model, the load is modeled by two terms including the balanced and unbalanced parts. The unbalanced share is supplied by the inverters (DC bus) and the balanced term of load is supplied by the grid. The designed system is resilient under the events like grid outage and short circuits. As well, the system properly regulates and controls the load variations and unbalances.
This paper presents a control mechanism on high voltage direct current (HVDC) transmission line for frequency/voltage regulation, fault ride through (FRT) capability, and cyber‐attack/fault ...detection. The network under study consists of two areas with different frequencies that are connected through one 300 km HVDC line. The proposed control system regulates the frequency in both areas by managing power through HVDC line. The converters on both sides of HVDC line are controlled to handle faults on the DC and AC sections as well as improving fault ride through capability. The control strategies are implemented and operated depending on fault/cyber‐attack type and behaviour. In this respect, the control mechanism may change the firing angle of converters, switch their operating mode from rectifier to converter and vice‐versa or even block the converters. The proposed paradigm successfully distinguishes between the cyber‐attacks and faults. The simulations in MATLAB software validate that the proposed mechanism realizes all the objectives and the cyber‐attacks are completely identified and separated from the faults.
•Integrated system including DFIG, battery storage, TCR and TSC is implemented.•Set of TCR-TSC-DFIG is controlled to compensate voltage sag-swell.•Set of DFIG-battery is controlled to damp out ...oscillations and power regulation.•Proper control loop is designed to improve DFIG resilience under three-phase fault.•Set of TSC-TCR-battery balances the unbalanced time-varying load.
This paper presents a novel control scheme in doubly-fed induction generators (DFIG) wind turbine for operation under time-varying unbalanced loads. The proposed control scheme is implemented on a DFIG connected to the external grid. Additional equipment such as battery, thyristor-controlled reactor (TCR) and thyristor-switched capacitor (TSC) are integrated to the DFIG. These devices are integrated to DC link, grid side and rotor side converters. The developed control scheme aims to achieve several purposes simultaneously including voltage compensation, damping fluctuations, regulating frequency, increasing resilience, and balancing the unbalanced time-varying loads. Each purpose is realized by designing a separated control loop on DFIG, battery and TCR-TSC. All the designated control loops are operated coordinately. The non-linear time-domain modelling and simulations are carried out in MATLAB software and demonstrate that the proposed multi-purpose control plan can optimally utilize set of DFIG/battery/TCR/TSC and achieve all the objectives efficiently.
A resilient control system in the island microgrid including AC and DC buses is designed here. The DC bus is supported by fuel cell, solar cell and battery and the AC bus is equipped with diesel ...generator and wind turbine. The AC bus is sectionalized into three sub‐buses that enables to continue operation when one section is not functioning. The connection between DC and AC buses is made by two parallel three‐phase lines each line made by three single‐phase inverters. The objectives are to eliminate the harmonics, the unbalanced load management, dealing with outage of resources and short circuits, providing backup strategies and supplying critical loads under all events. The simulations are performed by MATLAB/Simulink. It is demonstrated that the resilient control technique can achieve all the defined purposes at the same time. The harmonics are eliminated, the unbalanced load issues are dealt with and the microgrid has sufficient resilience against outages and faults.
PDF
