DC microgrids are introduced to reduce the conversion stages needed for connection of DC sources to the DC loads. They employ the droop control algorithm for managing the power flow from sources to the loads. However, the droop control functionality is affected by circuit parameters, especially line resistances. As a consequence, load sharing as the primary objective of the droop controller lacks accuracy. Parallel-connected converters have mismatched output voltages, resulting in circulating currents. This paper proposes an adaptive droop control algorithm for suppressing circulating currents in a low voltage DC microgrid. Line resistances are estimated through mathematical calculations and droop parameters are adjusted accordingly. Moreover, a distributed secondary controller is proposed to improve the load sharing accuracy and eliminate the effect of line resistances. The secondary controller shifts the droop controller voltage setpoint according to the converter current. Both of the proposed methods result in an accurate load sharing; Each of the participating converters has the rated current and consequently circulating current is suppressed. The effectiveness of the proposed method is verified through simulation and hardware-in-the-loop (HIL) setup.

The need for independent power generation has increased in recent years, especially with the growing demand in microgrid systems. In a microgrid with several generations of different types and with all kinds of loads of variable nature, an optimal power balance in the system has to be achieved. This optimal objective, which results in minimal energy losses over a specific period of time, requires an optimal location and sizing of the distributed generations (DGs) in a microgrid. This paper proposes a new optimization method in which both optimal location of the DGs and their generation profile according to the load demand profile as well as the type of DG are determined during the life time of the DGs. The types of DGs that are considered in this paper are diesel generators and wind turbine. The method is based on simultaneously minimizing the cost of the investment and operation of the DGs, the cost of power delivered by the the external grid as well as the cost of power losses in the network. The proposed method is tested on the IEEE standard radial distribution network considering time-varying loads and the wind speed every hour of a day.

DC microgrids are gaining interest by the increase in DC loads and renewable resource penetrations. Photovoltaic (PV) arrays are the primary renewable resources utilized in DC microgrids with variations in their productions. Power variations are seen as disturbances from other sources’ point of view. The droop control method is frequently used to control DC microgrids and assures power sharing among parallel-connected converters. It is of great interest to assess droop controller functionality in rejecting disturbances, and maintain constant output voltage. Therefore, there is a need for a comprehensive converter and controller modeling to study the effect of disturbances on the system behavior. In this paper, the converter’s small-signal model is utilized in deriving the system state space model. Via the derived model, the effect of different circuit parameters on time and frequency responses is studied. The line resistances’ effect on the parallel operation of converters is also studied. To verify the droop controller’s functionality, the converter’s output impedance is derived. Disturbances are applied to the load current, and the system response is analyzed. Finally, the DC microgrid plug and play feature is addressed by proposing an algorithm for deriving the multiple converters’ mathematical model. Simulations and hardware-in-the-loop (HIL) experiments are conducted to verify the mathematical model and controllers’ performance.

Background: The coronavirus disease 2019 (COVID-19) dramatically impacts healthcare delivery. Pulmonary diagnostic procedures have had frequent disruptions during this pandemic. Objectives: This study aimed to discover how the COVID-19 pandemic affected pediatric flexible fiberoptic bronchoscopy. Methods: This retrospective cross-sectional study was carried out on pediatric patients who underwent fiberoptic bronchoscopy at a tertiary pediatric hospital affiliated to Tehran University of Medical Sciences. Procedural analysis was done from 20 March 2019 to 20 February 2020 (the pre-pandemic period) and 20 March 2020 to 20 February 2021 (during the pandemic period). The two groups were compared with regard to bronchoscopic indications and findings. Results: Our results from the data registry showed that within (group 1), 290 patients vs. 241 patients from 20 March 2020 till 20 February 2021 (group 2) were admitted to the operation room at least once for bronchoscopy procedures. Although the findings of foreign body aspiration in bronchoscopy were more frequent in group 2, this difference was not significant in the two groups (P = 0.055). The number of cases without abnormality in group 2 was significantly less than in group 1 (P = 0.006). The prevalence of Laryngomalacia was also significantly higher in group 2 (P = 0.000). Conclusions: Our results confirmed the reduction of bronchoscopy in children after the COVID-19 epidemic. However, there was no change in the immediate indications for bronchoscopy, and this pandemic had the most significant impact on elective bronchoscopy.

Background: Functional constipation (FC) is a common issue in pediatric healthcare, causing significant physical and emotional distress for patients and their families. Objectives: This study aimed to investigate the prevalence of behavioral issues in children diagnosed with functional constipation, exploring their characteristics and relationship with various factors. Methods: We conducted a case-control study involving 107 children and adolescents (aged 2 to 18 years) with chronic functional constipation as the case group and 107 children without this condition as the control group. The Strengths and Difficulties Questionnaire (SDQ) was employed to evaluate different aspects of behavioral patterns. Results: The comparison of various behavioral components assessed by the SDQ between the case and control groups revealed significantly higher average scores for emotional symptoms (0.85 ± 0.81 vs. 0.55 ± 1.03, P = 0.019), peer relationship problems (1.76 ± 2.23 vs. 0.76 ± 1.18, P = 0.001), and prosocial behavior (8.12 ± 1.87 vs. 7.42 ± 1.64, P = 0.002) in children with chronic functional constipation. Within the chronic constipation group, peer relationship issues were more common in boys, whereas girls exhibited more problems with prosocial behavior. Moreover, issues related to hyperactivity/inattention and prosocial behavior were more frequent in older children with chronic constipation. Conclusions: Chronic functional constipation in children is strongly associated with behavioral changes and problems, which are influenced by the demographic and anthropometric features of the patients.