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In this study, the authors investigate the secondary control of microgrids (MGs) in the presence of cyber imperfections such as delay and/or noise, and system disturbances. The existence of cyber imperfections and disturbance could bring in system uncertainty that will seriously degrade the effectiveness of most existing secondary control such as proportional–integral–derivative (PID), etc. To tackle these issues, a biologically‐inspired reinforcement learning technique has been proposed which adjusts its parameters to the perturbed system setpoints generated by the cyber imperfections and system disturbances. The learning capability and low computational complexity of the proposed controller make it a promising approach to take cyber imperfections and system disturbances into account, where traditional control methodologies are not suitable due to their vulnerability to the cyber imperfections. First, an emotional learning‐based secondary control structure is proposed, where the impacts of cyber imperfection and disturbance have been captured efficiently. Then, the real‐time update laws are developed for generating the proper emotional signals (ESs) to stabilize the frequency and voltage. Ultimately, using the generated ESs, the secondary control of MGs is achieved. The Lyapunov analysis has been provided to prove the stability of the proposed design. Moreover, MATLAB/Simulink‐based simulations demonstrate the effectiveness of the proposed algorithm.

To improve ride comfort in railway vehicles, the suppression of vertical bending vibration and rigid-body-mode vibration in the car body is essential. In this paper, a system is proposed that aims to reduce bending and rigid-body-mode vibration simultaneously by introducing damping control devices in the primary and secondary suspensions. The technique involves a control system of primary vertical dampers and air springs; the former are used to suppress the first bending mode vibration; the latter, to suppress the rigid-body-mode vibration. The results of both simulations and vehicle running tests on the Sanyo—Shinkansen line demonstrate that this system reduced vertical vibrations in the bogies and the car body using the sky-hook control theory. In the running tests in particular, the system reduced the vertical vibration acceleration PSD peak value in the first bending mode to almost 20 per cent and in the rigid body mode to almost 50 per cent compared with the case when the system was not used. As a result, the ride quality level LT (a widely used index of ride comfort in Japan) decreased by at least 3 dB, indicating greater ride comfort.

This study proposes a secondary voltage and frequency control scheme based on the distributed cooperative control of multi-agent systems. The proposed secondary control is implemented through a communication network with one-way communication links. The required communication network is modelled by a directed graph (digraph). The proposed secondary control is fully distributed such that each distributed generator only requires its own information and the information of its neighbours on the communication digraph. Thus, the requirements for a central controller and complex communication network are obviated, and the system reliability is improved. The simulation results verify the effectiveness of the proposed secondary control for a microgrid test system.

With the rapid development of power electronics technology, microgrid (MG) concept has been widely accepted in the field of electrical engineering. Due to the advantages of direct current (DC) distribution systems such as reduced losses and easy integration with energy storage resources, DC MGs have drawn increasing attentions nowadays. With the increase of distributed generation, a DC MG consisting of multiple sources is a hot research topic. The challenge in such a multi-source DC MG is to provide voltage support and good power sharing performance. As the control strategy plays an important role in ensuring MG’s power quality and efficiency, a comprehensive review of the state-of-art control approaches in DC MGs is necessary. This paper provides an overview of the primary and secondary control methods under the hierarchical control architecture for DC MGs. Specifically, inner loop and droop control approaches in primary control are reviewed. Centralized, distributed, and decentralized approach based secondary control is discussed in details. Key findings and future trends are also presented at last.

Background Chronic Migraine (CM) is a disabling condition, worsened when associated with Medication Overuse (MO). Mindfulness is an emerging technique, effective in different pain conditions, but it has yet to be explored for CM-MO. We report the results of a study assessing a one-year course of patients’ status, with the hypothesis that the effectiveness of a mindfulness-based approach would be similar to that of conventional prophylactic treatments. Methods Patients with CM-MO (code 1.3 and 8.2 of the International Classification of Headache Disorders-3Beta) completed a withdrawal program in a day hospital setting. After withdrawal, patients were either treated with Prophylactic Medications (Med-Group), or participated in a Mindfulness-based Training (MT-Group). MT consisted of 6 weekly sessions of guided mindfulness, with patients invited to practice 7–10 min per day. Headache diaries, the headache impact test (HIT-6), the migraine disability assessment (MIDAS), state and trait anxiety (STAI Y1-Y2), and the Beck Depression Inventory (BDI) were administered before withdrawal and at each follow-up (3, 6, 12 after withdrawal) to patients from both groups. Outcome variables were analyzed in separate two-way mixed ANOVAs (Group: Mindfulness vs. Pharmacology x Time: Baseline, 3-, 6-, vs. 12-month follow-up). Results A total of 44 patients participated in the study, with the average age being 44.5, average headache frequency/month was 20.5, and average monthly medication intake was 18.4 pills. Data revealed a similar improvement over time in both groups for Headache Frequency (approximately 6–8 days reduction), use of Medication (approximately 7 intakes reduction), MIDAS, HIT-6 (but only for the MED-Group), and BDI; no changes on state and trait anxiety were found. Both groups revealed significant and equivalent improvement with respect to what has become a classical endpoint in this area of research, i.e. 50% or more reduction of headaches compared to baseline, and the majority of patients in each condition no longer satisfied current criteria for CM. Conclusions Taken as a whole, our results suggest that the longitudinal course of patients in the MT-Group, that were not prescribed medical prophylaxis, was substantially similar to that of patients who were administered medical prophylaxis.

We present results on the beneficial effects of compensatory secondary control strategies in a sample who failed the entrance exam at an university. Based on the action phase model of developmental regulation we assumed that failing the exam represents the passing of a developmental deadline. We thus hypothesized that compensatory secondary control is associated with a more positive trajectory of satisfaction with life. Multi-group structural equation models showed that (1) compensatory secondary control was associated with higher levels of and a steeper increase in satisfaction with life in the group who failed but not for the group who passed and that (2) in the group who failed the exam, the slope coefficient indicated a significantly steeper increase of satisfaction with life in those who reported higher compensatory secondary control. These results show that letting go a goal can sometimes be more adaptive than persistent goal striving.

In alternating current (AC) microgrids, the prevalent approach for controlling the power distribution between generators and loads is droop control. This decentralized technique ensures accurate power sharing; however, its utility is restricted by significant drawbacks. Notably, in scenarios involving dissimilar power sources, mismatched impedance lines, or meshed microgrids, conventional droop control fails to ensure effective reactive power sharing among inverters, often leading to notable circulating currents. Hence, the primary objective of this paper is twofold: firstly, to examine limitations inherent to conventional droop control; secondly, to introduce a robust power-sharing methodology for AC microgrids. This novel approach is specifically designed to achieve consistent sharing of active and reactive power across meshed topology microgrids. The technique considers the presence of distributed power loads and the dynamic nature of the topology. Despite the attainment of satisfactory active and reactive power sharing, deviations in voltage and frequency occasionally manifest. To address this issue, a supplementary control mechanism is proposed as a third phase. This secondary control method focuses on reinstating the microgrid's voltage and frequency to rated values, all while upholding the precision of power sharing. The efficacy of this multi-stage methodology is rigorously validated through simulations using MATLAB/Simulink and practical experimentations.

In recent years, DC microgrids supplying constant power loads (CPLs) have attracted significant attention due to their impact on overall system stability, which is attributed to their electrical characteristics that exhibit negative incremental impedance. This paper examines a secondary control strategy aimed at ensuring accurate power sharing and voltage restoration within an islanded DC microgrid supplying a constant power load. The droop control function is typically used in the primary control layer to facilitate power sharing among distributed generators (DGs). However, differing load profiles may cause the DC bus voltage to deviate from its nominal value. To restore the DC bus voltage to its nominal value while maintaining accurate power sharing, a primary and secondary control scheme is proposed. This scheme employs an integrated control strategy combining sliding mode control for the primary control level and H-infinity control for secondary control. The approach is based on a two-time-scale stability analysis, i.e., the settling time of the primary control must be faster than that of the secondary control. Additionally, compared to most existing methods, the proposed approach requires no global information and depends exclusively on DC bus voltage feedback, eliminating the need for passive loads in parallel with the CPL. A test system of an islanded DC microgrid feeding a CPL is created using Matlab and PSIM software to assess the proposed method. An experimental prototype comprising two DGs and a tightly voltage-controlled boost converter emulating a CPL is developed to demonstrate the proposed approach and confirm the theoretical results.

In an islanded DC microgrid with multiple distributed generators (DGs), the droop control is employed to realize proportional current sharing among the DGs in the microgrid. The action of the droop control causes a deviation in the DC bus voltage which is exacerbated by the line impedance between the DG and the DC bus. In this paper, an advanced distributed secondary control scheme is proposed to simultaneously achieve accurate voltage regulation and cooperative current sharing in the islanded DC microgrid system. The proposed distributed secondary controller is introduced in the cyber layer of the system, and each controller shares information with neighbouring controllers via a communication network. The distributed technique maintains the reliability of the overall system if some part of the communication link fails. The proposed controller uses the type-II fuzzy logic scheme to adaptively select the secondary control parameters for an improved response of the controller. The sufficient conditions to guarantee the stability of the proposed controller are derived using the Lyapunov method. Comprehensive tests under different operating scenarios are conducted to demonstrate the robustness of the proposed control scheme.

Objectives: To study the effect of Vitamin D 3 supplementation on metabolic control in an obese type 2 diabetes Emirati population. Methods: This randomized double-blind clinical trial was conducted with 87 vitamin D-deficient obese, type 2 diabetic participants. The vitamin D-group ( n =45) and the placebo group ( n =42) were matched for gender, age, HbA1c and 25-hydroxy vitamin D (25(OH) D) at the baseline. The study was divided into two phases of 3 months each; in phase 1, the vitamin D-group received 6000 IU vitamin D 3 /day followed by 3000 IU vitamin D 3 /day in phase 2, whereas the placebo group ( n =42) received matching placebo. Results: After supplementation, serum 25(OH) D peaked in the vitamin D-group in phase 1 (77.2±30.1 nmol/l, P =0.003) followed by a decrease in the phase 2 (61.4±18.8 nmol/l, P =0.006), although this was higher compared with baseline. In the placebo group, no difference was observed in the serum 25(OH) D levels throughout the intervention. Relative to baseline serum, parathyroid hormone decreased 24% ( P =0.003) in the vitamin D-group in phase 2, but remained unchanged in the placebo group. No significant changes were observed in blood pressure, fasting blood glucose, HbA1c, C-peptide, creatinine, phosphorous, alkaline phosphatase, lipids, C-reactive protein or thyroid stimulating hormone concentrations compared with baseline in either group. Conclusions: Six months of vitamin D 3 supplementation to vitamin D-deficient obese type 2 diabetes patients in the UAE normalized the vitamin D status and reduced the incidence of eucalcemic parathyroid hormone elevation but showed no effect on the metabolic control.