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Background Allergic disorders are common health problems worldwide with significant socio-economic impacts. The best diagnostic method using allergenic extract is the skin prick test. Regarding the effects of geo-climatic factors and allergenic extract source material quality, the aim of study was to determine the safety and efficacy of some in-house-developed allergenic extracts. Methods Forty-five different allergenic extracts, including common regional pollen, foods, and dog and cat hair, as well as positive and negative extracts, were prepared from domestic sources using optimum extraction methods. All extracts passed stability and sterility testing, and sterile final products containing 50% glycerin in 10 and 20 w/v concentrations were used. Skin prick testing was performed on volunteers and immediate or late side effects were recorded. Results In total, 56 students (mean age: 21.2±2.3y, M/F ratio: 1.07) participated in this study. For inhalant allergens, all extracts except dog hair extract caused positive responses. Salsola kali (Russian thistle) and Fraxinus velutina (ash tree) were the most common grass and tree pollen extracts, respectively. Of 18 different food extracts, five, including egg white, tomato, fig, melon, and green pepper caused skin reactivity in only one person. No participant reported any immediate or late side effects, including large local reaction or systemic response. Conclusion The result of the current study confirmed the safety of all our in-house-developed allergenic extracts. Regarding efficacy, almost all inhalant and five food allergens caused positive skin responses.

Background Vaccine efficiency has a significant role in the public perception of vaccination. The current study was designed to evaluate the efficacy of COVID-19 vaccines (AZD-1222, Sputnik-V, Sinopharm, and Covaxin) and the effect of age and gender on vaccine efficacy. We evaluated the efficacy of these vaccine between 214 health care employees in Iran. Blood samples were taken from all participants at day 0 and 14 days after the second dose. Humoral responses were evaluated by SARS-CoV 2 Neutralization Ab Detection kit. Results The frequency of immunized individuals in the Sputnik V and AZD-1222 groups was 95% and 93%, respectively. This rate was 73% and 70% for Sinopharm and Covaxin vaccines. Comparison of the results obtained from the effectiveness of the vaccines between female and male groups did not demonstration a significant difference. Moreover, comparison of the results obtained from the effectiveness of vaccines between age groups showed that the rate of immunization in participants

In small/medium-sized isolated power networks with low rotational inertia and high penetration of renewables, generation/load contingency events may cause large frequency excursions, potentially leading to cascading failures and even blackouts. Therefore, it is crucial for system operators to be able to monitor the state of the network in real-time and predict the maximum possible frequency deviations at all times. This paper presents a real-time frequency stability (RTFS) tool developed by the Australian Energy Market Operator (AEMO) and operationalized in the control room for the South West Interconnected System (SWIS) to ensure that the available spinning reserve is sufficient and fast enough to arrest frequency excursions under any conditions, and particularly low-inertia ones. To reduce the computational burden and complexity of the different turbine-governor models, a simple first-order lag function with two adjustable variables has been used for each of the generator. These adjustable parameters, along with other key model parameters such as load damping and inertia, have been calibrated against actual frequency response using high-speed fault recorder data from historical events. As demonstrated in several case studies, the real-time tool has proven to be accurate at predicting the trajectory of system frequency after credible contingencies, thus suggesting that similar implementations could be carried out elsewhere while power systems worldwide progress towards lower inertia.

This paper presents a novel closed-form solution for a low-order system frequency response (SFR) model that is accurate for all time periods and an accompanying approximation for representing primary frequency responses at two different speeds while still maintaining mathematical tractability. This allows for the inclusion of both fast frequency responses (e.g. from battery energy storage systems) and more conventional responses (e.g. from thermal generation) in a single SFR formulation. The closed-form expressions can be efficiently used in applications that use the SFR model such as frequency stability studies and security-constrained unit commitment (SCUC) studies.

A new custom power device (CPD) is introduced for real-time control of reactive power and improving the overall network voltage quality of smart grid (SG) at fundamental and harmonic frequencies, respectively. The idea is to take advantage of the online smart meter data transmitted from each bus to the SG central control to concurrently perform the static synchronous compensator and the active power line conditioner operations by optimal compensations of fundamental reactive power and harmonic currents at selected optimal buses. The proposed strategy involves two particle swarm optimization algorithms. The first algorithm is implemented for the worse operating condition to determine the optimal locations and sizes of CPDs while the second algorithm relies on smart meter information to continuously compute fundamental and harmonic reference currents for real-time operation and control of the allocated CPDs. The objective functions are cost minimizations associated with bus voltage regulations, network total harmonic distortions voltage and custom device sizing while the constraints include upper limits for CPD sizes, fundamental, and harmonic bus voltages. Detailed simulations are performed in MATLAB/Simulink to evaluate the performances of allocated CPDs in controlling the reactive power and voltage quality of a distorted 15-bus SG with six nonlinear loads according to the IEEE-519 standard.

This paper proposes a new constant-frequency space-vector hysteresis current control (CF-SVHCC) technique for three-level neutral-point diode-clamped (TL-NPC) inverters in shunt active power filter applications when applied to three-phase isolated neutral point (INP) systems. The proposed techniques is developed based on two recognized modulation methods, space-vector pulsewidth modulation and adaptive hysteresis-band current control. The proposed technique consists of two alternating adaptive hysteresis-band strategies around the error-current vector in the $$\alpha \beta $$ stationary reference frame (SRF). The first strategy is designed with the purpose of utilizing the medium- and large-voltage vectors of the TL-NPC inverter to keep the error-current vector within the adaptive hysteresis boundary, while the second one is designed according to the small-voltage vectors of the TL-NPC inverter to balance its neutral point voltage. The main part of this proposed technique is a supervisory controller that operates in SRF to effectively avoid inter-phase dependency. This smart controller systematically uses the zero-voltage vectors and the nonzero-voltage vectors associated with the alternating adaptive hysteresis-band strategies in order to prevent high switching frequency and maintain the switching frequency constant in INP systems, respectively. The proposed CF-SVHCC performance is validated by extensive simulation studies for both steady-state and transient conditions.

This paper proposes a new constant frequency space-vector hysteresis-band current control (CF-SVHCC) in the stationary reference frame (SRF) for three-level active power filter applications when applied to isolated neutral point (INP) systems. CF-SVHCC is designed based on two recognized modulation methods: 1) space-vector modulation and 2) adaptive hysteresis current control. The proposed technique consists of a simple circular hysteresis strategy around the current-error vector in SRF with the purpose of employing the zero- and nonzero-voltage vectors of the three-level voltage source inverter. CF-SVHCC continuously estimates an adaptive outer hysteresis-band in the SRF using the inverter switching signals by a simple and fast artificial neural network method called the adaptive linear neuron algorithm. The main part of CF-SVHCC is a supervisory control unit that operates in the SRF to avoid interphase dependency and systematically uses the voltage vectors associated with the estimated outer hysteresis-band to prevent a high switching frequency and, in turn, maintain the switching frequency constant. CF-SVHCC retains most benefits of the conventional HCC and also introduces additional advantages, including a constant switching frequency and the interphases independency in three-phase INP systems.

Distributed generations (DGs) are predicted to perform an increasing role in the future power system. Expose of DGs can change the fault current during a grid disturbance and disturb the existing distribution system protection. Solid-state fault current limiters (SSFCLs) can provide a quick system protection during severe faults and are expected to advance the reliability and stability of the power system. SSFCLs are categorized into R- (resistive) and L- (inductive) types by the fault current limiting impedance. An L-type SSFCL is more effective in suppressing the voltage drop during faults. On the other hand, an R-type SSFCL is more effective in consuming the acceleration energy of generators during faults. Therefore, applying both functions lead to the improvement of the power quality and transient stability of the power system. This paper aims to investigate the performance of an inductive–resistive-type solid state fault current limiter (SSFCL-LR) that captures the features and advantages of inductive SSFCLs (SSFCL-Ls) and resistive SSFCLs (SSFCL-Rs) on an electric power network with the doubly-fed induction generator wind-turbine (DFIG-WT), which is a representative renewable energy source. Its connection to a power network simply increases the short-circuit current during a fault toward its maximum nominal level, which is closer to the rating of the circuit breaker, when compared to the case without the DFIG-WT system. This can aggravate the reliability of the overall power system. Detailed laboratory experiments and simulations are performed to demonstrate the capability of SSFCL-LR in simultaneously controlling the fault current, improving the power quality and enhancing the transient stability of the IEEE benchmark four-machine two-area system with induction generator wind turbines (IG-WT) and DFIG-WTs. PSCAD/EMTDC was used in order to analyze the power system characteristics of the SSFCL-LR unit.

Among the four basic dynamic voltage restorer (DVR) topologies, the network-side shunt-connected DVR (NSSC-DVR) has a relatively poor performance and is investigated in this paper. A new configuration is proposed and implemented for NSSC-DVR to enhance its performance in compensating (un)symmetrical deep and long voltage sags and mitigate voltage harmonics. The enhanced NSSC-DVR model includes a three-phase half-bridge semi-controlled network-side-shunt-connected rectifier and a three-phase full-bridge series-connected inverter implemented with a back-to-back configuration through a bidirectional buck-boost converter. The network-side-shunt-connected rectifier is employed to inject/draw the required energy by NSSC-DVR to restore the load voltage to its pre-fault value under sag/swell conditions. The buck-boost converter is responsible for maintaining the DC-link voltage of the series-connected inverter at its designated value in order to improve the NSSC-DVR capability in compensating deep and long voltage sags/swells. The full-bridge series-connected inverter permits to compensate unbalance voltage sags containing zero-sequence component. The harmonic compensation of the load voltage is achieved by extracting harmonics from the distorted network voltage using an artificial neural network (ANN) method called adaptive linear neuron (Adaline) strategy. Detailed simulations are performed by SIMULINK/MATLAB software for six case studies to verify the highly robustness of the proposed NSSC-DVR model under various conditions.

Utilization of plug-in electric vehicles (PEVs) in residential feeders is gaining popularity in recent years due to the societal awareness about greenhouse gas emission and the increasing of petrol price. The potential for network stress and congestion due to uncoordinated charging of PEVs is significant as they represent sizeable unbalanced loads with unpredictable locations, plug-in times, charging rates and durations. This paper aims to mitigate the detrimental impacts of electric vehicle charging on smart grid by implementing a decentralized coordinated PEV charging algorithm that will also improve the power quality of smart grid. The idea for the individual PEV chargers is to acquire distribution transformer loading through the smart meters to dynamically coordinate their charging times, rates and durations in order to improve the overall system voltage profile, reduce transformer stress and control current imbalance. Simulation results will be generated and analysed for an unbalanced three-phase 62 node residential network populated with PEV chargers using the Simulink-Matlab software.

Low frequency oscillations (LFOs) are load angle oscillations that have a frequency between 0.1-2.0 Hz. Power system stabilizers (PSSs) are very effective controllers in improvement of the damping of LFOs. PSSs are designed by linearized models of the power system. This paper presents a new model of the power system that has the advantages of the Single Machine Infinite Bus (SMIB) system and the multi machine power system. This model is named a single machine normal- bus (SMNB). The equations that describe the proposed model have been linearized and a lead PSS has been designed. Then, particle swarm optimization technique (PSO) is employed to search for optimum PSS parameters. To analysis performance of PSS that has been designed based on the proposed model, a few tests have been implemented. The results show that designed PSS has an excellent capability in enhancing extremely the dynamic stability of power systems and also maintain coordination between PSSs.

Some of the earliest power system stability problems included spontaneous power system oscillations at low frequencies. These Low-Frequency-Oscillations (LFOs) are related to the small-signal stability of a power system and are harmful to obtain the maximum power transfer. A contemporary solution to this problem is the addition of Power System Stabilizers (PSSs) to the automatic voltage regulators on the generators in the power system. In this paper, allocation of PSSs in an interconnected power system with inter-area modes has been determined by eigenvalue analysis, and PSSs for the allocated generators have been designed by a frequency response method. Furthermore, for designing PSSs by the frequency method, this paper proposed a new linear power system model which can consider both local and inter-area oscillations of the power network. Designed PSSs based on the proposed model improved damping performance of PSSs which have been designed by the Single-Machine-Infinite-Bus (SMIB) model. The stabilization performance of the designed PSSs (by the proposed approach and linear power system model) on the LFO modes have been verified in two multi-machine power system standard models (IEEE 9-bus and 14-bus).

In this paper, it is aimed to investigate the impact of the various solid-state fault current limiters (SSFCLs) on several electric power networks with the wind-turbine power generation (WTPG). Distributed generations (DGs) are predicted to perform an increasing role in the future electrical power system. Expose of the DG, can change the fault current during a grid disturbance and disturb the existing distribution system protection. Fault current limiters (FCLs) can be sorted into L-types (inductive) and R-types (resistive) by the fault current limiting impedance. In this paper, a new SSFCL has been proposed. SSFCLs can provide the fast system protection during a rigorous fault. The act of dynamic damping enhancement via the SSFCL is appraised in the presence of the wind-turbine power generation. Hence, its efficiency as a protective device for the wind-turbine system is confirmed via some case studies by time-domain simulation based on the PSCAD/EMTDC.

Distributed generators are acquiring more attention in power systems because they can avoid distribution and transmission upgrade requirements and improve power quality issues. Islanding is one of the problems that arise with integrating these resources into the distribution system. In this article, a novel hybrid islanding detection technique is proposed which uses average rate of voltage change and capacitor bank tap switching. The proposed method is tested on a real system and different load characteristics with different dependence coefficients to voltage and frequency are studied. The power system is perturbed only when the method suspects that islanding has occurred. The proposed method could detect islanding conditions with very small power mismatches in them.

Solid-state fault current limiters (SSFCL) in power systems are alternative devices to limit prospective short circuit currents from reaching lower levels. Fault current limiters (FCL) can be classified into two categories: R-type (resistive) FCLs and L-type (inductive) FCLs. L-type FCL uses an inductor to limit fault level and is more efficient in suppressing voltage drop during a fault. In contrast, R-type FCL is constructed with a resistance and is more effective in consuming the acceleration energy of generators during a fault. Both functions enhance the transient stability of the power system. In the present paper, a novel SSFCL is proposed to enhance power system transient stability and power quality. The proposed SSFCL uses both functions of an L-type and R-type FCL. SSFCL consists of four diodes, one self-turn-off IGCT, a current-limiting by-pass inductor (L), and a variable resistance parallel with an inductor for improvement of power system stability and prevention of over-voltage across SSFCL. The main advantages of the proposed SSFCL are the simplicity of its structure and control, low steady-state impedance, fast response, and the existence of R-type and Ltype impedances during the fault, all of which improve power system stability and power quality. Simulations are accomplished in PSCAD/EMTDC.

A space-vector hysteresis modulation (SVHM) technique is presented in this paper for three-level neutral-point-clamped (TL-NPC) multilevel inverter for active power filter (APF) applications. The main responsibility of this modulation technique is to force the actual current to reach the reference current and, simultaneously, balance the capacitor voltages. This scheme is implemented in the stationary reference frame (SRF) to avoid interphase dependency in three-phase floated neutral point (TP-FNP) systems. The space-vector-based method permits for the efficient application of zero-voltage vectors and avoids high switching frequencies triggered by phase interaction in TPFNP systems. The approach comprises of performing two alternative hysteresis strategies around the error vector in SRF. Then, based on the present location of it, the next voltage vector is selected to minimize the next error vector and also balance the capacitor voltages. The performance of the proposed technique is investigated and verified through detailed simulation studies for both steady-state and transient conditions.

The Hysteresis current control (HCC) is a popular modulation technique used in active power filter (APF) applications owing to its simplicity of implementation, fast current response and peak current limiting capability. Despite these advantages, it has a major disadvantage when applied to three-phase isolated neutral point (INP) systems: interphases dependency causes very high-switching frequencies. To overcome this problem, this paper presents a new space-vector hysteresis current control (SVHCC) modulation for APFs when applied to three-phase INP systems. The space-vector-based method allows for the efficient use of zero-voltage vectors and prevents high switching frequencies caused by phase interference. The approach comprises of initially performing two hysteresis bands around the error vector in the αβ stationary reference frame (SRF) and then selecting the next voltage vector based on the present location of the error vector to reduce the next error vector. The proposed approach is verified through detailed simulations using MATLAB software.

Active power filters (APFs) are widely accepted power electronic devices for compensating harmonic currents produced by nonlinear loads. The conventional technology used for APFs is a proportional-plus-integral (PI) controller. However, both the conventional approaches for determining the PI coefficients and also its structure may not provide satisfactory results under transient operating conditions such as a sudden change of load. Therefore, this paper proposes a proportional-integral-derivative fuzzy logic controller (PID-FLC) to improve the steady-state and transient performances of the conventional APF controllers. First, particle swarm optimization (PSO) is utilized to determine the optimal coefficients of the proposed PID-FLC. Then, the direct current control approach is used to generate the reference harmonic signals from the non-sinusoidal load current while an adaptive hysteresis-based current control is selected to control the compensating currents. Simulation results for a power system connected to a nonlinear load are generated to investigate the dynamic performance of APF equipped with the conventional-PI (C-PI), optimized-PI (OPT-PI), optimized-PID (OPT-PID) and optimized-PID-FLC (OPT-PID-FLC) controllers using

In this paper, an adaptive configuration for PID type fuzzy logic controller (FLC) is proposed to improve the performances of both conventional PID (C-PID) controller and conventional PID type FLC (C-PID-FLC). The proposed configuration is called adaptive because its output scaling factors (SFs) are dynamically tuned while the controller is functioning. The initial values of SFs are calculated based on its well-tuned counterpart while the proceeding values are generated using a proposed stochastic hybrid bacterial foraging particle swarm optimization (h-BF-PSO) algorithm. The performance of the proposed configuration is evaluated through extensive simulations for different operating conditions (changes in reference, load disturbance and noise signals). The results reveal that the proposed scheme performs significantly better over the C-PID controller and the C-PID-FLC in terms of several performance indices (integral absolute error (IAE), integral-of-time-multiplied absolute error (ITAE) and integral-of-time-multiplied squared error (ITSE)), overshoot and settling time for plants with and without dead time.