This paper proposes a newly-formulated Perturb and Observe (P&O) method for Maximum Power Point Tracking (MPPT) in PV systems. The new formulation considers the effect of solar irradiation level on tracking the maximum power point (MPP). The formulated P&O method is tested under standard test condition (STC) to achieve tracking efficiency 99.98% against 98.4% for the conventional P&O method, 99.5% for the improved and 99.85 for the adaptive versions of the P&O method irrespective of the location of the initial operating point to the right or left of the MPP. The higher the tracking efficiency, the closer is the operation of the PV module to the MPP with a subsequent capture of maximum electric energy available in the incident solar radiation. At constant irradiation level, the tracking efficiency reaches 99.98% for the formulated method against 98.4% for the conventional P&O and 83.6–98.5% for the improved and adaptive versions. The amplitude of output power oscillations around the MPP is reduced to 0.05% of its average value for the formulated method against 1.02% for the conventional P&O, 0.5% for the improved and 0.8% for the adaptive versions. Also, the smaller the oscillations’ amplitude, the closer is the operating point to the MPP. The proposed formulation of P&O tracks successfully the MPP under various conditions including the Ropp irradiation profile, step and ramp changes of irradiation level. However, the conventional P&O method fails to track the MPP under Ropp and ramp changes of irradiation level.

One of the major concerns of carbon fiber-reinforced nylon 6 composites (CF/Nylon 6) is its sensitivity to environmental degradation, especially hygrothermal aging. In this study, neat nylon 6 plates and unidirectional CF/Nylon 6 laminates with different fiber orientations manufactured by hot compression method were subjected to water absorption tests by immersing them in 80 °C and 98 °C hot water for various time durations. The corresponding flexural mechanical properties, including the flexural modulus and flexural strength, of the as-prepared samples before and after water absorption were evaluated by using three-point bending tests. The effects of immersion time, fiber orientation, and water temperature on the flexural properties are discussed. Flexural cyclic tests were conducted to evaluate the stiffness degradation of neat nylon 6 and unidirectional CF/Nylon 6 laminates. Optical observation and scanning electron microscopy were used to observe the fracture behavior of unidirectional CF/Nylon 6 laminates before and after water absorption. Results indicated that the flexural modulus and strength of unidirectional CF/Nylon 6 laminates in different fiber orientations decreased by ≈ 8%–60% and ≈40%–60% after hot water immersion, which was mainly caused by the weakened matrix (the cleavage reaction of the main chain and plasticization of the matrix) and weakened interfacial properties (attack on the interface by hot water). The fracture behavior of 0° CF/Nylon 6 laminates after water immersion tended to be more ductile than those without hot water immersion.

This research article investigated the effect of stacking sequence of glass fibers on the notched and unnotched tensile strength of glass fibers plies reinforced epoxy matrix composites fabricated by the hand lay-up technique. The orientation of glass fabrics was kept at [(0/90)]5, [(45/-45)]5 and [(0/90), (45/-45), ]s and all the laminates were prepared using five plies for different stacking sequences with fiber volume content of 38.6 vol.% with different ratios of the specimen hole diameter to the specimen width with three different values (0.1, 0.2, 0.5). The notch sensitivity of these composites was evaluated applying Whitney-Nuismer mathematical model. The results indicated that the composites with [(0/90)]5 stacking sequence displays the highest tensile unnotched strength, whereas the composites with [±45°]5 stacking sequence displays the least strength. Moreover, the notch sensitivity of [±45°]5 composites is almost higher than those of other stacking sequences with different D/W ratios. On the other hand, the notch sensitivity of [(0/90), (45/-45), ]s composites is slightly lower than those of [(0/90)]5 composite structures for different D/W ratios. Moreover, SEM micrographs indicates the most common failure modes for [(0/90), (45/-45), ]s and [(45/-45)]5 are more significant delamination and matrix cracking than that of [(0, 90)]5.

This research article investigated the effect of stacking sequence of glass fibers on the notched and unnotched tensile strength of glass fibers plies reinforced epoxy matrix composites fabricated by the hand lay-up technique. The orientation of glass fabrics was kept at [(0/90)]5, [(45/-45)]5 and [(0/90), (45/-45), ]s and all the laminates were prepared using five plies for different stacking sequences with fiber volume content of 38.6 vol.% with different ratios of the specimen hole diameter to the specimen width with three different values (0.1, 0.2, 0.5). The notch sensitivity of these composites was evaluated applying Whitney-Nuismer mathematical model. The results indicated that the composites with [(0/90)]5 stacking sequence displays the highest tensile unnotched strength, whereas the composites with [±45°]5 stacking sequence displays the least strength. Moreover, the notch sensitivity of [±45°]5 composites is almost higher than those of other stacking sequences with different D/W ratios. On the other hand, the notch sensitivity of [(0/90), (45/-45), ]s composites is slightly lower than those of [(0/90)]5 composite structures for different D/W ratios. Moreover, SEM micrographs indicates the most common failure modes for [(0/90), (45/-45), ]s and [(45/-45)]5 are more significant delamination and matrix cracking than that of [(0, 90)]5.

This research article investigated the effect of stacking sequence of glass fibers on the notched and unnotched tensile strength of glass fibers plies reinforced epoxy matrix composites fabricated by the hand lay-up technique. The orientation of glass fabrics was kept at [(0/90)]5, [(45/-45)]5 and [(0/90), (45/-45), ]s and all the laminates were prepared using five plies for different stacking sequences with fiber volume content of 38.6 vol.% with different ratios of the specimen hole diameter to the specimen width with three different values (0.1, 0.2, 0.5). The notch sensitivity of these composites was evaluated applying Whitney-Nuismer mathematical model. The results indicated that the composites with [(0/90)]5 stacking sequence displays the highest tensile unnotched strength, whereas the composites with [±45°]5 stacking sequence displays the least strength. Moreover, the notch sensitivity of [±45°]5 composites is almost higher than those of other stacking sequences with different D/W ratios. On the other hand, the notch sensitivity of [(0/90), (45/-45), ]s composites is slightly lower than those of [(0/90)]5 composite structures for different D/W ratios. Moreover, SEM micrographs indicates the most common failure modes for [(0/90), (45/-45), ]s and [(45/-45)]5 are more significant delamination and matrix cracking than that of [(0, 90)]5.

This research investigated the effect of different environmental conditions including moisture, saline and alkaline conditions on the notch sensitivity of short and 2D plain woven glass fibers reinforced epoxy matrix composites fabricated by the hand lay-up technique with fiber volume content of 23.5 and 38.6 vol.%, respectively. The test was carried out through open hole tension test at constant ratio of (D/W = 0.2) and the notch sensitivity of these composites under different environments was evaluated by comparing the notched tensile strength and the characteristic distance (do) of these composites applying Whitney-Nuismer mathematical model. The results indicated that the environmental exposure has a pronounced negative effect on the notched tensile strength of all composites compared to the unconditioned state (virgin state). Moreover, the fracture zone of the composites under the alkaline environment is smooth and shows much less fiber pull out validated by SEM micrographs which distinguishes brittle failure.

This research investigated the effect of different environmental conditions including moisture, saline and alkaline conditions on the notch sensitivity of short and 2D plain woven glass fibers reinforced epoxy matrix composites fabricated by the hand lay-up technique with fiber volume content of 23.5 and 38.6 vol.%, respectively. The test was carried out through open hole tension test at constant ratio of (D/W = 0.2) and the notch sensitivity of these composites under different environments was evaluated by comparing the notched tensile strength and the characteristic distance (do) of these composites applying Whitney-Nuismer mathematical model. The results indicated that the environmental exposure has a pronounced negative effect on the notched tensile strength of all composites compared to the unconditioned state (virgin state). Moreover, the fracture zone of the composites under the alkaline environment is smooth and shows much less fiber pull out validated by SEM micrographs which distinguishes brittle failure.

This research investigated the effect of different environmental conditions including moisture, saline and alkaline conditions on the notch sensitivity of short and 2D plain woven glass fibers reinforced epoxy matrix composites fabricated by the hand lay-up technique with fiber volume content of 23.5 and 38.6 vol.%, respectively. The test was carried out through open hole tension test at constant ratio of (D/W = 0.2) and the notch sensitivity of these composites under different environments was evaluated by comparing the notched tensile strength and the characteristic distance (do) of these composites applying Whitney-Nuismer mathematical model. The results indicated that the environmental exposure has a pronounced negative effect on the notched tensile strength of all composites compared to the unconditioned state (virgin state). Moreover, the fracture zone of the composites under the alkaline environment is smooth and shows much less fiber pull out validated by SEM micrographs which distinguishes brittle failure.

Fault current calculations inside a grid-connected and isolated AC microgrid is one of the major challenges due to the fault current contributions of inverter-based distributed generators units, which are different in location and inverter control during the fault. Therefore, this paper is aimed at calculating fault current for grid-connected and isolated microgrids using two methods; virtual impedance and the proposed method. The proposed method is used to calculate the short circuit current contribution of DG is controlled to analyze the equivalent model of inverter-based DG. The inverter control limits its current to 2p.u of the inverter rating. The proposed algorithm is tested on a standard IEEE 33-bus distribution network with 5 DGs using MATLAB code programs. The results show that the impact of q DG on the fault current is significant especially when faults occur at busses near to the DG location. The fault current value, calculated using the proposed method, is less than its value calculating by the virtual impedance method by more than 30% for grid-connected microgrid and by approximately 50% for the isolated microgrid.

This paper is aimed at investigating MPPT of PV system controlled by SPWM which is generated by comparing sinusoidal wave with variable frequency sawtooth wave. Perturb and Observe (P&O) method is used for MPPT control of PV system. NPC three-phase three-level converter with LCL filter is designed to produce output voltage with minimum Total Harmonic Distortion (THD) and high efficiency. The simple and fast method to get MPP of PV system with variable irradiation is digital control where the maximum power point is obtained from look-up table for the values of optimum voltage that achieve the maximum power for each irradiance value is used for digital control signal in microcontroller. The output voltage harmonic of multi-level three-phase inverter is controlled using SPWM control. THD of output voltage of multi-level three-phase inverter is 22% of stand-alone and grid-connected PV system. Small rate LCL filter is used to limit voltage harmonics within medium and low voltage limits (5%). THD output voltage of LCL filter is 4.9% and 3.51% of stand-alone and grid-connected PV system respectively