Power quality has become an important issue for electric power engineering. Nowadays, the distribution electric networks have unbalanced operating regimes, mainly produced by the great number of single-phase loads. Unbalanced line currents produce unbalanced voltage drops on the three phases of the supply system. Consequently, the voltage system within the supply network will become unbalanced. Voltage unbalance influences different components of the electric networks: the effects on the motors are the growths of losses, supplementary heating, and finally, the motors life is shorted. In the distribution and transmission electric networks the main effect of the unbalanced currents is the existence of additional power losses. Taking into account the above mentioned aspects, it is necessary to study the propagation of unbalance through the electric power system, upstream from the LV distribution level. By using the symmetrical components theory, transformers with different types of connections were studied, and their influence on the unbalance propagation was analyzed. A numerical example is presented for the propagation of unbalance from the secondary side of a transformer with Yz_n connection to its primary side.

Fuzzy-based control systems have demonstrated a remarkable ability to control nonlinear processes, a characteristic commonly observed in power systems, particularly in the context of power quality enhancement. Despite this, an updated and comprehensive literature review on the applications of fuzzy logic in the domain of power quality control has been lacking. To address this gap, this study critically examines published research on the effective and efficient use of fuzzy logic in resolving quality issues within power systems. Data sources included the Web of Science and academic journal databases, followed by an evaluation of target articles based on predefined criteria. The information was then classified into seven categories, including control system type, features of the fuzzy logic controller, fuzzy logic inference strategy, power quality issue, control device, implementation methodology (efficacy testing), and efficiency improvement. Our study revealed that fuzzy-based control systems have evolved from simple type-1 fuzzy controllers to advanced control systems (type-2 fuzzy and hybrid) capable of effectively addressing complex power quality issues. We believe that the insights gained from this study will be useful to both experienced and inexperienced researchers and industry engineers seeking to leverage fuzzy logic to enhance power quality control.

The sustainable development concept has revived the interest for daylighting as any day lit area has very promising energy-saving opportunities; according to some specialists, the potential energy savings can exceed 40%. However, daylight is a dynamic source of lighting, i.e. the illuminance from the sky is not constant, and the variations in daylight can be quite large depending on season, location or latitude, and cloudiness. As a result, electric lighting control systems will be needed from time to time to adapt the lighting systems to changing lighting conditions. Classic control systems, based on continuous dimming present some difficulties to adjust their performances to the rapid changes in daylight and to occupants' preferences. Taking into account these aspects, fuzzy control could be a better solution. The paper analyzes the possibility to implement this new technique in daylighting control and presents the structure of a fuzzy controller proposed by authors; its operation rules and the influence on the imposed value of the illuminance level are also studied.

Daylighting has become a more important feature of recent constructions due to the sustainable design movement, and suitable lighting controls provide building operators with the means to manage the way lighting energy is used in buildings more efficiently. Unfortunately, classic control systems, based on continuous dimming present some difficulties to adjust their performances to the rapid changes in daylight. Therefore, fuzzy control could be a better solution. The paper analyzes the possibility to implement this new technique in the closed-loop daylighting control including shading control and presents the structure of a fuzzy controller proposed by authors; its operation rules and the influence on the imposed value of the illuminance level are also studied.

The paper presents a new technique to mitigate the voltage unbalance in LV distribution grids using distributed generation (DG). Usually, public LV networks supply many single phase consumers; in this case, the unbalanced line currents produce the unbalance of standard symmetrical supply voltage system. This voltage system negatively influences other three-phase loads operating in the same system, i.e. motors, transformers, capacitor banks etc. Consequently, the utility must guarantee to these consumers a balanced voltage system that; this condition can be obtained by using distributed generation. The paper contains aspects regarding the unbalance in LV distribution grids, distributed generation and analyzes the opportunity of involving DG in voltage unbalance mitigation.

A software tool dedicated for the analysis of power signals containing harmonic and interharmonic components, unbalance, voltage dips and voltage swells is presented. The software tool is a virtual instrument, which uses innovative algorithms based on time and frequency domains analysis to process power signals. In order to detect the temporary disturbances, edge detection is proposed, whereas for the harmonic analysis Gaussian filter banks are implemented. Considering that a signal recovery algorithm is applied, the harmonic analysis can be made even if voltage dips or swells appear. The virtual instrument input data can be recorded or online signals; the last ones being get through a data acquisition board. The virtual instrument was tested using both virtually created and real signals from measurements performed in distribution networks. The paper contains a numeric example made on a synthetic digital signal and an analysis made in real-time