Detection and mitigation methods of power quality disturbances

The voltage sags and harmonic currents are the most common disturbances in the power system. These disturbances are mainly caused by the power electronic-based devices and nonlinear loads used commonly in the industrial plants, commercial and residential areas. The term ?power quality? has emerged with the increasing of the disturbances in the power systems recently. This term is used to express the quality of the electricity service by the electricity authorized and end-users.The power electronic based devices are proposed to mitigate the negative effects of the power quality disturbances and used in the power system applications. The utilization of these devices has increased for the improvement of power quality in recent years. Many methods based on time and frequency domains are proposed by the researchers to control these devices. The control algorithms of these devices perform the analysis of the voltage and current signals simultaneously. The analysis of these signals can be divided into two main topics. The first topic is the detection of the disturbances and the second topic is the generation of the compensation signal for mitigating the disturbances. The fast detection of the disturbances and accurate calculation of the compensation signal are the important issues for the control algorithms of these devices.In this thesis, the control algorithms of conventional methods such as Fourier Transform, Wavelet Transform, Reference-Frame Transformation Methods, Fuzzy Logic and Artificial Neural Networks are examined for the disturbances detection and compensation and illustrated graphically. The advantages and disadvantages of these methods are also analyzed and given in details. In additions, new methods for the harmonic currents extraction, voltage sag detection and compensation for the negative effects of these disturbances are proposed. The performance comparisons of the conventional and proposed methods are realized by using the power quality mitigation devices such as Active Power Filter (APF) and Dynamic Voltage Restorer (DVR) in PSCAD simulation program.