Investigation of inverter structures used in flexible alternative current transmission systems and custom power devices

Nowadays energy is essential in every field and every place where the human activity is existed. Energy cost and environmental issues has delayed not only construction of the new power plants but also delayed the new transmission lines, but the demand for energy increases day by day and power requirements has been caused to use the electric power systems as an alternative solution. In order to run the electric power systems reliable and safe power electronics technologies were used. Improvements in power electronics technology, increase the reliability and funtionality of the caused the power electronics based control device FACTS (Flexible Alternative Current Transmission Systems) and custom power devices and make them to be preferred. FACTS and custom power devices is performing an important role to raise the power transmission capacity of the network to the utmost level, providing the high power quality at the common connection port of the distribution system and decreasing the harmonic waves. Therefore it is commonly used and accepted in the electric energy sector. STATCOM (Static Synchronous Compensator), is used in the transmission lines as a kind of FACTS device. In the distribution line special power device is used known as DSTATCOM (Distribution Static Synchronous Compensator). The most important unit of the STATCOM and DSTATCOM are inverters. In the literature numerous inverter structure are advised and used in many implementations. In this thesis study two level and multi-level inverter structures were examined where used in the FACTS devices and two level inverter, diode clamping inverter, cascade inverter, capacitor clamped inverter structures were used. Then these inverter structures were modeled and simulations were performed on MATLAB/Simulink environment. Simulations were analyzed in three phases. In the first stage simulation has been performed by swithcing the inverters with SPWM (Sine Pulse Width Modulation) neutrally. In the second stage a motor load system was analyzed by these inverter structures. Motor load has been used as a load and simulation was analyzed according to it. In these simulations Total Harmonic Distortion (THD) of inverters which modulation index value was changed, and analysis were made by using MATLAB FFT tool. In line with these results, both advantages and disadvantages of inverter structures are explained. In addition, examples applications in the literature are presented.