A NEW FUZZY BASED THREE-PHASE SYMMETRICAL MULTILEVEL CONVERTER USING VOLTAGE SOURCE INVERTER

Multi-level inverters have obtained great attention as a single stage inverter. Although, they need high number of components, but due to their advantages such as generating output voltage with extremely low distortion factor , low dv/dt, small output filter size, low electromagnetic interface , and low total harmonic distortion, still have great attention be extended , for extra number of output voltage levels ,it is a modular type and it can by adding additional modular stages. To maximize the number of voltage levels the impact of the proposed topology is its proficiency using a reduced number of isolated dc voltage sources and electronic switches. Here we are using the fuzzy controller compared to other controllers i.e. The fuzzy controller is the most suitable for the human decision-making mechanism. In addition, using the fuzzy controller for a nonlinear system allows for a reduction of uncertain effects in the system control and improve the efficiency. A new design and implementation of a three-phase multilevel inverter for distributed power generation system using low frequency modulation and sinusoidal pulse width modulation for various modulation is presented in this paper. To verify the control technique and performance of the topology by using simulation results. INTRODUCTION Many multilevel converter topologies and wide variety of control methods have been developed, due to their advantages such as generating output voltage with extremely low distortion factor , low dv/dt, small output filter size, low electromagnetic interface , and low total harmonic distortion , still have great attention. Multi-level inverters great attention as a single stage inverter. Practically, all of these advantages appear strongly as the number of dc-power sources increased as in the case of renewable energy systems Although this topology uses only one single dc-source, but it has many limitations due to capacitors, existence of three-phase transformer, and high voltage stress on the H-bridge switches as the number of levels is increased. To produce ac voltage waveforms with higher amplitude and near sinusoidal waveform general concept of is to utilize isolated dc sources or a bank of series capacitors. There are three conventional types of named as neutral point diode clamped [7], flying capacitor [8], and cascaded HBridge [9]. Almost all of them are suffering from increased components number per level, and complex control architecture [9]. Among the different topologies for, they can be classified into two main categories: 1) single dcsource inverter such as, and inverters; 2) multi-dc sources inverters such as inverter. While, multi-dc sources inverter is divided into symmetrical and nonsymmetrical topologies. principally, compared to symmetrical topologies nonsymmetrical topologies produce more voltage levels. For more voltage levels almost all of these topologies can be extended by increasing the number of the primary configuration (basic cell). A new hybrid cascaded inverter was presented. Its operation depends on constructing unidirectional staircases waveforms generated from a series connected cells. Each cell consists of one capacitor and four switching devices. Many topologies were presented in the last decade focusing on minimizing the basic multilevel topologies drawbacks. A new topology presented named multilevel dc link. It consists of a group of basic cells connected in series configuration. However, compared to the conventional topologies, this topology requires increased number of components and high voltage stresses. The authors presented a topology named transistor-clamped H-bridge . The primary cell can produce five-levels per pole in the output voltage. However, it suffers also from the increased components counts, requirements of electrolytic capacitors, complex control methodology. While, the a new single dc-link power supply topology presented, the presented topology generates seventeen voltage levels (0,E/16 ,E/8 ,3E/16 ,E/4 ,5E/16 ,3E/8 ,7E/16 ,E/2 ,9E/16 ,5E/8 ,11E/16 ,3E/4 ,13E/16 ,7E/8 ,15E/16 and E) on the output voltage INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume VII /Issue 1 / SEP 2016 IJPRES by using three level flying capacitor inverter and cascades H-bridge. However, this topology utilizes a single dc-power supply. It uses increased number of electrolytic capacitors as floating dc-power supplies. A new double sub-module circuit presented. The presented cell generates a three output voltage levels across its terminals using eight switches and two capacitors. It improved the voltage balancing over capacitors at low switching frequencies; however extra components compared with the equivalent half bridge modules required. A modified flying capacitors topology presented; to produce five levels for pole voltages it requires three dc-power supplies, nine capacitors, and 36 switching devices. It suffers from the same limitation founded and capacitor's voltage balancing problems. For large scale application some topologies were presented. They basically use a dc-ac inverter stage to convert the dc output voltage from the PV modules to the required ac-voltages.This configuration suffers from many limitations like increasing components counts, high cost, noise, low efficiency, and big installation size. Based on a nested arrangement, a new subfamily of was presented in [18]. The nested actually lay in multi dc-power sources topologies category. They have two configurations; one produces an odd number of output voltage levels and the other is belonging to even number of output voltage levels. In order to generate a four voltage levels, it requires three dc-power supplies, four capacitors, and 18 switches. However, it has no diodes compared to the inverters but it requires two extra dc-power supplies. Besides, it uses electrolytic capacitor that has increased the system cost and size. In order to generate three voltage levels, it requires five switches, two capacitors and two diodes. Different basic cells were presented named as clampdouble cell. Compared to the half and full-bridge inverters, it has higher semiconductor losses than the half-bridge inverter [23]. Another basic cell is named five-level cross-connected circuit was presented in [22]. It generates five output voltage levels. However, it requires six switching devices and two capacitors for its operation. Modified cells were created by combining common known basic cells such as half bridge, full bridge, that can be connected in series, in parallel, in cascaded, or in cross configurations. The resulting cells aim to overcome the basic cells drawbacks. The resulting cells are classified as mixed commutation cells, asymmetrical commutation cells, cross-connected commutation cells, clamped double commutation cells, and T-connected. However, all of them suffer from electrolytic capacitor limitations. Based on components per level factor a comparison strategy has been proposed in this paper. To produce one voltage level across the output pole this factor is used to define the required components. Therefore, it acts as a comparison tool that is describing how the different topologies of fully utilize their components. If this factor has a high value, to produce one pole voltage level and vice versa this indicates that a large number of components counts is required. Therefore, the research target is to decrease this factor F = N + N + N + N + N + N