Comparison Study and Simulation of the Main Multilevel Inverter Topologies for Different Output Voltage Levels

Abstract

This paper discusses the difference between the three fundamental types of multilevel inverter (MLI) topologies, which are the neutral-point-clamped, the flying capacitors and the cascaded H-bridges. The sinusoidal pulse width modulation technique was used to simulate the output voltages and currents of the MLI inverters. The total harmonic distortion (THD) was estimated for each topology and each voltage level. Moreover, the simulation results indicate that the cascaded structure exhibited a lower THD value even when increasing the number of the output voltage. Furthermore, a new key parameter was defined as cost efficiency factor and used to compare the three topologies. Evaluation results of this factor indicate that the cascaded structure was the most advantages as it reduces stress effect on the inverter switches by eliminating the power diodes and capacitors.Keywords: Multilevel Inverter, Sinusoidal Pulse-width modulation, Cost efficiency IntroductionThe fast growth of PV power application industry requires the development of new technologies to maximize the energy yield of the PV systems [1]. This technology concerns the electrical power operation control and transfer in between the PV sources and the customers, to keep the supply of the electric power in a way to match the international standard requirement for power supply [2]. One of the weak points of the PV systems is the incapability conversion from the DC voltage to the AC voltage before connecting to the power network [3]. This conversion is performed by inverters, which are used in power system application and uninterrupted power supplies industries [4]. Improvement of the output voltage required an appropriate control of the waveform on the inverter to reduce its respective harmonic and electromagnetic effect by the diminution of switching operations and hence the filter size [5]. The limitations of the conventional inverters in the case of power or harmonic effect lead to the usage of the multilevel inverter (MLI) technology which promises some advantages over the conventional inverter especially for high power applications [6]. Three main topologies for multilevel inverter are used. The first structure is known as the neutral-point-clamped (NPC) [7], the second as the flying capacitor (FC) [8] and the third as the cascaded H-bridge with separate DC sources [9]. They are characterized by many features such as low total harmonic distortion (THD) of generated output voltage, reduced size of the filter and increased the system efficiency [10]. Thus, aspect lead the MLI topologies to find their application in PV system on the low cost and high performance [11]. New combined topology have been reported, such as three-phase MMLI, where the authors developed to reduce the components number and improve the output voltage level [12]. Moreover, the MLDCL topology which is based on cascaded H-bridge topology connected with half H-bridges cells in a series configuration in purpose to reduce the components number. However, this topology shows a hi...