Reduced Device count 7-Level Asymmetrical Multilevel Inverter with Various Modulation Schemes

Multilevel inverters offers various applications in voltage ranging from medium to high such as in renewable sources, industrial drives, blowers, conveyors and fans. Multilevel inverters are key technology in various industries operations and becoming more and more popular day by day because of its many advantages over 2-level inverter such as less THD in output waveform, voltage stress on switches and less electromagnetic interference. This paper presents a new asymmetrical MLI topology for 7-level inverter which require less number of switches and driver circuits as compared to other conventional MLI topologies. This proposed MLI topology here is implemented with different pulse width modulation techniques, which requires less amount of power switches and voltage sources to reduce the complexity of circuit as compared to other MLI configurations. MATLAB/Simulation is used to simulate the results of 7-level MLI inverter topology. Index Terms Multilevel inverter (MLI), seven level inverter, asymmetric topology, total harmonic distortion (THD), multicarrier pulse width modulation. I.INTRODUCTION A multilevel inverter is a power electronic device which is capable of providing desired alternating voltage level at the output using multiple lower level DC voltages as an input. Mostly a two-level inverter is used in order to generate the AC voltage from DC voltage. Multilevel Inverters have come upon with broad applications, especially high power and medium voltage drives, distributed generation, HVDC transmission, static VAR compensation, electric vehicular technology and many more [1-2]. The main advantage of multilevel inverter over two level inverters configurations are decrease total harmonic distortion (THD), decrease dv/dt stress across devices, less electromagnetic interference (EMI), less common mode voltage and improve use of rail voltage etc. Several multilevel topologies have been classified as the diode clamped multilevel inverter (DCMLI) [2], the flying capacitor multilevel inverter (FCMLI) [3], the cascaded H-bridge multilevel inverter (CHBMLI) [4]. The diode clamped and flying capacitor converter configurations function with the single DC source but the number of device increase parabolically with the number of output levels raises production cost and complicated control. In cascaded H-bridge multilevel inverter uses full H-Bridge connected in series to produce inverter AC from separated DC sources but major disadvantage is requirement of multiple DC – sources, which is not feasible in many applications. In Multilevel inverters the basic principle is to use low voltage switches for getting high output voltage by dividing the supply voltage among the power electronics switches. An asymmetric topology [5] is presented which uses one voltage sources and two switches are the basic unit. One more dc voltage source and a switch is connected with the basic unit to generate more level in output voltage. These units are connected in series in order to achieve more levels. Usage of unidirectional and bidirectional switches makes the multilevel inverter of large size. The proposed topology [9] consists of two dc voltage source and six power electronic switches. This topology is compared with various topologies to show its advantages. The proposed is stimulated in MATLAB for 7-level inverter. It can also be used for three phase system. II. PROPOSED TOPOLOGY AND ITS OPERATION A new topology for 7-level base on asymmetrical multilevel inverter is shown in Fig.1. It consists of six power electronic switches written as Sw1, Sw2, Sw3, Sw4, Sw5, Sw6 and two dc voltage sources of different rating named as V1 and V2. Out of six switches two switches are bidirectional (Sw2, Sw6) and other four switches are unidirectional (Sw1, Sw3, Sw4, Sw5). International Journal of Science, Engineering and Technology Research (IJSETR) Volume 7, Issue 6, June 2018, ISSN: 2278 -7798 408 All Rights Reserved © 2018 IJSETR L O A D SW1