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Cascaded Multilevel Inverter for Induction Motor Drive

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Abstract
In this paper presents ,a symmetrical five level cascaded inverter topology for Induction motor drive. It can continuously works at lower power stage. For this symmetrical circuit, when the number of level is increased, the voltage and power will also get increased. For reducing harmonics the Sinusoidal PWM method is used. The multilevel inverter gives the output to drive the three phase Induction motor .Its overall system performance is developed by employing multilevel inverter. It increases the act of the entire system in terms of harmonics and tension in the bearings of a motor. The torque ,phase voltage and speed characteristics are observed. The THD for different modulation index is estimated. The power factor is increased. The simulation of the circuit is attained by using MATLAB/simulink.
INDEX TERMS:Cascaded multilevel inverter, Induction motor drive, THD.
I.Introduction
In recent times Cascaded Multilevel inverter has grown to be very popular in large power AC supplies and adjustable-speed drive appliances. it has the advantages of adjustability and modularity. Flying capacitor, diode clamped and cascaded multilevel inverters are the topologies of multilevel inverters. The cascaded multilevel inverter is composed by H-bridge inverter connected in series. Each H-bridge unit has separate dc supplies[1]. The number of output-phase voltage levels in inverter is expressed by m= 2S-1+1,s denotes the number of DC sources available in the inverter circuit. The multilevel voltage source inverters exclusive configuration allows them to attain high voltages. They does not require any additional components like voltage sharing circuit, transformer for increasing the power levels . They are individually suitable to high voltage automobile drives ,because of low output voltage total harmonic distortion. Basically, the number of power cells in a Cascaded inverter is requirement is depends on its operating voltage[2]. the need of components in the Cascaded H-bridge multilevel inverter is less at the same voltage level as compared to other types of inverter. The common utility of the multilevel inverter is to produce a preferred voltage level. Its produces the staircase output waveform. The optimized sinusoidal PWM technique is used for minimizing the number of semiconductor switching devices Sanjiv Kumar and Pramod Agarwal presented ,the nine level inverter topology for an open end winding induction motor drive. in this the nine level inverter output is obtained by connecting the three-level inverter at both ends which feeding power to each end of the open-end induction motor[5]. The five level cascaded MLI is designed for improving induction motor drive performances. The proposed system does not require clamping diodes and capacitor bank[3]. There are several modulation techniques used for reducing switching losses in the symmetrical cascaded inverter . The POD sinusoidal PWM technique is used for producing pulses for MLI. At every level in the inverter, a predetermined DC voltage is added with the reference voltage wave. so its reduces the inverter’s switching losses at lower speed level.
The major benefit in this control scheme is that, at lower speed levels out of two, though the inverter switching accumulates only in one inverter ,other one is preset at one level[4]. therefore switching losses are reduced and also efficiency of whole system gets developed. This paper is organized as follows: Section 2 explores Induction motor drives using multi level inverter and its block diagram Section 3 deals Topology of five level cascaded inverter and POD PWM Technique. Section 4 gives about simulation diagram .Section 5 investigates the results by simulation, also it gives the conclusion about multilevel inverter used for drive application .

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