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Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

Performance Comparison Of Multi-Level Inverter Fed Induction Motor Drive G.Durgasukumar1, M.K.Pathak2, S.P.Srivastava2 1

Electrical Engineering Department, IIT Roorkee, India Email: durgadee@iitr.ernet.in {mukesfee, satyafee}@iitr.ernet.in

Abstract— Multi-level inverter has emerged as an important topology in the area of high power-medium voltage energy control applications due to their good harmonic rejection capability. This paper presents the application of simplified space vector pulse width modulation (SVPWM) method for three-level, five-level and seven-level diode clamped inverters feeding a threephase Induction motor. This paper compares total harmonic distortion values of voltage waveforms of Induction motor to the conventional two-level inverter drive using diode clamped multi-level inverter (Three, five and seven level).

inverter has presented. This method cannot identify the sector containing the reference space vector. Although these methods propose general SVPWM algorithms for multilevel inverter, the coordinate transformations used in these algorithms are somewhat complicated. In [9], a new simplified space vector pulse width modulation (SVPWM) method for three-level inverter is proposed. In [10-11], a new 3-D SVM in natural coordinates is applied to conventional four-leg voltage source converters showing the advantages of using these coordinates. In [12-13], a novel threedimensional (3-D) space-vector algorithm for four-leg multilevel converters is presented. This technique greatly simplifies the selection of the 3-D region where a given voltage vector is supposed to be found. In this paper, a simple SVPWM method for three-level, above three-level inverter and comparison of total harmonic distortion presented. By using the new SVPWM strategy, effective time calculation and switching sequence selection are easily done like conventional two-level inverter. Simulation studies are carried out using 3-Phase, 50HP, 400V, 50Hz, and 1500RPM induction machine.

Index Terms— Multi-level inverter, SVPWM, Three-level inverter, Five-level inverter, Seven-level inverter, Induction motor, Total harmonic distortion (THD).

I. INTRODUCTION In high power applications, the switching frequency of the power device has to be restricted below 1 KHz unlike in conventional two level due to the increased switching losses and also the level of dc-bus voltage[1]. Many researchers have worked on the space vector modulation of multilevel inverters [2]-[11]. In [2], a method of SVPWM for high level inverters that represents output vector in three-dimensional Euclidean space is presented. The method is based on the fact that increasing the number of levels by one always forms an additional hexagonal ring. In [3], the hexagon representing space vector diagram is flatten and the reference voltage vector is normalized in order to reduce computations of the algorithm. In [4], a SVPWM with a predictive current control loop have presented. In the current error is calculated and the switching state is selected when the value of the error is less. In [5], a space vector modulation allows reduction in the inverter output voltage distortion due to turn-off, turn-on and dead times. In [6], a simple space vector pulse width modulation algorithms for a multilevel inverter for operation in the over-modulation range have presented. In [7], a relationship between space-vector modulation and carrier-based pulse-width modulation for multilevel inverter has presented. In [8], a generalized method of space vector pulse-width modulation for multilevel

II. SIMPLIFIED SVPWM FOR MULTI LEVEL INVERTER A. Basic principle The space-vector diagram of any multi-level inverter is composed of six hexagons, which can be reduced insteps further into the space-vector diagrams of conventional two-level inverters. The space vector diagram three-level inverter and its two level hexagons are shown in Fig. 3(a) and 3(b). A multi-level spacevector plane is transformed to the two-level space-vector plane by using the two steps. 1) From the location of a given reference voltage, one hexagon has to be selected. 2) The original reference voltage vector has to be subtracted by the amount of the center voltage vector of the selected hexagon. Determination of switching sequence and the calculation of the voltage vector duration time is done as in conventional two-level SVPWM method.

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