Open Loop Control of Three Level Space Vector Pulse Width Modulation of Neutral Clamped Multilevel I

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IJIRST –International Journal for Innovative Research in Science & Technology| Volume 3 | Issue 11 | April 2017 ISSN (online): 2349-6010

Open Loop Control of Three Level Space Vector Pulse Width Modulation of Neutral Clamped Multilevel Inverter Fed Induction Motor Praveen O PG Student Department of Electrical & Electronics Engineering Mar Baselios College of Engineering and Technology, Trivandrum, Kerala, India

Dr. Nisha G. K Associate Professor Department of Electrical & Electronics Engineering Mar Baselios College of Engineering and Technology, Trivandrum, Kerala, India

Abstract Speed control of Induction motor drive is one of the major problem faced in almost all industries and leading sectors. In this paper a technique is implemented for a better speed control for induction motor drives using a multilevel inverter. Multilevel inverter have lower distortion of output voltages and Total Harmonic Distortion (THD) of machine currents under steady state operating conditions can be minimized. The switching angle for the pulse is selected to reduce the harmonic distortion. In this drive system it has advantages like reduced total harmonic distortion and higher torque. The model of the multilevel inverter system is fed with SVM method to control the induction motor. The simulations are performed using MATLAB/SIMULINK software and the results are presented. Keywords: Neutral Point Clamped Inverter NPC, Space Vector Pulse Width Modulation, Induction Motor _______________________________________________________________________________________________________ I.

INTRODUCTION

Induction motor is the most commonly used electrical machine in almost all level of voltage in industrial applications, because of its low cost and increased reliability. Due to development of high power and low cost power electronic devices in the area has provided a larger area of application for the ac drives. Hence, ac drives like induction motor drives along with power electronic converters have replaced the dc motor drives in industries. Selection of suitable power electronic converter is the difficulty in using ac drives lies. When using Pulse Width Modulation (PWM) for the control of the power electronic converter, duty ratio input needs to be in a specific range or this can create stability issues. Thus, the power conversion stage is playing a vital role.A multilevel inverter is a good choice for replacing the conventional voltage source inverters or current source inverters. It has many advantages like reduced voltage stress, increased quality of output voltage and increased power rating. In this paper, a neutral point clamped MLI with three levels is designed for induction motor drives. A three level space vector is used to generate switching pulses for the neutral point clamped MLI. The performance of MLI fed induction motor drive is done for various operating conditions. II. NEUTRAL POINT CLAMPED INVERTER The neutral point clamped inverter provides multiple voltage levels through connection of the phases to a series bank of capacitors. In the original invention, the concept can be extended to any number of levels by increasing the number of capacitors in the design [1]-[2]. The additional level was the neutral point of the dc bus, so the name neutral point clamped inverter was introduced. But, with an even number of voltage levels, the neutral point is not accessible, and the term Multiple Point Clamped (MPC) is sometimes applied [3].Early descriptions of this topology were limited to three-levels where two capacitors are connected across the dc bus resulting in one additional level [4]. Due to capacitor voltage balancing issues, the diode-clamped inverter implementation has been mostly limited to the three-level. Because of industrial developments over the past several years, the three-level inverter is now used extensively in industry applications. Although most applications are medium-voltage, a three-level inverter for 480V is on the market. Although the structure is more complicated than the two-level inverter, the operation is straightforward and well known. Each phase node can be connected to any node in the capacitor bank [5]-[7].Connection of the a-phase to junctions can be accomplished by switching transistors Sa1 and Sa2 both off or both on respectively as shown in Fig. 1. These states are the same as the two-level inverter yielding a line-to-ground voltage of zero or the dc voltage.

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