International Journal of Power Electronics and Drive System (IJPEDS) Vol.2, No.2, June 2012, pp. 138~150 ISSN: 2088-8694  138 Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS Three Phase Two Leg Neutral Point Clamped Converter with output DC Voltage Regulation and Input Power Factor Correction B. Sirisha, N. Susheela, P. Satishkumar Department of Electrical Engineering, Osmania University, Hyderabad e-mail:sirishab2007@yahoo.com, satish_8020@yahoo.co.in, nsusheela2007@yahoo.com Article Info ABSTRACT Article history: Received Jan 15 th , 2012 Revised Apr 17 th , 2012 Accepted Apr 27 th , 2012 A three-phase neutral point clamped (NPC) converter is presented for power factor correction and dc-link voltage regulation. The adopted converter has simpler circuit configuration compared to three level PWM converters A simplified space vector pulse width modulation scheme (SVPWM) is adopted to track line current commands. Using a simplified SVPWM algorithm, the calculate time for the time duration of voltage vector is reduced. The adopted NPC converter has less power switches compared with the conventional three-level NPC converter. Only eight power switches and four clamping diodes with voltage stress of half the dc bus voltage are used in the circuit configuration. Based on the proposed control algorithm, a reference voltage vector is generated on the ac terminal for drawing the sinusoidal line currents with unity power factor. Computer simulation results based on MATLAB/SIMULINK are presented to verify the validity and effectiveness of the proposed control strategy. Keyword: neutral point clamped converter, space vector modulation, power factor Copyright © 2012 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Dr. P.Satishkumar, Department of Electrical Engineering, Osmania University, Hyderabad Email: satish_8020@yahoo.co.in 1. INTRODUCTION Diode or phase-controlled rectifiers are widely utilized in the front-end converter for the uncontrollable or controllable DC-bus voltage in industrial and commercial applications. However, low power factor and non sinusoidal line currents are drawn from the AC source owing to a large electrolytic capacitor used on the DC link. Power pollutants such as reactive power and current harmonics result in line-voltage distortion, heating of the transformer core and electrical machines, and increased losses in the transmission and distribution line. To meet the relevant standards in Europe and America, several current wave-shaping solutions have been proposed to achieve power factor correction and current-harmonic reduction. Multilevel rectifiers and inverters have been proposed for high power and medium-voltage applications because they provide advantages such as the low voltage rating of power semiconductors and low voltage harmonics. However, the disadvantages of the multilevel rectifiers are the large number of power semiconductors in the circuit, a complex control scheme and the neutral-point voltage balance problem. In industrial applications with a unidirectional power flow, conventional multilevel converters are too expensive and complicated to implement. A three-phase three-level AC/DC converter with fewer power switches is presented to achieve almost unity power factor, to regulate the DC-link voltage and to achieve fast dynamic response. The circuit topologies of multilevel inverters can be classified into neutral point diode clamped (NPC) inverters [12–13], flying capacitor clamped inverters [14–15], and cascade full bridge inverters. Three-phase three-level NPC converters were proposed in [18–20] to draw the sinusoidal line currents in phase with mains voltages. The input power factor is close to unity. However, twelve power switches and six clamping diodes are used in the circuit configuration.