ACTA ELECTROTEHNICA © 2012 – Mediamira Science Publisher. All rights reserved. 16 Using Five-Level Inverter NPC Topology for Harmonic Compensation of Electric Low-Voltage A. MORSLI, N. OULD CHERCHALI, A. TLEMÇANI and M.S. BOUCHERIT Abstract - The objective of this paper is to improve the quality of the energy transfer from the power supply to the load, and to reduce the harmful effects of the harmonic generated by non-linear loads. In this paper, the problem of the degradation of the current in the installations electric is imposed, which ensues directly from the proliferation of the non-linear loads, to resolve it; a five levels inverter with Neutral Point Clamping (NPC) structure is used as Active Power Filter shunt (APFs). The compensation process is based on concept of P-Q Algorithm. it provides effective compensation for harmonics. Keywords - NPC topology; SPWM four carriers; Active Power Filter Shunt (APFs); THD 1. INTRODUCTION The increasing use of control systems based on power electronics in industry involves more and more disturbance problems in the level of the electrical power supply networks [1-2]. Non-linear electronic components such as diode/thyristor rectifiers, switched mode power supplies, arc furnaces, incandescent lighting and motor drives are widely used in industrial and commercial applications. These non-linear loads create harmonic or distortion current problems in the transmission and distribution network [3]. The harmonics induce malfunctions in sensitive equipment, over voltage by resonance and harmonic voltage drop across the network impedance th at affect power quality [4-5]. Traditionally passive LC filters have been used to compensate the harmonic distortion and the reactive power; but passive filters are large in size, have ageing and tuning problems and resonate with the supply impedance [6]. Recently Active Power Line Conditioners (APLC) or Active Power Filters (APF) overcome these problems and are designed for compensating the harmonics and suppressing the reactive power simultaneously [7]. Since basic principles of active filter compensation were proposed by Gyugyi and Strycula in 1976 [8]. In 1984, Hirofumi Akagi introduced a new concept of instantaneous reactive power (p-q theory) compensators [9]. It dealt with three- phase system, being later worked by Watanabe and Aredes for three-phase four wires power systems [10]. The shunt active power filter compensation process is based on the instantaneous real-power theory; it provides good compensation characteristics in steady state as well as transient states [11]. The instantaneous real-power theory generates the reference currents Manuscript received November 4, 2011. required to compensate the distorted line current harmonics and reactive power. It also tries to maintain the dc-bus voltage across the capacitor constant. Another important characteristic of this real-power theory is the simplicity of the calculations, which involves only algebraic calculation [12]. Multi-level inverters can operate not only with PWM techniques but also with amplitude modulation (AM), improving significantly the quality of the output voltage waveform. With the use of amplitude modulation, low frequency voltage harmonics are perfectly eliminated, generating almost perfect sinusoidal waveforms, with a THD lower than 5 %. The first part consist on using Three-Phase Inverter a Five-Level NPC Topology, the second, method of instantaneous power where we see instantaneous active and reactive powers then apparent power, reactive power and distortion power, in third part an application of the five-level inverter with NPC structure on an Active Power Filter shunt (APFs) and finally exposing th simulation results using Matlab/Simulink. 2. MULTILEVEL INVERTER ILLUSTRATION 2.1. Schematic Diagram Fig 1(a) shows a two level inverter. Fig 1(b) shows a three level inverter. Fig 1(c) shows N level inverter. Vdc Vdc/N-1 Vdc/2 Vdc/2 Vdc/N-1 Vdc/N-1 Vdc/N-1 (a) (b) (c) Fig. 1. Schematic Diagram of (a) Two Level Inverter, (b) Three Level Inverter and (c) N Level Inverter.