Paper for EPE-PEMC 2002, Authors: J. Pontt et Al. 1 Paper for EPE-PEMC 2002, Topic 3: Control of Converters, Dialog Presentation “Low Switching Frequency PWM with Selective Harmonic Elimination for Three-Phase Three-Level Inverters” J. Pontt, J. Rodriguez, R. Benavides, R. De Solminihac, M. Müller Departamento de Electrónica - Universidad Técnica Federico Santa María Casilla 110-V, Valparaíso, Chile, Tel:+56-32-654554, Fax:+56-32-797468 E-Mail : jpo@elo.utfsm.cl Abstract – Low Switching Frequency Modulation with Harmonic Elimination for Three-Level Inverters reduces harmonic distortion at the Three-Phase load, EMI emissions and thermal stress in power switches. The calculation algorithm for the 3-, 5-, and 7-Angle-Scheme and the remaining harmonics up to the order 31 are presented. Experimental results verifies the expectations. Keywords: Multilevel converters, Three-Level Inverters, Converter control, Low Harmonic distortion. I. Summary Three-Level Inverters are employed for medium voltage high-power applications [1], [2], [3]. Optimized pulse pattern with low switching frequency should be used for the required performance and reliability, specially in industrial systems with 4-Quadrant operation within a harsh environment like mining facilities, considering also multiconverter 12-Pulse connections [4], [6], [8]. The selective harmonic elimination with few switching angles is becoming a very useful technique for reducing selected harmonics, allowing losses reduction and lower thermal stressing in the power semiconductors [1]. Indeed, thermal behavior is a very important issue in high-power converters for conveyors drives located in tunnels with poor ventilation [4]. Other methods like vector modulation techniques like [7] have some disadvantages in the upper region of modulation indexes. In order to configure the modulation control, the remaining harmonics should be also considered to avoid possible resonance [5]. This work presents a calculation algorithm based on Newton technique and experimental evaluation for the 3-, 5-, and 7- Angle-Scheme and the evaluation of the remaining harmonics up to the order 31. II. Selective Harmonic Elimination. A. Principle. The principle of the selective harmonics elimination is based on Fourier analysis of the Three-Level Inverter voltage. The generalized waveform of the neutral voltage of a NPC Inverter concerning the number of commutations in a quarter of a period is shown in figure 1. π 2π V U-0 ωt DC link /2 -DC link /2 α 1 α 2 α 3 α Ν ... Fig. 1 Neutral voltage waveform. The corresponding Fourier Series: ( ) t n a V n n o u ω ∑ ∞ = - ⋅ = ,... 5 , 3 , 1 sin (1) And the coefficients a n describing the harmonic voltage contents are given by:       - = ∑ = + N k k k n n n a 1 1 ) cos( ) 1 ( 4 α π (2) 0 = n b (3)