Análise e implementação de técnicas de modulação em largura de pulso para uso em inversores trifásicos.

Abstract

Pulse W i d t h Modulation (PWM) techniques for three-phase inverters are analyzed and implemented in this thesis. The analytical treatment in this study covers since P WM principle using BessePs functions to the clamped modulating signals used in recent PWM modulators. A rigorous mathematical development introduces the apportioning factor concept as the parameter to establish the correlation between the per phase and vector P WM techniques. As a consequence a relation between the carrier-based and programmable counter-based methods have been established. To unify different PWM techniques and their implementation, the known concept of ordered voltage segment is used to introduce a new switching pattern representation, which is a set of three ordered switching functions. Also, in the vector approach, the concept of determining in which sector the reference vector is located is treated from the representation of the vectors in tri-dimensional coordinate system.This allows to define the behaviour of the pattern switching in a mathematical basis, disregarding the P W M technique. Different P WM strategies are compared in terms of the both THD and RMS value of the current ripple i n the P WM inverter. For this second performance index, the mathematical expressions are developed in detail. Logic signals derived from the comparison among the sinusoidal references are employed to identify the ordered voltage segment practically. I n general this thesis defines a standard procedure to design either carrier-based or programmable counter-based PWM modulators, including those specified to control pulsed DC link converters. The same approach is used to synthesize an A ppli cat ion-Specific Integrated Circuit (ASICj, which is specified to implement the techniques discussed in this thesis by use of the concept of apportioning factor.