Low cost digital module for demonstration of modulation strategies in DC-to-AC converters

Abstract

This paper presents the development of an educational digital module able to generate control signals considering several modulation strategies for DC-to-AC converters, single and three-phase, to achieve the integration with power modules usually available in educational power converter kits. The designed system uses an accessible and low-cost microcontroller (PIC18F4520) and also shows a simple and user friendly interface. System outputs are made of a LCD display and the control signals related to the implemented modulations. Regarding the single phase modulations, the module contains carrier based strategies with sinusoidal (SPWM), trapezoidal (TPWM) and third harmonic injection (THIPWM) control signals, there is also Selective Harmonic Elimination (SHE) that is not a carrier based strategy. Considering three phase systems two cases of Six-Steps modulation (120° and 180°) have been implemented, besides an evolution of this technique which is the Space Vector Modulation (SVM). The modulations are validated considering the DC-to-AC converter feeding a resistive inductive load.