Assessment of Total Harmonic Distortion in Buck-Boost DC-AC Converters using Triangular Wave and Saw-Tooth based Unipolar Modulation Schemes

Abstract

This paper presents an assessment of the levels of total harmonic distortion (THD) in buck-boost DC-AC converters using triangular wave and saw-tooth unipolar based-modulation schemes. This paper seeks to identify a better technique for mitigating the total harmonic distortion on buck-boost DC-AC converters under unipolar carrier-based modulation schemes. This was achieved by subjecting the buck-boost DC-AC converter under triangular wave-based and saw-tooth based-unipolar modulation schemes. The voltage and current output of the buck- boost DC-AC converter under each scheme was analysed using a power GUI Fast Fourier Transform (FFT) analytical tool resident in the MATLAB Simulink environment unlike with the conventional scheme of computing the percentage of THD. The test system was obtained by a combination of DC-DC buck-boost converter, H-bridge based-insulated unipolar gate transistors, and a logic control unit. It was realized that THD of 0.2865%, peak output voltage of 294.1V and current of 9.805A were obtained by using the saw-tooth based-unipolar modulation scheme, whereas a THD of 0.1479%, peak output voltage of 297.4V and current of 9.53A were obtained by using the triangular wave based-bipolar modulation scheme on the same Buck-boost DC-AC converter circuit. The results imply a high power factor utilization and low power loss in the triangular wave based-unipolar modulation scheme compared to the saw-tooth based-unipolar modulation technique for improving the performance characteristics of the buck-boost converter system. This study showed that power drives and heavy load machines based-power electrical loads are required to use the saw-tooth based-unipolar modulation (STBUM) scheme for high current and low THD%, whereas sensitive power electrical loads such as hospital equipment and communication industries based-power electronic devices are required to use the triangular wave-based unipolar modulation (TWBUM) scheme due to low current and THD%.