PIC Based Bipolar and Unipolar SPWM for Pure Sine Wave Single-Phase Inverter

This paper presents a detailed comparative study of bipolar and unipolar Sinusoidal Pulse Width Modulation (SPWM) techniques in DC-AC inverters, focusing on their efficacy in reducing harmonic distortions, which are detrimental to power system performance. Both SPWM strategies are implemented using the cost-effective and high-performance PIC18F2431 microcontroller, tasked with controlling a single-phase inverter to produce a pure sine wave output. An in-depth analysis of Total Harmonic Distortion (THD) levels at various modulation index reveals that while both SPWM methods significantly curtail harmonics, the unipolar SPWM inverter exhibits a more uniform THD reduction across the entire modulation range. Conversely, the bipolar SPWM inverter, though starting with higher THD levels, demonstrates a drastic reduction as modulation index increase, especially when enhanced by the application of an LC low-pass filter. This filter is instrumental in further refining the inverter's output, achieving impressively low THD values below 1% at full modulation, and ensuring a high-quality sinusoidal AC waveform. The comparative results accentuate the nuanced performance differences between the two SPWM strategies and underscore the critical role of LC filters in optimizing inverter output for a variety of power applications.