Enhanced SHEPWM for Portable PV Instruments with Second and Odd Harmonic Mitigation

This paper presents an enhanced selective harmonic elimination pulse-width modulation (SHEPWM) scheme tailored for portable photovoltaic (PV)-powered instruments. In conventional SHEPWM techniques, the inherent waveform symmetry is exploited to naturally cancel even harmonics, allowing the focus to be solely on suppressing odd-order harmonics. However, practical PV systems often exhibit nonidealities—such as device mismatches, dead time, and load imbalances—that disrupt ideal symmetry and introduce significant second-harmonic distortion. To address these challenges, the proposed scheme introduces additional design constraints to actively cancel the second harmonic in conjunction with selected odd harmonics (e.g., the third and fifth). A segmented constant function is modeled and a Fourier series expansion is employed to derive analytical expressions for the harmonic coefficients. Simulation on portable circuits verify that the proposed technique significantly reduces total harmonic distortion (THD) and improves output quality, making it highly suitable for the demanding application requirements of portable PV-powered instruments.