Grid-Tied PV System with Small DC-Link Capacitor and Low-Frequency Ripple-Free Maximum Power Point Tracking

Abstract: This paper proposes a grid-tied cascaded multilevel inverter (CMI) PV system based on current-fed dual- active-bridge (CF-DAB) dc-dc converters using small dc-link capacitors. The cascaded multilevel inverter (CMI) has many advantages, such as modularity, low harmonic spectra, high ac voltage application with low device rating and low electro-magnetic interference (EMI). In addition, distributed maximum power point tracking (MPPT) terminal for segmented PV arrays can be achieved by CMI PV converter. The low-frequency ripple-free MPPT is also realized in the proposed converter. A novel variable step-size MPPT algorithm is proposed to ensure high MPPT efficiency and fast maximum power extraction under rapid irradiation change. Fast tracking speed under rapid irradiation change and high MPPT efficiency were realized for the PV system.

Keywords: Current-fed dual-active-bridge (CF-DAB), dual-active-bridge (DAB), high frequency link (HFL), low- frequency ripple, maximum power point tracking (MPPT).