Photovoltaic differential power converter trade-offs as a consequence of panel variation

Abstract

Photovoltaic (PV) elements have inherent variation between cells and panels due to manufacturing tolerance, degradation, and situational differences. This variation increases over system lifetime and creates maximum power point current mismatch that reduces output power when PV elements are strung in series. Traditionally, mismatch loss is addressed using cascaded converters. However, this research examines a differential converter architecture that achieves higher efficiency by processing a fraction of the total power. The effect of PV maximum power point (MPP) current variance on output power is modeled and examined using Monte Carlo simulation for the series string architecture with and without bypass diodes, and the PV-to-Bus and PV-to-PV differential power processing (DPP) architectures at various power ratings. Hot spotting can be a problem that significantly reduces output power. PV elements at fault can be bypassed, passively or actively, to reduce power loss. Simulation results show that both DPP architectures employing active bypass are able to compensate mismatch over the 25-year lifetime of a PV system with converters sized at approximately 10-20% of the panel ratings.