PV power harvesting scheme for nanogrid applications using meteorological data

Abstract

This paper presents a direct power harvesting scheme for a PV module using online measurements of meteorological data (solar irradiance and temperature) to be employed for residential standalone applications at nanogrid scale (less than 5 kW). The proposed power harvesting scheme is investigated with both step-down and step-up converters. With both converters, two controllers (PI and ON/OFF) are employed to adjust the chopper duty cycle (in case of PI controller) such that the actual PV power is well controlled to the instantaneous maximum PV power computed from the meteorological data model, or to restrict the actual PV power between upper and lower limit oscillating around the maximum value (in case of ON/OFF controller). The proposed scheme is characterized by fast transient response and good accuracy with low computation complexity thanks to the elaborated meteorological data model of the PV module. Compared with the commonly used perturb and observe (P&O) technique, the proposed scheme has better performance under rapid variation of atmospheric conditions. Under partial shading condition the P&O technique fails to track the global maximum power point and can trap in one of local maximum power points, the proposed scheme suffers also from low capability to plug (handle) the non-uniform irradiance into the maximum power calculation model. Therefore, the system performance under partial shading condition is dragged down due to inaccurate computation of instantaneous maximum PV power. Consequently, the application area of such scheme is limited to low power nanogrid PV systems composed of few PV modules where commercially available temperature and solar irradiance transducers can be embedded with the control system without dramatic increase to the initial cost of the overall system.