Online condition monitoring of Photovoltaic (PV) cells by implementing electrical impedance spectroscopy using a switch-mode DC-DC converter
Linda Shelembe, Paul Barendse
Abstract
This work focuses on the real-time condition monitoring of Photovoltaic (PV) cells by implementing electrical impedance spectroscopy (EIS) using a boost converter. In residential or industry PV applications with storage, solar panels are connected to a battery through a charge controller with a dcdc converter. This set-up makes using a dc-dc converter for condition monitoring ideal for PV cells. The bandwidth of a PV cell is greater than 100kHz, as such, to obtain the impedance information of the cells, the dc-dc converter would need a switching frequency of at least ten times this bandwidth - which will be achieved by using Silicon Carbide (SiC) MOSFETS. The nonlinear relationship between the EIS duty cycle and the EIS control voltage signal, was characterized for signal injection. A QFT control law that treats the EIS frequency and PV's capacitive parameters as structured uncertainties, was designed to ensure robust signal injection. The simulation results show that the online system adequately performs EIS and gives good impedance results comparable to a Frequency Response Analyzer (FRA).