PV cell impedance requirements for inductor-less power optimizers

Abstract

Renewable energy sources and in particular solar energy represent our mean to mitigate global warming and reduce the dependency from fossil fuel. Also, photovoltaic panels allow for production of clean energy anywhere, also in the urban environment where, unfortunately, non-ideal working conditions such as partial shading happen often and can reduce the performance of the photovoltaic panels. To maximize the energy produced by these panels, new solutions are proposed where DC-DC converters are attached to the panel. This fact makes the system more complex, due to the necessary extra components, and add losses and volume especially from the inductor of the DC-DC converter.
In this study, a different approach has been studied to facilitate integration of DC-DC converter in photovoltaic panels. Photovoltaic cells as semiconductor devices have an intrinsic capacitance. Moreover, the metallization of the cell, especially on the back, can be redesigned to increase its inductance. Therefore, solar cells can in theory be redesigned to manipulate their output impedance and this impedance could replace the input filter of the DC-DC converter that is used to control the operating point of the photovoltaic panel. This will enable the design of novel solar modules whose operating point is controllable through inductor-less power converters.
To determine the values of the capacitance, inductance and resistance that a photovoltaic cell should have so as to allow inductor-less power conversion as efficient as in a conventional solution with module-level power optimizers, a model of a photovoltaic panel that uses one or more of these “special” cells has been developed. Simulations have been done for a single solar cell and for a photovoltaic module of 96 solar cells. The simulation results provide information for the values of ripples and efficiency of the system so as to determine values of the capacitance, inductance, and resistance of the special cells to replace the components of the converter and also the number of such cells that a PV module should have. Comparison with conventional systems is also performed to compare it with the proposed solution.