SoC-based embedded real-time simulation of mismatched photovoltaic strings

The real time simulation is a key tool for the implementation of monitoring and diagnostic methods as well as of model-based control strategies in modern photovoltaic systems. Under the hypothesis that all the cells of the photovoltaic array operate in the same temperature and irradiance conditions and have the same degradation level, the values of the parameters appearing in the single diode equivalent circuit referred to one cell are scaled up to the whole array, so that the simulation is not computationally demanding at all. Unfortunately, when mismatching effects have to be taken into account, including partial shadowing phenomena and uneven degradation of the cells, the simulation is not as straightforward as in the previous case. A numerical method, which has been recently presented in literature, allows to simulate a large mismatched photovoltaic array with a low computational effort. It exploits a suitable formulation of the non linear system of equations leading to an inverse Jacobian matrix formulated explicitly. In this paper it is shown the process for engineering such a numerical method by using a low cost system-on-chip device available on the market. The analysis presented shows the critical aspects of the implementation, if the computing time has to be minimised for real-time simulation purposes. The advantages offered by the system-on-chip are explored in order to deploy in the best way the algorithm functions on the ARM processor and on the FPGA available therein. Implementation results show the performance of the proposed approach, especially in terms of computation time and use of resources.