Nonlinear Analysis Methods Applied on Grid-Connected Photovoltaic Systems Driven by Power Electronic Converters

Abstract

A novel nonlinear method of analysis is deployed in detail with the aim to design suitable controllers with guaranteed stability for grid-connected photovoltaic (PV) systems driven by power converters. By this method, all the system nonlinearities are considered in order to allow a reliable analysis in a wide range of operation and to avoid instabilities that as shown in this article can be occurred by inappropriate design. To this end, first, a detailed accurate nonlinear dynamic model is presented for the PV system by including a cascade-mode control scheme. Then, considering the closed-loop system and incorporating the concept of input-to-state stability (ISS), a rigorous novel stability analysis is developed, which achieves to prove asymptotic stability of the desired equilibrium point. A multistep process is deployed, in which the control-loops operating in cascade-mode are involved. However, since the cascaded-mode control scheme and analysis is based on the time-scale separation principle, a systematic tuning method is conducted for the accurate gain selection of both inner-loop and outer-loop controllers, which is based on the construction of suitable Lyapunov functions. To further validate the overall analysis, experimental results are carried out.