Model Identification of a Photovoltaic System for a DC Microgrid Simulation

Residential microgrids are mainly based on renewable energy sources (i.e., mainly on photovoltaic panels), energy storage systems (that enable time-shift between production and consumption), and on power converters representing control points that by proper operation ensure overall system stability and quality of power supply. For optimal techno-economical microgrid operation, i.e. microgrid voltage level control and power flow management, the models of microgrid components involved must be known. In this paper we verify a single-diode five-parameters equivalent electrical model of a photovoltaic array by experiments, and based on the verified model propose a new power production model suitable for microgrid power flow optimization applications. Microgrid components are connected to a common power link via an appropriate power converter in order to ensure components' maximum efficiency and the overall system stability. Simulation of DC/DC power converters on a switching level requires significant computational efforts due to high switching frequencies (10-100 kHz). However, it is shown that dynamical behaviour of a DC/DC power converter in closed control loop can be replaced by a PT2 dynamic element with good approximation accuracy. All equivalent electrical models presented in this paper are implemented in the professional simulation platform for power electronic systems Plexim PLECS.