Emulation of Photovoltaic arrays with shading effect for testing of grid-connected inverters

This paper deals with the development of a Photovoltaics (PV) emulator for testing grid-connected inverters, taking the shading effect on the panels into account. The Single Exponential Model (SEM) of a PV array is used with appropriate approximations. The shading effect is modeled for a configuration of series connected panels, with bypass diodes, and two irradiance levels. This PV modeling is used in a retroactive loop in order to output a voltage reference corresponding to the current measured at the output of the emulator. After being regulated by a Proportional-Integral (PI) controller, this reference produces the duty cycle for the Pulse Width Modulation (PWM) of the DC/DC converter, whose objective is to reproduce this voltage. The emulation is tested first with a resistive load, where it is observed that the characteristic curves of the panels are accurately reproduced, and then on a commercial grid-connected inverter. A Graphical User Interface (GUI) is developed to allow modifying online the test parameters and observe the results in a convenient way so as to properly assess the response of the inverter and its Maximum Power Point Tracking (MPPT) capability. In particular, several tests validate the operation of the emulator, in a reference situation, at the start-up of the inverter and for changing atmospheric conditions.