Grid-forming and Power Tracking by Photovoltaic Systems without Battery Storage

An overall photovoltaic power plant control concept with grid-forming availability without battery storage is proposed. Grid-forming voltage-source converter control is usually studied decoupled from the primary source. Recent studies consider the voltage drop on the DC side for grid-forming control. Until now, the photovoltaic generator and DC-DC converter dynamics are not included. However, it is necessary to consider the overall system dynamics for control design with the objective of fast power control. A generalized control scheme for a two-stage photovoltaic generator model consisting of an aggregated single-diode model of the photovoltaic voltage-controlled current source and a DC-DC converter for tracking the requested power combined with a grid-forming voltage-source converter is presented. For this purpose, the classical maximum power tracking is extended by a generalized demanded tracking. The performance of the approach is evaluated using relevant test cases with active and reactive power requests, grid events like grid voltage drop, phase angle step changes, and fluctuations of the primary energy resource.