Provision of Upward Power Reserve Control for Frequency Regulation by PV Plants

Solar power generation is continuously increasing to meet the growing demand for clean and sustainable energy. Therefore, Power Reserve Control (PRC) is essential in modern Photovoltaic (PV) power systems, as they must provide ancillary services to the grid, including frequency support. This paper proposes a control strategy for the provision of upward power reserve to support frequency regulation by stand-alone PV plants. This is achieved by operating the PV in normal conditions at a working point different from the optimal Maximum Power Point (MPP). This working point, called the Flexible Power Point (FPP), is determined using a piecewise linear approximation of the power-voltage characteristic of a photovoltaic plant. This allows the PV plant to increase its active power generation proportionally to the frequency deviation when required to support the system regulation. Differently from the more conventional linear approximation, the use of the piecewise linearization allows the PV plant to modify its active power generation with high accuracy and provide, in this way, a fast frequency containment reserve service equivalent to the classical droop delivered by traditional generators.