A generic model of two-stage grid-connected PV systems with primary frequency response and inertia emulation

• Dynamic model of a grid-connected PV system with frequency response capabilities.
• Developed model concerns PV systems which are not equipped with energy storage.
• PV station operates with controlled droop/inertia gains and power reserves.
• Frequency-dependent PV power modulation achieved via the DC/DC converter.
• Parameter sensitivity analysis for the droop and inertia frequency controller.

Photovoltaic (PV) stations are increasingly becoming subject to grid code requirements that include frequency response and active power control capability. The main goal of this paper is to propose a generic model for a two-stage grid-connected PV system with frequency response capability, suitable for power system studies. The proposed model includes a suitable control scheme, which provides both droop and inertial response, as well as the ability to operate at a scheduled active power reserve, enabling thus the provision of under-frequency response. A linearized small-signal model is developed to assess the stability of the proposed PV power control loop when the PV generator provides frequency response, whereas time-domain simulations are performed in order to quantify the benefits achieved by droop-type and inertia frequency controllers, including a discussion on the selection of their parameters. The analysis demonstrates the satisfactory performance of the proposed PV system model, which provides all functionality required by grid codes in the context of active power control.