A Supervisory Frequency Support Control Scheme for Distributed PV

Increasing penetration of Photovoltaic (PV) generation brings an opportunity, and sometimes necessity, for this new resource to provide ancillary services such as frequency support. Recent efforts toward this goal focused mainly on the large-scale PV plants, and the proposed methods may not be easily adopted for distributed PV, which are smaller in size and connected to distributed systems. In this paper, we propose a novel control scheme for the same purpose but focusing on distributed PV. To address the diversities among distributed PV, we first derive a reduced-order aggregate model to represent their overall dynamic behavior. Then, using this model, a tracking linear quadratic regulator (LQR) based controller is used as a supervisory controller that can control a group of distributed PV to provide frequency support. We also propose an inversion method for the controller to invert the control signals for aggregate model back to each individual PV. The proposed reduced-order aggregate model is validated against a group of distributed PV systems represented by detailed nonlinear models. We also demonstrate the effectiveness of the control scheme, as well as the inversion method, through time-domain simulations using a standard test system.