Control Paradigms For Distributed Energy Resources (Ders) To Engineer Inertial And Primary Frequency Response In Power Grids

Abstract

Power networks have to withstand a variety of disturbances that affect system frequency, and the problem is compounded with the increasing integration of intermittent renewable generation. Following a large-signal generation or load disturbance, system frequency is arrested, leveraging primary frequency control provided by governor action in synchronous generators. This work proposes a framework for distributed energy resources (DERs) deployed in transmission and distribution networks to provide (supplemental) inertial and primary frequency response. This work is divided into two parts, transmission and distribution level design process. Particularly, we demonstrate how synthetic inertia and power-frequency droop slopes for individual DERs can be designed so that the system frequency conforms to prescribed transient and steady-state performance specifications at the transmission level and the distribution feeder presents guaranteed frequency-regulation characteristics at the feeder head. Furthermore, the droop and inertial coefficients are engineered such that injections of individual DERs conform to a well-defined fairness objective that does not penalize them for their location on the distribution feeder. At the transmission level, our approach is grounded in a second-order lumped-parameter model that captures the dynamics of synchronous generators, and frequency-responsive DERs endowed with inertial and droop control. A key feature of this reduced-order model is that its parameters can be related to those of the originating higher-order dynamical model. This allows one to systematically design the DER inertial and droop-control coefficients leveraging classical frequency-domain response characteristics of second-order systems. At the distribution level, the approach we adopt leverages an optimization-based perspective and suitable linearizations of the power-flow equations to embed notions of fairness and information regarding the physics of the power flows within the distribution network into the droop slopes. This optimization-based method is centered around classical economic dispatch. The accuracy of the model-reduction method and demonstration of how DER controllers can be designed to meet steady-state-regulation and transient-performance specifications for an illustrative network composed of a combined transmission and distribution network with frequency-responsive DERs is also presented.