Provision of Contingency Frequency Services for Virtual Power Plants With Aggregated Models

The growth of variable renewable generations will reduce synchronous inertia, and the demand for managing contingency frequency support is growing. Distributed energy resources (DERs) can provide contingency frequency support via the virtual power plant (VPP). Given that the VPP may cover thousands of DERs with diverse characteristics and response latency, this paper proposes to use equivalent aggregation models for the VPP to participate in contingency reserve services. First, the equivalent aggregation model for the VPP's aggregated frequency response is developed, accurately and concisely restoring the DER aggregation's capability to stop the system frequency from falling. On this basis, the VPP's performance-to-cost map is constructed, which specifies the minimal cost to achieve the same performance as different equivalent aggregation models. In order to encourage DERs to report their response latency accurately, additional latency is penalized based on the resulting cost increase. A sensitivity-based method in the matrix form is developed to estimate the marginal increasing cost due to the increasing latency. Numerical studies are conducted to validate the equivalent aggregation model's effectiveness and illustrate how latency affects response performance and aggregation cost.