Requirements for Interdependent Reserve Types

TL;DR

This paper develops reserve requirement formulas for interdependent primary frequency response and fast frequency response reserves in ERCOT, considering system inertia and generator capabilities, to improve frequency stability amid increasing renewable energy.

Contribution

It introduces new reserve requirement formulas that couple PFR and FFR reserves with system inertia, providing first principles insights into reserve limits and equivalency ratios.

Findings

Derived reserve limits based on generator ramping capabilities

Proposed a new reserve requirement formula accommodating equivalency ratios

Applied insights to a large Texas test case

Abstract

As renewable energy penetration increases and system inertia levels drop, primary frequency control is becoming a critical concern in relatively small interconnections such as the Electric Reliability Council of Texas (ERCOT). To address this problem ERCOT is implementing a number of market rule changes including the introduction of a new Fast Frequency Response (FFR) reserve type to the electricity market. This FFR reserve type aims to help the traditional Primary Frequency Response (PFR) reserve type in arresting frequency decline in the event of a large generator outage. This paper derives reserve requirements to ensure sufficient reserve to arrest frequency decline before reaching the critical frequency threshold while coupling PFR reserve, FFR reserve, and system inertia. The general reserve requirement places limits on the amount of PFR reserve that can be provided by each unit based on its ramping capabilities. Two such limits are derived from first principles and another is proposed that is capable of accommodating the equivalency ratio introduced in previous work. These PFR reserve limits also provide first principles insight into equivalency ratios, which have only been studied empirically in the past. High-level insights are provided on a large Texas test case.