Requirements for Interdependent Reserve Types Providing Primary Frequency Control

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. Highlevel insights are provided on a large Texas test case.

Requirements for Interdependent Reserve Types

“…Our main results extend our previous work in [14] and [15], which provide a first principles derivation of a requirement that couples PFR and FFR reserve. The proposed reserve requirement has two components.…”

“…This section presents the rate-based PFR reserve limit originally derived in previous work [14], [15].…”

“…References [14], [15] prove that the rate-based PFR reserve limit serves as a sufficient condition for adequate reserve procurement. In order for this result to hold, we must impose two assumptions regarding the response of the system.…”

“…Proof: Provided in [14] and [15]. In addition to Assumption 1, [14] and [15] assume the frequency falls below ω 2 in response to the outage of size L and the FFR reserve deployment does not overshoot causing a positive power imbalance.…”

“…Proof: Provided in [14] and [15]. In addition to Assumption 1, [14] and [15] assume the frequency falls below ω 2 in response to the outage of size L and the FFR reserve deployment does not overshoot causing a positive power imbalance. When these additional assumptions are violated the result still holds because the frequency will still not fall below ω 2 > ω 0 .…”