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.

Highlights

  • T HE electric power system is experiencing unprecedented penetration levels of wind and solar generation

  • Electric Reliability Council of Texas (ERCOT) has introduced a new frequency response service intended to improve primary frequency response, redefined the frequency response reserve products considered in the electricity market, and proposed the introduction of real-time co-optimization [5], [6]

  • This paper focuses on reserve types providing primary frequency control, which is of critical concern for low inertia systems [1]

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Summary

INTRODUCTION

T HE electric power system is experiencing unprecedented penetration levels of wind and solar generation. In the context of these new ERCOT rules, this paper derives novel reserve requirements that ensure sufficient primary frequency response reserve to accommodate a pre-defined generator outage. ERCOT recently introduced a third sub-set of RRS that is capable of contributing to primary frequency control termed Fast Frequency Response (FFR) reserve [5]. Reference [17] uses a general model of a generator that is capable of accommodating FFR reserve; they utilize a pre-determined frequency trajectory, which would effectively determine the time when the FFR reserve is deployed We contribute to this literature by deriving novel reserve requirements that couple PFR and FFR reserve while accurately modeling the FFR reserve as being deployed at a time that varies with the frequency trajectory due to the frequency threshold for activation.

A GENERAL RESERVE REQUIREMENT
Inertia and Frequency Dynamics
Primary Frequency Response Reserve and Droop Control
Fast Frequency Response Reserve
RATE-BASED PFR RESERVE LIMITS
Simple Turbine Governor Model
Sufficient Condition for Satisfying Frequency Threshold
PROPORTIONAL PFR RESERVE LIMITS
EQUIVALENCY RATIO PFR RESERVE LIMITS
Reformulating the Equivalency Ratio Reserve Requirement
Equivalency Ratio Approximation
REAL-TIME CO-OPTIMIZATION
A Practical Approximation
Texas Test Case
Numerical Results
Findings
VIII. CONCLUSION
Full Text
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