System Inertial Frequency Response estimation and impact of renewable resources in ERCOT interconnection

This paper presents observations and challenges related to integration of renewable resources with respect to frequency control with primary focus on Inertial Frequency Response in ERCOT Interconnection. Frequency Control, in general, can be categorized into Inertial, Primary and Secondary Frequency Responses based on the response time. In ERCOT Interconnection, currently, the primary and secondary frequency response can be achieved by employing adequate control settings and Ancillary Service procurement. The Inertial Frequency Response described in this paper refers to the total synchronous mass connected to the Grid which includes motor loads as well as synchronous generators. Maintaining minimum level of Inertial Frequency Response with unit commitments can be crucial to ensure reliable integration of renewable resources. A trend in decline of Inertial Frequency Response with respect to increasing renewable resources has been observed according to recorded frequency events in the past four years in ERCOT Interconnection. Since Inertial Frequency Response dictates the change in frequency due to supply demand mismatch, it is important to maintain adequate system inertia in real-time operations. Therefore, an on-line tool is developed for the purpose of providing an estimation of system wide Inertial Frequency Response to potentially assist System Operators to maintain adequate system inertia. The unit of the estimated Inertial Frequency Response is MW/0.1 Hz. This unit is recognized to be more practical for System Operator to evaluate the system condition.