Inertia considerations within unit commitment and economic dispatch for systems with high non-synchronous penetrations

Abstract

The priority dispatch status of non-synchronous renewable generation (wind, wave, solar), and increasing levels of installed high voltage direct current interconnection between synchronous systems, is fundamentally changing unit commitment and economic dispatch (UCED) schedules. Conventional synchronous plant, the traditional provider of services which ensure frequency stability - synchronising torque, synchronous inertia and governor response - are being displaced by marginally zero cost non-synchronous renewables. Such a trend has operational security implications, as systems - particularly synchronously isolated systems - may be subject to higher rates of change of frequency and more extreme frequency nadirs/zeniths following a system disturbance. This paper proposes UCED-based strategies to address potential shortfalls in synchronous inertia associated with high non-synchronous penetrations. The effectiveness of the day-ahead strategies is assessed by weighing the cost of the schedules against the risk level incurred (the initial rate of change of frequency following a generation-load imbalance), and the level of wind curtailment engendered.