Fast frequency regulation and synthetic inertia in a power system with high penetration of renewable energy sources: Optimal design of the required quantities

Abstract

Abstract Fast primary regulation and synthetic inertia supply are two novel ancillary services for power system frequency control. Although general agreement about their definition is still missing, these services have started to be recognized and inserted into the grid codes of some transmission system operators, especially to handle isolated systems with large penetration of non-programmable renewable energy sources. The main goal here is to propose a methodology to quantify the capacity needed for each service, in order to guarantee system stability and security when the regulation margins of the conventional generation for standard primary frequency control have already been exploited. In terms of control theory, identifying the required service amounts means computing the values of the gains associated to the related controllers. These are found by solving a non-linear optimization problem: the functional to be minimized is related to the maximum value of the power exchanged for each service after an imbalance and to the relative costs of such maximum power exchanges, while constraints are defined to limit the amplitude and the gradient of the response of grid frequency to the imbalance. The optimization procedure has been tested on an annual scenario for the power system of the Sardinia island: more precisely, with reference to predictions for 2030 of the hourly operating conditions of the system, control parameters have been optimized for each hour, by assuming the loss of the maximum generation or of the maximum absorption as the imbalance source. The most critical situation found in the simulations is for the loss of the maximum absorption: a high gain for the synthetic inertia controller and an even higher gain for the fast primary controller are needed to avoid both the curtailment of renewables and load shedding.