Abstract
Power system inertia is being reduced because of the increasing penetration of renewable energies, most of which use power electronic interfaces with the grid. This paper analyses the contribution of inertia emulation and droop control to the power system stability. Although inertia emulation may appear the best option to mitigate frequency disturbances, a thorough analysis of the shortcomings that face real-time implementations shows the opposite. Measurement noise and response delay for inertia emulation hinder controller performance, while the inherently fast droop response of electronic converters provides better frequency support. System stability, expressed in terms of rate of change of frequency (ROCOF) and frequency nadir, is therefore improved with droop control, compared to inertia emulation.
Highlights
Stability of Power Systems with HighIn recent years, most electric power systems are undergoing a deep transformation due to the increasing share of renewable energy sources (RES) in their generation mix, both due to plummeting installation costs and environmental concerns
Whenever there is a power imbalance between the mechanical power supplied to a synchronous generator and the electrical power supplied by the generator to the grid, there will be a change in the kinetic energy of the rotor to ensure that power balance is always kept
B ren b conv where Rdroop is the droop constant of the droop control loop, referred to the renewable power base, Sb ren ; Rsys is the system equivalent droop constant, referred to the system power base, Sb sys ; Rconv is the conventional generation droop constant, referred to its power base, Sb conv ; Kd is the gain of the virtual inertia loop, in s; Hconv is the inertia constant of the conventional generation, referred to conventional generation base, in s; and p is the renewable penetration
Summary
Most electric power systems are undergoing a deep transformation due to the increasing share of renewable energy sources (RES) in their generation mix, both due to plummeting installation costs and environmental concerns. VSG includes all the control algorithms that implement the behaviour of a synchronous generator through a model of the machine, either as voltage-to-current or current-to-voltage, and with various model orders, from very detailed to very simple These implementations are roughly equivalent to a real SG, in the sense that they are self-synchronizing and they exhibit an intrinsic inertial response, and their impact in lowering ROCOF and frequency nadir (minimum frequency during an excursion) is similar. This paper analyses the contribution of both inertia emulation and droop control algorithms to frequency regulation Both controls are implemented in a doubly-fed induction generator (DFIG) wind power system and their impact during a frequency event is analysed regarding frequency nadir, ROCOF, and system stability. The RES penetration is considered in the analysis and it is found to have a major impact in system stability The impact of both inertia emulation and droop control algorithms on frequency nadir and ROCOF during a frequency event is analysed through simulation. At partial load operation, where maximum power is extracted from wind by using Maximum Power Point Tracker (MPPT) control; and secondly at full load, where the inertial response can be replaced from the wind through the pitch control
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