Abstract
Decarbonization of power systems has put Renewable Energy Sources (RES) at the forefront when it comes to electric power generation. The increasing shares of converter-connected renewable generation cause a decrease of the rotational inertia of the Electric Power System (EPS), and consequently deteriorate the system capability to withstand large load-generation imbalances. Low-inertia systems are subjected to fast and large frequency changes in case of in-feed loss, where the traditional primary frequency control is not sufficient to preserve the frequency stability and to maintain the frequency above the critical value. One possible solution to this rising problem is seen in Fast Frequency Response (FFR) provided by the High-Voltage Direct-Current (HVDC)-based systems. This paper presents the adaptive FFR control of HVDC-based systems for frequency stability enhancement in the low-inertia system. The EPS is considered as a “black box” and the HVDC response is determined only using the locally measured frequency change. Sliding Mode Control (SMC) of the Modular Multilevel Converter (MMC) was developed and demonstrated to provide faster and more appropriate frequency response compared to the PI controller. The described adaptive HVDC control considers the size of disturbance and the inertia of the power system, and it is verified by simulations on the IEEE 39 bus test system implemented in MATLAB/Simulink for different system configurations and different sizes of disturbance.
Highlights
With the rising penetration of converter-connected renewable generation and phasing-out of coal generation plants that are directly connected to the power grid, the rotational inertia of the ACElectrical Power System (EPS) is decreasing
This paper proposes the adaptive control of the High-Voltage Direct-Current (HVDC) link for frequency stability enhancement in low-inertia systems
HVDC links can provide fast frequency support, and present a valuable tool in a low-inertia system that is sensitive to disturbance in terms of frequency stability
Summary
With the rising penetration of converter-connected renewable generation and phasing-out of coal generation plants that are directly connected to the power grid, the rotational inertia of the AC. Droop control is a typical control scheme for HVDC-based frequency support that has been proposed multiple times [12,13,14,15] It is simple and can be implemented, it does not effectively utilize the fast response capabilities of HVDC-based systems, since the output active power increases gradually. This paper presents an adaptive control for fast frequency support for HVDC-based power systems that considers the magnitude of disturbance and the system inertia. The proposed method fully exploits the fast, dynamic capabilities of HVDC converters (providing fast, almost instantaneous, step increase of output active power), contrary to the grid-forming controls where the active power injection is gradually increasing [24,25,26].
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