Abstract
As the share of power converter-based renewable energy sources (RESs) is high, a microgrid, in islanded mode, is more vulnerable to frequency instability due to (1) sudden power imbalance and (2) low inertia. One of the most common approaches to address this issue is to provide virtual inertia to the system by appropriately controlling the grid-side converter of the RESs. However, the primary frequency controller (PFC) presented in this paper focuses on the fast compensation of power imbalance without adding inertia to the system. The proposed method is based on estimating the real-time power imbalance caused by a disturbance and compensating it using multiple small-scale distributed battery energy storage systems (BESSs). The power imbalance is estimated by observing the initial rate of change of frequency (RoCoF) following a disturbance. Based on the estimated power imbalance and the rating of the BESSs, the reference power for the BESSs is determined. The BESSs are controlled in grid-following mode to compensate for the power imbalance. The performance of the proposed PFC is verified using a Typhoon real-time simulator for various scenarios and is compared with the conventional virtual synchronous generator (VSG) controller.
Highlights
It is assumed that the number of the battery energy storage systems (BESSs) may be more the frefrequency-to-load transfer function (FLTF) of one synchronous generators (SGs) may be used by multiple BESS to determine their reference power
The FLTF of one SG may be used by multiple BESS to determine their reference power
The closed-loop system of the proposed primary frequency controller (PFC) is shown in Figure 6, where ∆PD represents the power imbalance caused by a change in load or change in the power output from the renewable energy sources (RESs)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In the absence of physical inertia, the frequency of the inverter changes suddenly with a change in its output power when operated with the conventional droop-based control. To provide inertia to the system, a virtual synchronous generator (VSG) control was proposed in [16] This method controls the frequency of a grid-connected inverter to mimic the characteristic of a droop-controlled SG. Similar to the droop controller, various control techniques are explored to improve the performance of the VSG controller [18,19,20,21,22,23] These techniques are based on adaptively modifying the virtual inertia and damping provided by the grid-connected inverter.
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