Abstract
Microgrid frequency and voltage regulation is a challenging task, as classical generators with rotational inertia are usually replaced by converter-interfaced systems that inherently do not provide any inertial response. The aim of this paper is to analyse and compare autonomous primary control techniques for alternating current (AC) and direct current (DC) microgrids that improve this transient behaviour. In this context, a virtual synchronous machine (VSM) technique is investigated for AC microgrids, and its behaviour for different values of emulated inertia and droop slopes is tested. Regarding DC microgrids, a virtual-impedance-based algorithm inspired by the operation concept of VSMs is proposed. The results demonstrate that the proposed strategy can be configured to have an analogous behaviour to VSM techniques by varying the control parameters of the integrated virtual-impedances. This means that the steady-state and transient behaviour of converters employing these strategies can be configured independently. As shown in the simulations, this is an interesting feature that could be, for instance, employed for the integration of different dynamic generation or storage systems, such as batteries or supercapacitors.
Highlights
The increasing penetration of distributed generation (DG) systems is shifting the current electric grid from the classical top-down structure to a decentralized one
The frequency and voltage regulation of alternating current (AC) and direct current (DC) microgrids is a challenging task that is being widely studied in the literature
This is mainly due to the fact that, in microgrids, classical synchronous generators with rotational inertia are replaced by converter-interfaced DG or energy storage systems (ESSs) that do not inherently contribute in the dynamic response of the system
Summary
The increasing penetration of distributed generation (DG) systems is shifting the current electric grid from the classical top-down structure to a decentralized one. Other approaches employ virtual-capacitors for the integration of different types of ESSs on a DC microgrid [27] These strategies improve the transient response and stability of DC microgrids, their control is usually composed of cascaded voltage and current proportional-integral (PI) regulators that have a direct impact on the response of converters under sudden power variations. The main contribution of this paper is the development and comparative study of a virtual-impedance control strategy for DC microgrids that reproduces the behaviour of VSMs, based on the study carried out in [28] Unlike classical approaches, this technique does not include any cascaded PI regulator. The paper concludes with the most important remarks of the analysis
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