Coordinated control for medium voltage DC distribution centers with flexibly interlinked multiple microgrids

The design of an effective protection system for inverter-based microgrids is a complicated engineering challenge. This is due to the fact that inverters have limited fault current capabilities, and that the conventional overcurrent protection is not suitable for inverter-based microgrids. This paper introduces a novel protection method for inverter-based microgrid using a current-only polarity comparison. The proposed method is based on the phase difference between the pre-fault and fault current components. The method responds to faults in both grid-connected and autonomous operation modes and provides a new way to identify faulted sections. Simulations of an inverter-based microgrid with a relay model are conducted using PSCAD/EMTDC software. The results show that the proposed method can detect faults in inverter-based microgrids.

Section: Case Studymentioning

confidence: 99%

A Protection Method for Inverter-based Microgrid Using Current-only Polarity Comparison

Wang

Jing

2020

“…In [11], a perturb and observe voltage regulator and capacitor compensator circuit are proposed to regulate the voltage while delivering the maximum power at full load. For AC/DC hybrid power grids, a cooperative control method is available to eliminate the DC bus voltage oscillation caused by the access to distributed generation, energy storage, and other components [12], [13].…”

Section: Introductionmentioning

confidence: 99%

Localization of Oscillation Source in DC Distribution Network Based on Power Spectral Density

Zhao

Peng

Xian

et al. 2023

Direct current (DC) bus voltage stability is essential for the stable and reliable operation of a DC system. If an oscillation source can be quickly and accurately localized, the oscillation can be adequately eliminated. We propose a method based on the power spectral density for identifying the voltage oscillation source. Specifically, a DC distribution network model combined with the component connection method is developed, and the network is separated into multiple power modules. Compared with a conventional method, the proposed method does not require determining the model parameters of the entire power grid, which is typically challenging. Furthermore, combined with a novel judgment index, the oscillation source can be identified more intuitively and clearly to enhance the applicability to real power grids. The performance of the proposed method has been evaluated using the MATLAB/Simulink software and PLECS RT Box experimental platform. The simulation and experimental results verify that the proposed method can accurately identify oscillation sources in a DC distribution network.

“…However, this system still encounters the problem of oscillation when voltage margin selection is inappropriate. Tradeoff coefficients related to DC voltage deviation are set to switch the control mode of the margin controller so that the response speed and adjustment speed of the controller are accelerated when the DC voltage deviation of the system is large [15]- [17], but the design of the controller and selection of tradeoff coefficients are complicated. This is because the smooth switching between different modes depends entirely on the trade-off coefficients, which are calculated based on complex hyperbolae.…”

Section: Introductionmentioning

confidence: 99%

Coordinated Control Strategy for Operation Mode Switching of DC Distribution Networks

Liu

Huang

Hong

et al. 2020

Due to the advantages such as low line cost, low transmission loss, and high power supply reliability, DC distribution networks have become the main development trend for future distribution networks. In this paper, a typical DC distribution network with multiple voltage levels is considered as a research object. It is proposed that the interface converters between DC buses with different voltage levels be implemented through the series-parallel combination of full-bridge LLC resonant converters. To realize the decentralized self-discipline control of DC voltage under various working conditions, different slack buses are prepared according to the voltage ranges of the DC buses, and the voltage regulation modes of the DC distribution network are divided into main voltage regulation mode, backup voltage regulation mode, and off-grid voltage droop regulation mode. By introducing a voltage coefficient related to DC voltage deviation as a basis for mode switching, the voltage fluctuations caused by slow switching between control modes in the method of traditional voltage margin control is reduced, facilitating fast and smooth switching between different voltage regulation modes. Finally, a simulation model for DC distribution networks is constructed utilizing MATLAB/Simulink. Simulation results verify the effectiveness and feasibility of the proposed voltage regulation modes and switching methods for DC distribution networks. Finally, an experimental platform is also constructed to verify the feasibility of the mode switching method proposed in this paper.