Centralized Protection Strategy for Medium Voltage DC Microgrids

Abstract

Abstract-1 This paper presents a centralized protection strategy for medium voltage dc (MVDC) microgrids. The proposed strategy consists of a communication-assisted fault detection method with a centralized protection coordinator and a fault isolation technique that provides an economic, fast, and selective protection by using the minimum number of dc circuit breakers (DCCBs). The proposed method is also supported by a backup protection which is activated if communication fails. The paper also introduces a centralized self-healing strategy that guarantees successful operation of zones that are separated from the main grid after the operation of the protection devices. Furthermore, to provide a more reliable protection, thresholds of the protection devices are adapted according to the operational modes of the microgrid and the status of distributed generators (DGs). The effectiveness of the proposed protection strategy is validated through real-time simulation studies based on the hardware in the loop (HIL) approach.Index Terms-Adaptive protection, centralized protection, smart dc microgrids. I. INTRODUCTIONDue to the increasing penetration of DGs, especially in the form of renewable energy systems (RES), the concept of microgrids has been proposed as a method for DG integration into the electrical grids. Microgrid is a common concept in both ac and dc systems and is defined as a smallscale low or medium voltage grid consisting of loads and DGs. Such a system is capable of operating in both islanded and grid-connected modes [1]. Because of the advantages of the dc networks over the ac grids, and also because of the new developments in the technology of voltage source converters (VSCs), nowadays there is a major interest in dc grids in both research and industrial realms [2][3][4][5].At the present moment, protection is one of the most important challenges in the development of dc microgrids. Protection issues mainly arise due to the particular behavior of the fault current in VSC-based networks [6]. When a fault occurs in a dc grid, firstly, the dc-link capacitor is discharged causing the voltage of the main dc bus to drop precipitously. Then, the energy stored in the cable This work was supported in part by the Spanish Ministry of Economy and Competitiveness under Project ENE2013-48428-C2-2-R. The work of M. Monadi was supported by the Ministry of Science, Research, and Technology, Iran.M. Monadi is with Technical University of Catalonia (UPC) Barcelona, Spain and Shahid Chamran University of Ahvaz, Ahvaz, Iran (e-mail: meh_monadi@yahoo.com).C. Gavriluta is with the Grenoble Electrical Engineering Laboratory (G2ELab), France (email: catalin.gavriluta@g2elab.grenoble-inp.fr).A. Luna, J. I. Candela are with Technical University of Catalonia (UPC) Barcelona, Spain. (e-mails: luna@ee.upc.edu, candela@ee.upc.edu) P. Rodriguez is with Technical University of Catalonia (UPC) Barcelona, Spain and Abengoa research, Sevilla, Spain (e-mail: prodriguez@ee.upc.edu).inductance is also discharged through the freewheeling dio...

Distributed generation hybrid AC/DC microgrid protection: A critical review on issues, strategies, and future directions

“…The LL faults create very serious harm to the safety of the system, and it has low fault impedance characteristics. On the other hand, the LG faults are the most frequently occurring faults that cause damage by the grounding system type in the DC network . During the selection of the suitable grounding system type, many related factors are taken into account like lessening the stray current, minimization of touch current for enhancing the personal safety, and fault current amplitude .…”

“…On the other hand, the LG faults are the most frequently occurring faults that cause damage by the grounding system type in the DC network. 27,28 During the selection of the suitable grounding system type, many related factors are taken into account like lessening the stray current, minimization of touch current for enhancing the personal safety, and fault current amplitude. 29 The corrosion is the main consequence of stray current, and this forces to design a protection scheme with minimum stray current.…”

Fast Fault Protection Based on Direction of Fault Current for the High-Surety Power-Supply System

“…13 can be converted to the V ce_n and V ce_n of SSCB using (7). The V ce_n and V ce_p are derived as given in (11). (11) It should be noticed that the current at the first valid point used for calculation should be larger than I min .…”

IEC 61850-Based Centralized Busbar Differential Protection with Data Desynchronization Compensation

“…For example, the authors of [2,3] used IEC 61850 to (respectively) adapt the 67/67N protection of main ring systems featuring distributed energy resources and to improve the fault detection times of protection relays in different substations. IEC 61850 has also been usefully applied to microgrids and distribution networks [4][5][6][7]. The authors of [4,5] proposed centralized protection strategies for microgrids and the authors of [6] proposed the design of microgrid plug-and-play functions in accordance with IEC 61850.…”

“…IEC 61850 has also been usefully applied to microgrids and distribution networks [4][5][6][7]. The authors of [4,5] proposed centralized protection strategies for microgrids and the authors of [6] proposed the design of microgrid plug-and-play functions in accordance with IEC 61850. In [7], the three-level coordinated control was proposed for voltage regulation in distribution networks and its effectiveness was validated by experiment through a real communication link.…”