Dynamic modeling, sensitivity assessment, and design of VSC-based microgrids with composite loads

Zhao, Zhuoli,Yang, Ping,Bottrell, Nathaniel,Lai, Loi Lei,Green, Timothy C. The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.1

Microgrids are seen as useful for increasing the flexibility of distribution networks and integrating large amounts of distributed generations. Ensuring the dynamic stability of power converter-dominated microgrids that is robust to a range of load conditions is a significant challenge and essential for ensuring reliability. Induction motor (IM) loads are widespread and have substantial impacts on the dynamic behavior and stability characteristics of low-inertia microgrids. The stability assessment and design of microgrids considering composite loads have not been sufficiently addressed in the current literature, where static loads are commonly used to simplify the modeling and analysis. In this paper, the dynamic stability of voltage source converter-based microgrids is investigated, considering composite loads as dynamic element. A complete state-space model of the microgrid with both IM load and static load is developed. Participation factor analysis is conducted to identify the contribution of the composite loads to the dominant oscillatory modes of the microgrid. Furthermore, sensitivity assessment of the dominant eigenvalues is presented to further identify the appropriate ranges of variations in the control parameters, operating conditions and operating points of the microgrid. It is shown that composite loads in a realistic microgrid significantly affect the dominant oscillatory modes and, consequently, the system stability margin. Ignoring the composite load dynamics in microgrid stability studies may lead to misleading analytical results. Simulations based on MATLAB/Simulink and experimental tests based on a laboratory prototype microgrid are implemented to demonstrate the theoretical analysis.

Characteristic analysis of three-phase four-leg inverter based load unbalance compensator for stand-alone microgrid

G. H. Kim,C. Hwang,J. H. Jeon,G. S. Byeon,J. B. Ahn,C. H. Jo 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

This paper analyses a three-phase four-leg voltage sourced inverter (VSI) based load unbalance compensator (LUC) including its control algorithm, which is a component of a microgrid. The purpose of proposed threephase four-leg VSI based LUC is to improve power quality of the stand-alone microgrid. Power quality of the microgrid which was installed in Mara-island, Korea is analysed using a real operational data. In this work, the microgrid in Mara-island which includes a photovoltaic power generation system, a diesel generator, a battery energy storage system, and a power management system is modelled in PSCAD/EMTDC, and proposed three-phase four-leg VSI based LUC is also modelled and applies to the microgrid. Power flow and stability of the modelled microgrid with the LUC is analysed under variable irradiance and unbalance loads. The results show that the proposed LUC helps to improve stability of the stand-alone microgrid. The proposed three-phase four-leg VSI based LUC and its control algorithm can be effectively utilized to the stand alone microgrid which has large unbalance loads.

저압계통 연계형 마이크로그리드의 보호감시 시스템

정태영(Tae-Young Jyung),백영식(Young-Sik Baek) 대한전기학회 2011 전기학회논문지 Vol.60 No.1

This paper mainly proposes the protective coordination scheme of the microgrid system. The microgrid protection is identical to the conventional protection system separating the normal part and contingency part to reduce damage when the contingency occur at power cables, facilities. But they are different in the protection type. The conventional protection system only considers unidirectional current. However the microgrid protection should be considered not only unidirectional current but also backfeed current because various microsources and loads are installed in the microgrid system. In case the contingency occurs in microsource, when microgrid is interconnected to grid, the protection system should be configured to not separate microgrid from grid before the microsource is isolated to microgrid. And in case of fault occur in power system, the microsources should not isolated to microgrid before the static switch at PCC is tripped to separate from power system. Considering these characteristic of microgird, this paper proposes the protective coordination scheme of microgrid and implemented the on-line real time monitoring system. Especially in case the microgrid is connected to low voltage distribution system with 220/380V voltage level, the proposed protection method with power IT technology can solve the problems when the existing protective devices only applied to the microgrid system.

A Hybrid Framework for Adaptive Protection of Microgrids Based on IEC 61850

Akhtar Hussain,Hak-Man Kim 보안공학연구지원센터 2016 International Journal of Smart Home Vol.10 No.5

Microgrids can operate both in grid-connected and islanded modes. It is essential to protect microgrids against all types of faults in both of the operation modes. Conventional overcurrent protection schemes are not adequate for microgrids due to bidirectional flow of fault current and limited flow of fault current through semiconductor devices. In addition, the setting values of all the concerned relays need to be updated after any change in system operating conditions. Centralized and decentralized adaptive protection schemes are generally used for protection of microgrids. In this paper, a hybrid adaptive protection scheme has been proposed for protection of microgrids. Computational burden and data storage is distributed among the local controllers and the central controller. A gateway is proposed for communicating between the serial interfaced devices and the IEC 61850 process bus. Finally, a framework has been introduced for implementing the proposed hybrid protection scheme for adaptive protection of microgrids by using IEC 61850-based intelligent electronic devices (IEDs).

Optimal Sizing and Sitting of Smart Microgrid Units under Pool Electricity Market

Seyed Mehdi Hakimi,Amin Hajizadeh 대한산업공학회 2017 Industrial Engineeering & Management Systems Vol.16 No.3

This paper presents an approach for optimal sizing and sitting of distribution generation units in smart microgrid under pool electricity market to reduce total cost and power loss of whole smart microgrid. The costs comprise capital cost, replacement cost, operation and maintenance cost, fuel cost, reliability cost, power loss cost and selling and buying electricity cost. The new idea of this paper is the investigation of pool electricity market aspects in optimization of smart microgrid. On the other hand, cost minimization of smart microgrid is related to their bidding strategies. Therefore two different optimization tools are considered. First, a game-theoretical (GT) model has been used for bidding strategy of smart microgrid as a price-maker, in a long-term electricity market. Secondly, a particle swarm optimization (PSO) algorithm is employed to obtain the best cost value of smart microgrids construction. This study was performed for the Ekbatan residential complex in Tehran, Iran. It has three smart microgrids consist of renewable energy resources. They participate in a long-term electricity market as a price maker. The results show that the proposed method is more effective and has lower cost in finding optimum size and location of distribution generation in smart microgrids.

An interval type-2 fuzzy logic based strategy for microgrid protection

Bukhari, Syed Basit Ali,Haider, Raza,Saeed Uz Zaman, Muhammad,Oh, Yun-Sik,Cho, Gyu-Jung,Kim, Chul-Hwan IPC Science and Technology Press 2018 International journal of electrical power energy s Vol.98 No.-

<P><B>Abstract</B></P> <P>The concept of microgrids has been introduced to facilitate the integration of the distributed energy resources (DERs) into distribution networks in a more economical, reliable and environment-friendly manner. One of the critical challenges associated with microgrids is devising an appropriate protection strategy. This is because the fault current level continuously varies owing to the existence of DERs and to the fact that the microgrid can operate in grid-tied and islanded modes. This paper proposes a new protection strategy for microgrids using an interval type-2 fuzzy logic system. The proposed strategy considers various uncertainties associated with faults and employs two different fuzzy systems to detect, classify, and locate the faults in microgrids. The phase angle between superimposed modal voltage and modal current is used as an input to the fuzzy system designed to identify the fault direction. The significant feature of the proposed strategy is that it can protect the microgrid after a single-phase tripping event. To validate the effectiveness of the proposed strategy, we have performed extensive simulations using MATLAB/SIMULINK. The simulation results show that the proposed strategy can detect, classify, and isolate various faults in the microgrid. Moreover, the strategy also provides backup protection in case of failure of the primary protection.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Develop a new microgrid protection strategy based on interval type-2 fuzzy logic system. </LI> <LI> Considers various uncertainties associated with faults in microgrids. </LI> <LI> Identify fault direction using phase angle between superimposed modal voltage and modal current. </LI> <LI> Capable to protect the microgrid after a single-phase tripping event. </LI> </UL> </P>

An Algorithm to Enhance the Profit Margin of Electric Vehicle Owners and Resilience of Multi-microgrid Using EV

Ali Asfand Yar,Hussain Akhtar,Baek Ju-Won,Man-Kim Hak 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.4

Improvement in the electric vehicles (EVs) area and the expanding number and greatness of catastrophic events have drawn in the consideration of analysts to use the put-away energy in EVs and upgrade the versatility of force frameworks. Microgrids are viewed as a possible source to take care of these issues. Nearby assets accessible in the microgrid are utilized to improve the strength of the system, for example, battery energy storage system. An extra battery energy storage system to improve the resiliency of the system might prompt an expansion in capital expenses. Consequently, in this article, existing EVs in the microgrid parking lot is utilized revenue-driven acquiring and fl exibility upgrades with next to no extra capital expense. In the normal operation scenario, using the proposed strategy EV energy is sold to the MGs in the system off ering the highest bidding cost, resulting in raise in the profi t margin for the EV owners. In the case of contingencies, the proposed scheme supplies energy from grid-connected microgrids to islanded microgrids through accessible EVs. The strategy to supply energy is carried out in three steps. In the fi rst step, required energy and available energy in the EVs is informed to the central energy management system (CEMS). In the second step, CEMS decides the microgrid to supply energy to the islanded microgrid among grid-connected microgrids. Finally, the microgrid chosen by the CEMS to supply energy to islanded microgrid concludes which EV ought to be sent among the accessible EVs. Simulations have been carried out to show the viability of the proposed scheme.

Optimal design and financial feasibility of a university campus microgrid considering renewable energy incentives

Husein, Munir,Chung, Il-Yop Elsevier 2018 APPLIED ENERGY Vol.225 No.-

<P><B>Abstract</B></P> <P>Microgrids are gradually being recognized as an important option for sustainable and reliable energy, especially in university and military campuses. In this paper, we investigate the technical and financial feasibility of deploying a microgrid in a university campus. We consider various incentives such as renewable energy investment-based incentives, tax benefits, and grid ancillary services. In this study, we developed a microgrid planning model, called Microgrid Decision Support Tool (MDSTool). The model is structured into two sub-models—performance and economic models. Performance model simulates the optimal operation of the microgrid and is used to analyze energy usage and investigate technical feasibility. The economic model calculates all the system cash flows, its purpose is to determine the optimal sizing of distributed energy resources and financial feasibility. The overall model is used to design a campus microgrid at Seoul National University, South Korea. The results show that renewable energy incentives, tax benefits, and grid ancillary services influence both the financial feasibility and renewable energy penetration in a microgrid.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Microgrid decision support model is developed. </LI> <LI> Incentives, tax benefits, and grid ancillary services are considered in the model. </LI> <LI> Incentives, tax benefits, and grid ancillary services affect both optimal sizing and financial feasibility. </LI> <LI> Optimal microgrid was found to decrease energy cost by 42% and emissions by 15%. </LI> </UL> </P>

AC and DC Microgrids: A Review on Protection Issues and Approaches

Sohrab Mirsaeidi,Xinzhou Dong,Shenxing Shi,Bin Wang 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.6

Microgrid is a convenient, reliable, and eco-friendly approach for the integration of Distributed Generation (DG) sources into the utility power systems. To date, AC microgrids have been the most common architecture, but DC microgrids are gaining an increasing interest owing to the provision of numerous benefits in comparison with AC ones. These benefits encompass higher reliability, power quality and transmission capacity, non-complex control as well as direct connection to some DG sources, loads and Energy Storage Systems (ESSs). In this paper, main challenges and available approaches for the protection of AC and DC microgrids are discussed. After description, analysis and classification of the existing schemes, some research directions including coordination between AC and DC protective devices as well as development of combined control and protection schemes for the realization of future hybrid AC/DC microgrids are pointed out.

Multi-Microgrids System Reliability Assessment Considering Difference Characteristics and Inter-Connection Ability among Microgrids

Xingyou Zhang,Bo Chen,Fei Wang,Xin Wang,Yan Cheng,Guanglei Li 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.5

Connecting neighbor microgrids into a multi-microgrids system (MMS) is one of research hotspots in the field of microgrids. This paper analyzes difference of distributed generators configuration and load types among each microgrid in a MMS. A method to evaluate the influence of dynamic behaviors and energy exchange behaviors on power supply reliability of microgrids in a MMS is proposed in this paper. A reliability assessment algorithm which takes account of connectivity ability among microgrids and intermittence characteristics of distributed energy, different load type and energy exchange behavior is also proposed in this paper. Since the proposed model can characterize dynamic behavior of microgrids in a MMS, the proposed method is of great significance for design and operation of a MMS.