Abstract:With the advent of distributed energy sources in low voltage distribution systems, direct power supply through these sources to local loads as microgrids is becoming a reality. Different microgrid architectures will appear in near future. Microgrids can be operated in an islanded or grid connected modes. Different control techniques will be implemented for smooth operation of microgrids. The objective of this special topic is to address and disseminate state-of-the-art R&D results on microgrids to bring together researchers from both academia and industry with the goal of fostering interactions among stakeholders. This special topic provides a timely overview of various research topics on microgrids. We have 7 high-quality papers in this special topic.

Abstract:This paper proposes a new method for the planning of stand-alone microgrids. By means of clustering techniques, possible operating scenarios are obtained considering the daily patterns of wind and load profiles. Then,an approximate analytical model for reliability evaluationof battery energy storage system is developed in terms ofthe diverse scenarios, along with multistate models for wind energy system and diesel generating system. An optimal planning model is further illustrated based on the scenariosand the reliability models, with the objective of minimizing the present values of the costs occurring within the project lifetime, and with the constraints of system operation and reliability. Finally, a typical stand-alone microgrid is studied to verify the efficiency of the proposed method.

Abstract:With high penetration of distributed energy resources (DERs) into power systems, microgrid has showed great advantages of enabling efficient and reliable operation of distribution grids with high flexibilities and robustness. This paper discusses the recent advancementsof microgrid development with particular focus on different dispatch, and control schemes using distributed communication technologies, load management technology,and protection strategies applied in a microgrid environ-ment. It also describes typical R&D activities and projects worldwide in e.g. European Union (EU), Japan and the United States (US). Based on comprehensive review, it is convinced to conclude that microgrids could provide electricity supply with higher efficiency, reliability and quality to regional customers and will make contributions to smart grids development at large.

Abstract:Microgrids are being developed as a building block for future smart grid system. Key issues for the control and operation of microgrid include integration technologies and energy management schemes. This paper presents anoverview of grid integration and energy management strategies of microgrids. It covers a review of power electronics interface topologies for different types of distributed generation (DG) units in a microgrid, a discussion of energy management strategies, as well as the DG interfacing converter control schemes. Considering the intermittent natureof many renewable energy based DG units, the ancillary services of DGs using the available interfacing converterrating are also discussed in the paper.

Abstract:This paper presents control methods for hybrid AC/DC microgrid under islanding operation condition. The control schemes for AC sub-microgrid and DC sub-microgrid are investigated according to the power sharing requirement and operational reliability. In addition, the key control schemes of interlinking converter with DC-link capacitor or energy storage, which will devote to the proper power sharing between AC and DC sub-microgrids to maintain AC and DC side voltage stable, is reviewed.Combining the specific control methods developed for AC and DC sub-microgrids with interlinking converter, the whole hybrid AC/DC microgrid can manage the power flow transferred between sub-microgrids for improving onthe operational quality and efficiency.

Abstract:Modern electric power systems have increased the usage of switching power converters. These tightly regulated switching power converters be have as constant power loads (CPLs). They exhibit a negative incremental impedance in small signal analysis. This negative imped-ance degrades the stability margin of the interaction between CPLs and their feeders, which is known as the negative impedance instability problem. The feeder can bean LC input filter or an up stream switching converter.Active damping methods are preferred for the stabilization of the system. This is due to their higher power efficiency over passive damping methods. Based on different sources of damping effect, this paper summarizes and classifies existing active damping methods into three categories. The paper further analyzes and compares the advantages and disadvantages of each active damping method.

Abstract:In this paper, a synchronized control strategy of double fed induction generator that can provide reserve capability and primary frequency support for microgrid is firstly developed. The microgrid based small signal stability performance is investigated under multiple operating conditions. The effect of three categories of key controller parameters on dominant eigenvalues is studied by sensitivity analysis, including: 1) active power drooping coefficient; 2)reactive power drooping coefficient; 3) parameters of outerloop excitation current control. Finally, some constructive suggestions on how to tune controller parameters to improve microgrid’s small signal stability performance are discussed.

Abstract:We consider the microgrid operation control technology including design of microgrid operation control system, MG control device and control strategy. We pay much attention on microgrid operation control device which is core control device. In order to solve the contradiction of quick speed about microgrid operation mode shift and slow speed about the management system, three-layers control architecture based on IEC61850 is designedand adaptive control strategy is used on MG operation control system. The system has been applied in a distributed generation/energy storage power station. The actual operation shows that the system can be effectively and flexibly connected to distribution network.

Abstract:This paper aims at putting forward view points regarding the use of stability technology to prevent and control cascading outages by examining recent black out events. Basedon the inquiry reports of the 2011 Southwest America blackout and the 2012 India power blackouts, event evolution featuresare first summarized from a stability perspective. Then acomparative analysis is conducted so as to propose suggestions of effective measures, either preventive or emergency, which could have avoided the blackouts. It is shown that applications of several mature technologies can create opportunities of preventing or interrupting the cascading development. These include offline dynamic simulation, online stability analysis and preventive control, real-time situational awareness and automatic emergency control. Further R & D directions aregiven to address the challenges of modern power systems aswell. They cover system fault identification criterion of pro-tection and control devices, verification of adaptability ofcontrol effect to system operating conditions, real-time oper-ational management of emergency control measures and improvement of simulation accuracy.

Abstract:This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC) based high-voltage direct current (HVDC) system under a converter-side AC fault. Based on the system operating condition, a control and protection strategy against the fault with normal blocking of the converter is proposed. In practical, applications encountering such afault, the MMC at the fault side may experience different conditions of blocking failure. The blocking failures may occur on: the whole converter; ` one converter arm; ′one sub-module (SM)/several SMs of one converter arm; ?other conditions. The phenomenon of the multi-terminalHVDC (MTDC) system following the fault is analyzedunder the first three conditions with real-time simulations using the real-time digital simulator (RTDS). Based on theimpact of different conditions on the MTDC system, the necessity of utilizing special control and protection is dis-cussed. A special control and protection strategy is proposed for emergency conditions, and its effectiveness is verified by real-time simulation results.

Abstract:This paper analyzes the problems of the relay protections and secondary circuits of traditional substations,and introduces the hierarchical protection and control system of smart substations based on the technologies like IEC61850 Standard, electronic instrument transformer, processlevel network, and wide area optical fiber communication network, etc. The hierarchical protection and control system includes three levels: local area protection, substation area protection and control, and wide area protection and control.These three levels are combined to solve the problems of the relay protections in traditional substations, thus improving protection performance and control capability of the system.