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In a previous paper, we constructed an explicit dynamical correspondence between certain Kleinian reflection groups and certain anti-holomorphic rational maps on the Riemann sphere. In this paper, we show that their deformation spaces share many striking similarities. We establish an analogue of Thurston's compactness theorem for critically fixed anti-rational maps. We also characterize how deformation spaces interact with each other and study the monodromy representations of the union of all deformation spaces., Comment: 56 pages, 13 figures. Final version, to appear in Geom. Funct. Anal

In the marine gear system, the vibration of gears is transmitted to the ship foundation through shafts, bearings, housing, and isolators, and then the underwater noise is generated. Analyzing the vibration transfer properties and identifying the critical path can provide guidance to the low-noise design of the gear system. In this paper, a coupled gear-housing-foundation dynamic model is proposed for a flexible supported gear system, in which the flexibility of each subsystem and the coupling relationship between them are taken into account. The transferring process of gear vibration is divided into different layers between gears, shafts, bearings, housing, isolators, and ship foundation. Based on the vibration power flow (VPF) theory, detailed layering vibration transfer path analyses of the gear isolation coupled system are carried out for both location path and direction path, and the main paths are identified in a broad speed range. The results indicate that though the gear vibration transferred to the foundation attenuate layer by layer, there may be reverse VPF in some special location path and direction path under resonance conditions.

Primary electrodeposition is an accepted strategy to elucidate the nucleation and growth kinetics of metal electrodes. Nevertheless, when confronted with the phase transition process caused by bi-active metals such as NaK liquid alloys, the research process becomes complex and elusive. Herein, we have reduced the intricate issues to relatively simple initial alloying behaviors. Two exchange diffusion mechanisms of the Na atom embedded in K crystals and K atom embedded in Na crystals are investigated by first-principles density functional theory (DFT) calculation and mechanical simulation. As a result, the process of embedding the Na atom in K crystals shows a better thermodynamic stability and lower activation barrier and structural stress than those of the other. The abovementioned conclusions are further proved by stepwise Na and K electrodeposition experiments, and the prepared NaK alloy electrode displays excellent electrochemical performance. Our findings correlate the original alloying mechanism model specification with electrodeposition experimental verification and provide strategies to achieve controllable NaK electrode construction.

Hybrid Energy Storage System has been widely applied in aerospace, electric vehicle, and microgrid applications. The advantages are that they include complimentary technologies with both high power and energy capabilities. HESS have the potential to be useful to the bulk power systems, for example to increase the value of energy produced by variable generation resource through enabling participation in ancillary service markets. Actualizing the benefits of HESSs requires optimizing the combined ramping capability of aggregated HESS resources. To provide quality ancillary service, source of HESSs locating at multiple sites of variable generation resource must be optimally sized and cohesively controlled. Optimizing aggregated resources can be formulated as an optimization problem. Successfully solving this problem not only requires using effective solution methods but also depends on accurately and rapidly setting the necessary parameters in the problem formula. This article proposes a novel framework with double-layer structure to solve the optimization problem of aggregating ramping capability. Program developed on the upper layer focuses on solving the optimization of aggregating ramping capability among multiple HESSs and is compatible with most existing optimization algorithms. Program on lower layer of the framework targets at optimizing the local control of a single HESS based on a thorough analytics of HESS operation strategy presented in this article. Result of local optimization is also provided to upper layer program for updating the parameters in formula of optimization problem. Real time hardware-in-the-loop test is conducted to verify the performance of the optimization framework developed. The work presented is expected to provide guidance for implementing this framework in practical operation.

Semiconductor photocatalysis is considered to be a promising technique to completely eliminate the organic pollutants in wastewater. Recently, S-scheme heterojunction photocatalysts have received much attention due to their high solar efficiency, superior transfer efficiency of charge carriers, and strong redox ability. Herein, we fabricated an S-scheme heterostructure BiOCl/MoSe

In this paper, we establish an explicit correspondence between kissing reflection groups and critically fixed anti-rational maps. The correspondence, which is expressed using simple planar graphs, has several dynamical consequences. As an application of this correspondence, we give complete answers to geometric mating problems for critically fixed anti-rational maps., 49 pages, 14 figures. The last two sections of v1 are moved to the sequel of this paper. Final version, to appear in Forum of Math. Sigma

With the development of urbanization, the environment is the key to the safety of residents’ life and health and the United Nations’ Sustainable Development Goals (SDGs). Urban environmental changes and microclimate problems have attracted widespread attention. For the SDGs, monitoring the urban microclimate more accurately and effectively and ensuring residents’ environmental health and safety is particularly important when designing applications that can replace the traditional fixed-point urban environment or pollution monitoring. Based on the BeiDou Navigation Satellite System platform, this paper proposes a fine-granularity urban microclimate monitoring method using wearable multi-source (PM2.5, PM10, and other air pollutants) sensors innovatively, which includes the satellite position function by adopting the satellite pseudo-range differential positioning technology, environmental data perception through the embedded system and wireless transmission, as well as the GIS data processing and analysis system. The wearable sensor acquires position and service information data through the satellite positioning system and acquires environmental parameters through integrated mobile multi-source sensors. The data are cached and wirelessly transmitted to the cloud server for digital processing. The urban microclimate is evaluated and visualized through algorithm and map API. Mobile monitoring can be flexibly applied to complex and diverse urban spaces, effectively realizing all-weather, all-directional, and accurate microclimate monitoring of urban environmental quality.

This paper proposes a dynamic frequency support scheme of a supercapacitor energy storage system (SCESS) in coordination with run-of-the-river-based pumped storage hydropower (PSH) to enhance the short-term frequency stability in a power system that has a high penetration of renewable energy. To achieve this, the proposed coordinated frequency controller (CFC) enables the SCESS and PSH plant to provide the frequency response. The CFC scheme employs a dynamic droop characteristic in parallel with an integral controller and a distribution function. The dynamic droop characteristic determines the power production for frequency regulation employing a variable gain, which varies with the total capacity of the frequency control units and magnitude of the system frequency error with time; the gain increases with the frequency error, and thereby, arresting the frequency nadir at a higher level than in the conventional droop characteristic. In addition, the distribution function dispatches the power from the dynamic droop and integral controller to the control units in proportion to their headrooms; furthermore, the distribution function considers a sudden loss of generation from an SCESS by its operational constraint during the frequency support. Thus, the proposed dynamic frequency support scheme can enhance the short-term frequency stability for a frequency event.

Growing trends in the deployment of inverter-based renewable energy will decrease the inertia and frequency control capability of electric power systems by replacing conventional power plants; thus, the frequency of future power systems might be dynamic. This study proposes a capability-coordinated frequency control (CCFC) scheme of a virtual power plant (VPP) including adjustable-speed pumped storage hydropower (AS-PSH), a wind power plant (WPP), and an energy storage system to support the frequency nadir and reduce the steady-state error of system frequency. The CCFC scheme is based on a hierarchical-control structure in which a CCFC organises the output of local frequency control units. To support the frequency nadir, the CCFC dispatches weighted frequency errors that are proportional to the available headroom of the units; thus, the errors are forwarded separately with a system frequency error to the primary control loop of each unit and thereby arrest the frequency nadir at a higher value than a system without the CCFC. To reduce the steady-state error of the system frequency, the CCFC determines a partial active power command by additionally feeding an integrator of the CCFC with a modified frequency error that depends on the unit with the largest control.

Moser's shadow problem asks to estimate the shadow function $\mathfrak{s}_b(n)$, which is the largest number such that for each bounded convex polyhedron $P$ with $n$ vertices in $3$-space there is some direction ${\bf v}$ (depending on $P$) such that, when illuminated by parallel light rays from infinity in direction ${\bf v}$, the polyhedron casts a shadow having at least $\mathfrak{s}_b(n)$ vertices. A general version of the problem allows unbounded polyhedra as well, and has associated shadow function $\mathfrak{s}_u(n)$. This paper presents correct order of magnitude asymptotic bounds on these functions. The bounded case has answer $\mathfrak{s}_b(n) = \Theta \big( \log (n)/ (\log(\log (n))\big$. The unbounded shadow problem is shown to have the different asymptotic growth rate $\mathfrak{s}_u(n) = \Theta \big(1\big)$. Results on the bounded shadow problem follow from 1989 work of Chazelle, Edelsbrunner and Guibas on the (bounded) silhouette span number $\mathfrak{s}_b^{\ast}(n)$, defined analogously but with arbitrary light sources. We complete the picture by showing that the unbounded silhouette span number $\mathfrak{s}_u^{\ast}(n)$ grows as $\Theta \big( \log (n)/ (\log(\log (n))\big)$.

This paper presents a real-time simulation and hardware-based approach for systematic integration of Distributed Energy Resources (DERs) in advanced distribution grids with a special focus on resilience. Advanced distribution grids are considered to be functionally more sophisticated than traditional ones. The desirable advanced functionalities include – reconfiguration, real-time sensing, DERs, self-healing, etc. Some of these functionalities are currently being realized by microgrids as well. However, it is not feasible to convert each section of a distribution grid into a microgrid, but can be instituted with functionalities by design and controls at relatively lower costs. Interconnection of DERs, including energy storage to improve reliability and resilience is presented in details. Resilience of distribution grids is gaining greater importance and research towards enhancing it utilizing DERs is a key area. A real-time resilience framework with Analytical Hierarchical Processes (AHP) is developed that adapts to changing configurations, DERs, switching operations, grid conditions, etc. to provide an accurate and adoptable composite resilience metric. This framework and the composite resilience metric can play a unique role in operational and design decisions for operating future distribution grids. Advanced functionalities such as scenario-based reconfiguration in distribution grids are considered, with resilience metrics as performance criteria for choosing a preferred combination. Simulations are performed using Digital Real-Time Simulator (DRTS) and characterized response of flow battery validated against actual flow battery hardware is imposed to provide realistic results. Reconfiguration program is interfaced with DRTS for bi-directional real-time communication. Key contributions include enhancement of resilience of distribution grids using energy storage system under dynamic operating conditions.

In this paper, we develop a theory on the degenerations of Blaschke products $\mathcal{B}_d$ to study the boundaries of hyperbolic components. We give a combinatorial classification of geometrically finite polynomials on the boundary of the main hyperbolic component $\mathcal{H}_d$ containing $z^d$. We show the closure $\overline{\mathcal{H}_d}$ is not a topological manifold with boundary for $d\geq 4$ by constructing self-bumps on its boundary., 68 pages, 34 figures. Final version, to appear in J. Eur. Math. Soc. (JEMS)

In this paper, we study hyperbolic rational maps with finitely connected Fatou sets. We construct models of post-critically finite hyperbolic tree mapping schemes for such maps, generalizing post-critically finite rational maps in the case of connected Julia set. We show they are general limits of rational maps as we quasiconformally stretch the dynamics. Conversely, we use quasiconformal surgery to show any post-critically finite hyperbolic tree mapping scheme arises as such a limit. We construct abundant examples thanks to the flexibilities of the models, and use them to construct a sequence of rational maps of a fixed degree with infinitely many non-monomial rescaling limits., Comment: 45 pages, 26 figures. Final version, to appear in J. Lond. Math. Soc

Pumped storage hydro (PSH) based generation of electricity is a proven grid level storage technique. A new configuration i.e., adjustable speed PSH (AS-PSH) power plant is modeled and discussed in this paper. Hydrodynamic models are created using partial differential equations and the governor topology adopted from an existing, operational AS-PSH unit. Physics-based simulation of both hydrodynamics and power system dynamics has been studied individually in the past. This paper demonstrates a co-simulation of an AS-PSH unit between penstock hydrodynamics and power system events in a real-time environment. Co-simulation provides an insight into the dynamic and transient operation of AS-PSH connected to a bulk power system network. The two modes of AS-PSH operation presented in this paper are turbine and pump modes. A general philosophy of operating in turbine mode is prevalent in the field when the prices of electricity are high and in the pumping mode when prices are low. However, recently there is renewed interest in operating PSH to also provide ancillary services. A real-time co-simulation at sub-second regime of AS-PSH connected to the IEEE 14 bus test system is performed using digital real-time simulator and the results are discussed.

In this paper, we show that one can naturally associate a limiting dynamical system $F: T\longrightarrow T$ on an $\R$-tree to any degenerating sequence of rational maps $f_n: \hat\C \longrightarrow \hat\C$ of fixed degree. The construction of $F$ is in $2$ steps: first we use barycentric extension to get $\E f_n : \Hyp^3 \longrightarrow \Hyp^3$; second, we take appropriate limit on rescalings of hyperbolic space. An important ingredient we prove here is that the Lipschitz constant depends only on the degree of the rational map. We show that the dynamics of $F$ records the limiting length spectra of the sequence $f_n$., Comment: 41 pages, 5 figure. Final version

Optimal active power dispatch is a well-studied problem in power system research. The conventional solutions are usually centralized, thus are inflexible and susceptible to single-point-failure. In this paper, a fully distributed solution for optimal active power dispatch is proposed. The proposed solution can consider not only constraints of supply–demand balance and generation bounds but also the line flow constraints. To balance computational efficiency and effectiveness, DC power flow was used to check for line flow constraint violations. In this way, both the optimality and feasibility of the obtained solution can be guaranteed. The operations of projected gradient calculations and global situational awareness acquisition are fully distributed and implemented using a multi-agent system. In the multi-agent system, an agent could have two function modules for information discovery and generation optimization. The lower-level information discovery module finds the unified price and congestion prices based on the consensus algorithm. With the discovered information, the upper-level generation optimization module adjusts generation settings based on the projected gradient algorithm. Simulation studies of power systems with different scales verify the effectiveness of the proposed solution.

Big data has potential to unlock novel groundbreaking opportunities in power grid that enhances a multitude of technical, social, and economic gains. As power grid technologies evolve in conjunction with measurement and communication technologies, this results in unprecedented amount of heterogeneous big data. In particular, computational complexity, data security, and operational integration of big data into power system planning and operational frameworks are the key challenges to transform the heterogeneous large dataset into actionable outcomes. In this context, suitable big data analytics combined with visualization can lead to better situational awareness and predictive decisions. This paper presents a comprehensive state-of-the-art review of big data analytics and its applications in power grids, and also identifies challenges and opportunities from utility, industry, and research perspectives. The paper analyzes research gaps and presents insights on future research directions to integrate big data analytics into power system planning and operational frameworks. Detailed information for utilities looking to apply big data analytics and insights on how utilities can enhance revenue streams and bring disruptive innovation are discussed. General guidelines for utilities to make the right investment in the adoption of big data analytics by unveiling interdependencies among critical infrastructures and operations are also provided.

The ever-increasing demand for more reliable and flexible energy supply for customers has pushed up the Microgrids (MGs) to the center stage in the developments of distribution networks. The integration of the MGs can provide the customers with better service compared with traditional radial-configured distribution networks with a single generation source. Yet, to motivate more and more MGs developer and practitioner to trade with the distribution network and thus, to improve the quality-of-service of energy consumers, a proper mechanism for energy trading is more than necessary. In this paper, we first analyzed the energy-supply cost for an MG, including power generation cost, distribution cost, transaction cost and service cost. Then we proposed a mechanism of energy trading for multiple MGs integrated distribution network, and this mechanism aims at maximizing the overall benefits of the MG. A case study is also provided to demonstrate that the proposed mechanism is effective and can be used to guide the energy trading of MGs with the quality of service for energy supply being taken into consideration.

The ever-increasing demand for more reliable and flexible energy supply for customers has pushed up the distributed generation technology to the center stage in the development of distribution networks. If managed and coordinated efficiently, the distributed generators (DGs) can provide distinct benefits to the suppliers as well as energy consumers. In this paper, a distributed optimization method is proposed to coordinate the multiple DGs in the distribution network (DN) as well as to achieve the optimal operation among them. To optimize the power generation DGs in the DN is actually equivalent to solve the AC optimal power flow (OPF) problem. By defining new variables, the OPF problem is first transformed to a convex second-order cone program (SOCP) problem. By applying alternating direction method of multipliers (ADMM), the SOCP problem is decomposed to the bus level, and it is then solved in a distributed manner. The proposed control enables the autonomous operation of DGs in the distribution network while still achieves the optimality. Simulation studies further demonstrate the effectiveness of the proposed approach.

Optimal scheduling of hydrogen production in dynamic pricing power market can maximize the profit of hydrogen producer; however, it highly depends on the accurate forecast of hydrogen consumption. In this paper, we propose a deep leaning based forecasting approach for predicting hydrogen consumption of fuel cell vehicles in future taxi industry. The cost of hydrogen production is minimized by utilizing the proposed forecasting tool to reduce the hydrogen produced during high cost on-peak hours and guide hydrogen producer to store sufficient hydrogen during low cost off-peak hours.

Supercapacitor technology has reached a level of maturity as a viable energy storage option available to support a modern electric power system grid; however, its application is still limited because of its energy capacity and the cost of the commercial product. In this paper, we demonstrate transient models of supercapacitor energy storage plants operating in coordination with run-of-the-river (ROR), doubly-fed induction generator hydropower plants (HPP) using a conceptual system control architecture. A detailed transient model of a supercapacitor energy storage device is coupled with the grid via a three-phase inverter/rectifier and bidirectional DC-DC converter. In addition, we use a version of a 14-bus IEEE test case that includes the models of the supercapacitor energy storage device, ROR HPPs, and synchronous condensers that use the rotating synchronous generators of retired coal-powered plants. In this paper, we emphasize the control coordination among the components of the power system. The control actions must be coordinated and prioritized based the capability, response time, the power rating, and the energy content of the components.

Since the introduction of Plug-in Electric Vehicles (PEVs), scientists have proposed leveraging PEV battery packs as distributed energy resources for the electric grid. PEV charging can be controlled not only to provide energy for transportation but also to provide grid services and to facilitate the integration of renewable energy generation. With renewable generation increasing at an unprecedented rate, most of which is non-dispatchable and intermittent, the concept of using PEVs as controllable loads is appealing to electric utilities. If incentivized suitably, this could serve as an additional driver for PEV adoption. It has been widely proposed that PEVs can provide valuable grid services, such as load shifting to provide voltage and frequency regulation. The objective this work is to address the degree to which PEVs can provide grid services and mutually benefit the electric utilities, PEV owners, and auto manufacturers.

A thyristor-controlled supercapacitor energy storage (SES) system is proposed in this work to improve the transient stability of a synchronous generator located in a power network. To check how effective the proposed SES in augmenting the transient stability of the generator is, its performance is compared to that of a thyristor-controlled superconductive magnetic energy storage (SMES) system. Both symmetrical and unsymmetrical faults are considered in the power network. Simulation results demonstrate the effectiveness and validity of the proposed method in enhancing the transient stability of the synchronous generator. Moreover, the performance of proposed SES is found to be better than that of SMES. Overall, it can be inferred that the proposed thyristor-controlled SES technique provides a simple and effective means of transient stability improvement of synchronous generator.

Background & Aims Cachexia, which includes muscle wasting, is a frequent complication of pancreatic cancer. There are no therapies that reduce cachexia and increase patient survival, so it is important to learn more about its mechanisms. The zinc transporter ZIP4 promotes growth and metastasis of pancreatic tumors. We investigated its effects on muscle catabolism via extracellular vesicle (EV)-mediated stimulation of mitogen-activated protein kinase 14 (p38 MAPK). Methods We studied nude mice with orthotopic tumors grown from human pancreatic cancer cell lines (AsPC-1 and BxPC-3); tumors were removed 8 days after cell injection and analyzed by histology. Mouse survival was analyzed by Kaplan–Meier curves. ZIP4 was knocked down in AsPC-1 and BxPC-3 cells with small hairpin RNAs; cells with empty vectors were used as controls. Muscle tissues were collected from mice and analyzed by histology and immunohistochemistry. Conditioned media from cell lines and 3-dimensional spheroid/organoid cultures of cancer cells were applied to C2C12 myotubes. The myotubes and the media were analyzed by immunoblots, enzyme-linked immunosorbent assays, and immunofluorescence microscopy. EVs were isolated from conditioned media and analyzed by immunoblots. Results Mice with orthotopic tumors grown from pancreatic cancer cells with knockdown of ZIP4 survived longer and lost less body weight and muscle mass than mice with control tumors. Conditioned media from cancer cells activated p38 MAPK, induced expression of F-box protein 32 and UBR2 in C2C12 myotubes, and also led to loss of myofibrillar protein myosin heavy chain and myotube thinning. Knockdown of ZIP4 in cancer cells reduced these effects. ZIP4 knockdown also reduced pancreatic cancer cell release of heat shock protein (HSP) 70 and HSP90, which are associated with EVs, by decreasing CREB-regulated expression of RAB27B. Conclusions ZIP4 promotes growth of orthotopic pancreatic tumors in mice and loss of muscle mass by activating CREB-regulated expression of RAB27B, required for release of EVs from pancreatic cancer cells. These EVs activate p38 MAPK and induce expression of F-box protein 32 and UBR2 in myotubes, leading to loss of myofibrillar myosin heavy chain and myotube thinning. Strategies to disrupt these pathways might be developed to reduce pancreatic cancer progression and accompanying cachexia.

Supercapacitors are finding wider applications in modern power systems due to a controllable fast dynamic response. Use of power electronically interfaced supercapacitors for frequency support is a proven technique. In practical applications the heat generated from the Equivalent Series Resistance (ESR) can significantly reduce the life of supercapacitor. Hence thermal issues must be addressed for optimal operation. It is infeasible to use traditional optimization control methods to mitigate the impacts of frequent cycling due to the lack of active thermal management. This paper proposes a Front End Controller (FEC) using Generalized Predictive Control based on real time receding optimization. The constraints in the optimization are based on thermal management to enhance the efficiency of utilization life of the supercapacitors. A rigorous mathematical derivation is provided and supporting simulation results are obtained using Real Time Digital Simulator to demonstrate the effectiveness of the proposed technique.

Background: High-volume hemofiltration (HVHF) is widely used for blood purification in critically ill patients with systemic inflammatory syndromes. The purpose of this study was to evaluate the effect of HVHF on mortality at different follow-up periods in critically ill patients. Methods: We systematically searched PubMed, Embase, and the Cochrane Library through April 2017 to identify trials that evaluated the effect of HVHF on mortality in critically ill patients. Summary relative risks (RRs) and 95% confidence intervals (CIs) were employed to calculate the treatment effect using a random effects model. Eleven trials involving 1048 critically ill patients were included in this study. Results: The summary results indicated no significant differences between HVHF and usual care for the incidence of 28-day mortality (RR: 0.93; 95%CI: 0.80–1.08; P = .321), 7-day mortality (RR: 0.72; 95%CI: 0.50–1.03; P = .072), 60-day mortality (RR: 1.00; 95%CI: 0.86–1.16; P = .997), and 90-day mortality (RR: 1.01; 95%CI: 0.88–1.16; P = .927). Subgroup analysis suggested HVHF significantly reduced the risk of 28-day mortality (RR: 0.64; 95%CI: 0.42–0.97; P = .035) if pooled the study sample size < 100. Conclusion: Our findings suggest HVHF significantly reduced the incidence of 28-day mortality when pooled the study sample size < 100. Further, HVHF had a marginal effect on the incidence of 7-day mortality.

Microgrid power systems strike a balance between maintaining system stability and insuring a high utilization efficiency of pulsed power loads. In microgrids, pulsed power loads' high power-consumption challenges the generators' low generation capacity. Super capacitors were proposed to replace the generators for powering pulsed power loads. Charging super capacitor is expected to be complete rapidly without affecting the system stability. This paper takes input constraints into account for computing optimal control reference signal. This paper also applies generalized predictive control algorithm to realize robust closed-loop control in a complex microgrid power system, where precise model is hard to be built. Test results show the proposed control strategy can successfully achieve desired control effect that both system stability and rapid charging speed can be realized.

This paper presents a real-time simulation with a hardware-in-the-loop (HIL)-based approach for verifying the performance of electrolyzer systems in providing grid support. Hydrogen refueling stations may use electrolyzer systems to generate hydrogen and are proposed to have the potential of becoming smarter loads that can proactively provide grid services. On the basis of experimental findings, electrolyzer systems with balance of plant are observed to have a high level of controllability and hence can add flexibility to the grid from the demand side. A generic front end controller (FEC) is proposed, which enables an optimal operation of the load on the basis of market and grid conditions. This controller has been simulated and tested in a real-time environment with electrolyzer hardware for a performance assessment. It can optimize the operation of electrolyzer systems on the basis of the information collected by a communication module. Real-time simulation tests are performed to verify the performance of the FEC-driven electrolyzers to provide grid support that enables flexibility, greater economic revenue, and grid support for hydrogen producers under dynamic conditions. The FEC proposed in this paper is tested with electrolyzers, however, it is proposed as a generic control topology that is applicable to any load.

Microgrid (MG) islanding is considered as an effective measure to minimize power outage and therefore to maximize usage of renewable energy resources. One of the most challenging technical difficulties associated with islanding is out-of-phase reclosing caused by asynchronism of MG with the electric power system (EPS). In this paper, a novel control methodology is proposed to synchronize MG with the main power grid so that smooth transition from islanded mode to grid-tied mode can be guaranteed. Synchronization is achieved by eliminating the voltage phase angle difference across the circuit breaker/recloser at the point of common coupling (PCC). The proposed control employs synchrophasor measurements transmitted via Internet Protocol (IP) communications. A MG hardware testbed with multiple distributed generators and loads is built to validate the performance of the proposed method.