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The penetration of large-scale renewable generation leads to a shortage of primary frequency regulation resources as well as increasing regulation demand. By exploiting the thermal capacity of buildings, the authors achieve linear power–frequency characteristics comparable to turbine droop control via clustering a number of air-conditioning units (ACs) to participate in primary frequency regulation without affecting indoor comfort. Due to the bandwidth limitations and latency in communication, the real-time centralised control method face great challenges. This study proposes a two-level coordinated state-estimation method to reduce the coordination burden, in which a central coordinator and local controller for each AC are involved. The central coordinator periodically gathers the working state of every AC and estimated thermal parameters individually, then broadcasts this identified model parameters – the coordination information – to each local controller. Resorting to a state-estimation method considering the coordinated information and local measurements, local controller determines whether to toggle the state of local AC to realise a fast frequency response. Simulation results show that the approach can effectively manage a large number of ACs with heterogeneous parameters to provide a primary frequency regulation service without inducing a rebound effect.

Four designed precure cycles were applied to carbon/benzoxazine prepregs to realize different precure degrees. The quality of laminates in quasi-isotropic stacking sequence made from these precured prepregs was evaluated by void content. The effects of precure degree on tensile and dynamical mechanical properties of the laminates have been investigated. The dynamical mechanical properties of laminates with different precure degree were found to vary little from each other, while the static tensile properties (such as strength and modulus) were in negative correlation with the precure degree and the void content. Microstructures of different laminates after fracture show that the precure procedure contributes to an increase of interfacial strength. The availability of prepregs can be determined precisely by the established relation between the precure degree of prepregs and the mechanical properties of the laminates, which is likely to be an improvement on quality/cost optimization of composite manufacturing process.

In this study, the feasibility of multifunctional structural lithium ion batteries (LIBs) based on carbon fiber reinforced plastic (CFRP) composites was investigated. T700S carbon fabrics undertook the roles of both reinforcements and electrode materials in structural batteries. The co-continuous structural electrolytes were prepared by in-situ cure of liquid electrolyte and epoxy resin with the abilities of both load bearing and lithium ion transport. The structural electrolytes were cured with the carbon fabrics to process the CFRP composites. With the increase of liquid electrolyte/epoxy mass ratio, a trade-off relationship was found between the mechanical performance and electrochemical properties of both the structural electrolytes and the corresponding CFRP composites. The CFRP composites based on liquid/epoxy structural electrolytes were proved to have the ability to insert and extract lithium, and can be considered as the potential candidate for the multifunctional structural LIBs. The strategy of functionalizing the LIBs with structural performance via CFRP composites could be helpful for the overall system to provide a mass reduction as well as increase the energy efficiency at a system-level.

Recyclable lightweight materials with advanced processing techniques are essential for the sustainable development of future transportation. Thermoplastic composites lattice structures were developed to meet this demand. An additive manufacturing method is presented here to fabricate such lattice structures by reversible assembly of several long-fiber reinforced thermoplastic composite parts (LFTCPs) which were economically processed by injection molding. The resulting thermoplastic lattice structures (density of 30 kg·m −3 ) assembled with different sequences and connections are structurally evaluated and compared. Out-of-plane compression tests revealed that their mechanical properties were more sensitive to the presence of the connections rather than their assembly sequence, although their structural failure mode was always brake of inclined struts followed by fracture of the horizontal struts. Potential solutions to the problem of internal stresses, induced during assembly, are also explored by designing novel LFTCPs. The novel fabrication route for thermoplastic lattice structures will improve the prospects for their industrial application.

Power systems are the typical cyber-physical systems in which the closed-loop hierarchical control systems (HCSs) are widely used to ensure their stable and safe operation. To describe the coupling operation mechanism of an HCS and power grid by expanding current steady-state power flow analysis theory, we propose an information-energy flow model and develop a matrix-based computational approach. With the help of the methods, we can directly calculate the mutual influence of the cyber and physical parts. Since the mechanism of power flow computation is mature, we focus on the cyber side, proposing an information-flow-oriented network model as well as a matrix-based computation method for its information flow. In particular, we develop a minimum-cut-set-based partition and equivalence method to address a complex cyber network with non-linearity issues associated with data processing. Subsequently, we discuss cyber-physical sensitivity and vulnerability issues. In the case study, we calculate the information-energy flow of an IEEE 14-node system with real time-voltage stability monitoring and control application and compare the results with simulation results. The similarity of the results between the two methods verifies the effectiveness of our approach.

Composite space mirror can completely replicate the high-precision surface of mould by replication process, but the actual surface accuracy of the replication composite mirror always decreases. Lamina thickness of prepreg affects the layers and layup sequence of composite space mirror, and which would affect surface accuracy of space mirror. In our research, two groups of contrasting cases through finite element analyses (FEA) and comparative experiments were studied; the effect of different lamina thicknesses of prepreg and corresponding lay-up sequences was focused as well. We describe a special analysis model, validated process and result analysis. The simulated and measured surface figures both get the same conclusion. Reducing lamina thickness of prepreg used in replicating composite space mirror is propitious to optimal design of layup sequence for fabricating composite mirror, and could improve its surface accuracy.

In this work, the aramid fiber/epoxy interfacial normal bonding property and interfacial shear property were estimated by transverse fiber bundle tensile (TFBT) test and 45° fiber bundle tensile (45FBT) test, respectively. The fracture surfaces of the fiber bundle samples after the mechanical test were observed to investigate the micro failure mechanisms. The interfacial debonding was found coupled with fibrillation of the fiber surface due to the apparent skin/core structure of aramid fibers. Furthermore, the multiscale model based on the generalized methods of cells (GMC) considering the skin/core structure and the fiber/matrix interphase was established to calculate the micro stresses. The interfacial normal strength (IFNS) in the TFBT specimen and interfacial shear strength (IFSS) in the 45FBT specimen were determined by the combination of the experimental and analytical results. Eventually, the effects of skin/core stiffness and thickness on the calculated IFNS and IFSS values were investigated.

Rational models of frequency-dependent network equivalents (FDNEs) must be passive to ensure numerical stability in time domain simulations. Therefore, passivity enforcement is an essential step in FDNE rational modeling procedures; however, current approaches are either not guaranteed or not efficient. Here, a positive real lemma based semidefinite programming model is first implemented to guarantee the passivity of the result obtained. Second, this paper incorporates an approach to significantly improve efficiency while guaranteeing passivity by exploiting an important feature of rational models: that constituent complex-pole terms corresponding to dominant resonance peaks can be adjusted to be passive through minor changes, and a partition-based scheme is proposed. Numerical investigations demonstrate that the proposed method is efficient while introducing little additional modeling error.

As one of significant parts of structural power composites, structural electrolytes have desirable mechanical properties like structural resins while integrating enough ionic conductivity to work as electrolytes. Here, a series of polyethylene glycol (PEG)-epoxy-based electrolytes filled with nano-silica were prepared. The ionic conductivity and mechanical performance were studied as functions of PEG content, lithium salt concentration, nano-silica content and different curing agents. It was found that, PEG-600 and PEG-2000 content in the epoxy electrolyte system had a significant effect on their ionic conductivity. Furthermore, increasing the nano-silica content in the system induced increased ionic conductivity, decreased glass transition temperature and mechanical properties, and more interconnected irregular network in the cured systems. The introduction of rigid m-xylylenediamine resulted in enhanced mechanical properties and reasonably decreased ionic conductivity. As a result, these two-phase epoxy structural electrolytes have great potential to be used in the multifunctional energy storage devices.

In this work, mechanical properties of a T800 carbon fiber/modified epoxy composite material were researched by using a dynamic mechanical analyzer (DMA) operated under flexural mode. The dynamic mechanical behavior was investigated by DMA at a fixed frequency of 1 Hz. Because mechanical properties of the material were influenced by both time and temperature, its viscoelastic modulus was also considered and accomplished by conducting DMA multiple-frequency dynamic mechanical experiments. Based on the experimental data, master curves of the storage (E′) and the loss moduli (E″) at a pre-selected reference temperature were constructed as a function of frequency. The shift factor along the frequency axis was also determined as a function of temperature. Expression of the relaxation modulus in the time domain at the reference temperature was obtained by using vector fitting method. The numerical algorithm result showed excellent correlation to experimental data over the entire range of relaxation. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

In distribution networks, there are slow controlling devices and fast controlling devices for Volt-VAR regulation. These slow controlling devices, such as capacitors or voltage regulators, cannot be operated frequently and should be scheduled tens of minutes ahead (Hereafter named as slow control). Since of the uncertainties in predicting the load and distributed generation, the voltage violations cannot be eliminated by fast controlling devices with improper schedule of the slow controlling devices. In this paper we propose dual time-scale coordination for the Volt-VAR control scheme, corresponding to slow and fast control. In the case of slow control, a robust voltage and reactive power optimization model is developed. This guarantees that subsequent fast controls can maintain the system's voltage security if the uncertain parameters vary within predefined limits. This nonconvex optimization problem is relaxed to a mix integer second order conic problem, and the dual form of its sub-problem is also derived. Then a column-and-constraint generation algorithm was used to solve the robust convexified model. A conventional deterministic optimization model can be used to determine the fast control mechanism. Numerical tests were conducted on a real distribution feeder in China, a balanced IEEE 69-bus and unbalanced 123-bus benchmark distribution networks. The simulation results show that solving the deterministic model is not always feasible and voltage violation may occur. The robust model was shown to be effective with respect to all possible scenarios in the uncertainty set, with little compromise in terms of network losses., 22 pagse, ams.org

Carbon fiber reinforced polymer, CFRP, composite materials have been used to fabricate space mirror. Usually the composite space mirror can completely replicate the high-precision surface of mould by replication process, but the actual surface accuracy of replicated space mirror is always reduced, still needed further study. We emphatically studied the error caused by layup and curing on the surface accuracy of space mirror through comparative experiments and analyses, the layup and curing influence factors include curing temperature, cooling rate of curing, method of prepreg lay-up, and area weight of fiber. Focusing on the four factors, we analyzed the error influence rule and put forward corresponding control measures to improve the surface figure of space mirror. For comparative analysis, six CFRP composite mirrors were fabricated and surface profile of mirrors were measured. Four guiding control measures were described here. Curing process of composite space mirror is our next focus.

Carboxyl functionalized carbon fibers with preserved tensile strength and electrochemical properties were acquired through a simple chemical oxidation method, and the proposed underlying mechanism was verified. The surface of carboxyl functionalizing carbon fibers is necessary in acquiring functional groups on the surface of carbon fibers to further improve the thermal, electrical or mechanical properties of the fibers. Functionalization should preserve the tensile strength and electrochemical properties of carbon fibers, because the anodes of structural batteries need to have high strength and electrochemical properties. Functionalized with mixed H 2 SO 4 /HNO 3 considerably reduced the tensile strength of carbon fibers. By contrast, the appearance of H 3 PO 4 preserved the tensile strength of functionalized carbon fibers, reduced the dispersion level of tensile strength values, and effectively increased the concentration of functional acid groups on the surface of carbon fibers. The presence of phosphoric acid hindered the over-oxidation of turbostratic carbon, and consequently preserved the tensile strength of carbon fibers. The increased proportion of turbostratic carbon on the surface of carbon fibers concurrently enhanced the electrochemical properties of carbon fibers.

A new hierarchical multi-area power system state estimation method is proposed in this paper. Instead of exchanging boundary measurements or state estimates, the proposed technique is based on exchanging the sensitivity functions of local state estimators. The main benefit of the proposed scheme is the improved convergence speed, which also reduces the amount of information exchange required. Extensive numerical results involving IEEE standard systems and a utility scale system are presented.

The modular multilevel converter-multi-terminal high-voltage direct current (MMC-MTDC) system is a superior alternative applied to the integration of large-scale renewable energy due to its technical advantages compared with the conventional high-voltage direct current. Based on power systems computer aided design/electro magnetic transient in DC system (PSCAD/EMTDC), a four-terminal MMC-MTDC transmission system for a wind farm integration model is built and then several scenarios, simulation results and corresponding analyses about the dynamic reactive power characteristics are presented. The result shows that MMC-MTDC has a rapid and independent alternating current (AC) voltage regulation ability and effective dynamic reactive power reserves, which has a positive effect under wind power stochastic fluctuations and AC fault conditions.

With the integration of distributed generation systems, distribution networks and transmission networks have become more coupled, especially, with respect to voltage problems. This paper presents a decentralized reactive power optimization method for integrated transmission networks and distribution networks based on the generalized Benders decomposition (GBD). The second-order conic programming relaxation technique is used to make the subproblem (distribution network model) convex, which can guarantee that the GBD process converges. An improved GBD iteration procedure is proposed by exploiting the special structure of the problem, which does not need to generate optimal cut. Moreover, a revised feasible cut generating approach is also developed to improve the efficiency. Theoretical analysis and numerical tests show that the convergence of this decentralized method is guaranteed and the coordinated optimization scheme outperforms conventional separated methods by eliminating overvoltage and reducing network loss in the active distribution network.

Tie-line scheduling (TS) becomes a practical need for growing interconnection of regional power grids and the increasing integration of renewable energy. In electricity markets without a coordination organization, TS should be handled in a fully decentralized manner, where the impact of contingencies should also be considered for operational reliability. In this paper, the contingency-constrained TS (CCTS) problem is formulated using a two-stage robust optimization (RO) scheme to consider the $N-k$ security criterion. This robust model is decomposed and handled by the alternating direction multiplier method (ADMM) in a fully decentralized way, where the column-and-constraint generation (C&CG) is incorporated to solve the regional robust subproblems. Three computational strategies are also developed to enhance the computation efficiency of the decentralized algorithm. Numerical simulations are given to study the computational performance, the solution quality, and scalability of the proposed method.

This paper proposes a fully distributed control method for dc microgrids to realize power balance and bus voltage recovery without central coordination. Based on peer-to-peer communication, distributed generators and energy storage systems need only exchange information between neighbors over a sparse communication network, and hence there is a minimal communication burden. By combining the equal increment rate criteria and a subgradient algorithm, this distributed control method can efficiently regulate the bus voltage to the nominal value with minimum generation cost. In addition, the proposed method can improve the utilization of renewable energy generation via reasonable power sharing among distributed generators. Both islanded mode and grid-connected mode were simulated as case studies. The results indicate that the method is reliable, scalable, and flexible over centralized schemes. Influences of communication delays and failures of communication links are also discussed in numerical tests.

In this letter, an improved real-time, short-term voltage stability monitoring method is introduced. The impact of voltage magnitude oscillation on the calculation of the Lyapunov exponent is analyzed, and a phase rectification method to eliminate the negative influence of oscillation is proposed. The simulation work was conducted on the provincial power grid at Guangdong in China. Based on our simulation results, the proposed method is expected to improve the effectiveness of short-term voltage stability monitoring.

Conventionally, the urban distribution network planning task is conducted manually with the aid of planning software. It is difficult and time-consuming to artificially determine the candidate line set for a new urban area from scratch. Moreover, in most existing planning models, customers within a block are regarded as a single load point, which is inaccurate and may lose plasticity for the planned network. In this paper, we propose the candidate line set generating strategy via exploiting the street layout. For each block, an optimization solution is presented to determine the location and number of local distribution transformers which are influenced by the block shape and its load demand. Finally, we develop a mixed integer linear programming (MILP) model for urban distribution network planning which can be solved analytically. Based on the spatial load forecast, the proposed model can simultaneously generate the optimal locations and capacities of substations and feeders for the distribution network. Numerical tests based on the geographical information system (GIS) of a planned industrial park at a city in China, show that the proposed model is effective and practical.

In order to comprehensively understand the effect of composite materials on the structural response, a novel multiscale numerical model is presented in this work to study the global buckling and localized responses of composite cylindrical shells with trapezoidal corrugated cores. Treated as hierarchical structures, the investigation of composite shells includes carbon fiber-reinforced composites at micro-scale, fiber–matrix laminates at meso-scale, as well as corrugated shells at macro-scale. The well-established locally-exact homogenization theory is firstly introduced to generate the microstructural effective coefficients, which are then transferred to the lamination theory. Finally, a simplified structural homogeneous representative volume element (RVE) is established with equivalent properties to a part of cylindrical structures with inner and outer skins embedded with corrugated cores, significantly facilitating the finite element (FE) simulations. The simplified structure is validated against the 3D full-scale analysis with good agreement for critical loads of different buckling modes. The global buckling performance of corrugated cylinders is then demonstrated by considering the effect of constituent materials, fiber volume fraction and geometric parameters. More importantly, benefited from a top-down procedure, the localized stress distributions are recovered using the three-stage multiscale model, to predict the possible crack initiations starting within the microstructures.

In this study, an improved method is developed to test the compressive strength of single fibers. Two improvements were carried out compared with the previous work, and they were composed of: (1) a skillful device for preparing the compression sample with the advantage of greatly saving time and highly efficiency; (2) an improved system for directly testing the single fiber’s compressive strength with high accuracy and repeatability. More than fifteen qualified samples were successfully prepared within two hour compared with even only one sample in a day for the poor manipulation accuracy of previous work. Compressive strength of single fiber was tested based on four kinds of PAN-based carbon fibers. Experimental results from the new method show great agreement with the data published, which prove the designed method and improved device is more applicable for testing the compressive strength of single fiber in the optimization of cost and efficiency.

A hot-press tackifying process was used to improve the mechanical properties of cured laminates in vacuum-assisted resin transfer molding by placing a thermoplastic film into the preforms at various pressures and temperatures. Three modified preforms were prepared at 0.1, 0.3, and 0.6 MPa using an autoclave, and the laminates were then produced via vacuum-assisted resin transfer molding. The mechanical properties of the modified laminates were tested and compared to those of the unmodified ones. The fiber volume fractions of the modified laminates decreased with increasing pressure. The tensile strength of the modified laminates at the three pressures improved by 16.78%, 41.21%, and 29.47%, respectively, compared to the unmodified samples. Modified laminates at 0.3 MPa showed better results than those at 0.1 and 0.6 MPa, which were all better than the unmodified samples. The modulus of the modified laminates from vacuum-assisted resin transfer molding was improved by 2.48%, 19.01%, and 13.22%, respectively. The effect of the hot-press tackifying in improving the tensile strength and modulus of a laminate on a pre-impregnated laminate (prepreg) using the autoclave was studied and compared to that of the unmodified case. Here, the tensile strength increased by 32.5% and 12.3%, respectively.

Hundreds of cascading trip faults have occurred in recent years in Chinese wind farms, leading to challenges in the secure operation of the power system. To prevent cascading trip faults, the concept of a voltage security region (VSR) has been discussed in previous studies. However, the VSR proposed in previous work cannot provide decoupled voltage control ranges for each wind farm, which would be a more promising and applicable solution for wind farms in China. In addition, with increasing wind farm active power penetration, the VSR of a wind power integration area may not exist. In this situation, the control centre must curtail some wind power to guarantee security. Thus, this study proposes an iterative VSR model to guarantee secure operation and obtain a larger VSR in wind farms considering wind power curtailment. In each wind farm, the VSR is designed to guarantee normal operation of each wind turbine generator, while in the control centre, the region is designed to guarantee normal operation both under normal conditions and N–1 contingencies considering wind power curtailment. The proposed VSR demonstrated good performance in a simple test case and in a real system in Northern China using a Monte Carlo method.

Distributed generations (DGs) introduce significant uncertainties to restoration of active distribution networks, in addition to roughly estimated load demands. An adjustable robust restoration optimization model with a two-stage objective is proposed in this paper, involving the uncertain DG outputs and load demands. The first stage generates optimal strategies for recovery of outage power and the second stage seeks the worst-case fluctuation scenarios. The model is formulated as a mixed-integer linear programming problem and solved using the column-and-constraint generation method. The feasibility and reliability of the strategies obtained via this robust optimization model can be guaranteed for all cases in the predefined uncertainty sets with good performance. A technique known as the uncertainty budget is used to adjust the conservativeness of this model, providing a tradeoff between conservativeness and robustness. Numerical tests are carried out on the modified PG&E 69-bus system and a modified 246-bus system to compare the robust optimization model against a deterministic restoration model, which verifies the superiority of this proposed model.

This work aims at developing a hot sizing process on composite materials to correct the profiles of composite structures during manufacture. Hot sizing experiments were carried out at 150 °C with different sizing loads and hot sizing periods for L-shaped composite beams made of carbon fiber plain-weave fabric and epoxy resin. To predict the springback in hot sizing process, a corresponding finite element simulation method was developed using stress relaxation equations determined at the same temperature. Excellent agreements between the predicted and observed results were obtained. The effects of the component thickness and 45° ply percentage on the springback rate were investigated by simulation. Springback rate in hot sizing process on composite materials ranges from 60% to 95%. In conclusion hot sizing process is proved to be a valid method for compensation for the process-induced deformation (PID) of L-shaped composite beams.

As a vital part of structural power composites, structural electrolyte should achieve ionic conducting and load bearing functions simultaneously. In the present work, a novel method was established for optimizing the morphology and multifunctionality of a liquid/epoxy based structural electrolyte by adding different contents of organoclay (organically modified layered silicates, OLS). The OLS content had a substantial effect on the liquid/epoxy co-continuous morphology. The introduction of OLS changed the epoxy microstructure from the interconnected flakes to the parallel ridges. The increase of OLS content led to a more compact epoxy network and a more interpenetrated conductive phase. However, an excessive amount of OLS could cause the agglomeration and make the morphology parallel interconnected bars. The variation in morphology accounted for the multifunctionality increase in the structural electrolytes. The optimal formulation was determined with the best properties of 211 MPa in tensile modulus and 0.09 mS/cm in ionic conductivity, approaching the inferior limit of the multifunctional performance for a structural electrolyte. As a promising candidate for structural power composites, this co-continuous structural electrolyte containing ionic liquid, epoxy resin and OLS shows great potential to be used in the multifunctional energy storage devices. Keywords: Structural electrolyte, Organoclay, Mechanical properties, Ionic conductivity

A device was designed to study compaction behavior and permeability of preforms in vacuum-assisted resin transfer molding, consisting of a pressure control module, a pressure test module, a thickness test module, and an experimental plate. It can also be used to test the effects of resin flow and the post-filling process on the thickness variation of preforms. Four tests were conducted with the device: (1) compaction tests on preforms of 1, 15, 20, and 25 layers in dry and wet states; (2) in-plane permeability tests on preforms of 1, 5, 10, and 20 layers; (3) transverse permeability tests for 20 layers preforms; (4) determination of the effects of resin flow and post-filling time on preform thickness variation with two liquids. The results show the in-plane permeability decreases as the number of layers increases, and the value for 20 layers is about 62% of one layer. Preform thickness is affected by the liquid viscosity and post-filling time, and the averaged thicknesses of edible oil and Cycom890 resin were 2.12 and 2.03 mm, respectively, at post-filling times of 30 and 40 min, which represent a decrease by 1.9% and 2.9%, respectively, compared with the cases in which there was no post-filling process.

The transverse fiber bundle (TFB) test has recently been implemented to evaluate carbon fiber/epoxy bonding strength. Due to limitations of the specimen manufacturing process, the fiber volume fraction has a particular significant influence on the TFB test results. TFB specimens with different fiber volume contents were prepared by different fiber impregnation processes. A multiscale model with different fiber volume contents was established to simulate the damage process. Both experimental and analytical results show that TFB bonding strength increases with decrease of fiber volume content. Hence, the fiber volume fraction effect should be considered when using the TFB test as a characteristic of interfacial strength.

Cascading trip faults in large-scale wind power centralized integration areas bring new challenges to the secure operation of power systems. In order to deal with the complexity of voltage security regions and the computation difficulty, this paper proposes an autonomous voltage security region (AVSR) for each wind farm and the point of common coupling (PCC) substation, whose voltage can be controlled in a decoupled way. The computation of the AVSR can be completed using a stepwise search method exchanging voltage and power information between the control center and the wind farms. At each wind farm, an AVSR is determined to guarantee the normal operation of each wind turbine generator (WTG), while in the control center, each region is designed in order to guarantee secure operation both under normal conditions and after an N -1 contingency. A real system in Northern China was used to carry out case studies to verify the effectiveness of the AVSRs proposed, and good performance was demonstrated using the Monte Carlo method.

Large-scale wind farms are typically geographically separated from load centers and distributed in different control areas. Therefore, interregional energy dispatch is important for wind power generation via sharing spinning reserve capacity among interconnected systems. However, existing tie-line scheduling methods in China do not provide satisfactory performance in accommodating the recent large-scale integration of wind power. In this paper, we describe a coordination framework for tie-line scheduling and power dispatch to operate multi-area systems. Tie-line flows are updated hourly to hedge uncertainty in the near future, preserving the operational independence of areas. The coordinated tie-line scheduling problem is formulated using two-stage adaptive robust optimization to account for uncertainties in the available wind power and is solved using a column-and-constraint generation method in a coordinate-and-decentralize manner. Comparative simulations show that the method is effective in enabling further wind power penetration and can improve economic efficiency in multi-area systems. A case study using a large-scale power system demonstrates the benefits and scalability of the method in practice.

Interface thickness and modulus of carbon fiber (CF) reinforced polyamide 6 (PA 6) composites with different thermal histories are characterized as 331–394 nm and 0.24–0.30 times to fiber modulus, respectively. Transverse fiber bundle (TFB) test is firstly employed for evaluating semi-crystalline PA 6 interfacial adhesion. TFB Failure mechanisms are schematically given. Besides enhanced molecular entangling on fiber surface, increased matrix toughness is also found to have a great effect on improved TFB results. Droplet micro-debonding results show that decreasing cooling rate and increasing annealing temperature both decrease interfacial shear strength (IFSS) though residual PA 6 on carbon fiber surface increases. In the end, the above data are normalized together with some previous measured parameters. It shows that quenching of the CF/PA 6 composites and subsequent annealing are shown to give similar results as slow cooling. Relationships between each other are also discussed.

This work concentrates on the assessment of carbon fiber/epoxy interfacial shear strength by 45° fiber bundle tensile (45FBT) test. The 45FBT samples for three different carbon fiber/epoxy systems were prepared and tested. The multiscale model based on the generalized methods of cells (GMC) was established to simulate the tensile damage process and analyze the interfacial stress state. The interfacial shear strength in 45FBT specimen was calculated. The 45FBT test was compared with the transverse fiber bundle tensile (TFBT) test. The applicability of the 45FBT test was finally discussed.

In present study, the optimization injection processes for manufacturing the composite pipe key-part and K/T type joints in vacuum-assisted resin transfer molding (VARTM) were determined by estimating the filling time and flow front shape of four kinds of injection methods. Validity of the determined process was proved with the results of a scaling-down composite pipe key-part containing of the carbon fiber four axial fabrics and a steel core with a complex surface. In addition, an expanded-size composite pipe part was also produced to further estimate the effective of the determined injection process. Moreover, the resin injection method for producing the K/T type joints via VARTM was also optimized with the simulation method, and then manufactured on a special integrated mould by the determined injection process. The flow front pattern and filling time of the experiments show good agreement with that from simulation. Cross-section images of the cured composite pipe and K/T type joints parts prove the validity of the optimized injection process, which verify the efficiency of simulation method in obtaining a suitable injection process of VARTM.

This study presents a comprehensive optimisation model that combines reactive power (VAR) optimisation and network reconfiguration to minimise power losses and eliminate voltage violations. In this model, the reactive power of distributed generators (DGs), VAR compensators, the position of tap-changer and the states of branches are formulated as continuous and discrete decision variables. The original non-convex three-phase optimisation model was converted to a mixed-integer second-order cone programming model using the second-order cone relaxation, big-M method and piecewise linearisation. The results of numerical tests showed that the proposed model can achieve significant additional gains in network loss reduction and voltage violation mitigation. This developed method can be used as a basic analysis tool for active distribution networks operation schedule or planning.

Generation maintenance scheduling has system level and equipment level aspects. At the system level, large-scale integration of wind power brings about significant challenges for classical generator maintenance scheduling. At the equipment level, forced outages of power equipment caused by wear affect maintenance decisions. Here, the authors report a robust optimisation model for maintenance scheduling considering wind power integration and forced outages of equipment. An uncertainty set is used to describe fluctuations in the wind power, and a method to control the conservativeness of the robust model is developed. An outage model is used to describe the impact of the operating conditions on maintenance decisions. The effects and advantages of the model are demonstrated via numerical simulations.

Wind power integration could be restricted by inflexible operation of combined heat and power (CHP) units due to the strong linkage between power generation and heating supply in winter. Utilization of the heat storage capacity of existing district heating network (DHN) is a cost-effective measure to enhance power system operational flexibility to accommodate large amounts of variable wind power. In this paper, transmission-constrained unit commitment (UC) with combined electricity and district heating networks (UC-CEHN) is formulated with a linear DHN model to coordinate short-term operation of electric power and district heating systems. The heat storage capacity of the DHN is modeled by capturing the quasi-dynamics of pipeline temperature. Both deterministic and robust models are developed to incorporate UC with the linear DHN model. Case studies are carried out for two test systems to show the potential benefits of the proposed method in terms of wind power integration and efficient operation.

A multivariate statistical analysis (MSA)-based power-grid-partitioning method is proposed. Considering the effectiveness of automatic voltage regulation of generators, network modelling is based on the quasi-steady-state sensitivity of voltage with respect to reactive power. The MSA-based power-grid-partitioning method contains two stages: a quantitative method for determining the appropriate number of zones and allocation of nodes into a number of zones. The proposed method is applied to an automatic voltage control system and an N − 1 robust pilot node selection method is presented. Simulation studies on IEEE 14-bus, 39-bus systems and a real provincial power system in China are described to illustrate the effectiveness of the proposed method.

In this work, epoxy resin viscosity was calculated by using reference viscosity and “viscosity-cure” shift factor which was established to research the dependence of viscosity on curing degree. The predicted results were compared with experimental data and the agreements between them were better than those in reference. Generalized Maxwell model was used to characterize the viscoelastic behavior of epoxy resin and the relaxation modulus was modeled by Prony series. A simple model of stress relaxation times was derived as functions of viscosity and stiffness. The stress relaxation times at different curing degrees were calculated after acquiring the stress relaxation times at the reference curing degree. The relaxation modulus predicted by this method agreed well with experimental data. The above results showed that these models could well be used to predict the viscosity and relaxation modulus of thermosetting resin during cure. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

In this work, load transfer efficiency (LTE) is quantitatively expressed as a specific formula and characterized through electrical resistance method. Single carbon fiber (CF) reinforced polyamide 6 (PA6) microcomposites with eight different thermal histories were prepared. Polarizing optical microscope (POM) was used to observe crystal morphologies. Tensile properties of neat PA6 with different thermal histories were tested. All the above results show that electrical resistance method is an effective way to characterize CF/PA6 microcomposite interface LTE. Water quenched CF/PA6 microcomposites have a highest LTE of 94.2%, while LTE decreased to 34.3% at the bottom for 200°C annealing treated specimens. POM results show that decreasing nonisothermal cooling rate results in larger spherulites and transcrystallites but lower nucleus density, while annealing treated samples nearly have no change and still keep quite transparent. It is also very interesting to find that there is an antisymmetric relationship between LTE and matrix modulus of nonisothermal/isothermal crystallization samples, and LTE drops more for the annealing treated specimens under the similar modulus, which ascribes to radial residual stress releasing during annealing treatment. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Traditional outage model for the power equipment usually focus on the behavior of the equipment under random factors, and the availability of the power equipment in system analysis is usually confined to the steady value. However, this model may be inaccurate in the short term analysis, where the transient process of availability has not ended yet. Furthermore, the power equipment in the short term analysis might be influenced by both random factors and deterministic factors, yet the impact of deterministic factors cannot be completely reflected in the traditional outage model. Based on the above issues, a Markov-based transient outage model is proposed in this paper, which describes the deterioration and repair process of an equipment. Both the corrective maintenance and preventive maintenance are concerned in the model. The preventive maintenance in the model is considered as deterministic event, in which the start time and duration are both scheduled. Meanwhile the corrective maintenance and the unexpected failure are modeled as random events. The transient state probability and availability of equipment under preventive maintenance is derived. The effect of deterministic events on the availability of equipment is analyzed on numerical tests. The proposed model can be used in the short-term reliability assessment and maintenance scheduling in actual systems.

Fluctuations in wind power in geographically distributed areas are typically complementary, and therefore a coordinated multi-area dynamic economic dispatch may enable greater wind power penetration in interconnected power systems. Here we describe a decentralized approach based on a modified generalized Benders decomposition in which locally optimal cost function of each area is introduced. The technique exhibits rapid convergence and does not require parameter tuning. It is suitable for multi-area interconnected systems with a hierarchical control architecture. Comparative numerical simulations demonstrate that the performance of our method is favorable in terms of accuracy, convergence and computational efficiency. A case study on a real power system is also carried out to demonstrate the potential of this technique to increase wind power penetration.

A series of functionalization methods was used to functionalize carbon fibers. These functionalization methods were all simple. In addition, these methods exhibit excellent carboxyl functionalization effects. Besides, except for H3PO4/H2SO4/HNO3 chemical oxidation method, these functionalization methods are all popular methods. The demands for multifunctional structural electrode materials are high. Hence, the functionalization needs to preserve the tensile strength and electrochemical properties while increasing the concentration of acidic groups on the surface of carbon fibers. As proven, the H3PO4/H2SO4/HNO3 chemical oxidation method is the most promising functionalization method compared with any other methods. This method preserved the tensile strength of carbon fibers and moderately increased capacity, displayed positive effect on electrochemical kinetics, decreased the charge-transfer impedance, and ensured the stability and reversibility of capacity. Because of its preserved properties and the functionalized surface, this kind of functionalized carbon fibers is more suitable for using as the anode of multifunctional structural lithium-Ion batteries. The appearance of H3PO4 hindered the formation of defects on turbostratic structure of carbon fibers. The modification on the surface of electrode material could also affect the electrochemical properties of carbon fibers.

As one of the most promising structural anode materials, carbon fibers (CF) have gained much attention. One of the central problems in their application is retaining their tensile strength and simultaneously improving their electrochemical properties. Herein, we report reduced graphene oxide/SnO2@carbon fibers (rGO/SnO2@CF) with wrinkled surfaces, fabricated via a simple hydrothermal method followed by heat treatment. This material exhibits prominent tensile properties, improved reversible capacity, excellent cycling stability and significantly enhanced first cycle coulombic efficiency. Compared to the reversible capacity at the 20th cycle, the rGO/SnO2@CF retained 93.6% reversible capacity after 100 cycles at 50 mA g−1, corresponding to a capacity fading of only 0.08% per cycle. The Weibull scale parameter and shape parameter of rGO/SnO2@CF were up to 4.63 GPa and 7.87, respectively. Our measurements revealed that the positive influence of rGO effectively countervailed the negative influence of the hydrothermal process on the tensile strength; the interleaved structure of rGO/SnO2 prevented the dispersion degree of tensile strength from decreasing; the synergistic effect of rGO and SnO2 enhanced the properties of the carbon fibers, including the tensile strength and the electrochemical properties; the formed rGO network structure and bicontinuous electronic transport pathway are in favor of the cycling stability.

Rational approximation of frequency-dependent network equivalents with vector fitting (VF) is widely used in power system analysis; however, a detailed examination of methods to determine the order of the model has not been reported. The traditional order identification method of the frequency response resonance peak is conservative, as demonstrated in this paper. We discuss the essential relationships between VF and Prony analysis (PA). A PA-based method is then proposed to identify the order of model, considering the resonance peaks. The method is computationally inexpensive, and the precision can be adjusted easily. Numerical investigations demonstrate the validity and efficiency of the method.

This paper describes a fully distributed power dispatch method that can achieve fast frequency recovery and minimal generation cost for autonomous microgrids. The method is comprised of two stages. In the first stage, a subgradient-based consensus algorithm is used to recover frequency. The equal increment rate criteria is incorporated into this algorithm to achieve a minimal regulating cost, obtained by economically distributing power among distributed energy resources. Control signals updated with latest local measurements are executed in each iteration step to speed up the frequency recovery procedure. In the second stage, an average consensus algorithm is applied to resolve frequency oscillations caused by measurement errors. Numerical tests are described to demonstrate the validity of the proposed method and its applicability in the presence of communication time delay is discussed.

Rational models of frequency-dependent network equivalents (FDNEs) have been used in real-time digital simulator (RTDS) for power-system simulation. However, this can lead to a computational burden issue; the application of FDNEs may result in a loss of real-time simulation features because the computational cost of the FDNE component exceeds the limits of RTDS. The authors describe a solution that combines compacting and partitioning of the FDNEs, whereby the former reduces the redundancy in the mathematical model and the latter allows us to exploit parallel computer architectures. Then they describe the results of numerical simulations that demonstrate the effectiveness of the approach. Moreover, the proposed simulation solution is not limited to the applications of FDNEs in RTDS, it solves a set of subsistent computational issues when apply rational models in real-time electromagnetic transients programs tools.