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The promise of improved system efficiency, reliability, and higher renewable energy hosting capability of the Integrated Energy System concept has driven the development of innovative network coupling technologies and energy system integration methods. Co-ordinated design and operation of the traditionally separate energy systems, including electric power, gas, and heat will lead to the optimal use of synergies between energy networks and bring forth numerous benefits to the energy sector. To fully understand the potential and quantitatively assess the operation performance of the combined energy networks, a unified modeling and simulation framework using an extended MANA formulation is proposed in this paper, which is capable of incorporating arbitrary gas network configurations and unbalanced power networks in a systematic manner needed. A case study with combined power and gas networks via EnergyHubs is implemented to demonstrate the application of the proposed method.

Real-time simulation of large-scale active distribution networks exhibiting a wide range of time-scales puts forward higher requirements for simulation accuracy and efficiency. This paper presents an extendable method and design for the real-time simulation of active distribution networks utilising high-performance hardware field programmable gate arrays. In the aspect of numerical algorithm, a high-accuracy and stable multirate simulation algorithm is proposed. The entire active distribution network is decoupled into different subsystems by their inherent time-scales and distinct time steps are used to solve the subsystems. Then root-matching method is adopted to form the exponential difference equations that represent the behaviours of the electric distribution network being modelled, which eliminates the truncation errors and thus provides a highly accurate time-domain solution. To handle the interface between the subsystems, a multirate interfacing method is proposed. The hardware design of the multirate interfaces is presented as well. With the multirate algorithm, a fully functional extendable real-time simulator based on field programmable gate arrays is designed and implemented. Two modified IEEE 33-node systems with photovoltaics and energy storage are simulated on the 4-field-programmable-gate-arrays-based real-time simulator. Simulation results are compared with the commercial simulation tool PSCAD/EMTDC to validate the correctness and effectiveness of the proposed method and design.

Using data from the China Household Income Project Survey (CHIPS 2013), this paper investigates the relationship between household registration control and the educational investment for the left-behind children from both theoretical and empirical perspectives by citing a theoretical model that includes factors such as household registration control, work schedules of agricultural migrants, and the educational investment for the left-behind children, as well as an empirical analysis using a mediation test model. The findings show that (1) deregulation of urban household registration helps migrant workers increase their investment in education-based human capital of their left-behind children, and the findings remain robust when the key independent and dependent variables are replaced. (2) By further using the mediation effect analysis, we find that the change in the duration of working outside the city plays a complementary mediating role between the two, and the mediation effect of the duration of working outside the city remains robust under the conditions of changing the key independent variables and changing the mediation effect test method. (3) Blockchain technology can strengthen the positive relationship between education investment and left behind children's learning outcomes.

This paper is related to research on parallelization techniques for the simulation of electromagnetic transients (EMTs). It presents a new approach based on a parallel-in-time equation grouping and reordering (PEGR) technique whose original theoretical formulation is modified, extended and generalized from state-space to the modified-augmented-nodal analysis (MANA) formulation method. The highly efficient sparse linear solver KLU is incorporated in the approach for power system network matrix solution. The proposed approach is implemented with OpenMP Multithreading for CPU-based parallelization. Test results show that EMT simulations can be accelerated by exploiting the intrinsic independency of certain solution procedures using the PEGR technique.

Modern power electronic circuits contain numerous switches driven by high frequency controllers and can cause discontinuities in time-domain simulation methods. This paper presents numerical problems resulting from discontinuities when simulating power electronic circuits. Limitations in existing methods are analyzed. Three new methods are proposed to improve accuracy and computational performance.

With a high penetration of power electronic equipment, transient simulation for power electronic circuit has been a main challenge for performance improvement of the electromagnetic transient simulation tools. In this paper, two new solvers for the matrix exponential-based simulation method are proposed based on the dense output formula and Pade approximation of different orders. The proposed solvers are implemented with the optimal combination of numerical integration method and interpolation method. Both solvers are L-stable. One has 3rd-order accuracy which is more accurate than existing simulation tools in power electronic simulation. The other solver achieves 1st-order accuracy with a lower precision numerical integration method than the same-order algorithms and is appealing from computation speed perspective. Numerical studies including TCR circuit and two types of VSC-HVDC systems are conducted to demonstrate the effectiveness of the proposed solvers.

With the extensive application of power electronic equipment in power systems, electromagnetic transient (EMT) simulation involving power converters becomes more challenging. Due to its multithreads and high throughput architecture, the graphics processing unit (GPU) can be used to accelerate those EMT simulations. A GPU-based matrix exponential method and its memory management for power converter transient simulation are proposed in this paper. A parallel exponential integration algorithm is established from two aspects to fully utilize the GPU multithreads capability. The matrix exponentials which are recomputed with the on/off state changes of power electronic switches are cached in GPU memory. The simulation efficiency is improved by reusing the cached data and reducing heterogeneous data transmission between CPU and GPU. Several strategies are experimented to manage the cache memory considering the EMT simulation workflow. The proposed memory management expands the simulation capability by substantially reducing the memory requirement and maintains the speed advantage of the GPU-based simulator. The proposed method is tested on wind power plants of different scales with power electronic interfaced wind generators. Simulation results indicate that the proposed method and its memory management expand the simulation capability and achieve speedups.

This paper proposes an accurate dense output formula for exponential integrators. The computation of matrix exponential function is a vital step in implementing exponential integrators. By scrutinizing the computational process of matrix exponentials using the scaling and squaring method, valuable intermediate results in this process are identified and then used to establish a dense output formula. Efficient computation of dense outputs by the proposed formula enables time integration methods to set their simulation step sizes more flexibly. The efficacy of the proposed formula is verified through numerical examples from the power engineering field.

Facing the increasingly complex power system transient characteristics, the electromagnetic transient simulation tools are gaining popularity, thanks to their detailed modeling of power system equipment and high fidelity simulation results. Consequently, the Electro-Magnetic Transient Programs are increasingly used in simulation studies of higher dimensions and wider range of scales, which challenges the circuit-based algorithmic design of these programs. This paper proposes to use explicit integration formulas based on the matrix exponential function in the transient simulations of large-scale wind farms, which possess both high efficiency of explicit methods and numerical stability of implicit methods. A Krylov subspace-based order reduction technique embedded into the integration formulas was developed to specifically address the simulation needs of high dimensional EMT model of detailed wind farms. Numerical studies are conducted based on a realistic large-scale wind farm, where the proposed state space modeling framework is established, and the matrix exponential-based algorithm is implemented and compared against a set of classical stiff ODE solvers. Simulation tests with different fault types and fault locations are presented, showing a superior computation speed for studies with both equivalent and detailed wind farm modeling. On the other hand, numerical errors of the new algorithm are shown to be at least one order of magnitude smaller than other solvers in the range of typical step sizes, under the same simulation setting. These properties ensure an efficient, reliable and highly scalable simulation capability for the computation challenges in the studies of large-scale wind farms.

Magnesium and aluminum were bonded successfully by using Mg–Al eutectic alloy as the solder under different pressures at 450 °C in atmosphere. The microstructures of the Mg/Al joints were characterized by SEM, the composition analyzed by EDS, and their bond strengths measured by the bend test. The results show that the bond strength of these Mg/Al joints is improved with increasing of holding pressure, while the holding time has no much effect on it. To demonstrate the potential application of the Mg–Al eutectic alloy solder, magnesium plate was coated with aluminum foil by this process and its corrosion resistance was evaluated by electrochemical test. It shows that the corrosion resistance of the magnesium plate with aluminum coating was remarkably improved, which exhibits a similar corrosion behavior to that of aluminum.

Dianthus chinensis , Dianthus barbatus and Dianthus superbus are members of the Caryophyllaceae and are grown widely as ornamental plants. Information about relative genetic relationships can facilitate breeding programs. Here, we have compared two polymerase chain reaction (PCR)-based systems (sequence-related amplified polymorphisms (SRAPs) and inter-simple sequence repeats (ISSRs)) and morpological trait measurements for their relative effectiveness in estimating the genetic diversity found between 22 Chinese pink ( D. chinensis ) inbred-lines, one accession of D. barbatus and one accession of D. superbus . Interspecific differences were readily detected but the markers were less reliable in distinguishing the accessions according to their region of origin or in separating the wild species from the cultivars. Morphological traits were found to be the least effective genetic markers. The relative effectiveness of the three systems as markers for genetic diversity was concluded to be SRAP > ISSR > morphological traits, but the combined data from ISSR + SRAP analyses was superior to all three. The information generated by the SRAP marker system correlated more closely with morphological variability than did the ISSR marker system. The morphological markers of plant height/crown size ratio, lower leaf length, ovary shape index and calyx length showed strong correlations with the genetic diversity index (GD ij , PPB(II) and PSB) as generated by the percentage of polymorphic bands and percentage of special bands of the PCR-based markers.