Electric Power System Applications Research Articles

Monotone Splitting Sequential Quadratic Optimization Algorithm with Applications in Electric Power Systems

In this paper, we propose a new sequential quadratic optimization algorithm for solving two-block nonconvex optimization with linear equality and generalized box constraints. First, the idea of the splitting algorithm is embedded in the method for solving the quadratic optimization approximation subproblem of the discussed problem, and then, the subproblem is decomposed into two independent low-dimension quadratic optimization subproblems to generate a search direction for the primal variable. Second, a deflection of the steepest descent direction of the augmented Lagrangian function with respect to the dual variable is considered as the search direction of the dual variable. Third, using the augmented Lagrangian function as the merit function, a new primal–dual iterative point is generated by Armijo line search. Under mild conditions, the global convergence of the proposed algorithm is proved. Finally, the proposed algorithm is applied to solve a series of mid-to-large-scale economic dispatch problems for power systems. Comparing the numerical results demonstrates that the proposed algorithm possesses superior numerical effects and good robustness.

Evaluating a dendritic neuron model for wind speed forecasting

Because of the intrinsic complexity and chaotic nature of wind speed time series, an appropriate model for accurately forecasting the moving tendency is required. In this paper, we propose an evolutionary dendritic neuron model (EDNM) to carry out wind speed forecasting. The model is trained via adaptive differential evolution with the linear population size reduction (L-SHADE) algorithm. Specifically, a mutual-information-based approach and the false nearest neighbours method are used to calculate the time delay and embedding dimensions, respectively. Then, the phase space of the wind speed time series is reconstructed based on the time delay and embedding dimensions, and the characteristics are analysed. The maximum Lyapunov exponent is applied to confirm the chaotic properties of the wind speed time series. Finally, EDNM trained by L-SHADE is used to predict the wind speed for Sotavento, which is located near Galicia, Spain. This study is the first, to the best of our knowledge, to use a dendritic neuron model to implement such real-world prediction. Extensive experimental results show that the proposed EDNM can perform better than other state-of-the-art models in terms of different assessment criteria. Therefore, the proposed method has high potential for practical applications in electric power systems.

Interface-Strengthened Polymer Nanocomposites with Reduced Dielectric Relaxation Exhibit High Energy Density at Elevated Temperatures Utilizing a Facile Dual Crosslinked Network.

High-temperature ceramic/polymer nanocomposites with large energy density as the reinforcement exhibit great potential for energy storage applications in modern electronic and electrical power systems. Yet, a general drawback is that the increased dielectric constant is usually achieved at the cost of decreased breakdown strength, thus leading to moderate improvement of energy density and even displaying a marked deterioration under high temperatures and high electric fields. Herein, a new strategy is reported to simultaneously improve breakdown strength and discharged energy density by a step-by-step, controllable dual crosslinking process, which constructs a strengthened interface as well as reduces molecular chains relaxation under elevated temperatures. Great breakdown strength and discharged energy density is achieved in the dual crosslinked network BT-BCB@DPAES nanocomposites at elevated temperatures when compared to noninterfacial-strengthened, BT/DPAES composites, i.e., an enhanced breakdown strength and a discharged energy density of 442 MV m-1 and 3.1 J cm-3 , increasing by 66% and 162%, and a stable cyclic performance over 10 000 cycles is demonstrated at 150 °C. Moreover, the enhancement through the synergy of two crosslinked networks is rationalized via a comprehensive phase-field model for the composites. This work offers a strategy to enhance the electric storage performances of composites at high temperatures.

Conjoint Knowledge Discovery Utilizing Data and Content with Applications in Business, Bio-medicine, Transport Logistics and Electrical Power Systems

Conjoint Knowledge Discovery Utilizing Data and Content with Applications in Business, Bio-medicine, Transport Logistics and Electrical Power Systems

Significantly enhanced permittivity and energy density in dielectric composites with aligned BaTiO3lamellar structures

A significant improvement of permittivity and energy density will enable the miniaturization of dielectric capacitors and promote integration for applications in electrical power and defense systems.

Asymmetric alicyclic amine-polyether amine molecular chain structure for improved energy storage density of high-temperature crosslinked polymer capacitor

Crosslinked structure is proved to be efficient to improve breakdown strength (EB), thermal stability and charge-discharge efficiency (η) of polymer film capacitors, which is of great interest for their application in electric power systems and electrical automobile industry. However, highly crosslinked molecular networks usually lead to weak polarization ability of polymer, which greatly restrict their energy storage density (Ud). To improve polymers’ high-field polarization ability while guaranteeing their EB and thermal stability, we propose the asymmetric molecular chain structure in crosslinked network of epoxy resin by attaching ring-like alicyclic amine (ACA) and linear polyether amine (PEA) on phenol via Mannich reaction. The film exhibits high Ud up to 9.12 Jcm−3 at 550 MVm−1 and ambient temperature with 90% efficiency, which is a record high value for Ud among single-layer polymer under the same condition. At 200 MVm−1 and 120 °C, a future operating condition towards electric-vehicle applications, prepared film still exhibits Ud of 1 Jcm−3 with 90% efficiency, which is twice of the state-of-the-art BOPP. The results prove that the asymmetric ACA-PEA structure can greatly improve Ud of crosslinked polymer film while maintaining superior energy storage efficiency at high temperature. This work paves a new way for the material design of high-performance polymer film capacitor.

Echo state network based ensemble approach for wind power forecasting

Accurate and reliable wind power forecasting is of great significance for the economic and safe operation of electric power and energy systems. However, due to the negative factors such as inaccurate numerical weather prediction and frequent ramping events, previous wind power prediction methods are difficult to meet actual needs for practical applications. To this end, this paper originally proposes a new wind power prediction method with high accuracy based on echo state network. This method is a hybrid of wavelet transform, echo state network and ensemble technique. Wavelet transform is used to decompose raw wind power time series data into different frequencies with better outliers and behaviors. Then, we adopt the echo state network to automatically learn the nonlinear mapping relationship between input and output in each frequency. Later, ensemble technique is applied to deal with the model misspecification and data noise problems, which are common in wind power prediction, thereby reducing the uncertainty of wind power forecasting and improving prediction accuracy. Finally, we use wind power data from real wind farms in Belgium and China to verify the feasibility and effectiveness of the proposed method. The simulation results show that the proposed method is superior to other benchmark algorithms in prediction accuracy, which indicates that the method has high potentials for practical application in real electric power and energy systems.

Dipole-relaxation dynamics in a modified polythiourea with high dielectric constant for energy storage applications

Enhancing dipole polarization has been demonstrated as an effective approach to increase the dielectric constant of polymer dielectrics and thus to improve their discharged energy density for energy storage applications in electrical power and electronic systems. However, further optimization to get a higher dielectric constant and lower polarization loss hinges upon a more insightful understanding of the dynamics of dipole relaxation. Here, we demonstrate an approach, based on the Dissado-Hill dielectric response model, to probe the dynamics of dipole polarization in an all organic polythiourea (PDTC-HK511) composed of p-phenylene diisothiocyanate (PDTC) as rigid segments and Jeffamine® HK511 as flexible segments. Our results reveal that PDTC-HK511 possesses strong subglass transition β and γ relaxation processes in conjunction with the quasi-DC diffusion process at relatively high temperature and a low frequency range. The γ relaxation enhances the dielectric constant by 20%–25% but causes no apparent loss at the operating temperature and frequency conditions due to the high flexibility and short relaxation time of the dipole orientation. In comparison to β relaxation, the weak interactions and much shorter relaxation time of dipoles in γ relaxation evidenced the large flexibility of dipole movement. This work provides deeper insight into the dipole movement and aids future rational designs of polymers for dielectric energy storage.

Power system education and research applications using free and open-source, graphical and multiplatform PSP-UFU software

This article presents a new free and open-source computer platform that is capable of performing power flow simulations, balanced and unbalanced short-circuits, besides transitory and dynamic stability studies with user-defined controls. The software, called Power Systems Platform from the Federal University of Uberlândia (PSP-UFU), has as its goal to aid in the areas of research and education. Through an interface aligned with the CAD tool, the construction of any electric network and control system is permitted by the directing of visual elements. Standard software architecture was used in the development of the platform, as well as standardisation and documentation, which are necessary practices for an understanding into the source code and software development by third parties. The software possesses an excellent computational performance and a friendly and intuitive interface, which all go on to make it ideal for educational applications in electric power systems.

Performance Analysis of Z-Source Fed Cascaded Multilevel Inverter

Three phase multilevel inverters are frequently utilized in moderate and high power industries by minimizing the electromagnetic interference (EMI), enhancing the voltage profile and improving the power capacity. Although various converter topologies are developed for multilevel inverters (MLIs), Z-source MLIs are widely used for higher voltage applications. Z-source MLIs diminishes the total harmonic distortion (THD), and it has good stability and efficacy for various electrical power system applications. This paper aims to develop a three phase Z-source seven-level cascaded H-bridge (CHB) inverter with multicarrier PWM control techniques. The Z-source CHB inverter with multicarrier PWM control is modeled and its performance investigation with shoot through and non-shoot through modes is carried out in MATLAB/Simulink software platform.

Synergy of micro-/mesoscopic interfaces in multilayered polymer nanocomposites induces ultrahigh energy density for capacitive energy storage

High-energy-density dielectric materials are highly desirable for the miniaturization and integration of modern electronics and power modules for applications in electrical power, communication, medical and defense systems. However, the conventional polymer nanocomposites with nanofillers randomly dispersed exhibit a limited energy storage performance (e.g. discharged energy density <15 J/cm3 and efficiency <70%). Here, we demonstrate the multilayer structure as an effective route to polymer nanocomposites that concurrently have ultrahigh discharge energy density and high efficiency. Compared to the random-dispersed nanocomposites, the rationally designed multilayered polymer nanocomposites are capable of integrating the suppressed effects of dielectric/electrode and dielectric/dielectric interfaces on charge injection and migration to remarkably enhance the breakdown strength and are expected to deliver an unprecedentedly high energy density of ∼35.4 J/cm3 (an enhancement of ∼1100% over the bench-mark biaxially-oriented polypropylene). This work provides insight into the design and fabrication of polymer nanocomposite with high energy density and discharge efficiency for capacitive energy storage applications.

Behavior and functional modeling methods of doubly salient electromagnetic generators for aircraft electrical power system applications

The Doubly Salient Electromagnetic Generator (DSEG) is a promising candidate in aircraft generator application due to the simplicity, robustness and reliability. However, the field windings and the armature windings are strongly coupled, which makes the inductance characteristics non-linear and too complex to model. The complex model with low precision also leads to difficulties in modeling and analysis of the entire aircraft Electrical Power System (EPS). A behavior level modeling method based on modified inductance Support Vector Machine (SVM) is proposed. The Finite Element Analysis (FEA) inductance data are modified based on the experiment results to improve the precision. A functional level modeling method based on input–output characteristics SVM is also proposed. The two modeling methods are applied to a 9 kW DSEG prototype. The steady state and transient process precision of the proposed methods are proved by comparing with the experiment results. Meanwhile, the modeling time consumption, the application time consumption and the calculation resource demand are compared. The DSEG behavior and functional modeling methods provide precious results with high efficiency, which accelerates theoretical analysis and expands the application foreground of the DSEG in the aircraft EPS.

Excellent energy storage performance and thermal property of polymer-based composite induced by multifunctional one-dimensional nanofibers oriented in-plane direction

As advanced dielectric materials for the applications in electronics and electrical power systems with the ever-increasing requirements, the polymer-based dielectric nano-composites are brilliantly emerging. However, there are long standing challenges of the unsatisfactory electric breakdown strength and the heat accumulation induced by dielectric loss of composite. In this study, we propose an artificial nano-composite with excellent comprehensive performance by controlling the orientation of one-dimensional (1D) 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZCT NFs) and adjusting the interaction between BZCT NFs and poly(vinylidene fluoride) (PVDF) matrix via SiO2 buffer layer. Remarkably, PVDF nano-composite with only 3 vol% aligned BZCT NFs coated by SiO2 (BZCT@SiO2 NFs, 3 vol% Aligned BZCT@SiO2-PVDF) possesses an impressive energy storage performance, including the superior Weibull characteristic breakdown strength (Eb) of ~576 kV/mm and the ultrahigh discharged energy density (Ue) of ~18.9 J/cm3. Meanwhile, the temperature distribution in this typical composite is more homogeneous according to the test and simulation results. This demonstrated work not only opens a new door to preparing an excellent performance of polymer-based dielectric nano-composites, but also points out a route to the industrialization of energy storage dielectrics.

La/Mn Codoped AgNbO3 Lead-Free Antiferroelectric Ceramics with Large Energy Density and Power Density

Dielectric materials with high energy density have attracted much attention due to their potential applications in modern electronics and electrical power systems. In this work, a large energy stor...

Enhancing conjugation degree and interfacial interactions to enhance dielectric properties of noncovalent functionalized graphene/poly (vinylidene fluoride) composites

Introducing conductive nanofillers into a dielectric polymer is the most common way to tailor percolative composites with high dielectric constant. However, it usually contributes to large increase of dielectric loss, thereby restricting the improvement of practical energy storage capability. In this study, by regulating the conjugation degree of graphene derivatives and their interfacial interactions with polymer matrix, high dielectric constants were achieved for graphene/polymer composites and the loss was suppressed at a relatively low level. Electrochemical exfoliated graphene with high conjugation degree modified with a carboxyl-riched perylene derivative via π-π stacking interaction was used as a conductive nanofiller. Due to the high conjugation degree of graphene and carboxyl groups-induced high interfacial interactions with PVDF matrix, a high dielectric constant (ε = 480) was obtained at a low filler content of 0.74 vol% and the dielectric loss was suppressed as low as 0.27. The enhanced dielectric properties could be reasonably explained by a proposed model. This research provides a new and promising route for researchers to construct graphene/polymer composites with good dielectric properties for applications in modern electronics and electric power systems.

Analytical modeling of parabolic linear collectors for solar power plant

An analytical model for the parabolic trough collector (PTC) having its absorber tubes fitted with serrated twisted tape inserts using therminol VP-1 as working fluid for high temperature applications in solar thermal electric power system was developed taking radiative terms into account. The model takes radiative terms into account, for the development of the mathematical expressions for collector efficiency factor, collector heat removal factor, outlet fluid temperature and thermal efficiency. A computer program in C++ language, based on mathematical models was developed, to estimate the temperature rise of fluid for evaluation of the performance of PTC under specified conditions. For numerical simulations, three different twist ratios, x = 1,2.5,4 and mass flow rates ranging from 0.06 kg/s to 0.16 kg/s (3000 ≤ Re ≤ 9000) and dimensionless insolation, Ψ(t) = 0.2 to 1.0 are used. This study demonstrates that twisted tape insert shows great promise for enhancing the performance of the PTC. The maximum value of outlet fluid temperature, useful heat gain and thermal efficiency are 452.52 K, 17711 W and 79.22 %, respectively for x = 1, Ψ(t) = 1.0 and mass flow rate of 0.16 kg/s.

Feasibility study of a simulation software tool development for dynamic modelling and transient control of adiabatic compressed air energy storage with its electrical power system applications

The field of large-scale electrical energy storage is growing rapidly in both academia and industry, which has driven a fast increase in the research and development on adiabatic compressed air energy storage. The significant challenge of adiabatic compressed air energy storage with its thermal energy storage is in the complexity of the system dynamic characteristics arising from the multi-physical (pneumatic, thermal, mechanical and electrical) processes. This has led to a strong demand for simulation software tools specifically for dynamic modelling and transient control of relevant multi-scale components, subsystems and whole systems with different configurations. The paper presents a feasibility study of a simulation tool development implemented by the University of Warwick Engineering team to achieve this purpose. The developed tool includes a range of validated simulation models from the fields of pneumatics, thermodynamics, heat transfer, electrical machines and power grids. The structure of the developed tool is introduced and a component library is built up on the Matlab/Simulink platform. The mathematical descriptions of key components are presented, which precedes a presentation of four case studies of different applications. The case studies demonstrate that the simulation software tool can be used for dynamic modelling of multi-scale adiabatic compressed air energy storage components and systems, real performance analysis, dynamic control strategy implementation and feasibility studies of applications of adiabatic compressed air energy storage integrated with power grids. The paper concludes that the continued development and use of such a tool is both feasible and valuable.

Dielectric and energy harvesting properties of FeTiNbO6/PVDF composites with reinforced sandwich structure

Flexible dielectrics have been the major enabler for a number of applications in advanced electronic and electrical power systems. As an important flexible dielectric material, polymer composites are promising in raising the poor dielectric properties of neat polymer of current use. In this study, a class of topological‐structure modulated multilayer composites comprising a percolation layer (FeTiNbO6[FTN]/polyvinylidenefluoride [PVDF]) intercalated between two insulating layers (PVDF or BaTiO3[BT]/PVDF) are assembled into sandwich structures by a facile hot‐pressing method. For the prepared sandwich structure, FTN/PVDF film acts as a semiconductive layer to raise dielectric permittivity, while two insulating layers at top and bottom of composite are used to suppress conductivity and dielectric loss. Resulted from the unique performances of the FTN/PVDF film and strong interfacial polarization, the sandwich composite possesses improved dielectric and insulation properties. Moreover, compared with FTN/PVDF, the BT20‐FTN40‐BT20 has lower dielectric loss and higher insulation properties, and after poling at 20 kV/mm for 6 h, it exhibits excellent vibration energy harvesting properties in cantilever mode. Thus, a piezoelectric energy harvester constructed from this sandwich composite can be used for self‐driving wireless sensors. POLYM. COMPOS., 40:E570–E578, 2019. © 2018 Society of Plastics Engineers

Simulating command injection attacks on IEC 60870-5-104 protocol in SCADA system

IEC 60870-5-104 is an international standard used for tele-control in electrical engineering and power system applications. It is one of the major principal protocols in SCADA system. Major industrial control vendors use this protocol for monitoring and managing power utility devices. One of the most common attacks which has a catastrophic impact on industrial control systems is the control command injection attack. It happens when an attacker injects false control commands into a control system. This paper presents the IEC 60870-5-104 vulnera-bilities from the perspective of command and information data injection. From the SCADA testbed that we setup, we showed that a success-ful control command injection attack can be implemented by exploiting the vulnerabilities identified earlier.

Dielectric Loss Suppression of Silver/Poly(vinylidene fluoride) Composite Films with Polydopamine

ABSTRACTThe preparation and dielectric properties of silver-polydopamine/poly(vinylidene fluoride) (Ag-PDOP/PVDF) composite films with suppressed dielectric loss are reported. The dielectric loss tangents of the composite films were found to be rather low similar to that of pure PVDF over the frequency range 100 Hz to 30 kHz, almost regardless of the Ag content, and even lower than that of pristine PVDF in the relatively high frequency region. The nanoscale structure comprised of Ag nanoparticles (Ag NPs), isolated by the PDOP coating and the PVDF matrix, hindered the formation of percolative networks, resulting in the decreased conduction loss in the composite films, even at a high filler loading. The strong interfacial interaction between the Ag@PDOP particles and the PVDF matrix also contributed to the restrained interfacial loss. Consequently, these composite films had higher permittivity and smaller dielectric loss than the PVDF matrix at relatively high frequencies, and would thus be attractive for physically small capacitor applications in electronics and electric power systems.