Nonlinear Load Model Research Articles

Load balancing transmission technology of network communication based on phase spectrum compensation

In order to improve the load balance scheduling transmission ability of multi-frequency network communication in high-order nonlinear system, load balance design is needed. A load balance transmission method of multi-frequency network communication in high-order nonlinear system based on phase spectrum compensation is proposed. The time domain model of high-order nonlinear system multi-frequency network communication load is constructed by multi-frequency modulation phase spectrum compensation method. The feature detection of high-order nonlinear system multi-frequency network communication load is realized by high-order statistical feature connection identification and communication load balancing method. The autocorrelation constraint parameters of high-order nonlinear system multi-frequency network communication load are analyzed. The multi-dimensional array networking structure model of high-order nonlinear system multi-frequency network communication load is constructed by spatial spectral density analysis method. Combined with phase spectrum compensation and signal detection methods, the extracted high-order nonlinear system multi-frequency network communication load spectrum features are adaptively scheduled and filtered. In the wireless communication networking environment, load balance transmission of communication load in multi-frequency network of high-order nonlinear system is realized. The simulation results show that this method has better balance and lower error rate in multi-frequency network communication load balancing transmission, which improves the accuracy of multi-frequency network communication load balancing scheduling in high-order nonlinear systems.

Support Vector Machines Model of the Nonlinear Hydrodynamics of Fixed Cylinders

Abstract Data-driven modeling is considered as a prospective approach for many conventional physical problems including ocean applications. Among various machine learning techniques, support vector machine stands out as one of the most widely used algorithms to establish models connecting pertinent features to physical quantities of interest. This paper takes the experimental data for a fixed cylinder in shallow water as the baseline data set and explores the modeling of nonlinear wave loads by the support vector machine (SVM) regression method. Different feature and target selections are studied in this paper to establish the nonlinear mapping relations from ambient wave elevations and kinematics to nonlinear wave loads. The performance of the SVM regression model is discussed and compared with nonlinear potential flow theory focusing on the overall statistics (standard deviation and kurtosis), which is critical for fatigue and extreme statistics analysis.

Fatigue damage and residual life of secondary lining of high-speed railway tunnel under aerodynamic pressure wave

To investigate the fatigue behaviours of tunnel secondary lining under the aerodynamic effects produced by the running high-speed railway (HSR) trains, we proposed a dual fatigue damage accumulation model (DFDAM). In our model, a nonlinear variable load model was nested inside an equal-damage nonlinear model. The nonlinear variable load model was used to calculate the fatigue damage of a tunnel secondary lining after a single HSR train travelled through the tunnel, and the equal-damage nonlinear model was adopted to calculate the fatigue damage after multiple HSR trains travelled through the tunnel. Our proposed model was verified by comparison with laboratory fatigue testing results obtained by other researchers. The proposed model was also used to study the aerodynamic fatigue behaviours of a practical HSR tunnel project. The results show that the damage accumulation produced during the train running inside the tunnel is approximately the same as that of after an HSR train tail leaves the tunnel exit. Thus, after an HSR train leaves the tunnel exit, the influences of the aerodynamic pressure on the tunnel secondary lining cannot be ignored. The damage accumulation of a tunnel secondary lining associated with multiple HSR trains passing increases monotonically with the increase of the consumed life fraction. In contrast, the residual life of the fatigue damage decreases monotonically. This study can serve as a reference for studying the operational safety of HSR tunnels.

Nonlinear modelling of aerodynamic self-excited forces: An experimental study

The bridge aerodynamics research community is currently discussing several nonlinear wind load models for bridge decks, but no definite conclusion on which model is superior to the others is currently available. In this paper, we use experimental data for a double-deck section model tested in an advanced forced vibration rig to study the observed nonlinearities and to gain insight into what characteristics the nonlinear load model should be capable of modelling. Single harmonic horizontal, vertical and pitching motion; combined motion; and stochastic motion are considered. This approach allows the investigation of a more extensive range of nonlinear behaviours than regular wind tunnel testing. The typical nonlinear characteristics observed are mean drift, deviation from superposition and harmonic distortion. Further, we introduce a simple response-surface model for force prediction using polynomial combinations of the inputs and its derivatives. The model helps to gain further insight into the nonlinearity of the problem at hand and to select which refined modelling approach can be used in future work.

Effect of dynamic load models on WAC operation and demand-side control under real-time conditions

The vast majority of the proposed Wide Area Control (WAC) methodologies is tested and evaluated under the assumption that the system consists only of constant power loads. However, in practice power systems are dominated by non-linear loads, which can potentially affect the smooth operation of the wide area controller and deteriorate the system’s stability. This paper is firstly focused on examining the impact of various and commonly used non-linear load models (static and dynamic), such as the exponential, exponential dynamic, ZIP and ZIP-Induction Motor (ZIP-IM) load models on the WAC performance. Real-time simulations on the IEEE 39-bus dynamic test system indicate that the load recovery dynamics of the exponential dynamic load model have a severe impact on the WAC operation, leading the system to instability. Furthermore, it is illustrated that, loads with constant power/current/impedance characteristics have limited effect on the WAC damping capability, even with dynamics included. To address the impact of the exponential dynamic loads on the WAC performance, a novel wide area controller is proposed for coordinating simultaneously all the synchronous generators and controllable loads of the system. Finally, the effect of the size and flexibility of the controllable demand on the performance of the proposed scheme is also investigated, while the robustness of the proposed scheme is evaluated under measurement errors and erroneous generator parameters.

SIMULATION OF A STATIC SYNCHRONOUS COMPENSATOR FOR A POWER SUPPLY SYSTEM WITH A NON-LINEAR LOAD

The purpose of the work is developing a simulation model of factory’s the power system, with a nonlinear load model, which is a 12-pulses thyristor invertor and a model of a static synchronous compensator, which is multi-level voltage invertor, based on H-bridge invertor. Also defining preliminary parameters for the design of a static synchronous compensator in order to meet the requirements for power factors and limits of voltage harmonic and interharmonic distortion specified for the point of common connection to the mains supply. The analytical and numerical methods of mathematical programming and control of electromechanical systems were used. VisualStudio and PSIM software products for developing a control system for electromechanical systems and compiling a simulation model of an industrial power supply system were used. As a result of the research, a simulation model of the power supply system of an industrial enterprise, a model of a nonlinear load and a static synchronous compensator were developed. The rated power of the static synchronous compensator is determined to reduce the consumption of reactive power and the magnitude of the higher harmonics of the current, at the point of common connection, during operating a non-linear load.

Design of Efficient Power Filter with Reduced Distortion Using Control Algorithm

The electrical distribution system is facing undesirable power quality disturbances due to different types of linear/nonlinear loads on the supply system. The objective of the project is to reduce the distortion level in voltage or current input to the load and at the output of the filter. To design a simple but highly viable hybrid active power buffer that is capable of feeding less distorted voltage to the nonlinear load model. To present an optimal controlling of these buffers so as to minimize the voltage distortion by designing a different algorithm for the same. Comparing the THD levels of the output voltage waveform with the standard controlling method with the proposed control design to further enhance the proposed design such that it is practically feasible to be implemented in grid system having renewable energy resources. In this work, a power filter has been designed using different algorithms with an objective to reduce the Total Harmonic Distortion in the voltage output waveforms. The total harmonic distortion in the voltage output waveform being fed to the load using only the PQ_RLS algorithm is found to be 2.18 %. In the case of the output voltage from the power buffer using PQ_RLS algorithm, the THD level is 0.17 %. The distortion level in the output voltage waveforms in both the cases being fed to the load when compared, it is found that RLS algorithm in combination with PQ algorithm is more effective in reducing the distortion as compared to standard RLS method or PQ method.

ANFIS Supervised PID Controlled SAPF for Harmonic Current Compensation at Nonlinear Loads

ABSTRACT The smart devices comprise extensive embedding of small-size AC power-driven power electronics components. This improves the smart automation in the majority of applications in the industry and home system. But, the nonlinear characteristics of such component introduces several higher-order harmonics and generates possible deviation in performance measures. The long-term persistence of harmonic distortions in the current distribution may result in system failure and depreciation in system efficiency. This paper presents a soft computing technique for reactive power compensation of harmonic current using adaptive neural fuzzy interface system (ANFIS). The smart ANFIS supervises the PID controller for adequate gate signaling to shunt active power filter (SAPF) by hysteresis current control. The neural network is trained by adaptive data set of error and deviation in error with respect to hysteresis current control. The nonlinear load model is subjected to transformer-less SAPF to avoid the presence of insertion losses and improves the system compatibility. The proposed system reduces the harmonic distortion from 92.23 to 0.49% in the nonlinear power converter model with improved 0.99 power factor. Additionally, the proposed system is absolutely feasible and novel for real-time application in smart devices with adequate transient and regression response. The proposed system is realized for individual effects of PID, ANN and ANFIS to justify the candidature of the soft computing technique in real-time applications as per IEEE 519 standard.

Network-based analysis of long-term voltage stability considering loads with recovery dynamics

This study investigates the influence of network structures on long-term voltage stability of power systems considering loads with recovery dynamics. A power system model with load dynamics is established in terms of a network graph and the aggregate nonlinear recovery load model. Stability conditions are proposed for static and small-disturbance voltage stability of power systems, which reveal the interactions between network graph, load demand and load characteristics and sheds new light on the static and small-disturbance voltage stability mechanisms. The impact of the penetration of renewable energy sources is discussed as one illustration. The Monte Carlo method is used for case studies of several widely established IEEE power network test cases. Small-world, scale-free and random networks are considered for the generation of a broad range of network topologies. The simulation results are consistent with the stability conditions. The study in this paper may provide guidance in network planning and operation of power systems.

Optimal conductor selection and capacitor placement in radial distribution system using nonlinear AC load flow equations and dynamic load model

Optimal conductor selection and capacitor placement in radial distribution system using nonlinear AC load flow equations and dynamic load model

Small-Disturbance Voltage Stability of Power Systems: Dependence on Network Structure

This paper investigates the impact of network structures on small-disturbance voltage stability of power systems in the long-term. A differential-algebraic model is established in terms of network topology characteristics and the aggregate nonlinear recovery load model. We define the weighted load connectivity (WLC) as an index to indicate the stability of network structures. Then robust stability assessment is used to eliminate the impact of uncertain recovery time of loads. The Monte Carlo method is used to study the relationship between WLC and small-disturbance voltage stability (SDVS) for a broad range of network topologies and parameters. We discover from the simulation results that the network with a larger value of WLC has a stronger ability to maintain SDVS. To further study the impact of renewable energy sources (RESs), we improve the system model by including an inverter-based distributed generator in parallel with each aggregated nonlinear dynamic load. The simulation results of the Hong Kong power grid show that the WLC can still indicate the stability of network structures effectively, and the systems with more stable network structures are less impacted by the penetration of RESs. The proposed WLC appears useful in providing guidance for power network planning and operation.

Divisible Nonlinear Load Distribution on Complete b-Ary Trees

This paper investigates the problem of a divisible nonlinear load distribution on homogeneous complete b -ary tree networks. Classic models of nonlinear computational loads omit several steps in processing the load and yield only an approximate distribution for fractional loads. This paper considers a new model of nonlinear computational loads that includes all load processing steps and yields a practical solution to distribute fractional loads. Two algorithms to distribute a divisible nonlinear load on homogeneous complete b -ary tree networks are proposed. Closed-form expressions for the parallel processing time and speed-up for complete b -ary trees are also derived. This paper demonstrates that the asymptotic speed-up of the proposed algorithms is the number of processors in a multicomputer system. The proposed algorithms improved the classic algorithm in terms of speed-up.

Development of an acute, short-term exposure model for phosgene

Phosgene is classified as a chemical warfare agent, yet data on its short-duration high concentration toxicity in a nose-only exposure rat model is sparse and inconsistent. Hence, an exposure system for short-term/high concentration exposure was developed and characterized. Herein, we report the median lethal concentration (LC50) for a 10-min nasal exposure of phosgene in a 24-h rat survival model. Male Wistar rats (Envigo) weighing 180–210 g on the day of exposure, were exposed to phosgene gas via nose-only inhalation using a system specifically designed to allow the simultaneous exposure and quantification of phosgene. After 24 h, the surviving rats were euthanized, the lung/body mass ratio determined, and lung tissues analyzed for histopathology. Increased terminal airway edema in the lungs located primarily at the alveoli (resulting in an increased lung/body mass ratio) coincided with the observed mortality. An LC50 value of 129.2 mg/m3 for a 10-min exposure was determined. Furthermore, in agreement with other highly toxic compounds, this study reveals a LC50 concentration value supportive of a nonlinear toxic load model, where the toxic load exponent is >1 (ne = 1.17). Thus, in line with other chemical warfare agents, phosgene toxicity is predicted to be more severe with short-duration, high-concentration exposures than long-duration, low-concentration exposures. This model is anticipated to be refined and developed to screen novel therapeutics against relevant short-term high concentration phosgene exposures expected from a terrorist attack, battlefield deployment, or industrial accident.

Effects of femoral head diameter on the predicted acetabular cup wear volume of CP-Ti and UHMWPE hip implants

Numerical investigation is a method capable to study the expensive and long-time duration wear problems in biotribology. The technique has been used to predict the wear of hip implants specially those made from metal on polymer biomaterials. This research studied the effect of commercially pure titanium (CP-Ti) femoral head diameter on the wear volume of ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Diameter variations are 22 mm, 28 mm and 32 mm. Hip implant models were created and the numerical approximations conducted with the finite element method. Wear calculations used a nonlinear load and contact area mathematical model. A Python script was developed to proceed the calculations. Accurate wear predictions can be obtained with the use of fine elements those maximum contact loads are closer to the physiological load. Verification with experimental data on the 32 mm femoral head model shows a good agreement with error rates below 1%.

Buckling analysis of FGM plates under uniform, linear and non-linear in-plane loading

The paper investigates the buckling responses of functionally graded material (FGM) plate subjected to uniform, linear, and non-linear in-plane loads. New nonlinear in-plane load models are proposed based on trigonometric and exponential function. Non-dimensional critical buckling loads are evaluated using non-polynomial based higher order shear deformation theory. Navier’s method, which assures minimum numerical error, is employed to get an accurate explicit solution. The equilibrium conditions are determined utilizing the principle of virtual displacements and material property are graded in the thickness direction using simple Voigt model or exponential law. The present formulation is accurate and efficient in analyzing the behavior of thin, thick and moderately thick FGM plate for buckling analysis. It is found that with the help of displacement-buckling load curve, critical buckling load can be derived and maximum displacement due to the instability of inplane load can be obtained. Also, the randomness in the values of transverse displacement due to inplane load increases as the extent of uniformity of the load on the plate is disturbed. Furthermore, the parametric varying studies are performed to analyse the effect of span-to-thickness ratio, volume fraction exponent, aspect ratio, the shape parameter for non-uniform inplane load, and non-dimensional load parameter on the non-dimensional deflections, stresses, and critical buckling load for FGM plates.

Comparative analysis for optimum position of A PWM based UPFC and ASVC applied to multi-machine systems with non-linear load model

Comparative analysis for optimum position of A PWM based UPFC and ASVC applied to multi-machine systems with non-linear load model

Offshore Wind Turbine Nonlinear Wave Loads and Their Statistics

The development of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines is presented. Explicit expressions are derived for the time-domain nonlinear exciting forces in a sea state with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory (FIT). The method is validated against experimental measurements with good agreement. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed. The identification of the inertia and drag coefficients of a generalized nonlinear wave load model trained against experiments using support vector machine learning algorithms is discussed.

Volterra Kernels Assessment via Time-Delay Neural Networks for Nonlinear Unsteady Aerodynamic Loading Identification

Reduced-order modeling using the Volterra series approach has been successfully applied in the past decades to weakly nonlinear aerodynamic and aeroelastic systems. However, aspects regarding the identification of the kernels associated with the convolution integrals of Volterra series can profoundly affect the quality of the resulting reduced-order model (ROM). An alternative method for their identification based on artificial neural networks is evaluated in this work. This relation between the Volterra kernels and the internal parameters of a time-delay neural network is explored for the application in the reduced-order modeling of nonlinear unsteady aerodynamic loads. An impulse-type Volterra-based ROM is also under consideration for comparison. All aerodynamic data used for the construction of the ROMs are obtained from computational fluid dynamics (CFD) simulations of the NACA 0012 airfoil using the Euler equations. Prescribed inputs in pitch and in plunge degrees of freedom at different freestream Mach numbers are used to evaluate the range of applicability of the obtained models. For weakly nonlinear test cases, the modeling performance of the neural network Volterra ROM was comparable to the impulse-type ROM. Additional accuracy and adequate modeling of stronger nonlinearities, however, could only be attained with the inclusion of the neural network kernels of higher order in the Volterra ROM. A generic expression is derived for the kernel function of th-order from the internal parameters of a time-delay neural network.

Divisible Nonlinear Load Distribution on Heterogeneous Single-Level Trees

This work studies the divisible nonlinear load distribution problem on heterogeneous single-level tree networks with a collective communication model. The goal is to find a feasible distribution that minimizes the parallel processing time. The classical model of nonlinear computational loads omits many processing steps, and yields only an approximate solution to distribute fractional loads. This work considers a new model of nonlinear computational loads that includes all of processing steps of the load. This model can simplify recursive equation for the size of fractional loads and yield a practical solution to distribute fractional loads. This work proposes two new methods which incorporates a new nonlinear computational model to distribute a divisible nonlinear load on heterogeneous single-level tree networks. Closed-form expressions for the parallel processing time and speed-up for single-level tree networks are derived. This work demonstrates that the asymptotic speed-up of the proposed algorithm is $m+1$ where $m$ is the number of child processors in a single-level tree network. We show that our algorithm improved the previous method in terms of speed-up.

Energy Loss Allocation in Smart Distribution Systems with Electric Vehicle Integration

This paper presents a three-phase loss allocation procedure for distribution networks. The key contribution of the paper is the computation of specific marginal loss coefficients (MLCs) per bus and per phase expressly considering non-linear load models for Electric Vehicles (EV). The method was applied in a unbalanced 12.47 kV feeder with 12,780 households and 1000 EVs under peak and off-peak load conditions. Results obtained were also compared with the traditional roll-in embedded allocation procedure (pro rata) using non-linear and standard constant power models. Results show the influence of the non-linear load model in the energy losses allocated. This result highlights the importance of considering an appropriate EV load model to appraise the overall losses encouraging the use and further development of the methodology