Generalized Load Model Research Articles

Generalized load modeling approach considering multiple distributed generation integration

To solve the problem of node characteristic uncertainty caused by the connection of multiple distributed generations to the original load node, a new method for modeling the steady-state characteristics of generalized load nodes based on scene clustering was proposed. Scenario clustering takes into account three factors: wind farm output fluctuation, photovoltaic output fluctuation, and demand-side power load fluctuation, and extracts typical scenarios of generalized load data. According to the uncertainty change of node characteristics in different scenarios, the clustering data is segmented and refined, and its probability distribution is counted. Clustering information, probability information, and maximum value are used as three types of features of generalized load and are custom encoded as 12-dimensional feature vectors as neural network inputs. To improve the identification performance of generalized load features, the back propagation (BP) dichotomy neural network is used to build a unified model of node features. The simulation results show that the proposed method can not only model accurately but also introduce probability information through statistical data samples, which can provide an auxiliary reference for the prediction and regulation of generalized loads.

A Generalized Load Model Considering the Fault Ride-Through Capability of Distributed PV Generation System

Considering the voltage stability problem brought by large-scale distributed PV access to the distribution network, this paper proposes a generalized load model that considers the fault ride-through capability of distributed PV. Firstly, the detailed model of the distribution network is established, and the detailed model is calibrated based on the measured data, the simulation errors are below 1%. And then establish a generalized load model considering distributed PV high and low voltage traversal ability. The sensitivity analysis results are used to rank the parameters to be identified, and the parameters with higher sensitivity are identified. The parameters are obtained from the detailed model and measured data, and four sets of parameters are identified and simulated under different PV penetration rates and fault conditions. The calculated fitting errors are less than 1%. The results show that the generalized load gray box model of the distribution network with distributed PV high and low voltage ride-through capability can reflect the dynamic characteristics of the distribution network well.

Research on the Influence of Traction Load on Transient Stability of Power Grid Based on Parameter Identification

The traction load of electrified railways is a special user of the power system, which will have a significant impact on and pose a challenge to the power system after grid connection. Considering the impact and fluctuation of traction load connected to the power grid, this paper proposed a method to study the influence of traction load on the transient stability of the power grid based on parameter identification. Firstly, according to the operation characteristics of traction load, a comprehensive traction load model based on the measurement-based method of induction motor parallel power function model is selected, and the objective function of parameter identification is determined. Then, the specific steps of using the improved gray wolf optimizer (IGWO) algorithm to achieve the parameter identification of the traction comprehensive load model are introduced, including chaotic map, nonlinear convergence factor, and individual position update. Next, with the IEEE39 bus system as the network background, the load parameters identified by the measured data of a line of the Beijing–Shanghai high-speed railway are imported into the Power System Analysis Software Package (PSASP) 7.0 for transient simulation to analyze the impact of traction load on the transient stability of the power grid. Finally, three typical load models are compared with the traction load model to draw relevant conclusions, and it is verified that the traction load characteristics are different from the general load model, which provides reference for the connection of electrified railway traction load to the power grid and the economic and technical construction of the power system.

A multi-model architecture based on deep learning for aircraft load prediction

Monitoring aircraft structural health with changing loads is critical in aviation and aerospace engineering. However, the load equation needs to be calibrated by ground testing which is costly, and inefficient. Here, we report a general deep learning-based aircraft load model for strain prediction and load model calibration through a two-phase process. First, we identified the causality between key flight parameters and strains. The prediction equation was then integrated into the monitoring process to build a more general load model for load coefficients calibration. This model achieves a 97.16% prediction accuracy and 99.49% goodness-of-fit for a prototype system with 2 million collected flight recording data. This model reduces the effort of ground tests and provides more accurate load prediction with adapted aircraft parameters.

A composite load model aggregation method and its equivalent error analysis

Although load modeling techniques have been widely applied in practical power system studies, the equivalence of aggregate load models needs to be further illustrated since equivalent load models are commonly adopted to describe the overall characteristics of distributed multi-level power loads in practical scenarios. Driven by two basic aggregation steps, a general composite load model aggregation method is proposed for the first time with load network topology well considered. On this basis, detailed equivalent error analysis of load model aggregation is conducted in order to explain the possible error factors and their influence mechanisms on the equivalent accuracy. Case study results for the modified IEEE 39-bus system have validated the overall feasibility of the proposed model aggregation method and the influence of each error factor under different scenarios. Finally, practical effectiveness of the derived aggregate model is further proved with field measurements in a real-world load system. In this way, the equivalence of adopting aggregate load models can be clearly demonstrated, thus providing necessary foundation for the practical applications of composite load modeling.

Analytic solution to swing equations in power grids with ZIP load models.

This research pioneers a novel approach to obtain a closed-form analytic solution to the nonlinear second order differential swing equation that models power system dynamics. The distinctive element of this study is the integration of a generalized load model known as a ZIP load model (constant impedance Z, constant current I, and constant power P loads). Building on previous work where an analytic solution for the swing equation was derived in a linear system with limited load types, this study introduces two fundamental novelties: 1) the innovative examination and modeling of the ZIP load model, successfully integrating constant current loads to augment constant impedance and constant power loads; 2) the unique derivation of voltage variables in relation to rotor angles employing the holomorphic embedding (HE) method and the Padé approximation. These innovations are incorporated into the swing equations to achieve an unprecedented analytical solution, thereby enhancing system dynamics. Simulations on a model system were performed to evaluate transient stability. The ZIP load model is ingeniously utilized to generate a linear model. A comparison of the developed load model and analytical solution with those obtained through time-domain simulation demonstrated the remarkable precision and efficacy of the proposed model across a range of IEEE model systems. The study addresses the key challenges in power system dynamics, namely the diverse load characteristics and the time-consuming nature of time-domain simulation. Breaking new ground, this research proposes an analytical solution to the swing equation using a comprehensive ZIP model, without resorting to unphysical assumptions. The close-form solution not only assures computational efficiency but also preserves accuracy. This solution effectively estimates system dynamics following a disturbance, representing a significant advancement in the field.

General Cutting Load Model for Workload Simulation in Spindle Reliability Test

As the key functional component of the machine tool, the reliability test of the spindle is necessary to verify the reliability of the machine tool. In the reliability test, the cutting load model is the guideline of workload simulation and is the prerequisite to ensure the accuracy and effectiveness of the long-term experiment. However, the existing load models usually aim at the specific cutting force at the tool-tip, thereby ignoring the versatility, maneuverability, and accuracy of the load model when applied in the spindle reliability test. In this study, a general cutting load model for the machine tool spindle is established in a form of radial-axial-torque decomposition, and the radial force is simplified as non-rotating status for the maneuverability of conducting a load simulation. The difference between rotating and non-rotating radial force on the reliability calculation is also discussed and corrected using bearing fatigue analysis. A spindle reliability test platform with radial force, axial force, and torque simulation is developed according to the cutting load model, while the loading spectrum is compiled for conducting the spindle reliability test. This research is of great engineering value for the designing of the spindle reliability test.

A generalized voltage stability indicator based on the tangential angles of PV and load curves considering voltage dependent load models

The majority of traditional techniques for voltage stability assessment do not account for load power-voltage characteristics and assume a constant PQ load model, which is proven unreliable especially if the system load contains a large percentage of induction motor loads. This work presents a generalized voltage stability index which has two important features. First, it is applicable to general load models including ZIP, exponential, and induction motor loads. Second, it can be used for both measurement-based and model-based voltage stability assessment. The key idea of this index is that at the collapsing point, the system P-V curve and the load P-V curve share the same tangent line. Thus, the tangential angle between the two curves is an appropriate indicator of proximity to voltage collapse when voltage-dependent loads like ZIP and motor are considered. The performance of the proposed index is tested on both the IEEE 14-bus system and the 181-bus WECC system. The results show that the proposed index gives a good and reliable assessment of system stability. In addition, it demonstrated a consistent behavior, always reaching a value of 0.0 at the stability limit which enables the definition of a threshold for taking corrective measures.

Generalized Load Modeling Considering Inverter Capacity Limitation

This paper aims at the problem of the generalized modeling considering the capacity limitation of inverter. Firstly, how the inverter capacity limitation can influence the generalized load fault response of the grid-connected point was analyzed. Then, the idea of fitting the piecewise function was proposed and applied to the training process of the generalized load artificial with neural network class model. To be clearer, fault samples were jointly trained at the same time to learn different segmentation characteristics. The modeling and simulation results show that the proposed method can improve the generalization ability and stability of the artificial neural network class model in generalized load modeling.

Recursive Bayesian-Based Approach for Online Automatic Identification of Generalized Electric Load Models in a Multi-Model Framework

Electric loads are essential for power system dynamic simulation. However, load modeling is one of the most challenging topics due to the diversity and time-varying behavior of the load. When considering the intervention of rapidly developing distributed generation (DG), load modeling becomes more difficult. In this paper, a new solution for determining the unknown generalized load model is proposed. The radial basis function (RBF) neural network-based sub-models of generalized load are stored in the form of a sub-model bank. A recursive Bayesian approach is used to identify the sub-models and then merge them into one generalized load model according to their probabilities. The proposed method can be implemented online and adapt to describing the diversity and time-varying behavior of the generalized load. Numerical studies are carried out using both simulation data and actual measurements. The comparisons with other load modeling methods verify the advantages of the proposed method.

Optimal Power Factor Regulation of Dispersed Wind Farms under Diverse Load and Stochastic Wind Conditions Based on Improved Firefly Algorithm

Aiming at the instability of voltage and large network loss of dispersed wind farms (DWFs) integration into distribution network (DN), an optimal power factor regulation method based on improved firefly algorithm is proposed. Firstly, the generalized load model based on the static voltage characteristics is analyzed. Then reactive power capabilities of DWFs are thoroughly discussed and the influences of DWFs with variable power factor on network loss and voltage profile are presented. In order to reduce network loss and enhance power quality, optimal power factor regulation of DWFs based on improved firefly algorithm (IFA) is proposed. Finally, results of the benchmark IEEE-33 node system show the feasibilities and validities of the proposed method and the superiorities of proposed IFA are revealed by comparison with the existing algorithms.

EXTREME ENVIRONMENTAL LOAD MODELS FOR WAVE AND CURRENT RESPONSE SURFACE METHOD

The three most uncertain environmental design loads acting on offshore structures are wave height, current and wind velocity. If the reliability of structure is to be determined, then we need to have limit state function for load which requires that we should transform the environmental loads into load model. Load model, which predicts the load, will ultimately affect the design resistance and thus its final impact on cost could be large. Since, there are many offshore structures located in different offshore regions in Malaysia, the calibration of the environmental load model, should be evaluated to determine which model fits best. To obtain the environmental load model, response surface technique is generally applied. Load models suggested by DNV and ISO code are analysed to determine the best model fit for local conditions of Malaysia. Base shear, wave height and current velocity are used in a linear fit to determine polynomial response surface. The results showed that due to the geography of Malaysia different regions might have to use specific load models instead of a general load model for all regions.

철도 부하의 이동성을 반영한 변전소 정태부하모델링 수립에 대한 연구

Nowadays, it is expected that mobility loads such as electric railways and electric vehicles will be penetrated gradually and affect on the power system stability by their load characteristics. Various researches have been carried out about electric vehicles for the recent decade though the load of electric railway could be forecasted because of the specified path and timetable, is a field with a long historic background. Some precise 5th polynomial equations are required to analyze the power system stability considering mobility load to be increased in the immediate future while the electric railway dispatching simulator uses load models with constant power and constant impedance for the system analysis. In this paper, seasonal urban railway load models are established as the form of 5th polynomial equations and substation load modeling methods are proposed merging railway station load models and general load models. Additionally, load management effects by the load modeling are confirmed through the case studies, in which seasonal load models are developed for Seoul Subway Line No. 2, Gyeongui Line and Airport Railroad and the substation load change is analyzed according to the railway load change.

Multi-State Load Models for Distribution System Analysis

Recent work in the field of distribution system analysis has shown that the traditional method of peak load analysis is not adequate for the evaluation of emerging distribution system technologies. Voltage optimization, demand response, electric vehicle charging, and energy storage are examples of technologies with characteristics having daily, seasonal, and/or annual variations. In addition to the seasonal variations, emerging technologies such as demand response and plug-in electric vehicle charging have the potential to receive control signals that affects their energy consumption. To support time-series analysis over different time frames and to incorporate potential control signal inputs, detailed end-use load models that accurately represent loads under various conditions, and not just during the peak load period, are necessary. This paper will build on previous end-use load modeling work and outline the methods of general multi-state load models for distribution system analysis.

Vandal Loads and Induced Vibrations on a Footbridge

The paper describes a study to characterize intentional human dynamic loads (vandal loads) and their induced effects on a footbridge. A numerical model to characterize the dynamic behavior of the footbridge has been developed, is experimentally validated, and is used to numerically simulate the response induced by groups of pedestrians synchronized at critical bridge frequencies. The vandal load associated with a single pedestrian is characterized and compared with definitions in the literature. The response is then calculated considering the measured load and compared with the measured response to the excitation induced by a single pedestrian or a group with varying dimensions. The definition of a general load model for vandal excitation, including a tentative definition for synchronization is discussed.

A Full-Bridge Resonant Inverter With Modified Phase-Shift Modulation for High-Frequency AC Power Distribution Systems

The design of a resonant inverter for high-frequency ac (HFAC) power distribution systems is complicated by the following three factors: 1) A number of electronic loads located in different locations are connected to the resonant inverter, the impedance, and the power factor of the equivalent load of which varies over a wider range than a system with a certain load; 2) the resonant inverter is subject to an input-line voltage varying over a wide range; and 3) the characteristics of the resonant inverter depend on the load impedance. It is mandatory to operate the inverter with zero-voltage switching under various load conditions of different power factors and over wide input variations. It is further desirable that multiple resonant inverters can be paralleled with simple current-sharing control (CSC). A phase-shift- modulation (PSM)-controlled full-bridge series-parallel resonant inverter is proposed for the HFAC power distribution architectures. A new PSM method is proposed with which the phase angle of the inverter output voltage is independent of the modulation signal of the phase-shift modulator. Such a feature allows multiple resonant inverters to operate in parallel with a magnitude CSC. The resonant inverter is analyzed with a general nonresistive load model, and the design curves are developed. A prototype resonant inverter system is designed and implemented with an operation frequency of 1 MHz, a rated output power of 150 W, and a sinusoidal output voltage of 1-MHz 28-V rms. The proposed resonant inverter has the advantages of high efficiency over wide input/output line variations, high waveform quality of the output voltage, and phase-angle independence of the voltage-feedback/feed-forward control and CSC.

A generalized load modeling technique using actual recorded data and its use in a harmonic load flow program

This paper consists of two parts. While the first part presents a new time domain load modeling technique that is based on actual recorded steady-state power system measurements, the second demonstrates the incorporation of the developed load model into a harmonic load flow program that is based on the bus admittance matrix method. The developed load model, a perfectly general one, can be used to model linear or nonlinear loads in the presence or absence of harmonic distortion. Conceptually it is shown that the calculation of the power components by using the developed model becomes an easy task, even in the presence of harmonic distortion. The problem of power factor correction in the presence of harmonic distortion is finally addressed and it is shown that the developed method yields better results than the conventional method of power factor correction.

Power-system load representation

The paper concerns the representation of distributed loads of mixed but known composition. A general load model is employed which relates relative changes in active-and reactive-load demand to relative changes in applied voltage and frequency in terms of a set of four characteristic parameters. The object is to identify analytically the resultant characteristic parameters at a principal load busbar, taking into account the effects of feeders and distribution transformers as well as load composition. The analysis may start at any network level where load characteristics are known. An example is given, illustrating the application of the method.