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In this paper optimal location and sizing of Non-dispatchable Distributed Generation (NDG) based distributed generation (DG) is investigated by considering uncertainty of NDG. In present study a solar photovoltaic (SPV) is considered as NDG because SPV based DG has uncertain nature of generated power because it is powered by solar irradiance which has uncertain characteristics. To investigate the uncertainty of intermittent nature of solar irradiance Beta Probability Density Function (BPDF) based PDF is considered for addressing the uncertainty of solar insolation. For determining the optimal size of DG unit an analytical based methodology is developed. In this study optimal capacity of NDG is estimated by deriving the expressions of DG unit at each bus. Further, a multi-objective index factor (MIF) is designed in order to find out the candidate bus for DG placement. The proposed technique is applied on IEEE 33-bus distribution network. The obtained results reveal that proposed technique provide almost similar result to that of other method which is available in literature.

The power consumption of buildings over the course of each minute, hour, day and season plays a major role in how this load influences the Electric Power System voltage and frequency, and vice versa. This consumption is based on the building’s load component types, efficiencies, and how they consume power and react to changes in real time. Due to this complexity, standard full-building load models are typically voltage-invariant. This paper proposes a novel framework to transform these voltage-invariant building load models into fully time- and voltage-dependent load profiles using available data on the voltage sensitivity of individual load components. While a voltage-dependent building model could theoretically be generated from static load models of every component in a building, this approach faces two challenges: first, load models representing all load components are impractical to develop for all possible load component types; second, building energy consumption is never measured or modeled at the individual component level. The proposed framework compiles available component data in the form of static ZIP load model parameters, and maps them into the end use categories utilized by standard building modeling programs. The voltage sensitivity of each end use category is then bounded by the extrema of the component models within it. This framework is applied to a load profile case study representing the aggregate U.S. residential building stock. In addition to the minimum/maximum conditions, a load profile based on typical load composition and weighted ZIP parameters is generated for the same building stock. The results show that for a 10% drop in voltage, using the least sensitive ZIP parameters, active power is expected to be 3% to 14% lower than nominal, depending on the season and time of day. Using the most sensitive ZIP parameters, the active power is expected to be 9% to 20% lower than nominal, also depending on the season and time of day.

The proliferation of photovoltaics (PV) in distribution systems brings about voltage stability problems. This paper proposes an algorithm to calculate extreme bifurcation intervals considering deep PV penetration levels. The paper applies the sandglass-hyper-ellipsoid-cone model to analyze the correlations among net bus loads representing bidirectional power flows for different PV penetration levels. Using the net bus load model, three extreme bifurcation points on voltage stability limit hypersurface are formulated where two of these points represent the voltage stability bifurcation interval in the forecasted net bus loading direction. An iterative method is applied to obtain bifurcation solutions. The validity of the proposed method is verified by using the IEEE 3-bus system, the IEEE 33-bus system and the IEEE 123-node test feeder. The numerical results demonstrate that the proposed sandglass-hyper-ellipsoid-cone net bus load model and solutions are effective in managing correlated net bus load forecast errors in distribution systems with PV integration.

The results of ambient signals-based load modelling are more sensitive to phasor measurement unit (PMU) measurement errors due to the relatively smaller disturbance magnitudes of ambient signals. To analyse the impact of PMU measurement errors, the stochastic distributions and frequency spectra of PMU measurement errors are required. In this study, the measurement errors of Sifang CDS361 PMU are experimentally tested, and then their impacts on load modelling results are analysed. The following contributions have been made in this study. Firstly, the stochastic distributions and frequency spectra of PMU measurement errors are experimentally tested, from which it can be concluded that systematic errors occupy a larger proportion compared with accidental errors. Secondly, the impacts of PMU measurement errors on load modelling results are analysed. It can be concluded that accidental errors have more severe impacts on the accuracy of both dynamic and static load models. Besides, systematically errors also impact the accuracy of static load models. Thirdly, the function of low-pass filters in recovering measurement signals from PMU measurement errors and enhancing the accuracy of load modelling results are validated. It can be further concluded that load model parameters can be accurately identified with current PMU measurement accuracy.

Accurate representation of system loads is critical for performing power system dynamic studies. As of date, in positive sequence bulk power system dynamic studies, the WECC composite load model is the state-of-the-art model for representing the aggregated behavior of loads at the substation bus. Although used widely, this model is continuously undergoing improvements to ensure that a reasonable representation of different load components can be obtained. One such refinement is the development of a model for representing the aggregated response of VFDs. This paper proposed a generic positive sequence model used to capture the aggregated response of a large number of VFDs connected at a load bus for bulk system dynamic studies. The model was developed and validated using laboratory test measurements of response different VFDs to voltage sags.

This paper introduced a three method used for controlling electrical power systems for multimachinesunder dynamic loads by using artificial intelligence.This paper includes complete descriptions of the three method used to controlling dynamicpower system stability through the method of recognizing pattern and proposition of suitablecontrol systems for re-adjusting the machines in power system for instable cases. PSATprogram had been used in analyzing the stability in the power systems. In this paper, thestudied power system included dynamic load model, the program gave excellent results insuitable time, and the used network consists of 14 bus bars – 5 generators. قدم ھذ البحث ثلاث طرق تستخدم للتحکم في أنظمة الطاقة الکھربائية للآلات المتعددة تحت الأحمال الديناميکية باستخدام الذکاءالاصطناعي.يتضمن ھذا البحث وصفا کاملا للطرق الثلاثة المستخدمة للتحکم في استقرار نظام الطاقة الديناميکي من خلال طريقة التعرفعلى النموذج واقتراح أنظمة تحک م مناسبة لإعادة ضبط الآلات في نظام الطاقة للحالات غير المستقرة. وقد استخدم برنامجفي تحليل الاستقرار في أنظمة الطاقة. في ھذا البحث ، تضمن نظام الطاقة المدروس نموذجا للحمل الديناميکي ، حيث PSATحقق البرنامج نتائج ممتازة في وقت مناسب ، وتتکون الشبکة المستخدمة من ١٤ قضيب ناقل - ٥ مولدات

In this paper, a revised framework of the Optimal Capacitor Placement (OCP) problem in a radial distribution system is presented. In contrast to the classical methods, which is highlight for an optimal solution of a single feeder, the proposed method is considered all of the feeders within a subregion. Additionally, the proposed method is performed by simultaneous placement capacitors by considering acquired capacitor banks as durable articles allocated with limitation of a budget acquired for each fiscal year. This can be achieved by using signals of and incremental energy loss and the concept of reactive power compensation zone. To clarify, a 5-feeders substation of a north-eastern PEA region 2 with three levels load model is adopted as a test system. The obtained results can reflect the impact of a latest capacitor to energy loss in a system.

Multi-distributed generation and compensators are one of the practical ways to improve the performance of power network. Although each of these devices increases the efficiency of distribution system, the combination of DG and compensator can be more useful. So in this study, the performance of capacitor bank (as traditional compensator) and DSTATCOM (as modern compensator) is evaluated in the distribution system with multi-DG. The load model of the network is also considered as sensitive to voltage-frequency and various customers’ daily load patterns. For getting the best result, simultaneous placement of different types of DGs and compensators is done by the combination of multi-objective whale optimization algorithm and analytical hierarchy process. Technical, economic, and environmental indices are considered as objective functions of this study. The results of the simulation using the IEEE 69-bus distribution system show the proper performance of compensators in the increasing of efficiency of DG units during the different condition of operation.

This paper is a test case study based paper. In this paper, line indices-based approach is utilized for testing the effect of various load models on estimation of maximum acceptable load at weak bus of a particular power system. It has lot of importance for the voltage stability analysis. Based on result analysis, most preferable load at a bus or substation is also identified. Different exponential-type load models and composite load models are considered in this work. The change of weak bus voltage and maximum load for various load models are analyzed. Each line loss and total loss in the system for different load models are also analyzed. Methodology of this work is implemented on standard IEEE 14 bus test case system. All the simulations of this work are implemented in MATLAB 2019a.

Islanding detection is one of the most important requirements for the operation of distributed generation (DG) and renewable energy resources. Due to the fact that there are different types of nonlinear loads in the distribution network, considering the linear RLC load model cannot warrant the reliable performance of the islanding detection methods (IDMs) in real network conditions. In this paper, the effect of nonlinear load on the performance of the IDMs is evaluated. For this purpose, a novel approach based on sensitivity analysis with respect to the load nonlinearity level is proposed and the performance of various IDMs is studied. The results of sensitivity analysis show that the higher (lower) the level of load nonlinearity, the easier (more difficult) it will be to detect islanding. The simulation results confirm the effectiveness of the proposed method.

This paper proposes a novel modulated model predictive control (MMPC) method based on voltage-error vector analysis for a direct matrix converter. The proposed method is based on model predictive control and includes a modulation scheme. It utilizes the voltage-error vector, which is derived from discrete-time load model, to reduce the available switching states/voltage vectors in prediction process, resulting in reduced calculation efforts compared with the conventional MMPC. The effectiveness of the proposed method is verified by the hardware-in-the-loop experimental results.

An integrated Matlab model comprising of an electro-mechanical actuator (EMA) model, load model and state model has been constructed to investigate the cargo door actuator motion control, operation and working states, of which, a Simulink® servomotor system model is adopted to mimic the EMA actuator, a SimMechanics® model is used to compute the actuator's load, a Stateflow® state transition model is employed to simulate the working process. The results indicated that the motion is well controlled, generated load force is valid, working states and their transition logics are reasonable. The simulation verified the effectiveness and easiness of the integrated modelling method.

Frequency is a particularly important operating parameter in power systems, and power system frequency characteristics analysis lays the foundation of frequency stability analysis and control. Different simulation models will have different effects on the results of simulation calculation, especially the accuracy of load model will play a vital role in the final simulation results of power grid. In this paper, typical static load model and induction motor model are introduced and frequency characteristics are analyzed. A parameter aggregation method of load model based on adjusting performance weighting is proposed. The effectiveness of the load equivalence method is verified by an example of Fujian power grid.

Due to the high penetration of renewable energy and the wide application of electronic devices in the distribution systems, it becomes more complicated to formulate an accurate load model than ever before. For some cases, the formulation cannot be successfully established via the traditional modelling approaches. Therefore, how to establish an accurate load model under the new challenges is drawing a great deal of attention. In this paper, measurement based method using recurrent neural network (RNN) is proposed for constructing an accurate equivalent of active distribution systems, and an application scheme of the proposed model is presented. With the purpose of thoroughly investigating the performance of the proposed RNN based load model in an electric power system, it is applied to reproduce the dynamic behaviors of active distribution systems. In the testing scenario, the performance of the RNN model is evaluated by two types (i.e. using the same disturbance cases and different new disturbance cases).

DOI: 10.26650/electrica.2018.02248In this paper, simple approximate formulasare established to estimate active and reactive power losses in distributionnetworks. The developed formulas based on load profiles are derived fromElgerd’s power loss formulas. A simple model is also proposed to estimate theload profile while considering several parameters, such as the average loaddemand and the load limitations. Derivation of the load model and the lossformulas are presented along with their applications on two distributionnetworks. The results show that the loss formulas, which depend on the proposedload profile, can estimate the power losses in distribution networks with highprecision., DOI: 10.26650/electrica.2018.02248In this paper, simple approximate formulas are established to estimate active and reactive power losses in distribution networks. The developed formulas based on load profiles are derived from Elgerd’s power loss formulas. A simple model is also proposed to estimate the load profile while considering several parameters, such as the average load demand and the load limitations. Derivation of the load model and the loss formulas are presented along with their applications on two distribution networks. The results show that the loss formulas, which depend on the proposed load profile, can estimate the power losses in distribution networks with high precision.

This paper presents a new state estimation (SE) method including equality constraints to model voltage dependent loads and zero injections. Formulation of conventional SE, assuming simple constant power model for the system's loads, is modified to incorporate voltage dependent load models. Assuming reliable load models and zero injections, it is analytically proved that modeling the equality constraints leads to better SE accuracy. To numerically validate the analytical findings, the proposed SE method is implemented on the IEEE 118-bus test system and the large-scale real-world Iran’s power system, and its obtained results are compared with the results of conventional SE. Also, it is shown that considering voltage dependent load model in SE formulation leads to better performance of bad data detection. Moreover, it is illustrated that the accuracy of the proposed SE has low sensitivity to load model identification error.

In this short communication, a generic measurement-based voltage stability indicator (VSI) is presented with voltage dependent load models incorporated. It uses the angle difference between the tangent lines of the load characteristic curve and the PV curve. Based on the Thevenin equivalent estimated from the measurements, the proposed VSI can be easily applied to both the ZIP and the exponential load models. Time domain simulation results on both load models demonstrate that the proposed VSI accurately indicates voltage instability and outperforms a conventional VSI which is based on a constant power load model.

One of the major issues in simulation and control of power system dynamics is load modelling. More accurate load models in power system stability analysis increases the accuracy of simulation results. If inappropriate model is used for the load, the obtained results may contain a high degree of error. In majority of analysis, the loads are usually considered as a constant impedance element. Whereas, such a model is not only accountable for the stability analysis of power system but also may sometimes lead to opposite results. Due to the variation of the load and also the variation of the composition of the load components, it would be difficult to provide a fixed model for electrical loads similar to those of other elements of the power system. A method for modelling the power system loads via genetic algorithm is presented in this paper. This methodology is performed based on the composite load model. In order to get an accurate load model, several scenarios are considered. The particular method of this paper is that after obtaining the load model parameters corresponding to each of the scenarios, various values obtained for the parameters are averaged. Finally, the validity of the obtained parameters is testified with some other scenarios. The results reported in this paper indicate that the existing load models satisfactorily describe the actual behaviour of the physical load and can be reliably estimated using the identification techniques presented herein.

This paper presents an evaluation of the main convergence characteristics of multiphase power flow methods in unbalanced distribution systems. Two widely used methods for solving unbalanced power flows are analyzed: methods based on Newton–Raphson (NR) and methods based on backward forward sweep (BFS). The limits and robustness of the BFS method and NR method are tested in the following aspects: (i) variation of the X/R ratio, (ii) load’s increase up to the convergence limit, (iii) load model impacts (ZIP model), and (iv) voltage regulators modeling impacts. Some models presented in the literature were implemented and tested. Tests are performed on the IEEE 34 and IEEE 123 systems. Analytical explanations are also presented.

A medium term stochastic load model using the hourly AMI load data aggregated at transformers and feeders is introduced. Load model frequency domain statistical parameters are derived from spectral analysis of AMI data. The load model is driven by a weather index based on Heating-Cooling Day Degree. This index is incorporated into the model using local, hourly weather data. Advantages of the proposed load model are discussed. Performance comparisons between the proposed model and several time-domain methods are presented.

One very important charge condition that can produce a catastrophic failure during the starting of grinding mills is the compacting of the load inside the mill, especially after long downtimes. This condition is usually named frozen load and the load remains locked to the mill shell and after a half turn drops damaging the mill body and bearings. Therefore, the mill protection system must give an early detection of this condition and aborts the start before the compacted mill charge falls hitting the bottom of the mill shell. Actual protection schemes against locked load use fix torque or current trip values and do not consider the effect of the specific charge inside the mill on each startup. This paper presents the development of a robust estimation and protection algorithm of locked load condition based on drive and process signals. The proposed algorithm includes a locked load model used to define torque, rms current and power thresholds for the existing starting charge conditions, and compares the locked load signals to the online estimation of drive variables. This comparison is used to detect the beginning of charge cascading, and the threshold values are used to command the starting abortion. Main advantage of the proposed protection algorithm is that considers the effect of the mill charge and charge position, and therefore gives an accurate and safe detection of locked load for any charge condition during the mill starting. Proposed algorithm was evaluated using field records of an 8.2 MW semi-autogenous (SAG) mill drive confirming its ability to handle startups with different charge conditions.

In electrical systems especially isolated wind and diesel based hybrid systems, voltage control has been achieved in several works from adequate supply of reactive power using STATCOM/SVC as dynamic compensators. However, in most of the existing works, studies are performed only with static loads which do not have any influence of previous system conditions. In such available studies, the two major concerns were (i) cost based studies, and (ii) control techniques of dynamic compensation. The electrical systems are always influenced by the unrealistic load modelling in such systems which is almost untouched in available works and therefore motivate the authors to work on it. Realistic loads are of composite nature that composes the blend of characteristics that acquire static as well as dynamic nature of the load. In present work, the authors are interested to investigate the lower cost of reactive power with composite load for best proportion of dynamic and static compensations. The study is done in MATLAB software with 10% step increment in reactive power demand and input wind power to analyse compensation effect for extreme voltage deviation of pu at load end as recommended by several energy policies and standard IEC 60038.

In this chapter, various factors that may affect the importance of load model parameters have been investigated. These include load size, stochastic dependence among load model parameters, load model type and load location. The chapter describes how each of these factors affects the established importance of load model parameters. Finally, for load locations specifically, it tries to identify critical load locations for each type of power system stability irrespective of the specific load models on these locations.

This chapter discusses different power system stability indices used for the load model parameter ranking. Firstly it introduces the power system stability indices used for four types of power system stability studies in this research. Following that it provides a critical review and comparison of different types of stability indices.

After identifying the important load model parameters for power system stability studies, the next question is how accurately these parameters need to be modelled. This chapter solves this problem by obtaining the accuracy levels required for different load model parameters in order to achieve certain confidence levels of chosen power system stability indices. The accuracy levels of chosen critical load model parameters have been obtained for different load models, different power system stability studies and different loading conditions. This chapter thus provides guidance for determining the required accuracy of load models for individual loads in power system based on their influence on different types of power system stability studies.

Voltage stability is a challenging issue for a power system with high penetration level. Two voltage stability indices are proposed in this paper to quantitatively evaluate the steady-state voltage stability and the short-term voltage stability respectively. The steady-state voltage stability metric is based on voltage collapse proximity indicator (VCPI) and considers the priorities of different transmission lines. The short-term voltage stability index evaluates not only the extent of the voltage deviation, but also the voltage recovery time, which is critical to the wind-penetrated power system. Complex load model is also considered in this paper to address the adverse impact of the induction motor loads on the power system. The New England 39-bus test system is used to demonstrate the effectiveness of the proposed indices in PSSE.

With the rapid construction of UHV AC-DC interconnected power grids, it is increasingly important to ensure the voltage stability of interconnected systems. In this paper, a continuous power flow algorithm for voltage-source converter (VSC) AC-DC system considering static load characteristics is proposed. It establishes an index for evaluating voltage stability based on the load margin and identified the weak region of the system. The effects of load model changes on voltage stability (VS) are analyzed in various scenarios. The relationship between DC control mode and system VS is further considered. The effectiveness of the proposed method is verified by an improved 10-node example.

The objective of this paper is to explore how optimal load model parameters impact the results of dynamic simulations in power systems. We focus on identifying the parameters for CLOD composite models that are widely used in power industry to represent major loads in dynamic simulations. This model accounts for the diversity of load components by representing a variety of elements, including large and small motors and static loads. We use evolutionary-based optimization methods to minimize the error between PMU measurements and dynamic PSS/E simulations for fault-induced voltage events. We compare the simulations results obtained using optimized load models with those of generic models that are often used in the industry. We provide simulation results based on real-life data from Alberta’s electrical power system.

This paper proposes a hybrid approach to estimate the parameters of Z-IM Load Model from on-line measurements obtained from tap changes of transformers. For this aim, the model equations were linearized to use the information provided by small disturbances. The approach proposed applies a heuristic (Mean Variance Mapping Optimization) and a nonlinear (Trajectory Sensitivity) methods in cascade to optimize convergence. Simulation results shows the adequacy of the hybrid method for load model. The entire process took, in average, 24 seconds to converge. All the codes used for this work were written in Python 2.7.

This paper presents the mechanism analysis of short-term voltage stability based on a double-generator-one-load model. A double-generator-one-load (DGOL) model of power system is introduced. Compared with other existing simplified model, the DGOL model not only includes the dynamic of motor, but also takes the interactions of generators into consideration. Then, this paper analyses the mechanism of voltage stability based on DGOL model, and proposes a quantitative index (RAV ratio) to evaluate the influence of rotor angle variation on short-term voltage stability. At last, the simulation work is introduced to illustrate the advantage of the proposed simplified model and analysis method.

This paper continues the pursuit of getting a deeper understanding regarding the transient stability of low-frequency AC railway power systems operated at 16 2/3 Hz synchronously to the public grid. The focus is set on the impact of different load models. A simple constant-current load model is proposed and compared to a previously proposed and studied load model in which the train’s active power is regulated. The study and comparison is made on exactly the same cases as and grid as with the already proposed and more advanced load model. The railway grid is equipped with a low-frequency AC high-voltage transmission line which is subjected to a fault. The study is limited to railways being fed by different distributions of RFC (Rotary Frequency Converter) types. Both AT (auto transformer) and BT (booster transformer) catenaries are considered. The RFC dynamic models are essentially Anderson-Fouad models of two synchronous machines coupled mechanically by their rotors being connected to the same shaft. The differences in load behaviour between the proposed constant-current load model and the previously proposed and studied voltage-dependent active power load model are analyzed and described in the paper.

Modelling of voltage dependent load is always a current topic due to existence of an adequate load model is a prerequisite for calculation of steady states and the analysis of transient regimes of power systems. Given that it is important to know the load model parameters, we have performed the measurements in electric power system of Bosnia and Herzegovina (EPS BIH). The main idea is to identify the values of voltage parameters of dynamic load model. Therefore, this paper describes the dynamic load models and the methodology for exponential dynamic load model parameter identification. It also presents the voltage parameters of dynamic load model for a node in EPS BIH and compares them to similar published studies, concluding that the difference in given parameter values is the consequence of local load characteristics.

Load modelling has a significant impact on operation mode arrangement, transient stability analysis, small disturbance stability calculation and other aspects in power system. It is an important basis and issue for the decision-making of dispatching operation department. As a novel research field of measurement-based identification method, load model parameter identification via ambient PMU signal has gained some developments. This article reviews the current research status of ambient data-based load parameter identification, outlines its basic principle and typical framework, and expounds three technical routes. By summarizing the characteristics of various methods, the future research direction is prospected.

Power system control requires verified models of all its elements: generators, transformers, transmission lines, and power system loads. To identify load model parameters, the measurement data are used. The paper discusses the possibility of using steady-state measurements instead staged field test data. This requires taking into account an unobvious effect-the network response. The network response is due to the probabilistic nature of the power and voltage changes and the correlation between them. The network response effect is demonstrated using a probabilistic load model and a simple power supply scheme.

Available transfer capability (ATC) needs to be declared well in advance by the system operator to reserve transactions and avoid any congestion in the network. In this paper, an optimal power flow based approach has been utilized for bilateral/multi-transactions deregulated environment to obtain the ATC. The ATC has been obtained with generalized unified power flow controller (GUPFC) and interline power flow controller (IPFC) for intact and line contingency cases. The impact of ZIP load model has been evaluated on the ATC with both the devices. The main contribution of the paper is the comparison of the ATC obtained with. GUPFC and IPFC for intact and contingency cases with constant P,Q load model and ZIP load model. The results have been determined for intact and line contingency cases taking simultaneous as well as single transaction cases. The results obtained are also compared with DC/AC and PTDFs. The proposed method have been applied for IEEE 24 bus RTS.

Summary In deregulated rate structure, the performance evaluation of distribution system for energy efficiency includes; loss minimization, improved power quality, loadability limit, reliability and availability of supply. Energy efficiency changes with the variation in loading pattern and the load behaviour. Further, the nature of load at each node is not explicitly of any one type rather their characteristics depend upon the node voltages. In most cases, load is assumed to be constant power (real and reactive). In this paper voltage dependent practical loads are represented with composite load model and the energy efficiency performance of distribution system for practical loads is evaluated in different configurations of 33-node system.

Effective building/house energy management has been considered as an efficient way to mitigate the fluctuation of renewable energy in power distribution system. This article studies the operation scheduling problem for microgrid with high penetration of solar power and thermostatically controlled loads. Based on the established photovolaic model and thermostatically controlled load model, an optimal operation strategy for microgird is proposed. The scheme is based on the rolling horizon optimization strategy, where the control window continues to proceed with the update of real-time information, aiming to minimize the total operation costs over the current control window. Differential evolution algorithm is used to solve the proposed model, and the simulation results validate the efficiency of the proposed method.

Microgrids (MGs) are characterized by faster dynamics than conventional grid-connected distributions systems. This is in part due to the lack of inertia of inverter-interfaced distributed energy resources such as photovoltaic and energy storage systems. In this context, load dynamics considerably affects the transient stability performance of MGs, especially if disconnected from the main grid. The aim of the paper is to analyze the influence of the load modeling and the load composition in the transient stability assessment of a medium voltage MG during islanding transition. The MG we analyze consists of a photovoltaic power plant, two battery energy storage systems, a synchronous generator and different classes and types of load, which we consider representative for the problem of interest. The system is implemented in the EMTP-RV simulation environment. The importance of appropriate load modeling for the adequate analysis of the transient response of an islanding microgrid is also addressed and discussed.

Load modeling is a crucial part of modeling a power system. Traditional load model identification methods are mainly based on post large disturbance response, which cannot be conducted without large disturbance events. In this paper, a new approach of ambient signals based load model parameter identification is proposed to solve this problem, through which the time-varying load model parameters can be identified more frequently. First, the composite load model structure and the measurement based identification approach are introduced. Then, a two-stage identification framework to identify the load model parameters from ambient signals is proposed. In the first stage, the electromagnetic parameters are identified using an optimization method, with the predicted error as the objective function and the differential evolution as the optimization algorithm. In the second stage, the mechanical parameters are identified using linear regression. Finally, the effectiveness of the proposed identification method is validated through the simulation results in Guangdong Power Grid with practically measured ambient signals data. The proposed two-stage identification framework has shown its ability to accurately identify the load model parameters from ambient signals and the advantage over the other identification approaches.

This paper presents measurement-based evaluation of static load characteristics of demands in administrative buildings, which are an important class of commercial customers. Typical values of the parameters of static exponential load model are determined from the long-term measurements of voltage, active and reactive powers at the low voltage sides of secondary transformer substations. The average model parameter values are determined for different seasons, for characteristic days of the week and for specific time intervals during the characteristic days. The presented results also consider dependencies of the load model parameters on the variations of ambient temperature.

In this paper, an efficient method is proposed for optimal allocation and sizing of Thyristor Controlled Series Compensator (TCSC) to improve the technical and economic indices of a power network with deterministic and stochastic load models. First, the compensator allocation is done in the transmission system with the deterministic load model. After calculating the technical and economic indices of the network in the presence of a deterministic load model, the proposed method is applied to the system with a stochastic load model. The two-point estimation method is used for simulating the stochastic conditions. The indices of voltage deviation and economics of the system are optimized for selecting the optimal location and size of TCSCs. The economic index comprises loss cost, cost of the produced active power of generators and also the costs of installation, operation and maintenance of TCSCs. The multi-objective particle swarm optimization (MOPSO) is utilized to optimize the objective functions. After the multi-objective optimization, the fuzzy decision method is employed to extract one of the Pareto-optimal solutions as the best compromise one. For evaluating the proposed method, comprehensive simulations have been performed on the IEEE 39-bus network by using MATLAB/Matpower software. The simulation results clearly prove the remarkable performance of the proposed method in improving the technical and economic indices of the system.

To model the load area and simplify the electrical network, a multi-port area load equivalent modelling method (ALEEM) based on the extended generalized ZIP load model (EGZIP) is proposed. Different from the traditional ZIP load, the EGZIP load model incorporates the voltage magnitudes and voltage phase angles of all boundary buses, which can equivalently model the area load with multiple boundary buses more accurately. The load flow calculation considering the EGZIP is derived and analyzed. Also, based on the hierarchical and partitioning characteristics of the power grid, a multi-port equivalent strategy is proposed to reduce the number of parameters to be identified in the equivalent model. For parameter identification, the currents measured at varying operation conditions on the boundary bus are used to construct the least square estimation (LSE) problem. The interior point method is used to identify the model parameters. The simulation test conducted on the 87 bus system proves the equivalent model derived from the proposed ALEEM based on EGZIP has higher accuracy and the multi-port equivalence strategy can reduce both the number of parameters to be identified and the time consuming on equivalent process.

This paper proposes a new generalized power load modeling method, which contains multiple RBF neural network model structures. Firstly, based on the RBF neural network, a sub-model is built to describe typical load characteristics. It breaks through the limitations of load components, and adapts to the diverse development of modern power system. Then, based on Bayesian estimation theory, multiple typical load models are merged into one integrated load model. It solves the problem of insufficient generalization ability of traditional load model, and adapts to the time variation of power load. Finally, the proposed method was applied in IEEE 14-bus test system. The results obtained proved its validity.

The simulation precision of the classic load model (CLM) is affected by the increasing proportion of installed energy storage capacity in the grid. This paper studies the all-vanadium redox flow battery (VRB) and proposes an equivalent model based on the measurement-based load modeling method, which can simulate the maximum output of the VRB energy storage system and fit the external characteristic of the system precisely in the occurrence of large disturbance and continuous small disturbance. The equivalent model is connected to CLM to form a generalized synthesis load model (GSLM), which considers the parameters of distribution network and reactive power compensation. Compared with CLM, GSLM has better structures and can describe the load characteristics of distribution network with energy storage system more precisely. Simulation results validate the effectiveness and good parameter stability of GSLM, and show that the higher the proportion of energy storage in the grid is the better description ability GSLM has.

In this paper, a novel load model structure considering multi-level low-voltage release characteristics is proposed. In the proposed model, three-level low-voltage release characteristic parameters are introduced into the existing synthesis load model (SLM) to simulate the load low-voltage release characteristics during disturbance. Next a load model parameter calculation method considering load multilevel low-voltage release characteristics is proposed. Calculating the per-unit value of a single device type real load power relative to the total load node real power, and using the per-unit value as a weighted factor for polymerization, the each stage action voltage and low-voltage release average delay time constant in the synthesis load of low-voltage multi-level release characteristic parameters can be derived. Then based on the percentage of actual load losses after disturbance, multilevel low-voltage release proportion parameters is determined by fault fitting method. These three parameters can be further revised iteratively to make the error between actual load loss and calculation load loss to be minimum. Thus the low-voltage multi-level release characteristics of the load is accurately simulated. The practical calculation case of Shanghai power grid shows that low -voltage multi-level release characteristic parameters generated by the proposed load model structure and the proposed method for determining the load model parameters, can well describe the load low-voltage multi-level release characteristics.

This paper analyzes the essence of commutation failure of HVDC transmission systems, and points out that the load model has an important influence on commutation failure. The Commutation Failure Immunity Index (CFII) is used to quantitatively calculate the influence of the load type and percentage of the induction motor load on the commutation failure. It is proposed that the induction motor load can provide the rotary inertia to the system at the instant of fault, suppress the converter bus voltage drop and reduce the probability of commutation failure. The above discussion is verified by electromagnetic transient simulation.

Practice shows that the frequency characteristics of the load have important influence on analysising the safety and stability of the power grid. In order to improve the accuracy of the load model, a comprehensive load model considering load frequency characteristics is established based on the static load frequency factor and the frequency dependent part of induction motor model. For the parameter of the load model, a new composite modeling method based on the combination of statistical comprehensive method and measurement-based modeling approach is proposed to calculate and check the parameters of the model. Finally, a simulation example is given to illustrate the effectiveness of the proposed composite modeling method considering load frequency characteristics

This paper establishes a generic severity function that can be used to produce power system security risk profiles. It is illustrated by analyzing the impacts of system load attributes on the small-disturbance rotor angle stability of a power system. The load attributes contributing to the oscillatory modes can be considered as inherent uncertain variables within power systems and include load power variations, load composition, and load model parameters. Uncertainty in the renewable power generation is also incorporated in the probabilistic modelling and risk assessment to demonstrate the flexibility of the approach. A novel approach is proposed to select the severity functions to logically represent small-disturbance security margin. The risk profile of a power system has been presented considering the probability density functions (pdfs) of power system critical modal damping and a selected set of severity functions. The analysis techniques developed are illustrated with a modified version of the 68-bus NETS-NYPS power system with a high amount of renewable power penetration. The relative importance of the load attributes and the impact of these attributes on stability boundaries has been identified at varying risk levels with respect to their contribution to small-disturbance stability.