Equivalent Generator Research Articles

Circuit Models to Study the Radiated and Conducted Susceptibilities of Multiconductor Shielded Cables Connected to Non-linear Load

This paper presents an efficient Multiconductor Shielded Cable model, for conducted and radiated coupling, developed for circuit applications. In the case of radiated coupling, the interaction of the external incident field is modeled by equivalent voltage and current generators placed on shield only. The model works in frequency and time domain with linear and non-linear loads, respectively. Different applications are presented, for validation and physical interpretation. Finally, we will discuss the effect of the connection of the voltage limiter on the induced voltages.

Photovoltaic mono and bifacial module/string electrical model parameters identification and validation based on a new differential evolution bee colony optimizer

Well estimating the electrical model parameters of the photovoltaic (PV) module/string serves to develop an accurate simulator and a fault diagnosis tool. Several based evolutionary techniques were proposed to identify the unknown circuit equivalent PV generator (PVG) parameters. Whereas most of them have not been examined to various real operating conditions of solar irradiance and PV cells temperature. That requires larger search range than the adopted one in the literature. Enlarging the search range imposes more computational time and high exploration and exploitation features. Hence, a novel hybrid differential evolution and artificial bee colony intelligence (nDEBCO) approach is proposed. In terms of convergence quality, CPU execution time, number of function evaluations (NFE), and error standard deviation (StD). The newly developed approach permits to accurately identify the PV module/string unknown parameters with suitable implementation complexity. Mono-facial CLS 220P PV string has been utilized employing an adequate experimental setup with online implementation. 1080 I-V curves have been measured and estimated, where the overall RMSE ± StD is below 0.02 ± 1e−16. The nDEBCO outperforms the present-day published works, for common case studies in the literature with two based root mean square error (RMSE) objective functions namely Lambert W function (LWF) and classic. It yields 7.73006268e− 4 of RMSE, 7.8785e− 18 of StD, and 2150 NFE under ODM with LWF for RTC France PV cell. Bifacial PV module has been evaluated and the electrical parameters have been extracted within less than 1.36 s of CPU run time and not>8.0299631e− 3 ± 6.9096e− 16 of RMSE ± StD for front and rear faces. Additionally, the parameter identification procedure has been well validated to simulate the real partial shading scenarios of the studied PV string with a RMSE less than 0.045 and 0.397% of power maximum point absolute error.

Piecewise linear approximations for hydropower production function applied on the hydrothermal unit commitment problem

In a centralized-based dispatch market, the network-constrained hydrothermal unit commitment (NCHTUC) determines generation decisions that minimize the expected operating cost, usually in a day-ahead planning horizon. In this context, hydropower offers unique flexibility features, and an adequate representation is crucial for overcoming operation challenges. However, due to computational burden, simplifications on hydropower production function (HPF) modeling are necessary since NCHTUC is a large-scale nonlinear discrete optimization problem. The plant-based HPF piecewise linear approach is the most common simplification presented for real-life cases. In this case, the generating units (GUs) of a plant are aggregated and represented by a single equivalent generator. Although this approach reduces the size and the complexity of the NCHTUC significantly, several operating issues are not considered adequately, especially the forbidden zones and the nonlinearities of the GUs. In this paper, we present a new approach that considers the nonlinearities and forbidden zones of the HPF via aggregation of the GUs and piecewise mixed-integer linear approximation in an innovative way. Experiments are performed in a modified version of the IEEE 118-bus system to verify the approach’s effectiveness, analyzed in terms of the relation between computation burden and the HPF approximation quality.

Weighted Dynamic Aggregation Modeling of Induction Machine-Based Wind Farms

This paper presents Weighted Dynamic aggregation (WD agg) method to obtain an equivalent Wind Turbine Generator (WTG) for an induction machine-based wind farm using its dynamic model. The suggested approach obtains the equivalent d-q model of the induction generators considering the contribution of each unit in the model. The challenges in the aggregation of a large-scale wind farm are the variation of wind speeds at different zones and differences in the WTGs parameters. Compared with the existing methods such as Full aggregation (Full agg), Zone aggregation (Zone agg), and Semi aggregation (Semi agg), the suggested WD agg method provides an accurate single unit equivalent model for a large-scale wind farm while taking into account various wind speed zones and unequal WTG parameters. The proposed method is evaluated through time-domain simulation of a 4-WTG and a large-scale 20-WTG Doubly-Fed Induction Generator (DFIG) wind farms and their aggregated models. These simulations cover combinations of different wind speeds and WTGs parameters. Also, a 4-WTGs fixed-speed wind farm is studied to show the generality of the proposed method. Comparing WD model with the detailed response of the wind farm verifies the accuracy of the method in both steady-state and transient behaviors.

Online Equivalent Method of External Network Based on Measurement Information

How to acquire the accurate equivalent network of external system in the interconnected power grid has always been a challenging issue in the fields of both academic and engineering. This paper proposes a new method for online equivalence of the external network based on the measurement information of the internal network. Firstly, it builds an equivalent network of the external system, including the coupled branches between each of the boundary node, the equivalent generators and the equivalent lines from corresponding boundary nodes to them. Then, based on the SCADA (Supervisory Control and Data Acquisition) measurement information, an optimization model to estimate the parameters of the equivalent network is constructed, with the minimization of the mismatch between the boundary’s measurement and the calculation value of the equivalent network being the objective and the parameters of each line of the equivalent network within the reasonable range being the constraints. In order to reduce the calculation scale, measure is adopted to remove the coupled lines whose electrical distances (or impedances) are larger than a relative big threshold. The impedance range of each line in the equivalent network is determined by ward equivalent method under the condition of maximum and minimum operation mode. The model is solved by interior point method, which owns the satisfactory convergency performance. The solution of the model makes each of the calculated value of the equivalent network at the boundary node closest to the measured value, while all the parameters of the equivalent network within a practical range. The results of an example demonstrate the validity and effectiveness of the model and method proposed in the paper.

Orthogonal Components Forming of the Microprocessor-Based Protection Input Signals

The use of orthogonal components (OS) is the main direction of determining information parameters in microprocessor relay protection and automation of electric power systems. Most of the measuring devices used in modern protection and automation devices can be implemented using known operating systems. Digital non-recursive frequency filters based on discrete Fourier transform are used for OS selection. The main disadvantage of these filters is their low performance that exceeds the period of industrial frequency. For the construction of high-speed measuring devices, this time of establishing the true output signal is often unacceptable. The article proposes to form the equivalent signal OS in microprocessor defenses based on the values of the cosine and sine axes of the main harmonic formed using a discrete Fourier transform, by multiplying them by a correction factor, which is a function of the values of the input signal amplitude and its main harmonic. The proposed algorithm for generating OS input signals in microprocessor defenses is characterized by high performance in transient modes and has wide functionality. A block diagram of an OS equivalent signal generator has been developed, all blocks of which can be implemented according to known schemes on a microelectronic and microprocessor element base. The OS shaper model is implemented in the MatLab-Simulink dynamic modeling environment. The model functioning was checked using two types of test actions, viz. a sinusoidal signal with a frequency of 50 Hz (idealized action) and a signal close to the real secondary current of a short-circuit current transformer. As a result of the performed calculations, a significant (up to two times) in the speed of the proposed method of OS formation in comparison with the formers based on the discrete Fourier transform, frequency properties of both formers being identical.

Towards a labelling for green energy production units: Case study of off-grid solar PV systems

This paper proposes a new label called ECO2E/KEG for energy production units. So far, appliances and buildings labelling has been developed to support initiatives against global warming issues. Labels were then set up in order to help people in the choice of efficient electrical appliances or buildings from energy consumption point of view. From our knowledge, no labelling has been developed for energy production units yet. ECO2E/KEG is an alphanumeric index which gives information on the ecological performance of the energy production units, and on the relative cost of these clean units compared to conventional diesel generators. The alpha index is calculated by considering emissions avoided by the production units. A classification system in five groups, ranging from A (the most ecological system) to E (the least ecological system) allows green unit classification, according to their alpha index. The numerical index is obtained by comparing the LCOE of the energy produced by the green production units over their lifetime with the LCOE of the energy produced by an equivalent diesel generator over the same duration of the project. Five classes are also defined for this index ranging from 1 (the most economical system) to 5 (the least economical system).

Modeling of a Current Injection System for Susceptibility Study

This article deals with the model of a high current injection system associated with its electrical generation–transformation–distribution chain able to reproduce differential or common-mode parasitic currents and voltages induced by the coupling between a nuclear electromagnetic pulse radiation on a global electrical network. Due to the quite complexity of the current injection system, the chosen modeling approach was to use the well-known equivalent Thevenin generator. Because of several hundreds of amperes and volts of current and/or voltage generated and their relatively large spectral occupancy of some tens of megahertz, the measurement of currents and voltages needed to build the model, were carried out with adequate sensors and equipment. Once the model built, the generators have been integrated into Spice circuit simulation tool in order to predict the differential and the common- mode currents and voltages induced at the input of switch-mode power supplies and, for later studies, at some different nodes.

Processing of ECG Waveforms to Increase the Diagnostic Accuracy of the ECG Stress Test for Transient Myocardial Ischemia

An approach to increasing the diagnostic accuracy of the ECG stress test for transient myocardial ischemia is considered. It is proposed to modify the decision rule by including an additional procedure for assessing the temporal dynamics of the equivalent cardiac generator in the ST-T segment. The results of evaluating the sensitivity and specificity of diagnosis in a group of subjects are presented.

Voltage Stability Enhancement for Microgrid Using an SVC

This paper presents comparative simulation results of a Microgrid (MG) system using a Static Var Compensator (SVC) for improving the voltage stability of the studied system. An Adaptive Neural Fuzzy Inference System (ANFIS) controller is designed based on the feedback signals to control the proposed SVC. For simplicity, the studied MG system can be modeled as an equivalent small scale wind turbine generator (WTG) combine with a Solar Photovoltaic (PV) and a Battery that connected to the common AC bus. A time-domain approach based on nonlinear model simulations is systematically performed. By observing the simulation results it can be concluded that the designed ANFIS controller for SVC can offer better damping characteristics of the studied MG system under severe operating conditions

«Digital Twin» technology in medical information systems

Given the high mortality rate from cardiovascular diseases and the need to transfer medicine to a more high-tech level of development, the authors propose the use of digital twin technology for the diagnosis and treatment of heart diseases. As a digital twin of the human heart, it is proposed to use the combination of an equivalent electric heart generator and the of D. Noble computer heart model within the subsystem for supporting medical decision-making. The use of such digital twin will make it possible to reliably conduct non-invasive cardiodiagnosis to select drugs within the treatment regimen.

An Equivalent Scheme for Calculating Short-Circuit Currents in a Traction Power Supply System with Two-Way Power Supply

The cause of a methodological error in the calculations of short-circuit currents as exemplified in the power supply of a traction network with two-way supply has been shown. It is to be noted that, in an actual power supply circuit, two adjacent traction substations are connected along the 110 (220)-kV lines by mutual resistance, whereas there is no such connection in the designed arrangement. On the basis of the designed scheme, a new equivalent circuit is formed, in which the resulting traction power circuit remains unchanged. The transformation of the initial circuit has enabled removing the error and calculating the short-circuit voltages in the traction network explicitly. Replacement of a symmetric three-phase external power supply system and a traction transformer with an equivalent single-phase circuit when calculating two-phase short-circuit currents in the traction network is shown to be viable. The validity of replacement of a symmetrical three-phase network for a single-phase one has been proved both by transformation of the three-phase equivalent circuit and by means of the equivalent generator method. It is established that, despite the difference in phase resistances of substations with Y/Δ and Y/Y transformer connection circuits, equations for determination of two-phase short-circuit currents prove to be the same.

Rotor inertia adaptive control and inertia matching strategy based on parallel virtual synchronous generators system

Active power oscillations and frequency fluctuations appear simultaneously in virtual synchronous generator (VSG) systems with fixed rotor inertia and damping coefficients. Thus, an optimisation control strategy to self-adjust the parameters is proposed in this study to suppress the power oscillations and frequency fluctuations. A small-signal model of parallel VSG systems is established, and the impact of rotor inertia and damping coefficients on the output active power is analysed. Then, the parameter optimisation control for the self-adjusting inertia and damping coefficients is introduced according to the rate of change and the deviation of virtual rotor electrical angular velocity. Notably, the changes and deviations are limited in a range to ensure the dynamic and steady-state performance of the system. Based on the principle of the equivalent synchronous generator, a virtual inertia matching method for parallel VSG systems is accordingly obtained. The feasibility of the proposed control method is verified by extensive simulations. The results confirm that this method can not only suppress the power oscillation in the transient connection of the VSGs to the AC bus, but also improve the frequency support. In turn, it ensures that the load power is proportionally distributed among the VSGs.

Online estimation of power system separation as controlled islanding scheme in the presence of inter-area oscillations

Abstract This paper presents an online scheme of wide area out of step protection of synchronous generators to controlled islanding of power system based on inter-area signals gathered from wide area measuring systems (WAMS) data. The proposed scheme provides an online criterion of critical splitting times for online estimation of both unstable inter-area oscillations and inter-area transient instability scenarios. In this regard, according to meaning of the center of inertia (COI), coherent generators are identified and represented as equivalent virtual generators within different oscillating areas. The proposed strategy is an extension of conventional RRdot relay from which by measuring the COI of inter-area rotor angle oscillation ( δ C O I ) within two oscillating areas, a new adaptive δ C O I - Δ δ C O I locus curve is extracted. For online prediction of both inter-area transient scenarios, two different curves are provided which by extending them within unit curve, the main inter-area relay zone is developed. The proposed strategy is an online and non model-based scheme from which the emergency decisions are obtained individually according to different operational and topological conditions. The proposed approach is studied within two different cases including modified IEEE 39 bus test system and a practical Iran national power grid from which considering some typical wide area out of step scenarios, the proposed scheme is evaluated within time domain simulations. Studies indicate the promising results of wide area out of step prediction in the presence of different types of inter-area oscillations.

Real-Time Transient Stability Assessment Using Dynamic Equivalents and Nonlinear Observers

This paper presents a new method for detecting the early stages of unstable conditions in large-scale power systems. A reduced order dynamic model is introduced for each control area that includes an aggregated generator and associated controllers. An innovative nonlinear observer proposed that can simultaneously estimate the parameters and states of the model benefiting from available online measurements. A sensitivity analysis is used to improve the efficacy and performance of the proposed estimator. The estimated states of the proposed equivalent generator model are then used to define a Real-Time Transient Stability (RTSA) index. The recommended RTSA index demonstrates to be a clear measure of the distance to instability and prevents economic losses due to blackouts and cascading system trips. The PSS/E simulation results on two case studies using show the excellent performance of the proposed index.

Passivity-Based Design of Sliding Modes for Optimal Load Frequency Control

This paper proposes a distributed sliding mode (SM) control strategy for optimal load frequency control (OLFC) in power networks, where besides frequency regulation, minimization of generation costs is also achieved (economic dispatch). We study a nonlinear power network of interconnected (equivalent) generators, including voltage and second-order turbine-governor dynamics. The turbine-governor dynamics suggest the design of a sliding manifold such that the turbine-governor system enjoys a suitable passivity property, once the sliding manifold is attained. This paper offers a new perspective on OLFC by means of SM control, and in comparison with the existing literature, we relax required dissipation conditions on the generation side and assumptions on the system parameters.

Research on Frequency Fuzzy Adaptive Additional Inertial Control Strategy for D-PMSG Wind Turbine

The traditional additional inertial control (T-AIC) strategy can provide frequency support for the directly-driven wind turbine with a permanent magnet synchronous generator (D-PMSG). However, due to the fixed control coefficients, the frequency modulation effect is poor under load and wind speed disturbances. In order to improve the frequency transient response of D-PMSG, a fuzzy adaptive additional inertial control strategy (FA-AIC) is proposed in this paper. A simplified D-PMSG model is established for the complexity and low calculation speed. A single-machine grid-connected system composed of a D-PMSG and an equivalent synchronous generator set (ESGS) is taken as the background and analysis of the principle of T-AIC. The proportional and derivative coefficient initial values in T-AIC are tuned by simulating the static characteristics and inertial response characteristics of the conventional synchronous generator set, and fuzzy control technology is introduced to adjust the proportional and derivative coefficients adaptively based on the frequency deviation and the frequency deviation change rate under load or wind speed disturbances. The simulation verification indicates that T-AIC, kinetic energy (KE)-based gain-AIC and FA-AIC all can utilize the D-PMSG additional inertial response to provide frequency support for grid-connected systems. Compared with T-AIC and KE-based gain-AIC, the proposed FA-AIC can not only provide more effective frequency support during load disturbances, but also suppress the frequency fluctuation caused by the wind speed variation and displays a better dynamic frequency regulation effect.

A Dynamic Equivalent Method for Electromagnetic Transient Simulation and Its Application in East China Power Grid

There is an inherent limitation when unbalanced faults in AC system are studied in large scale AC/DC power systems with electromechanical transient simulation. In order to make the electromagnetic transient simulation which is accurate in these situations possible, dynamic reduction must to be done. A method based on support strength of generators is proposed. According to the connection form of low-voltage network with 500kV skeleton buses and whether there are generators in it, three reduction schemes are used to replace the corresponding low-voltage network. The dynamic parameters of equivalent generators are obtained by a time domain aggregation method. The equivalent results of planning data of East China Power Grid in 2020 show that, the method has high accuracy in power flow analysis as well as short circuit calculation. The proposed method greatly simplifies the original system while the characteristic of dynamic response remains.

Power converter junction temperature measurement using infra‐red sensors

Studies demonstrate that the power converter has one of the highest failure rates in a wind turbine, with a key failure driver being the power module junction temperature ( T j ). This paper details an experimental setup for simplified emulation of wind turbine conditions on a power converter with infra-red sensing of IGBT T j . Results are compared to previous simulation work for a PMSG wind turbine, with the same trend of increasing mean T j with wind speed found, and the need to use an equivalent generator reactance in highlighted. A commercial-scale prototype for more accurate wind turbine converter emulation is also detailed.

A Novel Measurement-Based Dynamic Equivalent Model of Grid-Connected Microgrids

For transient stability studies of power systems with high penetration of microgrids, models of the connected microgrids must be used. In this paper, a novel dynamic equivalent model is proposed for grid-connected microgrids using measurement data of point of common coupling (PCC). The proposed equivalent model includes electrical components, such as synchronous generator (SG), voltage source converter (VSC), and active and reactive loads. The proposed equivalent model contains different controllers, such as excitation system, governor, and VSC's controllers. All SG-based distributed generation (DG) units of the microgrid are represented by one equivalent SG, while an equivalent VSC represents converters-based DGs. Similarly, a parallel active and reactive static load is considered in the equivalent model to represent the static loads of the microgrid. In order to make the equivalent model more efficient, accurate, and valid at different operating points, a series resistance and reactance are utilized to connect the equivalent generator to the PCC. The final goal is to identify the parameters of the equivalent components such that the equivalent model behaves as like as the detailed microgrid facing different disturbances. The identification procedure is carried out by means of a genetic algorithm using measurement data at the PCC. To show the effectiveness and accuracy of the proposed model, the identified equivalent model is studied at different operating points and the results are compared with the original detailed model.