Steady-state Equivalent Circuit Research Articles

Performance Evaluation and Dynamic Characteristics of a Self-Excited Induction Generator for Pico Hydro Power Plants

The dynamic performance of an isolated three-phase squirrel cage self-excited induction generator (SEIG) in a Pico Hydro Power Plant (PHPP) is examined in this work. The investigation is carried out with the help of MATLAB/Simulink for mathematical modeling and simulation of the proposed system under various operational situations. The SEIG model, which was created using the steady-state equivalent circuit approach, included the electrical, magnetic, and mechanical components of the SEIG and PHPP. The dynamic behavior of the SEIG is explored under a variety of operating situations. The effects of load variations, speed fluctuations, and other disturbances on the voltage and frequency of the generator are examined. The experiment results were used to validate the simulation results. This research has implications for the design and optimization of PHPP using SEIGs.

Analysis and Control of PWM Buck-Boost AC Chopper Fed Single-Phase Capacitor Run Induction Motor

Single phase capacitor-run induction motors (IMs) are used in various applications such as home appliances and machine tools; they are affected by the sags or swells and any fault that can lead to disturb the supply and make it produce rms voltage below or above the rated motor voltage, which is 220V. A control system is designed to regulate the output voltage of the converter irrespective to the variation of the load and within a specific range of supply voltage variation. The steady-state equivalent circuit of the Buck-Boost chopper type AC voltage regulator, as well as the analysis of this circuit are presented in this paper. Switching device for the regulator is an IGBT Module. The proposed chopper uses pulse width modulation (PWM) control technique to chop the input voltage into segments in order to guarantee rated rms voltage supplied to the load, which is capacitor-run induction motor. Proportional integral (PI) controller is used to obtain very small steady state error, stable and fast dynamic response, and robustness against variations in the line voltage. The complete system is simulated using software package, and the results are obtained to verify the proposed control method.

Improved Efficiency Optimization Control for Brushless Doubly Fed Induction Generator–DC System by Regulating Stator Frequency

Taking into account the relatively low efficiency of brushless doubly fed induction generator (BDFIG) at present, the efficiency optimization is important to promote the industrial application of BDFIGs. The power winding (PW) frequency of the BDFIG–dc system is with the additional freedom of control, which provides an important condition for efficiency optimization. In this article, based on the loss analysis of the power converter and the improved steady-state equivalent circuit of BDFIG considering iron loss, the loss model of BDFIG–dc system is derived. Furthermore, the system loss model is established with the PW frequency of BDFIG as the main state variable. From the proposed loss model, the maximum efficiency of BDFIG–dc system can be achieved by optimizing the PW frequency. The comprehensive simulation and experimental results demonstrate that proposed efficiency optimization control strategy can increase the efficiency of both the standalone and grid-connected BDFIG–dc systems by 0.2–7.8% under different operation conditions.

Vector-Controlled Dual Stator Multiphase Induction Motor Drive for Energy-Efficient Operation of Electric Vehicles

ABSTRACT This paper proposes an Indirect Field Oriented Controlled Dual Stator Multiphase Induction Motor (IFOC-DSMIM) as a traction unit in an Electric Vehicle (EV) for the enhancement of its fuel economy and average loading capacity. The performance of the drive is studied by loading it under standard drive cycles that include free running, acceleration, and braking conditions using the MATLAB/Simulink environment. Its performance analysis is carried out to obtain efficiency curves under the three modes of excitation using a steady-state equivalent circuit approach. Studies on load sharing between the two stators, speed tracking and torque-producing capability of the drive are executed on its dynamic model and the simulation results are depicted. The average energy efficiency of the vehicle with the proposed DSMIM drive system is at least 10% higher than a Single Stator Multiphase Induction Motor (SSMIM) drive under different load percentages. Furthermore, under 75% of rated load conditions the energy efficiency is 20% higher. Thus, the proposed DSMIM configuration promises to provide a sizeable energy saving in the EV system, reducing the energy cost and increasing the driving range.

Improved Moth Flame Optimization Approach for Parameter Estimation of Induction Motor

The effective deployment of electrical energy has received attention because of its environmental implications. On the other hand, induction motors are the primary equipment used in many industries. Industrial facilities demand the maximum percentage of energy. This energy demand is determined by the operating circumstances imposed by the internal characteristics of the induction motor. Because internal parameters of an induction motor are not immediately measurable, they must be obtained through an identification process. This paper proposed an improved version of moth flame optimization (IMFO) for the efficient parameter estimation of induction motors. A steady-state equivalent circuit of the induction motor is employed for the simulation. The proposed technique handles the parameter estimation problem better than moth flame optimization (MFO), particle swarm optimization (PSO), the flower pollination algorithm (FPA), the tunicate swarm algorithm (TSA), and the sine cosine algorithm (SCA). The anticipated IMFO reduces the cost function by 49.38% as compared with the basic version of MFO.

Design and Experimental Evaluation of an In-Wheel Flux-Switching Machine for Light Vehicle Application

Restrictive regulations regarding emissions and fossil fuel consumption lead to the electric vehicle being an alternative to replace conventional internal combustion engine vehicles. The pure electric powertrain technology and the charging infrastructure are still immature in some markets, where increasing the overall vehicle efficiency by energy harvesting means can be a more viable solution. This paper presents the design and experimental validation of an in-wheel flux-switching machine for regenerative braking in a light passenger vehicle. Later, the energy can be used for fuel handling and reforming, performance enhancement, increasing efficiency, and reducing emissions. Feasibility and technological challenges are also discussed. The Maxwell–Fourier method and a novel steady-state equivalent circuit presented in this paper are used for geometry sensitivity analysis and optimization routine.

An Efficient Air-Gap Flux Density Analysis Method for the Design of Induction Machines

The magnetic field distribution in the air gap is of great importance in the design of rotary machines. In this article, an efficient analytical method is presented, which is capable of plotting the air-gap flux density waveform of induction machines (IMs) less time-consuming than the finite element method (FEM) does. The proposed method, based on the product of the current linkage waveform and the permeance waveform, utilizes the calculations of the steady-state equivalent circuit to ensure the accuracy and an equivalent air-gap reluctance model to take into account both the slot opening effect and the rotor movement. The method is tested on a general IM with different load cases and different design parameters, and the results are compared to the FEM calculations. It can be concluded that the proposed analytical method is an efficient option in the motor design to investigate the influence of the parameters on the flux density distribution.

Performance analysis of single-phase interior permanent magnet synchronous motor

Single-phase permanent magnet synchronous motor has been tipped as an alternative to single-phase induction motor due to its high efficiency and torque density. Consequently, a proper performance analysis of the motor is required to cope with the stator imbalance in order to prevent pulsation in the torque performance. This paper presented the dynamic and steady-state analysis of a single-phase interior permanent magnet synchronous motor. In this analysis, a proper combination of direct-quadrature (d-q) reference frame, and symmetrical component analyses were used. The symmetrical components analysis was used to obtain the steady state performance while the dynamic performance was obtained from d-q analysis. The symmetrical components cope with the imbalance and hence the resulting torque pulsation which may results in heating of the motor. The results obtained agreed with the theoretical analysis and yielded a unique steady state equivalent circuit and phasor diagram. The models of the motor were simulated using MATLAB/Simulink. A prototype of the motor was developed and experimentation was carried out to validate the dynamic performance.

A new starting capability assessment method for induction motors in an industrial islanded microgrid with diesel generators and energy storage systems

Induction motor (IM) startup can cause voltage dip disturbances and is detrimental to the stable operation of industrial islanded microgrids. Firstly, this study investigates the active power characteristics of the diesel generator and battery energy storage system (BESS) with IM based on the steady-state equivalent circuit to determine the starting capability of an islanded microgrid. Then, the starting conditions and the stable feasible region of the diesel generator and BESS with IM are further deduced considering different mechanical power models. A new Starting Capability Index (SCI) for the IM of the islanded microgrid with diesel generators and BESS is proposed to assess the microgrid's overall starting capability and arrange the starting sequence during motor startup in different locations of islanded microgrids. Based on SCI, a strategy to determine the starting sequence of multiple IMs in the islanded microgrid is proposed to improve the quantities of IM startups and the microgrid's dynamic performance. Two cases of an islanded microgrid with diesel generators and BESS are tested using MATLAB/ SIMULINK to verify the effectiveness of the proposed methods.

Optimal Design of a Short Primary Double-Sided Linear Induction Motor for Urban Rail Transit

Linear induction motors (LIMs) have been widely used in rail transit. However, Due to the breaking of the primary core and the large air gap, the efficiency and power factor of LIMs are seriously damaged, causing a large amount of energy waste. To improve the efficiency and power factor of LIMs for urban rail transit, we present a new optimization method for the design of a short primary double-sided linear induction motor (SP-DLIM) with a rated speed of 45 km/h and small thrust. The method is based on a steady state equivalent circuit model and the differential evolutionary algorithm (DEA). Moreover, the design constraints and the objective functions are proposed for the optimization problem. Finally, the optimized SP-DLIM is simulated by 2D transient finite element method (FEM). The 2-D transient FEM results verify the accuracy of the optimization method proposed in this paper.

Design and performance analysis of a dual stator multiphase induction motor using finite element method

A new Dual Stator Multiphase Phase Induction Motor (DSMIM) configuration is proposed and described in this paper. Steady state equivalent circuit of DSMIM is developed and its performance parameters are calculated. The efficiency curves plotted under different excitation modes of the machine assists in operating it at a better efficiency for wider load range. Thus, the proposed configuration can be utilized in Electric Vehicles (EV) to efficiently support a sudden load change during acceleration, cruising and uphill driving patterns. A Finite Element Method (FEM) based design of the machine is done using MAGNET software. The electromagnetic performance of DSMIM is analyzed through the flux patterns obtained at different excitation modes. Its electromechanical performance is studied by analyzing the current, torque and speed developed under load driven conditions. The article also proposes an ideology behind the mechanical arrangement of DSMIM for fabrication. The simulation results are included to illustrate the performance of DSMIM. The results are compared and validated with the analytical results obtained through equivalent circuit approach.

A Steady-State Equivalent Circuit of TSCAOI Configured Induction Generator for Renewable Energy Conversion Systems

3-phase cage induction machines, operated in two series-connected and one-isolated (TSCAOI) winding configuration, have been proposed to generate standalone single-phase electricity at variable speeds for renewable energy conversion systems. However, the steady-state behaviour and performance of this particular generator are not yet to be theoretically investigated. This paper therefore presents the first theoretical investigation based on the steady-state equivalent circuit model for standalone TSCAOI configured generators. Moreover, this paper is the first to adopt the winding function approach to derive a dynamic mathematical model for TSCAOI configured generators. This approach not only eliminates the cumbersome mathematical manipulation required in all previous papers related to TSCAOI configured generators but also provides a visual insight into the resulting winding distribution of the machine. In order to investigate the load and excitation characteristics pertinently, the dynamic model is transformed into two different equivalent circuit models by appropriate selected transformation matrix. Using these two models, this paper identified the impacts of system parameters on the load and excitation characteristics, as well as on the level of voltage unbalance. Experimental results of a prototype generator under various operating conditions are presented, together with simulated results, to demonstrate the accuracy of the proposed investigations.

Generalized Formulation of Steady-State Equivalent Circuit Models of Grid-Forming Inverters

Abstract: This work proposes positive- and negative-sequence equivalent circuits of grid-forming inverters for steady-state analysis. The proposed models are especially attractive for performing long-duration voltage regulation analysis and short-circuit studies involving grid-forming inverters. Our proposed equivalent circuit models are based on the inverter’s voltage and current control loops in the αβ and dq frames. For this reason, they operate according to prescribed control functions and specified impedances (i.e., filter impedance, current limiter block, virtual admittance block, and PI/PR controller block). The equivalent circuit model accuracy is validated by comparing system steady-state voltage and current responses obtained by detailed time-domain models in PSCAD/EMTDC to those by the equivalent circuit models implemented in steady-state load flow program (e.g., OpenDSS). Two distinct control structures implemented in the αβ and dq frames are used for the validation. Single line-to-ground and line-to-lineto-ground faults are simulated in a small islanded microgrid as well as the IEEE 34-node test feeder. Fault impedances varying from 0 to 5 ohms are simulated. We show that the equivalent models precisely replicate the steady-state response of the detailed time-domain models.

Review of Steady-State Electric Power Distribution System Datasets

Publicly available grid datasets with electric steady-state equivalent circuit models are crucial for the development and comparison of a variety of power system simulation tools and algorithms. Such algorithms are essential to analyze and improve the integration of distributed energy resources (DERs) in electrical power systems. Increased penetration of DERs, new technologies, and changing regulatory frameworks require the continuous development of the grid infrastructure. As a result, the number and versatility of grid datasets, which are required in power system research, increases. Furthermore, the used grids are created by different methods and intentions. This paper gives orientation within these developments: First, a concise overview of well-known, publicly available grid datasets is provided. Second, background information on the compilation of the grid datasets, including different methods, intentions and data origins, is reviewed and characterized. Third, common terms to describe electric steady-state distribution grids, such as representative grid or benchmark grid, are assembled and reviewed. Recommendations for the use of these grid terms are made.

Fault Current Analysis of Type-3 WTs Considering Sequential Switching of Internal Control and Protection Circuits in Multi Time Scales During LVRT

As Type-3 wind turbine (WT) has already become a typical type of highly penetrated power sources in modern power systems, characterizing its properties during grid fault is a basic requirement for system analysis. However, many significant factors have not been considered in the existing analytical methods and results, such as various switching of internal control and protection circuits in low voltage ride through (LVRT) solutions. In this paper, performance of Type-3 WT during LVRT is first illustrated and summarized as the sequential switching characteristic in multi time scales, viz., instant control, ac control, dc voltage control, and rotor speed control time scales. Thus, for magnitude drops in stator voltage, a mathematical model is proposed to understand this characteristic and fault current analysis's features. Then, an analytical method, based on the operational inductance, is proposed so that fault current components, with the sequential switching considered, can be depicted with a unified and simple analytical expression. By identifying magnitude of symmetrical current, the transient and steady-state equivalent circuits of Type-3 WT are proposed to estimate momentary current and electrical power approximately. Finally, analytical results are verified by comparisons with real-time simulation results of a detailed 1.5 MW WT model in RT-LAB.

Effect of DC-Link Voltage Limitation on Postfault Steady-State Performance of Asymmetrical Six-Phase Induction Machines

The asymmetrical six-phase induction machine represents the most common multiphase machine type used in many high-power industrial applications. While a body of research covering control of the machine under fault conditions has been published in the literature, corresponding studies to investigate the dc-link voltage design requirements under postfault operation in a simple and efficient manner have not met the same interest. To this end, this paper first introduces the machine steady-state equivalent circuit under one open-phase fault, which simplifies the estimation of different machine characteristic curves instead of using tedious mathematical techniques. As far as the machine parameters are concerned in this paper, a modified locked-rotor test based on the derived equivalent circuit is also proposed to fully estimate the parameters of different subspaces using a simple technique without the need for additional tests. The proposed steady-state circuit is also used to understand the effect of the secondary subspace impedance, neutral configuration, and the postfault control strategy on the maximum achievable torque for a limited dc-bus voltage. The minimum dc-link voltage magnitude to provide rated output under postfault operation is also given. The proposed concepts have been experimentally verified using a prototype asymmetrical six-phase machine.

Voltage Oriented Decoupled Control Scheme for DFIG’s Grid Side Converter

This paper proposes a novel voltage oriented decoupled control scheme for the DFIG’s Grid Side Converter (GSC) of a 2.3Mw, 690V, 50Hz, 6 pole doubly-fed induction generator (DFIG) based wind generation system. For Rotor Side Converter (RSC), slip and constant V/Hz control scheme along with a feedback control via PWM is selected but not explained in this paper.Based on the per-phase steady state equivalent circuit model of a DFIG, relationship between stator and rotor voltages is developed. Voltage oriented decoupled control scheme for GSC is designed in such a way that it can keep the dc link voltage constant by regulating grid reactive power when required. The space vector modulation (SVM) algorithm is explained breifly and implemented for the two-level GSC. MATLAB/SIMULINK (R2015a) software validates the proposed control scheme for GSC.

Iron Loss Prediction Using Modified IEM-Formula during the Field Weakening for Permanent Magnet Synchronous Machines

During field weakening operation time (FWOT), the total iron loss rises and affects the accuracy of loss prediction and efficiency, especially if a large range of FWOT exists due to a large voltage drop that was rooted from the resistance of the used material. Iron loss prediction is widely employed in investigations for a fast electrical machine analysis using 2D finite element analysis (FEA). This paper proposes harmonic loss analytically by a steady-state equivalent circuit with a novel procedure. Consideration of skin effects and iron saturation are utilized in order to examine the accuracy through the relative error distribution in the frequency domain of each model from 50 to 700 Hz. Additionally, this comparative study presents a torque-frequency-field density calculation over each single term of the modified institute of electrical machines formula (IEM-Formula). The proposed analytical calculation is performed using 2D FEA for a classic and modified IEM-Formula along with experimental verifications on a surface-mounted permanent magnet synchronous generator (PMSG) for a wind generation application.

Dynamic and steady state modeling of permanent magnet induction machine

PurposeModeling electric machines is one of the powerful approaches for analyzing their performance. A dynamic model and a steady-state model are introduced for each electric machine. Permanent magnet induction machine (PMIM) is a dual-rotor electric machine, which has various advantages such as high-power factor and low magnetizing current. Studying PMIM and its modeling might be valuable. The purpose of this paper is to introduce a simple and accurate method for dynamic and steady-state modeling of PMIM.Design/methodology/approachIn this paper, arbitrary dqo reference frame is used to model PMIM. First, three-phase dynamic equations of stator and rotors are introduced. Then, they are transferred to an arbitrary reference frame. The voltage and magnetic flux equations aligned at dqo axes are obtained. These equations give the dynamic model. To investigate the results, PMIM simulation is performed according to obtained dynamic equations. Simulation results verify the analytic calculations.FindingsIn this paper, dynamic equations of PMIM are obtained. These equations are used to determine dynamic equivalent circuits of PMIM. Steady-state equations and one phase equivalent circuit of the PMIM using phasor relations are also extracted.Originality/valuePMIM equations along dqo axes and their dynamic and steady-state equivalent circuits are determined. These equations and the equivalent circuits can be transformed to different reference frames and analyzed easily.

An Analytical Method for Probabilistic Modeling of the Steady-State Behavior of Secondary Residential System

Effective modeling of secondary residential system is critical for numerous demand side innovations in smart grid, such as distributed generation and energy storage integration, residential micro-grid operation, and demand response programs. Traditionally, Monte Carlo simulation (MCS) method is used to establish the model by capturing the random usage patterns of home appliances. Yet, the computational effort is tremendous, especially for a large group of residential loads. To address this issue, an analytical method is proposed in this paper. The result is a time varying probabilistic steady-state equivalent circuit model whose parameters are characterized by means and covariance matrices. The proposed method consists of three main components with regard to the derivation of state probability distributions for individual appliances, modeling of aggregated secondary feeder with all appliances, and unscented transformation to combine the aggregated secondary feeder model and service transformer model. The effectiveness and efficiency of the proposed method are evaluated based on extensive numerical results and by comparing the results with that obtained by MCS method.