Speed-sensorless torque control of induction machine based on carrier signal injection and smooth-air-gap induction machine model

A speed-estimation technique for induction machines, based on carrier signal injection and the standard two-axis smooth-air-gap induction machine model, is presented. The proposed speed-estimation technique can work over a wide range of operating points, including fundamental dc excitation. The stability of the algorithm is analyzed using a two-time-scale approach. Based on the estimated rotor speed, a torque controller is designed. Experimental results are presented confirming the validity of this approach. A method to reduce torque ripple generated by the injected carrier signals is also introduced.     

Modeling and control of a wind turbine driven doubly fed induction generator

This paper presents the simulation results of a grid-connected wind driven doubly fed induction machine (DFIM) together with some real machine performance results. The modeling of the machine considers operating conditions below and above synchronous speed, which are actually achieved by means of a double-sided PWM converter joining the machine rotor to the grid. In order to decouple the active and reactive powers generated by the machine, stator-flux-oriented vector control is applied. The wind generator mathematical model developed in this paper is used to show how such a control strategy offers the possibility of controlling the power factor of the energy to be generated.     

Analysis of a single-phase induction machine with a shiftedauxiliary winding

This paper extents the method of multiple reference frames to the analysis of asymmetrical induction motors with nonorthogonal stator windings, with particular emphasis on the permanent split capacitor (PSC) machine. The predictions of the method are verified by comparison to both experimental results and to results obtained using a machine variable computer simulation. Once verified, the method is used to derive the transfer function relating rotor speed to load torque disturbance, which is of particular interest when analyzing PSC machines driving compressor loads. It is shown that the transfer function exhibits a distinct resonant point, and that the magnitude of the resonant peak increases as the motor approaches synchronous speed. It is also shown that the magnitude of the resonant peak may be lowered by increasing rotational inertia or rotor resistance     

Compensation of network voltage unbalance using doubly fed induction generator-based wind farms

A control strategy for compensating AC network voltage unbalance using doubly fed induction generator (DFIG)-based wind farms is presented. A complete DFIG dynamic model containing both the rotor and grid side converters is used to accurately describe the average and ripple components of active/reactive power, electromagnetic torque and DC bus voltage, under unbalanced conditions. The principle of using DFIG systems to compensate grid voltage unbalance by injecting negative sequence current into the AC system is described. The injected negative sequence current can be provided by either the grid side or the rotor side converters. Various methods for coordinating these two converters are discussed and their respective impacts on power and torque oscillations are described. The validity of the proposed control strategy is demonstrated by simulations on a 30 MW DFIG-based wind farm using Matlab/Simulink during 2 and 4% voltage unbalances. The proposed compensation strategy can not only ensure reliable operation of the wind generators by restricting torque, DC link voltage and power oscillations, but also enable DFIG-based wind farms to contribute to rebalancing the connected network.     

Genetic algorithm-based induction machine characterization procedure with application to maximum torque per amp control

There has been considerable research in developing improved induction motor models. One recently developed model simultaneously includes magnetizing path saturation, leakage saturation, and a highly flexible transfer function approach to represent the rotor circuits. This alternate QD model (AQDM) is also computationally efficient in that it is noniterative at each time step. It is considerably more accurate than the classical QD model (CQDM). However, the suggested characterization procedure is complicated and time consuming. This paper proposes a new characterization procedure for the AQDM. The proposed procedure employs a genetic algorithm (GA) as an optimization engine to identify the parameters of the AQDM by simultaneously considering per-phase fundamental frequency impedance and stand-still frequency response (SSFR) impedance. The proposed approach is validated by comparison of current ripple predictions (to validate high-frequency model behavior) and by application to maximum torque per ampere control design (to validate fundamental frequency model behavior). The proposed procedure is significantly more straightforward than the other published method of obtaining AQDM parameters.     

Voltage-frequency control of a self-excited induction generator

A new strategy for controlling voltage and frequency of a self excited induction generator (SEIG) is presented. The SEIG operates in the linear region of the core magnetizing curve, so that efficiency and performance are upgraded. An external excitation circuit, comprising permanently connected capacitors and electronically switched inductances is used. The external circuit allows to compensate for the generator reactive demand. A detailed analysis is performed, showing some salient aspects related to the connection of the external excitation circuit on the control performance. Asynchronous switching is used, but some important considerations must be taken into account related to the instantaneous phase angle between stator voltage and external inductor current at the switching instant, if good transient response is desired. Sliding mode controllers are proposed, showing good dynamic response and robust behavior upon changes in load and generator parameters. Computer simulations are used to demonstrate the validity of the proposed scheme     

Modeling a ground-coupled heat pump system by a support vector machine

This paper reports on a modeling study of ground coupled heat pump (GCHP) system performance (COP) by using a support vector machine (SVM) method. A GCHP system is a multi-variable system that is hard to model by conventional methods. As regards the SVM, it has a superior capability for generalization, and this capability is independent of the dimensionality of the input data. In this study, a SVM based method was intended to adopt GCHP system for efficient modeling. The Lin-kernel SVM method was quite efficient in modeling purposes and did not require a pre-knowledge about the system. The performance of the proposed methodology was evaluated by using several statistical validation parameters. It is found that the root-mean squared (RMS) value is 0.002722, the coefficient of multiple determinations (R²) value is 0.999999, coefficient of variation (cov) value is 0.077295, and mean error function (MEF) value is 0.507437 for the proposed Lin-kernel SVM method. The optimum parameters of the SVM method were determined by using a greedy search algorithm. This search algorithm was effective for obtaining the optimum parameters.The simulation results show that the SVM is a good method for prediction of the COP of the GCHP system. The computation of SVM model is faster compared with other machine learning techniques (artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS)); because there are fewer free parameters and only support vectors (only a fraction of all data) are used in the generalization process.     

Analysis of the induction machine parameter identification

This paper analyzes the numerical identifiability of the electrical parameters of induction machines. Formulations of the single and double-cage induction machine, with and without core-losses in both models, are developed. The impossibility of identifying all the parameters of these models when only external measurements (voltage, current, speed and torque) are used is shown. One proposed solution is the formulation of machine equations by using the minimum number of parameters (which are identifiable parameters). As an application example, the parameters of a double-cage induction machine are identified using steady-state measurements corresponding to different angular speeds     

PMSG发电系统不平衡电网下网侧变流器控制研究

文章通过对电网不平衡情况下风力发电系统的分析,提出了以抑制负序不平衡电流为主要控制方法的网侧变流器控制策略。为维持不平衡下直流母线电压的稳定,提出电流微分前馈的控制方法,结合以上两点控制方法设计出电网不平衡下永磁直驱风力发电系统网侧变流器综合控制策略,该控制方法结构相对简单、有效,并具有一定的低电压穿越能力。最后在Matlab/Simulink下仿真验证了3 MW永磁直驱风机控制的有效性。     

Modeling and control of a SOFC-GT-based autonomous power system

In this article, a dynamic, lumped model of a solid oxide fuel cell (SOFC) is described, as a step towards developing control relevant models for a SOFC combined with a gas turbine (GT) in an autonomous power system. The model is evaluated against a distributed dynamic tubular SOFC model. The simulation results confirm that the simple model is able to capture the important dynamics of the SOFC and hence it is concluded that the simple model can be used for control and operability studies of the hybrid system. Several such lumped models can be aggregated to approximate the distributed nature of important variables of the SOFC. Further, models of all other components of a SOFC-GT-based autonomous power system are developed and a control structure for the total system is developed. The controller provides satisfactory performance for load changes at the cost of efficiency.     

An induction machine model for predicting inverter-machineinteraction

The conventional qd induction motor model typically used in drive simulations is very inaccurate in predicting machine performance, except perhaps for the fundamental component of the current and the average torque near rated operating conditions. Predictions of current and torque ripple are often in error by a factor of two to five. This work sets forth an induction machine model specifically designed for use with inverter models to study machine-inverter interaction. Key features include stator and rotor leakage saturation as a function of current and magnetizing flux, distributed effects in the rotor circuits, and a highly computationally efficient implementation. The model is considerably more accurate than the traditional qd model, particularly in its ability to predict switching frequency phenomena. The predictions of the proposed model are compared with those of the standard qd model and to experimental measurements on a 37 W induction motor drive     

Hybrid-secondary uncluttered induction (HSU-I) machine

A new hybrid-secondary uncluttered induction (HSU-I) machine is introduced. The hybrid secondary includes the effective-resistance, inverter, and magnetic switch options. The rotor current is magnetically coupled to the stator through an uncluttered rotating transformer. This machine can be used as a cost-effective slip-energy-controlled adjustable-speed induction motor that operates below synchronism and the wide speed-range motor drives and generators that operate below and above the synchronous speed of the line frequency     

Doubly fed induction machine state variables model and dynamicresponse

A state variables model in terms of d-q component displacements is deduced from linearized complex variable equations describing small-signal dynamic performance of the doubly fed induction machine. A state variables model in terms of magnitude and phase displacements of both stator and rotor voltages is deduced and studied. Transfer functions are also described. Study of the dynamics shows that the regions of instability are influenced by the variations of speed, of RMS value, and of phase angle of rotor applied voltage. This state variables model in polar coordinates eliminates the computations for the intermediate d-q components     

Transient thermal characteristics of induction machine rotor cage

Thermal analysis of an induction machine cage rotor during stall conditions forms an important part of design calculations. The study of rotor circuit thermal behavior is also useful to identify causes of failure in large cage rotor induction machines. The authors present a three-dimensional finite-element-based electrical-thermal analysis of the bar and end-ring area of a large rotor to examine its thermal characteristics during a stall. Details of temperature variations at key locations in the bar and end ring are provided. The calculations are compared to experimental results, and the advantages and limitations of the solution technique for rotor analysis are discussed     

Modeling and simulation of saturated induction motors in phasequantities

This paper proposes a new model for saturated induction motors. The saturation effects are incorporated in the magnetizing inductance and the stator mutual inductances, taking into account the nonuniform distribution of magnetic saturation within the motor core. The proposed model can be used to analyze the manner in which the induction motors interact with the supply network or power source, since it can predict the motor current/voltage harmonics produced by magnetic saturation. Experimental tests show that the proposed model represents with reasonable accuracy (8%) the motor saturation effects at nominal stator voltage as well as for overvoltage operation     

Unbalanced transients-based maximum likelihood identification of induction machine parameters

The paper describes an effective formulation of a maximum-likelihood identification algorithm for linear estimation of the equivalent-circuit parameters of cage-type (single cage and double cage) or deep-bar induction motors with measurement and process noises. A complete generalized model for symmetrical and asymmetrical test analysis of induction machines is developed for this purpose. The paper outlines the theory and reasoning behind the proposed statistical-based treatment of online data derived from generalized least-squares estimator and a Kalman filter. The method is successfully applied to online double-line independent finite-element (FE) short-circuit-simulated records of a deep-bar-type induction motor.     

Optimal design of a multi-stage capsule handling multi-phase pipeline

Based on the least-cost principle, a methodology has been developed for the determination of the optimal size and optimal spacing between two successive pumping stations of an inclined up or down spherical capsule pipeline. The analysis indicates that the optimum diameter increases with increase in throughput as well as specific gravity of the capsule, whereas the optimum spacing has a trend opposite to that of optimum diameter. The capsule velocity is found to decrease with increase in capsule specific gravity and is always within the prescribed practical limits. As one would expect, the friction factor increases with increase in specific gravity of the capsule; however, in each case it decreases with increase in Reynolds number. The procedure can be applied to obtain the optimal size of the fluid pipeline by simply dropping the cost of the capsule term from the total cost. The procedure outlined is of a versatile nature and can be used for the design of the cylindrical capsule pipeline as well.     

Steady and transient states thermal analysis of a 7.5-kW squirrel-cage induction machine at rated-load operation

The lumped-parameter thermal model is used to predict both the steady-state and transient solution to the temperatures within a 7.5-kW induction machine. The system of nonlinear ordinary differential equations and algebraic equations which describe the thermal behaviour of the machine in transient and steady states, respectively, were solved numerically using the Fourth-order Runge-Kutta method and the Gauss-Siedel method, respectively. The model performance is validated by experimental measurements on the test machine at rated load operation. The results show that there is a good agreement between the measured and predicted steady and transient states temperatures at rated load condition.     

Modeling and control of a wind fuel cell hybrid energy system

This paper describes a hybrid energy system consisting of a 5 kW wind turbine and a fuel cell system. Such a system is expected to be a more efficient, zero emission alternative to wind diesel system. Dynamic modeling of various components of this isolated system is presented. Selection of control strategies and design of controllers for the system is described. Simnon is used for the simulation of this highly nonlinear system. Transient responses of the system for a step change in the electrical load and wind speed are presented. System simulation results for a pre-recorded wind speed data indicates the transients expected in such a system. Design, modeling, control and limitations of a wind fuel cell hybrid energy system are discussed.     

Modelling and control of a marine current turbine-driven doubly fed induction generator

This paper deals with the modelling and control of a variable speed doubly fed induction generatorbased marine current turbine with and without tidal current speed sensor. The proposed maximum power point tracking control strategy relies on the resource and the marine turbine models that were validated by experimental data. The sensitivity of the proposed control strategy is analysed regarding the swell effect because it is considered as the most disturbing one for the resource model. Tidal current data from the Raz de Sein (Brittany, France) are used to run simulations of a 7.5-kW prototype over various flow regimes. Simulation results are presented and fully analysed.