Experimental characterization procedure for use with an advanced induction machine model

An advanced induction motor model that includes stator leakage saturation, rotor leakage saturation, magnetizing saturation, and distributed system effects in the rotor circuits has been set forth. This model is considerably more accurate than traditional models, particularly in terms of predicting switching-frequency dynamics. The model proposed is very general in terms of the range of magnetic properties that can be incorporated. This paper provides suggestions for specific forms for the leakage and magnetizing characteristics and derives the resulting small-signal impedance and large-signal steady-state equivalent circuit. Based on these results, a test procedure for experimentally characterizing the machine is developed. The application of the procedure to a 50-hp test machine is included as an example.     

Passivity-based sliding mode position control for induction motor drives

In this paper, a passivity-based sliding-mode controller is proposed to control the motion of an induction motor. At first, the induction motor is proved to be a state strictly passive system. Then, a sliding-mode position controller with an adaptive load torque estimator is designed to control the position of the induction motor such that the chattering effects associated with a classical sliding-mode position controller can be eliminated. The stability analysis of the overall position control system is carried out by the passivity theory. The proposed approach is robust with regard to variations of motor mechanical parameters and load torque disturbances. Finally, experimental results are included to demonstrate that good position tracking can be obtained without the rotor flux observer.     

Impact of cross-saturation on accuracy of saturated inductionmachine models

Cross-saturation in smooth air-gap AC machines has been a subject of controversy in the 1980s. The discussions were based on the model of a saturated AC machine with d-q axis winding currents acting as state-space variables. The recently introduced concept of generalised flux and generalised inductance has enabled the derivation of a series of models of saturated smooth air-gap AC machines for various selections of state-space variables. All the models, except for the winding flux model, contain explicit terms that describe cross-saturation. The aim of this paper is to compare behaviour of various models when cross-saturation is neglected. Two transients of a single-cage induction machine are analysed: motor starting with increased voltage; and induction generator self-excitation. Some experimental results are included. It is shown that the impact of cross-saturation on accuracy depends on the type of the model. All the models that ask for a time derivative of the generalised inductance yield poor results if cross-saturation is neglected. However, the models that require a time derivative of the inverse of the generalised inductance are basically unaffected. Thus these models can be simplified without any loss of accuracy     

Angle of attack distribution on wind turbines in yawed flow

This paper presents a new approach to model the induction for wind turbines in yawed flow to find the effective angle of attack distribution along the blades. There is an inherent difficulty in determining the angle of attack required by aeroelastic codes as input to tabulated airfoil data. Unlike two‐dimensional (2D) conditions where the angle of attack is the angle between the unperturbed flow and the airfoil chord, for the rotating blade, the incoming flow is bended because of rotation and affected by the induction of the blade circulation and the tip and root vortices, making the definition of the angle of attack uncertain. In this work, the analogy with 2D potential flows suggests that a coupling term between the unperturbed geometric angle of attack and the unitary velocity in the radial direction should be included to calculate the effective angle of attack seen by the blade strips. The model introduces two radially dependent interferences on the geometric angle, obtained from axial flow conditions that give the effective angle of attack under arbitrarily yawed flow conditions. The model gives a uniform treatment to the radial flows associated with yawed conditions or coned rotors and can be applied directly to calculate the effective angle of attack distribution on coned rotors in yawed flow. The accuracy of the method compares with results obtained from conventional or higher degree of complexity methods. The model can be incorporated into blade element momentum theory codes as an option to calculate angle of attack distributions. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal efficiency analysis of induction motors fed byvariable-voltage and variable-frequency source

The authors discuss the efficiency analysis and experimental data for an induction motor fed by a variable-voltage and variable-frequency (VVVF) source. Nonideal factors (core saturation, source harmonics, and skin effect) affecting the efficiency are included in the analysis to yield practical results from computer simulation. Based on the simulated results, an experimental system, composed of a DC link power converter with a VVVF feature, a dynamometer and a PC/AT, was developed to evaluate the efficiencies of the induction motor from low to rated speed and torque. Both analysis and experimental results indicate that the efficiency with VVVF is superior to that of constant flux operation. Experimental results showed that 10-15% improvement in the efficiency of a 2 hp induction motor at 0.4 per unit load using VVVF can be achieved as compared to the constant flux operation     

A Hybrid Converter System for High-Performance Large Induction Motor Drives

A hybrid converter system employing a combination of a load-commutated inverter (LCI), a dc–dc buck converter, and a voltage-source inverter (VSI) is proposed for the large induction motor drives. The VSI ensures the safe commutation of the LCI with active commutation angle control over all speed regions. By replacing capacitor banks and a forced dc-commutation circuit, this system can eliminate all drawbacks related to these circuits in the conventional LCI-based induction motor drives. Sinusoidal motor current and voltage waveforms are achieved with the VSI providing the reactive and harmonic power to the motor, resulting in high-performance drives. The buck converter enables both the VSI and the LCI to be fed from the single-diode rectifier. As a result, the dc-link inductor size can be reduced and the LCI is operated without the controlled rectifier. In addition, faster dynamic response can be obtained through the VSI and the buck converter operation. Finally, the buck converter performs the dc-link current control to ensure minimum VSI rating. The feasibility of the proposed hybrid circuit for the high-power drive systems is verified by computer simulation for a 500-hp induction motor. Experimental results are also included for a 1-hp induction motor laboratory setup controlled by the proposed hybrid system.     

Decomposed, Reduced Order Model for Double-Cage Induction Machines

A method is presented and validated for increasing the computational efficiency in simulating double-cage induction machines where stator transients are to be included. Iterative decomposition is used to separate the flux-linkage equations into decoupled fast and slow subsystems, after which the model order of the fast subsystem is reduced by neglecting the heavily damped fast transients caused by the starting cage. The two decoupled subsystems along with the equation for the very slowly changing slip constitute a three time-scale model for the machine which resulted in more than doubling computational speed.     

Validation and modification of the Blade Element Momentum theory based on comparisons with actuator disc simulations

A comprehensive investigation of the Blade Element Momentum (BEM) model using detailed numerical simulations with an axis symmetric actuator disc (AD) model has been carried out. The present implementation of the BEM model is in a version where exactly the same input in the form of non‐dimensional axial and tangential load coefficients can be used for the BEM model as for the numerical AD model. At a rotor disc loading corresponding to maximum power coefficient, we found close correlation between the AD and BEM model as concerns the integral value of the power coefficient. However, locally along the blade radius, we found considerable deviations with the general tendency, that the BEM model underestimates the power coefficient on the inboard part of the rotor and overestimates the coefficient on the outboard part. A closer investigation of the deviations showed that underestimation of the power coefficient on the inboard part could be ascribed to the pressure variation in the rotating wake not taken into account in the BEM model. We further found that the overestimation of the power coefficient on the outboard part of the rotor is due to the expansion of the flow causing a non‐uniform induction although the loading is uniform. Based on the findings we derived two small engineering sub‐models to be included in the BEM model to account for the physical mechanisms causing the deviations. Finally, the influence of using the corrected BEM model, BEM_cor on two rotor designs is presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Symbolically aided model development for an induction machine in virtual test bed

A new phase-domain induction machine model for use in power system dynamic simulation is developed with the aid of a symbolic tool. The symbolic tool can automatically construct a time-domain power system component model in the resistive companion form (RCF) that is widely used in time-domain simulators. The automatic differentiation technique (ADT) is utilized within the context of a symbolic modeling language, and the tool has been implemented for the virtual test bed (VTB) simulation environment. The new induction machine model was used to study start-up transients of an induction motor. The new model was verified by comparing the simulation results to those obtained from a standard d-q model. This paper also demonstrates that a symbolically assisted technique can provide an efficient and rapid path for developing complex nonlinear device models for power system simulations.     

Simulation of induction machinery for power system studies

A simple, fast, and accurate algorithm for determining induction-machine transient behavior is presented. The differential equations for the full-order model of induction machines are simplified and solved using linear system techniques. Examples show that the algorithm is accurate for large disturbances and requires as little as 29% of the CPU time required by the full-order model. The algorithm may offer computational advantages in some studies of large-scale power systems where the detailed induction machine models can not be used due to the complexity of the overall system and where the overall CPU time may be costly     

Investigation of capacitor-excited induction generators and permanent magnet alternators for small scale wind power generation

This paper examines two electric generator options for use in autonomous wind systems producing asynchronous electric power. The first makes use of a capacitor-excited squirrel-cage induction generator feeding a battery bank and an induction motor driven centrifugal pump. The second uses a permanent magnet alternator. Results obtained from field tests and laboratory experiments are included.A model to calculate the wind energy captured by a commercial 5 kW wind turbine, used in the field tests, is presented. This information is then used in a cost benefit analysis based on the present value method.     

Machine modeling and universal controller for vector-controlled induction motor drives

Developments of machine model and a universal controller for vector-controlled induction motor drives are presented in this paper. The machine representations associated with vector-control methods referring to various frames, including stator, rotor, and air-gap flux frames, can be derived simply by selecting different state variables; thereby clearly identifying the relationship between machine modeling and vector control. Moreover, a universal vector controller for induction motor drives fed by a voltage-controlled voltage source inverter is presented. It is shown in this paper that various vector controllers, including rotor flux-oriented controller, stator flux-oriented controller and air-gap flux-oriented controller, can be realized by simply changing few parameters. It is demonstrated by experimental results that the developed universal vector controller for various vector-control approaches can be implemented using the same hardware with a minor change to software associated with parameters; and thereby confirming the theoretical analysis.     

Transient Modeling and Parameter Estimation of Field Aligned Starting

Field aligned starting (FAS) is a new technique for starting three-phase cage induction motors on single-phase supply lines with minimal inrush currents. It uses a simple energy storage system to generate a very high impulsive torque by which the motor is started before being connected to the mains supply. The spinning motor can then be connected to the mains to operate in a standard Steinmetz connection without incurring high inrush currents, if the moment of mains connection is properly timed. This paper presents a transient model and an accompanying parameter estimation method through which the transient behavior of three-phase induction motors operated with FAS can be analyzed. The proposed model is based on instantaneous symmetrical components and is used to investigate a 3 kW motor started under various operating conditions. The proposed parameter estimation method and the developed transient model are both validated by experimental results.     

A transient induction motor model including saturation and deep bareffect

Transient cage induction motor models for use in inverter-fed drives and controllers are reviewed. A simple transient model is presented that includes rotor deep bar effect and magnetic saturation of the magnetising and rotor leakage flux paths. The improved model requires motor details in the form of simple impedance versus frequency characteristics which can be obtained from a variety of external sources. These can range typically from detailed steady-state finite-element solutions to simple experimental measurements. The model is verified experimentally using a 75 kW, 4 pole vector controlled AC motor drive     

Comparison of a CFD Analysis and a Thermal Equivalent Circuit Model of a TEFC Induction Machine With Measurements

For a totally enclosed fan-cooled induction machine, two methods of numerical analysis are compared with measurements. The first numerical method is based on computational fluid dynamics (CFDs) and the second one uses a thermal equivalent circuit (TEC). For the analysis based on CFD, a 3-D induction machine including housing is modeled. The numeric solution of the flow equations is determined for stationary temperature distributions. For the TEC, a discretized one-and-a-half-dimensional model of the induction machine is considered. With the TEC model, stationary and transient operating conditions can be simulated. Measurement results are determined by iron–copper–nickel sensors embedded in the stator winding and the housing, as well as by an IR sensor for measuring the rotor temperature. With these measurement signals, stationary and transient operating conditions can be analyzed. For stationary operating conditions, additionally, the housing temperatures are determined by an IR camera. The investigated simulation and measurement methods reveal different local and global temperatures, and thus, only certain aspects and characteristics of the obtained temperatures can be compared. Nevertheless, certain conclusions can be drawn from comparing these aspects considering the actual restrictions of each of the applied methods.      

Efficiency of three wind energy generator systems

This paper presents a method to calculate the average efficiency from the turbine shaft to the grid in wind energy converters. The average efficiency of three 500 kW systems are compared. The systems are: a conventional grid-connected four-pole induction generator equipped with a gear, a variable-speed synchronous generator equipped with a gear and a frequency converter, and a directly driven variable-speed generator equipped with a frequency converter. In this paper it is shown that a variable-speed generator system can be almost as efficient as one for constant speed, although it has much higher losses at rated load. The increased turbine efficiency that variable speed leads to has not been included in this paper. It is also found that a directly driven generator can be more efficient than a conventional four-pole generator equipped with a gear     

近地面长导体感应电压的研究

为查明引起人体暂态电击的根本原因并找出有效的防止措施,利用电磁暂态软件EMTP-ATP建立了某500kV输电线路下方近地面长导体的感应电压的分析模型,着重分析了近地面长导体的电磁感应电压,并对比了实测电压值与计算电压值。结果表明,近地面长导体的电磁感应电压可忽略,近地面长导体良好接地可有效避免人体暂态电击。     

Transient analyses of transverse flux homopolar linear machineswith unified prototype

In this paper, the operating characteristics of a transverse flux homopolar linear machine prototype is investigated under various specifications by using the generalized 3-dimensional mathematical model as developed by C.T. Liu et al. (1993). From the computer-aided analysis results, it can be observed that such a model can be easily adapted to the forms suitable for the related transient analyses on those transverse flux linear induction, reluctance, synchronous, and oscillating machines. Thus the feasibility of using the proposed unified linear machine prototype to supply a common structure for realizations of various transverse flux homopolar linear machines can be verified, and a reliable design reference for the associated applications of linear machine systems is also provided     

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     

Real-time rotor effective wind speed estimation based on actuator disc theory: Design and full-scale experimental validation

The use of state estimation techniques offers a means of inferring rotor effective wind speed from standard measurements of wind turbines. Typical wind speed estimators rely upon a pre-computed quasi-steady aerodynamic mapping, which describes the relationship between pitch angle and tip-speed ratio and the power coefficient. In practice, the static mapping does not capture the influence of turbine structural dynamics and atmospheric turbulence, inevitably resulting in poor performance of the wind speed estimation. In addition, the turbine aerodynamic properties might not be easily accessible. Thus, this paper presents a rotor effective wind speed estimation method that obviates the requirement for prior knowledge of turbine power coefficients. Specifically, the proposed method exploits a simple actuator disc model, where the aerodynamic power and thrust coefficients can be characterized in terms of axial induction factors. Based on this insight and standard turbine measurements, real-time estimation of rotor effective wind speed and axial induction factors can then be achieved using a simplified turbine drive-train model and an extended Kalman filter. In addition, the actuator disc model can be updated easily over time by calibrating solely two correction factors. Thus, the proposed algorithm presents an alternative for estimating the rotor effective wind speed, which is valuable for numerous applications, for example, LiDAR-assisted control and coherence studies.