Antero Arkkio

Ride-Through Analysis of Doubly Fed Induction Wind-Power Generator Under Unsymmetrical Network Disturbance

This paper presents a ride-through simulation study of a 2-MW wind-power doubly fed induction generator (DFIG) under a short-term unsymmetrical network disturbance. The DFIG is represented by an analytical two-axis model with constant lumped parameters and by a finite element method (FEM)-based model. The model of the DFIG is coupled with the model of the active crowbar protected and direct torque controlled (DTC) frequency converter, the model of the main transformer, and a simple model of the grid. The simulation results show the ride-through capability of the studied doubly fed wind-power generator. The results obtained by means of an analytical model and FEM model are compared in order to reveal the influence of the different modeling approaches on the short-term transient simulation accuracy

Interdependence of Demagnetization, Loading, and Temperature Rise in a Permanent-Magnet Synchronous Motor

The demagnetization of permanent magnets in permanent-magnet machines has been under discussion in many publications lately. Demagnetization models have been used, for example, to optimize the machine structures but there have been no studies on how the demagnetization is coupled with the loading and temperature-rise of the machine and how this coupling should be modeled. In this paper, we model the dynamics of the demagnetization of a dovetail machine under a constant load torque. We show that the thermal model should be included in the demagnetization calculations. The demagnetization will cause an increase of the copper losses, which will increase the temperatures of the machine. This will cause more demagnetization and might lead even to a stall in a situation in which a model neglecting the thermal effects predicts stable operation without additional demagnetization.

Performance Study of a Doubly Fed Wind-Power Induction Generator Under Network Disturbances

Transient performance of a 1.7-MW wind-power doubly fed induction generator (DFIG) under network disturbances is studied using a coupled field-circuit simulator. The simulator consists of the finite-element method model of a DFIG coupled with the circuit model of the frequency converter, a transformer, and a simple model of the network. The simulation results show the transient behavior of the DFIG when a sudden voltage dip is introduced. The field-circuit simulator is experimentally validated by full-power measurement

Finite element analysis of cage induction motors fed by static frequency converters

A calculation of induction motors based on the finite-element analysis of the magnetic field is presented. The field is assumed to be two-dimensional, and the time dependence of the field and the motion of the rotor are modelled by the Crank-Nicholson time-stepping method. The nonsinusoidal voltage supplied by the frequency converter is imposed on the formulation through the circuit equations of the winding. The method was tested using the properties of a 15-kW cage induction motor. The results obtained for the current and torque show good agreement with the measured results. The method was also used successfully for computing the resistive losses of the rotor winding and for analyzing the effect of the bar shape on the resistive losses. >

Hysteresis model for finite-element analysis of permanent-magnet demagnetization in a large synchronous motor under a fault condition

This paper describes a rare-earth-transition metal alloy permanent-magnet (Nd/sub 2/Fe/sub 14/B) hysteretic behavior model within finite-element analysis. The present work analyzes the demagnetization states of permanent magnets during fault conditions in a permanent-magnet synchronous motor and characterizes the ability of the motor to sustain the designed rated outputs after the fault conditions occur.

Comparison of Demagnetization Models for Finite-Element Analysis of Permanent-Magnet Synchronous Machines

We have studied a few simple demagnetization models, which are quick and easy to implement in finite-element calculations, and compared them with measured recoil behavior of Nd-Fe-B magnet material, also using a hysteresis model for comparison. The models are used to estimate post-demagnetization performance of an overloaded surface magnet synchronous machine. Two of the simple models, the sloped linear model and the exponent function model, give the most accurate results without significantly increasing the computation time.

Power Limits of High-Speed Permanent-Magnet Electrical Machines for Compressor Applications

The maximum-power limits for high-speed permanent-magnet (PM) electrical machines for air compressor applications are determined in the speed range 20000-100000 r/min. For this purpose, five PM machines are designed and the electromagnetic, thermal, and mechanical designs of each machine are simultaneously performed. The critical values of the thermal and mechanical constraints are considered in order to obtain the maximum powers of the electrical machines. The electromagnetic losses generated in the machine are the output parameters of the electromagnetic design and input parameters for the thermal design. The thermal design is performed using a multiphysics method, which couples computational-fluid-dynamics equations with heat-transfer equations. The mechanical design considers the retention of the rotor elements against the huge centrifugal forces that arise during the high-speed operation and also the rotor dynamics properties of the rotor. The reliability of these design techniques is experimentally validated in the paper. The obtained maximum-power limit defines the speed-power region, in which the high-speed PM electrical machines intended for compressor applications can have a safe operation.

A General Model for Investigating the Effects of the Frequency Converter on the Magnetic Iron Losses of a Squirrel-Cage Induction Motor

We present a comprehensive analysis of iron losses in an inverter-fed induction motor. We performed experimental and numerical investigations to assess the additional losses produced by a pulsewidth modulated (PWM) supply compared to a sinusoidal supply. We developed an iron-loss model, called the hybrid model, and incorporated it into a two-dimensional (2-D) finite-element method (FEM) to investigate the losses. The model predicts the B-H loops and the ensuing iron losses. We also used a traditional iron-loss model based on the statistical theory for the sake of comparison. We solved the nonlinear dynamic equations of the FEM by the fixed-point method and the Crank-Nicolson time-stepping scheme. We found the hybrid model to be fairly accurate in reproducing the iron losses obtained experimentally on a squirrel-cage induction motor operated under several different conditions. The numerical analysis also provided interesting results regarding the role of the PWM supply in characterizing the behavior and distribution of iron losses in the geometry of the motor.

Inverted and Forward Preisach Models for Numerical Analysis of Electromagnetic Field Problems

This paper discusses the use of the inverted (B-based) Preisach model and its incorporation into the finite-element method (FEM). First, the B-based Preisach model is studied thoroughly along with the forward (H-based) Preisach model, highlighting the advantages and disadvantages of both models. The study confirms that, in addition to the main purpose of the B-based model—to compute the magnetic field H directly-the B-based model can overcome the congruency problem. Thus, the B-based model proves to be more accurate than the B-based model. Second, the paper suggests that incorporating the B-based Preisach model into FEM models results in relatively accurate, computationally efficient simulations. The method has been validated by simulating hysteresis torque in a high-speed induction motor, and a comparative investigation of the effectiveness, accuracy, and efficiency of the models has been conducted

Comparison of the Unbalanced Magnetic Pull Mitigation by the Parallel Paths in the Stator and Rotor Windings

An eccentric rotor creates an electromagnetic force between the rotor and stator of an electrical machine. This force tends to further increase the rotor eccentricity and may severely degrade the performance of the machine, causing acoustic noise, vibration, excessive wear of bearing, rotor and stator rubbing, and so forth. Parallel connections are known to be a simple yet effective remedy for the problems associated with rotor eccentricity. We have investigated two common types of electrical machines running with eccentric rotors. We examined operation over a wide whirling frequency range. We numerically evaluated and compared the effects of parallel connections in the stator and rotor windings on the eccentricity force. We found that the parallel stator windings can be more effective in mitigating the unbalanced magnetic pull than the rotor cage (or damper winding), which normally has many more parallel circuits.