Standard Induction Machine Research Articles

Increasing efficiency of induction motor by predictive control system

Standard squirrel-cage induction machine is widely used in industrial enterprises due to its advantages in terms of reliability, durability and economic efficiency. However, one of its disadvantages is that it suffers from a power dissipation factor due to its inability to balance active and reactive power consumption. Especially when the SCIM is running at no load condition or during the initial start-up, the power factor or useful operation and performance are drastically reduced. Therefore, improving the power factor of the induction machine is an actual topic for the following article, and has had some interesting solutions for several years. In this thesis, two different induction motor control algorithms (frequency converter and Predictive torque control) are included and a clear comparison between them is given. The main focus of this article is to design an induction motor control system using the two algorithms mentioned above, analyse the performance of different control methods, and experimentally verify these algorithms by comparing simulations and experimental results.

Dynamic and Steady State Modelling of the Doubly Fed Twin Stator Induction Generator With Core Loss.

This paper presents dynamic and steady state models of the brushless doubly fed twin stator induction machine (BDFTSIM) with emphasis on its use as a generator. The dynamic models are presented in the general reference frame. The models include the effects of core loss on both the stator and the rotor. The frequency on the rotor of the BDFTSIM is much higher than in a standard induction machine so that core losses can not be neglected. The performance analysis indicates the feasibility of the BDFTSIM as a variable speed wind generator

Modeling and Dynamic Performance Analysis of Brushless Doubly Fed Induction Machine Considering Iron Loss

Brushless doubly fed induction machine (BDFIM) which is able to operate in both induction mode and synchronous mode, has received increasing attention of researchers, in the last three decades. It could be considered as an emerging competitor for older structures, due to the substantial features such as brushless structure and requiring a fractionally rated frequency converter. The iron loss which constitutes a significant portion of total power losses is higher in BDFIM in contrast with standard induction machine. Even though it is essential to consider the iron loss effect on dynamic behavior of BDFIM, there is still no comprehensive study in the literature. The aim of this paper is to propose a dynamic model of BFIM in general reference frame in which the iron loss is taken into account. This model which is credible for all BDFIM operation modes including synchronous one, facilitates the performance analysis of BDFIM and implementation of the various control techniques. The supplementary simulations and experiments confirm that the proposed model is an appropriate candidate for BDFIM drives. Because of the complex structure of BDFIM, determination of the iron loss isn't straightforward. In this paper, a practical approach is introduced to calculate the iron loss of BDFIM in terms of frequency variations. The experimental data derived from a D132s prototype BDFIM is then compared with the calculated data from the finite element analysis (FEA).

Auslegung eines synchronen Reluktanzrotors für den Stator einer 11-kW-Asynchronmaschine

This paper first describes a general method for the design of a synchronous reluctance rotor, which uses the field lines in an anisotropic rotor to shape the flux barriers and combines this with known design rules from the literature. This straightforward method is now used to design a rotor for the stator of a three-phase, four-pole, 11 kW standard induction machine. In some electromagnetic studies the influence of the essential rotor parameters (number of flux barriers, ratio of the magnetically non-conductive material in the rotor and the used method for the radial width ratios of adjacent barriers) is analyzed by means of finite element simulations in order to find a suitable rotor topology. In addition, the dimensioning of the mechanical ribs is discussed to manufacture a prototype rotor, which is then inserted into the stator of the cage induction machine. Finally, both the reluctance rotor and the squirrel cage rotor of the induction machine are used to present measurement results for the heating at the rated point and the efficiency at normalized operating points, so that both types of machines can be compared.

Torque/Power Density Optimization of a Dual-Stator Brushless Doubly-Fed Induction Generator for Wind Power Application

The brushless doubly-fed machine has attractive features to be employed in highly reliable wind turbine systems. However, the existing brushless doubly-fed topologies primarily work by the principle of modulation and suffer from low torque/power density, inferior efficiency, and high level of time and spatial harmonic distortion. This paper presents a simple design optimization approach for torque/power density optimization of a dual-stator brushless doubly-fed induction generator, which, unlike the modulation types, is inherently free of harmonic-related issues. An analytical average torque model with a full set of geometrical, electromagnetic, and thermal constraints is developed based on the power flow of generating operation. The optimized results exhibit comparable torque per volume and torque per weight to standard industrial induction machines with the similar size, synchronous speed, and power loss per-unit area. Mechanical considerations, manufacturing costs, and control aspects are also discussed to show the high potential in superseding existing doubly-fed induction generators. Finite-element analysis and experimental results of a 3.7-kW prototype are used to validate the effectiveness of the optimization.

Parameters identification of a brushless doubly fed induction machine using pseudo‐random binary signal excitation signal for recursive least squares method

Accurate brushless doubly fed induction machine (BDFIM) control is considered as a good alternative to traditional generators. Therefore, the knowledge of the parameters accuracy is necessary to design high-performance drives. In this study, an offline identification method to identify the BDFIM parameters is presented. This study investigates the input signal effects on the accuracy of the identified parameters. The similarity between BDFIM frequency model and the standard induction machine frequency model has been verified by comparing the step responses of the corresponding transfer functions. The obtained results would be a motivation for online identification techniques and BDFIM field-oriented control strategies. The proposed identification method has been validated by performing experimental results.

Evaluation of the Efficiency of Line-Start Permanent-Magnet Machines as a Function of the Operating Temperature

The standard squirrel-cage induction machine has nearly reached its maximum efficiency. In order to further increase the energy efficiency of electrical machines, the use of permanent magnets in combination with the robust design and the line start capability of the induction machine is extensively investigated. Many experimental designs have been suggested in literature, but recently, these line-start permanent-magnet machines (LSPMMs) have become off-the-shelf products available in a power range up to 7.5 kW. The permanent magnet flux density is a function of the operating temperature. Consequently, the temperature will affect almost every electrical quantity of the machine, including current, torque, and efficiency. In this paper, the efficiency of an off-the-shelf 4-kW three-phase LSPMM is evaluated as a function of the temperature by both finite-element modeling and by practical measurements. In order to obtain stator, rotor, and permanent magnet temperatures, lumped thermal modeling is used.

A coupled‐circuit model for a DFIG operating under unbalanced conditions

PurposeThe purpose of this paper is to describe the principles of a coupled‐circuit model for a doubly‐fed induction generator (DFIG) and to present evidence of the validity of this versatile and powerful technique and the advantages it offers when used for modeling and analysis of DFIG operation in unbalanced conditions. This paper also investigates the winding fault induced changes in the machine stator steady‐state current spectrum with a view to DFIG condition monitoring.Design/methodology/approachThe presented model is based on the summation of harmonic winding inductances. It comprises of a set of standard induction machine electromechanical equations where a connection matrix that defines a particular balanced/unbalanced winding configuration of interest is conveniently incorporated in the expressions. This model is therefore capable of representing both open‐ and short‐circuit stator and rotor winding faults while also taking into account higher order air‐gap field harmonics. Model predictions are verified in this work through comparison with corresponding experimental data obtained from a purpose built 30 kW DFIG laboratory test rig. The paper involves a number of healthy and faulty operating scenarios.FindingsAdvantages and validity of the employed model are illustrated in time and frequency domain for different steady‐state balanced/unbalanced winding DFIG operating conditions. It is also shown in both predicted and measured data that the considered winding asymmetries give rise to additional harmonic components in the stator current spectrum.Research limitations/implicationsThe importance of considering higher order air‐gap field harmonics when modeling induction machine behavior is outlined in this work.Practical implicationsThis paper identifies changes in the DFIG stator current harmonic content spectra that are winding fault induced. These may have the potential to constitute reliable fault indicators.Originality/valueThe paper discusses a harmonic conductor distribution‐based modeling method aimed predominantly at frequency domain analysis of DFIG electrical quantities. It is shown that DFIG stator current spectrum is rich in higher order harmonic components and that manner in which these are manifested is heavily influenced by the presence of winding unbalance.

Test Signal Based Speed Estimation for Induction Motor Drives

In the first part of the paper an estimation method for sensorless control employing a test signal based reference model is presented. The method estimates the slip frequency by a comparison of the measured test signal impedance curves while the machine is in operation with curves from a test signal based reference model. The reference model which describes the test signal behaviour of the machine is measured during DC magnetisation of a cold machine at steady state and constant rotor flux linkage. During normal machine operation the machine temperature and the stator frequency differ from these conditions and, thus, have a negative influence on quality of the estimation. In the second part of the paper the impact of these disturbances is investigated and two compensation strategies are presented. Measurements on two different standard induction machines which are not especially designed for sensorless control show that the estimation method allows safe operation at standstill and even at zero frequency.

Theoretical and Experimental Reevaluation of Synchronous Reluctance Machine

This paper theoretically introduces and develops a new operation diagram (OPD) and parameter estimator for the synchronous reluctance machine (SynRM). The OPD demonstrates the behavior of the machine's main performance parameters, such as torque, current, voltage, frequency, flux, power factor (PF), and current angle, all in one graph. This diagram can easily be used to describe different control strategies, possible operating conditions, both below- and above-rated speeds, etc. The saturation effect is also discussed with this diagram by finite-element-method calculations. A prototype high-performance SynRM is designed for experimental studies, and then, both machines' [corresponding induction machine (IM)] performances at similar loading and operation conditions are tested, measured, and compared to demonstrate the potential of SynRM. The laboratory measurements (on a standard 15-kW Eff1 IM and its counterpart SynRM) show that SynRM has higher efficiency, torque density, and inverter rating and lower rotor temperature and PF in comparison to IM at the same winding-temperature-rise condition. The measurements show that the torque capability of SynRM closely follows that of IM.

Design Study of Doubly-Fed Induction Generators for a 2MW Wind Turbine

A design study for a 2 MW commercial wind turbine is presented to illustrate two connection methods for a standard doubly-fed induction machine which can extend the low speed range down to 80% slip without an increase in the rating of the power electronic converter. This far exceeds the normal 30% lower limit. The low speed connection is known as induction generator mode and the machine is operated with a short circuited stator winding with all power flow being through the rotor circuit. A two loop cascaded PI control scheme has been designed and tuned for each mode. The purpose of this paper is to present simulation results which illustrate the dynamic performance of the controller for both doubly-fed induction generator connection methods for a 2 MW wind turbine. A simple analysis of the rotor voltage for the doubly-fed connection method is included as this demonstrates the dominant components that need to be considered when designing such advanced control strategies.

Performance of HF signal injection techniques for zero-low-frequency vector control of induction Machines under sensorless conditions

A number of HF signal injection techniques have been proposed for the sensorless zero-low-frequency control of induction machines (IMs). This paper reviews these methods and experimentally investigates their performance under true sensorless conditions for a standard cage IM with closed rotor slots. Implementation techniques covering hybrid methods, saliency decoupling, and saliency orientation are discussed. The paper concludes that, while HF techniques can outperform observer-based methods at low frequencies, the robust performance required for industrial application still presents a research challenge.

New Time-Discrete Modulation Scheme for Matrix Converters

While the known modulation strategies for matrix converters are based on pulsewidth modulation (PWM)-or vector modulation-this paper presents a novel time-discrete modulation method based on real-time prediction calculation to select the switching states. The decision about which switching state is to be set for the following sampling period is made by the use of a predictive quality function. Using this approach, unity displacement factor is seen at the supply side with minimum line current distortion while the load currents follow their reference values with good accuracy. The quality function is derived from a mathematical model of the matrix converter and the controlled system. Measurements taken on a model plant, consisting of a matrix converter and a standard induction machine with a rated output power of 11 kW, show that the matrix converter, equipped with the control method presented here, offers advantages over systems with conventional frequency converters, especially in terms of the input current distortion.

Design of Grid-Connected Induction Generators for Wind Power Generation

The design of an induction machine for grid connected wind energy applications should be different from isolated wind electricity generation and motor applications. Commonly, standard induction machines are used as grid connected induction generators. However, such machines are designed for motor operation and have more reactive power consumption and greater no-load losses than necessary. This paper presents a design for an induction generator exclusively for grid connected applications by reducing both reactive power consumption and no-load losses. The theoretical performance of the proposed generator is compared with the conventional induction motor used as a generator. Evolutionary programming is used as a tool for design optimization of both generator and motor.

Lamination Design Variations for Improved Performance of Zero Speed Sensorless Controlled Induction Machines

To realise a high-dynamic controlled operation of induction machines the flux position has to be estimated during operation of the drive. Omitting the shaft sensor leads to a deterioration of the performance at low fundamental frequencies if fundamental wave models of the machine are applied. To determine the flux position at zero speed without shaft sensor it is thus necessary to use parasitic, non-fundamental wave effects of standard induction machines, such as spatial saturation, slotting, or other anisotropy.These effects are not evident in normal operation but can be exploited using the high frequency or transient electrical behaviour of the machine. All sensorless zero speed schemes currently published thus make use of a high frequency or transient excitation of the machine in addition to the fundamental wave, which are both impressed by the inverter. The machine reaction on this high frequency excitation is measured and the flux and/or rotor position signal estimated using special algorithms and signal processing techniques.However, it turned out in the past that the shape of the lamination and especially the slot geometry have strong influence on the high frequency/transient electrical response of the machine. Before realising a sensorless controlled drive it is thus advantageous to have a look at the design of the machine as not any design is suitable for a specific sensorless control algorithm.The presented investigation is thus focused on the influence of the lamination geometry on the resulting signals of a sensorless control scheme. The sensorless control method applied is usually denoted as INFORM-method in literature and is based on a transient excitation with voltage pulses.In the transient electrical current response of the machine there are always all saliencies present. The two most prominent saliencies are caused by saturation and slotting. Their modulations in the control signals have to be extracted and separated in order to obtain the flux or the rotor position of the machine. Currently the interaction of the saliencies limits the practical application of these methods.To investigate the mentioned influence, measurements have been performed on five machines with different lamination geometry By comparing the extracted saliencies of these machines, the influence of slot design on the sensorless control signals is depicted.Thus the magnitudes of the two saliencies can be influenced by a proper adjustment of the geometry This association is shown for the saturation saliency in Fig. 1. Depending if the flux or rotor position is to be used for the machine control the corresponding saliency can be boosted and the others attenuated. This results in a more reliable extraction and separation ofthe saliencies and a more robust control.

Magnetising method for speed sensorless controlledinduction motor drives

In speed-sensorless controlled standard induction machine drives a start without torque is only possible if the rotor speed of the demagnetised machines is known. A new method is proposed, which allows a fast and accurate identification of the rotor speed of demagnetised machines without a speed or position sensor.

A new zero-frequency flux-position detection approach for direct-field-oriented-control drives

This paper presents a novel approach to estimate the instantaneous position of the air-gap flux in standard induction machines at low and zero speed. The proposed approach is based on the generation of a high-frequency rotating field that, interacting with the main field, generates a high-frequency zero-sequence flux component. By demodulating such a component, which is always present, irrespective of speed and load levels, it is possible to detect the air-gap flux position. The proposed method allows one to overcome some key drawbacks of sensorless approaches based on high-frequency voltage injection and, compared to previous sensorless schemes exploiting the third harmonic voltage, improves the accuracy and extends the operating area up to zero speed. Experimental tests are shown in order to practically confirm the expected features of the proposed system.

A self-tuning closed-loop flux observer for sensorless torque control of standard induction machines

This paper proposes a self-tuning closed-loop flux observer, which provides field-oriented torque control for induction machines without a tachometer. The proposed algorithm combines the best features of harmonic detection and stator voltage integration through the use of a new tuning scheme. The observer accuracy and robustness is augmented by a parameter-independent accurate-speed detector, which analyzes magnetic saliency harmonics in the stator current. The harmonic-detection scheme provides accurate rotor-speed updates during steady-state operation down to 1-Hz source frequency. This additional speed information is used to tune the rotor-resistance parameter of the observer. The tuned observer exhibits improved dynamic performance, accurate steady-state speed control and an extended range of control near zero speed. The algorithm requires no special machine modifications and can be implemented on most existing low- and medium-performance drives. The closed-loop nature of the flux observer, combined with the harmonic-detection scheme, provides flux and speed error feedback, which significantly increases the robustness of sensorless control across the entire speed range.

Transfer Functions of the Slip-Controlled Induction Machine

The use of a feedback loop to regulate the slip frequency of an inverter-driven induction machine is viewed as replacing the normal independent control of stator frequency with independent control of slip frequency. For steady-state conditions the two modes of operation are shown to produce characteristics analogous to shunt and series dc machines. A method employing closed-form transfer functions, a reduced set of nondimensional parameters, and a general root locus diagram is used to present the dynamic characteristics of controlled slip frequency operation and to compare performance with conventional operation. The parameter range in the general diagram is sufficient to incorporate nearly all standard induction machines over a wide size and frequency range. The results demonstrate that the ratio K of the rotor transient time constant to the static electromechanical time constant is a critical parameter in the comparison of the two modes. Since this parameter tends to increase with machine size, the relative advantages of slip frequency control are shown to be machine-size dependent. Inclusion of a speed-control loop regulating machine voltage is also Considered and shown to be described by the same general root loci. The performance of this closed-loop system is also shown to be very dependent on K and hence on machine size.