Starting of three-phase reluctance motors connected to a singlephase supply

An analysis of the starting process of a three-phase reluctance motor when fed from a single-phase supply is presented. This analysis is aimed, mainly, at the determination of the variations in the different machine parameters as it pulls into synchronism. Special attention is given to the calculation of both the positive and negative sequence impedances. These impedances play an important role in the proper selection of the phase converter capacitance needed for ensuring satisfactory operation. For this purpose, the symmetrical component concept along with classical synchronous machine theory have been effectively employed. The devised mathematical model could also help in studying the asynchronous operation of synchronous machines when fed from either three-phase or single-phase power supplies. The effect of the value of the selected phase converter capacitance on the performance of the reluctance motor during starting and normal running conditions is investigated     

Determination of starting current in three-phase induction motors

The author reviews the existing conversion methods which determine the starting current in three-phase induction motors and points out their weaknesses. A theoretical base is found for the determination of starting current, and an accurate method called the regression estimate method is proposed     

An improved delta-star switching scheme for reactive power saving in three-phase induction motors

It is proposed that a capacitor can be connected permanently across each phase winding of a three-phase induction motor along with the conventional delta-star switching, for further saving in VARh at reduced loads on the motor. The method of choosing a suitable value for the capacitor and the criteria to be adopted for calculating the power output at which the star to delta switching is to be made are also explained. The experimental results on a 3- phase, 4-pole, 415 V, 50 Hz, 3.3 kW induction motor verify the advantages in adding the capacitor to the phase winding of the motor. Compared to using only a single delta connected stator winding or a delta-star switching, the advantages of the proposed addition of a capacitor, are also demonstrated through a case study conducted on a 400 V, 250 kW motor. Any further improvement in grid side power factor can be achieved by employing a static synchronous compensator (STATCOM) of reduced VAR rating.     

A complete lumped equivalent circuit of three-phase squirrel-cage induction motors using two-dimensional finite-elements technique

The paper presents the use of the finite element technique for determining the parameters of a three-phase squirrel-cage induction motor. The common parameters in addition to the core losses and ratio of number of turns are obtained from the finite-element field solutions. The magnetizing characteristic and core losses curve are used to determine the flux distribution within the motor structure. The linear time harmonic vector potential field solution is used for the inductances computation. The accuracy of the finite-element application is verified using the available precise results.     

Method for in-field evaluation of the stator winding connection of three-phase induction motors to maximize efficiency and power factor

The performance of the oversized three-phase induction motors can be improved, both in terms of efficiency and power factor, with the proper change of the stator winding connection, which can be delta or star, as a function of their load. A practical method is proposed to quickly and easily evaluate which stator winding connection is more appropriate for the actual motor load profile, in order to increase the motor efficiency and power factor. This new method is suitable for in-field evaluation, because it requires only the use of inexpensive equipment and has enough accuracy to allow a proper decision to be made. The automatic change of the stator winding connection, as a function of the motor line current, is also analyzed. When properly applied, these methods can lead to the improvement of the efficiency and power factor of permanently oversized motors, motors with a load variation between low load and near full load during their duty cycle, and/or motors driving high-inertia, low duty cycle loads. The proposed methods are particularly suitable to industrial plants where typically many electric motor systems are oversized and/or can have a wide load variation. In these conditions, the active and reactive electrical energy bill can be significantly reduced.     

Application of fuzzy logic to induction motors condition monitoring

This letter applies fuzzy logic to induction motors condition monitoring. The preliminary results show that fuzzy logic can be used for accurate induction motors fault diagnosis if the input data are processed in an optimized way     

Transient performance of series connected three phase slip-ringinduction motors

The possibility of operating a three phase slip-ring induction motor as a series connected motor is explored. The merits and drawbacks of this mode of operation are discussed. For this purpose, the necessary mathematical models along with the corresponding computer simulation are developed and experimental verification of the theoretical results is also carried out. It has been found in general that operation of slip-ring induction motors as series connected motors is possible providing that the rotor winding is connected in a sequence opposite to that of the stator winding. This adds flexibility to the modes of operation of these motors. Moreover synchronous operation is also possible, providing that the series connected motor is driven initially at twice its synchronous speed and then connected to the supply     

PSPICE simulation of single-phase induction motors

Dynamic analysis of a single-phase induction motor is studied using PSPICE software. The machine dynamics are presented by a set of nonlinear time-varying differential equations. The equations which define the motor operation are represented in an orthogonal system. The electric circuit presenting this set of equations is determined and solved by PSPICE software for simulation of the motor. The simulation results are compared with those obtained by EMTP and the experiment. Good agreements are observed for both cases     

Transient thermal analysis of induction motors

Induction machines transient thermal analysis has been a subject of interest for electric machine designers in their effort to improve machine reliability and in rotor design optimisation. The study of transient thermal behavior is useful to identify causes of failure in induction machines. This paper presents a 2-D transient analysis of induction machines using the available heat transfer coefficients in literature. A generalised finite element code developed with Galerkin's weighted residual technique is used for analysis. The model is applied to one squirrel-cage totally-enclosed fan cooled machine of 3.7 kW and another surface cooled machine of 5.7 kW. The predicted temperatures compare well with test results. The advantages and limitations of this model are discussed     

Parasitic torques in saturated induction motors

A method for analyzing the performance of induction machines for parasitic torques is described. Such torques arise from the interactions of fundamental and harmonic components of air flux density due to geometrical considerations such as slotting, and saturation effects. Parasitic torques arise under balanced sinusoidal drive conditions. However, they are greatly exacerbated under nonsinusoidal drive conditions. The technique described for analysis is applicable to both cases     

Losses due to rotational flux in three phase induction motors

This paper discusses rotational losses and how they are produced in the core materials of induction motors. These losses are largely caused by flux that rotates in the plane of the machine laminations. This suggests that steel specification for applications to rotating machines should be given in terms of rotational loss data as a material characteristic, in much the same fashion as Epstein test results are provided for alternating losses. If a standardized test for rotational losses were to be used, steel producers could rationally investigate the effects of composition and processing variables. This is necessary in order to produce low loss steels for motor applications. Reduction of rotational losses in motor cores could significantly lower AC machine operating costs and contribute to the growing interest and design of high efficiency induction motors. The paper describes a test procedure for determining rotational losses in a sample. It then compares the results with standardized tests from an Epstein test procedure. It is seen that there are significant differences in loss results obtained for the rotational test versus the alternating current test. The authors have investigated a time harmonic finite element formulation utilizing Magnet 2D, a commercially available package. The paper includes a brief analysis of a typical problem using this tool     

Tracking control technique for induction motors

A novel application is presented of the tracking control technique to induction motor drive systems. By this technique, the position or the speed of the rotor can follow a preselected track (a time history of rotor position or velocity). An algorithm for the design of the tracking controller is developed. The induction motor model and the controller are modified to allow the inclusion of the nonlinear modes in the system without excessive computations. A simple and realistic criterion for selecting the proper reference tracks during starting, speed control and braking is proposed. The controller developed, is tested on a full-size nonlinear analog simulator. All test results show the effectiveness of the scheme in position-tracking applications such as robotics and manipulators     

Design of a three-phase self-excited induction generator

The main goals in the design of a self-excited induction generator (SEIG) are minimizing the rotor resistance and increasing the flux density until the magnetic circuit of the generator saturates. In this paper, a computer design package was developed in order to investigate the best way to obtain these goals. By reducing the stator core length by 40%, the frequency regulation and the voltage drop were reduced. The frequency regulation decreased from 10% to 4% and the voltage drop decreased from 30% to 6%. In addition, voltage and frequency regulations in the standard ranges were obtained in the present design without any regulation devices     

Smooth starting of slip ring induction motors

The starting of three-phase wound rotor induction motors by stepped resistances added in the rotor circuit suffers from several problems. This paper suggests a novel method of motor starting by inserting a parallel combination of resistance, inductance and capacitance in the rotor circuit. The proposed method guarantees a smooth and high starting torque over most of the starting period besides a controlled starting current. A mathematical model is developed based on a frequency domain quasi-steady state equivalent circuit. An optimization technique is then applied to determine the values of the rotor added elements such that minimum starting time is achieved subject to current and torque constraints. Experimental verification has been carried out and the computed results are in good agreement with the measured values     

Harmonic losses of single-phase induction motors undernonsinusoidal voltages

Parameters of a capacitor-start, capacitor-run single-phase induction motor with closed or semi-closed rotor slots are measured and a model for the investigation of the performance of the machine in the frequency domain under the influence of harmonic voltages is presented. An algorithm, taking into account the nonlinear rotor leakage inductance, is established. This algorithm is applied to estimate the current in the time domain, and the harmonic losses at rated-load operation without and with run capacitors are calculated. Computational results are compared with those from experimentation and the differences between both are discussed     

三相光伏并网逆变器准比例谐振控制器设计

近年来,光伏并网逆变器的电流控制技术成为研究热点,文章针对传统电流控制技术的不足之处,将准比例谐振控制引入到光伏并网逆变器的电流控制中,利用其在谐振频率处增益无穷大和较大带宽的特点,消除稳态误差,提高抗干扰能力。仿真结果表明,设计的准比例谐振控制器能实现三相光伏并网逆变器的电流无误差跟踪,具备抗电网干扰能力,具有较好的动、稳态性能。     

Starting transients of three phase synchronous motors connected toa single phase supply

Balanced operation of three phase synchronous motors have been dealt with extensively in the literature. However, unbalanced operation has not received as much attention. One of the interesting unbalanced modes of these motors is their operation from a single phase supply. Such a mode of operation can be of special importance in remote areas where only single phase supply is available or in the case of an open circuited single line fault. In this paper, the possibility of operating three phase synchronous motors from a single phase supply through the use of a phase balancer capacitor is explored. The criteria for selecting the required phase balancer capacitor is presented and the analysis of the behaviour of such motors during the starting process is carried out. For this purpose, a rigorous state space mathematical model has been developed. The validity of this model have been verified experimentally     

Determination of radial-forces in relation to noise and vibrationproblems of squirrel-cage induction motors

The radial electromagnetic forces in induction motors play an important role in the production of audible noise and vibrations. The magnetic flux pulsations at the iron surfaces produce these radial forces, which act on the stator and rotor structures. An analysis for the calculation of the various field harmonics and radial forces in squirrel cage induction motors is presented in this paper. To verify the validity of the analysis, a squirrel cage induction motor is analyzed. Theoretical and experimental results are presented with a view to determine the actual role played by the air-gap harmonic fields on the radial forces. Also, the effects of loading on the radial forces and the ensuing vibrations are closely examined     

Losses influenced by third-harmonic flux in induction motors

The trend toward increasing flux density in modern induction motors results in the increase of third-harmonic flux in the magnetic paths. The effects of third-harmonic flux on energy losses in induction motors are discussed. The shapes of flux distributions in various sections of an induction motor are interrelated. The most saturated section normally has a flattened shape of flux density distribution. The effects of the shapes of flux density distribution on losses are compared from the third-harmonic flux standpoint. The losses influenced by the third-harmonic flux may be controlled through lamination punching designs and winding connections     

A thermometric approach to the determination of iron losses insingle phase induction motors

This contribution describes a novel technique for evaluating the iron loss density distribution in a single phase induction motor using the temperature time method. This is achieved by measuring the temperature gradient which exists at any point within the machine when it is isolated from the supply. This method was used when the motor was lightly loaded. The measurements were carried out on a 200 W, 220 V, 4-pole, 1.6-A single phase induction motor