NEW DEVELOPMENT OF TORQUE ANALYSIS OF SYNCHRONOUS MACHINE

ABSTRACT

By using a multi-loop model, a new technique for analysing the torque of a synchronous machine is presented in this paper. The electro-magnetic torque of the machine which is very difficult to calculate in some operation conditions by other methods, can be obtained from the inductances of the machine and the currents of every loop of the machine, then the average torque and the pulse torque by Fast Fourier Technique. Comparing the results obtained by the new technique with an established method, the new method is justified.     

INVESTIGATIONS ON DYNAMIC BEHAVIOR OF PERMANENT MAGNET BRUSHLESS DC MOTOR DRIVE

ABSTRACT

Permanent magnet brushless dc (PMBLDC) motors are increasingly being used in a wide range of applications such as machine tools, robotics and high precision servo applications. A comprehensive analysis which includes modeling and simulation of PMBLDC motor drive is presented in this paper. A mathematical model of the drive is developed with a view to studying the transient response of current controlled voltage source inverter (VSI) fed PMBLDC motor. The drive system consists of discrete PID(Proportional, integral plus derivative) speed controller, the reference current generator, the position sensor, an inverter and the motor. Each part of the drive system is modeled separately and then integrated to study the dynamic behavior of the drive system. The study also examines the effectiveness of the drive system during starting, load perturbation, speed reversal and dc link voltage fluctuation.     

ANALYSIS OF CONVERTER CONTROLLED DC SERIES MOTOR. I. STEADY STATE ANALYSIS

ABSTRACT

The steady state and transient analysis methods of converter-fed dc series motor reported so far do not take into account the nonlinearity of the magnetic circuit. Furthermore, for transient analysis discontinuous conduction has been neglected and only first order model has been reported though series motor is essentially a second order system. In the present paper steady-state and transient analysis methods have been presented for fully-controlled and half-controlled converter-fed dc series motor taking the nonlinearity and discontinuous conduction into account.

The paper has been divided into two parts. Part I presents various approximations for the nonlinearity of the magnetic cir-circuit methods of calculating steady state performance and a method of calculating a suitable value of filter inductance. Theoretical deductions have been verified experimentally

Part II of the paper presents the methods of transient analysis     

DESIGN ASPECTS OF ENDTURN BANDS AND COIL SUPPORTS WITH REFERENCE TO COMMUTATION OF DC MACHINES

ABSTRACT

Influence of metallic endturn restraining bands and coil supports on commutation of dc machines is explored. A study of material type, temperature, speed of rotation, material thickness, permeability, and insulation spacing reveals that an axially conducting cylinder in the endturn area of a dc machine can be shown to act like an artificial addition of interpole turns, the number of which is variable with the conditions of operation. An expression is derived for the calculation of the effective number of these turns. Supporting experimental evidence is presented.     

EMF AND INDUCTANCES OF A TRANSFER FIELD SYNCHRONOUS MACHINE

ABSTRACT

This paper further develops the theory of the TF machine and examines the waveform of emf, and also the inductance variations of the machine, and compares these with test results. It is shown that it is possible, without special rotor profiling or the use of chorded or specially connected windings, to obtain in this machine inductance variations similar to those of a well designed, conventional, cylindrical rotor synchronous machine. This is also a necessary condition for satisfactory dc operation. The emf of such a machine would, for all practical purposes, be regarded as free of harmonics.     

DESIGN OF SATURABLE REACTORS FOR APPLICATIONS IN POWER CONDITIONING SYSTEMS

ABSTRACT

This paper presents the design of saturable chokes for use in power electronics and power conditioning systems. The inductances computed based on the finite-element field solution are compared with the estimated nonlinear inductances from the actual measurements. The results have shown the adequacy of the developed three-dimensional finite-element (FE) simulation. The calculated field solutions are used to assist the quantitative study of the influence of the nonlinear choke air gap on the inductance characteristics for intended application in the choke design.     

EMPLOYMENT OF THREE-PHASE COMPACT OSCILLATOR MODELS FOR REPRESENTING COMPREHENSIVELY TWO SYNCHRONOUS GENERATOR SYSTEMS

ABSTRACT

The paper deals with a new representation method for analyzing the operation of a two synchronous machine system. Each represented machine is considered as a complex oscillator. The oscillator represents many of the machine properties including a voltage regulation provision. The model attained in this way is relatively compact, and yet it describes each of the phases dynamic processes directly at the line frequency.

A series of simulation results which demonstrate the effect of load changes on other mechanical and electric variables in the two machine system is presented. The process of synchronization is also simulated in detail. The simulation results are compared to the results of experimental work. The similarity between experiments and simulations.suggests that the new method should be helpful in power system analysis. The main value of the method is in the analysis of relatively small generator systems where the interaction between mechanical transients and electric transients should be treated in detail. It is believed that the relatively new method which was previously employed by us mainly for investigating single machine systems is now shown to be potentially adequate for multimachine systems as well.     

ANALYSIS OF CONVERTER CONTROLLED DC SERIES MOTOR. II. TRANSIENT ANALYSIS

ABSTRACT

The steady state and transient analysis methods of converter-fed dc series motor reported so far do not take into account the nonlinearity of the magnetic circuit. Furthermore for transient analysis discontinuous conduction has been neglected and only first order model has been reported though series motor is essentially a second order system.

Various approximations for the nonlinearity of the magnetic circuit and steady state analysis have been described In Fart I of the paper. The present paper (Part II) describes the methods of transient analysis for fully-controlled and half-controlled converter controlled dc series motor taking the nonlinearity and discontinuous conduction into account. First order as well as second order models have been considered. Calculated performance has been verified experimentally.     

A NEW DYNAMICAL MODEL OF RECTIFIED OUTPUT AC GENERATORS

ABSTRACT

This paper is devoted to the statement of a new method for studying the dynamical behaviour of rectified output AC generators, The association synchronous machine-rectifier is considered as a whole and analyzed as a commutator DC machine with mobile brushes. The general equation of sliding contacts circuits is applied to work out the electrical equations of the generator and the relation defining the position of the brushes of the equivalent DC machine. Saturation effects are introduced by the classical Rothert method.

The equations are used to analyse the steady-state and transient behaviour of a three-phase, round-rotor synchronous machine connected through a bridge rectifier to an inductive load.

The theoretical results are compared with experimental measuremements, a good agreement is obtained for steady-state and transients.

The non-linear differential equations set describing the system can be linearized to work out its transfer function and analytical stability conditions, these results are useful for the study of excitation systems.     

ANALYSIS OF THE INTERFERENCE SYNCHRONOUS MACHINE

ABSTRACT

Interference synchronous machines operate at different speeds of the fundamental air gap field and of the rotor, because the fundamental permeance wave is produced by interference of open stator and rotor slots the numbers of which being slightly different. In the literature different names are used for this remarkable electrical machine (“Synchronous inductor motor”, “Vernier reluctance motor”). Interference synchronous machines are used as homopolar frequency generators with an axial field coil, as continuous running reluctance motors and as single- or double, - stack step motors with an axial permanent magnet.

In this paper the field of the interference synchronous machine is analysed by field wave theory. Speed,phase angle and length of the largest field waves reveal how synchronous and cogging torques are produced. Voltage and torque equations are derived by axis theory from the simplest model that is possible with five rotor teeth. The theory is applied on a fifty rotor teeth double-stack step motor. The inductances are determined by a difference method field calculation. The torque of the motor is then calculated and compared with measured values.     

CALCULATION OF THE LOCKED ROTOR CURRENTS AND TORQUE IN INDUCTION MACHINES

ABSTRACT

The analysis of certain end-winding vibration problems requires an accurate knowledge of the transient currents in an induction motor during the early part of the start-up period where the time rates of change of current are the highest. This paper details the derivation of expressions for the winding currents assuming that the machine remains at rest during the period of interest. Under these conditions, the currents are shown to contain three time dependent components, one of which is oscillatory, the remaining two being damped exponentials. The rates of decay of the exponential components are particularly important to some aspects of the vibration problem and they are shown to be dependent on the winding resistances and inductances and also upon the degree of coupling between stator and rotor.     

NON-TRANSFORMATIONAL MATRIX ANALYSIS OF ELECTRICAL MACHINERY

ABSTRACT

The general theory of electrical machines based on space phasor representation of space waves is explained. Harmonics of both the winding distribution and air-gap irregularities are taken into account for any winding asymmetry. Complex winding factors, symmetrical components of instantaneous values, and the winding inductances referring to the air-gap field are obtained during derivation of equation without the use of transformations. All quantities involved are physically defined. The method represents a common basis for analysis and design.     

SIMPLE DIGITAL SIMULATION FOR STEADY-STATE PERFORMANCE OF STATIC KRAMER DRIVE

ABSTRACT

The available methods of analysis of Static Kramer Drive are based on the assumption of constant current in the dc link. Because of this, power factor cannot be calculated accurately. It is also not possible to predict various voltage and current waveforms. The present paper describes a simple digital simulation method, which does not suffer from these limitations. Predicted results have been verified experimentally     

A DIGITAL METHOD FOR TRANSIENT ANALYSIS OF SATURATED SALIENT POLE SYNCHRONOUS MACHINES

ABSTRACT

A digital model for transient analysis of salient pole synchronous machines operating in the magnetically saturated regions is developed. Machine parameters used in this model are derived in terms of design particulars, with provisions for magnetic saturation using the magnetization characteristics of stator and rotor cores. Machine inductances are treated as additional clamped variables, continuously being updated during transient performance calculations. The model developed can be particularly useful in predicting transient characteristics of machines during early design stages, which facilitates implementation of necessary design modifications. Although certain transient tests are not feasible on the shop floor, this model can predict such test results. Results of this study include comparisons between model results, laboratory tests, short circuit data obtained by classical methods.     

POWER CONTROLLER FOR A WIND-TURBINE-DRIVEN TANDEM INDUCTION GENERATOR

ABSTRACT

A controller for delivering either constant power or maximum power from a wind-turbine-driven grid connected induction generator with double stator windings, one fixed and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described. The load torque of the generator is controlled by varying the angular displacement between the two stators. The generator can feed power to the grid at variable speed and constant frequency and is termed a Tandem Induction Generator.

Dynamic models for the wind energy conversion system are proposed for both controlled and uncontrolled operation to predict changes in shaft speed to shifts in wind speed using data pertaining to a commercial wind turbine. Results based on laboratory tests on a 1hp tandem machine driven by a dc motor demonstrating the feasibility of both controllers are presented. A steady state model of the tandem generator is also proposed and compared to measurements made on the test machine.     

ANALYSIS OF THE HVDC TURBINE GENERATOR TORSIONAL INTERACTIONS

Abstract

In the recent past it has been found that HVDC transmission systems and turbine-generator shaft torsional dynamics can interact in an unfavourable manner. This paper presents a detailed linearised state space model of AC/DC system to study this torsional interaction. The model developed is used to study the effect of various system parameters, such as, dc line loading, converter firing angle, the firing scheme employed. The results obtained are compared with those given in [ 3 ]     

STUDY OF THE HVDC-TORSIONAL INTERACTIONS THROUGH DIGITAL DYNAMIC SIMULATION

Abstract

This paper presents the detailed dynamic digital simulation for the study of phenomenon of torsional interaction between HVDC-Turbine generator shaft, dynamics using the novel converter model presented in [ 1 ] The system model includes detailed representation of the synchronous generator and the shaft dynamics, the ac and dc network transients. The results of a case study indicate the various factors that influence the torsional interaction.     

DC BRAKING CHARACTERISTICS OF DOUBLE-SIDED LINEAR INDUCTION MOTORS

ABSTRACT

An analysis of dc braking performance of linear induction motors is presented. Specific phenomena such as longitudinal end-effects and transverse edge-effects are taken into account. Computed results are compared with test results available for the dc braking characteristics of the existing largest double-sided linear induction motor.