ROLE OF TORQUE ANGLE IN INVERTER-FED INDUCTION MOTOR DRIVES

ABSTRACT

It is shown from the induction motor differential equations that changes in load torque, speed reference and torque angle are accompanied by a transient change in the speed of the air-gap mmf. The time constant associated with the torque angle change is different for a voltage source and a current source inverter-fed induction motor. This aspect throws light on the instability of current source inverter-fed induction motor on open loop operation. Evidently, the solution to overcome this instability is to use the torque angle for feedback control. It is proved that torque angle feedback alone is not sufficient for stabilization of the current source inverter-fed induction motor.     

The Minimum Input Power Conditions for Induction Motors Fed from Variable Frequency Sources

ABSTRACT

A simplified analytical method, based on the equivalent circuit of an induction motor, is presented for computing the frequency and voltage corresponding to the minimum input power. This optimum operating condition is determined for a specified torque and within a specified speed range. It is shown that the optimal per unit slip lies between the limits of zero and r₂/x₂     

TRANSIENT AND STEADY-STATE ANALYSIS OF A VOLTAGE CONTROLLED INDUCTION MOTOR DRIVE WITH DELTA CONNECTED WINDINGS

ABSTRACT

This paper deals with the transient and steady-state analysis of a voltage controlled induction motor (VCIM) drive with delta connected windings. Symmetrically triggered back-to-back connected thyristor pairs are used in each of the three lines to effect change in terminal voltage. Using a three-phase stator side equivalent circuit of the induction motor, the state equations for different modes of operation are formed and solved using a digital computer. The results of the transient and steady-state analysis for a specified triggering angle and load torque are presented and compared with those for a wye connected motor.     

Digital Simulation Of A Vector Current Controlled Axially-Laminated Anisotropic (ALA) Rotor Synchronous Motor Servo-Drive

ABSTRACT

It has been recently demonstrated that axially laminated anisotropic (ALA) rotor reluctance motors have high torque density, power factor and efficiency due to unusually high L_d/L_q ratios. For variable-speed vector-controlled drives no starting cage on the rotor is required. Through digital simulations this paper explores the steady-state torque and power factor capabilities and the transient performance of a vector ac current-controlled ALA-rotor motor drive. Fast torque and speed responses are demonstrated for a two-pole motor up to a speed of 2500 rpm. Good performance down to 0.1 rpm is obtained through an adaptive proportional integral (PI) speed controller.     

COMPUTER CONTROL OF THYRISTORIZED INDUCTION MOTORS AND ON-LINE PERFORMANCE PREDICTIONS

ABSTRACT

This paper describes a method of modelling the dynamic behaviour of thyristor controlled induction motors. Real time operational verification of the model is achieved by interfacing the drive system to a computer. The steady state torque produced by the motor is described as a function of firing angle, extinction angle and speed. The model concentrates on the open loop transfer functions of induction machines for small perturbations in motor speed and firing angles. The non-linear characteristics of the open loop transfer function has been discussed. The solutions presented here can lead to a comprehensive closed loop analysis for the dynamic behaviour of induction motors in industrial applications.     

Analysis and application of three-phase induction motor voltagecontroller with improved transient performance

An improved transient performance of three-phase inductance machines with controlled thyristor triggering is presented. A recently developed dynamic function for the thyristor triggering angle is utilized. The triggering angle function influences the phase modulation of the machine-supplied voltage such that the normal transient problems are avoided. Simulation of transients, based on the analytical solution of the machine differential equations, for all modes of operation is provided. The simulation model results show that a smooth switching process for an induction machine, running at any speed, for both motor and generator operation, is achievable. The beneficial effect of the suggested function is smoothing the transient flux, currents and torque is illustrated. Application of the function to different switching conditions is performed with actual laboratory tests     

SPEED AT BREAKDOWN TORQUE OF A SINGLE-PHASE INDUCTION MOTOR

ABSTRACT

The purpose of this paper is to present an “exact” analytical expression to calculate speed at breakdown torque and the breakdown torque of single-phase induction motors. From the theoretical expression for torque developed by a single-phase motor, a sixth order polynomial in speed at breakdown torque is obtained, and solved, using a well known method. A real root for per unit speed, i.e. the ratio of speed to the synchronous speed, that lies between 0 and 1 is selected and the actual breakdown torque is determined by substituting it in the torque equation. The breakdown torque, also termed as maximum torque, so obtained has been found to yield better correlation between the predicted and the tested results than the only existing empirical relation. Steps to calculate speed at maximum torque are also suggested. For an arbitrarily selected single-phase induction motor, a curve of speed at breakdown torque as a function of r₂/X is also included for the purposes of illustration and understanding.     

SPEED AND CURRENT CONTROL OF DC MOTOR IN CONTINUOUS CURRENT OPERATION

ABSTRACT

In this paper we present a non-linear rigurous model of a d.c. motor fed from single phase thyristor bridge. The current and speed control are realized by ; internal current loop with proportional controller and external speed loop with proportional-integral one without zero. This model has been linearised around a steady state operating point to study the behaviour of the system for small perturbations. Analytical formulas are given for the controller parameters for any desired response. A general method of simulation is presented to study the behaviour of the system, taking into account all the discontinuities which may be occur in such a system.     

DESIGN OF A MICROPROCESSOR BASED SLIP-POWER RECOVERY DRIVE

ABSTRACT

The complete design of a microprocessor based slip power recovery drive is described. The control scheme is implemented using the INTEL 8085 microprocessor and the flow chart of the speed controller is given. The set of nonlinear differential equations describing the dynamics of the system are linearized about an operating point which are then used to study the stability of the prototype control system in the z-domain and the design of the controller is presented. The experimental results agree closely with the predicted ones.     

SINGLE-PHASE MOTOR INDUCTION-RUN PERFORMANCE

ABSTRACT

Based on the rotating-field theory and the ‘exact’ equivalent circuit of a single-phase induction motor operating on its main winding only, accurate solutions are derived for the salient features of its torque to speed performance at pull-out and zero torque, to enable the torque-speed plot to be readily compiled with sufficient accuracy for preliminary-design purposes. The torque, current, power factor and efficiency at any speed are also derived for use in the final-design stage, again on the assumption that the airgap mmf is sinusoidally distributed. However, in order to be strictly applicable to many modern designs, the analysis is extended to cover in a simple manner the general case of significant space-harmonic mmfs being present in the airgap.     

ANALYSIS OF DISCONTINUOUS CONDUCTION IN A PWM DC CHOPPER DRIVE SYSTEM

ABSTRACT

This paper is concerned with the problem of analysis of quasi-steady and transient processes in a p.w.m. d.c. chopper drive system. An analitycal approach to the performance analysis of a d.c. separately excited motor fed from a chopper and operated in the region of discontinuous conduction is presented. The system equations are solved to obtain closed form solutions for motor current and speed, for quasi-steady as well as transient conditions. The solution for quasi-steady state condition corresponding to any set of operating conditions/voltage, chopper duty factor, load torque/ and mechanical characteristics of the drive are directly obtained.

Performance analysis of the system presented in this paper can be directly extended to a more complicated systems/for example, containing RLC input or output filter/.     

A NEW APPROACH TO PERFORMANCE ANALYSIS OF CHOPPER CONTROLLED D.C. MOTOR DRIVE

ABSTRACT

An analytical method for performance analysis of a d.c. separately excited motor fed from a chopper is presented. The motor input voltage is represented as a series of step-voltages with a time phase difference. The system equations are solved to obtain closed-form solutions for motor current and speed, for transient as well as steady state conditions. The method presented is superior to existing methods in that the solution is in closed-form, and does not make recourse to recursive numerical techniques. The solutions for steady state condition corresponding to any set of operating conditions (voltage, chopper duty factor, load torque) can be directly obtained. The computational effort and time needed is therefore extremely small as compared to other methods.     

PERFORMANCE ANALYSIS OF A D.C. DRIVE ELECTROMECHANICAL SYSTEM WITH ELASTIC COUPLING AND PULSATING LOAD TORQUE

ABSTRACT

This paper presents the analysis of a d.c. motor drive with a pulsating load torque and elastic mechanical link between the motor and the load. A mathematical model of the system using State Space technique is given and the equations are solved to obtain closed-form solutions for motor speed and current under transient and steady state conditions. The analysis reveals that the system performance is significantly affected by elasticity of the shaft and the nature of pulsation of load torque     

Ac Line Harmonics Caused by Three-Phase Half-Controlled Converters with DC Motor Load

ABSTRACT

This paper gives a study of line harmonics generated by three-phase half controlled bridge converters feeding separately excited D.C. motor. Analytical expressions for line current are given and dominant current and voltage harmonics have been computed for a typical system. The study shows that current has predominant low order harmonics, the second harmonic being significantly large as compared to other harmonics. The line voltage, however, has significant higher order harmonic components as well Line current harmonics are dependent on motor operating speed, whereas the voltage distortion factor is nearly independent of speed. On the other hand, percent current harmonics are nearly independent of torque, but the voltage harmonics and voltage distortion factor are dependent on load torque.     

Transient Analysis of Three-Phase SCR Controlled Induction Motors

The problem of simulating the transient performance of thyristor controlled three-phase induction motors is discussed. A method of solution by digital simulation using phase variables has been developed and is presented. The method enables transient current, speed, and electromagnetic torque patterns to be predicted for run-up conditions and conditions of operating mode transition. Application of the method is illustrated and sample results are presented and discussed.     

CALCULATION OF THE PULL-OUT TORQUE OF HYBRID STEPPING MOTORS IN THE HALF-STEP MODE

ABSTRACT

A method is described for predicting the pull-out torque/speed characteristics of hybrid stepping motors operating in the half-step excitation mode. The analysis assumes initially a linear magnetic circuit in order to derive an expression for the pull-out torque. Subsequently, the important effect of magnetic non-linearity is introduced into the calculation method by appropriate adjustment of the flux-linkage coefficients using an iterative computational routine. A comparison of experimental and predicted results is presented for a commercial 1.8°(200 step/revolution) stepping motor     

AN ELECTROMECHANICAL NETWORK MODEL FOR FREQUENCY CONTROLLED INDUCTION MOTORS

ABSTRACT

An electromechanical network model valid for small values of slip under steady state and dynamic conditions is given for frequency controlled induction motors. The model has been developed using the perturbation equations in the synchronously rotating reference frame and neglecting stator resistance and stator transients. Bode plots of incremental transfer functions relating speed and load torque as well as speed and stator frequency under constant volts/Hz control mode obtained from the exact and approximate models are compared with those of the electromechanical network model. The usefulness of the model in steady state and dynamic studies is discussed     

SWITCHING TRANSIENTS IN KRAMER DRIVE

Abstract

This paper deals with the torque, speed and current transients of a Kramer drive consequent to switching. Various starting conditions have been considered and torque, speed and current transients are computed in each case. Effect of D.C. motor field current, load torque, system inertia and filter inductance of these transients have been discussed. Experimental results are also presented     

磁动势法五相永磁力矩电机转矩分析

五相永磁力矩电机由于极数与槽数相近,含有丰富的磁动势谐波,磁动势谐波会影响电机的转矩性能。为此,采用磁动势法分析电机的电磁转矩,通过磁能和虚位移原理推导出了电机电磁转矩的解析表达式,揭示了具有相同空间次数的定子和转子磁动势谐波相互作用才能产生电磁转矩的规律。通过对五相永磁力矩电机的定、转子磁动势谐波与电磁转矩关系的分析,指出与与主波转速一致的定子和转子磁动势谐波相互作用能提高五相永磁力矩电机的平均电磁转矩。利用Ansoft有限元软件仿真分析了电机在正弦波、梯形波和方波供电下的定子磁动势、转子磁动势以及转矩性能。结果表明,非正弦供电能够增加电机的电磁转矩,但也带来了转矩脉动,验证了磁动势法分析五相永磁力矩电机转矩的有效性和正确性。     

DC Kiln Drive Motors

The most important considerations in applying dc drive motors and thyristor power supplies to a cement kiln are their procurement, maintenance, and operating costs; and equipment reliability in the cement plant environment. Drive requirements and their effect on motor size are discussed. Efficiency comparisons at several speeds for three different designs of dc drive motors are made. Two motor kiln drives with motors connected in series and also in parallel are discussed. Recommendations for applying each connection with regard to drive horsepower and voltage are made. Included is a brief discussion on applying dc motors by taking a part of the total speed range as constant horsepower rather than taking the entire speed range as constant torque.