DC Dynamic Braking Performance of Linear Induction Motors

Abstract

Polyphase double-sided flat linear induction motor with non-magnetic conducting wide secondary operating in the dc dynamic braking mode is analyzed using field theory techniques. One-dimensional, One-dimensional space harmonic, Two-dimensional in the secondary plane, and Three-dimensional models are employed and performance is predicted. Predicted braking thrusts are compared to experimental results obtained elsewhere.     

Dynamic Braking of Induction Motors Using DC Injection

ABSTRACT

Dynamic braking of 3-phase induction motors through dc injection in commonly used in applications such as cranes and hoists. The paper analyses the performance of a slip ring induction motor with dc injection and derives expressions for the optimum values of injection voltage and rotor resistance. Digital computer simulation of the sequence of operations like motoring and braking is also given.     

A NEW METHOD FOR THE SYNTHETIC DETERMINATION OF THE LOSSES OF THREE–PHASE INDUCTION MOTORS

ABSTRACT

A new method for the synthetic determination of the losses of three–phase induction motors by means of direct tests is described. The tests are carried out with a reduced supply voltage and a reduced braking torque: subsequent calculations to refer the results to rated values are then applied.

Using this procedure, a considerable extension of the power range over which direct methods can be employed becomes possible, whilst avoiding the use of correspondingly more powerful braking devices.

A few experimental tests confirm the validity of the proposed method. Moreover, the potentialities of the method are discussed; then a few error analysis considerations are developed; finally, some possible thermal referring procedures are proposed.     

Braking Scheme for Vector-Controlled Induction Motor Drives Equipped With Diode Rectifier Without Braking Resistor

This paper deals with sensorless vector control of pulsewidth-modulated inverter-fed induction motor drives equipped with a three-phase diode rectifier. An electronically controlled braking resistor across the dc link is not used. Instead, the power regenerated during braking is dissipated in the motor while a dc-link overvoltage controller limits the braking torque. Losses in the motor are increased by an optimum flux-braking controller, maximizing either the stator voltage or the stator current depending on the speed. Below the rated speed, the braking times are comparable to those achieved using a braking resistor. The proposed braking scheme is very simple and causes no additional torque ripple. Experimental results obtained using a 2.2-kW induction motor drive show that the proposed scheme works well.     

TRANSIENT ANALYSIS OF BRAKING MODE OPERATION OF INDUCTION MOTOR FED FROM A VARIABLE FREQUENCY SOURCE

ABSTRACT

The transient behaviour of a three phase induction motor in the braking mode is investigated when the motor is fed from a variable frequency source. Appropriate voltage and frequency conditions to ensure minimum stopping time for plugging as well as for the case when plugging is used in conjunction with regenerative braking are identified. A dynamic model has been developed using the theory of instantaneous symmetrical component and associated operational equivalent circut and therefrom the transient performance of the motor in both the cases are compared with that of the normal plugging.     

Constant Torque Operation of Induction Motors Using Chopper in Rotor Circuit

A novel control scheme is investigated for operating induction motors in the constant torque mode. The basic control schemes and analysis of the steady-state performance of the system are presented. Circuit models are used to predict the performance characteristics. A new dc dynamic braking method is proposed and studied that provides very fast braking. Experimental results are presented to verify the theoretical predictions and demonstrate the feasibility of the control schemes.     

PERFORMANCE AND ANALYSIS OF CHOPPER FED D.C. SERIES MOTOR UNDER REGENERATIVE BRAKING

ABSTRACT

The paper presents a method of analysis and performance of chopper fed dc series motor under regenerative braking. The method of analysis takes into account the nonlinearity of the magnetic circuit, armature reaction, effect of commutation pulse and source inductance. Equations have been derived for the calculation of (a) machine speed-torque characteristics (b) regenerative power and efficiency of regeneration, and (c) current ripple and filter inductance value. The method also shows the prediction of stability at low speeds and conditions for failure of regeneration. The effects of chopper operating frequency, source inductance, commutation capacitor and input-filter capacitor on regenerative power and efficiency of regeneration, and stability of braking have been described. Theoretical deductions have been verified experimentally     

DYNAMIC BRAKING RESISTOR-REACTOR SWITCHING STRATEGIES THROUGH A NOVEL LINEAR TRANSFORMATION TECHNIQUE

ABSTRACT

Optimum switching strategies for dynamic braking resistor and shunt reactor is proposed for transient stability of a single machine infinite bus power system. The strategy is derived through a novel method of transforming the nonlinear dynamic model of the system to linear one. The simple optimum strategies derived from the linear model was observed to be very effective in stabilization.     

A Novel Method of Multistage Dynamic Braking of Three-Phase Induction Motors

An effective braking system suitable for three-phase induction motor drives is discussed. Braking is achieved in four stages using an electronic switching circuit. Initially, a single capacitor is connected across two of the motor terminals allowing single-phase self-excitation. Following a certain speed drop, a second capacitor is added across the same terminals to sustain self-excitation and reduce the speed further. In the third stage magnetic braking is achieved by short circuiting the third terminal. Finally, the motor is brought to a standstill by dc injection. A method of determining minimum capacitor requirements is presented for both single-phase and symmetrical application. Experimental results are included, demonstrating the validity of theoretical results regarding capacitor requirements, and indicating the effectiveness of the proposed braking scheme.     

FORCED OSCILLATIONS IN A TUBULAR LINEAR INDUCTION MOTOR

ABSTRACT

A method of obtaining forced sustained oscillations in a tubular linear induction motor (TLIM) is presented. Equations of motion of the motor/controller system are formulated and solved for various operating conditions. The performance of the system is thus evaluated. Results obtained from the analysis are compared with the experimental results     

TANGENTIAL FORCE DISTRIBUTION AND FORCE PULSATION IN A LINEAR RELUCTANCE MOTOR

ABSTRACT

A study of normal flux density, tangential force distribution and force pulsation is made on a segmented secondary linear reluctance motor. Appropriate analysis is included in a form convenient for numerical study. Results are obtained numerically for two different linear reluctance motor geometries corresponding to laboratory models. Some experimental results are compared with numerical results. The numerical results show that the normal flux density and the tangential force distribution vary with linear displacement but in a less severe manner than the same variables in a linear induction motor. The tangential force pulsation is significantly large and the normal force pulsation is less severe.     

Electronic Motor Braking

Electronic motor brakes (EMB's) can be applied to both new and existing machines to provide a rapid nonmechanical adjustable braking profile. They can also be used to supplement the braking torque of existing brake motors, forming a complete sequential braking system for demanding applications. The EMB stops without friction or wear. It also provides for an adjustable soft stop and can be mounted remotely from the motor. The new brake stops an ac induction motor by applying dc to the motor stator, thus providing braking torque within the ac motor. The EMB has two adjustments-braking current and braking time-which allow the selection of almost any braking profile. A positive lockout prevents the motor from being restarted during the braking phase. The typical electronic braking current is two to three times rated full-load current of the motor. Thus the heating effects upon the motor caused by the application of dc during the stopping function are minimal, particularly when compared to other electronic braking techniques such as plugging. The EMB becomes a part of the industry's only complete sequential braking package when combined with a motor-mounted friction disk brake which is spring-set and electrically releases to stop the load in the event of power failure and to provide a holding function. Together, the two types of brakes can offer an adjustable soft-stop profile with secure holding, as well as the ability to stop or slow down high inertia loads, yet stop them in the event of a power failure.     

MEASUREMENT OF PARAMETERS OF DC MACHINES

ABSTRACT

The methods for measuring the leakage inductances and the nonlinear magnetic parameters of the dc machine are presented. The methods to obtain the mechanical load characteristics of the whole mechanical system and to separate the friction and iron losses in the dc machine or various torques in the whole mechanical system follow from an inspection of the mathematical model of dc machines.

The practical measurement of the inductances of a 5 kW dc machine is described to show the procedure of the methods in detail     

PERFORMANCE ANALYSIS OF LOAD COMMUTATED INVERTER FED CAGE INDUCTION MOTOR DRIVE

ABSTRACT

An approach, to analyse the performance of a variable speed cage induction motor drive fed from load commutated inverter (LCI), is presented. Induction motor with an appropriate capacitor across its stator terminals constitutes the load on the inverter. A fully controlled bridge converter, supplied by a variable dc voltage source, commutated with the back emf of the motor, acts as an inverter. An algorithm to compute the motor performance, is developed using equivalent circuit representation of the system. Strategies for the selection of control variables, in order to achieve the desired speed range for satisfactory performance of the drive are given. The performance of a 3-hp, cage induction motor fed from LCI is computed, using the developed algorithm for wide range of speed; and is verfied experimentally.     

Capacitor braking of double-cage induction motors

Capacitor braking relies on the self-excitation process and represents a well-established technique of braking of single-cage induction machines. However, there appear to be no papers on the capacitor braking of double-cage induction motors. Since the self-excitation process constitutes the basis of capacitor braking, a correct representation must include the effects of main flux saturation in the induction machine model used. The paper first summarises the mathematical model of a saturated double-cage induction machine and then presents experimental results together with results of a comprehensive simulation study. Both symmetrical three-phase and asymmetrical single-phase capacitor braking techniques are considered. The results are shown for two different double-cage induction machines. The experimental and simulation results are found to be in good agreement.     

Analysis of Low-Speed Linear Induction Motors with Narrow Secondaries

Abstract

This paper describes a 2-dimensional mathematical model developed for the analysis of low-speed, double-sided, polyphase flat linear induction motor with narrow non-magnetic secondary. Transverse-edge effect thrust correction factors are derived and performance predicted.     

电梯回生电阻的温升研究

为了限制再生制动状态时电梯变频器直流侧的泵升电压,通常采用能耗制动的方式通过回生电阻消耗过剩的能量,从而使电容两端的电压维持在安全范围内.然而处在工作过程中的回生电阻发热严重威胁着变频器的工作安全,因此提出用MATLAB/SIMULINK软件搭建VVVF交流调速仿真模型,分析加入制动前后变频器工作状况,以求解出满足制动要求的电容电压波形.同时,通过C＋＋编程求解出短期发热过程中电阻的温升特性曲线,以便研究电阻的温升趋势,采取相应的冷却措施.     

FORCES IN A SINGLE-SIDED LINEAR INDUCTION MOTOR

ABSTRACT

This paper examines a number of the assumptions which are frequently made in the analysis of linear induction motors. Thrust and attractive force measurements made on a 2-m diameter test wheel fitted with an iron-backed aluminum sheet secondary and an arc-type primary are compared with results from three-dimensional field analyses. Among the effects which are examined in the paper are the curvature of the machine, the winding overhang, the finite permeability, conductivity and thickness of the backing iron.     

A SINGLE PHASE LINEAR TRAVELLING WAVE INDUCTION MOTOR

ABSTRACT

A simplified analysis of a single phase linear travelling wave induction machine is described. The analysis shows that the design goodness factor is independent of variation in the width of the airgap, and predicts that the performance of the machine will not be degraded by an increase in airgap. A machine designed and constructed on the basis of the analysis, was used to investigate the possibility of varying the airgap to control the speed. The results of these investigations are fully discussed.