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.     

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.     

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     

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.     

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.     

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.     

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.     

Experimental Studies on a Novel Braking System for Induction Motors

The results are presented of an experimental investigation of a novel multistage braking method (already reported by the authors in an earlier paper), which employs a graded capacitor system using single phase self-excitation followed by magnetic braking and a small dc injection at the end. Certain experimental observations have enabled a significant simplification of the control circuitry over the earlier reported one. A series of experiments were performed on a laboratory setup to determine the various transients during braking, in order to assess the suitability of the windings and the capacitor system. The effects of the capacitor value on the initial rate of fall in speed, the braking time, and the peak transients of voltages and currents were studied. Braking performance under this scheme is compared with that under the normal dc injection method. Typical experimental recordings are presented. Finally, certain useful experimental criteria for choosing suitable values of capacitors and the time delays between successive stages of switching are discussed.     

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.     

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.     

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.     

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.     

COMPARATIVE STUDY OF TWO QUADRANT CHOPPERS

ABSTRACT

The paper presents a comparative study of chopper circuits capable of providing two quadrant operation of do separately excited motor consisting of forward motoring and braking. The comparative study deals with the motor performance characteristics, motor armature current ripple, supply current harmonics, regenerated power, efficiency of regeneration and steady-state transfer characteristics.     

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.     

Development of an Induction Machine Commutated Thyristor Inverter for Traction Drives

Several designs detailing the construction of brushless cage-rotor induction machines operating at unity or leading power factor at the 35-hp level have recently been published [1]-[3]. The experimental machine combines the torque characteristics of a conventional cage induction machine with the leading power-factor (PF) capability of an overexcited dc field synchronous condenser into one unit using a common cage rotor and a common stator core. The ability of this machine to naturally commutate a high-power current-source thyristor inverter is apparent without any need for capacitors. The preferred adjustable speed propulsion arrangement consists of a mains-fed phase-delay-rectifier (PDR), high-voltage dc link, and a current-source inverter powering a ten-pole traction motor with constant V/Hz control. The drive system provides continuously variable torque during motoring, and regenerative braking modes and specific details are given for a 150-hp cage-rotor traction motor and converter, capable of natural commutation up to 200 Hz, currently under development.     

SUPERCONDUCTING LOW VOLTAGE DC TRANSMISSION NETWORKS

ABSTRACT

A new paradigm for electric power transmission based on high temperature superconducting dc. networks is studied as a feasible alternative to ac power transmission systems. The dc network operates at generation voltages allowing for direct connection of the generators to the rectifiers, eliminating the need for high voltage insulation and transformers. The overall system consists of a mesh connected, low voltage, high current dc superconducting transmission system, supplied by unit connected generators and feeding many small inverters to pass controlled levels of real and reactive power to ac loads. This paper introduces the concept of a superconducting dc mesh. Inverter topologies and control strategies required for interfacing the ac distribution systems to the dc mesh. The paper presents a conceptual overview of the operation of the system based on simulation studies.     

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.     

IMPEDANCE SPECTROSCOPY STUDY ON TRAP-CONTROLLED SPACE-CHARGE-LIMITED CONDUCTION OF Cr-DOPED SrTiO3 THIN FILMS

ABSTRACT

The electrical conduction properties of 0.2% Cr-doped SrTiO₃ thin film in metal–insulator–metal (MIM) structure was investigated by using dc and impedance spectroscopic measurements at room temperature. The dc measurement shows that the electronic conduction is the trap-controlled space-charge-limited current (SCLC) conduction. The impedance study shows that the electrical conduction is bulk-limited conduction. The behavior of the bulk resistance obtained in the equivalent circuit model from the impedance analysis is also consistent with the trap-controlled space-charge-limited conduction with exponential trap distribution.