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.     

MODIFIED ASYNCHRONOUS CASCADE MACHINE SYSTEM

ABSTRACT

The modelling of the modified asynchronous cascade machine system is done in order to study the features of such system under field-oriented frame of reference. The modified machine system has two stator windings and two sections of rotor winding on the same shaft One of the stator windings is connected to the ac network while the other winding is connected to an inverter capable of controlling power flow in both directions. This system can be operated in a wide speed range and both sections of the rotor winding can produce useful torque.     

ANALYSIS OF A SERIES-DELTA CONNECTED TANDEM INDUCTION MOTOR

Abstract

A tandem induction motor comprised of two independently housed stator windings, one housing stationary and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described. When the motor is fed from a single source, altering the position of the moveable stator changes shaft speed in a similar manner to operating a normal induction motor at variable terminal voltage

This paper presents an equivalent circuit model of the tandem induction motor for series-delta connected stator windings. Using the equivalent circuit stator current, power factor, and torque are calculated and then compared to laboratory test results obtained from a 3 kW tandem motor test rig     

PERFORMANCE STUDY OF A CHOPPER-CONTROLLED INDUCTION MOTOR

Abstract

In this paper, the speed of an induction motor is controlled using a chopper circuit on the rotor side. Analysis of transient, including switching power supply and changing in duty cycle of chopper, and steady-state performance of the chopper-controlled induction motor are predicted-Analysis and simulation consider the induction motor equations from the rotor side where a diode bridge is connected. Experimental results are obtained to verify predicted behaviour based on this digital simulation.     

A SOLID STATE RESISTANCE CONTROLLER FOR 3-PHASE SLIP-RING INDUCTION MOTOR

ABSTRACT

A solid state rotor resistance controller incorporating triacs for varying the speed of 3-phase slip-ring Induction motor delivering a constant load torque is presented. Using this controller, it is possible to vary the speed of the motor continuously from a definite minimum speed to a definite maximum speed. The controller is simpler and more reliable compared to phase controlled or chopper controlled resistance controllers.     

A Photovoltaic-based Improved Excitation Control Strategy of Three-phase Self-excited Induction Generator Suitable for Wind Power Generation

Abstract—Self-excited induction generators are extensively used for wind power generation in remote and grid-isolated areas. It is challenging to maintain constant voltage and frequency under variable loads and variable wind speed conditions for such kinds of generators. This article proposes a hybrid reactive power control technique for induction generators through a fixed capacitor bank connected at the stator terminals and a strategically switched inverter source. The inverter's DC bus is connected to a photovoltaic panel and a storage battery. This scheme provides stable voltage output with changing loads and widely varying wind speeds. The capacitor provides the bulk excitation current for the induction generator, while the inverter provides the additional reactive current desired to regulate the generator output voltage under variable wind speeds and variable loads. Suitable simulations and experiments validate the proposed concept.     

Co-Ordinated Self-Tuning Control for Turbine and Exciter of a Turboalternator

ABSTRACT

Multivariable minimum variance self-tuning control of the exciter voltage and turbine speed of an isolated a–c turbogenerator system connected to a large-scale power network is considered. Simulation studies, employing a high-order non-linear representative system model are reported, with emphasis on rigorous assessment of performance within an operational context. Three-phase faults, with and without permanent line-switching, dynamic and transient stability, are amongst problems addressed, and comparison with conventional control philosophies is made. Convergence of the self-tuning algorithm under a wide range of operating conditions is demonstrated, and results indicate that a self-tuning controller, based on minimal advance plant knowledge, provides a viable, robust alternative to conventional schemes within the power system environment.     

The Mathematical Model and Computer Simulation of an LCI Drive

ABSTRACT

A mathematical model of a LCI drive with it's control system is developed and the difference for the model between low speed and high speed is discussed. The computer simulating results of a 320 kw LCI drive, comparing with the experiment results are presented.     

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.     

A Comparative Sub-synchronous Resonance Analysis of Grid-connected Doubly Fed Induction Generator Based and Permanent Magnet Synchronous Generator Based Wind Farms

Abstract—This article aims to investigate the sub-synchronous resonance issue that may be caused by the wind farms connected to an electrical network through a series-compensated transmission line. Two wind turbine types based on a doubly fed induction generator and a permanent magnet synchronous generator are modeled for sub-synchronous resonance analysis in detail, and the proportional and integral parameters of the control loops are optimized based on a computational intelligence method. The studies are carried out on the IEEE first benchmark model. Small-signal analysis is conducted to reveal the impacts of series compensation level, parameters of proportional and integral controllers, and wind speed on the existing oscillatory modes.     

IMPEDANCES OF CYLINDRICAL ACTIVE AND RECTANGULAR PASSIVE ROTOR-CONDUCTORS

Abstract

The impedance connected with the electromagnetic field in cylindrical active and rectangular passive conductors of the rotor of a squirrel-cage motor is calculated. A distribution of the Joule power between these conductors is also examined. The investigations are made by using the Bubnov-Galerkin method. Graphs of the resistance, reactance and distribution power coefficient are drawn.     

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.     

DIGITAL SIMULATION OF A RECTIFIER LOADED SYNCHRONOUS MACHINE

ABSTRACT

The digital computer simulation of a rectifier loaded synchronous generator is described in this paper. The digital model of the synchronous generator with either a controlled or uncontrolled rectifier bridge deals efficiently with the complex commutation conditions when the source impedance is significant. From the equations developed in this paper, the performance of synchronous generators with or without damper windings, connected to controlled or uncontrolled bridge-rectifier loads, can be predicted from given loading data, field current, load current, generator speed and bridge delay angle. The approach described in this paper is valid for any bridge topology, and analysis of abnormal fault conditions presents no difficulties once the appropriate transformation matrix is available. The numerical analysis includes calculation of the performance of a synchronous generator with rectifier bridge loads for a variety of operating conditions.     

LINEAR SYNCHRONOUS HOMOPOLAR MOTOR (LSHM)—A DESIGN PROCEDURE FOR PROPULSION AND LEVITATION SYSTEM

ABSTRACT

This paper develops a design procedure of LSHM as an integrated propulsion and levitation means for high speed vehicles. The main specific phenomena such as field winding drag force are accounted for by a new analytical method proposed in the paper.

A numerical example for a full scale vehicle of 36 tonnes and 100 m/s is given to illustrate the application of the design procedure to yield the main parameters and performance characteristics of the motor.     

CHARACTERISTICS OF A VARIABLE SPEED SYNCHRONOUS MOTOR

ABSTRACT

Theoretical analysis of the steady state and transient characteristics of a variable speed synchronous motor is presented for two types of control namely voltage control and current control while the supply frequency to the armature is controlled by the instantaneous rotor speed. A laboratory experimental scheme using cycloconverters is described which is used to verify the torque-speed characteristics of the motor with voltage control.     

STUDY OF A HIGH VOLTAGE D-C GENERATOR

Abstract

A new high voltage d-c generator is presented. It is made of several transformer units in such a way that insulation problems can be conveniently solved. Several rectifying units are thus fed by alternation voltages, and are series connected. The object of the paper is to describe the electromagnetic behavior of this system, and to give a method to predict the external characteristics. A practical example is given, so that theoretical formulas are checked against experiment.     

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.     

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.     

THE SUPERCONDUCTING PADDLEWHEEL AS AN INTEGRATED PROPULSION LEVITATION MACHINE FOR HIGH SPEED GROUND TRANSPORTATION

ABSTRACT

The rotary superconducting motor, RSM, is shown to provide economical propulsion as well as levitation on a thinner aluminum track than “conventional” repulsion magnetic suspension.

With the RSM, thrust and braking are provided by controlling the relative speed of rotation of the motor essentially independent of lift at all forward speeds.

Using thin-plate theory, the lift and drag forces on the rotary superconducting motor are evaluated as a function of the forward speed of the vehicle as well as the relative speed of rotation of the motor. Although significant power is dissipated in the track through eddy current losses, evaluation of the energy consumption of the RSM over a route profile of 750 km with 5 intermediate stops shows this propulsion levitation system to have an energy consumption of 0.76 MJ/seat-km - significantly lower than other means of propelling and levitating high speed ground transportation.     

Ferroelectrics as a versatile solid state platform for integrated optics

Abstract

A high speed electro-optic scanner is demonstrated on a ferroelectric LiTaO₃ crystal. The scanner shows a deflection of 39.5 mrad/kV, 13 resolvable spots per kV, and shows no degradation of performance upto 10MHz of driving field. Integration of the scanner with quasi-phase-matched frequency doublers and lenses is discussed.