POSITION CONTROL OF A TWO DEGREE-OF-FREEDOM ACTUATOR

Abstract

The paper describes control of a helical-motion induction motor (HMIM) which can be used in a tandem arrangement of two units to form a direct-acting, two degree-of-freedom actuator capable of producing pure rotary motion, pure linear motion, or helical motion. A microprocessor-based controller is designed to drive this closed-loop position control actuator. A proportional control with high gain about command position is implemented to give a desired stiffness coefficient. Using the microprocessor system, an artificial viscous damping is introduced to enhance the dynamic performance.     

EFFECTS OF INDUCTION MOTOR LOAD ON DYNAMIC STABILITY OF POWER SYSTEMS

Abstract

A study of the effects of induction motor load on the dynamic stability of power systems is presented in this paper. The power system is modelled as a multivariable system with load dynamics considered in the feedback path. The induction motor is represented by a transfer function matrix relating bus voltage magnitude and frequency to the active power and reactive power of the motor

Multivariable Nyquist criterion and eigenvalue analysis are used to investigate the effects of induction motor dynamics on system stability     

TORQUE CHARACTERISTICS OF A SELF-CONTROLLED SYNCHRONOUS MOTOR

ABSTRACT

This paper presents a study of the torque characteristics of a self-controlled synchronous motor drive in which motor terminal voltages are used for inverter synchronization. Torque control techniques for normal operation and for starting are considered. A control strategy which optimizes the motor power factor and torque is studied. Experimental results are given.     

QUICK AND PRECISE POSITION CONTROL OF ULTRASONIC MOTORS WITH TWO CONTROL INPUTS

ABSTRACT

Ultrasonic motor (USM) has an excellent performance and many useful features. Since this motor is superior in holding torque and high response characteristic, it has been expected to use as position servomotor for small motors.

There have been reported some mathematical models of the ultrasonic motor. however, these models are too complex to apply for control of the motor. Therefore position controllers based on PI control or fuzzy control have been proposed in recent years. It is difficult to control the ultrasonic motor with high-performance using such controllers, thus simple and convenient mathematical model is necessary for precise control.

This paper presents a new position control scheme of ultrasonic motor, it consists of a PI controller and an adaptive controller which compensates the speed characteristic variations with online parameter identification. Moreover, this system controls both driving frequency and phase difference in order to achieve a quick and precise position control. The effectiveness of proposed control.scheme is demonstrated by experiments.     

MEASUREMENTS OF IRON LOSSES IN SINGLE-/PHASE SQUIRREL CAGE MOTORS

ABSTRACT

To determine the iron losses of a shaded pole motor, the authors have removed the shading ring, thus obtaining a single phase motor of particular characteristics. Using Veinott's method, they first obtained 60 Watts under normal conditions, that is to say, 30 Watts per kilogram of lamination. To check this value, they tried to set up two other methods, which are the object of the present paper. In both methods, the motor is represented by the equivalent circuit of a single phase-motor without iron losses, in parallel with a constant resistance which absorbs a power equal to the iron losses (which are thus assumed constant).

The first method is based on some geometrical properties of the impedance diagram of a single phase motor. The second method is analytical. A modification of Veinott's method is then presented to explain the results.     

IMPROVEMENT OF THE PERFORMANCE OF A SUPERCONDUCTING TURBOGENERATOR THROUGH USE OF A CONTROLLABLE REACTIVE POWER COMPENSATOR

ABSTRACT

This paper presents the dynamic performance of a superconducting turbo-generator which employes a thyristor controlled static reactive power compensator at its terminals. The application of the fast acting compensator external to the machine, in a power system, is foreseen as one possible alternative to alleviate the excitation problems which arise on account of the extremely large field time constant of a superconducting generator. This application is compatible with the fast development in the rating of static compensators and imminent use of superconducting machines in the future.

The paper dwells on the transient aspects of performance to evaluate the feasibility of use of an external controller for voltage and also incorporating stabilizing signals. Simulation of the load rejection and transient stability dynamic performance of the superconducting alternator with and without thyristor controlled static compensator brings out its superiority over the field forcing techniques usually used with the conventional generators.     

电动汽车用SRM数字化驱动系统的设计

设计了以TMS320LF2407为主控制器，电动汽车用开关磁阻电动机数字化驱动系统。给出了系统的硬件电路和软件框图。采用转矩矢量控制策略，有效地抑制了转矩脉动。仿真及实验结果表明：系统硬件简单、实用性好，具有良好的动态和静态特性。     

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 METHODOLOGY OF SECURE AND OPTIMAL OPERATION OF A POWER SYSTEM FOR DYNAMIC CONTINGENCIES

ABSTRACT

Just as in static security constrained optimization of power systems, there is need to do preventive scheduling if the system state is found to be insecure through dynamic contingency analysis. Current work in this area based on energy functions and sensitivity considerations only computes another feasible and normal operating point either through the controlling u.e.p or the potential energy boundary surface method. In this paper we use the hybrid method which involves integration of the system equations only once till the controlling u.e.p is reached to compute the energy margin. Based on the sensitivity of the energy margin to generation powers, rescheduling is done through an OPF algorithm resulting in a secure but optimal solution. Results on a 3 machine, 9 bus system are very encouraging. This methodology could form a basis for integrating current OPF packages into the DSA package.     

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/.     

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.     

THYRISTOR CONVERTER-FED SYNCHRONOUS MOTOR DRIVE

ABSTRACT

The development, design and construction of a variable speed drive using a synchronous motor is described in this paper. At first, the operation of motor with a current-fed, motor e. m. f. commutated inverter is explained. The working of control circuitry is explained next with the aid of logic and functional blocks. The power circuit, comprising the converter, inverter and motor has been reduced to simple blocks so that the controller design by hand computations becomes possible. It has also been shown that the digital simulation based on simplified block diagram is accurate enough for obtaining the responses of the system to step changes in speed reference and load on motor.     

CLOSED LOOP PERFORMANCE OF INDUCTION MOTORS WITH CONSTANT VOLTS/HERTZ CONTROL

ABSTRACT

Characteristics of a closed loop induction motor drive, supplied from a variable frequency voltage source, and operating under constant volts/hertz control are presented. The motor linearized equations in the synchronously rotating reference frame are used to analyse the drive dynamic performance. It is shown that this performance can be greatly improved by including a properly designed speed controller in the drive structure. Thus, the decrease in stability, associated with the open loop motor operation is eliminated and the resulting drive gives satisfactory performance over the entire input frequency range. The experimental results, which confirm the validity of the motor dynamic model are also included.     

SOLID-STATE CONTROL OF A WIND-DRIVEN SELF-EXCITED INDUCTION GENERATOR

ABSTRACT

The paper analyses a system of autonomous induction generator directly feeding,without a d.c link, an induction motor. The generator is driven by a wind energy turbine and the motor is driving a water pump. The analysis is based upon a mathematical model that accounts for the various nonlinearities and mutual interactions of the system elements. Investigations of such a system revealed that it can be controlled to extract the maximum available wind energy by proper adjustment of the terminal voltage of the generator. The required control strategy is formulated, then it is implemented by a static VAR controller which supplies the induction generator with necessary reactive power.     

CONCEPTS OF STATIC VAR SYSTEM CONTROL FOR ENHANCING POWER TRANSFER IN LONG TRANSMISSION LINES

ABSTRACT

This paper is concerned with the influence of different levels of complexity in modelling various constituent subsystems on the dynamic stability of power systems compensated by static var systems (SVS) operating on pure voltage control. The system components investigated include thyristor controlled reactor (TCR) transients, SVS delays, network transients, the synchronous generator and automatic voltage regulator (AVR). An overall model is proposed which adequately describes the system performance for small signal perturbations. The SVS performance is validated through detailed nonlinear simulation on a physical simulator.     

A DYNAMIC INDUCTION MOTOR MODEL INCLUDING SPACE HARMONICS

ABSTRACT

An induction motor model is presented which can be used to compute dynamic characteristics and which includes both asynchronous and synchronous parasitic torque effects owing to space harmonics. A new transformation is given which eases computation and enables the stability of the synchronous parasitic torque to be determined. The model is applied to the computation of the direct on line starting characteristic for a four pole, three phase cage machine with 36 stator slots and 28 rotor slots.     

ANALYTICAL APPROACH TO THE OPERATION OF A SYNCHRONOUS MACHINE ASSOCIATED WITH A THYRISTOR BRIDGE

ABSTRACT

A synchronous machine associated with a thyristor bridge operates normally under unbalanced conditions which are described and studied in the present paper. Natural cut-off thyristors is used in the present system where the gates of thyristors are controlled by the rotor position. It is assumed that the machine has salient poles and damper windings. Both motor and generator operations are contemplated.

An analytical approach has been used, and the exact shape of the currents has been considered. The commutation problem is studied in detail, taking into consideration the transient effects of the armature circuits and the limited value of the smoothing reactor. The different expressions are given in terms of the classical machine constants which can be directly measured or furnished by the manufacturer. Comparison between theoretical and practical results are given.     

DESIGN OF VARIABLE SPEED INDUCTION MOTOR DRIVE WITH A CURRENT-FED INVERTER

ABSTRACT

A closed-loop speed control scheme with reversing and regenerating capability for a squirrel-cage induction motor is described. The scheme makes use of a fully-controlled bridge for a.c. to d.c. conversion, a currend-fed inverter for generation of variable frequency a.c. supply for motor and an analogue tachogenerator for speed feedback signal. The current-reference signal is generated by a novel slip calculator. This paper describes the slip calculator and the design of controllers based on an approximate model of motor. Experimental results validating the methods used for design of controllers are also presented.     

MODIFIED SLIDING MODE (MSM) VERSUS PI SPEED CONTROL OF A CURRENT-CONTROLLED FIELD-ORIENTED INDUCTION MOTOR DRIVE

ABSTRACT

This paper describes the dynamic performance of a new, modified sliding mode (MSM), speed control system for an existing current-controlled field-oriented induction motor drive with rather robust rotor flux estimator.

Extensive digital simulations and some test results prove the superiority of IBM versus PI in terms of reduced speed overshooting, response quickness, and robustness to rotor resistance variation. The rotor flux estimator amplitude and phase error during severe transients has also been investigated through digital simulations.     

A VARIABLE VOLTAGE AND FREQUENCY SCHEME TO OPTIMIZE THE EFFICIENCY OF A WIND-DRIVEN INDUCTION GENERATOR

ABSTRACT

The most recent approaches to harness energy from the wind utilizing induction generators has been made possible by advances in induction motor control using power electronic drives. The freedom in adjusting terminal voltage or current, and frequency al lows operation of the induction machine to fit any desired characteristic. The purpose of this paper is to propose a scheme using this technology to convert wind energy to electricity at maximum wind turbine power and induction generator efficiency. The Electromagnetic Transients Program (EMTP) is used to simulate the control of the induction generator. Simulation results show that this system operates as predicted in a stable fashion at the desired operating point.