TORQUE VECTOR CONTROL (TVC) OF AXIALLY-LAMINATED ANISOTROPIC (ALA) ROTOR RELUCTANCE SYNCHRONOUS MOTORS

Abstract

Axially-laminated anisotropic (ALA) rotor reluctance synchronous motors (RSMs) have been proved recently capable of higher torque density, higher power factor and efficiency compared to their induction motor counterpart with the same stator. Vector current control systems have been proposed for such drives, based on maximum available torque constant current angle or minimum current for a given torque constant current angle or combined current-voltage control. In an effort to do away with the current controller limitations, especially in the high speed region, the paper proposes a torque vector control (TVC) system which is a direct stator flux and torque control through a table of optimum switchings in the voltage-source PWM inverter. A sliding mode speed controller is added. Extensive digital simulations are presented. They demonstrate the TVC fast response, wide speed range and load rejection performance.     

TORQUE VECTOR CONTROL (TVC) OF AXIALLY-LAMINATED ANISOTROPIC (ALA) ROTOR RELUCTANCE SYNCHRONOUS MOTORS

Abstract

Axially-laminated anisotropic (ALA) rotor reluctance synchronous motors (RSMs) have been proved recently capable of higher torque density, higher power factor and efficiency compared to their induction motor counterpart with the same stator. Vector current control systems have been proposed for such drives, based on maximum available torque constant current angle or minimum current for a given torque constant current angle or combined current-voltage control. In an effort to do away with the current controller limitations, especially in the high speed region, the paper proposes a torque vector control (TVC) system which is a direct stator flux and torque control through a table of optimum switchings in the voltage-source PWM inverter. A sliding mode speed controller is added. Extensive digital simulations are presented. They demonstrate the TVC fast response, wide speed range and load rejection performance.     

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     

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.     

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.     

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.     

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.     

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.     

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     

速度推算转差频率矢量控制

本文提出一种带有速度推算算法的转差频率矢量控制。这一新的控制方案用速度推算算法取代常规转差频率矢量控制系统中的速度传感器,具有适用性广的优点。速度推算算法为转矩电流的指令值与定子电流转矩分量之差的积分,是根据一种新的感应电动机模型得到的。实现起来非常容易,本文对所提出的控制方案,在各种运行条件下进行了系统试验,实验结果表明,系统具有较好的动、静态性能。     

CHARACTERISTICS OF AN ASYNCHRONIZED SYNCHRONOUS GENERATOR

ABSTRACT

Theoretical steady state and transient characteristics of an asynchronised synclironous ( a.s.) generator, having excitation with full compensation for the emf induced in the field windings, are presented. Also transient characteristics of an a.s. generator, having excitation with field current feedback and slip feedback, are presented taking into consideration the ceiling voltage of the exciter

Finally a novel experimental excitation scheme using cyclo-converters and field current feedback is described, using which the steady state power, reactive power versus torque angle curves of a laboratory a.s. generator are obtained for the entire range ( 0 - 180° elec) of the torque angle at synchronous speed.     

A MODAL APPROACH TO THE TRANSIENT ANALYSIS OF SYNCHRONOUS MACHINES

ABSTRACT

A novel method for calculating the transient currents, flux linkages and electromagnetic torque of a synchronous machine following a sudden voltage disturbance is presented. The solution is obtained for a sudden change from an arbitrary balanced to an arbitrary unbalanced voltage condition. Since minimum constraints are placed on the disturbance, many typical types of transients such as three-phase and line-to-line short-circuit faults can be accommodated. Complete solutions for all machine currents are obtained as explicit functions of time. Any number of rotor circuits can be included and full allowance is inherently made for coupling between all stator and rotor circuits. Constant speed is assumed but no additional approximations are made other than those implicit in the derivation of Park's Equations. The technique incorporates the state space concept of modal analysis in its implementation. Closed form solutions obtained by the modal theory are compared with standard solution techniques     

DESIGN PROCEDURE FOR A SMALL SELF-CONTROLLED INVERTER-FED SYNCHRONOUS MACHINE WITH A PERMANENT MAGNET ROTOR

ABSTRACT

The object of the paper is the analytical study of a small permanent magnet inverter fed synchronous machine in order to find an optimal design. The inside flux density created by both the stator windings and the rotor magnet is calculated. This allows the design of the stator of the machine. Then, the variation of the torque as a function of the inner diameter is derived for a given outer diameter of the rotor (6.5 mm) leading to the rotor dimensions. Our final choice has been 2.75 mm corresponding to a torque of 68 10^?4 mN (experiment: 69). Nominal speed is around 6000 rpm for a 12 V direct current supply voltage. A simple model of the machine is developed and results are shown.     

A MICROPROCESSOR BASED CONTROL OF DC MOTOR DRIVES USING PROPORTIONAL-INTEGRAL (P-I) AND INTEGRAL-PROPORTIONAL (I-P) CONTROLLERS

ABSTRACT

This paper presents a Microprocessor based Digital control system for a DC Motor Drive using the commonly used P-I (Proportional-Integral) controller and a relatively new I-P (Integral-Proportional) controller. The relative merits and demerits of both P-I and I-P controllers are evaluated and compared. Important aspects, such as, the starting speed and current response; responses to step changes in the speed reference and the load torque; error signal processing; gain sensitivity, etc. are analyzed. It is shown that the I-P control scheme offers some distinctive advantages over the P-I control scheme. Some experimental and simulation results 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.     

ESTIMATION OF ROTOR VOLTAGE VECTOR ON THE DOUBLE EXCITED INDUCTION MACHINE USED IN WECS

ABSTRACT

The aim of this work is to estimate and control the rotor voltage of a double excited induction machine DEIM that is necessary to operate it as a generator in wind energy conversion systems (WECS), with speed range extending from the sub synchronous range to double the synchronous speeds. For efficient power generation, the DEIM is to be operated at its rated electric torque which is realised by having both rotor and stator currents magnitudes constant throughout the whole operating range. Also the angle between the rotor current and stator current is kept constant irrespective of the rotor speed.     

Computer-Aided Analysis of a Converter-Fed Saturated Synchronous Motor Drive

ABSTRACT

A method of numerical simulation for evaluation of the performances of a variable speed synchronous motor drive is developed. The machine has rotor saliency with armature and damper windings. Magnetic saturation in both d and q axes are also taken into consideration. The model is focused specially for analysis of a self-controlled reluctance motor drive fed either by voltage source inverter or current commutated inverter. The computer solution permits accurate calculation of current, voltage, and torque waveforms. Sample calculations for highly saturated converter-fed reluctance motor drive are presented including comparison with practical tests.     

ANALYSIS OF STATE FEEDBACK CONTROL OF CHOPPER DRIVEN SEPARATELY EXCITED D.C. MOTOR

ABSTRACT

Armature voltage control of d.c. motor speed to a set point in the face of large step torque changes can be treated as a regulation problem in linear system theory. By proper pole assignment, one can have complete control over the dynamics of the closed loop system. The control input comes out as a function of the states, motor speed and armature current respectively, and integral of the output (speed error). The paper deals with separately exicited d.c. motors fed from a thyrister chopper circuit controlled by the state feed back signal. Discontinuous mode of current conduction in the chopper gives rise to unwanted swings in the dynamic response of the system. The proposed approach models the system taking discontinuous mode of current conduction into account, obtains the feed-back constants and predicts the oscillations that may come into picture at low shaft torques. Also a time varying model in proposed and this gives the designer an insight into the working of the system and guides him in his choice of the feedback coefficients. The proposed regulation method has been tested on a laboratory model d.c. motor, and the experimental and the theoritically predicted response curves are found to be in agreement     

THYRISTOR CONTROLLED PULSATING FIELD RELUCTANCE MOTOR SYSTEM

ABSTRACT

Integral horsepower pulsating field reluctance motors are treated when operating in dc-supplied, fixed voltage, thyristor controlled variable speed systems. A thyristor controller with two operating modes is described. Exciting MMF differential equations are put into normalized forms, simplifying their solutions, which are given. Three parameters Q, p and x_rs concisely character= rize motor, MMF differential equations and torque. For typical speed/torque curves thyristor control angles are determined. Optimum pole- and gap dimensions are investigated on the basis of published permeance charts.     

Control Algorithm for the Inverter Fed Induction Motor Drive with DC Current Feedback Loop Based on Principles of the Vector Control

ABSTRACT

This paper brings out a control algorithm for VSI fed induction motor drives based on the converter DC link current feedback. It is shown that the speed and flux can be controlled over the wide speed and load range quite satisfactorily for simpler drives. The base commands of both the inverter voltage and frequency are proportional to the reference speed, but each of them is further modified by the signals derived from the DC current sensor. The algorithm is based on the equations well known from the vector control theory, and is aimed to obtain the constant rotor flux and proportionality between the electrical torque, the slip frequency and the active component of the stator current. In this way, the problems of slip compensation, Ri compensation and correction of U/f characteristics are solved in the same time. Analytical considerations and computer simulations of the proposed control structure are in close agreement with the experimental results measured on a prototype drive.