Differential-Algebraic Approach to Speed and Parameter Estimation of the Induction Motor

This thesis considers a differential-algebraic approach to estimating the speed and rotor time constant of an induction motor using only the measured terminal voltages and currents. It is shown that the induction motor speed satisfies both a second-order and a third-order polynomial equation whose coefficients depend the stator voltages, stator currents, and their derivatives. Further, it is shown that as long as the stator electrical frequency is nonzero, the speed is uniquely determined by these polynomials. The speed so determined is then used to stabilize a dynamic (Luenberger type) observer to obtain a smoothed speed estimate. With full knowledge of the machine parameters and filtering of the sensor noise, simulations and experiments indicate that this estimator has the potential to provide low speed (including zero speed) control of an induction motor under full load. A differential-algebraic approach is also used to obtain an estimate of the rotor time constant of an induction motor, again using only the measured stator voltages and currents. Experimental results are presented to demonstrate the practical use of the identification method

Recent Advances in Robust Control

Robust control has been a topic of active research in the last three decades culminating in H_2/H_\infty and \mu design methods followed by research on parametric robustness, initially motivated by Kharitonov's theorem, the extension to non-linear time delay systems, and other more recent methods. The two volumes of Recent Advances in Robust Control give a selective overview of recent theoretical developments and present selected application examples. The volumes comprise 39 contributions covering various theoretical aspects as well as different application areas. The first volume covers selected problems in the theory of robust control and its application to robotic and electromechanical systems. The second volume is dedicated to special topics in robust control and problem specific solutions. Recent Advances in Robust Control will be a valuable reference for those interested in the recent theoretical advances and for researchers working in the broad field of robotics and mechatronics

Harjattoman tasavirtamoottorin arviointi opto-mekaanisessa paikkasäätösovelluksessa

This thesis evaluates the applicability of a micro-sized brushless direct current (DC) mo- tor in an opto-mechanical positioning application. Brushless DC motors are electronically commutated motors that use permanent magnets to produce the airgap magnetic field. The motor is powered through an inverter or switching power supply which produces an AC electric current to drive each phase of the motor. Optimal current waveforms are determined by the motor controller based on the desired torque, speed or position requirements. The benefits of a brushless motor over conventional brushed DC motors are a high power to weight ratio, low noise and a long operating life. The purpose of this thesis is to find out the performance potential of such motors and determine methods to achieve it. Firstly, a motor model and an exact motor classification is presented. A literature review is made to discuss state of the art control methods and hardware configurations for dynamic position control. Based on the literature review, a control scheme with field-oriented control based torque control and cascaded PI controlled speed and position loops was selected for further evaluation. Experimental positioning tests were executed for two motors with different power transmission setups. Tests were performed with both, a hardware and software implemented, motor controllers. Results show promising performance. It was shown that the required acceleration is feasible with both, geared and direct drive, transmissions. Field-oriented control was shown as a well performing method to control torque but special caution was needed to implement a reliable position sensing solution in a small size as the control algorithm is intolerant for inaccurate and noisy position data. The conventional PI based position controller was effective in cases with no feedback related harmonics or motor related torque ripple but was not capable in handling ripple caused by a non-ideal system. Quality variances were seen between motors which were originated from mechanical defects and non-idealities in the stator structure. Further research is needed to achieve a better settling performance through filtering undesired feedback harmonics, better tuning and thus minimizing undesired vibrations.Tämän diplomityön tarkoituksena on arvioida pienikokoisen harjattoman tasavirtamoottorin soveltuvuutta opto-mekaaniseen paikkasäätösovellukseen. Harjattomat tasavirtamoottorit ovat elektronisesti ohjattuja moottoreita, joissa ilmavälin magneettivuo luodaan kestomagneeteilla. Moottorille syötetään virtaa taajuusmuuttajalta, joka muodostaa halutunlaisen vaihtovirran jokaiselle moottorin vaiheelle. Syötettävää virtaa ohjataan moottorinohjaimelta määritettyjen vääntö-, nopeus- ja paikkavaatimusten perusteella. Harjattoman DC-moottorin edut verrattuna perinteiseen harjalliseen DC-moottoriin ovat hyvä teho-painosuhde, hiljainen käyntiääni ja pitkä käyttöikä. Diplomityön tavoitteena on kartoittaa kyseisen moottorityypin suorituskyky paikkasäädössä ja tutkia keinoja saavuttaa haluttu taso. Alan tutkimuksessa ja kirjallisuudessa tunnettuja suorituskykyisiä säätömenetelmiä ja laite- sekä komponenttikokoonpanoja on koostettu kirjallisuuskatsauksessa. Tämän perusteella kokeellisiin testeihin valittiin säätöarkkitehtuuri vektorisäätöön perustuvalla virransäädöllä sekä PI-pohjaisilla nopeus- ja paikkasäätimillä. Kokeellisilla paikoitustesteillä arvioitiin kahden moottorin suorituskykyä erilaisilla voimansiirtovaihtoehdoilla. Testit suoritettiin sekä ohjelmistopohjaisella että sovelluskohtaiseen mikropiiriin toteutetulla laitepohjaisella säätimellä. Tulokset osoittavat että vaaditun kiihtyvyyden saavuttaminen on mahdollista sekä vaihteellisella että suoravetoisella voimansiirrolla. Vektorisäätö osoittautui suorituskykyiseksi virransäätömenetelmäksi, mutta moottorin asentomittauksen luotettava toteutus vaati erityishuomiota, sillä vektorisäätöalgoritmi on herkkä paikkadatan tarkkuudelle. PI-säätimillä toteutettu paikkasäätö osoittautui toimivaksi, mutta herkäksi moottorin epäideaalisuuksille sekä häiriöille takaisinkytkennässä. Moottoreiden välillä havaittiin laatueroja mekaanisissa toleransseissa ja staattorin rakenteessa. Lopullisen asettumisajan saavuttaminen vaatii lisätutkimusta. Erityishuomiota on kiinnitettävä harmonisten komponenttien suodattamiseen sekä systeemin säätöön, jotta ei-toivotut värinät saadaan minimoitua

Sensorless control of induction machine

AC drives based on fully digital control have reached the status of a maturing technology in a broad range of applications ranging from the low cost to high performance systems. Continuing research has concentrated on the removal of the sensors measuring the mechanical coordinates (e.g. tachogenerators, encoders) while maintaining the cost and performance of the control system. Speed estimation is an issue of particular interest with induction motor electrical drives as the rotor speed is generally different from the speed of the revolving magnetic field. The advantages of sensorless drives are lower cost, reduced size of the machine set, elimination of the sensor cable and reliability. However, due to the high order and nonlinearity of the IM dynamics, estimation of the angle speed without the measurement of mechanical variables becomes a challenging problem. Variety of solutions has been proposed to solve this problem in the literature. In this thesis work, by combining the variable structure systems and Lyapunov designs a new sensorless sliding mode observer algorithm for induction motor is developed. A Lyapunov function is chosen to estimate the rotor flux of an induction motor under any initial condition based on the principle that the aim of the vector control of IM is to keep the rotor flux magnitude constant from zero to nominal speed. Additionally, an observer estimating the rotor speed and the rotor time constant of the machine simultaneously has been proposed that stems from the flux estimation. The proposed method is very suitable for closed loop high-performance sensorless drives and it is believed that with its new approach it will help many researchers in their further work in the field of sensorless vector control of IM

Control of synchronous motor drives with an LC filter

Electric motors can experience voltage stress over the motor terminals due to the short rise time of the voltage pulse at the inverter output and the impedance mismatch between the lead cables and the motor. This overvoltage degrades the motor insulation, thus reducing the motor lifespan. The problems can be avoided by using a sinusoidal LC filter in the inverter output, limiting the overvoltage and dampening high-order harmonics. However, the existing control methods for LC-filtered synchronous motors are infeasible for plug-and-play drives, in which the motor data or user input are not required. This is because the methods either contain several cascaded control loops, require cumbersome parameter tuning, are sensitive to parameter errors, or the range of operating speeds is limited. Nevertheless, recently developed observer-based volts-per-hertz control shows advantages through relatively low sensitivity to parameter errors, simplicity and generality of the control algorithm, and reliance on common control gains for all synchronous motor types. These attributes indicate that the observer-based volts-per-hertz control can be used for medium-performance drives ensuring robust and stable operation at a wide range of speeds. This thesis develops observer-based volts-per-hertz control for synchronous motor drives with an LC filter. The two designed methods are based on two different observer types (reduced-order and full-order) with two state feedback control laws. The methods are further linearized by means of small-signal linearization, the control strategies are simulated in Simulink, and experimental measurements validate the simulations. The measurement results show a satisfactory performance of the permanent magnet synchronous motor with both methods. However, the control performance of the synchronous reluctance motor is poor when the full-order observer is used. The thesis subsequently provides several suggestions for future work improvements

Precision Control of a Sensorless Brushless Direct Current Motor System

Sensorless control strategies were first suggested well over a decade ago with the aim of reducing the size, weight and unit cost of electrically actuated servo systems. The resulting algorithms have been successfully applied to the induction and synchronous motor families in applications where control of armature speeds above approximately one hundred revolutions per minute is desired. However, sensorless position control remains problematic. This thesis provides an in depth investigation into sensorless motor control strategies for high precision motion control applications. Specifically, methods of achieving control of position and very low speed thresholds are investigated. The developed grey box identification techniques are shown to perform better than their traditional white or black box counterparts. Further, fuzzy model based sliding mode control is implemented and results demonstrate its improved robustness to certain classes of disturbance. Attempts to reject uncertainty within the developed models using the sliding mode are discussed. Novel controllers, which enhance the performance of the sliding mode are presented. Finally, algorithms that achieve control without a primary feedback sensor are successfully demonstrated. Sensorless position control is achieved with resolutions equivalent to those of existing stepper motor technology. The successful control of armature speeds below sixty revolutions per minute is achieved and problems typically associated with motor starting are circumvented.Research Instruments Ltd

Advances in Rotating Electric Machines

It is difficult to imagine a modern society without rotating electric machines. Their use has been increasing not only in the traditional fields of application but also in more contemporary fields, including renewable energy conversion systems, electric aircraft, aerospace, electric vehicles, unmanned propulsion systems, robotics, etc. This has contributed to advances in the materials, design methodologies, modeling tools, and manufacturing processes of current electric machines, which are characterized by high compactness, low weight, high power density, high torque density, and high reliability. On the other hand, the growing use of electric machines and drives in more critical applications has pushed forward the research in the area of condition monitoring and fault tolerance, leading to the development of more reliable diagnostic techniques and more fault-tolerant machines. This book presents and disseminates the most recent advances related to the theory, design, modeling, application, control, and condition monitoring of all types of rotating electric machines

Performance comparisons of doubly-fed machines

This research project aims at evaluating a conversion system based on the emerging Brushless Doubly Fed Reluctance Machine (BDFRM) through a comparative experimental study with a traditional and well established slip-ring counterpart, the Doubly Fed Induction Machine (DFIM). One of the main objectives is to establish whether this alternative machine is worthy of industrial consideration in variable speed applications with limited speed ranges (e.g. wind turbines, pump-like drives etc.) in terms of control, reliability, efficiency and power factor performance as major criteria. Such kind of work has not been reported in the open-literature to date and represents the main contribution of the project being undertaken. A conventional and widely used parameter-independent vector control (VC) scheme has been selected for the operation of both the machines using a shaft-position sensor. The VC algorithm has been simulated and implemented in real-time on state-of-the-art eZdsp development platform based on the TMS320F28335 Digital Signal Controller (DSC). The control code has been derived from a programme written in C++ using the corresponding compiler, the Code Composer Studio (CCS). Comprehensive computer simulations have been done in Matlab/Simulink using the parameters obtained by off-line testing of the DFIM and BDFRM prototypes, which have been built in the same stator frame for comparison purposes. The simulation results have been experimentally verified on two identical test rigs where a commercial 4-quadrant cage induction machine V/f drive has been used as a prime mover or load for either the DFIM or the BDFRM subject to their operating mode. The preliminary experimental results on two small-scale prototypes have shown that the BDFRM can achieve competitive performance to the similarly rated DFIM and as such should warrant further investigation and increasing interests of both academic and industrial communities as a potential large-scale wind generator or a pump drive

Advanced Computational-Effective Control and Observation Schemes for Constrained Nonlinear Systems

Constraints are one of the most common challenges that must be faced in control systems design. The sources of constraints in engineering applications are several, ranging from actuator saturations to safety restrictions, from imposed operating conditions to trajectory limitations. Their presence cannot be avoided, and their importance grows even more in high performance or hazardous applications. As a consequence, a common strategy to mitigate their negative effect is to oversize the components. This conservative choice could be largely avoided if the controller was designed taking all limitations into account. Similarly, neglecting the constraints in system estimation often leads to suboptimal solutions, which in turn may negatively affect the control effectiveness. Therefore, with the idea of taking a step further towards reliable and sustainable engineering solutions, based on more conscious use of the plants' dynamics, we decide to address in this thesis two fundamental challenges related to constrained control and observation. In the first part of this work, we consider the control of uncertain nonlinear systems with input and state constraints, for which a general approach remains elusive. In this context, we propose a novel closed-form solution based on Explicit Reference Governors and Barrier Lyapunov Functions. Notably, it is shown that adaptive strategies can be embedded in the constrained controller design, thus handling parametric uncertainties that often hinder the resulting performance of constraint-aware techniques. The second part of the thesis deals with the global observation of dynamical systems subject to topological constraints, such as those evolving on Lie groups or homogeneous spaces. Here, general observability analysis tools are overviewed, and the problem of sensorless control of permanent magnets electrical machines is presented as a case of study. Through simulation and experimental results, we demonstrate that the proposed formalism leads to high control performance and simple implementation in embedded digital controllers