Variable structure controller and observer applied to induction machine

This work will propose the control of an induction machine in field coordinates with imposed stator current based on theory of variable structure control and sliding mode. We describe the model of an induction machine in field coordinates with imposed stator current and we show the design of variable structure control and sliding mode to get a desirable dynamic performance of that plant. To estimate the inaccessible states we will use a state observer (estimator) based on field coordinates induction machine. We will present the results of simulations in any operation condition (start, speed reversal and load) and with parameters variation of the machine compared to a PI control scheme.

Influence of Travelling Current Linkage Harmonics on Inductance Variation, Torque Ripple and Sensorless Capability of Tooth-Coil Permanent-Magnet Synchronous Machines

This paper introduces an important source of torque ripple in PMSMs with tooth-coil windings (TC-PMSMs). It is theoretically proven that saturation and cross-saturation phenomena caused by the non-synchronous harmonics of the stator current linkage cause a synchronous inductance variation with a particular periodicity. This, in turn, determines the magnitude of the torque ripple and can also deteriorate the performance of signal-injection-based rotor position estimation algorithms. An improved dq- inductance model is proposed. It can be used in torque ripple reduction control schemes and can enhance the self-sensing capabilities of TC-PMSMs

The evolution of personality in patients with mild cognitive impairment.

Aims: To describe personality traits and their changes in mild cognitive impairment (MCI) and control subjects. Methods: Sixty-three MCI and 90 control subjects were asked to describe their current personality traits by the Structured Interview for the Five-Factor Model (SIFFM). For each subject, a close relative retrospectively assessed these descriptions both as to the previous and current personality traits, using the Revised NEO Personality Inventory, Form R (NEO-PI-R). Results: Self-assessed MCI subjects reported significantly lower scores in the openness dimension than control subjects [F(1, 150) = 9.84, p = 0.002, ηp(2) = 0.06]. In current observer ratings, MCI subjects had higher scores on neuroticism [F(1, 137) = 7.55, p = 0.007, ηp(2) = 0.05] and lower ones on extraversion [F(1, 137) = 6.40, p = 0.013, ηp(2) = 0.04], openness [F(1, 137) = 9.93, p = 0.002, ηp(2) = 0.07], agreeableness [F(1, 137) = 10.18, p = 0.002, ηp(2) = 0.07] and conscientiousness [F(1, 137) = 25.96, p < 0.001, ηp(2) = 0.16]. Previous personality traits discriminated the groups as previous openness [odds ratio (OR) = 0.97, 95% confidence interval (CI) = 0.95-0.99, p = 0.014] and conscientiousness (OR = 0.96, 95% CI 0.94-0.98, p = 0.001) were negatively related to MCI group membership. In MCI subjects, conscientiousness [F(1, 137) = 19.20, p < 0.001, ηp(2) = 0.12] and extraversion [F(1, 137) = 22.27, p < 0.001, ηp(2) = 0.14] decreased between previous and current evaluations and neuroticism increased [F(1, 137) = 22.23, p < 0.001, ηp(2) = 0.14], whereas no significant change was found in control subjects. Conclusions: MCI subjects undergo significant personality changes. Thus, personality assessment may aid the early detection of dementia. © 2013 S. Karger AG, Basel.

On the Condition Monitoring of Induction machines

The research of condition monitoring of electric motors has been wide for several decades. The research and development at universities and in industry has provided means for the predictive condition monitoring. Many different devices and systems are developed and are widely used in industry, transportation and in civil engineering. In addition, many methods are developed and reported in scientific arenas in order to improve existing methods for the automatic analysis of faults. The methods, however, are not widely used as a part of condition monitoring systems. The main reasons are, firstly, that many methods are presented in scientific papers but their performance in different conditions is not evaluated, secondly, the methods include parameters that are so case specific that the implementation of a systemusing such methods would be far from straightforward. In this thesis, some of these methods are evaluated theoretically and tested with simulations and with a drive in a laboratory. A new automatic analysis method for the bearing fault detection is introduced. In the first part of this work the generation of the bearing fault originating signal is explained and its influence into the stator current is concerned with qualitative and quantitative estimation. The verification of the feasibility of the stator current measurement as a bearing fault indicatoris experimentally tested with the running 15 kW induction motor. The second part of this work concentrates on the bearing fault analysis using the vibration measurement signal. The performance of the micromachined silicon accelerometer chip in conjunction with the envelope spectrum analysis of the cyclic bearing faultis experimentally tested. Furthermore, different methods for the creation of feature extractors for the bearing fault classification are researched and an automatic fault classifier using multivariate statistical discrimination and fuzzy logic is introduced. It is often important that the on-line condition monitoring system is integrated with the industrial communications infrastructure. Two types of a sensor solutions are tested in the thesis: the first one is a sensor withcalculation capacity for example for the production of the envelope spectra; the other one can collect the measurement data in memory and another device can read the data via field bus. The data communications requirements highly depend onthe type of the sensor solution selected. If the data is already analysed in the sensor the data communications are needed only for the results but in the other case, all measurement data need to be transferred. The complexity of the classification method can be great if the data is analysed at the management level computer, but if the analysis is made in sensor itself, the analyses must be simple due to the restricted calculation and memory capacity.

Oikosulkumoottorin roottorivaurioiden tunnistaminen staattorivirran avulla

Diplomityössä esitellään menetelmiä sauvarikon toteamiseksi. Työn tarkoituksena on tutkia roottorivaurioita staattorivirran avulla. Työ jaetaan karkeasti kolmeen osa-alueeseen: oikosulkumoottorin vikoihin, roottorivaurioiden tunnistamiseen ja signaalinkäsittelymenetelmiin, jonka avulla havaitaan sauvarikko. Oikosulkumoottorin vikoja ovat staattorikäämien vauriot ja roottorivauriot. Roottorikäämien vaurioita ovat roottori sauvojen murtuminen sekä roottorisauvan irtoaminen oikosulkujenkaan päästä. Roottorivaurioiden tunnistamismenetelmiä ovat parametrin arviointi ja virtaspektrianalyysi. Työn alkuosassa esitellään oikosulkumoottorien rakenne ja toiminta. Esitellään moottoriin kohdistuvia vikoja ja etsitään ratkaisumenetelmiä roottorivaurioiden tunnistamisessa. Lopuksi tutkitaan, kuinka staattorimittaustietojen perusteella saadut tulokset voidaan käsitellä FFT -algoritmilla ja kuinka FFT -algoritmi voidaan toteuttaa sulautettuna Sharc -prosessorin avulla. Työssä käytetään ADSP 21062 EZ -LAB kehitysympäristöä, jonka avulla voidaan ajaa ohjelmia RAM-sirusta, joka on vuorovaikutuksessa SHARC -laudassa oleviin laitteisiin.

Position sensorless electrically excited synchronous motor drive for industrial use based on direct flux linkage and torque control

Synchronous machines with an AC converter are used mainly in large drives, for example in ship propulsion drives as well as in rolling mill drives in steel industry. These motors are used because of their high efficiency, high overload capacity and good performance in the field weakening area. Present day drives for electrically excited synchronous motors are equipped with position sensors. Most drives for electrically excited synchronous motors will be equipped with position sensors also in future. This kind of drives with good dynamics are mainly used in metal industry. Drives without a position sensor can be used e.g. in ship propulsion and in large pump and blower drives. Nowadays, these drives are equipped with a position sensor, too. The tendency is to avoid a position sensor if possible, since a sensor reduces the reliability of the drive and increases costs (latter is not very significant for large drives). A new control technique for a synchronous motor drive is a combination of the Direct Flux Linkage Control (DFLC) based on a voltage model and a supervising method (e.g. current model). This combination is called Direct Torque Control method (DTC). In the case of the position sensorless drive, the DTC can be implemented by using other supervising methods that keep the stator flux linkage origin centered. In this thesis, a method for the observation of the drift of the real stator flux linkage in the DTC drive is introduced. It is also shown how this method can be used as a supervising method that keeps the stator flux linkage origin centered in the case of the DTC. In the position sensorless case, a synchronous motor can be started up with the DTC control, when a method for the determination of the initial rotor position presented in this thesis is used. The load characteristics of such a drive are not very good at low rotational speeds. Furthermore, continuous operation at a zero speed and at a low rotational speed is not possible, which is partly due to the problems related to the flux linkage estimate. For operation in a low speed area, a stator current control method based on the DFLC modulator (DMCQ is presented. With the DMCC, it is possible to start up and operate a synchronous motor at a zero speed and at low rotational speeds in general. The DMCC is necessary in situations where high torque (e.g. nominal torque) is required at the starting moment, or if the motor runs several seconds at a zero speed or at a low speed range (up to 2 Hz). The behaviour of the described methods is shown with test results. The test results are presented for the direct flux linkage and torque controlled test drive system with a 14.5 kVA, four pole salient pole synchronous motor with a damper winding and electric excitation. The static accuracy of the drive is verified by measuring the torque in a static load operation, and the dynamics of the drive is proven in load transient tests. The performance of the drive concept presented in this work is sufficient e.g. for ship propulsion and for large pump drives. Furthermore, the developed methods are almost independent of the machine parameters.

Analysis and Control of Excitation, Field Weakening and Stability in Direct Torque Controlled Electrically Excited Synchronous Motor Drives

Direct torque control (DTC) is a new control method for rotating field electrical machines. DTC controls directly the motor stator flux linkage with the stator voltage, and no stator current controllers are used. With the DTC method very good torque dynamics can be achieved. Until now, DTC has been applied to asynchronous motor drives. The purpose of this work is to analyse the applicability of DTC to electrically excited synchronous motor drives. Compared with asynchronous motor drives, electrically excited synchronous motor drives require an additional control for the rotor field current. The field current control is called excitation control in this study. The dependence of the static and dynamic performance of DTC synchronous motor drives on the excitation control has been analysed and a straightforward excitation control method has been developed and tested. In the field weakening range the stator flux linkage modulus must be reduced in order to keep the electro motive force of the synchronous motor smaller than the stator voltage and in order to maintain a sufficient voltage reserve. The dynamic performance of the DTC synchronous motor drive depends on the stator flux linkage modulus. Another important factor for the dynamic performance in the field weakening range is the excitation control. The field weakening analysis considers both dependencies. A modified excitation control method, which maximises the dynamic performance in the field weakening range, has been developed. In synchronous motor drives the load angle must be kept in a stabile working area in order to avoid loss of synchronism. The traditional vector control methods allow to adjust the load angle of the synchronous motor directly by the stator current control. In the DTC synchronous motor drive the load angle is not a directly controllable variable, but it is formed freely according to the motor’s electromagnetic state and load. The load angle can be limited indirectly by limiting the torque reference. This method is however parameter sensitive and requires a safety margin between the theoretical torque maximum and the actual torque limit. The DTC modulation principle allows however a direct load angle adjustment without any current control. In this work a direct load angle control method has been developed. The method keeps the drive stabile and allows the maximal utilisation of the drive without a safety margin in the torque limitation.

Analytic evaluation of three-phase short circuit demagnetization and hysteresis loss risk in rotor-surface-magnet Permanent-Magnet Synchronous Machines

Permanent magnet synchronous machines (PMSM) have become widely used in applications because of high efficiency compared to synchronous machines with exciting winding or to induction motors. This feature of PMSM is achieved through the using the permanent magnets (PM) as the main excitation source. The magnetic properties of the PM have significant influence on all the PMSM characteristics. Recent observations of the PM material properties when used in rotating machines revealed that in all PMSMs the magnets do not necessarily operate in the second quadrant of the demagnetization curve which makes the magnets prone to hysteresis losses. Moreover, still no good analytical approach has not been derived for the magnetic flux density distribution along the PM during the different short circuits faults. The main task of this thesis is to derive simple analytical tool which can predict magnetic flux density distribution along the rotor-surface mounted PM in two cases: during normal operating mode and in the worst moment of time from the PM’s point of view of the three phase symmetrical short circuit. The surface mounted PMSMs were selected because of their prevalence and relatively simple construction. The proposed model is based on the combination of two theories: the theory of the magnetic circuit and space vector theory. The comparison of the results in case of the normal operating mode obtained from finite element software with the results calculated with the proposed model shows good accuracy of model in the parts of the PM which are most of all prone to hysteresis losses. The comparison of the results for three phase symmetrical short circuit revealed significant inaccuracy of the proposed model compared with results from finite element software. The analysis of the inaccuracy reasons was provided. The impact on the model of the Carter factor theory and assumption that air have permeability of the PM were analyzed. The propositions for the further model development are presented.

Cost Reduction of Permanent Magnet Synchronous Machines

Electrical machine drives are the most electrical energy-consuming systems worldwide. The largest proportion of drives is found in industrial applications. There are, however many other applications that are also based on the use of electrical machines, because they have a relatively high efficiency, a low noise level, and do not produce local pollution. Electrical machines can be classified into several categories. One of the most commonly used electrical machine types (especially in the industry) is induction motors, also known as asynchronous machines. They have a mature production process and a robust rotor construction. However, in the world pursuing higher energy efficiency with reasonable investments not every application receives the advantage of using this type of motor drives. The main drawback of induction motors is the fact that they need slipcaused and thus loss-generating current in the rotor, and additional stator current for magnetic field production along with the torque-producing current. This can reduce the electric motor drive efficiency, especially in low-speed, low-power applications. Often, when high torque density is required together with low losses, it is desirable to apply permanent magnet technology, because in this case there is no need to use current to produce the basic excitation of the machine. This promotes the effectiveness of copper use in the stator, and further, there is no rotor current in these machines. Again, if permanent magnets with a high remanent flux density are used, the air gap flux density can be higher than in conventional induction motors. These advantages have raised the popularity of PMSMs in some challenging applications, such as hybrid electric vehicles (HEV), wind turbines, and home appliances. Usually, a correctly designed PMSM has a higher efficiency and consequently lower losses than its induction machine counterparts. Therefore, the use of these electrical machines reduces the energy consumption of the whole system to some extent, which can provide good motivation to apply permanent magnet technology to electrical machines. However, the cost of high performance rare earth permanent magnets in these machines may not be affordable in many industrial applications, because the tight competition between the manufacturers dictates the rules of low-cost and highly robust solutions, where asynchronous machines seem to be more feasible at the moment. Two main electromagnetic components of an electrical machine are the stator and the rotor. In the case of a conventional radial flux PMSM, the stator contains magnetic circuit lamination and stator winding, and the rotor consists of rotor steel (laminated or solid) and permanent magnets. The lamination itself does not significantly influence the total cost of the machine, even though it can considerably increase the construction complexity, as it requires a special assembly arrangement. However, thin metal sheet processing methods are very effective and economically feasible. Therefore, the cost of the machine is mainly affected by the stator winding and the permanent magnets. The work proposed in this doctoral dissertation comprises a description and analysis of two approaches of PMSM cost reduction: one on the rotor side and the other on the stator side. The first approach on the rotor side includes the use of low-cost and abundant ferrite magnets together with a tooth-coil winding topology and an outer rotor construction. The second approach on the stator side exploits the use of a modular stator structure instead of a monolithic one. PMSMs with the proposed structures were thoroughly analysed by finite element method based tools (FEM). It was found out that by implementing the described principles, some favourable characteristics of the machine (mainly concerning the machine size) will inevitable be compromised. However, the main target of the proposed approaches is not to compete with conventional rare earth PMSMs, but to reduce the price at which they can be implemented in industrial applications, keeping their dimensions at the same level or lower than those of a typical electrical machine used in the industry at the moment. The measurement results of the prototypes show that the main performance characteristics of these machines are at an acceptable level. It is shown that with certain specific actions it is possible to achieve a desirable efficiency level of the machine with the proposed cost reduction methods.

Development of an instrumentation system embedded on FPGA for real time measurement of mechanical vibrations in rotating machinery

The real-time monitoring of events in an industrial plant is vital, to monitor the actual conditions of operation of the machinery responsible for the manufacturing process. A predictive maintenance program includes condition monitoring of the rotating machinery, to anticipate possible conditions of failure. To increase the operational reliability it is thus necessary an efficient tool to analyze and monitor the equipments, in real-time, and enabling the detection of e.g. incipient faults in bearings. To fulfill these requirements some innovations have become frequent, namely the inclusion of vibration sensors or stator current sensors. These innovations enable the development of new design methodologies that take into account the ease of future modifications, upgrades, and replacement of the monitored machine, as well as expansion of the monitoring system. This paper presents the development, implementation and testing of an instrument for vibration monitoring, as a possible solution to embed in industrial environment. The digital control system is based on an FPGA, and its configuration with an open hardware design tool is described. Special focus is given to the area of fault detection in rolling bearings. © 2012 IEEE.

Técnica de projeto de controlador fuzzy aplicada ao acionamento vetorial de motor de indução

Este trabalho investiga uma estratégia de controle fuzzy Takagi-Sugeno aplicada ao controle de velocidade do motor de indução. A estratégia implementa uma interpolação ponderada entre um conjunto de controladores locais previamente projetados. Ao ocorrer variações nas condições operacionais do motor de indução, os ganhos da lei de controle são ajustados automaticamente, de modo a manter satisfatório o desempenho do sistema de controle. Para o projeto do controlador fuzzy a representação em espaço de estados da planta foi considerada sob a forma de um sistema aumentado, incluindo-se uma nova variável de estado que, nesse caso, foi selecionada como sendo a integral do erro de velocidade. Tal formulação permitiu o projeto de controladores locais com a estrutura PI, através de realimentação completa de estados, com posicionamento de pólos. Como variáveis de operação para o chaveamento fuzzy dos controladores locais, foram selecionados as variáveis velocidade angular do rotor e a componente da corrente de estator responsável pelo torque elétrico do motor. Em seguida, a estabilidade do controlador fuzzy Takagi- Sugeno projetado foi comprovada através do critério de Lyapunov, para isso o problema de estabilidade foi escrito na forma de LMIs. O desempenho do controlador fuzzy Takagi-Sugeno foi avaliado através de estudos de simulação, e seus resultados comparados ao desempenho de um controlador PI convencional, para a regulação da velocidade do rotor. Os resultados obtidos nas simulações mostram que o emprego da estratégia proposta torna o sistema mais robusto a variações paramétricas no sistema de acionamento.

Implementação e análise do desempenho de técnicas de monitoramento através de medição de vibração e correlação com corrente estatórica

A crescente demanda por energia elétrica aliada à grande importância deste setor para o sistema econômico nacional tem levado o governo e empresas particulares a investirem em estudos que possibilitem melhorar o desempenho dos sistemas envolvidos nesse processo, em virtude dos relevantes ganhos que esta iniciativa pode produzir. Neste contexto, esse trabalho é uma contribuição ao estudo do desenvolvimento de uma metodologia de diagnóstico de defeitos para a máquina hidrogeradora número 3 da Usina Hidrelétrica de Coaracy Nunes, localizada no Estado do Amapá. Em muitas situações os métodos de análise de vibrações são utilizados para detectar a presença de falhas nesse tipo de máquina, neste trabalho também será utilizada a análise dos sinais de corrente para fornecer indicações similares. Este trabalho tem por objetivo apresentar uma metodologia de diagnóstico de defeito em máquinas elétricas através dos sinais de vibração e correlação com a análise da corrente do estator. No decorrer deste trabalho apresenta-se uma revisão bibliográfica das técnicas de monitoramento e diagnóstico das condições das máquinas elétricas, através dos ensaios de vibração correlacionados com as características da corrente estatórica. O resultado da correlação da medição de vibração com a medição de corrente se baseia em uma metodologia implementada por um sistema de aquisição e de processamento de dados desenvolvido na plataforma LabView. Os resultados experimentais foram obtidos a partir de defeitos mecânicos (desbalanceamento mecânico e defeitos nas pistas, externa e interna dos rolamentos) induzidos em uma bancada experimental concebida com intuito de representar um sistema de geração. Finalizando, os sinais de vibração e corrente foram analisados e comparados para verificar se os defeitos que foram evidenciados pelo método convencional de vibração alteravam o comportamento dos sinais de corrente. Os bons resultados desse trabalho mostram a viabilidade em estudos futuros nesta área.

Multiclassificador inteligente de falhas no domínio do tempo em motores de indução trifásicos alimentados por inversores de frequência

Os motores de indução desempenham um importante papel na indústria, fato este que destaca a importância do correto diagnóstico e classificação de falhas ainda em fase inicial de sua evolução, possibilitando aumento na produtividade e, principalmente, eliminando graves danos aos processos e às máquinas. Assim, a proposta desta tese consiste em apresentar um multiclassificador inteligente para o diagnóstico de motor sem defeitos, falhas de curto-circuito nos enrolamentos do estator, falhas de rotor e falhas de rolamentos em motores de indução trifásicos acionados por diferentes modelos de inversores de frequência por meio da análise das amplitudes dos sinais de corrente de estator no domínio do tempo. Para avaliar a precisão de classificação frente aos diversos níveis de severidade das falhas, foram comparados os desempenhos de quatro técnicas distintas de aprendizado de máquina; a saber: (i) Rede Fuzzy Artmap, (ii) Rede Perceptron Multicamadas, (iii) Máquina de Vetores de Suporte e (iv) k-Vizinhos-Próximos. Resultados experimentais obtidos a partir de 13.574 ensaios experimentais são apresentados para validar o estudo considerando uma ampla faixa de frequências de operação, bem como regimes de conjugado de carga em 5 motores diferentes.

Simulation and control of a stepping motor

Open-loop operatlon of the stepping motor exploits the inherent advantages of the machine. For near optimum operation: in this mode, however, an accurate system model is required to facilitate controller design. Such a model must be comprehensive and take account of the non-linearities inherent in the system. The result is a complex formulation which can be made manageable with a computational aid. A digital simulation of a hybrid type stepping motor and its associated drive circuit is proposed. The simulation is based upon a block diagram model which includes reasonable approximations to the major non-linearities. The simulation is shown to yield accurate performance predictions. The determination of the transfer functions is based upon the consideration of the physical processes involved rather than upon direct input-outout measurements. The effects of eddy currents, saturation, hysteresis, drive circuit characteristics and non-linear torque displacement characteristics are considered and methods of determining transfer functions, which take account of these effects, are offered. The static torque displacement characteristic is considered in detail and a model is proposed which predicts static torque for any combination of phase currents and shaft position. Methods of predicting the characteristic directly from machine geometry are investigated. Drive circuit design for high efficiency operation is considered and a model of a bipolar, bilevel circuit is proposed. The transfers between stator voltage and stator current and between stator current and air gap flux are complicated by the effects of eddy currents, saturation and hysteresis. Frequency response methods, combined with average inductance measurements, are shown to yield reasonable transfer functions. The modelling procedure and subsequent digital simulation is concluded to be a powerful method of non-linear analysis.

A Luenberger state observer for stator resistance estimation in sensorless induction motor drives

The primary objective of this paper is to elimination of the problem of sensitivity to parameter variation of induction motor drive. The proposed sensorless strategy is based on an algorithm permitting a better simultaneous estimation of the rotor speed and the stator resistance including an adaptive mechanism based on the lyaponov theory. To study the reliability and the robustness of the sensorless technique to abnormal operations, some simulation tests have been performed under several cases. The proposed sensorless vector control scheme showed a good performance behavior in the transient and steady states, with an excellent disturbance rejection of the load torque. © 2013 Praise Worthy Prize S.r.l. - All rights reserved.