High performance current control is critical to the success of the switched reluctance motor (SRM). Yet high motor phase nonlinearities in the SRM place extra burden on the current controller, rendering it the weakest link in SRM control. In contrast to linear motor control techniques that respond to current error, the deadbeat controller calculates the control voltage by the current command, phase current, rotor position and applied phase voltage. The deadbeat controller has demonstrated superior response in three-phase inverter current control, PM motor current control, and other relatively linear control applications. This study will investigate the viability and performance of a deadbeat controller for the highly nonlinear SRM. The need for an accurate deadbeat control model first motivates the investigation of experimental inductance measurement techniques. A deadbeat control law is then proposed through multiple revisions to demonstrate the benefit of the numerical method chosen to derive the controller and a current predictor that accounts for processor latency and PWM delay. The practical problems of loop delay, feedback noise, feedback filtering, and deadbeat controller parameter sensitivity are investigated by linear analysis, simulation, experimental implementation and nonlinear model analysis. Simulation and implementation verify deadbeat performance and various measures of transient performance are presented. To address the problem of SRM model error the study ends with a brief discussion of adaptive deadbeat control modifications for possible future research. / Master of Science

Orientador: Prof. Dr. Alfeu Joãozinho Sguarezi Filho / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2014. / A energia eólica tem seu interesse aumentado nos últimos anos como uma das mais importantes fontes de energia renováveis devido a sua característica ecologicamente correta. Um dos componentes principais do sistema de geração eólica é o aerogerador, que deve ser capaz de operar com velocidade variável do vento e deve estar conectado à rede elétrica mesmo com a presença de distúrbios elétricos, como afundamento de tensão. Este trabalho apresenta uma proposta de controlador direto de potência do tipo deadbeat para o Gerador de Indução com Dupla Alimentação (GIDA), onde tem-se seu estator conectado diretamente à rede elétrica e o seu rotor, conectado à rede elétrica com o emprego de um conversor bidirecional. O controlador proposto é projetado a partir do modelo matemático dinâmico discreto do GIDA para trabalhar durante a ocorrência de afundamentos de tensão sem o emprego de crowbar e sem danificar a máquina de indução. O GIDA e o controlador direto de potência deadbeat foram simulados com o emprego do pagote Simulink® do Matlab® e os resultados desta simulação são apresentados nesta dissertação, incluindo a operação do GIDA durante afundamento de tensão trifásico equilibrado. Para comprovar a capacidade de operação durante afundamento de tensão, foram realizados testes em bancada com o controlador direto de potência proposto e os resultados experimentais apresentados validam a correta operação do controlador direto de potência deadbeat na condição de falha da rede. / Wind energy is gaining interest in the last years as one of the most important renewable sources of energy due to its ecofriendly nature. One of the main components of the wind energy system is the wind generator, which must be able to work with variable wind speed and have to be connected directly to the grid even during faults, like symmetrical sag. This work presents a proposal of a direct power control deadbeat for Doubly-Fed Induction Generator (DFIG), where its stator is connected directly to the grid and its rotor is connected to the grid trough a bidirectional converter. The proposed controller is designed using the mathematical discretized dynamic model of DFIG, with the goal to withstand its operation during sag with no crowbar and avoiding damage to the induction machine. The DFIG and the direct power controller deadbeat were simulated using the suite Simulink® from Matlab® and the results are presented in this work, including the DFIG operation during symmetrical sag. For assuring the performance of the controller during sag, practical results with the proposed direct power controlled were performed using a test bench and the final results validate the correct design of the proposed deadbeat direct power controller.

Orientador: Prof. Dr. Alfeu J. Sguarezi Filho / Tese (doutorado) - Universidade Federal do ABC. Programa de Pós-Graduação em Energia, 2017. / Nesta pesquisa são propostos dois novos algoritmos de controle, operando a velocidade variável e robustos às variações nos parâmetros para um sistema eólico baseado no gerador de indução duplamente alimentado, cuja aplicação é realizada em condições normais de operação. Os controladores propostos são nomeados de Controle Direto de Potência (CDP) Deadbeat e do Controle Preditivo Generalizado com Horizonte Deslizante (CPG¿hd). O primeiro possui duas malhas de controle: uma para o desacoplamento do fluxo do estator e o controle das potências e a outra para o controle da corrente, essa malha é chamada de Deadbeat. O CDP calcula o vetor de tensão fornecido ao rotor a fim de garantir que a potência ativa e reativa atinjam seus valores de referência desejados. A dependência do algoritmo a parâmetros que tenham que ser sintonizados por meio de procedimentos heurísticos é nula quando é comparado com o controle Proporcional¿Integral ou Controle PI, sendo preciso somente calcular o coeficiente Gc. O segundo controlador, calcula os preditores para a corrente do rotor usando um horizonte de predição definido e assim obter as novas tensões do rotor que devem ser injetadas no sistema para controlar as potências ativa e reativa do estator com base nas equações do gerador. O CPG¿hd precisa de um parâmetro para sua sintonização chamado fator de peso do controlador, esse parâmetro faz parte da função de custo quadrática que deve ser minimizada, para obter um valor ótimo das tensões do rotor. Testes são feitos usando Matlab¿Simulink para os dois controladores operando sob condições normais de operação, ou seja: teste a velocidade fixa e teste a velocidade variável do rotor. Os mesmos testes são repetidos por meio de um protótipo de escala pequena disponível no LEPS . A dependência dos dois algoritmos às variações dos parâmetros foi também investigada, assim como a influência dos erros na estimativa desses parâmetros, obtendo-se um desempenho superior do controlador preditivo generalizado CPG¿hd sobre o CDP Deadbeat. / In this research two new control algorithms for a wind power system based on the Double Fed Induction Generator (DFIG) are proposed. The wind energy system is operating under normal conditions i.e. fixed rotor speed, variable rotor speed and under variations in DFIG parameters. The proposed controllers are named Direct Power Control (DPC) Deadbeat and Long¿range Generalized Predictive Control (GPC¿dq). The DPC calculates the sup- plied voltage vector to the rotor to ensure that the active and reactive power reaches their desired reference values. The algorithm dependence on parameters that have to be tuned by means of heuristic procedures is zero when its compared with the Proportional¿Integral (PI) Control, being necessary only estimate the Gc coeficient. The second controller evalu- ates the DFIG predictive rotor currents, using a defined long-range prediction horizon and thus obtain the new rotor voltages that have to be injected to controlling the active and reactive stator powers. The GPC¿dq needs a parameter for been tuned, this is called as a weighting factor and is a part of the quadratic cost function that has to be minimized, to obtain an optimal value of the rotor voltages. Tests are done using Matlab¿Simulink for the two controllers operating under normal operating conditions, ie: a fixed speed test and a variable rotor speed test. The same tests are repeated using a small scale prototype avai- lable in the LEPS. The dependence of the two algorithms on the parameter variations was also investigated, as well as the influence of the errors in the estimation of these parame- ters, obtaining a superior performance for the long¿range generalized predictive controller over the other one.

A novel hybrid pulse-width modulation (PWM) update method is proposed to eliminate the effect of the one-step control time delay Td one without losing the full duty cycle range. Without the Td one to cause linear phase shifts that limit the control bandwidth and affect closed-loop stability, a very high quality digital current control can be achieved, such as a high closed current loop bandwidth, strong robustness against disturbances, ability to reach a very high fundamental frequency compared to switching frequency, etc. In a conventional digital control implementation, a sampling period (Tsamp) is allocated for the execution of samplings and computations, and the update of PWM outputs is delayed until the beginning of the following sampling period. This delayed PWM update method is the cause of the Td one. Instead of the delayed PWM update, if the PWM outputs are updated immediately after algorithm computations, then the effect of the Td one can be eliminated; however, the computation time delay Td comp from the current sampling instant through algorithm computations to the PWM update instant causes a reduced duty cycle range. Each of these two conventional PWM update methods has some shortcomings. A hybrid PWM update method is proposed to circumvent the aforementioned shortcomings and to incorporate only the advantages. The proposed method improves the performance by updating the PWM outputs multiple times during a Tsamp, whereas the PWM outputs are updated only one time during a Tsamp in the conventional methods. In spite of the simplicity of the proposed method, the performance improvements in stability, robustness and response characteristics are significant. On the other hand, the proposed method can be easily applied to many PWM based digital controls because of its simplicity. Additional to the hybrid PWM update method, a hybrid control method is proposed to optimize the sequence of control operations. It maximizes the current loops' robustness and minimizes the delay from the sampling of outer control loops' variables, such as voltage and speed, to the duty cycle update instant. The minimum delay enables the maximization of the outer control loops' bandwidth. Additionally, a corrective neutral offset voltage injection method is proposed to correct small PWM output deviations that may occur with the hybrid PWM update method. Utilizing a three-phase voltage source inverter with a permanent magnet synchronous machine as the platform, a deadbeat current control and a high speed ac drive experiments have been conducted to demonstrate the feasibility and validity. Notable results include a closed current loop response of one Tsamp with the deadbeat control and a 500 Hz current fundamental frequency with 1 kHz switching frequency in the high speed ac drive. / Ph. D. / A novel hybrid pulse-width modulation (PWM) update method is proposed to improve the performance of power electronics applications. PWM is a modulation technique that is typically used in power electronics to encode a control signal. A delayed PWM update method and an immediate PWM update method are two conventional PWM update methods, and each of these conventional methods has shortcomings. The delayed PWM update method, as the name implies, delays the update of PWM outputs until the beginning of next cycle. This delayed update ensures that PWM signals have the full range; however, it causes an update delay in control loops, which degrades the control loops’ response speed. On the other hand, the immediate PWM update method, as the name implies, the update of PWM outputs is executed as soon as the control signals are available to be updated. This immediate update eliminates the update delay, but it loses the full range of PWM signals. The hybrid PWM update method is proposed to combine the delayed and immediate PWM update methods, in which the combination can eliminate the update delay without the loss of the full signal range. The proposed method is quite simple; however, the performance improvements in stability, robustness, and response characteristics are significant. On the other hand, the proposed method can be easily applied to many PWM based digital controls because of its simplicity. The proposed method is implemented on a three-phase voltage source inverter with a permanent magnet synchronous machine, and the feasibility and validity are demonstrated with a deadbeat current control algorithm and a high speed ac drive experiment. In the experiments, a very high quality digital current control is achieved, such as a high closed current loop bandwidth, strong robustness against disturbances, ability to reach a very high fundamental frequency compared to switching frequency, etc.

<p>This project deals with voltage source converters with energy storage capability. The main objective is to study the possible benefits of energy storage to a power system with a VSC as the interface between them.</p><p>First of all, a converter control system is proposed for a two level VSC. In the conventional converter control, the control system usually takes the voltage measured at the point where the converter is connected and calculates the reference voltage for the converter; with a modulation system the converter then produces the required 'average voltage'. In this project, a novel flux modulation scheme, combined with the deadbeat current control strategy, is proposed. The current controller is capable of controlling both positive and negative sequence current components. With flux modulation, the control system measures the bus flux and commands the converter to generate the required flux.</p><p>Based on the proposed control strategies, several application studies have been carried out.</p><p>The first application study investigates the effect of energy storage on the power quality at the point of common coupling when a system is subject to load disturbances. The voltage at PCC in a weak network is very sensitive to load changes. A sudden change in active load will cause both a phase jump and a magnitude fluctuation in the bus voltage, whereas reactive load changes mainly affect the voltage magnitude. With the addition of energy storage to a StatCom, it is possible to compensate for the active power change as well as providing reactive power support. In this thesis, some effective active power compensation schemes are proposed. Simulations and experiments have been performed to verify the compensation schemes. The results show that a StatCom with energy storage can significantly reduce phase jumps and magnitude deviations of the bus voltage.</p><p>pact of the energy storage on the performance of weak systems under fault conditions has been investigated. The investigation was done by studying an example system. The system model was established based on a real system, in which some induction motors driving pumps along a pipeline are fed from a radial transmission line. Studies show that for a weak system with induction motor loads, a StatCom with certain energy storage capacity will effectively improve the system recovery after faults. Although this incurs extra cost for the increasing dc voltage rating and size of the dc side capacitor, the overall rating of the converter can be reduced by utilization of the proposed active power compensation scheme.</p><p>The last case study investigates the possible use of a StatCom with energy storage to improve the power quality at the point of common coupling where a cyclic load is connected. Studies show that by providing both fast reactive and fast active power support to the network, not only the voltage magnitude can be well controlled, but also the voltage phase jump can be reduced significantly.</p>

The Permanent Magnet Synchronous Motor (PMSM, also known as the servo motor) is a crucial component within robotic servo systems. To optimally respond to the torque demands sent from the high-level motion controller, the PMSM current controller must track the reference with speed and precision. Nevertheless, the operation of servo motors could be compromised due to the nonlinearity of flux linkage and inaccuracies in parameters induced by unpredictable fluctuations in temperature. This Master’s thesis proposes a novel Robust Nonlinear Deadbeat Predictive Current Control (RN-DPCC) scheme to counter these challenges effectively. The nonlinear mappings between flux linkage and current on the dq-axis are established using polynomial fitting based on experimental data. Furthermore, the Nonlinear Deadbeat Predictive Current Control (N-DPCC) is derived using nonlinear feedforward. Meanwhile, Delayed Integral Action (DIA) is introduced as a robustness-enhancing measure for N-DPCC, thus evolving it into the Robust N-DPCC (RN-DPCC). Compared to conventional Integral Action (IA), DIA effectively curtails overshoot triggered by integral error and accelerates the current transient without incorporating additional tunable parameters. Numerical simulations that leverage the mathematical modeling of the converter and nonlinear PMSM are implemented using fundamental blocks in Simulink, which replicates the actual experimental setup employed within the Motor Control Lab at ABB Corporate Research. The effectiveness of employing nonlinear feedforward compensation is confirmed through a comparative analysis of the simulation results from N-DPCC and conventional Deadbeat Predictive Current Control (DPCC). The enhancements in transient response brought about by DIA are demonstrated through a comparison of RNDPCC and N-DPCC with IA. The robustness of RN-DPCC is demonstrated by comparing it with N-DPCC under conditions where parameter inaccuracies are present. / Den permanenta magnet-synkronmotorn (PMSM, även känd som servomotorn) är en avgörande komponent inom robotiserade servosystem. För att optimalt kunna reagera på momentkraven som skickas från högnivårörelsekontrollern måste PMSM-strömregulatorn följa referensen med hastighet och precision. Trots detta kan driften av servomotorer påverkas av ickelinjäriteter i flödeslänkningen och felaktigheter i parametrar som orsakas av oförutsägbara temperaturfluktuationer. Denna magisteravhandling föreslår en ny robust icke-linjär deadbeat-prediktiv strömreglering (RN-DPCC) för att effektivt hantera dessa utmaningar. De icke-linjära avbildningarna mellan flödeslänkning och ström på dq-axeln etableras med hjälp av polynomisk anpassning baserat på experimentella data. Dessutom härleds den ickelinjära deadbeat-prediktiva strömregleringen (N-DPCC) med hjälp av Ickelinjär feedforward. Samtidigt introduceras fördröjd integralåtgärd (DIA) som en robusthetsförbättrande åtgärd för N-DPCC, vilket förvandlar den till Robust N-DPCC (RN-DPCC). Jämfört med konventionell integralåtgärd (IA) minskar DIA effektivt överhäng som utlöses av integralfel och accelererar strömövergången utan att införa ytterligare justerbara parametrar. Numeriska simuleringar som utnyttjar den matematiska modelleringen av omvandlaren och den icke-linjära PMSM implementeras med hjälp av grundläggande block i Simulink, vilket återskapar den faktiska experimentella uppställningen som används i Motor Control Lab vid ABB Corporate Research. Effektiviteten i att använda icke-linjär framåtmatningskompensation bekräftas genom en jämförande analys av simulationsresultaten från N-DPCC och konventionell deadbeat-prediktiv strömreglering (DPCC). Förbättringarna i transientrespons som DIA medför demonstreras genom en jämförelse av RN-DPCC och NDPCC med IA. Robustheten hos RN-DPCC demonstreras genom att jämföra den med N-DPCC under förhållanden där parameterfel förekommer.

Static synchronous compensation (StatCom) is an application that utilizes a voltage source converter (VSC) to provide instantaneous reactive power support to the connected power system. Conventionally, StatComs are employed for reactive power support only. However, with the integration of energy storage (ES) into a StatCom, it can provide active power support in addition to the reactive power support. This thesis deals with the integration of ES into StatComs. The investigation involves the following aspects: possible benefits for power systems, main circuit design, and control strategies. As the basis of the investigation, a control scheme is proposed for two-level VSCs. It is a novel flux modulation scheme combined with the well-known deadbeat current control. The current controller is capable of controlling the positive sequence, the negative sequence, and the offset components of the converter current. With flux modulation, all the three above-mentioned components of the bus flux are controllable. This differs from the conventional voltage modulation scheme, in which only the positive and negative sequence components of the bus voltage are controllable. The difference between the proposed flux modulation scheme and the voltage modulation scheme is investigated regarding saturation of transformers in the connected system during fault recovery. The investigation shows that by controlling the offset component of the bus flux, the transformer saturation problem can be mitigated to a certain extent. The possible benefits of the additional active power support of StatComs are investigated through several case studies. Different active power compensation schemes are proposed. First, active power compensation for sudden load changes in weak systems is investigated. The proposed control strategies are verified through computer simulations and through experiments in a real-time simulator. It is shown that with active power compensation, both the phase jumps and magnitude variations in the voltage at the PCC can be reduced significantly. Secondly, the power compensation of cyclic loads is investigated. The results show that the power quality at the connection point can be improved regarding both phase jumps and magnitude variations. In the third case study, the fault-recovery performance of an example system is investigated, showing that improved performance can be achieved by the additional active power support. ES devices such as capacitors, supercapacitors, and batteries exhibit considerable variation in the terminal voltage during a charging/discharging cycle. A direct connection of ES devices to the dc side of a VSC requires a higher voltage rating of the VSC. Thus, the cost of the VSC has to be increased. In this thesis, a dual thyristor converter topology is proposed to interface ES devices with the dc side of the VSC. First, a cost comparison is performed to compare the total cost of the whole system with and without the proposed interface topology. A cost comparison between various types of ES is also presented, providing a guideline for the choice of ES at energy levels where several alternatives exist. Then, the dynamics of systems with the proposed interface topology are investigated. Control strategies are proposed and verified by computer simulations. Two different control methods for the dual-thyristor converter are compared. / QC 20100819

This project deals with voltage source converters with energy storage capability. The main objective is to study the possible benefits of energy storage to a power system with a VSC as the interface between them. First of all, a converter control system is proposed for a two level VSC. In the conventional converter control, the control system usually takes the voltage measured at the point where the converter is connected and calculates the reference voltage for the converter; with a modulation system the converter then produces the required 'average voltage'. In this project, a novel flux modulation scheme, combined with the deadbeat current control strategy, is proposed. The current controller is capable of controlling both positive and negative sequence current components. With flux modulation, the control system measures the bus flux and commands the converter to generate the required flux. Based on the proposed control strategies, several application studies have been carried out. The first application study investigates the effect of energy storage on the power quality at the point of common coupling when a system is subject to load disturbances. The voltage at PCC in a weak network is very sensitive to load changes. A sudden change in active load will cause both a phase jump and a magnitude fluctuation in the bus voltage, whereas reactive load changes mainly affect the voltage magnitude. With the addition of energy storage to a StatCom, it is possible to compensate for the active power change as well as providing reactive power support. In this thesis, some effective active power compensation schemes are proposed. Simulations and experiments have been performed to verify the compensation schemes. The results show that a StatCom with energy storage can significantly reduce phase jumps and magnitude deviations of the bus voltage. pact of the energy storage on the performance of weak systems under fault conditions has been investigated. The investigation was done by studying an example system. The system model was established based on a real system, in which some induction motors driving pumps along a pipeline are fed from a radial transmission line. Studies show that for a weak system with induction motor loads, a StatCom with certain energy storage capacity will effectively improve the system recovery after faults. Although this incurs extra cost for the increasing dc voltage rating and size of the dc side capacitor, the overall rating of the converter can be reduced by utilization of the proposed active power compensation scheme. The last case study investigates the possible use of a StatCom with energy storage to improve the power quality at the point of common coupling where a cyclic load is connected. Studies show that by providing both fast reactive and fast active power support to the network, not only the voltage magnitude can be well controlled, but also the voltage phase jump can be reduced significantly. / QC 20101124