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The structure of a permanent magnet generator (PMG) connected with an active front-end rectifier is very popular in the AC-DC architecture. Especially for certain applications like aircraft and vehicles, power density and efficiency is critical. Since the generator and the rectifier can be controlled simultaneously, it would be very desirable to develop a unified control. With this unified control, the boost inductors between the PMG and rectifier is eliminated, which significantly reduce the volume and the weight of the whole system and improve the system power density. Also the system efficiency can be improved with appropriate control strategy. In this thesis, a unified control for the permanent magnet generator and rectifier system is presented. Firstly, the unified model of the PMG and rectifier system is given as the basis to design the control system. Secondly, a unified control method for PMG and rectifier system is introduced. The design procedure for each control loops are presented in detail, including current control loop, voltage control loop, reactive control loop and speed and rotor position estimator loop. Thirdly, the hardware is developed and the experiment is conducted to verify the control strategy. Fourthly, a method to optimize the overall system efficiency by appropriate reactive power distribution is proposed. The two cases when the DC link voltage is flexible and the DC link voltage is fixed are considered. / Master of Science

Variable-speed Induction motor drives are nowadays used for various kinds of industrial processes, transportation systems, wind turbines and household appliances in the world. The majority of drives are for general purpose speed control applications where accurate speed control is not required for entire speed range. But for high dynamic drive application, very precise and fast control of induction motor drive is essential. For such applications, sophisticated and well-performing control design is a key issue. Precise and accurate torque control of the Induction Motor (IM) can only be accomplished by vector control and direct torque control. In terms of space vector theory, vector control implies that the instantaneous torque is controlled by way of the stator current vector that is orthogonal to the rotor flux vector. Precise knowledge of the rotor flux angle is therefore essential for a vector controlled IM. IMs do not allow the flux position to be easily measured, so most modern vector controlled IM drives rely on flux estimation. This means that the flux angle is derived from a flux estimator, using the dynamic model of the IM. Given that the rotor speed of the IM is measured by a mechanical shaft sensor. Flux estimation is a fairly easy task. However, vector control of IM without mechanical shaft speed sensor is of current interest in industrial environment. The driving motivations behind the development in sensorless control are lower cost, improved reliability and operating environment. In this thesis, a sensorless vector control scheme for rotor flux estimation using current error space phasor based hysteresis controller is proposed including the method for estimation of leakage inductance, Ls. For frequencies of operation less than 25 Hz, the rotor voltage and hence the rotor flux position is computed during the inverter zero voltage space vector using steady state model of IM. For above 25 Hz, active vector period and steady state model of IM is used. The whole rotor flux estimation scheme is dependent on current error space phasor and the steady state motor model, with rotor flux as a reference vector. Since no terminal voltage sensing is involved, dead time effects will not create problem in rotor flux sensing at low frequencies of operation. But appropriate device on-state drop are compensated at low frequencies (below 5 Hz) of operation to achieve a steady state operation up to less than 1 Hz. A constant switching frequency hysteresis current controller is used in inner current control loop for the PWM regulation, with smooth transition of operation to six-step mode operation. A simple Ls estimation based on current error space phasor is also proposed to nullify the deteriorating effect on rotor flux estimation. The parameter sensitivity of the control scheme to changes in the stator resistance Rs is also investigated. The drive scheme is tested up to a low frequency operation less than 1 Hz. The extensive simulation and experiment results are presented to show the proposed scheme’s good dynamic performance extending up to six-step operation. In contrast to vector control, direct torque control (DTC) method requires the knowledge of stator resistance only and thereby decreasing the associated sensitivity to parameters variation and the elimination of speed information. DTC as compared to vector control does not require co-ordinate transformation and PI controller. DTC is easy to implement because it needs only two hysteresis comparators and a lookup table for both flux and torque control. This thesis also investigates the possibilities in improvement of direct torque control scheme for high performance induction motor drive applications. Here, two schemes are proposed based on the direct torque control scheme for IM drive using 12-sided polygonal voltage space vectors for fast torque control. The torque control scheme based on DTC algorithm is proposed using 12-sided polygonal voltage space vector. The basic DTC scheme is used to control the torque. But the IM drive is open-end type. For torque control, the voltage space vectors orthogonal to stator flux vector in 12-sided polygonal space vector structure are used as hexagonal space vector based DTC scheme. The advantages achieved due to 12-sided polygonal space vector are mainly fast torque control and small torque ripple. The fast transient of torque with precise control is achieved using voltage space vector placed with a resolution of ±15. The torque ripple will be less as 6n±1 (n=odd) harmonic torque is totally eliminated from the whole range of PWM modulation. The comparative analysis of proposed 12-sided polygonal voltage space vector based DTC and conventional hexagonal space vector based DTC is also presented. Extensive simulation and experiment results are also presented to show the fast torque control at speeds of operation ranging from 5 Hz to the rated speed. The concept of 12-sided polygonal space vector based DTC is further extended for a variable speed control scheme using estimated fundamental stator voltage for sector identification. The conventional DTC scheme uses stator flux vector for identification of the sector and the switching vector are selected based on this sector information to control stator flux and torque. However, the proposed DTC scheme selects switching vectors based on the sector information of the estimated fundamental stator voltage vector and its relative position with respect to the stator flux vector. The fundamental stator voltage estimation is based on the steady state model of IM and information of synchronous frequency which is derived from computed stator flux using a low pass filter technique. The proposed DTC scheme utilizes the exact position of fundamental stator voltage vector and stator flux vector position to select optimal switching vector for fast control of torque with small variation of stator flux within hysteresis band. The present DTC scheme allows the full load torque control with fast transient response to very low speeds of operation below 5 Hz. The extensive simulation and experiment results are presented to show the fast torque control for speed of operation from zero speed to rated speed. However, the present scheme will have all the advantages of DTC scheme using stator flux vector for sector identification. All the above propositions are first simulated by MATLAB/Simulink and subsequently verified by an experimental laboratory prototype. The proposed control schemes are experimentally verified on a 3.7 kW IM drive. The control algorithms of the sensorless vector control using current error space phasor as well as DTC using 12-sided polygonal voltage space vector are completely implemented on a TI TMS320LF2812 DSP controller platform. These are some of the constituents for chapters 2, 3 and 4 in this thesis. Additionally, the first chapter also covers a brief survey on some of the recent progresses made in the field of sensorless vector control, direct torque control and current hysteresis controller. The thesis concludes with suggestion for further exploration.

In this thesis, shaft transducerless vector control of Interior Permanent Magnet (IPM) motor with speed and position estimation using saliency based high frequency signal injection and fundamental model based flux observer methods will be investigated. The magnetic saliency characteristic of a 2.2-kW IPM motor will be experimentally extracted by means of high frequency signal injection. High frequency signal injection method will be used to estimate the speed and position at zero and low speed based on the magnetic saliency of the IPM motor. At high speed, fundamental model based flux observer method will be utilized for speed and position estimation. Seamless transition between the two estimation methods will be provided. Using the estimated speed and position information, the motor will be closed loop vector controlled and the drive motion performance over wide speed and load range will be investigated. The IPM motor drive and the estimation/control algorithms will be modeled and their performance will be demonstrated by detailed computer simulations. A three-phase voltage source inverter and a motor test bench will be built, and the estimation/control algorithms will be implemented on a DSP based motor control platform. The IPM motor drive system will be tested in the laboratory and the theory and simulation results will be verified by the experiments.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Thesis proposes sensorless vector control schemes that combine designed observers in the discrete-time domain to estimate the rotor position and speed for a permanent magnet synchronous generator of non-salient poles. Two control schemes are proposed. The first scheme is based on a discrete sliding mode current observer in series with an adaptive electromotive force observer. Then, the sliding conditions that assure the sliding motion around the sliding surface are derived to ensure the stability of the current observer as well as an innovative design procedure is proposed for it. Moreover, the electromotive force observer is designed using Lyapunov s Discrete Direct Method, which provides the estimated rotor position and speed. The second scheme extends the developed methodology for the former, considering the parametric uncertainties and eliminating the high frequency components of chattering. The second scheme uses a discrete sliding mode current observer as in the first scheme. However, the electromotive force observer is replaced by a phase-locked loop in series with a discrete sliding mode robust differentiator, which follows the proposed methodology for the discrete sliding mode current observer. Experimental results validate the theoretical analysis and demonstrate the performance of the proposed control schemes considering a small scale wind energy conversion system. In addition, proposed schemes are compared with others of the literature. It should be noticed that the whole approach is carried out in discrete time domain making it suitable for a microcontroller or digital signal processor implementation. / Esta Tese propõe esquemas de controle vetorial sem sensores mecânicos de posição e de velocidade que combinam observadores projetados no domínio de tempo discreto para estimar essas variáveis para um gerador síncrono a ímãs permanentes de polos não salientes. Dois esquemas de controle são propostos. O primeiro esquema baseiase em um observador de corrente por modos deslizantes discretos em série com um observador adaptativo de força eletromotriz. Então, as condições de deslizamento que asseguram os modos deslizantes em torno da superfície de deslizamento são estabelecidas no domínio de tempo discreto para garantir a estabilidade do observador de corrente e um inovador procedimento de projeto para ele é proposto. Em seguida, o observador de força eletromotriz é projetado usando o método direto de Lyapunov discreto, que fornece a posição e a velocidade rotóricas estimadas. O segundo esquema estende a metodologia desenvolvida para o primeiro, considerando as incertezas paramétricas bem como eliminando as componentes de alta frequência de chattering. O segundo esquema usa um observador de corrente por modos deslizantes discretos como o primeiro. Entretanto, o observador de força eletromotriz é substituído por um retentor de fase em série com um diferenciador robusto por modos deslizantes discretos, que segue a metodologia proposta para o observador de corrente. Resultados experimentais validam a análise teórica desenvolvida e demonstram o desempenho dos esquemas de controle propostos considerando um sistema de conversão de energia eólica de pequeno porte. Além disso, os esquemas propostos são comparados com outros da literatura. Ressalta-se que a toda abordagem é desenvolvida no domínio de tempo discreto tornando-a apta para uma implementação em microcontroladores e em processadores digitais de sinais.