Within scope of this work, double-fourier analysis method of rapid calculation and detailed simulation method, which are used to investigate DC bus current harmonics in two level and three level three-phase inverters systematically, will be emphasized and two methods will be compared via applying different modulation techniques. In addition, DC bus currents will be investigated visually for various working conditions and modulation methods. After that, analysis methods will be applied and harmonic spectrums will be determined. After all, it will be showed that calculated harmonic spectrums could be treated as unified harmonics around certain frequencies and these unified harmonics could be reached easily via looking at predetermined table. Moreover, it will also be showed that unified harmonic values could be used to determine harmonic current components that are necessary for sizing DC bus capacitor and could be used in various inverter analysis.

In this thesis, high performance torque and speed control for a surface-mounted permanent magnet synchronous machine (PMSM) is designed, simulated and implemented. A three-phase two-level pulse width modulation voltage-source inverter (PWM-VSI) with power MOSFETs is used to feed the PMSM. The study has three objectives. The first is to compensate the voltage disturbance caused by nonideal characteristics of the voltage-source inverter (VSI). The second is to decouple the coupled variables in the synchronous reference frame model of the PMSM. The last is to design a load torque estimator in order to increase the disturbance rejection capability of the speed control. The angular acceleration required for load torque estimation is extracted through a Kalman filter from noisy velocity measurements. Proposed methods for improved torque and speed control performance are verified through simulations and experimental tests. The drive system is modeled in Matlab/Simulink, and control algorithms are developed based on this model. The experimental drive system comprises a three-phase VSI and a 385 W surface-mounted PMSM. Control algorithms developed in the study have been implemented in a digital signal processor (DSP) board and tested comprehensively. With the use of the proposed methods, a considerable improvement of torque and speed control performance has been achieved.

In this thesis, field oriented control of permanent magnet synchronous motors using three-level neutral-point-clamped inverter is studied. Permanent magnet synchronous motors are used in high performance drive applications. In this study, the permanent magnet synchronous motor is fed by three-level neutral-point-clamped inverter. For three-level neutral-point-clamped inverter different space vector modulation algorithms, which are reported in literature, are analyzed and compared via computer simulations. The voltage balance on dc-link capacitors is also analyzed and a software control method is implemented in conjunction with the space vector PWM modulation, utilized. Nonlinear effects such as dead-time, semiconductor voltage drop and delays in gate drive circuitries also present in neutral-point-clamped inverter. The effects of these nonlinearities are studied and a compensation method for these nonlinear effects is proposed. The theoretical results are supported with computer simulations and verified with experimental results.

An approach with ¡§consecutive orthogonal arrays (COA)¡¨ is proposed for solving the problems in designing power electronic circuits. This approach is conceptually based on the orthogonal array method, which has been successfully implemented in quality engineering. The circuit parameters to be determined are assigned as the controlled variables of the orthogonal arrays. Incorporating with the inferential rules, the average effects of each control variable levels are used as the indices to determine the control variable levels of the subsequent orthogonal array. By manipulating on COA, circuit parameters with the desired circuit performances can be found from an effectively reduced number of numerical calculations or experimental tests. In this dissertation, the method with COA is implemented on solving four problems often encountered in the design of power electronic circuits. The first problem one has to deal with is to find a combination with the best performance from a great number of analyzed results. The illustrative example is the design of LC passive filters. Using COA method, the desired component values of the filter can be effectively and efficiently found with far fewer calculations. The second design problem arises from the non-linearity of circuit. An experienced engineer may be able to figure out circuit parameters with satisfactory performance based on their pre-knowledge on the circuit. Nevertheless, they are always questioned whether a better choice can be made. The typical case is the self-excited resonant electronic ballast with the non-linear characteristics of the saturated transformer and the power transistor storage-time. In this case, the average effects of COA obtained from experimental tests are used as the observational indexes to search a combination of circuit parameters for the desired lamp power. The third problem is that circuit functions are mutually exclusive. The designers are greatly perplexed to decide the circuit parameters, with which all functions should be met at the same time. The method with COA is applied to design a filter circuit to achieve the goals of low EMI noise and high power factor simultaneously. Finally, one has to cope with the effects of the uncontrolled variables, such as: ambient temperature, divergence among different manufacturers, and used hours. By applying COA with inferential rules, electronic ballasts can be robustly designed to operate fluorescent lamps at satisfied performance under the influence of these uncontrolled variables.

Based on sliding-mode control theory, this thesis proposes an integrated design of robust speed controller and quantized current regulator to achieve the control of inverter for BLDC motor. Moreover, using Digital Signal Processor (DSP) as well as the proposed inverter technology as the control kernel, a fully digital drive module of Brushless DC motor (BLDC) is robustly designed to achieve the high-performance speed control. Under the influence of system disturbances, the designed drive module can obtain a good tracking response for speed and current control. According to the simulation and experimental studies, the proposed hybrid control strategy can simultaneously achieve the objective for the speed and current control of BLDC motor. Compared with traditional pulse-width modulation (PWM) based PID control, the better speed control performance can be conducted by the provided approach.

Η παρούσα διπλωματική εργασία έχει ως σκοπό την παράθεση και ανάλυση των μεθόδων που έχουν παρουσιαστεί αυτή τη στιγμή στη διεθνή βιβλιογραφία και αφορούν τον έλεγχο και συγχρονισμό σε δίκτυο των Διασπαρμένων Συστημάτων Παραγωγής Ισχύος (Δ.Σ.Π.Ι.). Στο πρώτο κεφάλαιο γίνεται μια εισαγωγή στη Διασπαρμένη Παραγωγή (Δ.Π.) και στα Δ.Σ.Π.Ι. Στο δεύτερο κεφάλαιο παρουσιάζονται και αναλύονται τα κύρια χαρακτηριστικά των στρατηγικών ελέγχου που σχετίζονται με τον έλεγχο των Δ.Σ.Π.Ι. Στο τρίτο κεφάλαιο γίνεται παρουσίαση και ανάλυση των μεθόδων που χρησιμοποιούνται για το συγχρονισμό των Δ.Σ.Π.Ι. με το δίκτυο. Στο τέταρτο κεφάλαιο, όμοια με προηγούμενα, έγινε προσπάθεια για παρουσίαση των στρατηγικών ελέγχου των Δ.Σ.Π.Ι. σε περίπτωση που έχουμε εσφαλμένο δίκτυο. / The aim of this master thesis , is the presentation and analysis of the control strategies which are implemented on the distributed power generation systems(grid connection. Moreover, grid synchronization methods of DPGS are presented and evaluated. Control strategies when running on grid faults are also presented.

No description available.

Recent advances in power electronics have lead to the wide spread adoption of advanced power supplies and energy efficient devices. This has lead to increased levels of harmonic currents in power systems, degrading the performance of electrical machinery and interfering with telecommunication services. Active filters provide a solution to these problems by compensating for the distorted currents drawn by non-linear loads. Optimal methods for controlling these active filters have been determined by computer simulation and experimental implementation. Methods used for isolating the harmonic content of an unbalanced three phase load current were compared by computer simulations. A technique based on the Fast Fourier Transform (FFT) was developed as part of this work and shown to perform favourably. Notch Filtering, Sinusoidal Subtraction, Instantaneous Reactive Power Theory, Synchronous Reference Frame and Fast Fourier Transform methods were simulated. The methods shown to be suitable for compensation of three phase unbalanced loads were implemented in a Digital Signal Processor to evaluate true performance. These methods were Notch Filtering, Sinusoidal Subtraction, Fast Fourier Transform, and a High Pass Filter based method. A completely digital hysteresis current controller for a three phase active filter inverter has been developed and implemented with a Field Programmable Gate Array. This controller interfaces directly to a digital signal processor and is resistant to electromagnetic interference. Results from the experimental hardware verified that the active filter model used for simulation is accurate, and may be used for further development of harmonic isolation methods. A technique using notch filtering gives the best performance for steady loads, with the FFT based technique giving the most flexible operation for a range of load current characteristics. Novel use of the FFT based harmonic isolation technique allows selective cancellation of individual harmonics, with particular application to multiple shunt filters connected in parallel.

This thesis describes a new concept, applicable to high-power current-sourced conversion (CSC), where a controllable firing-angle shift is introduced between series and parallel converters to enable independent active and reactive power control. The firing-shift concept solves a difficult problem, by giving thyristor based CSCs the control flexibility of pulse-width modulated (PWM) converters, but without a loss in efficiency or rating. Several configurations are developed, based on the firing-shift concept, and provide flexible, efficient solutions for both very high power HVDC transmission, and very high current industrial processes. HVDC transmission configurations are first developed for 4-quadrant high-pulse operation, based on the series connected multi-level current reinjection (MLCR) topology. Independent reactive power control between two ends of an HVDC link are proven under firing-shift control, with high-pulse operation, and without on-load tap changing (OLTC) transformers. This is followed by application of firing-shift control to a bi-directional back-to-back HVDC link connecting two weak systems to highlight the added dc voltage control flexibility of the concept. The fault recovery capability of an MLCR based ultra-HVDC (UHVDC) long distance transmis-sion scheme is also proven under firing-shift control. The scheme responds favourably to both ac disturbances and hard dc faults, without the risk of commutation failures and instability experienced during fault recovery of line-commutated conversion. The two-quadrant capability of very high current rectification is also proven with configurations based on phase-shifted 12-pulse and MLCR parallel CSCs. The elimination of the electro-mechanical OLTC/satruable reactor voltage control, the high-current CSC’s biggest shortcoming, greatly improves controllability and with firing-shift control, ensures high power-factor for all load conditions. This reduces the reactive power demands on the transmission system, which results in more efficient power delivery

No description available.