Browsing by Subject "Matrix Converter"

Now showing 1 - 3 of 3
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    Low voltage ride-through capability for matrix converter fed adjustable-speed Induction machine drives for industrial and wind applications.
    (2011-08) Prasad, Rashmi
    The matrix converter (MC) has been a subject of investigation since 1980, and with the rapid decline in semiconductor cost, better packaging concepts and the improvement in switching characteristics, it is now showing potential to replace the conventional dc link inverter rectifier structures. The MC finds its application wherever bidirectional power flow and controlled voltage and current in AC systems is needed and proves to be superior to its competitors when applied in certain specific environments and circumstances. Wind energy conversion systems (WECS) are also a recent growing research topic where use of MC as power electronic converter is being explored and compared to the performance of conventional voltage source based back-to-back converters. This thesis proposes to address one of the limitations of an MC, which is its ride-through capability. The proposed strategy may help to take matrix converters a step ahead in its struggle for commercialization. Ride-Through capability of an adjustable-speed drive (ASD) refers to the ability to avoid a system shut-down and thus unwanted delays in drive operation, leading to huge production losses, during short term power interruptions. In the context of wind energy systems, it refers to the grid requirement of the generating systems staying connected to the utility for a defined time during grid faults and disturbances. The ride-through behavior of the system with an MC is a challenging task, because of the absence of storage elements. Due to the direct connection between the grid and the generator/motor drives, any disturbance at the utility grid is immediately reflected on the machine behavior. The thesis comes up with a novel strategy to enhance the ride-through duration and achieve minimum possible flux deviation in the drive operation, during the voltage sag period, allowing minimum transients during power system restoration. With hysteretic control on the magnitude of motor current, the strategy comprises of keeping the motor continuously operating through a combination of input voltage vector application, aligned in the flux direction and zero vector application, along with discontinuation of MC switches. The strategy has been verified through simulation done in Matlab/Simulink. The ride-through behavior has been analyzed in integration with a wind energy system and various kinds of under voltage faults studied with different sag magnitudes for industrial applications. Ongoing research is aimed at improving the strategy based on experimental verification using laboratory prototype.
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    Power electronic transformers for AC-AC and AC-DC conversion with reduced number of switches
    (2013-08) Castelino, Gysler Fatima
    In this research, a novel reduced-switch Power Electronic Transformer is proposed for three-phase power conversion (three-phase AC to AC as well as three-phase AC to DC). The goal of this project is to reduce the weight and size of the power converter by replacing the low-frequency transformers with high-frequency transformers (HFTs). The novelty of these proposed topologies is that they have only two controlled switches on the primary side of the high-frequency transformers. Additionally, these switches operate at 50% duty ratio, hence they are easy to control. Pulse Width Modulation (PWM) control is only necessary in the converters on the secondary side of the HFT. The modulation strategies proposed in this work achieve nearly Zero Current Switching (ZCS) for these two primary switches. In the proposed three-phase AC to AC Power Electronic Transformer, a Matrix Converter (MC) is employed on the secondary side of the transformer. Matrix converter with nine four-quadrant switches is a `more-silicon' and nearly capacitor-less solution for AC to AC conversion. This single-stage AC-AC converter without any electrolytic capacitors translates to higher reliability and efficiency. High-frequency transformers have finite leakage inductance, hence, any switching in the primary or secondary of the transformer requires commutation of the transformer inductive currents. This problem of leakage energy commutation and the required protection are studied in detail in this thesis. Other features of this converter are bi-directional power flow and power factor correction. The second Power Electronic Transformer is proposed for three-phase AC to DC power conversion. This converter operates on the Dual Active Bridge (DAB) principle wherein the transformer leakage inductance is used for power transfer. Hence, this converter does not suffer from problems associated with leakage energy commutation and additional snubber circuits are not required for this converter. The proposed modulation provides the advantages of unity power factor on the AC side, galvanic isolation and bi-directional power flow capability. Both these PETs have been analyzed and simulated. Laboratory prototypes have been built and tested to verify the advantages of the proposed PETs.
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    SVPWM Technique with Varying DC-Link Voltage for Common Mode Voltage Reduction in a Matrix Converter and Analytical Estimation of its Output Voltage Distortion
    (2015-06) Padhee, Varsha
    Common Mode Voltage (CMV) in any power converter has been the major contributor to premature motor failures, bearing deterioration, shaft voltage build up and electromagnetic interference. Intelligent control methods like Space Vector Pulse Width Modulation (SVPWM) techniques provide immense potential and flexibility to reduce CMV, thereby targeting all the afore mentioned problems. Other solutions like passive filters, shielded cables and EMI filters add to the volume and cost metrics of the entire system. Smart SVPWM techniques therefore, come with a very important advantage of being an economical solution. HASH(0x31c3adc) This thesis discusses a modified space vector technique applied to an Indirect Matrix Converter (IMC) which results in the reduction of common mode voltages and other advanced features. The conventional indirect space vector pulse-width modulation (SVPWM) method of controlling matrix converters involves the usage of two adjacent active vectors and one zero vector for both rectifying and inverting stages of the converter. By suitable selection of space vectors, the rectifying stage of the matrix converter can generate different levels of virtual DC-link voltage. This capability can be exploited for operation of the converter in different ranges of modulation indices for varying machine speeds. This results in lower common mode voltage and improves the harmonic spectrum of the output voltage, without increasing the number of switching transitions as compared to conventional modulation. To summarize it can be said that the responsibility of formulating output voltages with a particular magnitude and frequency has been transferred solely to the rectifying stage of the IMC. Estimation of degree of distortion in the three phase output voltage is another facet discussed in this thesis. An understanding of the SVPWM technique and the switching sequence of the space vectors in detail gives the potential to estimate the RMS value of the switched output voltage of any converter. This conceivably aids the sizing and design of output passive filters. An analytical estimation method has been presented to achieve this purpose for am IMC. Knowledge of the fundamental component in output voltage can be utilized to calculate its Total Harmonic Distortion (THD). The effectiveness of the proposed SVPWM algorithms and the analytical estimation technique is substantiated by simulations in MATLAB / Simulink and experiments on a laboratory prototype of the IMC. Proper comparison plots have been provided to contrast the performance of the proposed methods with the conventional SVPWM method. The behavior of output voltage distortion and CMV with variation in operating parameters like modulation index and output frequency has also been analyzed.