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Browsing by Subject "Sag"

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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.