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Control and Power Portfolio Partnership
CONTROL OF DC/THREE-PHASE POWER CONVERTER
This project concerns DC/AC power converters. These take power from a DC energy source (such as batteries, fuel-cells, solar panels or, most importantly, the rectified output of a variable frequency AC generator) and they feed this power into the power grid at 50 Hz. The converters are built of electronic switches and filters consisting of inductors and capacitors. Controlling such a converter is a delicate task, since the controller has to insure that the output voltage is a clean sinusoid synchronized with the grid, the active power is maintained at a desirable level and the reactive power is small.
In its original form internal model-based controllers are computed algebraically to ensure closed-loop stability, tracking and disturbance rejection. Modern H-infinity control and recent advances in the theory of distributed parameter systems enable a radically different approach to internal model-based control, and they lead to a robust structure which allows internal models of very high order and with varying frequencies. Repetitive controllers are a particular case of such a structure with a very high order internal model, but which is easy to implement.
Traditional power generators cannot actively control the waveshape of the output voltage and rely on low source impednances. The power converters found in small scale generators have to apply waveshape control. One objective of this project is to explore repetitive H-infinity control to reduce the total harmonic distortion. Another objective of this project is to experimentally test repetitive controllers for DC to three phase converters with rectifier loads and with cyclic machine loads, as well as for active power filters. Since the converters are supposed to connect to the public utility grid, it is also necessary to generate a neutral line for the zero-sequence current components. The parallel connection of such converters to form isolated micro-grids is also being investigated.
This research has led to several journal publications and conference presentations; see the publications page of this web-site.
Two inverstigators, Dr George Weiss (PI) and Dr. Tim Green, and three
RAs, Dr. Qingchang Zhong, Dr. Jun Liang and Xinxin Wang, are working on
this project.