A novel feedback design method for mimo QFT with application to the X-29 flight control problem

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Title: A novel feedback design method for mimo QFT with application to the X-29 flight control problem
Author: Lan, Chen-Yang
Abstract: Quantitative Feedback Theory (QFT ) method employs a two degree of freedom control configuration that includes a feedback controller and a prefilter in the feedforward path . When applied to multi -input multi -output (MIMO ) systems , the QFT method calls for a special decomposition of the MIMO system . Specifically , the MIMO system is decomposed into multiple multi -input single -output (MISO ) equivalent systems , and is followed by the single -input single -output (SISO ) QFT design of each equivalent system . Depending on pole -zero structure of the equivalent SISO plants so obtained , the QFT design may become unnecessarily difficult /conservative or even infeasible . This situation is especially true for linear time invariant (LTI ) systems with non -minimum phase (NMP ) zero (s ) and unstable pole (s ) . This unnecessary design difficulty and the challenge of dealing with MIMO systems that have unstable poles and NMP transmission zeros in undesirable locations , when MIMO QFT is considered , is investigated and addressed in this research . A new MIMO QFT design methodology was developed using the generalized formulation . The key idea of the generalized formulation is to utilize appropriate modifications at the plant input and /or the output to obtain a better conditioned plant that in turn can be used to execute a standard MIMO QFT design . The formulation is based on a more general control structure , where input and output transfer function matrices (TFM ) are included to provide additional degrees of freedom in the typical decentralised MIMO QFT feedback structure , which facilitates the exploitation of directions in MIMO QFT designs . The formulation captures existing design approaches for a fully populated MIMO QFT controller design and provides for a directional design logic involving the plant and controller alignment and the directional properties of their multivariable poles and zeros . As a case in point Horowitz ?s Singular -G design methodology is placed in the context of this generalized formulation , and the Singular -G design for the X -29 is analysed and redesigned using both non -sequential and sequential MIMO QFT demonstrating its utility . The results highlight a fundamental trade -off between multivariable controller directions for stability and performance in classically formulated MIMO QFT design methodologies , which elucidate the properties of Singular -G designed controllers for the X -29 and validate the developed new MIMO QFT design method .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3006
Date: 2009-05-15

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A novel feedback design method for mimo QFT with application to the X-29 flight control problem. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3006 .

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