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Design of the control algorithm for a digital Mass Flow Controller


Marcello Colombino

Master Thesis, FS12 (10171)

This report illustrates the design process for the control algorithm of a digital Mass Flow Controller. At rst, the results of frequency domain system identi cation are presented showing the linearised behaviour of the system around several operating points. Subsequently the nonlinear behaviour is analysed and an empirical relationship is found between the linearised model and the ow-regime of operation. Subsequently, the interactions of the mass ow controller with the pressure regulator are investigated showing potential sources of uncertainty in the modelling. The control algorithm is designed following a mixed sensitivity approach and it is corrected to ensure robust stability with respect to the uncertainty previously discovered. A gain-scheduling strategy is developed in order to cope with the non-linear behaviour. A method for a modi ed extended Kalman lter is proposed and implemented, which reduces the e ect of sensor noise and sensor saturation. The control algorithm is then tested showing excellent behaviour in most reference tracking tasks with the exception of step references starting from zero and going to high ow regimes, where the behaviour is acceptable but not fully satisfactory. This is believed to be due to sticking e ects that the valve experiences at the opening point and will be the subject of future studies. The controller also performs well when the step references start from zero and go to extremely low ow regimes close to 0.01% of the sensor calibration, o ering thus a large operating range


Type of Publication:

(12)Diploma/Master Thesis

R. S. Smith

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% Autogenerated BibTeX entry
@PhdThesis { Xxx:2012:IFA_4176
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