MODELLING AND FLATNESS-BASED CONTROL OF A R2S~(?) TURBOCHARGER

摘要

The increasing demand for more fuel-efficient and low-emission combustion engines inrnvehicles makes turbocharging a key technology. Low CO2 emission vehicles require downsizedrnand down-speeded engines with higher boost demand which is achieved by using twornturbochargers in series (R2S?). The demands on the control system also increase with thernincreasing complexity of the turbocharging system. The number of actuators rises and thernmanner how to control the boost pressure changes significantly.rnThe concept of flatness based control requires a self-contained analytic description ofrnthe system. The proposed analytic model already takes into account the special requirementsrnof a flatness-based controller design.rnTherefore, in the first step, physical modelling of the non-linear control system, consistingrnof a R2S? turbocharger and engine, occurs. A theoretical physical approach is selectedrnhere; however, the response of various sub-models, i.e. turbine and compressor is emulated byrnstatic maps. Based on the complexity of the overall system and the fact that individual componentsrnoccur more than once and only differ in their parameters, in the first step the behaviourrnof the individual components is described, which are subsequently combined to an overallrnsystem. Moreover, this results in a modular design, which easily facilitates subsequentrnextensions and enhancements.rnThe derived models for the turbine and compressor of the turbocharger itself are comparedrnto the measured characteristic maps. The filling and emptying of the volumes in thernintake and exhaust side are described by balance equations for the mass and enthalpy. Thernfindings made for the tenth order space state model of the overall system are simplified to arnfifth order model. The reduced and the complete model are compared to real engine measurements.rnThe aim of the modelling is to show that the R2S? system is flat. Flat systems arernespecially suited for tracking control.