Helmut Kogler, Bernd Winkler, Rudolf Scheidl,
"Flatness Based Control of a Fast Switching Hydraulic Drive"
: Proceedings of the 2nd International Conference on Computational Methods in Fluid Power, FNPI'06, Aalborg, 8-2006
Flatness Based Control of a Fast Switching Hydraulic Drive
Sprache des Titels:
Proceedings of the 2nd International Conference on Computational Methods in Fluid Power, FNPI'06, Aalborg
Hydraulic switching control attempts to transfer concepts from modern electrical drive control to hydraulics. Both,
electrical and hydraulic switching systems allow to increase the efficiency of such drives. But it is more difficult to realise hydraulic than electrical converter principles. Especially wave propagation in the hydraulic fluid is a serious problem for the modelling. For evaluating control strategies one needs a compact mathematical model of wave propagation, preferably of lumped parameter type. In this paper, the flatness based control of the hydraulic equivalent of the electrical ‘Buck Converter’ is studied. Basically the converter consists, like its electrical pendant, of a hydraulic
inductivity and a hydraulic accumulator for pressure attenuation. The load is realised by a hydraulic cylinder with a mass and a corresponding dead load. In contrast to the electronic converter the dynamic behaviour of the hydraulic ‘Buck Conveter’ treated here is nonlinear, because of the valve characteristics, the gas spring of the accumulator, and the variable hydraulic capacity of the piston sided chamber of the cylinder. Furthermore, it is important to avoid cavitation. Because of the switching the system is discontinuous. To obtain a continuous model, which is essential for control strategies which rely on a continuous system, averaging of the two systems states into one averaged system must be performed. Furthermore, the properties of the system allow to observe several states of the system. A properly designed hydraulic switching drive in combination with a flatness based controller can achieve excellent performance, satisfactory accuracy, and increased efficiency.