Die lagerlose Pumpe für hohe Fluidtemperaturen

Bearingless motors consist of a drive system with an integrated magnetic bearing and are used in centrifugal pumps for high purity applications. The machine is constructed without the use of a drive shaft, dynamic seals, and conventional mechanical bearings, since the rotor is levitated in a magnetic field. This allows for a wear-free operation and prevents the contamination of process fluids. Bearingless pumps are employed in wet chemical etching processes in the semiconductor industry, since low contamination is required due to the small structures on the wafer. The reaction speed of etching processes depends strongly on the temperature of the used chemicals. Therefore, high fluid temperatures are required in order to increase processing speed and yield. State of the art, commercially available bellows pumps are rated for 210 °C and bearingless pumps can be used for fluid temperatures of 90 °C with passive air cooling and 180 °C with active water cooling. This work is focused on increasing the admissible fluid temperature of a passively cooled bearingless pump to 250 °C. The number of components and, therefore, the complexity, the cost and the probability of failure are minimized by omitting an active cooling system. Challenges include the appropriate choice of materials, the construction of the components and the development of a sensing and closed-loop control scheme for high temperatures. The temperature distribution in the pump is calculated by using a thermal model, which is based on the analysis of the temperature-dependent performance of the bearingless pump, the internal losses and the heat transfer mechanisms. The choice of materials and the construction of the pump are based on the results of the thermal model. The motor utilizes a novel closed-loop, angle sensorless control scheme for bearingless machines. The rotor angle is obtained with a two-stage estimator consisting of a model-based low-speed and a back electromotive force-based high-speed angle observer. The controller enables closed loop operation at all rotational speeds and at standstill. Two prototypes of the bearingless high temperature pump were constructed and manufactured. Both machines were tested with fluid temperatures of up to 250 °C without failure of components. This proves that bearingless pumps can be employed successfully in extreme temperature applications