Modulation Concepts for the Control of a Two-Phase Bearingless Slice Motor Utilizing Three-Phase Power Modules

Future application areas for bearingless pump systems will demand for highly compact and cost effective designs. This trend mainly has a major impact on the power electronics part of these systems. Up to now, full-bridge converters have been used in order to independently control the phases of the active magnetic bearing and the drive system. With the use of an interleaved half-bridge topology, the number of required power semiconductors is reduced by 25%. In this paper, novel modulation techniques are presented and comparatively evaluated in order to achieve a similar dynamic performance of the pump system as with the conventional full-bridge topology. The effects of a phase shift and of higher harmonics in the duty cycles are analyzed in detail. The proposed concepts are then implemented on a DSP board, and their feasibility is shown on a highly compact 1.5-kW prototype of the converter which is realized with two integrated three-phase power modules. Furthermore, it is shown that the higher harmonics injection does not have an impact on the average speed of the impeller and thus on the constant output flow of the pump.