Investigation of synchronous reluctance motors for feed drives in machine tools

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Today, the most widely used electrical machine type for feed drives and auxiliary drives, such as automatic tool changer in machine tool sector is the high-performance permanent magnet synchronous motor (PMSM). However, the production of such permanent magnets, which essentially consist of critical rare earth elements, is very expensive and unecological. Because of the price fluctuations of raw materials and the global competition in terms of price and quality, the demand for cost-effective and ecologically sustainable solutions for machine tool components is increasing. One possible alternative to permanent magnet synchronous motors is the so called synchronous reluctance motor (SynRM), which has become more and more attractive in the last few years due to its absence of permanent magnets. By optimizing the rotor geometries, the previously known disadvantages such as torque ripple and acoustic noise have already been significantly reduced. Commercial SynRM on the market shows a torque ripple under two percent. Due to the robust construction and the high energy-efficiency even under partial load, SynRM are now partly used in pump and fan applications to replace the conventional three-phase AC motors. This research project will investigate whether and to which extent the SynRM can be used as drive motors for feed axes and auxiliary axes in machine tools. Among other things, the aim is to investigate the potential of control algorithms to improve the torque ripple and to comparatively analyze the dynamic behaviors of machine axes with different types of motors.Similar to PMSM, the speed of a SynRM can easily be controlled with frequency inverters. The preliminary simulation study of a feed drive axis shows that SynRM can be applied in cost-effective feed axes. In this research project, different control techniques to optimize the performance of SynRM need to be investigated and further developed. The basic for this is a sufficiently accurate motor model, which describes the current and rotor angle dependent motor characteristics. The necessary parameters shall be identified on a motor test bench via various load profiles. The main objective is the development of a system with high bandwidth and low torque ripple. To this purpose, non-linear controllers and Luenberger observer for the nested control loops will be investigated. An axis test bench with a real-time control system will be set up for validation purpose. This allows the developed methods to be tested and allows a comparative investigation of different motor types.