Differential electromagnetic saliency of a permanent magnet synchronous machine with concentrated winding and a short-circuited rotor winding

• Applicant: Professor Dr.-Ing. Ingo Hahn
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: from 2010 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 172139969

Permanent magnet synchronous machines are widely used. The main advantages that result from the use of a permanent magnet rotor are a high power and torque density as well as high dynamics. However, an essential drawback is that the rotor position is always required for field-oriented control. This information is generally provided by a position sensor. This positions sensor increases the overall costs as well as the installation space, especially for small motors. Motion sensorless control is therefore highly desirable.Considering high speed, the position information is contained in the back-EMF. However, at low speed or standstill active position detection methods must be applied to estimate the rotor angle based on the position-dependent electromagnetic properties of the machine. Therefore, in literature usually the differential inductances at the operating point are evaluated. However, it is imaginable that using another quantity for sensorless position estimation instead could yield even better results. Furthermore, in literatur a concept referred to as ringed-pole machine is proposed which uses a short-circuited winding on the rotor surface to influence the differential inductances. As could be shown in the preceding project, the rotor winding also affects the differential HF-resistance which shows a strong frequency-dependence due to the interaction with the eddy currents in the steel lamination. This resistive saliency was also successfully used for sensorless position estimation.Therefore this project aims to an extension of the feasible region for sensorless control and to a minimization of the estimated position error by the use of an optimized short-circuited rotor winding. Thereby, no restrictions are made regarding the quantity from which the position information is extracted.As a first step, possible quantities which can be used for the position estimation are considered in general. Thereby, various quantities have to be derived from the measurable machine properties to investigate if the quality of the rotor position estimation can be improved by the use of an alternative estimation quantity. Afterwards, an experimental test setup has to be developed to investigate the influence of eddy currents on the effective HF-impedance of a coil. Additionally, the frequency dependence of the flux displacement in the electrical steel sheet has to be measured to evaluate, if this effect is negligible at common test signal frequencies. From the measurement results a machine model has to be derived by which the estimation quantity that yields the best sensorless results for a given machine can be identified. For this quantity, an optimized design of the short-circuited rotor coil has to be developed. Finally, this model and the optimization procedure has to be verified by an experimental test setup to show the potential of the derived theory.

• DFG Programme: Research Grants