Efficiency Optimization and Modelling of the Additional No-Load Losses of Low-Voltage Induction Motors Using Soft Magnetic Slot Closing Material

Abstract:
A crucial element of sustainable energy supply is the reduction of losses in all operating resources and system components up to the end application. Electrical machines take on the bidirectional conversion between mechanical and electrical energy. In high-voltage machines, soft magnetic slot closing materials are widely used to increase efficiency. The open slots in the laminated core are closed with materials made of soft magnetic composites after the preformed coils have been inserted. Ideally, the negative effects of the otherwise open slots on the machine's operational behaviour can thus be compensated. In low-voltage machines, the widespread use of soft magnetic slot closing materials has not yet been achieved. Therefore, the aim of this work is to investigate the possible optimization of the efficiency of low-voltage induction machines using soft magnetic slot closing materials. For this purpose, an analytical machine model is developed to calculate the steady-state operational behaviour. In contrast to the usual calculation practice, the nonlinear magnetization behaviour of the slot closing material as well as its total losses are considered. The necessary material properties of various slot closing materials are recorded in advance using a tailored measurement setup. In addition, the modelling focuses on the influence on the additional no-load machine losses. With appropriate dimensioning of the slot closing material, a reduction in losses of up to ten percent can be achieved for low-voltage induction motors, as demonstrated by measurements on several functional prototypes. The modelling approaches and material investigations presented can also be transferred to other electrical machines in the energy supply sector.