Investigation of the Magnetic Flux Bypass Compensation Method for Distance and Angle Measuring Systems

• Applicant: Professor Dr.-Ing. Ralf Werner
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives ; Measurement Systems
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 420036654

Modern electric drives, magnetic bearings and bearingless motors require one or more measuring systems for the determination of distances and rotation angles. For this purpose, sensorless systems are increasingly being used, which are usually simpler, more robust, more compact, more cost-effective and less sensitive to external influences than systems with sensors. However, there are two main problems with previous sensorless methods. First, the signal-to-noise ratio is low and limits the measurement accuracy or the dynamics of the system. Second, the system is sensitive to magnetic saturation. The degree of saturation influences not only the measurement signal, but also the measurement sensitivity. Even at relatively low mean flux densities this can become zero. In this case, the relationship between the actual measured variable and the measured value is no longer bijective.Therefore, a new method was developed for the construction and subsequent evaluation of such a sensorless system. A differentiation of the current signal, as with previous methods, is no longer necessary, but already takes place via the induction law. This eliminates the need for complex high bandwidth measurement of the current and considerably increases the signal-to-noise ratio. In addition, the saturation effect is compensated by means of a flux bypass. On the one hand, this allows a much lower dependence of the measurement signal on the degree of saturation to be achieved. On the other hand, the measurement sensitivity only disappears at significantly higher flux densities compared to previous methods. Since no separate carrier voltage, low-pass filters or demodulators are required, the bandwidth of the system is extremely high. For the assembly and electronic evaluation of a measuring system using the flow-bypass method, only components that are standard in electrical machine engineering are required.Within the scope of the proposed project, the flux bypass method is to be investigated with regard to the technical-physical limits for the accuracy, the signal-to-noise ratio and the maximum permissible degree of saturation. Further subjects of investigation are the influence of the material and the geometry of the flux bypass and their suitable dimensioning as well as the sensitivity to external influences. The results are verified using an experimental set-up of a sensorless flux bypass measurement system for the measurement of both rotation angles and distances.

• DFG Programme: Research Grants