In the field of sensorless control of permanent magnet synchronous motors (PMSMs), different techniques based on machine anisotropies have been studied and implemented successfully. Nevertheless, most proposed approaches extract the rotor position information from the measured machine currents, that, when applied to low-power machines, might require high-bandwidth current sensors. An interesting alternative is given by sensorless techniques that exploit the star-point voltage of PMSMs, such as the direct flux control technique. This work aims at analyzing the conditions of applicability of such technique by considering a more thorough description of the machine inductance matrix. After a comprehensive mathematical description of the technique and characterization of the machine anisotropy information that is extracted from the star-point voltage, simulation as well as experimental results conducted on a test machine are presented and discussed in order to validate the proposed theory.

Information obtained about magnetic anisotropy via neutral point voltage measurements can be used to estimate the position of synchronous and induction machines at all speeds including standstill. Due to its usually high signal-to-noise ratio, this estimation method can be an attractive alternative to approaches that acquire anisotropy information via current measurements. The position estimation method looked at in this paper relies on anisotropy information in the form of position-dependent inductance ratios. These are obtained through measurement of the voltage between the machine’s neutral point and an artificial neutral point during the application of different voltage vectors via a two-level switching inverter. We analyze the conditions placed on and the consequences of implementing necessary modifications to a standard space vector modulation. Five different modified modulation strategies are compared and investigated, including two newly proposed strategies which use only a minimal set of active and zero voltage vectors for measurement of the inductance ratios and therefore allow high utilization of available voltage and a high update rate of the estimated position. Experimental results for three low-power three-phase permanent magnet synchronous machines are presented which suggest that modulation strategies that use active measurement vectors in all three instead of only two axes of the machine are less susceptible to systematic deviations in the position estimation that presumably result from nonlinear machine properties. As part of the machine model, a normalizing inductance variation ratio is introduced, which simplifies expressions and supports the comparison of motors.

Zusammenfassung Sensorlose Ansteuerverfahren Strothmann, R.: Device and method for determining the rotational position of a rotor in an electric machine, US Patent 2009/0278485A1, Nov. 12, 2009; Schroedl, M.: Sensorless control of AC machines at low speed and standstill based on the INFORM method, in Proc. 1996 IEEE Conf. IAS, pp. 270–277; Holtz, J.: Developments in Sensorless AC Drive Technology, International Conference on Power Electronics and Drives Systems, pp. 9–16, ISBN 0-7803-9296-5, 2005; Thiemann, C., Mantala, C., Hördler, J., Trautmann, A., Groppe, D., Strothmann, R., Zhou, E.: New Sensorless Rotor Position Detection Technique of PMSM Based on Direct Flux Control, Proc. of the 2011 International Conference on Power Engineering, Energy and Electrical Drives, pp. 24-29, ISBN 978-1-4244- 9845-1, 2011; Nienhaus, M., Strothmann, R.: Sensorloses Ansteuerverfahren für elektronisch kommutierte Elektromotoren basierend auf der Rotorlageabhängigkeit der Stranginduktivitäten. SPS Drives. Nürnberg, 2014; Grasso, E., Kanapari, E., Nienhaus, M.: Analysis of Direct Flux Observation for field oriented control PMSM. Innovative Klein- und Mikroantriebstechnik (IKMT 2015) & IEEE Xplore, Köln, Germany, September 2015. für elektromagnetische Antriebe dienen vordringlich der Einsparung komplexitätssteigernder Rotorlagesensoren. Einzelne Verfahren ermöglichen es, neben der Rotorlagebestimmung auch auf weitere Zustandsgrößen und Parameter des Antriebssystems zu schließen. Nachfolgend wird ein Verfahren vorgestellt, das einen Positionierbetrieb vom Motorstillstand bis hin zu höchsten Drehzahlen unter anderem für bürstenlose Gleichstrommotoren (BLDC-Motoren) und permanenterregte Synchronmaschinen (PMSM) in Sternschaltung erlaubt. Neben der präzisen Rotorlageerkennung kann dieses Verfahren weitere Zustandsinformationen zum Antrieb liefern, ohne dass es dafür separater Sensoren bedarf. Der Motor selber wird so zu einem multifunktionalen Sensor erweitert.

In the above article [1], there are a few errors that are corrected in the following.