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Sensorless control of an external rotor PMSM in the whole speed range including standstill using DC-link measurements only

In this paper a concept is presented that allows the control of an external rotor permanent magnet synchronous machine by using DC-link current measurements only. For position detection, sensorless methods using just DC-link measurements are implemented "the INFORM" method in the low speed range including standstill and a back-emf based model for high speed. DC-voltage measurements are useful in case of varying DC-link voltage e.g. in generatoric mode. The presented algorithms result in a sensorless high torque-low-cost system that is vector controlled in the whole speed range and hence has higher performance compared to sensorless state of the art systems. The algorithms are implemented on a 16-bit DSP with PWM and capture/compare-units. The DC-link current measurement is interrupt-based and thus a time critical event that is triggered by the capture/compare-units of the space vector PWM. Its functionality, restrictions and limits are explained and discussed in detail. In the low speed range the PWM duty cycles are too short for interrupt-triggered DC-link current measurements. In this operation area, the sequence of the INFORM-method can directly be used to get current information. Furthermore the sensorless methods and their modifications for using DC-link measurements are extensively explained. Finally measurement results are presented, discussed and compared to a classical encoder-based vector oriented machine with respect to accuracy and noise.