Position sensorless control of PMSM by synchronous injection and demodulation of alternating carrier voltage

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Abstract
Synchronous machines with surface mounted permanent magnets (SMPMSMs) are very popular in industry due to their high efficiency and simple design and are therefore of special interest for position sensorless control. These types of machines typically have small inherent saliencies resulting in a low signal to noise ratio when measuring the rotor position using injected high frequency test signals. It is therefore necessary to avoid any interference between the current controller and the injected signal to achieve the highest possible performance under sensorless control. This paper proposes a novel method for integrating an alternating carrier injection scheme into a current control loop without requiring the commonly used band-pass filter. It uses a strictly synchronous injection and demodulation approach. This allows the high frequency components of the stator current to become completely invisible to the current controller and additionally to eliminate the dead time in the current control loop. Furthermore the demodulated alternating carrier will be unaffected by the fundamental component even during transient conditions. Moreover the proposed decoupling method does not require any motor parameter adjustment.

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