High-resolution sensorless position estimation using delta-sigma-modulated current measurement

Sensorless speed and position control of surface mounted permanent magnet synchronous machines (SMPMSMs) is of special interest in industrial automation due to their high efficiency and simple design. However these types of machines have no geometrical saliencies and the exploitable magnetic anisotropies result solely from magnetic saturation and are therefore very small. The measurable position dependent current components resulting from injected high frequency voltages are hence very small and a high resolution current measurement is needed. This paper proposes a novel technique for injecting an alternating carrier voltage. The high frequency current components are measured using delta-sigma-modulators. Suitable design of the low-pass filters and appropriate processing of the measured current values allows to achieve a very high signal to noise ratio. The proposed analytical approach to separate the high frequency current components from the fundamental wave current portion avoids any interference between the current controller and the high frequency voltage injection. Therefore the extracted position information will not be affected by the fundamental current components even during transient conditions. The separation scheme is free of any motor parameters and can cope with significant nonlinear inductances.