A back-electromotive force (back-EMF) based sensorless technique for isotropic surface-mounted permanent magnet synchronous motor (SPMSM) drive systems is considered in this paper. Differently from the case of application specific drives, in general purpose ones tuning represents an important challenge, especially if low speed operation or relatively fast dynamics is desired. The trade off between dynamics and steady state performances introduced by estimation noise, and in particular by inverter non linearity, is discussed. The influence of the parameters in the speed and position estimation loop is characterized analytically and experimentally. As a result, a procedure for the design of each of the estimation processing blocks is derived, which is parametric on the desired speed regulation bandwidth, taken as an input from the application requirements. Finally, the stabilizing effect of a constant positive direct axis current reference is demonstrated, which allows to obtain consistent improvements in control accuracy performances at low speed, at the cost of very small additional losses.
