Modelling the impact of the stator currents on inductance-based sensorless control of brushless DC-machines

High-Frequency Issues Using Rotating Voltage Injections Intended For Position Self-Sensing

“…As explained in [4], [24] and as illustrated in Fig. 2, the relation between δi and δψ S along any direction can be modeled as the contribution of two components:…”

“…Another correction must be performed if ψ PM is not oriented along the d-axis. This is generally due to a nonsinusoidal shape of the magnetic field in the air-gap and to a nonsinusoidal distribution of the stator windings [24], [36]. The misalignment between the xy frame and the qd frame is sometimes referred to as an estimation error.…”

“…Note that some papers use pre-filtering with band-pass (BPF) or band-stop filters on the current signal in order to extract the signal-injection current response before the demodulation [11], [19], [23], [26], [27], [36], [44], [45], [52], [56], [60], [61]: i i = BPF (i). This is however not required since (24) naturally removes the frequency content outside −ω i . Moreover, the fact to use operations directly based on the ratio between the current and the high-frequency voltage removes lagging problems [23], [56].…”

“…The moving average (25) can then be used as a LPF for the operation (24), selecting an integer multiple N of N i . Considering the case N i = 3, the characteristic of the moving averages shifted around −ω i = −ω s /3 is illustrated in Fig.…”

“…Misalignment between the anisotropy and the real rotor position can be due to significant stator currents [22], [23], [25], [33], [36], [39], [47]- [49], to the so-called secondary and multiple saliencies [23], [25], [48], or to more general spatial (slots) harmonics related to the conductor distributions and the nonsinusoidal magnetic-field [24], [25], [50]. These issues are largely addressed in the literature.…”