The non-intrusive methods rely on the SR motor characteristics for estimating the rotor position. Measurements at the terminals of phase voltage or mutual voltage and phase current during normal excitation are used to obtain the information, which allows rotor position to be detected. SR motor is normally operated in the saturation region of its magnetic characteristic. The methods using this non-intrusive approach will therefore need to consider the magnetic saturation effect. The flux linkage method [1], [2], the current gradient method [3] and the neural network methods [4], [5] are methods that are non-intrusive and take into account the magnetic saturation.
The flux linkage method was used in [1] and [2]. The current and voltage of the phase winding are measured and integrated to obtain the flux linkage value. This value is compared to a reference flux linkage value obtained from a predetermined family of flux linkage curves plotted as a function of phase current at various rotor positions. When the result of the comparison changes state, the estimated rotor position corresponding to the calculated flux linkage is equal to the reference rotor position. This information was used for current commutation purposes.
