Research on current zero-crossing switching method of segmented linear motor based on adaptive threshold

High Speed Segmented Linear Motor with antiparallel thyristor as segmented switch needs to switch between stator segments when the current crosses zero. Finding out the zero-crossing point of the current accurately makes the segmented switch realize accurate and continuous action when the three-phase current zero-crossing, which can reduce the current fluctuation of the motor and the impact on the inverter at the switching time. The traditional method determines current zero crossing by fixed threshold, because the stator current frequency and amplitude change range are large when the motor is running at different speeds and accelerations, the current sampling point is not within the threshold range, resulting in misjudgment of zero-crossing point, switch three-phase switching delay, switching current impact and so on. In view of the above situation, this paper presents a method to calculate the current zero-crossing threshold according to the current frequency and amplitude adaptive change, so that only one sampling point falls within the threshold when the current frequency and amplitude change. According to the calculated threshold, a zero-crossing switching method is proposed, which can change the trigger signal of the front and back switches respectively, so that the motor can accurately complete the segmented switching at the current zero-crossing point, reduce the current fluctuation during the switching, and ensure the continuous switching of the three-phase switch. The accuracy of the adaptive threshold calculation is verified by simulation, and the effectiveness of the switching method is verified by experiments.