Soft start motor control system for an irrigation system

A center-pivot irrigation system comprising:

• a center pivot;
• at least four irrigation spans extending end-to-end from the center pivot, each irrigation span including:
• a conduit section connected to conduit sections of adjacent irrigation spans for transporting an irrigation fluid from a fluid source to a field;
• a truss configured to support the conduit section;
• a plurality of fluid emitters connected to the conduit section for delivering the irrigation fluid to crops in the field;
• and
• a mobile tower connected to the truss and configured to move the truss, conduit section, and fluid emitters across the field, the mobile tower including:
• a wheel assembly for traversing the field;
• and
• a drive train having a single-speed motor for powering the wheel assembly;
• and
• a control system for controlling the single-speed motors of the drive trains, the control system configured to operate the single-speed motors of at least the outer two irrigation spans in:
• a start-up mode in which the control system gradually ramps a voltage applied to the single-speed motor from a pre-set starting voltage to a full speed voltage over a pre-set start-up time duration according to a linear voltage profile so as to gradually increase a speed of the single-speed motor from 0 rpms to a full speed;
• a full speed mode;
• and
• a wind-down mode in which the control system gradually ramps the voltage applied to the single-speed motor from the full speed voltage to a pre-set ending voltage over a pre-set wind-down time duration according to a linear voltage profile so as to gradually decrease the speed of the single-speed motor from the full speed to 0 rpms,
• at least one parameter of the start-up mode and at least one parameter of the wind-down mode being at least partially determined according to at least one of a motor size, a motor speed rating, and a tire size of the wheel assemblies.