A converterless motor-driven pump system includes an off-grid prime mover. The prime mover includes a rotational driveshaft that operates in response to a throttle or fuel input controller to control a rotation speed of the prime mover driveshaft. Operation of the throttle or fuel input controller is based on desired output characteristics of a pumping load. One or more electric power generators are driven by the off-grid prime mover to generate AC or DC power on an electrical bus shared by a plurality of variable speed electric motors. A plurality of pumps is connected to a common manifold shared by the plurality of pumps. The plurality of pumps is driven by the plurality of variable speed electric motors to generate a desired wellhead pressure or pumping load flow rate via the shared common manifold.