A converterless motor-driven pump system includes an off-grid prime mover, an electric power generator driven by the off-grid prime mover to generate a power output, an electric submersible pump (ESP) system, and a system controller. The ESP system includes a motor coupled to the electric power generator to receive the power output, and a pump driven by the motor to pump a fluid. The system controller includes a processor and a memory. The memory includes instructions that, when executed by the processor, cause the system controller to control the off-grid prime mover as a function of an operational parameter of the ESP system to maintain a desired operating point of the pump, and control the electric power generator to reduce the power output generated by the electric power generator while the desired operating point of the pump is maintained.