A power control system comprises a prime mover and a generator driven by the prime mover. A control device is coupled with the prime mover and the generator wherein the control device ascertains a power level of the generator and varies an output power of the prime mover according to the power level. The control device measures a duty cycle of a generator output power controller to ascertain the generator power level and generates a signal to a prime mover controller so that the generator duty cycle remains within a pre-determined range. The power control system may include a transmission wherein the control device operation may be conditioned on a state of the transmission. The power control system may include a speed converter coupled with the prime mover wherein the control device converts a speed of the prime mover according to the generator power level. The control device may operate to control an output power of the generator concurrently with controlling the output power of the prime mover.