An electrical generating system is driven by a variable speed prime mover through a constant speed drive. A speed control, as a proportional integrator responsive to frequency error, controls the constant speed drive. Stability and speed of response of the system are improved by the inclusion of one or more of the following in the speed control: a lead/lag filter between the output of proportional integrator and the constant speed drive; an adaptive gain circuit for the frequency error signal ahead of the proportional integrator; an adaptive integrator for delaying integrator operation on occurrence of a load current change; a nonlinear gain circuit in parallel with the proportional integrator to increase the control signal as the error signal increases; or load current or input speed bias signals added to the control signal to reduce the range of integrator output.