Abstract: A hydraulic drive system for use in driving a power generator has a hydraulic pump having an input for rotationally driving the hydraulic pump, a flow control valve in fluid communication with the hydraulic pump, a hydraulic motor having a first output and a second output coupled to a hydraulic fluid source, and a pressure regulator positioned intermediate the flow control valve and the hydraulic motor. The pressure regulator is in fluid communication with the hydraulic motor and the flow control valve, and maintains a hydraulic pressure at its input that is higher than at its output to prevent the hydraulic system from stalling. The system further comprises a power generator having an input shaft rotationally coupled to the hydraulic motor first output.