In general, a hydrostatic-driven electric generator consists of a hydrostatic motor and an electric generator. The types of the former mainly include gear motor, vane motor, radial piston motor, swash plate axial piston motor, and bent axis axial piston motor, and the types of the latter mainly include direct current generator, asynchronous generator, permanent magnet synchronous generator, electrically excited synchronous generator, and switched reluctance generator. To make the machine compact and efficient, according to performance comparison,it can be found that the swash plate axial piston motor and the permanent magnet synchronous generator are preferable candidates due to their advantages on efficiency, power density, andintegrate ability.There are several feasible structure integration schemes of the swash plate axial piston hydrostatic motor and the permanent magnet synchronous electric generator. Fig. 1 shows the schematic diagram of the evolution from the bulkiest to the most compact. Their characteristics are described as follows.Scheme (a) is the conventional structure where the shafts of the hydrostatic motor and the electric generator are connected through a coupling.In scheme (b), the shaft of the hydrostatic motor is directly operated on the shaft of the electric generator, and no coupling is required in comparison with scheme (a).In scheme (c), the hydrostatic motor and the electric generator are contained in one case and their rotors are fixed on one shaft.Therefore, one case and one pair of bearing can be saved in comparison with scheme (b).