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The present invention relates to a hybrid power-generating device and a power generating method thereof. The hybrid power-generating device is primarily comprised of: a primary electrical generator and an auxiliary electrical generator with different characteristics, both mechanically coupled to a p

The present invention relates to a hybrid power-generating device and a power generating method thereof. The hybrid power-generating device is primarily comprised of: a primary electrical generator and an auxiliary electrical generator with different characteristics, both mechanically coupled to a prime while enabling the rated power of the auxiliary electrical generator to be smaller than that of the primary electrical generator; wherein, as the prime is operating at a low rotation speed or at its initial operating stage, the auxiliary electrical generator is enabled to be driven and activated thereby; and as the operating speed of the driver is stabilized and reaches a predetermined value, the primary electrical generator is then being driven and activated thereby. By the aforesaid hybrid power-generating device, not only the overall performance and the stability of power grid are enhanced, but also the operating cost is reduced.

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What is claimed is: 1. A hybrid power-generating device, comprising: a back-to-back pulse-width modulation (PWM) power converter, further comprising: a rotor-side power converter, connected to the primary electrical generator's rotor: a grid-side power converter, connected to the electrical grid; a

What is claimed is: 1. A hybrid power-generating device, comprising: a back-to-back pulse-width modulation (PWM) power converter, further comprising: a rotor-side power converter, connected to the primary electrical generator's rotor: a grid-side power converter, connected to the electrical grid; a DC bus, disposed at a position between the rotor-side power converter and the grid-side power converter while having a voltage corresponding to the electrical grid; and an AC/DC power converter, connected to the auxiliary electrical generator's stator while connecting an output terminal thereof to the DC bus; a hybrid power generator, each further comprising: a primary electrical generator; and an auxiliary electrical generator, having characteristics different than those of the primary electrical generator while enabling the rated power of the auxiliary electrical generator to be smaller than that of the primary electrical generator; and a prime mover, mechanically coupled to the hybrid power generator for driving the same; wherein, as the prime mover is operating at a low rotation speed or at its initial operating stage, the auxiliary electrical generator is enabled to be driven and activated thereby; and as the rotation speed of the prime mover increases and reaches a predetermined value, the primary electrical generator is then being driven and activated thereby. 2. The hybrid power-generating device of claim 1, wherein the rated power of the auxiliary electrical generator is not larger than one third that of the primary electrical generator for facilitating not only the enhancement of overall performance and the stability of power grid, but also the reduction of operating cost. 3. The hybrid power-generating device of claim 1, wherein the primary electrical generator is a doubly-fed induction generator (DFIG) having its stator connected to an electrical grid; and the auxiliary electrical generator is a synchronous generator (SG). 4. The hybrid power-generating device of claim 1, wherein the DC bus is connected to a controlled dump load. 5. The hybrid power-generating device of claim 1, wherein the AC/DC power converter can be a uni-directional active boost converter or a bi-directional PMW-type power converter. 6. The hybrid power-generating device of claim 1, further comprising: a power supply unit, for providing regulated voltage sources for internal operations of the hybrid power-generating device, being capable of receiving electrical power from multiple power sources. 7. The hybrid power-generating device of claim 6, wherein one power source of the power supply unit is the DC bus or the auxiliary electrical generator. 8. The hybrid power-generating device of claim 1, further comprising: a controller, used for controlling the activation of each hybrid power generator, while capable of enabling any one of the primary and auxiliary electrical generators to respectively enter a control mode selected from the group consisting of a power control mode and a torque control mode. 9. The hybrid power-generating device of claim 1, wherein the prime mover can be an impeller in a wind power, a hydro power or the like fluid power system. 10. The hybrid power-generating device of claim 1, wherein the prime mover is an impeller having a plurality of blades with adjustable pitch angles, whose output power can be varied by the adjustment of the pitch angles of its blades. 11. The hybrid power-generating device of claim 10, wherein the pitch angle of each blade is adjusted and controlled by a pitch drive system. 12. The hybrid power-generating device of claim 1, wherein a short-circuit action is incorporated as a control function applied to the stator terminals of the auxiliary electrical generator for proving an auxiliary braking torque to the prime mover. 13. The hybrid power-generating device of claim 1, wherein the primary electrical generator can be an induction generator, a synchronous generator, a direct current generator or a reluctance generator. 14. The hybrid power-generating device of claim 1, wherein the auxiliary electrical generator can be a synchronous generator or a direct current generator. 15. A power generating method for a hybrid power-generating device, comprising steps of: i. providing a hybrid power generator, comprising a primary electrical generator and an auxiliary electrical generator while enabling the operating characteristics of the auxiliary electrical generator to be different from those of the primary electrical generator and the rated power of the auxiliary electrical generator to be smaller than that of the primary electrical generator, and a prime mover with adjustable blades, coupled to the hybrid power generator for driving the same; ii. enabling the auxiliary electrical generator to be driven and activated by the prime mover as the prime mover is operating at a low rotation speed or at its initial operating stage; and iii. enabling the primary electrical generator to be driven and activated by the prime mover as the operating speed of the prime mover increases and reaches a predetermined value; wherein, the hybrid power-generating device further comprises a back-to-back pulse-width modulation (PWM) power converter, which comprises: a rotor-side power converter, connected to the primary electrical generator's rotor; a grid-side power converter, connected to an electrical grid; and a DC bus, disposed at a position between the rotor-side power converter and the grid-side power converter while having a voltage corresponding to the electrical grid; and wherein, as the auxiliary electrical generator being connected to the AC/DC power converter while the output of the AC/DC power converter is connected to the DC bus and is able to charge the DC bus to a predetermined voltage level, and then the voltage of the DC bus is to be controlled by the grid-side converter. 16. The power generating method of claim 15, further comprising a voltage control procedure including steps of: firstly using the auxiliary electrical generator though an AC/DC power converter to charge a DC bus until the DC bus reaches a predetermined voltage level; and then using a power controller to regulate the DC bus at a predetermined voltage level. 17. The power generating method of claim 16, wherein the power controller is used for controlling the activation of the hybrid power generator, while capable of enabling the primary and auxiliary electrical generators to respectively enter a control mode selected from the group consisting of a power control mode and a torque control mode. 18. The power generating method of claim 15, wherein the AC/DC power converter charges and controls the voltage of the DC bus to rise in a ramp manner. 19. The power generating method of claim 15, wherein the AC/DC power converter can be a uni-directional active boost converter or a bi-directional PMW-type power converter. 20. The power generating method of claim 15, wherein the voltage control procedure further comprises a voltage balance procedure, being executed as soon as the electrical grid suffers a sudden voltage dip being evaluated as a faulted condition for maintaining the voltage of the electrical grid at a reasonable value, including steps of: rendering the DC bus to be controlled by the AC/DC power converter connected to the auxiliary electrical generator while enabling the grid-side power converter to generate reactive power for assisting the voltage recovery during the faulted condition; adjusting the pitch angles of the blades of the prime mover for decreasing captured wind energy thereby and thus reducing power generation of the hybrid power generator; rendering the output voltage of the auxiliary electrical generator to be used as an input of a power supply unit for providing power to internal operations of the hybrid power-generating device, by which the hybrid power-generating device can be maintained to operate normally even when the electrical grid is at a faulted condition; and enabling the primary electrical generator back to normal operation as soon as the faulted condition of the electrical grid is recovered. 21. The power generating method of claim 20, the voltage balance procedure further comprising the step of: enabling a controlled dump load for lowering the voltage of the DC bus as soon as the voltage of the DC bus is detected to exceed a specific level, which might occur because the foregoing adjusting of the pitch angles is not fast enough. 22. The power generating method of claim 15, wherein regulated voltage sources for the internal operations of the hybrid power-generating device is provided by the power supply unit, capable of receiving electrical power from multiple power sources. 23. The power generating method of claim 22, wherein one power source of the power supply unit is the DC bus or the auxiliary electrical generator. 24. The power generating method of claim 15, wherein at step (b), as soon as the prime mover reaches a rated rotation speed, the prime mover is directed to maintain to operate at that rated rotation speed by using the pitch drive system. 25. The power generating method of claim 24, wherein a short-circuit action is incorporated as a control function applied to the stator terminals of the auxiliary electrical generator for proving an auxiliary braking torque to the prime mover. 26. The power generating method of claim 15, wherein the rated power of the auxiliary electrical generator is not larger than one third that of the primary electrical generator for facilitating not only the enhancement of overall performance and the stability of power grid, but also the reduction of operating cost. 27. The power generating method of claim 15, wherein the primary electrical generator is a doubly-fed induction generator (DFIG); and the auxiliary electrical generator is a synchronous generator (SG). 28. The power generating method of claim 24, wherein the hybrid power generator is coupled to the prime mover through a gearbox for enabling the prime mover to drive the generator in an indirect manner. 29. The power generating method of claim 28, wherein a plurality of power generators are so incorporated in the hybrid power generator by enabling those to share a common driving shaft while using the driving shaft to connect those to the gearbox. 30. The power generating method of claim 24, wherein the prime mover is coupled directly to the auxiliary electrical generator for enabling the same to be driven directly by the prime mover. 31. The power generating method of claim 24, wherein the prime mover can be an impeller in a wind power, a hydro power or the like fluid power system. 32. The power generating method of claim 31, wherein the impeller has a plurality of blades with adjustable pitch angles, whose output power can be varied by the adjustment of the pitch angles of its blades. 33. The power generating method of claim 32, wherein the pitch angle of each blade is adjusted and controlled by a pitch drive system. 34. The power generating method of claim 15, wherein the primary electrical generator can be an induction generator, a synchronous generator, a direct current generator or a reluctance generator. 35. The power generating method of claim 15, wherein the auxiliary electrical generator can be an induction generator, a synchronous generator, a direct current generator or a reluctance generator.