(2) Description of the Related Art UPS systems are currently in wide use to insure uninterrupted, continuous operation of electrical loads in response to power line failure. Systems for use with telecommunication and computer equipment found in typical, unattended relay stations, are usually required to supply electrical loads in the range of 100 to 300 KW for many hours until line power can be restored. The conventional approach utilizes a diesel generator that starts in response to a power failure thereby driving a generator that supplies the electrical load.

Usually, a battery backup is provided to supply the load for a limited time after line failure occurs and until the diesel/generator reaches operational status. The size of the load requires a significant battery installation with attendant problems involving cost and maintenance; and for this reason, flywheel based UPS systems have been proposed.

A flywheel based UPS is described in the web site www. axiomca. com/ as follows :"A hybrid generator combines a diesel engine coupled with a generator via a flywheel system that provides a means of inertial storage. The flywheel uses normal power to build up and maintain its speed. When normal power fails, the flywheel inertial momentum is used to spin the generator to provide power until the engine can take over. Hybrid systems do not require banks of battery cells-saving large initial costs, space, and maintenance." While a diesel engine in a flywheel based UPS is extremely reliable, such a prime mover has the disadvantages of large physical size and weight, and of producing undesirable noxious emissions. An object of the present invention, therefor, is to provide a new and improved flywheel based UPS which overcomes these disadvantages.

Brief Summary of the Invention In accordance with the present invention, flywheel based UPS apparatus for supplying power to an electrical load upon the failure of line power includes a power turbine mounted on a shaft and having an inlet and an outlet. The turbine is constructed and arranged to be responsive to hot gases applied to the inlet for rotating the shaft and producing heat depleted gases that exhaust through the outlet. The apparatus also includes an electrical generating subsystem including a motor, a generator, and a flywheel all rigidly mounted on the shaft for rotation with the power turbine, a motor controller for causing said motor to rotate the shaft at a substantially constant speed only in response to the presence of line power to the electrical load, and an exciter having an active and an inactive state for causing said generator to produce electricity when the shaft rotates, but only when the exciter is in its active state. The apparatus further includes an enclosure for hermetically enclosing the power turbine, motor, generator, and flywheel only when the exciter is in its inactive state. Preferably, a vacuum is maintained in the enclosure for minimizing windage losses. Finally, the apparatus according to the invention includes a control responsive only to the loss of line power to the load for changing the state of the exciter from inactive to active whereby, in response to loss of line. power to the load, the generator is driven by the flywheel and supplies power to the load during wind-down of the flywheel.

Preferably, the enclosure includes a first valve operated by the control for applying hot gases to the inlet of the power turbine only in response to the loss of line power to the load, and a second valve operated by the control for venting the outlet of the power turbine to atmosphere only in response to the loss of line power. The invention also includes a prime mover operated by the control for producing hot gases in response to the loss of line power to the load, the hot gases being supplied to the first valve. Thus, during the time line power is present, the apparatus of the present invention operates in a standby mode in which the rotation of the flywheel and generator are maintained at their rated values in a sub-atmospheric environment, and the exciter of the generator prevents the latter from supplying power to the load. When, however, line power drops out, the exciter causes the generator to begin to supply power to the load. Rotation of the generator is maintained during wind-down of the flywheel as the prime mover is started and produces hot gases that are applied to the power turbine. The kinetic energy stored in the flywheel is sufficient to permit the generator to maintain power to the load until sufficient hot gases are produced to sustain generator operation.

Preferably, the prime mover is a gas turbine which includes a compressor mounted on a shaft and responsive to rotation for compressing air to produce combustion gases, a turbine mounted on the same shaft and responsive to combustion gases for driving the compressor and producing exhaust gases, and a starter connected to said shaft for rotating the same, the starter being responsive to a start signal for imparting rotation to the shaft in response to a start signal from the control for imparting rotation to the shaft until the compressor produces sufficient compressed air to enable the turbine to be operational thereby sustaining rotation of the compressor without operation of said starter. The control is responsive to the loss of line power for generating the start signal.

Preferably, the gas turbine is constructed and arranged so that the shaft thereof has a rotational speed of 30,000-80,000 RPM ; and the power turbine has a rotational speed of 6,000-30,000 RPM. Furthermore, the present invention includes a method for supplying power to an electrical load upon the failure of line power using a flywheel based UPS system. The method comprises the steps of providing a power turbine mounted on a shaft for responding to hot gases applied to an inlet and rotating the shaft; providing an electrical generating subsystem including a motor, a generator, and a flywheel all rigidly mounted on said shaft for rotation with said power turbine, a motor controller for causing said motor to rotate said shaft at a substantially constant speed-only in response to the presence of line power to said electrical load, and an exciter having an active and an inactive state for causing said generator to produce electricity and to supply power to said load when said shaft rotates if said exciter is in its active state, and for preventing said generator from producing power if said exciter is in its inactive state; hermetically enclosing said power turbine, motor, generator, and flywheel only when said exciter is in its inactive state; maintaining a vacuum in said enclosure; and. changing the state of said exciter from inactive to active control only when line power to said load is lost whereby, in response to loss of line power to said load, said generator is driven by said flywheel and begins to supply power to said load during wind-down of said flywheel.

Brief Description of the Several Views of the Drawings Embodiments of the present invention are described by way of example with reference to the accompanying drawings wherein: Fig. 1 is a block diagram of a flywheel based UPS apparatus in accordance with the present invention; Fig. 2 is a block diagram similar to the block diagram of Fig. 1, but showing the various components when the apparatus is in standby mode (i. e., power present); Fig. 3 is a block diagram similar to the block diagram of Fig. 1, but showing the various components when the apparatus is in operational mode (i. e., power absent); and Fig. 4 is a block diagram of another embodiment of the present invention.

Detailed Description of the Invention Referring now to the drawings, reference numeral 10 designates flywheel based UPS apparatus according to a first embodiment of the present invention for supplying power to electrical load 12 upon the failure of line power. Apparatus 10 includes power turbine 14 mounted on shaft 16 and having inlet 18 and outlet 19. The turbine is shown as a single stage, but multiple stages are appropriate in accordance with the power requirements of load 12. Regardless, turbine 14 is constructed and arranged so that when hot gases are applied to inlet 18, the gases expand in the turbine thus rotating the shaft and producing heat depleted gases that exhaust through outlet 19.

Apparatus 10 also includes electrical generating subsystem 20 that includes motor 22, generator 24, and flywheel 26 all rigidly mounted on shaft 16 for rotation with power turbine 14. Subsystem 20 includes motor controller 28 for causing motor 22 to rotate shaft 16 at a substantially constant speed only in response to the presence of line power to the electrical load as explained below, and exciter 30 having an active and an inactive state for causing said generator to produce electricity when the shaft rotates, but only when the exciter is in its active state.

Apparatus 10 further preferably includes enclosure 32 for preferably hermetically enclosing power turbine 14, motor 22, generator 24, and flywheel 26 only when exciter 30 is in its inactive state. Preferably, vacuum pump 34 is operational to maintain enclosure 32 for minimizing windage losses caused by rotation of turbine 14, flywheel 26, and generator 24. Finally, apparatus 10 includes control 36 responsive only to the loss of line power to the load for changing the state of the exciter from inactive to active whereby, in response to loss of line power to the load, generator 24 is driven by flywheel 26 and begins to supply power to load 12 during wind-down of the flywheel.

As shown in Fig. 1, control 36 is connected to the AC line power and operates to sense the presence or absence of AC line power. In response to the presence of AC line power, control 36 produces a control signal in signal line 37 connected to exciter 30 which is effective to maintain the exciter in its inactive state in which no voltage is supplied to the field coils of generator 24. As a result, the generator, although rotating, produces no power. Control 36 is also connected by signal line 38 to motor control 28, the control signal in line 3 8 serving to allow control 28 to supply power from the AC power line, via an AC/DC converter, to motor 22 as needed to maintain flywheel 26 at its rated speed which may be as high as 30,000 RPM during the time the apparatus is in its standby mode, which is shown in Fig. 2.

Apparatus 10 also includes first valve 40 operated by control 36 via control line 41 for applying hot gases in exhaust line 39 to inlet 18 of power turbine 14 only in response to the loss of AC line power to load 12, and second valve 42 operated by control 36 via line 43 for venting outlet 19 of power turbine 14 to atmosphere only in response to the loss of AC line power. Apparatus 10 further includes prime mover 44 operated by control 36 for producing hot gases in exhaust line 39 in response to the loss of line power to load 12.

Thus, exhaust line 39 constitutes means for supplying hot gases from the prime mover to first valve 40. Preferably, prime mover 44 is in the form of gas turbine 45.

Gas turbine 45 includes compressor 46 mounted on shaft 47 and responsive to rotation for compressing air to produce compressed air, burner assembly 48 in which fuel is burned for producing hot combustion gases, and turbine 49 mounted on shaft 47 and responsive to the combustion gases for driving the compressor and producing exhaust gases in exhaust line 39. The flow of fuel to burner assembly 48 is supplied by fuel valve 50 whose operation is controlled by control signals in line 51 produced by control 36.

When line power is present, no signal is present in line 51 with the result that fuel valve 50 is closed and no fuel flows into burner assembly 48. Finally, gas turbine 45 also includes starter 52 connected to shaft 47 for rotating the same in response to a start signal in line 53 generated by control. 36. A start signal is generated by control 36 only in response to the loss of AC line power sensed by the control.

Referring now to Fig. 2, reference numeral I OA designates the configuration of the apparatus according to the present invention when such apparatus is in its standby mode, i. e., apparatus lOA supplies no power to load 12. In this mode, AC line power is present and supplies power to load 12 and to control 36 which is effective to maintain exciter 30 in its inactive state and motor controller 28 in a state that supplies AC line power, via an AC/DC converter, to motor 22. Preferably, valves 40 and 42 are also held closed by control 36 with the result that enclosure 32 is preferably maintained at a sub-atmospheric condition by reason of the preferred operation of vacuum pump 34 thus minimizing windage losses as motor 22 drives generator 24, flywheel 26 and power turbine 14 at rated speed (e. g., 6,000-30,000 RPM). Control 36 also holds valve 50 closed preventing the addition of fuel to burner assemble 48 with the result that gas turbine 45 is non- operational. Thus, in its standby mode, the apparatus according to the present invention is prepared for a break in AC line power consuming only that amount of power required to maintain flywheel 26 at its rated rotational speed and to overcome windage losses in enclosure 32.

When AC line power is interrupted, the apparatus according to the present invention enters its operational mode with the configuration shown in Fig. 3 indicated by reference numeral lOB. The interruption of AC power is sensed by control 36 as well as motor control which responds by depowering motor 22. Control 36 produces a control signal in line 37 which changes the state of exciter 30 to active, and the resultant field current in generator 24, which is driven by the wind-down of flywheel 26, causes the generator to produce power that is supplied to rectifier 60. The output of the rectifier is conditioned, for example, by inverter 61 and supplied to AC load 12 simultaneously with the loss of AC line power. At the same time, control 36 produces a start signal that cause starter 52 to start gas turbine 45 by imparting rotation to shaft 47, and that cause fuel valve 50 to open. Compressor 46 quickly winds-up producing compressed air which is heated by the combustion of fuel in burner assembly 48 producing combustion gases that expand in turbine 49. Starter 52 remains operational until the compressor produces sufficient compressed air to enable the turbine to become operational and sustain rotation of the compressor.

Control 36 also opens valves 40 and 42 so that hot gases exhausted from turbine 49 are directed to the inlet to power turbine 14. The hot gases further expand in turbine 14 producing heat depleted exhaust gases that vent to atmosphere through open valve 42.

The time required for gas turbine 45 to reach operational speed from its non-operational mode is less than the time required for flywheel 46 to wind-down after detection of the loss of line power with the result that the power to load 12 is uninterrupted.

Preferably, the gas turbine and the power turbine operate at different speeds facilitating their design and construction, Specifically, the gas turbine may be constructed and arranged so that the shaft thereof has a rotational speed of 30,000-80,000 RPM. Units operating in this speed range are relatively small and very efficient. On the other hand, the power turbine can be designed to operate at rotational speeds in the range 6,000- 30, 000 RPM. The independence of the operational speeds of the gas turbine and the power turbine allows greater flexibility in design so that the power turbine size becomes practical.

When power is again restored, control 36 is effective to shut down the gas turbine and change the state of exciter 30 from active to inactive as motor 22 is restarted by motor control 28. Vacuum pump 34 is supplied with power from the line when such power is present and from generator 24 when line power is absent.

A further embodiment of the present invention is shown in Fig, 4 and is indicated by reference numeral 1 OC. This embodiment differs from the embodiment described above in that shaft 47A of gas turbine 4. SA is interconnected to shaft 16A of electrical generating subsystem 20 by way of means 70 which may take the fonn of a gear box or a straight-through coupling. If a gear box is utilized, the rotational speed of shaft 27A of the gas turbine may be made different from the speed of shaft 16A when this embodiment is in its operational mode. If necessary, a selectively operable clutch may be employed to disengage shaft 16A from shaft 45A when this embodiment is in its standby mode so that motor 22A will not have to drive the gas turbine while the AC line power is present.

Furthermore, if need be, or if preferred, a battery or batteries can be used to aid the flywheel in supplying power during transition from stand-by mode to operational mode.

Finally, the present invention includes a method for providing an uninteruptable power supply using the apparatus described above.

The advantages and improved results furnished by the apparatus and method of the present invention are apparent from the foregoing description of the preferred embodiment of the invention. Various changes and modifications may be made without. departing from the spirit and scope of the invention as described in the appended claims.