Abstract:
A continuous power supply may include a turbogenerator to provide power to supply the load and or an energy storage element and possibly also to the primary energy source. Utilizing an isolated DC bus architecture permits bi-directional power flow among interconnected elements.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 10/072,501, filed Feb. 5, 2002, now abandoned which claims the benefit of U.S. Provisional Application No. 60/266,639, filed Feb. 5, 2001, U.S. Provisional Application No. 60/270,354, filed Feb. 21, 2001, and U.S. Provisional Application No. 60/276,352, filed Mar. 16, 2001, each of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to continuous power systems, and more specifically to continuous power systems with back-up generation. 
     BACKGROUND OF THE INVENTION 
     What is needed is a turbogenerator based power supply with backup generation or an uninterruptable power supply. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a standby system for supplying power to a network when a preferred power supply system is unavailable. The network includes a coupling device adapted to be coupled between the preferred power supply system and a load. A DC bus is adapted to be coupled to the coupling device and the load. A power converter is coupled to the DC bus, and an energy storage device is coupled to the power converter. An electric power supply is adapted to be coupled between the energy storage device and the power converter. A sensor senses the energy capacity of the energy storage device. A controller is coupled to the sensor and to the electric power supply for controlling the operation of the electric power supply as a function of the energy capacity sensed by the sensor. 
     In addition, the invention provides a power supply with back-up generation including a power source connected to a first bi-directional converter, a turbogenerator/motor connected to a second bi-directional converter, a load connected to a converter, a DC bus interconnecting each of the converters, an energy storage element connected to the DC bus, a bus sensor element connected to the DC bus, and a supervisory control receiving bus sensor signals for controlling the turbogenerator. 
     These and other features and advantages of this invention will become further apparent from the detailed description and accompanying figures that follow. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is perspective view, partially in section, of an integrated turbogenerator system according to an embodiment of the invention. 
     FIG. 1B is a magnified perspective view, partially in section, of the motor/generator portion of the integrated turbogenerator of FIG.  1 A. 
     FIG. 1C is an end view, from the motor/generator end, of the integrated turbogenerator of FIG.  1 A. 
     FIG. 1D is a magnified perspective view, partially in section, of the combustor-turbine exhaust portion of the integrated turbogenerator of FIG.  1 A. 
     FIG. 1E is a magnified perspective view, partially in section, of the compressor-turbine portion of the integrated turbogenerator of FIG.  1 A. 
     FIG. 2 is a block diagram schematic of a turbogenerator system including a power controller having decoupled rotor speed, operating temperature, and DC bus voltage control loops according to an embodiment of the invention. 
     FIG. 3 is a block diagram schematic of a first example continuous power supply system with back-up generation according to an embodiment of the invention. 
     FIG. 4 is a block diagram schematic of a second example continuous power supply system with back-up generation. 
     FIG. 5 is a graphic illustration of an example control strategy for a continuous power supply system with back-up generation according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turbo Generator 
     With reference to FIG. 1A, an integrated turbogenerator  1  generally includes a motor/generator section  10  and a compressor-turbine section  30 . Compressor-turbine section  30  includes an exterior can  32 , a compressor  40 , a combustor  50  and a turbine  70 . A recuperator  90  may be optionally included. 
     Referring now to FIG.  1 B and FIG. 1C, motor/generator section  10  may comprise a permanent magnet motor generator having a permanent magnet rotor or sleeve  12 . Any other suitable type of motor generator may also be used. Permanent magnet rotor or sleeve  12  may contain a permanent magnet  12 M. Permanent magnet rotor or sleeve  12  and the permanent magnet  12 M disposed therein are rotatably supported within a permanent magnet motor/generator stator  14 . One or more compliant foil, fluid film, radial, or journal bearings  15 A and  15 B rotatably support permanent magnet rotor or sleeve  12  and the permanent magnet  12 M disposed therein. All bearings, thrust, radial or journal bearings, in turbogenerator  1  may be fluid film bearings or compliant foil bearings. A motor/generator housing  16  encloses a stator heat exchanger  17  having a plurality of radially extending stator cooling fins  18 . Stator cooling fins  18  connect to or form part of stator  14  and extend into an annular space  10 A between motor/generator housing  16  and stator  14 . Wire windings  14 W are wound on permanent magnet motor/generator stator  14 . 
     Referring now to FIG. 1D, combustor  50  may include a cylindrical inner wall  52  and a cylindrical outer wall  54 . Cylindrical outer wall  54  may also include air inlets  55 . Cylindrical walls  52  and  54  define an annular interior space  50 S in combustor  50  defining an axis  50 A. Combustor  50  includes a generally annular wall  56  further defining one axial end of the annular interior space of combustor  50 . One or more fuel injector inlets  58  may be associated with combustor  50  to accommodate fuel injectors which receive fuel from a fuel control element (or fuel pump)  50 P as shown in FIG. 2, and inject fuel or a fuel air mixture to an interior  50 S of combustor  50 . An inner cylindrical surface  53  is interior to cylindrical inner wall  52  and forms an exhaust duct  59  for turbine  70 . 
     Turbine  70  generally includes a turbine wheel  72 . An end of combustor  50  opposite annular wall  56  further defines an aperture  71  in turbine  70  exposed to turbine wheel  72 . A bearing rotor  74  may include a radially extending thrust bearing portion, bearing a rotor thrust disk  78 , constrained by bilateral thrust bearings  78 A and  78 B. Bearing rotor  74  is rotatably supported by one or more journal bearings  75  within a center bearing housing  79 . Bearing rotor thrust disk  78  at the compressor end of bearing rotor  74  is rotatably supported preferably by bilateral thrust bearings  78 A and  78 B. Journal or radial bearing  75  and thrust bearings  78 A and  78 B may be in the form of fluid film or foil bearings. 
     Turbine wheel  72 , bearing rotor  74  and a compressor impeller  42  may be mechanically constrained by a tie bolt  74 B, or other suitable technique, to rotate when turbine wheel  72  rotates. A mechanical link  76  mechanically constrains compressor impeller  42  to permanent magnet rotor or sleeve  12  and permanent magnet  12 M disposed therein causing permanent magnet rotor or sleeve  12  and permanent magnet  12 M to rotate when compressor impeller  42  rotates. 
     Referring now to FIG. 1E, compressor  40  may include compressor impeller  42  and a compressor impeller housing  44 . Recuperator  90  may have an annular shape defined by a cylindrical recuperator inner wall  92  and a cylindrical recuperator outer wall  94 . Recuperator  90  contains internal passages for gas flow. One set of passages  33  connects compressor  40  to combustor  50 . A second set of passages  97  connects a turbine exhaust  80  to a turbogenerator exhaust output  2 . 
     Referring again to FIG.  1 B and FIG. 1C, in operation, air flows into a primary inlet  20  and divides into compressor air  22  and motor/generator cooling air  24 . Motor/generator cooling air  24  flows into an annular space  10 A between motor/generator housing  16  and permanent magnet motor/generator stator  14  along a flow path  24 A. Heat is exchanged from stator cooling fins  18  to generator cooling air  24  in flow path  24 A, thereby cooling stator cooling fins  18  and stator  14  and forming heated air  24 B. Warm stator cooling air  24 B exits stator heat exchanger  17  into a stator cavity  25  where it further divides into stator return cooling air  27  and rotor cooling air  28 . Rotor cooling air  28  passes around a stator end  13 A and travels along rotor or sleeve  12 . Stator return cooling air  27  enters one or more cooling ducts  14 D and is conducted through stator  14  to provide further cooling. Stator return cooling air  27  and rotor cooling air  28  rejoin in a stator cavity  29  and are drawn out of motor/generator  10  by an exhaust fan  11  which is connected to rotor or sleeve  12  and rotates with rotor or sleeve  12 . Exhaust air  27 B is conducted away from primary air inlet  20  by a duct  10 D. 
     Referring again to FIG. 1E, compressor  40  receives compressor air  22 . Compressor impeller  42  compresses compressor air  22  and forces compressed gas  22 C to flow into a set of passages  33  in recuperator  90  connecting compressor  40  to combustor  50 . In passages  33  in recuperator  90 , heat is exchanged from walls  98  of recuperator  90  to compressed gas  22 C. As shown in FIG. 1E, heated compressed gas  22 H flows out of recuperator  90  to space  35  between cylindrical inner surface  82  of turbine exhaust  80  and cylindrical outer wall  54  of combustor  50 . Heated compressed gas  22 H may flow into combustor  54  through sidewall ports  55  or main inlet  57 . Fuel (not shown) may be reacted in combustor  50 , converting chemically stored energy to heat. Hot compressed gas  51  in combustor  50  flows through turbine  70  forcing turbine wheel  72  to rotate. Movement of surfaces of turbine wheel  72  away from gas molecules partially cools and decompresses gas  51 D moving through turbine  70 . Turbine  70  is designed so that exhaust gas  107  flowing from combustor  50  through turbine  70  enters cylindrical passage  59 . Partially cooled and decompressed gas in cylindrical passage  59  flows axially in a direction away from permanent magnet motor/generator section  10 , and then radially outward, and then axially in a direction toward permanent magnet motor/generator section  10  to passages  97  of recuperator  90 , as indicated by gas flow arrows  108  and  109  respectively. 
     As an additional optional feature, a low pressure catalytic reactor  80 A may be included between fuel injector inlets  58  and recuperator  90 . Low pressure catalytic reactor  80 A may include internal surfaces (not shown) having catalytic material (e.g., Pd or Pt, not shown) disposed on them. Low pressure catalytic reactor  80 A may have a generally annular shape defined by a cylindrical inner surface  82  and a cylindrical low pressure outer surface  84 . Unreacted and incompletely reacted hydrocarbons in gas in low pressure catalytic reactor  80 A react to convert chemically stored energy into additional heat, and to lower concentrations of partial reaction products, such as harmful emissions including nitrous oxides (NOx). 
     Gas  110  flows through passages  97  in recuperator  90  connecting from turbine exhaust  80  or catalytic reactor  80 A to turbogenerator exhaust output  2 , as indicated by gas flow arrow  112 , and then exhausts from turbogenerator  1 , as indicated by gas flow arrow  113 . Gas flowing through passages  97  in recuperator  90  connecting from turbine exhaust  80  to the exterior of turbogenerator  1  exchanges heat to walls  98  of recuperator  90 . Walls  98  of recuperator  90  heated by gas flowing from turbine exhaust  80  exchange heat to gas  22 C flowing in recuperator  90  from compressor  40  to combustor  50 . 
     Turbogenerator  1  may also include various electrical sensor and control lines for providing feedback to power controller  201  and for receiving and implementing control signals. The electrical sensor and control systems are shown in FIG.  2  and discussed in more detail below. 
     The integrated turbogenerator disclosed above is exemplary. Several alternative structural embodiments are described below. 
     In one alternative embodiment, a gaseous fuel mixture may replace air  22 . In this embodiment, fuel injectors may not be necessary. This embodiment may include an air and fuel mixer upstream of compressor  40 . 
     In another alternative embodiment, a fuel conduit connecting to compressor impeller housing  44  may conduct fuel directly to compressor  40 , for example. Fuel and air may be mixed by action of the compressor impeller  42 . In this embodiment, fuel injectors may not be necessary. 
     In another alternative embodiment, combustor  50  may be a catalytic combustor. 
     In still another alternative embodiment, geometric relationships and structures of components may differ from those shown in FIG.  1 A. Permanent magnet motor/generator section  10  and compressor/combustor section  30  may have low pressure catalytic reactor  80 A outside of annular recuperator  90 , and may have recuperator  90  outside of low pressure catalytic reactor  80 A. Low pressure catalytic reactor  80 A may be disposed at least partially in cylindrical passage  59 , or in a passage of any shape confined by an inner wall of combustor  50 . Combustor  50  and low pressure catalytic reactor  80 A may be substantially or completely enclosed with an interior space formed by a generally annularly shaped recuperator  90 , or a recuperator  90  shaped to substantially enclose both combustor  50  and low pressure catalytic reactor  80 A on all but one face. 
     An integrated turbogenerator is a turbogenerator in which the turbine, compressor, and generator are all constrained to rotate based upon rotation of the shaft to which the turbine is connected. The methods and apparatus disclosed herein are preferably but not necessarily used in connection with a turbogenerator, and are preferably but not necessarily used in connection with an integrated turbogenerator. 
     Control System 
     Referring now to FIG. 2, a turbogenerator system  200  includes a power controller  201  which has three substantially decoupled control loops for controlling (1) rotary speed, (2) temperature, and (3) DC bus voltage. A more detailed description of an appropriate power controller is disclosed in U.S. patent application Ser. No. 09/207,817, filed Dec. 08, 1998 in the names of Gilbreth, Wacknov and Wall, and assigned to the assignee of the present application. The disclosure of the &#39;817 application is incorporated herein in its entirety by this reference as though set forth in full hereafter. 
     Referring still to FIG. 2, turbogenerator system  200  includes integrated turbogenerator  1  and power controller  201 . Power controller  201  includes three decoupled or independent control loops. 
     A first control loop, temperature control loop  228 , regulates a temperature related to the desired operating temperature of primary combustor  50  to a set point, by varying fuel flow from fuel control element  50 P to primary combustor  50 . A temperature controller  228 C receives a temperature set point, T*, from a temperature set point source  232 , and receives a measured temperature from a temperature sensor  226 S connected to a measured temperature line  226 . Temperature controller  228 C generates and transmits over a fuel control signal line  230  to fuel pump  50 P a fuel control signal for controlling the amount of fuel supplied by fuel pump  50 P to primary combustor  50 . The fuel is controlled to an amount intended to result in a desired operating temperature in primary combustor  50 . A temperature sensor  226 S may directly measure the temperature in primary combustor  50  or may measure a temperature of an element or area from which the temperature in the primary combustor  50  may be inferred. 
     A second control loop, speed control loop  216 , controls speed of the shaft common to the turbine  70 , compressor  40 , and motor/generator  10 , hereafter referred to as the common shaft, by varying torque applied by the motor generator to the common shaft. Torque applied by the motor generator to the common shaft depends upon power or current drawn from or pumped into windings of motor/generator  10 . A bi-directional generator power converter  202  is controlled by a rotor speed controller  216 C to transmit power or current into or out of motor/generator  10 , as indicated by a bi-directional arrow  242 . A sensor in turbogenerator  1  senses the rotary speed on the common shaft and transmits that rotary speed signal over a measured speed line  220 . Rotor speed controller  216 C receives the rotary speed signal from measured speed line  220  and a rotary speed set point signal from a rotary speed set point source  218 . Rotary speed controller  216 C generates and transmits to generator power converter  202  a power conversion control signal on a line  222  controlling generator power converter  202 &#39;s transfer of power or current between AC lines  203  (i.e., from motor/generator  10 ) and a DC bus  204 . Rotary speed set point source  218  may convert a power set point P* to the rotary speed set point received from a power set point source  224 . 
     A third control loop, voltage control loop  234 , controls bus voltage on DC bus  204  to a set point by transferring power or voltage between DC bus  204  and any of (1) a Load/Grid  208  and/or (2) an energy storage device  210 , and/or (3) by transferring power or voltage from DC bus  204  to a dynamic brake resistor  214 . A sensor measures voltage on DC bus  204  and transmits a measured voltage signal over a measured voltage line  236 . A bus voltage controller  234 C receives the measured voltage signal from voltage line  236  and a voltage set point signal V* from a voltage set point source  238 . Bus voltage controller  234 C generates and transmits signals to a bi-directional load power converter  206  and a bi-directional battery power converter  212  controlling the transmission of power or voltage between DC bus  204 , load/grid  208 , and energy storage device  210 , respectively. In addition, bus voltage controller  234  transmits a control signal to control connection of dynamic brake resistor  214  to DC bus  204 . 
     Power controller  201  regulates temperature to a set point by varying fuel flow, adds or removes power or current to motor/generator  10  under control of generator power converter  202  to control rotor speed to a set point as indicated by bi-directional arrow  242 , and controls bus voltage to a set point by (1) applying or removing power from DC bus  204  under the control of load power converter  206  as indicated by bi-directional arrow  244 , (2) applying or removing power from energy storage device  210  under the control of battery power converter  212 , and (3) by removing power from DC bus  204  by modulating the connection of dynamic brake resistor  214  to DC bus  204 . 
     The method and apparatus disclosed above contain elements interchangeable with elements of the methods and apparatus below. 
     Referring now to FIG. 3, power supply  503  is shown combining a power source  500  with turbogenerator  1 . Power source  500  is connected to bi-directional load power converter  206  that is connected to DC bus  204 . Power Source  500  may be a utility grid, a local power network, or another power distribution, power storage, or power generation system. Bi-directional converter  206  enables power source  500  to either supply power  500 B to, or to consume power  500 A from DC bus  204 . 
     FIG. 3 also shows turbogenerator  1  connected to bi-directional generator power converter  202 . Converter  202  is connected to bi-directional power converter  212 A, which, in turn, is connected to DC bus  204 . Bi-directional converters  202  and  212 A enable turbogenerator  1  to either supply power  202 B to, or to consume power  202 A from, DC bus  204 . Converter  202  may be connected directly to DC bus  204  if converter  202  is designed to operate within the range of DC bus voltages  236  present on DC bus  204 . Direct connection  202 C of converter  202  to DC bus  204  would eliminate the need for converter  212 A. 
     FIG. 3 also shows AC load  208 A connected to converter  206 B that is connected to DC bus  204 . Load  208 A may consume power, indicated by flow arrow  605 A, from DC bus  204 . In the alternative, converter  206 B may be a bi-directional converter and load  208 A may supply power  605 B to DC bus  204 . 
     FIG. 3 also shows DC load  208 B on DC bus  204 . Load  208 B is connected to converter  212 C that is connected to DC bus  204 . Load  208 B may consume power  610 A from DC bus  204 . In the alternative, converter  212 C may be a bi-directional converter and Load  208 B may supply power  610 B to DC bus  204 . 
     FIG. 3 also shows DC load  208 C on DC bus  204 . Load  208 C is connected to DC bus  204 . Load  208 C may consume power  615 A from DC bus  204 . In the alternative, load  208 C may supply power  615 B to DC bus  204 . 
     FIG. 3 also shows energy storage  210  connected to bi-directional battery power converter  212  that is connected to DC bus  204 . Bi-directional converter  212  enables energy storage  210  to supply power  210 B to the DC bus  204 , or to consume power  210 A from the DC bus  204 . Energy storage  210  may be connected directly to the DC bus  204  if energy storage  210  is designed to operate within the range of DC bus voltages  236  present on DC bus  204 . The direct connection  210 C of energy storage  210  to DC bus  204  would eliminate the need for converter  212 . 
     FIG. 3 also shows a bus sensor  600  connected to DC bus  204  between DC bus connection  210 C and DC bus voltage measurement  236 . Bus sensor  600  may be used to measure bus status including the flow of power  210 A to, and the flow of power  210 B from, energy storage  210 . 
     FIG. 3 also shows a supervisory controller  511 . Controller  511  may be comprised of a plurality of processing elements. Controller  511  may have connections to bus sensor  600 , voltage sensor  236 , turbogenerator  1 , converter  202 , and converter  212 A. Controller  511  may also include functions comprising turbogenerator start, operation, stop, fault, and reporting/diagnostics. 
     In one embodiment, converter  202  and energy storage  210  may be connected directly to the DC bus. In an alternate embodiment, converter  202  may be connected directly to the DC bus and energy storage  210  may be connected to converter  212 . In a third embodiment, energy storage  210  may be connected directly to the DC bus and converter  202  may be connected to converter  212 A. 
     In a first mode of operation, power source  500  supplies power  500 B to DC bus  204 , enabling DC bus voltage to be controlled within a prescribed range. If power source  500  is unable to supply sufficient power to the DC bus  204  to maintain DC bus voltage at a required level, then DC bus  204  draws power  2101 B from energy storage  210 . Bus sensor  600  senses the flow of power  210 B from energy storage. Supervisory controller  511  starts turbogenerator  1  when the flow of power  2101 B from energy storage  210  exceeds prescribed limits. Turbogenerator  1  consumes power  202 A, from DC bus  204  during start. After reaching self-sustaining speed, turbogenerator  1  supplies power  202 B to DC Bus  204  and power exchange between DC bus  204  and energy storage  210  reverses as energy storage  210  is recharged by the flow of power  210 A from DC bus  204 . 
     In a second mode of operation, turbogenerator  1  may be supplying power  202 B to the DC bus  204 . Load  208  may be consuming power  605 A from DC bus  204  and power supply  500  may be consuming power  500 A from DC bus  204 . 
     In a third mode of operation, one or more of loads  208  may be supplying power to the DC bus as indicated by one or more of power arrows  605 B,  610 B, and or  615 B respectively. 
     A further embodiment of the power control system according to the invention is illustrated in FIG.  4 . FIG. 4 shows a block diagram schematic of an in-line uninterruptable power supply (UPS) having an electric power source for recharging an energy storage device. More specifically, FIG. 4 shows a UPS system  400  comprising a primary power source  402 , such as a utility power grid, coupled to a load  404  through a first bi-directional power converter  406 , a second bi-directional power converter  408 , and a DC bus  410 . An energy storage device  412  is connected to DC bus  410  through an optional DC/DC converter  414 . An electric power supply  416  is connected through a further converter  418  to a node  420  between energy storage device  412  and optional converter  414 . If power supply  416  produces an AC power signal, such as a turbogenerator/motor or wind turbine, convertor  418  is typically a bi-directional AC/DC converter. If power supply  416  produces a DC output, such as a fuel cell or a photovoltaic cell, then converter would either be omitted or is typically a DC/DC converter. A sensor  422  is connected to DC bus  410  preferably at or near node  420 . Sensor  422  monitors conditions on bus  410  and sends information to a controller  424 . Controller  424  is connected to electric power supply  416  to control the operation of electric power supply  416  as a function of the sensed conditions on bus  410 . 
     Electric power supply  416  may comprise any of a number of types of power sources. These may include a turbogenerator/motor, a fuel cell, a wind turbine, or photovoltaic cells. Energy storage device  412  may comprise a battery or an ultracapacitor, for example. Sensor  422  may comprise a voltage sensor for sensing the voltage at energy storage device  412  or a current sensor for sensing current into and out of energy storage device  412 , for example. 
     In one example of the embodiment of FIG. 4, sensor  422  comprises a voltage sensor; electric power supply  416  comprises a turbogenerator/motor; and energy storage device  412  comprises a battery. In a typical example, load  404  draws power from the primary power source, such as an electric utility grid,  402 . A failure of primary power source  402  causes load  404  to start drawing power from the energy storage device, such as a battery,  412 . As power is drawn from energy storage device  412 , the voltage on bus  410  decreases. This decrease is sensed by (voltage) sensor  422 . If sensor  422  senses a drop in DC bus voltage below a preset threshold, it will send a signal to controller  424 . Controller  424  sends a START command to turbogenerator/motor  416  to command it to start up. Typically, controller  424  waits for a predetermined period of time, usually on the order of 60-90 seconds, before sending the START command to allow for momentary fluctuations in power source  402 . 
     At the START command, current is caused to flow from battery  412  through converter  418  to turbogenerator/motor  416  to provide starting power for turbogenerator/motor  416 . Once turbogenerator/motor  416  has started and become self-sustaining, it reverts to generator mode and puts power back into the system. This operation is understood by persons skilled in the relevant art, and is described, for example, in the above-mentioned &#39;817 application. Where energy storage device  412  is a battery or equivalent rechargeable device, part of the output current from turbogenerator/motor  416  goes to recharge storage device  412 . The remaining output current is supplied to DC bus  410  to provide power to load  404 . Once storage device  412  is recharged, turbogenerator/motor  416  continues to provide power to load  404  via DC bus  410  until primary power source  402  comes back on line. 
     A feature of this embodiment is its simplicity. The operation of turbogenerator/motor  416  is controlled by a single voltage (or current) sensor  422 . Sensor  422  only needs to measure the voltage (or current) on DC bus  410 . If sensor  422  detects an adverse voltage or current change on bus  410  for a predetermined period of time, it sends a signal to controller  424  to cause turbogenerator/motor  416  to supply power until primary power source  402  comes back on line. 
     The operation of the embodiment of FIG. 4 is further illustrated by the graph of FIG.  5 . At a time t 1 , voltage sensor  422  senses a drop in voltage V B  across DC bus  420 . Sensor  422  detects the continuous drop in voltage due to the failure of primary source  402  and the corresponding drain on battery  412 . At a predetermined time t 2  after time t 1 , controller  424  sends a START command to turbogenerator/motor  416  to initiate a start sequence. Once turbogenerator/motor  416  has reached its self-sustaining operating condition and is generating power, which occurs very rapidly, between times t 2  and t 3 , turbogenerator/motor  416  supplies power PE to load  404  and a charging current Is to battery  412 . The rate of charging of battery  412  is a function of several factors, including the size and number of battery cells. These factors can be programmed into controller  424  during initial system setup. In one example, the rate of charging of battery  412  (e.g., ΔV B /Δt) is controlled. At time t 4 , battery  412  is fully charged and turbogenerator/motor  416  continues to provide power to load  404 . At time t 5 , primary power source  402  comes back on line. This may be detected by a small voltage spike on DC bus  410 . This spike is detected by voltage sensor  422 , which sends this information to controller  424 . Controller  424  then sends a SHUT DOWN command to turbogenerator/motor  416  to cause it to shut down. 
     In a variation of the foregoing embodiment, controller  424  can be programmed to send a START command to turbogenerator/motor  416  at predetermined times. For example, turbogenerator/motor  416  can be programmed to turn on at certain times of the day, such as when electric utility rates are high. Turbogenerator/motor  416  can then provide power to supplement or replace utility grid power. 
     Having now described the invention in accordance with the requirements of the patent statutes, those skilled in this art will understand how to make changes and modifications in the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.