Abstract:
A power controller provides a distributed generation power networking system in which bi-directional power converters are used with a common DC bus for permitting compatibility between various energy components. Each power converter operates essentially as a customized bi-directional switching converter configured, under the control of the power controller, to provide an interface for a specific energy component to the DC bus. The power controller controls the way in which each energy component, at any moment, will sink or source power, and the manner in which the DC bus is regulated. In this way, various energy components can be used to supply, store and/or use power in an efficient manner. The various energy components include energy sources, loads, storage devices and combinations thereof.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent applications Ser. No. 08/924,966 filed Sept. 8, 1997 for Everett R Geis. and Brian W. Peticolas, assigned to the assignee of the present application and now U.S. Pat. No. 5,903,116 and Ser. No. 09/003,078 filed Jan. 5, 1998 for Everett R. Geis, Brian W. Peticolas and Joel B. Wacknov, assigned to the assignee of the present application and now U.S. Pat. No. 6,031,294. This application claims the benefit of U.S. Provisional Application No. 60/080,457, filed on Apr. 2, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to power generation and processing systems and in particular to distributed generation power systems. 
     2. Description of the Prior Art 
     Conventional power generation and distribution systems are configured to maximize the specific hardware used. In the case of a turbine power motor, for example, the output or bus voltage in a conventional power distribution system varies with the speed of the turbine. In such systems, the turbine speed must be regulated to control the output or bus voltage. Consequently, the engine cannot be run too low in speed else the bus voltage would not be high enough to generate some of the voltages that are needed. As a result, the turbine would have to be run at higher speeds and lower temperatures, making it less efficient. 
     What is needed therefore is a power generation and distribution system where the bus voltage is regulated by a bi-directional controller independent of turbine speed. 
     SUMMARY OF THE INVENTION 
     The present invention provides in a first aspect, a power controller which provides a distributed generation power networking system in which bi-directional power converters are used with a common DC bus for permitting compatibility between various energy components. Each power converter operates essentially as a customized bi-directional switching converter configured, under the control of the power controller, to provide an interface for a specific energy component to the DC bus. The power controller controls the way in which each energy component, at any moment, will sink or source power, and the manner in which the DC bus is regulated. In this way, various energy components can be used to supply, store and/or use power in an efficient manner. The various energy components include energy sources, loads, storage devices and combinations thereof. 
     In another aspect, the present invention provides a turbine system including a turbine engine, a load, a power controller, an energy reservoir for providing transient power to the DC bus and an energy reservoir controller, in communication with the power controller for providing control to the energy reservoir. The power controller includes an engine power conversion in communication with the turbine engine, an utility power conversion in communication with the load and a DC bus. 
     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 drawing figures and the written description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a power controller according to the present invention. 
     FIG. 2 is a detailed block diagram of a power converter in the power controller illustrate FIG.  1 . 
     FIG. 3 is a simplified block diagram of a turbine system including the power architecture of the power controller illustrated in FIG.  1 . 
     FIG. 4 is a block diagram of the power architecture of a typical implementation of the power controller illustrated in FIG.  1 . 
     FIG. 5 is a schematic diagram of the internal power architecture of the power controller illustrated in FIG.  1 . 
     FIG. 6 is a functional block diagram of an interface between load/utility grid and turbine generator using the power controller according to the present invention. 
     FIG. 7 is a functional block diagram of an interface between load/utility grid and turbine generator using the power controller for a stand-alone application according to the present invention. 
     FIG. 8 is a schematic diagram of an interface between a load/utility grid and turbine generator using the power controller according to the present invention. 
     FIG. 9 is a block diagram of the software architecture for the power controller including external interfaces. 
     FIG. 10 is a block diagram of an EGT control mode loop for regulating the temperature of the turbine. 
     FIG. 11 is a block diagram of a speed control mode loop for regulating the rotating speed of the turbine. 
     FIG. 12 is a block diagram of a power control mode loop for regulating the power producing potential of the turbine. 
     FIG. 13 is a state diagram showing various operating states of the power controller. 
     FIG. 14 is a block diagram of the power controller interfacing with a turbine and fuel device. 
     FIG. 15 is a block diagram of the power controller in multi-pack configuration. 
     FIG. 16 is a block diagram of a utility grid analysis system for the power controller according to the present invention. 
     FIG. 17 is a graph of voltage against time for the utility grid analysis system illustrated in FIG.  16 . 
     FIG. 18 is a diagram of the power controller shown in FIG. 16, including brake resistor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring to FIG. 1, power controller  10  provides a distributed generation power networking system in which bi-directional (i.e. reconfigurable) power converters are used with a common DC bus for permitting compatibility between one or more energy components. Each power converter operates essentially as a customized bi-directional switching converter configured, under the control of power controller  10 , to provide an interface for a specific energy component to DC bus  24 . Power controller  10  controls the way in which each energy component, at any moment, will sink or source power, and the manner in which DC bus  24  is regulated. In this way, various energy components can be used to supply, store and/or use power in an efficient manner. 
     One skilled in the art will recognize that the particular configurations shown herein are for illustrative purposes only. In particular, the present invention is not limited to the use of three bi-directional converters as shown in FIG.  1 . Rather, the number of power converters is dependent on various factors, including but not limited to, the number of energy components and the particular power distribution configuration desired. For example, as illustrated in FIGS. 5 and 6, power controller  10  can provide a distributed generation power system with as few as two power converters. 
     The energy components, as shown in FIG. 1, include energy source  12 , utility/load  18  and storage device  20 . The present invention is not limited to the distribution of power between energy source  12 , energy storage device  20  and utility/load  18 , but rather may be adapted to provide power distribution in an efficient manner for any combination of energy components. 
     Energy source  12  may be a gas turbine, photovoltaics, wind turbine or any other conventional or newly developed source. Energy storage device  20  may be a flywheel, battery, ultracap or any other conventional or newly developed energy storage device. Load  18  may be a utility grid, dc load, drive motor or any other conventional or newly developed utility/load  18 . 
     Referring now to FIG. 2, a detailed block diagram of power converter  14  in power controller  10 , shown in FIG. 1, is illustrated. Energy source  12  is connected to DC bus  24  via power converter  14 . Energy source  12  may be, for example, a gas turbine driving an AC generator to produce AC which is applied to power converter  14 . DC bus  24  connects power converter  14  to utility/load  18  and additional energy components  36 . Power converter  14  includes input filter  26 , power switching system  28 , output filter  34 , signal processor  30  and main CPU  32 . In operation, energy source  12  applies AC to input filter  26  in power converter  14 . The filtered AC is then applied to power switching system  28  which may conveniently be a series of insulated gate bipolar transistor (IGBT) switches operating under the control of signal processor (SP)  30  which is controlled by main CPU  32 . One skilled in the art will recognize that other conventional or newly developed switches may be utilized as well. The output of the power switching system  28  is applied to output filter  34  which then applies the filtered DC to DC bus  24 . 
     In accordance with the present invention, each power converter  14 ,  16  and  22  operates essentially as a customized, bi-directional switching converter under the control of main CPU  32 , which uses SP  30  to perform its operations. Main CPU  32  provides both local control and sufficient intelligence to form a distributed processing system. Each power converter  14 ,  16  and  22  is tailored to provide an interface for a specific energy component to DC bus  24 . Main CPU  32  controls the way in which each energy component  12 ,  18  and  20  sinks or sources power, and DC bus  24  is regulated at any time. In particular, main CPU  32  reconfigures the power converters  14 ,  16  and  22  into different configurations for different modes of operation. In this way, various energy components  12 ,  18  and  20  can be used to supply, store and/or use power in an efficient manner. In the case of a turbine power generator, for example, a conventional system regulates turbine speed to control the output or bus voltage. In the power controller, the bi-directional controller independently of turbine speed regulates the bus voltage independently of turbine speed. 
     Operating Modes 
     FIG. 1 shows the system topography in which DC bus  24 , regulated at 800 v DC for example, is at the center of a star pattern network. In general, energy source  12  provides power to DC bus  24  via power converter  14  during normal power generation mode. Similarly, during the power generation mode, power converter  16  converts the power on DC bus  24  to the form required by utility/load  18 , which may be any type of load including a utility web. During other modes of operation, such as utility start up, power converters  14  and  16  are controlled by the main processor to operate in different manners. 
     For example, energy is needed to start the turbine. This energy may come from load/utility grid  18  (utility start) or from energy storage  20  (battery start), such as a battery, flywheel or ultra-cap. During a utility start up, power converter  16  is required to apply power from load  18  to DC bus  24  for conversion by power converter  14  into the power required by energy source  12  to startup. During utility start, energy source or turbine  12  is controlled in a local feedback loop to maintain the turbine revolutions per minute (RPM). Energy storage or battery  20  is disconnected from DC bus  24  while load/utility grid  10  regulates V DC  on DC bus  24 . 
     Similarly, in the battery start mode, the power applied to DC bus  24  from which energy source  12  is started may be provided by energy storage  20  which may be a flywheel, battery or similar device. Energy storage  20  has its own power conversion circuit in power converter  22 , which limits the surge current into DC bus  24  capacitors, and allows enough power to flow to DC Bus  24  to start energy source  12 . In particular, power converter  16  isolates DC bus  24  so that power converter  14  can provide the required starting power from DC bus  24  to energy source  12 . 
     Electronics Architecture 
     Referring to FIG. 3, a simplified block diagram of a turbine system  50  using the power controller electronics architecture of the present invention is illustrated. The turbine system  50  includes a fuel metering system  42 , turbine engine  58 , power controller  52 , energy reservoir conversion  62 , energy/reservoir  64  and load/utility grid  60 . The fuel metering system  42  is matched to the available fuel and pressure. The power controller  52  converts the electricity from turbine engine  58  into regulated DC and then it to utility grade AC electricity. By separating the engine control from the converter that creates the utility grade power, greater control of both processes is realized. All of the interconnections are comprised of a communications bus and a power connection. 
     The power controller  52  includes an engine power conversion  54  and utility power conversion  56  which provides for the two power conversions that take place between the turbine  58  and the load/utility grid  60 . One skilled in the art will recognize that the power controller  52  can provide a distributed generation power system with as few as two power converters  54  and  56 . The bi-directional (i.e. reconfigurable) power converters  54  and  56  are used with a common regulated DC bus  66  for permitting compatibility between the turbine  58  and load/utility grid  60 . Each power converter  54  and  56  operates essentially as a customized bi-directional switching converter configured, under the control of the power controller  10 , to provide an interface for a specific energy component  58  or  60  to the DC bus  66 . The power controller  10  controls the way in which each energy component, at any moment, will sink or source power, and the manner in which the DC bus  66  is regulated. Both of these power conversions  54  and  56  are capable of operating in a forward or reverse direction. This allows starting the turbine  58  from either the energy reservoir  64  or the load/utility grid  60 . The regulated DC bus  66  allows a standardized interface to energy reservoirs such as batteries, flywheels, and ultra-caps. The architecture of the present invention permits the use of virtually any technology that can convert its energy to/from electricity. Since the energy may flow in either direction to or from the energy reservoir  64 , transients may be handled by supplying energy or absorbing energy. Not all systems will need the energy reservoir  64 . The energy reservoir  64  and its energy reservoir conversion  62  are not contained inside the power controller  52 . 
     Referring to FIG. 4, the power architecture  68  of a typical implementation of the power controller  70  is shown. The power controller  70  includes a generator converter  72  and output converter  74  which provides for the two power conversions that take place between the turbine  76  and the load/utility grid  78 . In particular, the generator converter  72  provides for AC to DC power conversion and the output converter  74  provides for DC to AC power conversion. Both of these power converters  72  and  74  are capable of operating in a forward or reverse direction. This allows starting the turbine  76  from either the energy storage device  86  or the load/utility grid  78 . Since the energy may flow in either direction to or from the energy storage device  86 , transients may be handled by supplying energy or absorbing energy. The energy storage device  86  and its DC converter  84  are not contained inside the power controller  70 . The DC converter  84  provides for DC to DC power conversion. 
     Referring to FIG. 5, a schematic  90  of a typical internal power architecture, such as that shown in FIG. 4, is shown. The turbine has an integral PMG that can be used as either a motor (for starting) or a generator (normal mode of operation). Because all of the controls can be performed in the digital domain and all switching (except for one output contactor) is done with solid state switches, it is easy to shift the direction of the power flow as needed. This permits very tight control of the turbine during starting and stopping. In a typical configuration, the power output is a 480 VAC, 3-phase output. One skilled in the art will recognize that the present invention may be adapted to provide for other power output requirements such as a 3-phase, 400 VAC, and single-phase, 480 VAC. 
     Power controller  92  includes generator converter  94  and output converter  96 . Generator converter  94  includes IGBT switches  94 , such as a seven-pack IGBT module  94 , driven by control logic  98 , providing a variable voltage, variable frequency 3-phase drive to the PMG  100 . Inductors  102  are utilized to minimize any current surges associated with the high frequency switching components which may affect the PMG  100  to increase operating efficiency. 
     IGBT module  94  is part of the electronics that controls the engine of the turbine. IGBT module  94  incorporates gate driver and fault sensing circuitry as well as a seventh IGBT used to dump power into a resistor. The gate drive inputs and fault outputs require external isolation. Four external, isolated power supplies are required to power the internal gate drivers. IGBT module  94  is typically used in a turbine system that generates 480 VAC at its output terminals delivering up to 30 kWatts to a freestanding or utility-connected load. During startup and cool down (and occasionally during normal operation), the direction of power flow through the seven-pack reverses. When the turbine is being started, power is supplied to the DC bus  112  from either a battery (not shown) or from the utility grid  108 . The DC is converted to a variable frequency AC voltage to motor the turbine. 
     For utility grid connect operation, control logic  110  sequentially drives the solid state IGBT switches, typically configured in a six-pack IGBT module  96 , associated with load converter  96  to boost the utility voltage to provide start power to the generator converter  94 . The IGBT switches in load converter  96  are preferably operated at a high (15 kHz) frequency, and modulated in a pulse width modulation manner to provide four quadrant converter operation. Inductors  104  and AC filter capacitors  106  are utilized to minimize any current surges associated with the high frequency switching components which may affect load  108 . 
     Six-pack IGBT module  96  is part of the electronics that controls the converter of the turbine. IGBT module  96  incorporates gate driver and fault sensing circuitry. The gate drive inputs and fault outputs require external isolation. Four external, isolated power supplies are required to power the internal gate drivers. IGBT module  96  is typically used in a turbine system that generates 480 VAC at its output terminals delivering up to approximately 30 kWatts to a free-standing or utility-connected load. After the turbine is running, six-pack IGBT module  96  is used to convert the regulated DC bus voltage to the approximately 50 or 60 hertz utility grade power. When there is no battery (or other energy reservoir), the energy to run the engine during startup and cool down must come from utility grid  108 . Under this condition, the direction of power flow through the six-pack IGBT module  96  reverses. DC bus  112  receives its energy from utility grid  108 , using six-pack IGBT module  96  as a boost converter (the power diodes act as a rectifier). The DC is converted to a variable frequency AC voltage to motor the turbine. To accelerate the engine as rapidly as possible at first, current flows at the maximum rate through seven-pack IGBT module  94  and also six-pack IGBT module  96 . 
     Dual IGBT module  114 , driven by control logic  116 , is used to provide an optional neutral to supply 3 phase, 4 wire loads. 
     Startup 
     Energy is needed to start the turbine. Referring to FIGS. 3 and 4, this energy may come from utility grid  60  or from energy reservoir  64 , such as a battery, flywheel or ultra-cap. When utility grid  60  supplies the energy, utility grid  60  is connected to power controller  52  through two circuits. First is an output contactor that handles the full power (30 kWatts). Second is a “soft-start” or “pre-charge” circuit that supplies limited power (it is current limited to prevent very large surge currents) from utility grid  66  to DC bus  62  through a simple rectifier. The amount of power supplied through the soft-start circuit is enough to start the housekeeping power supply, power the control board, and run the power supplies for the IGBTs, and close the output contactor. When the contactor closes, the IGBTs are configured to create DC from the AC waveform. Enough power is created to run the fuel metering circuit  42 , start the engine, and close the various solenoids (including the dump valve on the engine). 
     When energy reservoir  64  supplies the energy, energy reservoir  64  has its own power conversion circuit  62  that limits the surge circuit into DC bus capacitors. Energy reservoir  64  allows enough power to flow to DC bus  62  to run fuel-metering circuit  42 , start the engine, and close the various solenoids (including the dump valve on the engine). After the engine becomes self-sustaining, the energy reservoir starts to replace the energy used to start the engine, by drawing power from DC bus  62 . In addition to the sequences described above, power controller  52  senses the presence of other controllers during the initial power up phase. If another controller is detected, the controller must be part of a multi-pack, and proceeds to automatically configure itself for operation as part of a multi-pack. 
     System Level Operation 
     Referring to FIG. 6, a functional block diagram  130  of an interface between utility grid  132  and turbine generator  148  using power controller  136  of the present invention is shown. In this example, power controller  136  includes two bi-directional converters  138  and  140 . Permanent magnet generator converter  140  starts turbine  148  (using the motor as a generator) from utility or battery power. Load converter  138  then produces AC power using an output from generator converter  140  to draw power from high-speed turbine generator  148 . Power controller  136  also regulates fuel to turbine  148  and provides communications between units (in paralleled systems) and to external entities. 
     During a utility startup sequence, utility  132  supplies starting power to turbine  148  by “actively” rectifying the line via load converter  138 , and then converting the DC to variable voltage, variable frequency 3-phase power in motor converter  136 . As is illustrated in FIG. 7, for stand-alone applications  150 , the start sequence is the same as the utility start sequence shown in FIG. 6 with the exception that the start power comes from battery  170  under the control of an external battery controller. Load  152  is then fed from the output terminals of load converter  158 . 
     Referring to FIG. 8, a schematic illustration  180  of an interface between utility grid  132  and turbine generator  148  using the power controller is illustrated. Control logic  184  also provides power to fuel cutoff solenoids  198 , fuel control valve  200  and igniter  202 . An external battery controller (not shown), if used, connects directly to DC bus  190 . In accordance with an alternative embodiment of the invention, a fuel system (not shown) involving a compressor (not shown) operated from a separate variable speed drive can also derive its power directly from DC bus  190 . 
     In operation, control and start power comes from either the external battery controller (for battery start applications) or from the utility, which is connected to a rectifier using inrush limiting techniques to slowly charge internal bus capacitor  190 . For utility grid connect operation, control logic  184  sequentially drives solid state IGBT switches  214  associated with load converter  192  to boost the utility voltage to provide start power to generator converter  186 . Switches  214  are preferably operated at a high (15 kHz) frequency, and modulated in a pulse width modulation manner to provide four quadrant converter operation. In accordance with the present invention, load converter  192  either sources power from DC bus  190  to utility grid  222  or from utility grid  222  to DC bus  190 . A current regulator (not shown) may achieve this control. Optionally, two of the switches  214  serve to create an artificial neutral for stand-alone applications (for stand-alone applications, start power from an external DC supply (not shown) associated with external DC converter  220  is applied directly to DC bus  190 ). 
     Solid state (IGBT) switches  214  associated with generator converter  186  are also driven from control logic  184 , providing a variable voltage, variable frequency 3-phase drive to generator  208  to start turbine  206 . Control logic  184  receives feedback via current sensors I sens  as turbine  206  is ramped up in speed to complete the start sequence. When turbine  206  achieves a self sustaining speed of, for example, approx. 40,000 RPM, generator converter  186  changes its mode of operation to boost the generator output voltage and provide a regulated DC bus voltage. 
     PMG filter  188  associated with generator converter  186  includes three inductors to remove the high frequency switching component from permanent magnet generator  208  to increase operating efficiency. Output AC filter  194  associated with load converter  192  includes three or optionally four inductors (not shown) and AC filter capacitors (not shown) to remove the high frequency switching component. Output contactor  210  disengages load converter  192  in the event of a unit fault. 
     During a start sequence, control logic  184  opens fuel cutoff solenoid  198  and maintains it open until the system is commanded off. Fuel control  200  may be a variable flow valve providing a dynamic regulating range, allowing minimum fuel during start and maximum fuel at full load. A variety of fuel controllers, including but not limited to, liquid and gas fuel controllers, may be utilized. One skilled in the art will recognize that the fuel control can be by various configurations, including but not limited to a single or dual stage gas compressor accepting fuel pressures as low as approximately ¼ psig. Igniter  202 , a spark type device similar to a spark plug for an internal combustion engine, is operated only during the start sequence. 
     For stand-alone operation, turbine  206  is started using external DC converter  220  which boosts voltage from a battery (not shown), and connects directly to the DC bus  190 . Load converter  192  is then configured as a constant voltage, constant frequency (for example, approximately 50 or 60 Hz) source. One skilled in the art will recognize that the output is not limited to a constant voltage, constant frequency source, but rather may be a variable voltage, variable frequency source. For rapid increases in output demand, external DC converter  220  supplies energy temporarily to DC bus  190  and to the output. The energy is restored after a new operating point is achieved. 
     For utility grid connect operation, the utility grid power is used for starting as described above. When turbine  206  has reached a desired operating speed, converter  192  is operated at utility grid frequency, synchronized with utility grid  222 , and essentially operates as a current source converter, requiring utility grid voltage for excitation. If utility grid  222  collapses, the loss of utility grid  222  is sensed, the unit output goes to zero (0) and disconnects. The unit can receive external control signals to control the desired output power, such as to offset the power drawn by a facility, but ensure that the load is not backfed from the system. 
     Power Controller Software 
     Referring to FIG. 9, power controller  230  includes main CPU  232 , generator SP  234  and converter SP  236 . Main CPU software program sequences events which occur inside power controller  230  and arbitrates communications to externally connected devices. Main CPU  232  is preferably a MC68332 microprocessor, available from Motorola Semiconductor, Inc. of Phoenix, Ariz. Other suitable commercially available microprocessors may be used as well. The software performs the algorithms that control engine operation, determine power output and detect system faults. 
     Commanded operating modes are used to determine how power is switched through the major converts in the controller. The software is responsible for turbine engine control and issuing commands to other SP processors enabling them to perform the generator converter and output converter power switching. The controls also interface with externally connected energy storage devices (not shown) that provide black start and transient capabilities. 
     Generator SP  234  and converter SP  236  are connected to power controller  230  via serial peripheral interface (SPI) bus  238  to perform generator and converter control functions. Generator SP  234  is responsible for any switching which occurs between DC bus  258  and the output to generator. Converter SP  236  is responsible for any switching which occurs between DC bus  258  and output to load. As illustrated in FIG. 5, generator SP  234  and converter SP  236  operate IGBT modules. 
     Local devices, such as a smart display  242 , smart battery  244  and smart fuel control  246 , are connected to main CPU  232  in power controller  230  via intracontroller bus  240 , which may be a RS 485  communications link. Smart display  242 , smart battery  244  and smart fuel control  246  performs dedicated controller functions, including but not limited to display, energy storage management, and fuel control functions. 
     Main CPU  232  in power controller  230  is coupled to user port  248  for connection to a computer, workstation, modem or other data terminal equipment which allows for data acquisition and/or remote control. User port  248  may be implemented using a RS232 interface or other compatible interface. 
     Main CPU  232  in power controller  230  is also coupled to maintenance port  250  for connection to a computer, workstation, modem or other data terminal equipment which allows for remote development, troubleshooting and field upgrades. Maintenance port  250  may be implemented using a RS232 interface or other compatible interface. 
     The main CPU processor software communicates data through a TCP/IP stack over intercontroller bus  252 , typically an Ethernet 10 Base 2 interface, to gather data and send commands between power controllers (as shown and discussed in detail with respect to FIG.  15 ). In accordance with the present invention, the main CPU processor software provides seamless operation of multiple paralleled units as a single larger generator system. One unit, the master, arbitrates the bus and sends commands to all units. 
     Intercontroller bus  254 , which may be a RS485 communications link, provides high-speed synchronization of power output signals directly between converter SPs, such as converter SP  236 . Although the main CPU software is not responsible for communicating on the intercontroller bus  254 , it informs converter SPs, including converter SP  236 , when main CPU  232  is selected as the master. 
     External option port bus  256 , which may be a RS485 communications link, allows external devices, including but not limited to power meter equipment and auto disconnect switches, to be connected to generator SP  234 . 
     In operation, main CPU  232  begins execution with a power on self-test when power is applied to the control board. External devices are detected providing information to determine operating modes the system is configured to handle. Power controller  230  waits for a start command by making queries to external devices. Once received, power controller  230  sequences up to begin producing power. As a minimum, main CPU  232  sends commands to external smart devices  242 ,  244  and  246  to assist with bringing power controller  230  online. If selected as the master, the software may also send commands to initiate the sequencing of other power controllers (FIG. 15) connected in parallel. A stop command will shutdown the system bringing it offline. 
     System I/O 
     The main CPU  232  software interfaces with several electronic circuits (not shown) on the control board to operate devices that are universal to all power controllers  230 . Interface to system I/O begins with initialization of registers within power controller  230  to configure internal modes and select external pin control. Once initialized, the software has access to various circuits including discrete inputs/outputs, analog inputs/outputs, and communication ports. These external devices may also have registers within them that require initialization before the device is operational. 
     Each of the following sub-sections provides a brief overview that defines the peripheral device the software must interface with. The contents of these sub-sections do not define the precise hardware register initialization required. 
     Communications 
     Referring to FIG. 9, main CPU  232  is responsible for all communication systems in power controller  230 . Data transmission between a plurality of power controllers  230  is accomplished through intercontroller bus  252 . Main CPU  232  initializes the communications hardware attached to power controller  230  for intercontroller bus  252 . 
     Main CPU  232  provides control for external devices, including smart devices  242 ,  244  and  246 , which share information to operate. Data transmission to external devices, including smart display  242 , smart battery  244  and smart fuel control  246  devices, is accomplished through intracontroller communications bus  240 . Main CPU  232  initializes any communications hardware attached to power controller  230  for intracontroller communications bus  240  and implements features defined for the bus master on intracontroller communications bus  240 . 
     Communications between devices such as switch gear and power meters used for master control functions exchange data across external equipment bus  246 . Main CPU  232  initializes any communications hardware attached to power controller  230  for external equipment port  246  and implements features defined for the bus master on external equipment bus  246 . 
     Communications with a user computer is accomplished through user interface port  248 . Main CPU  232  initializes any communications hardware attached to power controller  230  for user interface port  248 . In a typical configuration, at power up, the initial baud rate will be selected to 19200 baud, 8 data bits, 1 stop, and no parity. The user has the ability to adjust and save the communications rate setting via user interface port  248  or optional smart external display  242 . The saved communications rate is used the next time power controller  230  is powered on. Main CPU  232  communicates with a modem (not shown), such as a Hayes compatible modem, through user interface port  248 . Once communications are established, main CPU  232  operates as if were connected to a local computer and operates as a slave on user interface port  248  (it only responds to commands issued). 
     Communications to service engineers, maintenance centers, and so forth are accomplished through maintenance interface port  250 . Main CPU  232  initializes the communications to any hardware attached to power controller  230  for maintenance interface port  250 . In a typical implementation, at power up, the initial baud rate will be selected to 19200 baud, 8 data bits, 1 stop, and no parity. The user has the ability to adjust and save the communications rate setting via user port  248  or optional smart external display  242 . The saved communications rate is used the next time power controller  230  is powered on. Main CPU  232  communicates with a modem, such as a Hayes compatible modem, through maintenance interface port  250 . Once communications are established, main CPU  232  operates as if it were connected to a local computer and operates as a slave on maintenance interface port  250  (it only responds to commands issued). 
     Controls 
     Referring to FIG. 9, main CPU  232  orchestrates operation for motor, converter, and engine controls for power controller  230 . The main CPU  232  does not directly perform motor and converter controls. Rather, motor and converter SP processors  234  and  236  perform the specific control algorithms based on data communicated from main CPU  232 . Engine controls are performed directly by main CPU  232  (see FIG.  14 ). 
     Main CPU  232  issues commands via SPI communications bus  238  to generator SP  234  to execute the required motor control functions. Motor SP  234  will operate the motor (not shown) in either a DC bus mode or a RPM mode as selected by main CPU  232 . In the DC bus voltage mode, motor SP  234  uses power from the motor to maintain the DC bus at the setpoint. In the RPM mode, motor SP  234  uses power from the motor to maintain the engine speed at the setpoint. Main CPU  232  provides Setpoint values. 
     Main CPU  232  issues commands via SPI communications bus  238  to converter SP  236  to execute required converter control functions. Converter SP  236  will operate the converter (not shown) in a DC bus mode, output current mode, or output voltage mode as selected by main CPU  232 . In the DC bus voltage mode, converter SP  236  regulates the utility power provided by power controller  230  to maintain the internal bus voltage at the setpoint. In the output current mode, converter SP  236  uses power from the DC bus to provide commanded current out of the converter. In the output voltage mode, converter SP  236  uses power from the DC bus to provide commanded voltage out of the converter. Main CPU  232  provides Setpoint values. 
     Referring to FIGS. 10-12, control loops  260 ,  282  and  300  are used to regulate engine controls. These loops include exhaust gas temperature (EGT) control (FIG.  10 ), speed control (FIG. 11) and power control (FIG.  12 ). All three of the control loops  260 ,  282  and  300  are used individually and collectively by main CPU  232  to provide the dynamic control and performance required of power controller  230 . These loops are joined together for different modes of operation. 
     The open-loop light off control algorithm is a programmed command of the fuel device used to inject fuel until combustion begins. In a typical configuration, main CPU  232  takes a snap shot of the engine EGT and begins commanding the fuel device from about 0% to 25% of full command over about 5 seconds. Engine light is declared when the engine EGT rises about 28° C. (50° F.) from the initial snap shot. 
     Referring to FIG. 10, EGT control mode loop  260  provides various fuel output commands to regulate the temperature of the turbine. Engine speed signal  262  is used to determine the maximum EGT setpoint temperature  266  in accordance with predetermined setpoint temperature values. EGT setpoint temperature  266  is compared by comparator  268  against feedback EGT signal  270  to determine error signal  272 , which is then applied to a proportional-integral (PI) algorithm  274  for determining the fuel command required to regulate EGT at the setpoint. Maximum/minimum fuel limits  278  are used to limit EGT control algorithm fuel command output  276  to protect from integrator windup. Resultant output signal  280  is regulated EGT signal fuel flow command. In operation, EGT control mode loop  260  operates at about a 100 ms rate. 
     Referring to FIG. 11, speed control mode loop  282  provides various fuel output commands to regulate the rotating speed of the turbine. Feedback speed signal  288  is read and compared by comparator  286  against setpoint speed signal  284  to determine error signal  290 , which is then applied to PI algorithm  292  to determine the fuel command required to regulate engine speed at the setpoint. EGT control (FIG. 10) and maximum/minimum fuel limits are used in conjunction with the speed control algorithm  282  to protect output. signal  294  from surge and flame out conditions. Resultant output signal  298  is regulated turbine speed fuel flow command. In a typical implementation, speed control mode loop  282  operates at about a 20 ms rate. 
     Referring to FIG. 12, power control mode loop  300  regulates the power producing potential of the turbine. Feedback power signal  306  is read and compared by comparator  304  against setpoint power signal  302  to determine error signal  308 , which is then applied to PI algorithm  310  to determine the speed command required to regulate output power at the setpoint. Maximum/minimum speed limits are used to limit the power control algorithm speed command output to protect output signal  312  from running into over speed and under speed conditions. Resultant output signal  316  is regulated power signal turbine speed command. In a typical implementation, the maximum operating speed of the turbine is generally 96,000 RPM and the minimum operating speed of the turbine is generally 45,000 RPM. The loop operates generally at about a 500 ms rate. 
     Start Only Battery 
     Referring to FIG. 14, energy storage device  470  may be a start only battery. In the DC bus voltage control mode, start only battery  470  provides energy to regulate voltage to the setpoint command. Main CPU  472  commands the bus voltage to control at different values depending on the configuration of power controller  478 . In the state of charge (SOC) control mode, the start only battery system provides a recharging power demand when requested. Available recharging power is generally equivalent to maximum engine power less power being supplied to the output load and system parasitic loads. Main CPU  472  transmits a recharging power level that is the minimum of the original power demand and available recharging power. 
     Transient Battery 
     The transient battery provides the DC bus voltage control as described below as well as the state of charge (SOC) control mode described for the start only battery. The transient battery contains a larger energy storage device than the start only battery. 
     DC Bus Voltage Control 
     DC bus  462  supplies power for logic power, external components and system power output. TABLE 1 defines the setpoint the bus voltage is to be controlled at based on the output power configuration of power controller  478 : 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 B3 POWER OUTPUT 
                 SETPOINT 
               
               
                   
                   
               
             
             
               
                   
                 480/400 VAC Output 
                 800 Vdc 
               
               
                   
                 240/208 VAC Output 
                 400 Vdc 
               
               
                   
                   
               
             
          
         
       
     
     In the various operating modes, power controller  478  will have different control algorithms responsible for managing the DC bus voltage level. Any of the battery options  470  as well as SPs  456  and  458  have modes that control power flow to regulate the voltage level of DC bus  462 . Under any operating circumstances, only one device is commanded to a mode that regulates DC bus  462 . Multiple algorithms would require sharing logic that would inevitably make system response slower and software more difficult to comprehend. 
     System States 
     Referring to FIG. 13, state diagram  320  showing various operating states of power controller  478  is illustrated. Sequencing the system through the entire operating procedure requires power controller to transition through the operating states defined in TABLE 2. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 STATE 
                 SYSTEM 
                   
               
               
                 # 
                 STATE 
                 DESCRIPTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 Power Up 
                 Performs activities of initializing and testing 
               
               
                   
                   
                 the system. 
               
               
                 1 
                 Stand By 
                 Connects power to bus and continues system 
               
               
                   
                   
                 monitoring while waiting for a start command. 
               
               
                 2 
                 Prepare to 
                 Initializes any external devices preparing for the 
               
               
                   
                 Start 
                 start procedure. 
               
               
                 3 
                 Bearing 
                 Configures the system and commands the engine 
               
               
                   
                 Lift Off 
                 to be rotated to a predetermined RPM, such 
               
               
                   
                   
                 as 25,000 RPM. 
               
               
                 4 
                 Open Loop 
                 Turns on ignition system and commands fuel 
               
               
                   
                 Light Off 
                 open loop to light the engine. 
               
               
                 5 
                 Closed Loop 
                 Continues motoring and closed fuel control until 
               
               
                   
                 Acceleration 
                 the system reaches the no load state. 
               
               
                 6 
                 Run 
                 Engine operates in a no load self-sustaining state 
               
               
                   
                   
                 producing power only to operate the controller. 
               
               
                 7 
                 Load 
                 Converter output contactor is closed and system is 
               
               
                   
                   
                 producing power. 
               
               
                 8 
                 Re-Charge 
                 System operates off of fuel only and produces 
               
               
                   
                   
                 power for recharging energy storage device if 
               
               
                   
                   
                 installed. 
               
               
                 9 
                 Cooldown 
                 System is motoring engine to reduce EGT before 
               
               
                   
                   
                 shutting down. 
               
               
                 10 
                 Re-Start 
                 Reduces engine speed to begin open loop light 
               
               
                   
                   
                 when a start command is received in the 
               
               
                   
                   
                 cooldown state. 
               
               
                 11 
                 Re-Light 
                 Performs a turbine re-light in transition from the 
               
               
                   
                   
                 cooldown to warmdown state. Allows continued 
               
               
                   
                   
                 engine cooling when motoring is no longer 
               
               
                   
                   
                 possible. 
               
               
                 12 
                 Warmdown 
                 Sustains turbine operation with fuel at a 
               
               
                   
                   
                 predetermined RPM, such as 50,000 RPM, to 
               
               
                   
                   
                 cool when engine motoring is not possible. 
               
               
                 13 
                 Shutdown 
                 Reconfigures the system after a cooldown to 
               
               
                   
                   
                 enter the stand by state. 
               
               
                 14 
                 Fault 
                 Turns off all outputs when presence of fault 
               
               
                   
                   
                 which disables power conversion exists. Logic 
               
               
                   
                   
                 power is still available for interrogating 
               
               
                   
                   
                 system faults. 
               
               
                 15 
                 Disable 
                 Fault has occurred where processing may no 
               
               
                   
                   
                 longer be possible. All system operation is 
               
               
                   
                   
                 disabled. 
               
               
                   
               
             
          
         
       
     
     Main CPU  472  begins execution in the “power up” state  322  after power is applied. Transition to the “stand by” state  324  is performed upon successfully completing the tasks of the “power up” state  322 . Initiating a start cycle transitions the system to the “prepare to start” state  326  where all system components are initialized for an engine start. The engine then sequences through start states and onto the “run/load” state  328 . To shutdown the system, a stop command which sends the system into either “warm down” or “cool down” state  332  is initiated. Systems that have a battery may enter the “re-charge” state  334  prior to entering the “warm down” or “cool down” state  332 . When the system has finally completed the “warm down” or “cool down” process  332 , a transition through the “shut down” state  330  will be made before the system re-enters the “standby” state  324  awaiting the next start cycle. During any state, detection of a fault with a system severity level indicat ing the system should not be operated will transition the system state to “fault” state  335 . Detection of faults that indicate a processor failure has occurred will transition the system to the “disable” state  336 . 
     One skilled in the art will recognize that in order to accommodate each mode of operation, the state diagram is multidimensional to provide a unique state for each operating mode. For example, in the “prepare to start” state  326 , control requirements will vary depending on the selected operating mode. Therefore, the presence of a stand-alone “prepare to start” state  326 , stand-alone transient “prepare to start” state  326 , utility grid connect “prepare to start” state  326  and utility grid connect transient “prepare to start” state  326  will be required. Each combination is known as a system configuration (SYSCON) sequence. Main CPU  472  identifies each of the different system configuration sequences in a 16-bit word known as a SYSCON word, which is a bit-wise construction of an operating mode and system state number. In a typical configuration, the system state number is packed in bits  0  through  11 . The operating mode number is packed in bits  12  through  15 . This packing method provides the system with the capability of sequence through 4096 different system states in 16 different operating modes. 
     Separate “power up”  322 , “re-light”  338 , “warm down”  348  “fault”  335  and “disable”  336  states are not required for each mode of operation. The contents of these states are mode independent. 
     “Power Up” State 
     Operation of the system begins in the “power up” state  322  once application of power activates main CPU  472 . Once power is applied to power controller  478 , all the hardware components will be automatically reset by hardware circuitry. Main CPU  472  is responsible for ensuring the hardware is functioning correctly and configure the components for operation. Main CPU  472  also initializes its own internal data structures and begins execution by starting the Real-Time Operating System (RTOS). Successful completion of these tasks directs transition of the software to the “stand by” state  324 . Main CPU  472  performs these procedures in the following order: 
     1. Initialize main CPU  472   
     2. Perform RAM Test 
     3. Perform FLASH Checksum 
     4. Start RTOS 
     5. Run Remaining POST 
     6. Initialize SPI Communications 
     7. Verify Generator SP Checksum 
     8. Verify Converter SP Checksum 
     9. Initialize IntraController Communications 
     10. Resolve External Device Addresses 
     11. Look at Input Line Voltage 
     12. Determine Mode 
     13. Initialize Maintenance Port 
     14. Initialize User Port 
     15. Initialize External Option Port 
     16. Initialize InterController 
     17. Chose Master/Co-Master 
     18. Resolve Addressing 
     19. Transition to Stand By State (depends on operating mode) 
     “Stand By” State 
     Main CPU  472  continues to perform normal system monitoring in the “stand by” state  324  while it waits for a start command signal. Main CPU  472  commands either energy storage device  470  or utility  468  to provide continuous power supply. In operation, main CPU  472  will often be left powered on waiting to be started or for troubleshooting purposes. While main CPU  472  is powered up, the software continues to monitor the system and perform diagnostics in case any failures should occur. All communications will continue to operate providing interface to external sources. A start command will transition the system to the “prepare to start” state  326 . 
     “Prepare to Start” State 
     Main CPU  472  prepares the control system components for the engine start process. Many external devices may require additional time for hardware initialization before the actual start procedure can commence. The “prepare to start” state  326  provides those devices the necessary time to perform initialization and send acknowledgment to the main CPU  472  that the start process can begin. Once also systems are ready to go, the software shall transition to the “bearing lift off” state  328 . 
     “Bearing Lift Off” State 
     Main CPU  472  commands generator SP  456  to motor the engine  454  from typically about 0 to 25,000 RPM to accomplish the bearing lift off procedure. A check is performed to ensure the shaft is rotating before transition to the next state occurs. 
     “Open Loop Light Of” State 
     Once the motor  452  reaches its liftoff speed, the software commences and ensures combustion is occurring in the turbine. In a typical configuration, main CPU  472  commands generator SP  456  to motor the engine  454  to a dwell speed of about 25,000 RPM. Execution of the open loop light off state  340  starts combustion. Main CPU  472  then verifies that the engine  454  has not met the “fail to light” criteria before transition to the “closed loop accel” state  342 . 
     “Closed Loop Accel” State 
     Main CPU  472  sequences engine  454  through a combustion heating process to bring the engine  454  to a self-sustaining operating point. In atypical configuration, commands are provided to generator SP  456  commanding an increase in engine speed to about 45,000 RPM at a rate of about 4000 RPM/sec. Fuel controls are executed to provide combustion and engine heating. When engine  454  reaches “no load” (requires no electrical power to motor), the software transitions to “run” state  344 . 
     “Run” State 
     Main CPU  472  continues operation of control algorithms to operate the engine at no load. Power may be produced from engine  454  for operating control electronics and recharging any energy storage device  470  for starting. No power is output from load converter  458 . A power enable signal transitions the software into “load” state  346 . A stop command transitions the system to begin shutdown procedures (may vary depending on operating mode). 
     “Load” State 
     Main CPU  472  continues operation of control algorithms to operate the engine  454  at the desired load. Load commands are issued through the communications ports, display or system loads. A stop command transitions main CPU  472  to begin shutdown procedures (may vary depending on operating mode). A power disable signal can transition main CPU  472  back to “run” state  344 . 
     “Re-charge” State 
     Systems that have an energy storage option may be required to charge energy storage device  470  to maximum capacity before entering the “warmdown”  348  or “cooldown”  332  states. During the “re-charge” state  334  of operation, main CPU  472  continues operation of the turbine producing power for battery charging and controller supply. No out power is provided. When the energy storage device  470  has charged, the system transitions to either the “cooldown”  332  or “warmdown”  348  state depending on system fault conditions. 
     “Cool Down” State 
     “Cool down” state  332  provides the ability to cool the turbine after operation and a means of purging fuel from the combustor. After normal operation, software sequences the system into “cool down” state  332 . In a typical configuration, engine  454  is motored to a cool down speed of about 45,000 RPM. Airflow continues to move through engine  454  preventing hot air from migrating to mechanical components in the cold section. This motoring process continues until the engine EGT falls below a cool down temperature of about 193° C. (380° F.). Cool down may be entered at much lower than the final cool down temperature when engine  454  fails to light. The engine&#39;s combustor requires purging of excess fuel which may remain. The software always operates the cool down cycle for a minimum purge time of 60 seconds. This purge time ensures remaining fuel is evacuated from the combustor. Completion of this process transitions the system into the “shutdown” state  330 . For user convenience, the system does not require a completion of the enter “cooldown” state  332  before being able to attempt a restart. Issuing a start command transitions the system into the “restart” state  350 . 
     “Restart” State 
     Engine  454  is configured from the “cool down” state  332  before engine  454  can be restart. In a typical configuration, the software lowers the engine speed to about 25,000 RPM at a rate of 4,000 RPM/sec. Once the engine speed has reached this level, the software transitions the system into the “open loop light off” state to perform the actual engine start. 
     “Shutdown” State 
     During the “shutdown” state  330 , the engine rotor is brought to rest and system outputs are configured for idle operation. In a typical configuration, the software commands the rotor to rest by lowering the engine speed at a rate of 2,000 RPM/sec or no load condition, whichever is faster. Once the speed reaches about 14,000 RPM, the generator SP is commanded to reduce the shaft speed to about 0 RPM in less than 1 second. 
     “Re-light” State 
     When a system fault occurs where no power is provided from the utility or energy storage device  470 , the software re-ignites combustion to perform a warm down. The generator SP is configured to regulate voltage (power) for the internal DC bus. Fuel is added as defined in the open loop light off fuel control algorithm to ensure combustion occurs. Detection of engine light will transition the system to “warm down” state  348 . 
     “Warm Down” State 
     Fuel is provided when no electric power is available to operate engine  454  at a no load condition to lower the operating temperature in “warn down” state  348 . In a typical configuration, engine speed is operated at about 50,000 RPM by supplying fuel through the speed control algorithm. Engine temperatures less than about 343° C. (650° F.) causes the system to transition to “shutdown” state  330 . 
     “Fault” State 
     The present invention disables all outputs placing the system in a safe configuration when faults that prohibit safe operation of the turbine system are present. Operation of system monitoring and communications will continue if the energy is available. 
     “Disable” State 
     The system disables all outputs placing the system in a safe configuration when faults that prohibit safe operation of the turbine system are present. System monitoring and communications will most likely not continue. 
     Modes of Operation 
     The turbine works in two major modes—utility grid-connect and stand-alone. In the utility grid-connect mode, the electric power distribution system i.e., the utility grid, supplies a reference voltage and phase, and the turbine supplies power in synchronism with the utility grid. In the stand-alone mode, the turbine supplies its own reference voltage and phase, and supplies power directly to the load. The power controller switches automatically between the modes. 
     Within the two major modes of operation are sub-modes. These modes include stand-alone black start, stand-alone transient, utility grid connect and utility grid connect transient. The criteria for selecting an operating mode is based on numerous factors, including but not limited to, the presence of voltage on the output terminals, the black start battery option, and the transient battery option. 
     Referring to FIG. 14, generator converter  456  and load converter  458  provide an interface for energy source  460  and utility  468 , respectively, to DC bus  462 . For illustrative purposes, energy source  460  is a turbine including engine  454  and generator  452 . Fuel device  474  provides fuel via fuel line  476  to engine  454 . Generator converter  456  and load converter  458  operate as customized bi-directional switching converters under the control of controller  472 . In particular, controller  472  reconfigures the generator converter  456  and load converter  458  into different configurations to provide for the various modes of operation. These modes include stand-alone black start, stand-alone transient, utility grid connect and utility grid connect transient as discussed in detail below. Controller  472  controls the way in which generator  452  and utility  468  sinks or sources power, and DC bus  462  is regulated at any time. In this way, energy source  460 , utility/load  468  and energy storage device  470  can be used to supply, store and/or use power in an efficient manner. Controller  472  provides command signals via line  479  to engine  454  to determine the speed of turbine  460 . The speed of turbine  460  is maintained through generator  452 . Controller  472  also provides command signals via control line  480  to fuel device  474  to maintain the EGT of the engine  454  at its maximum efficiency point. Generator SP  456  is responsible for maintaining the speed of the turbine  460 , by putting current into generator  452  or pulling current out of generator  452 . 
     Stand-alone Black Start 
     Referring to FIG. 14, in the stand-alone black start mode, energy storage device  470 , such as battery, is provided for starting purposes while energy source  460 , such as turbine including engine  454  and generator  452 , supplies all transient and steady state energy. Referring to TABLE 3, controls for a typical stand-alone black start mode are shown. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 SYSTEM 
                 ENGINE 
                 MOTOR 
                 CONVERTER 
                 ENERGY STORAGE 
               
               
                 STATE 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
               
               
                   
               
             
             
               
                 Power Up 
                 — 
                 — 
                 — 
                 — 
               
               
                 Stand By 
                 — 
                 — 
                 — 
                 DC Bus 
               
               
                 Prepare to Start 
                 — 
                 — 
                 — 
                 DC Bus 
               
               
                 Bearing Lift Off 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Open Loop Light Off 
                 Open Loop 
                 RPM 
                 — 
                 DC Bus 
               
               
                   
                 Light 
               
               
                 Closed Loop Accel 
                 EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Run 
                 Speed 
                 DC Bus 
                 — 
                 SOC 
               
               
                 Load 
                 Speed 
                 DC Bus 
                 Voltage 
                 SOC 
               
               
                 Recharge 
                 Speed 
                 DC Bus 
                 — 
                 SOC 
               
               
                 Cool Down 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Restart 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Shutdown 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Re-light 
                 Speed 
                 DC Bus 
                 — 
                 — 
               
               
                 Warm Down 
                 Speed 
                 DC Bus 
                 — 
                 — 
               
               
                 Fault 
                 — 
                 — 
                 — 
                 — 
               
               
                 Disable 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
             
          
         
       
     
     Stand-alone Transient 
     In the stand-alone transient mode, storage device  470  is provided for the purpose of starting and assisting the energy source  460 , in this example the turbine, to supply maximum rated output power during transient conditions. Storage device  470 , typically a battery, is always attached to DC bus  462  during operation, supplying energy in the form of current to maintain the voltage on DC bus  462 . Converter/SP  458  provides a constant voltage source when producing output power. As a result, load  468  is always supplied the proper AC voltage value that it requires. Referring to TABLE 4, controls for a typical stand-alone transient mode are shown. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 SYSTEM 
                 ENGINE 
                 MOTOR 
                 CONVERTER 
                 ENERGY STORAGE 
               
               
                 STATE 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
               
               
                   
               
             
             
               
                 Power Up 
                 — 
                 — 
                 — 
                 − 
               
               
                 Stand By 
                 — 
                 — 
                 — 
                 DC Bus 
               
               
                 Prepare to Start 
                 — 
                 — 
                 — 
                 DC Bus 
               
               
                 Bearing Lift Off 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Open Loop Light Off 
                 Open Loop 
                 RPM 
                 — 
                 DC Bus 
               
               
                   
                 Light 
               
               
                 Closed Loop Accel 
                 EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Run 
                 Power &amp; EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Load 
                 Power &amp; EGT 
                 RPM 
                 Voltage 
                 DC Bus 
               
               
                 Recharge 
                 Power &amp; EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Cool Down 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Restart 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Shutdown 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Re-light 
                 Speed 
                 DC Bus 
                 — 
                 — 
               
               
                 Warm Down 
                 Speed 
                 DC Bus 
                 — 
                 — 
               
               
                 Fault 
                 — 
                 — 
                 — 
                 — 
               
               
                 Disable 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
             
          
         
       
     
     Utility Grid Connect 
     Referring to FIG. 14, in the utility grid connect mode, the energy source  460 , in this example the turbine is connected to the utility grid  468  providing load leveling and management where transients are handled by the utility grid  468 . The system operates as a current. source, pumping current into utility  468 . Referring to TABLE 5, controls for a typical utility grid connect mode are shown. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 SYSTEM 
                 ENGINE 
                 MOTOR 
                 CONVERTER 
                 ENERGY STORAGE 
               
               
                 STATE 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
               
               
                   
               
             
             
               
                 Power Up 
                 — 
                 — 
                 — 
                 N/A 
               
               
                 Stand By 
                 — 
                 — 
                 — 
                 N/A 
               
               
                 Prepare to Start 
                 — 
                 — 
                 DC Bus 
                 N/A 
               
               
                 Bearing Lift Off 
                 — 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Open Loop Light Off 
                 Open Loop 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                   
                 Light 
               
               
                 Closed Loop Accel 
                 EGT 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Run 
                 Power &amp; EGT 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Load 
                 Power &amp; EGT 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Recharge 
                 N/A 
                 N/A 
                 N/A 
                 N/A 
               
               
                 Cool Down 
                 — 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Restart 
                 — 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Shutdown 
                 — 
                 RPM 
                 DC Bus 
                 N/A 
               
               
                 Re-light 
                 Speed 
                 DC Bus 
                 — 
                 N/A 
               
               
                 Warm Down 
                 Speed 
                 DC Bus 
                 — 
                 N/A 
               
               
                 Fault 
                 — 
                 — 
                 — 
                 N/A 
               
               
                 Disable 
                 — 
                 — 
                 — 
                 N/A 
               
               
                   
               
             
          
         
       
     
     Utility Grid Connect Transient 
     In the utility grid connect transient mode, the energy source  460 , in this example the turbine, is connected to the utility grid  468  providing load leveling and management. The turbine that is assisted by energy storage device  470 , typically a battery, handles transients. The system operates as a current source, pumping current into utility  468  with the assistance of energy storage device  470 . Referring to TABLE 6, controls for a typical utility grid connect transient mode are shown. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 SYSTEM 
                 ENGINE 
                 MOTOR 
                 CONVERTER 
                 ENERGY STORAGE 
               
               
                 STATE 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
                 CONTROLS 
               
               
                   
               
             
             
               
                 Power Up 
                 — 
                 — 
                 — 
                 — 
               
               
                 Stand By 
                 — 
                 — 
                 — 
                 DC Bus 
               
               
                 Prepare to Start 
                 — 
                 — 
                 — 
                 DC Bus 
               
               
                 Bearing Lift Off 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Open Loop Light Off 
                 Open Loop 
                 RPM 
                 — 
                 DC Bus 
               
               
                   
                 Light 
               
               
                 Closed Loop Accel 
                 EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Run 
                 Power &amp; EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Load 
                 Power &amp; EGT 
                 RPM 
                 Current 
                 DC Bus 
               
               
                 Recharge 
                 Power &amp; EGT 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Cool Down 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Restart 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Shutdown 
                 — 
                 RPM 
                 — 
                 DC Bus 
               
               
                 Re-light 
                 Speed 
                 DC Bus 
                 — 
                 — 
               
               
                 Warm Down 
                 Speed 
                 DC Bus 
                 — 
                 — 
               
               
                 Fault 
                 — 
                 — 
                 — 
                 — 
               
               
                 Disable 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
             
          
         
       
     
     Multi-pack Operation 
     In accordance with the present invention, the power controller can operate in a single or multi-pack configuration. In particular, power controller, in addition to being a controller for a single turbogenerator, is capable of sequencing multiple systems as well. Referring to FIG. 15, for illustrative purposes, multi-pack system  510  including three power controllers  518 ,  520  and  522  is shown. The ability to control multiple controllers  518 ,  520  and  522  is made possible through digital communications interface and control logic contained in each controllers main CPU (not shown). 
     Two communications busses  530  and  534  are used to create the intercontroller digital communications interface for multi-pack operation. One bus  534  is used for slower data exchange while the other bus  530  generates synchronization packets at a faster rate. In a typical implementation, for example, an IEEE-502.3 bus links each of the controllers  518 ,  520  and  522  together for slower communications including data acquisition, start, stop, power demand and mode selection functionality. An RS485 bus links each of the systems together providing synchronization of the output power waveforms. 
     One skilled in the art will recognize that the number of power controllers that can be connected together is not limited to three, but rather any number of controllers can be connected together in a multi-pack configuration. Each power controller  518 ,  520  and  522  includes its own energy storage device  524 ,  526  and  528 , respectively, such as a battery. In accordance with another embodiment of the invention, power controllers  518 ,  520  and  522  can all be connected to the same single energy storage device (not shown), typically a very large energy storage device which would be rated too big for an individual turbine. Distribution panel, typically comprised of circuit breakers, provides for distribution of energy. 
     Multi-pack control logic determines at power up that one controller is the master and the other controllers become slave devices. The master is in charge of handling all user-input commands, initiating all inter-system communications transactions, and dispatching units. While all controllers  518 ,  520  and  522  contain the functionality to be a master, to alleviate control and bus contention, one controller is designated as the master. 
     At power up, the individual controllers  518 ,  520  and  522  determine what external input devices they have connected. When a controller contains a minimum number of input devices it sends a transmission on intercontroller bus  530  claiming to be master. All controllers  518 ,  520  and  522  claiming to be a master begin resolving who should be master. Once a master is chosen, an address resolution protocol is executed to assign addresses to each slave system. After choosing the master and assigning slave addresses, multi-pack system  510  can begin operating. 
     A co-master is also selected during the master and address resolution cycle. The job of the co-master is to act like a slave during normal operations. The co-master should receive a constant transmission packet from the master indicating that the master is still operating correctly. When this packet is not received within a safe time period, 20 ms for example, the co-master may immediately become the master and take over master control responsibilities. 
     Logic in the master configures all slave turbogenerator systems. Slaves are selected to be either utility grid-connect (current source) or standalone (voltage source). A master controller, when selected, will communicate with its output converter logic (converter SP) that this system is a master. The converter SP is then responsible for transmitting packets over the intercontroller bus  530 , synchronizing the output waveforms with all slave systems. Transmitted packets will include at least the angle of the output waveform and error-checking information with transmission expected every quarter cycle to one cycle. 
     Master control logic will dispatch units based on one of three modes of operation: (1) peak shaving, (2) load following, or (3) base load. Peak shaving measures the total power consumption in a building or application using a power meter, and the multi-pack system  510  reduces the utility consumption of a fixed load, thereby reducing the utility rate schedule and increasing the overall economic return of the turbogenerator. Load following is a subset of peak shaving where a power meter measures the total power consumption in a building or application and the multi-pack system  10  reduces the utility consumption to zero load. In base load, the multi-pack system  10  provides a fixed load and the utility supplements the load in a building or application. Each of these control modes require different control strategies to optimize the total operating efficiency. 
     A minimum number of input devices are typically desired for a system  510  to claim it is a master during the master resolution process. Input devices that are looked for include a display panel, an active RS232 connection and a power meter connected to the option port. Multi-pack system  510  typically requires a display panel or RS232 connection for receiving user-input commands and power meter for load following or peak shaving. 
     In accordance with the present invention, the master control logic dispatches controllers based on operating time. This would involve turning off controllers that have been operating for long periods of time and turning on controllers with less operating time, thereby reducing wear on specific systems. 
     Utility Grid Analysis and Transient Ride Through 
     Referring to FIGS. 16-18, transient handling system  580  for power controller  620  is illustrated. Transient handling system  580  allows power controller  620  to ride through transients which are associated with switching of correction capacitors on utility grid  616  which causes voltage spikes followed by ringing. Transient handling system  580  also allows ride through of other faults, including but not limited to, short circuit faults on utility grid  616 , which cleared successfully, cause voltage sags. Transient handling system  580  is particularly effective towards handling transients associated with digital controllers, which generally have a slower current response rate due to A/D conversion sampling. During a transient, a large change in the current can occur in between A/D conversions. The high voltage impulse caused by transients typically causes an over current in digital power controllers. 
     As is illustrated in FIG. 17, a graph  590  showing transients typically present on utility grid  616  is shown. The duration of a voltage transient, measured in seconds, is shown on the x-axis and its magnitude, measured in volts, is shown on the y-axis. A capacitor switching transient, such as shown at  592 , which is relatively high in magnitude (up to about 200%) and short in duration (somewhere between 1 and 20 milliseconds) could be problematic to operation of a power controller. 
     Referring to FIGS. 16-18, changes on utility grid  616  are reflected as changes in the magnitude of the voltage. In particular, the type and seriousness of any fault or event on utility grid  616  can be determined by magnitude estimator  584 , which monitors the magnitude and duration of any change on utility grid  616 . 
     In accordance with the present invention, the effect of voltage transients can be minimized by monitoring the current such that when it exceeds a predetermined level, switching is stopped so that the current can decay, thereby preventing the current from exceeding its predetermined level. The present invention thus takes advantage of analog over current detection circuits that have a faster response than transient detection based on digital sampling of current and voltage. Longer duration transients indicate abnormal utility grid conditions. These must be detected so power controller  620  can shut down in a safe manner. In accordance with the present invention, algorithms used to operate power controller  620  provide protection against islanding of power controller  620  in the absence of utility-supplied grid voltage. Near short or near open islands are detected within milliseconds through loss of current control. Islands whose load is more closely matched to the power controller output will be detected through abnormal voltage magnitudes and frequencies as detected by magnitude estimator  584 . 
     In particular, referring to FIG. 18, power controller  620  includes brake resistor  612  connected across DC bus  622 . Brake resistor  612  acts as a resistive load, absorbing energy when converter SP  608  is turned off. In operation, when converter SP  608  is turned off, power is no longer exchanged with utility grid  616 , but power is still being received from the turbine, which is absorbed by brake resistor  612 . The present invention detects the DC voltage between generator and output converters  602  and  606 . When the voltage starts to rise, brake resistor  612  is turned on to allow it to absorb energy. 
     In a typical configuration, AC generator  618  produces three phases of AC at variable frequencies. AC/DC converter  602  under the control of generator SP  606  converts the AC to DC which is then applied to DC bus  622  (regulated for example at 800 vDC) which is supported by capacitor  610  (for example, at 800 microfarads with two milliseconds of energy storage). AC/DC converter  604 , under the control of converter SP  608 , converts the DC into three-phase AC, and applies it to utility grid  616 . In accordance with the present invention, current from DC bus  622  can by dissipated in brake resistor  612  via modulation of switch  614  operating under the control of generator SP  606 . Switch  614  may be an IGBT switch, although one skilled in the art will recognize that other conventional or newly developed switches may be utilized as well. 
     Generator SP  606  controls switch  614  in accordance to the magnitude of the voltage on DC bus  622 . The bus voltage of DC bus  622  is typically maintained by converter SP  608 , which shuttles power in and out of utility grid  616  to keep DC bus  622  regulated at, for example, 800 vDC. When converter SP  608  is turned off, it no longer is able to maintain the voltage of DC bus  622 , so power coming in from the generator causes bus voltage of DC bus  622  to rise quickly. The rise in voltage is detected by generator SP  606 , which turns on brake resistor  612  and modulates it on and off until the bus voltage is restored to its desired voltage, for example, 800 vDC. Converter SP  608  detects when the utility grid transient has dissipated, i.e., AC current has decayed to zero and restarts the converter side of power controller  620 . Brake resistor  612  is sized so that it can ride through the transient and the time taken to restart converter  604 . 
     Referring to FIGS. 16 and 18, in accordance with the present invention, both the voltage and zero crossings (to determine where the AC waveform of utility grid  616  crosses zero) are monitored to provide an accurate model of utility grid  616 . Utility grid analysis system includes angle estimator  582 , magnitude estimator  584  and phase locked loop  586 . The present invention continuously monitors utility grid voltage and based on these measurements, estimates the utility grid angle, thus facilitating recognition of under/over voltages and sudden transients. Current limits are set to disable DC/AC converter  604  when current exceeds a maximum and wait until current decays to an acceptable level. The result of measuring the current and cutting it off is to allow DC/AC converter  604  to ride through transients better. Thus when DC/AC converter  604  is no longer exchanging power with utility grid  616 , power is dissipated in brake resistor  612 . 
     In accordance with the present invention, converter. SP  608  is capable of monitoring the voltage and current at utility grid  616  simultaneously. In particular, power controller  620  includes a utility grid analysis algorithm. One skilled in the art will recognize that estimates of the utility grid angle and magnitude may be derived via conventional algorithms or means. The true utility grid angle  0   AC , which is the angle of the generating source, cycles through from 0 to 2 χ  and back to 0 for example at a rate of 60 hertz. The voltage magnitude estimates of the three phases are designated V 1 mag , V 2 mag  and V 3 mag  and the voltage measurement of the three phases are designated V 1 , V 2  and V 3 . 
     A waveform, constructed based upon the estimates of the magnitude and angle for each phase, indicates what a correct measurement would look like. For example, using the first of the three phase voltages, the cosine of the true utility grid angle  0   AC  is multiplied by the voltage magnitude estimate V 1 mag , with the product being a cosine-like waveform. Ideally, the product would be equal to the voltage measurement V 1 . 
     Feedback loop  588  uses the difference between the absolute, magnitude of the measurement of V 1  and of the constructed waveform to adjust the magnitude of the magnitude estimate V 1 mag . One skilled in the art will recognize that the other two phases of the three-phase signal can be adjusted similarly, with different angle templates corresponding to different phases of the signal. Thus, magnitude estimate V 1 mag  and angle estimate  0   EST  are used to update magnitude estimate V 1 mag . Voltage magnitude estimates V 1 mag , V 2 mag  and V 3 mag  are steady state values used in a feedback configuration to track the magnitude of voltage measurements V 1 , V 2  and V 3 . By dividing the measured voltages V 1  by the estimates of the magnitude V 1 mag , the cosine of the angle for the first phase can be determined (similarly, the cosine of the angles of the other signals will be similarly determined). 
     In accordance with the present invention, the most advantageous estimate for the cosine of the angle, generally the one that is changing the most rapidly, is chosen to determine the instantaneous measured angle. In most cases, the phase that has an estimate for the cosine of an angle closest to zero is selected since it yields the greatest accuracy. Utility grid analysis system  580  thus includes logic to select which one of the cosines to use. The angle chosen is applied to angle estimator  582 , from which an estimate of the instantaneous angle of utility grid  616  is calculated and applied to phase locked loop  586  to produce a filtered frequency. The angle is thus differentiated to form a frequency that is then passed through a low pass filter (not shown). Phase locked loop  586  integrates the frequency and also locks the phase of the estimated instantaneous angle  0   EST , which may have changed in phase due to differentiation and integration, to the phase of true utility grid angle  0   AC . 
     In a typical operation, when the phase changes suddenly on measured voltage V 1 , the algorithm of the present invention compares the product of the magnitude estimate V 1 mag  and the cosine of estimated utility grid angle  0   EST  against the real magnitude multiplied by the cosine of a different angle. A sudden jump in magnitude would be realized. 
     Thus, three reasonably constant DC voltage magnitude estimates are generated. A change in one of those voltages indicates whether the transient present on utility grid  616  is substantial or not. One skilled in the art will recognize that there are a number of ways to determine whether a transient is substantial or not, i.e. whether abnormal conditions exist on the utility grid system, which require power controller  620  to shut down. A transient can be deemed substantial based upon the size of the voltage magnitude and duration. Examples of the criteria for shutting down power controller  620  are shown in FIG.  17 . Detection of abnormal utility grid behavior can also be determined by examining the frequency estimate. 
     On detecting abnormal utility grid behavior, a utility grid fault shutdown is initiated. When system controller  620  initiates a utility grid fault shutdown, output contactor is opened within a predetermined period of time, for example, 100 msec, and the main fuel trip solenoid (not shown) is closed, removing fuel from the turbogenerator. A warm shutdown ensues during which control power is supplied from generator  618  as it slows down. In a typical configuration, the warm-down lasts about 1-2 minutes before the rotor (not shown) is stopped. The control software does not allow a restart until utility grid voltage and frequency are within permitted limits. 
     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. For example, the power controller, while described generally, may be implemented in an analog or digital configuration. In the preferred digital configuration, one skilled in the art will recognize that various terms utilized in the invention are generic to both analog and digital configurations of power controller. For example, converters referenced in the present application is a general term which includes inverters, signal processors referenced in the present application is a general term which includes digital signal processors, and so forth. Correspondingly, in a digital implementation of the present invention, inverters and digital signal processors would be utilized. Such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.