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. Specifically
it relates to turbogenerator systems for such 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
US 5,550,410 describes an electrical generating and distribution system
using turbine generators connected to a DC bus.
US 5,512,811 and US 4,967,096 both describe aircraft systems in which
generators of the turbine engines are connected to the main aircraft DC electrical
bus, and in which electrical power is supplied to the generators to start the turbine
In particular US 5,512,811 describes a system comprising a turbogenerator,
a DC bus, and a first bi-directional power converter connected between the turbogenerator
and the DC bus. The first bi-directional power converter serves as an AC to DC converter
to supply power from the turbogenerator to the DC bus, and as a DC to AC converter
to supply power to the turbogenerator from the DC bus. The first bi-directional
power converter is configured to selectively operate in a DC bus mode to maintain
the DC bus voltage at a setpoint; and to selectively operate in an RPM mode during
startup of the turbogenerator to put current into the turbogenerator to rotate the
turbogenerator to a required setpoint start speed.
SUMMARY OF THE INVENTION
According to the present invention there is provided a turbogenerator
system as described in claims 1 to 15. There is also provided a method for controlling
a turbogenerator system as described in claims 16 to 23.
The present invention relates generally to the use of 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 an embodiment of the present invention a turbine system includes
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
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
- 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
illustrated in 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
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 an 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 convener
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.
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 18 regulates VDC
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.
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 then converts 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 generator 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 generator 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.
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 60 to DC bus 66 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 66 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 66. In addition to the sequences described above, power controller 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 146
starts turbine 148 (using the generator as a motor) 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 generator
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
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
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 Isens 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
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 R psig. Igniter 202, a spark type device similar
to a spark plug for an internal combustion engine, is operated only during the start
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
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, Arizona. 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 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 RS485 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
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
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.
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
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
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, generator 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.
Main CPU 232 issues commands via SPI communications bus 238 to generator
SP 234 to execute the required motor control functions. Generator 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, generator SP 234 uses power from the motor
to maintain the DC bus at the setpoint. In the RPM mode, generator SP 234 uses power
from the motor to maintain the engine speed at the setpoint. Main CPU 232 provides
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
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 20ms
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.
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:
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.
B3 POWER OUTPUT
480/400 VAC Output
240/208 VAC Output
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.
Performs activities of initializing and testing the system.
Closer power to bus and continues system monitoring while waiting
for a start command.
Prepare to Start
Initializes any external devices preparing for the start procedure.
Bearing Lift Off
Configures the system and commands the engine to be rotated
to a predetermined RPM, such as 25,000 RPM.
Open Loop Light Off
Turns on ignition system and commands fuel open loop to light
Closed Loop Acceleration
Continues motoring and closed fuel control until the system
reaches the no load state.
Engine operates in a no load self-sustaining state producing
power only to operate the controller.
Converter output contactor is closed and system is producing
System operates off of fuel only and produces power for recharging
energy storage device if installed.
System is motoring engine to reduce EGT before shutting down.
Reduces engine speed to begin open loop light when a start command
is received in the cooldown state.
Performs a turbine re-light in transition from the cooldown
to warmdown state. Allows continued engine cooling when motoring is no longer possible.
Sustains turbine operation with fuel at a predetermined RPM,
such as 50,000 RPM, to cool when engine motoring is not possible.
Reconfigures the system after a cooldown to enter the stand
Turns off all outputs when presence of fault which disables
power conversion exists. Logic power is still available for interrogating system
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 344, 346. 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 reenters the "standby" state 324 awaiting the next start
cycle. During any state, detection of a fault with a system severity level indicating
the system should not be operated will transition the system state to "fault" state
334. 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" 332, "fault"
334 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:
"Stand By" State
- 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)
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 start 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
"Open Loop Light Off" 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 a typical 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.
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).
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.
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'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.
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.
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.
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 "warm 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.
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.
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
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.
ENERGY STORAGE CONTROLS
Prepare to Start
Bearing Lift Off
Open Loop Light Off
Closed Loop Accel
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.
Utility Grid Connect
ENERGY STORAGE CONTROLS
Prepare to Start
Bearing Lift Off
Open Loop Light Off
Closed Loop Accel
Power & EGT
Power & EGT
Power & EGT
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.
Utility Grid Connect Transient
ENERGY STORAGE CONTROLS
Prepare to Start
Bearing Lift Off
Open Loop Light Off
Closed Loop Accel
Power & EGT
Power & EGT
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
ENERGY STORAGE CONTROLS
Prepare to Start
Bearing Lift Off
Open Loop Light Off
Closed Loop Accel
Power & EGT
Power & EGT
Power & EGT
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
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
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 converter SPs
606 and 608. When the voltage starts to rise, brake resistor 612 is turned on to
allow it to absorb energy.
In a typical configuration, AC motor 618 produces three phases of
AC at variable frequencies. AC/DC converter 602 under the control of motor 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 motor 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.
Motor 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 motor causes bus voltage of DC bus 622 to rise quickly. The rise in voltage
is detected by motor 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.
Referring to FIGS. 18 and 20, 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 608 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 0AC,
which is the angle of the generating source, cycles through from 0 to 2n and back
to 0 at a rate of 60 hertz. The voltage magnitude estimates of the three phases
are designated V1 mag, V2 mag and V3mag
and the voltage measurement of the three phases are designated V1, V2
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 0AC is multiplied by the voltage magnitude estimate
V1 mag, with the product being a cosine-like waveform. Ideally, the product
would be voltage measurement V1.
Feedback loop 588 uses the difference between the absolute magnitude
of the measurement of V1 and of the constructed waveform to adjusts the
magnitude of the magnitude estimate V1 mag. One skilled in the art will
recognize that the other two phases of three-phase signal can be adjusted similarly,
with different angle templates corresponding to different phases of the signal.
Thus, magnitude estimate V1 mag and angle estimate 0EST are
used to update magnitude estimate V1 mag. Voltage magnitude estimates
V1 mag, V2 mag and V3 mag are steady state values
used in a feedback configuration to track the magnitude of voltage measurements
V1, V2 and V3. By dividing the measured voltages
V1 by the estimates of the magnitude V1 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 0EST
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 0EST,
which may have changed in phase due to differentiation and integration, to the phase
of true utility grid angle 0AC.
In a typical operation, when the phase changes suddenly on measured
voltage V1, the algorithm of the present invention compares the product
of the magnitude estimate V1mag and the cosine of true utility
grid angle 0AC 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
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 of the invention as set forth in the following claims.