|Publication number||USRE41821 E1|
|Application number||US 11/019,150|
|Publication date||12 Oct 2010|
|Filing date||21 Dec 2004|
|Priority date||15 Mar 2001|
|Also published as||DE10296505T5, US6757590, US20020169523, WO2002078103A2, WO2002078103A3|
|Publication number||019150, 11019150, US RE41821 E1, US RE41821E1, US-E1-RE41821, USRE41821 E1, USRE41821E1|
|Inventors||Ricky M. Ross, Francis A. Fragola, Jr., Herbert C. Healy, Douglas Gibbons Young|
|Original Assignee||Utc Power Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (32), Non-Patent Citations (17), Referenced by (4), Classifications (20), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Reference is made here to related, patent application U.S. Ser. No. 09/782,402, filed Feb. 13, 2001 for System for Providing Assured Power for a Critical Load by the same inventive entities as herein and owned by the same assignee as herein, now U.S. Pat. No. 6,465,910 issued Oct. 15, 2002, which application/patent is incorporated herein by reference to the extent necessary, if at all, to provide essential and/or nonessential material.
This invention relates generally to power systems and to the control of fuel cell power plants, and more particularly to the control of multiple fuel cell power plants at a site. More particularly still, the invention relates to the control of multiple fuel cells at a site to provide a distributed resource in a utility grid.
Individual fuel cells have been used both experimentally and commercially in various configurations to power various electrical loads. In the main, the applications have relied on a single fuel cell, or fuel cell power plant, to supply electrical power to one or more loads at the site. While such sites may be mobile, as in the powering of the electric drive motor of a vehicle, in the main they are large and stationary. These applications have typically been individual commercial installations or buildings, perhaps involving computers or similar electronic data processing equipment or medical equipment requiring a reliable source of power.
To operate such fuel cell power plants, there are normally associated various controls for the direct control of the fuel cell itself and its production of DC electrical power, as well as additional controls for convening the DC power to AC power, for connecting and disconnecting power with the loads, etc. In some instances, the fuel cell power plant is connected to the loads in parallel with the normal electric utility grid, and may act in lieu of, or in addition to, the grid to supply power to the loads. In other instances, there may be multiple fuel cell power plants at a site, collectively connected to the loads in parallel with the utility grid. However, even in such configuration, the control of the fuel cells has typically been on an individual basis, with little or no provision for an integrated control arrangement to optimize the use of multiple fuel cell power plants interconnected with the utility grid and the loads.
When one or more fuel cell power plants are connected to the utility grid as well as the loads, they are said to be in a grid connected (GIC) configuration or mode. Alternatively, when those fuel cell power plants are connected only to the loads, they are said to be in grid independent (G/I) mode. In the G/I mode, the fuel cell power plants typically follow the load and apportion the load among the power plants. The transition from one such mode to the other, and the control of multiple fuel cell power plants relative to the loads present additional control complexities that have impeded the efficient and economic utilization of multiple fuel cell power plants as distributed resources in electric utility grids.
Accordingly, it is an object of the invention to provide a power system having a control arrangement for the efficient and economic utilization of multiple fuel cell power plants, e.g., fuel cells, at a site as a distributed resource in a utility grid.
It is a further object of the invention to provide a control arrangement to optimize the interrelationship between multiple fuel cell power plants and multiple loads at a site in order to enhance utilization of the plants as a distributed resource in a utility grid.
It is a still further object to provide a control arrangement for a multiple fuel cell power plant generation system at a site that coordinates operation of the fuel cell power plants in an integrated, or unified, manner in both the G/C and the G/I modes of operation.
The present invention concerns the control of multiple fuel cell power plants in a power system at a site, particularly as a distributed resource for inclusion in a utility grid. The invention further concerns the unified, or integrated, control of multiple fuel cell power plants at a site, both in a grid connected (G/C) mode to facilitate their use as a distributed resource in a utility grid network and in a grid independent (G/I) mode to optimize their value and utility as an/the independent power supply to one, or typically multiple, customer loads at the site.
Accordingly the present invention relates to a fuel cell-powered generating system at a site for inclusion as a distributed generating resource in a distributed generation utility power grid, and comprises multiple fuel cell power plants at the site, at least one, and typically multiple, loads located substantially at the site, and a site management system operatively connected to the multiple fuel cell power plants, the one or more loads, and the utility grid for controlling the fuel cell power plants in an integrated, or unified manner, in, alternatively, a grid connected mode of operation having the fuel cell power plants connected to the load(s) and to the power grid, and a grid independent mode having the fuel cell power plants connected to the load(s) independent of connection to the power grid. This integrated control provided by the site management system allows the utility to view the multiple fuel cell power plants at the site as a single, or unified, distributed generating resource when connected to the grid. Accordingly, as used in this context, the terms “integrated” and “unified” are viewed as being substantially synonymous. Moreover, the integrated control facilitates the operation of the site in the G/I mode where the fuel cells are typically load-following and have operated independently of one another. In this latter regard, the integrated control in the G/I mode further facilitates a load management (sharing and shedding) capability for assuring power to critical loads.
The fuel cell power plants each include control and logic capabilities for folding back (reducing) rated power levels to lesser levels, if necessary, in response to various power plant conditions, and for providing signals representative of the instant power level capability of the respective plants. As used herein in association with power capacity and load demand, the term “instant” is intended to be synonymous with “present”, “current”, or “instantaneous”. The site management system sums the individual power capacities of the respective fuel cell power plants and obtains a measure of the total instant power capacity of the multiple power plants at the site. This measure of total power capacity and the respective individual power capacity measures are used to provide a site power measure to the utility grid and to appropriately load each of the power plants in G/C mode, and are used in the G/I mode to appropriately load each of the power plants to operate in a unified manner and further, for a load shedding function. In this latter regard and assuming multiple loads, the site management system is operative to recognize the instant load demand, the instant total power capacity, and a predetermined prioritization of the loads in the event load demand exceeds instant total power capacity, and to selectively shed or disconnect loads in accordance with the schedule, if necessary.
The site management system includes at least one, and typically several, signal processing logic controllers cooperatively interacting with one another, the multiple fuel cell power plants, and the utility grid to perform the integrated control functions of the invention.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings.
The grid 10, the fuel cell power plants 18, and the loads 14 are interconnected and controlled through a Site Management System (SMS), represented by broken line block 11. The loads 14, here designated L1, L2, . . . Lx, are those of the customer at the site, and typically include one or more “critical” loads, such as computers, electronic data processing devices, and/or medical devices, that require a substantially continuous supply of power. Others of those loads 14 may be less critical, being able to tolerate brief or longer-term power interruptions. In a typical contactor array 13, there may be 12 individual, separately-controllable, contactors i.e., 1, 2, . . . X, with respective loads L1, L2 . . . Lx connected to a terminal thereof. Selective actuation of the individual contactors may be used to selectively connect and disconnect the respective loads from the power sources, as will be described hereinafter.
The utility grid bus 10, following step-down by transformer 20, normally provides power at 480 Vac and 60 Hz, as also do the fuel cell power plants 18 via lead, or bus, 15, through the delta-to-wye transformer 27. Switching gear, 12 serves to interconnect the fuel cell power plants 18 through bus 15, the loads 14 through a load power bus 39, and the utility grid 10. In this way, the fuel cell power plants 18 (or simply “fuel cells 18” or “power plants 18”) are available and connected for supplying power on a full time basis to the loads 14 or to the loads 14 and utility grid 10, for economical usage of the fuel cells. The switching gear 12 preferably includes a high current capacity, high speed, static (solid-state) switching arrangement and several inter-tie or breaker switches (not shown), as described in the aforementioned application U.S. Ser No. 09/782,402, now U.S. Pat. No. 6,465,910. The static switch, which may be pairs of counter-connected, silicon controlled rectifiers, serves as the main operational switch, and is closed during normal operation of the grid 10, to connect the grid 10 with the power plants 18 and loads 14, and is open if the grid goes out of limits or if an “enable” signal is removed. The breaker switches are typically electromechanical and may be automatically or manually actuated to selectively provide bypass paths around the static switch and/or to open otherwise closed paths. Global bypass breakers 19 connected to busses 15, 10 and 39, serve, when manually closed, to further bypass the switching gear 12, as during maintenance or a start-up or shutting down operation.
There are multiple fuel cell power plants 18 at the site, and it is the integrated control of and/or involving, those multiple power plants 18 which comprises the present invention. In an exemplary arrangement, five (5) such power plants 18 are located at the site and controlled by the SMS 11. Each power plant 18 is a 200 kw International Fuel Cells, LLC (formerly ONSI) PC25™ power plant, with the five units collectively being capable of providing up to 1 megawatt of power. Each such power plant 18 includes the basic fuel cell (F.C.), a Power Plant Controller (PPC), and a Power Conditioning System (PCS) which includes its own separate controller. The fuel cell, F.C., includes (not shown) a fuel stack assembly, ancillary fuel processing and delivery equipment, oxidant delivery equipment, and a water and steam management system, as is generally well known. The PPC includes the controls, logic and monitoring equipment directly associated with the operation and control of the respective F.C., as generally known, and including additional provision for evaluating the present power generating capability of the power plant 18, as will be described. The PCS contains a solid-state inverter and its controller which converts DC power to AC power at the desired voltage and frequency. Control of and by the PCS, as through its associated controller and the other controllers to be hereinafter discussed, further enables conversion of the mode of operation of a power plant 18 from G/C to G/I, and vice versa, as is generally known and will be better understood by reference to the aforementioned application U.S. Ser. No. 09/782,402, now U.S. Pat. No. 6,465,910. When used in G/C mode, the variable controlled by the PCS is power delivered (both real and reactive). When used in the G/I mode, the variables controlled are output voltage and frequency, and, if multiple power plants 18 are involved, phase. The output voltage of a three-phase system is, of course, controlled to be at a phase angle of 120° between each phase. The outputs of the several fuel cell power plants 18 are collectively joined by bus 15. Control signals may be exchanged between the several component portions of a power plant 18, i.e., the F.C, PPC, and PCS, via one or more signal paths, here collectively depicted for convenience as a common signal bus and I/O port 30.
In addition to the switching gear 12, the SMS 11 for the site includes three controllers which are responsible for coordinating integrated operation of the multiple power plants 18, first with respect to each other and with respect to the customer loads 14, and ultimately as a single power resource with respect to the utility grid.
A Site Management Controller (SMC) 31 provides direct control of the PCSs of the fuel cells 18 in response to mode indicating/controlling signals M1 and M2 Image Page 4 on lead 40 from logic associated with the static switch of switching gear 12, and further in response to a grid voltage reference signal 10′ provided by grid sensing circuitry 37. The grid sensing circuitry 37 typically includes a potential transformer (sensor) and a current transformer (sensor) to sense the voltage and current of grid 10 and provide respective signals thereof. The mode signals M1 and M2 from switching gear 12 are indicative of switching of the static switch, and thus the need for a mode change from G/C to G/I, or vice versa. Logic associated with the static switch receives a signal via lead 10″ from the grid sensing circuitry 37 and determines whether the grid is within limits or not. A change in this condition acts through the logic to “toggle” the static switch, as described in the aforementioned application U.S. Ser. No. 09/782,402, now U.S. Pat. No. 6,465,910, and to signal such action via the M1 and M2 signals on lead 40. The SMC 31 also includes provision for issuing load share control signals to each of the PCSs of the respective fuel cells 18, to apportion the load among the fuel cells 18 during load following operation in the G/I mode. That load sharing typically takes into account the present power generating capacity of each fuel cell 18, as provided by status signals from the fuel cell power plants 18, and apportions the load accordingly amongst them.
The SMC 31 is typically composed of computers, programmable logic, sensors, and control circuitry. The combination of the mode signals M1 and M2, and the information about grid voltage, phase and frequency provided on lead 10′, serve in the SMC 31 to provide, as outputs, further mode control signals D1 and D2 on lead 33′, a phase lock loop sync signal on lead 33″, and a voltage reference signal on lead 33′″. A signal bus 33 exchanges these control signals between the SMC 31 and the PCSs of the several power plants 18. The signal bus 33 also conveys, between the SMC 31 and each of the PCSs, the several load share status and control signals collectively represented as lead 33′″ to/from the SMC 31. These signals are used to apportion the load among the fuel cells 18 during load-following operation in the G/I mode. The “load sharing” algorithm takes into account the present power generating capacity of each fuel cell 18, as provided by status signals from the fuel cell power plants 18, and apportions the load accordingly amongst them.
The grid 10 voltage and current signals sensed by the grid sensing circuit 37 are also extended to a grid protection relay 26, which in turn is responsive to the grid voltage and current being in or out of limits to provide a control signal on lead 28. The lead 28 is connected to the switching gear 12, and the signal thereon serves to control one or more breaker switches in a manner to assure the load continues to have power during grid disturbances and also to protect the static switch, the grid 10, the power plants 18 and/or the loads 14 in the event of extreme conditions.
A second controller is the Load Shed Controller (LSC) 34, which is a programmable logic control comprised of appropriate standard integrated circuits. The LSC 34 provides high-speed load shed control in the G/I mode, as will be described below. The LSC 34 receives respective kilowatt (Kw) capacity signals from each of the power plants 18 (1 through n) via a signal bus 36, here collectively representative of all “n” of the signals. The respective Kw capacity signals are typically developed in the respective PPCs of each power plant 18, pass through the respective PCSs, and each extend to the LSC 34 via I.O. port 30 as a 4-20 ma signal via respective pairs, here collectively represented as lead 36. The development of the Kw capacity signals at the PPCs, and their eventual use in the various controls of the SMS 11, will be described below in greater detail. Suffice it to say at this juncture that the Kw capacity signals are a measure of the power generating capacity of the individual power plants 18, and find use in load sharing, load shedding, and in the overall control of the multiple power plants 18 as a unified, or singular, resource in a utility grid of distributed resources. Further, 2X signals (possibly 24 in number) are communicated between the LSC 34 and the X (possibly 12 in number) contactors 1 through X of the contactor array 13 via discrete signal lines, here represented for simplicity as a single lead 70. Half of these signals are representative of the status of the respective contactors, and the other half are responsible for controlling the opening or closing of the respective contactors. The LSC 34 also receives an indication, via lead 71 from the logic associated with the static switch of switching gear 12, of the mode status, and particularly entry into the G/I mode. This enables operativeness of the load shedding function in that mode, and vice versa.
The third controller is the Site Supervisory Controller (SSC) 29, which provides the operator interface for the power system 8, is responsible for integrated supervisory control of the system at a high level, and provides an interface between the customer (or operator) at the site and the utility. As with the LSC 34, the SSC 29 is a programmable logic control comprised of appropriate standard integrated circuits programmed to perform the required functions. A bus extender 38 connects the LSC 34 and the SSU 29 such that the two may be viewed collectively as a unit. The SSC 29 includes six interfaces with the remainder of the power system 8, as well as with the utility grid.
One of those interfaces is the interconnection of the LSC 34 with the SSC 29 via the bus extender 38. The LSC 34 communicates the 2X number of signals associated with contactor array 13 to the SSC 29 approximately every half second such that the SSC 29 has override capability of the customer load contactors 13 as well as monitoring the customer load status, when in G/I mode.
Another interface involves the communications between the SSC 29 and the individual power plants 18 via n pairs of Local Operator Interface (LOI) leads 54′, only one being shown connected to the SSC 29, and the connection with the PPCs of the power plants 18 being represented, for simplicity, as but part of a cumulative, multiple path, diverse signal communication bus 54. These signals include those necessary fur the routine supervisory control of the power plants 18, and are used to obtain data from the power plants 18 for both local display on the Local Human Machine Interface (HMI) 56 and for use at the utility dispatch Supervisory Control and Data Acquisition (SCADA) interface on lead 58 from/to the utility. A panel control 60 includes manual controls for various annunciators and, particularly, a mode switch input providing selection between a local operating mode (L) in which the power plants 18 are controlled individually, and a supervisory mode (S) in which the several power plants are operated as a unit. When the mode selector switch from panel control 60 is in the supervisory mode (S), as depicted in
A fourth interface with SSC 29 involves the grid protection relay 26 via lead 65. This connection reports the status of grid 10, and any faults or out of limit conditions therewith, such as current, voltage, phase or frequency abnormalities, as discerned by grid sensing unit 37 and applied through the GPR 26.
A fifth interface with the SSC 29 involves the provision of signals indicative of the power delivery by the several power plants 18, by means of a utility power meter 66 connected to power bus 15 and having a signal lead 67 connected to SSC 29, and indicative of the power delivered to/drawn by the loads 14, by means of a utility power meter 68 connected to load power bus 39. The power meter 68 is connected to bus 39 intermediate the contactors 13 and the global bypass 19, and has a signal lead 69 connected to SSC 29. The power meters 66 and 68 each typically include a potential (voltage) sensor and a current sensor (neither shown) for cumulatively determining power. These power readings are used by the SSC 29 and the LSC 34 for control actions to be hereinafter explained.
The sixth interface involves 2-way communication between the SSC 29 and the switching gear 12, as represented by the lead 72. The SSC 29 may provide discrete signals to the static switch control and to selected breaker switches to allow it to select the operating mode of the SMS 11 if necessary. Similarly, those switches return respective status signals to the SSC 29. The SSC 29 may provide an “enable” signal to the static switch, and when present allows the switch to operate autonomously based on the condition of grid 10 at the time. When the signal is “disabled”, it forces the static switch to open and cause power system 8 to operate in the G/I mode.
A local diagnostic terminal 73 is connected selectively through an “n-way” switch 74 and leads 54″ and 54, to the individual ones of the n-number of power plants 18 for obtaining diagnostic data. Also included is a remote diagnostic terminal (RDT) 61 connected through an “n-way” phone line sharer 63 to the individual n-number of power plants 18, via leads 54 and 54′″, for similarly obtaining diagnostic data.
Reference is now made to
Referring further to
An alternative to the algorithm depicted with respect to
During operation of the site-based power system 8 in the G/C mode, not only is the total capacity of the n fuel cell power plants 18 available to supply the demands of the local customer loads 14, but the nominally “infinite” resource of the utility grid 10 is also available. However, when operating in the G/I mode, the maximum power available is that represented by the Total Kw Capacity value 95 depicted in FIG. 3. In such instance, if the actual total power demand of the collective loads 14 (L1, L2, . . Lx) is greater than the Total Kw Capacity value, as because the latter is reduced because of power “foldbacks” at the power plants 18, some administrative action must be taken. According to an aspect of the invention, the customer loads 14 are arranged, or identified, according to a schedule of priorities. In the most refined instance, each of the total X number of loads has its own different relative priority. Alternatively, the loads 14 may be grouped, as for instance in high, medium, and low priority groups.
Then, in one embodiment, the total power demand of the loads 14, as indicated by the signal 69 from Utility Power Meter 68, is conveyed to SSC 29 where it is compared with the Total Kw Capacity signal 95 (of
Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made without departing the spirit and scope of the invention. For instance, the logic functions depicted in
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|U.S. Classification||700/286, 700/22|
|International Classification||H02J3/24, H02J13/00, G05D17/00, H02J3/38, H01M, G05D11/00|
|Cooperative Classification||Y10S429/90, Y02E60/7838, H02J3/387, H02J13/0062, Y04S10/12, H02J2001/004, Y04S40/124, Y02E40/72, Y02E60/74, Y04S10/30|
|European Classification||H02J3/38D2, H02J13/00F4B4|
|19 Sep 2011||FPAY||Fee payment|
Year of fee payment: 8
|5 Aug 2014||AS||Assignment|
Effective date: 20140718
Owner name: DOOSAN FUEL CELL AMERICA, INC., GEORGIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CLEAREDGE POWER, INC., CLEAREDGE POWER, LLC, CLEAREDGE POWER INTERNATIONAL SERVICE, LLC;REEL/FRAME:033472/0094