Patent Application
20120326516
Electrical power systems can be used to provide electrical power to one more loads such as buildings, appliances, lights, tools, air conditioners, heating units, factory equipment and machinery, power storage units, computers, security systems, etc. The electricity used to power loads is often received from an electrical grid. However, the electricity for loads may also be provided through alternative power sources such as fuel cells, solar arrays, wind turbines, thermo-electric devices, batteries, etc. The alternative power sources can be used in conjunction with the electrical grid, and a plurality of alternative power sources may be combined in a single electrical power system. Alternative power sources are generally combined after conversion of their DC output into an alternating current (AC). As a result, synchronization of alternative power sources is required.
In addition, many alternative power sources use machines such as pumps and blowers which run off auxiliary power. Motors for these pumps and blowers are typically 3-phase AC motors which may require speed control. If the alternative power source generates a direct current (DC), the direct current undergoes several states of power conversion prior to delivery to the motor(s). Alternatively, the power to the motors for pumps, blowers, etc. may be provided using the electrical grid, an inverter, and a variable frequency drive. In such a configuration, two stages of power conversion of the inverter are incurred along with two additional stages of power conversion for driving components of the AC driven variable frequency drive. In general, each power conversion stage that is performed adds cost to the system, adds complexity to the system, and lowers the efficiency of the system.
Operating individual distributed generators such as fuel cell generators both with and without a grid reference and in parallel with each other without a grid reference is problematic in that switch-over from current source to voltage source must be accommodated. Additionally, parallel control of many grid independent generators can be problematic.
The combination of various power sources also presents safety issues arising from the potential for inadvertent contact of high voltage nodes.
According to one embodiment, a fuel cell system includes at least one power module comprising at least one fuel cell segment configured to supply power to a DC IT load, a first inverter configured to supply an alternating current (AC) to or from an AC grid, a first DC bus electrically connected to an output of the at least one fuel cell segment and to an input for the first inverter, and configured to supply power to an input of the DC IT load, and a first isolating DC/DC converter positioned to isolate the DC IT load from at least one of the first inverter or the AC grid.
According to another embodiment, a method of operating a fuel cell system, includes the steps of supplying a direct current from at least one fuel cell segment to a DC IT load at least in part via a first DC bus and supplying an alternating current (AC) from an AC grid to a first inverter or receiving the AC from the AC grid at the first inverter, wherein the first inverter is connected to the first DC bus and wherein the DC IT load is isolated from at least one of the first inverter or the AC grid by an isolating DC/DC converter during the step of supplying the direct current.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.
The safety issues arising from the potential for inadvertent contact of high voltage nodes may be addressed by isolating power sources and buses from each other. In embodiments, a DC bus is isolated from connections to an AC grid. In other embodiments, low voltage and high voltage DC buses are isolated from each other.
DC/DC converter and an isolated downstream DC/DC converter according to embodiments.
Referring to
The IOM 104 may comprise one or more power conditioning components. The power conditioning components may include components for converting DC power to AC power, such as a DC/AC inverter 104A shown in
Each power module 106 cabinet is configured to house one or more hot boxes. Each hot box contains one or more stacks or columns of fuel cells 106A (generally referred to as “segments”), such as one or more stacks or columns of solid oxide fuel cells having a ceramic oxide electrolyte separated by conductive interconnect plates. Other fuel cell types, such as PEM, molten carbonate, phosphoric acid, etc. may also be used.
Fuel cells are often combined into units called “stacks” in which the fuel cells are electrically connected in series and separated by electrically conductive interconnects, such as gas separator plates which function as interconnects. A fuel cell stack may contain conductive end plates on its ends. A generalization of a fuel cell stack is the so-called fuel cell segment or column, which can contain one or more fuel cell stacks connected in series (e.g., where the end plate of one stack is connected electrically to an end plate of the next stack). A fuel cell segment or column may contain electrical leads which output the direct current from the segment or column to a power conditioning system. A fuel cell system can include one or more fuel cell columns, each of which may contain one or more fuel cell stacks, such as solid oxide fuel cell stacks.
The fuel cell stacks may be internally manifolded for fuel and externally manifolded for air, where only the fuel inlet and exhaust risers extend through openings in the fuel cell layers and/or in the interconnect plates between the fuel cells, as described in U.S. Pat. No. 7,713,649, which is incorporated herein by reference in its entirety. The fuel cells may have a cross flow (where air and fuel flow roughly perpendicular to each other on opposite sides of the electrolyte in each fuel cell), counter flow parallel (where air and fuel flow roughly parallel to each other but in opposite directions on opposite sides of the electrolyte in each fuel cell) or co-flow parallel (where air and fuel flow roughly parallel to each other in the same direction on opposite sides of the electrolyte in each fuel cell) configuration.
Power modules may also comprise other generators of direct current, such as solar cell, wind turbine, geothermal or hydroelectric power generators.
The segment(s) 106A of fuel cells may be connected to one or more DC buses 112 such as split DC bus(es), by one or more DC/DC converters 106B located in module 106. The DC/DC converters 106B may be located in the IOM 104 instead of the power modules 106.
The system may also optionally include an energy storage module 108, such as a bank of supercapacitors or batteries or one or more flywheels 108B. The storage device 108B may also be connected to the DC bus 112 using one or more DC/DC converters 108A as shown in
As shown in
The fuel cell system and the grid 114 may be electrically connected to the power supply 102A of the load 102 (e.g., an IT load having dual A and B side inputs). The power supply 102A may include using a control logic unit and an AC/DC converter to convert back up power from the grid 114 to DC power in case power from modules 106 is not available or not sufficient. Logic unit may be a computer or processor which switches power between the primary power from bus 112A and backup power from grid 114 using a switch or relay.
A second switch 116 controls the electrical connection between the IOM 104 and the grid 114. Switch 116 may controlled by the control logic unit or by another system controller.
The DC bus 203 may be of positive or negative polarity. In an embodiment, the DC bus 203 is a split (or bipolar) bus that includes a positive bus, negative bus and a neutral bus. For example, a bipolar DC bus 203 may provide +380 VDC at the positive bus relative to the neutral and −380 VDC at the negative bus relative to the neutral. The total magnitude of the voltage in this example as measured between the positive and negative buses is 760 VDC.
In an embodiment, the DC bus 203 is connected to a DC/AC inverter 218 that supplies 480 VAC to a grid 220. The DC power fed to the inverter 218 may be bipolar (+/−380 VDC) or unipolar (380 VDC). In still another embodiment, an inverter 216 is connected to a source of AC, such as grid or a diesel generator 240 and the DC bus 203. The DC output of the inverter 216 (Circle A) is passed through a rectifier 228 (e.g., a diode), such as a power factor corrected rectifier, that is used to prevent current from flowing from the DC bus 203 to the AC source 240. The AC source 240 may supply 120 VAC, 420 VAC, 208 VAC, 3-phase or 480 VAC, 3-phase.
In another embodiment, the DC bus 203 is connected to a DC/DC converter 214 to provide voltage to a DC storage device 224, such as a battery or a super capacitor. The energy stored in DC storage device 224 may be supplied back to the DC bus 203 via the DC/DC converter 214 (Circle C).
In an embodiment, the DC bus 203 is connected to one or more low voltage DC buses.
As illustrated a DC/DC down converter 202 connected to bus 203 supplies a first low voltage to a low voltage DC bus 1, a second down converter 204 (e.g., a Buck converter) connected to bus 203 supplies a second low voltage to a low voltage DC bus 2, a third down converter 208 connected in series with down converter 204 provides a third low voltage to low voltage DC bus 207 by down converting the high voltage (e.g., +/−380V) from bus 203 to a lower voltage. DC/DC converter 208 down converts the voltage output from DC/DC converter 204. Low voltage DC bus 207 may also be provided with power from different sources as discussed below. The DC voltage supplied to low voltage DC bus 1, low voltage DC bus 2 and the low voltage DC bus 207 may be positive or negative referenced to a common node or center tap, such as +/−48 VDC, or may be positive or negative unipolar referenced to ground.
In an embodiment, the DC/DC converters 202 and 204 may provide isolation between the input and output terminals (i.e., DC/DC converters 202, 204 are isolating converters). The outputs of these converters are thus unaffected by the noise that may introduced to the DC bus 203 by the grid 220, 240 and/or the inverters 210, 218.
In yet another embodiment, a “super” converter 204 is connected to bus 203 that provides multiple outputs to supply various low voltage DC buses. The super converter may also supply DC power to one or more inverters (not illustrated) to supply AC voltage to various AC buses (not illustrated).
The voltage on bus 207 may be set based on the requirements of DC load 222 (e.g., an ITC DC load). The desired voltage may be achieved by connecting one or more DC/DC converters in series to step down the voltage from the DC bus 203. For example, a series of DC/DC down converters 204 and 208 produces an output voltage of +/−48 VDC that supplies a DC load, such as an IT load, 222 made up of devices operating in an information technology (IT) system. The IT system may include one or more of computer server(s), router(s), rack(s), power supply connections and other components found in a data center environment. The DC/DC down converters 204 and 208 may be configured to produce other voltages, for example, unipolar 380V, unipolar 600V, +/−12 VDC, +/−24 VDC and +/−36 VDC.
In an embodiment, the DC/DC converter 208 may output a voltage that is determined by commands issued by the DC load 222. The DC/DC down converters 202, 204 and or 208 may also operate to produce a DC voltage suitable for charging an electric vehicle, for example, 600 VDC.
In another embodiment, the power on the low voltage DC bus 207 may be provided to a DC/DC converter 212 to charge a DC storage device 226 (Circle D), such as a battery or a super capacitor. The energy stored in DC storage device 226 may be supplied back to the low voltage DC bus 207 via the DC/DC converter 212.
The low voltage DC bus 207 may also be supplied (at Circle 2) by an AC source 240, such as grid or a diesel generator. The AC source 240 may supply 120 VAC, 420 VAC, 208 VAC, 3-phase and 480 VAC, 3-phase. The AC source 240 is connected to an inverter 210 (Circle B). The DC output of the inverter 210 is passed through at least one isolating DC/DC converter 209 (e.g., a Buck converter) to arrive at the desired voltage for low voltage DC bus 207. In an embodiment a rectifier 230, such as a power factor corrected rectifier (e.g., a diode), is used to prevent current from flowing from the low voltage DC bus 207 to the AC source 240.
It will be appreciated that connections to the grid through inverters 210, 216 and 218 may be bidirectional.
As illustrated in
DC bus 303. In an embodiment, the DC/DC converters 106B are non-isolating Buck converters which convert a high (e.g., 380 VDC) voltage to much lower voltage. Non-isolating converters 106B are more efficient than isolating converters. The low voltage DC bus 303 may be of positive or negative polarity. For example, the low voltage DC bus may be unipolar or bipolar +/−12 VDC, +/−24 VDC, +/−36 VDC and 48 VDC.
Isolation of the low voltage DC bus 303 from the AC signals produced by grid 220, 240 and/or inverters 218, 210 is provided via an isolating upconverting (boost) DC/DC converter 304 that supplies 380 VDC to the inverter 218 (i.e., converter 304 is an isolating converter which boosts the low voltage on bus 203 to a higher voltage). The inverter 218 supplies 480 VAC to a grid 220 (Circle 1). Isolation is also provided by an isolating DC/DC converter 209 as previously described.
As illustrated in
Isolation of the upstream DC bus 403 from the AC signals generated by the grid 220 and/or inverter 218 is provided via an isolating upconverting DC/DC converter 304 that supplies bipolar +/−380 VDC to the inverter 218. The inverter 218 supplies 480 VAC to a grid 220 (Circle 1).
In an embodiment, isolation is also provided by an isolating DC/DC down converting (e.g., Buck) converter 404 to a downstream DC bus 407. While only a single isolating DC/DC down converter 404 is illustrated, any number of such converters may be connected to upstream bus 403. Additional non-isolating down converters may be connected in series to isolating DC/DC down converter 404 to produce a desired low voltage supply for DC load 222.
The upstream bus may receive power from a DC storage device 424 (Circle D) and the grid 220 via an inverter 416 (Circle B). Due to the presence of isolating DC/DC converter 404, an isolating converter may be omitted between storage device 424 or grid 220 and DC load 222. The isolated DC downstream bus 407 may also be supplied down stream of isolating DC/DC converter 404 (at Circle 2) by an AC source 240, such as grid or a diesel generator. The AC source 240 may supply 120 VAC, 420 VAC, 208 VAC, 3-phase and 480 VAC, 3-phase. The AC source 240 is connected to an inverter 210 (Circle A). The DC output of the inverter 210 is passed through at least one isolating DC/DC converter 209 to arrive at the desired voltage for downstream bus 407. In an embodiment, a rectifier 230, such as a power factor corrected rectifier, is used to prevent current from flowing from the downstream bus 407 to the AC source 240.
It will be appreciated that connections to the grid through inverters 210, 416 and 218 may be bidirectional.
As illustrated in
In an embodiment DC bus A 503 provides +/−380 VDC to an inverter 218. The output of inverter 218, for example, 480 VAC, is provided to the grid 220 (Circle 1). The DC bus A 503 may also be supplied power from an AC source 240 through inverter 416 and from a DC storage device 424 (Circles B and D).
In an embodiment, DC bus B 504 may supply power to a DC load 222. The DC load may also be provided power from an AC source 240, such as grid or a diesel generator. The AC source 240 may supply 120 VAC, 420 VAC, 208 VAC, 3-phase and 480 VAC, 3-phase. The AC source 240 is connected to an inverter 210 (Circle A). The DC output of the inverter 210 is passed through at least one isolating DC/DC converter 209 to arrive at the desired voltage for DC bus B 504. In an embodiment, a rectifier 230, such as a power factor corrected rectifier, is used to prevent current from flowing from DC bus B 504 to the AC source 240 or DC storage device 226 (Circle C). Thus, the more efficient non-isolating converters are used to supply power to the grid, which is not affected by noise from the grid and/or the inverters, while the isolating converters are used to supply power to the IT load 222 which is affected by the grid noise and/or the inverters.
In an embodiment, the power modules 106 may be replaced by a DC generator, such as a micro turbine, wind turbine or PV array. The DC output is taken before the inverter stage.
In an embodiment, the various inverters and/or converters described above (e.g., described with respect to any one or more of
As will be appreciated, the voltage outputs of the systems illustrated in
The subsystem 1.1 may be connected to a subsystem 2 via a single or split bus. Subsystem 2 may be similar to the IOM 104 and the storage module 108 shown in
Subsystem 2 provides power to single or split DC bus in subsystem 1.2 via connection 201. The connection 201 may made in various ways, including via a direct connection 201.2 as illustrated in
Subsystem 1.2 includes a DC/DC converter 301. The DC/DC converter 301 may be similar to converter 106B shown in FIGS. 1A and 2-5) and may be a down-only converter, an up-only converter and a configurable converter that may be operated as either an up converter or a down converter (e.g., as a buck, boost or buck-boost converter). An output of DC/DC converter 301 supplies power to a DC load 222, such as an IT load.
Subsystem 1.2 may also supply power to or receive power from one or more DC/DC converters 302, 307 (subsystems 3) via a switching system, for example an or-gating device. The DC/DC converter 302, 307 may be down-only converters, up-only converters or configurable converters that may be operated as either an up converter or a down converter. In an embodiment, subsystem 3 comprises a switchable bidirectional DC bus that is connected to one or more subsystems 4.
Subsystem 4 may include either a bidirectional DC/DC converter 302 with one connection to the input bus and one connection to the output bus or it may include a direct connection bypassing the DC/DC converter 302 (in which case the converter 302 may be omitted).
The combination of subsystems 3 and 4 may be configured to provide at least one of the following:
1. A 800 grid connection attached either to an input of an AC/DC rectifier 701 (importing power from the grid) or to the output of a DC/AC inverter 602 (exporting power to the grid), or to both simultaneously (either to import or export power to/from the grid). The output of the 701 rectifier may be connected to either the input of a DC/DC converter 304 or to an input of a DC/DC converter 304 and the input of an inverter 602, or to the bidirectional DC bus only. The input of the inverter 602 may be connected to either the DC/DC bidirectional bus or a second output of DC/DC converter 304, or to the output of the rectifier 701 and the bidirectional DC bus. In an embodiment, the rectifier 701 is only used when the diode 201.1 of subsystem 2 is used.
2. An AC 801 source (for example, a grid or a diesel generator) connected to the input of an AC/DC rectifier 701. The output of the rectifier 701 is electrically connected to either the DC bidirectional bus or to a DC/DC converter 304.
3. Any suitable regulated or unregulated DC source 802 (for example, a wind farm, a solar array or another alternative power source) connected to either the input of a DC/DC converter 304 or the DC bidirectional bus.
In an embodiment, a first subsystem 3 is electrically connected to the DC bus ahead (i.e., on the input side) of the DC/DC converter 301 (see
Subsystem 1.2 may also provide power to one or more subsystems 5 as shown in
In an embodiment, a single subsystem 5 may be electrically connected to the DC bus ahead or behind the DC/DC converter 301 with respect to subsystem 1.1.
The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the order of steps in the foregoing embodiments may be performed in any order. Further, words such as “thereafter,” “then,” “next,” etc. are not intended to limit the order of the steps; these words are simply used to guide the reader through the description of the methods.
One or more block/flow diagrams have been used to describe exemplary embodiments. The use of block/flow diagrams is not meant to be limiting with respect to the order of operations performed. The foregoing description of exemplary embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
Control elements may be implemented using computing devices (such as computer) comprising processors, memory and other components that have been programmed with instructions to perform specific functions or may be implemented in processors designed to perform the specified functions. A processor may be any programmable microprocessor, microcomputer or multiple processor chip or chips that can be configured by software instructions (applications) to perform a variety of functions, including the functions of the various embodiments described herein. In some computing devices, multiple processors may be provided. Typically, software applications may be stored in the internal memory before they are accessed and loaded into the processor. In some computing devices, the processor may include internal memory sufficient to store the application software instructions.
The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The hardware used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some blocks or methods may be performed by circuitry that is specific to a given function.
The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the described embodiment. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the disclosure. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein.
This application claims priority under 35 U.S.C. §119(e) from provisional application No. 61/501,367 filed Jun. 27, 2011. The 61/501,367 provisional application is incorporated by reference herein, in its entirety, for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61501367 | Jun 2011 | US |
