Patent Application
20180191010
The field of the disclosure relates generally to fuel cells and, more particularly, to a protection circuit for controlling output power of fuel cells while transitioning between output power levels.
Many known electrical systems utilize one or more power sources to provide the necessary power to operate various electrical equipment. The electrical load on the power sources may vary over time and, under certain circumstances, may increase or decrease rapidly during a transient event or a planned ramp-up or ramp down of power output. Many known electrical systems, such as, for example, and without limitation, those that connect to an electrical grid, are required to transition between power levels within a certain amount of time. Some known electrical systems utilize power sources, such as, for example, and without limitation, batteries, that can ramp-up and ramp-down power output, i.e., transition between power levels, rapidly to satisfy the power demand of the load. Some known electrical systems utilize energy storage systems to store excess power when rapidly ramping-down power output and to supply excess power when rapidly ramping-up power output.
Many known electrical systems utilize fuel cells. Fuel cells generate power output via a chemical process that converts a chemical fuel, such as, for example, hydrogen, into electrical energy. Fuel cells are generally slow at transitioning between power levels. Fuel cells are particularly sensitive to sustained ramping-up and ramping-down, in that the rapid transition within the chemical process may have damaging effects on the fuel cells themselves. During a transient event or a planned ramp-up or ramp-down of power output, such electrical systems typically rely on energy storage systems, such as, for example, and without limitation, batteries, to provide relief. However, energy storage systems are expensive and the duration of relief provided by energy storage systems is limited by size and cost.
In one aspect, a protection circuit for a fuel cell coupled to a load is provided. The protection circuit includes a switch and a controller. The switch is coupled between the fuel cell and an auxiliary load. The switch is configured to selectively couple the auxiliary load to the fuel cell. The controller is coupled to the switch. The controller is configured to control the switch to couple the auxiliary load to the fuel cell when the load demands a reduction in power output from the fuel cell. The controller is further configured to maintain the power output from said fuel cell at an initial level.
In another aspect, an electrical system is provided. The electrical system includes a fuel cell, an inverter, and a protection circuit. The fuel cell is configured to generate an output power according to a chemical process. The inverter is coupled to the fuel cell and an electric load. The inverter is configured to demand the output power from the fuel cell for the electric load. The protection circuit is coupled to the fuel cell and the inverter. The protection circuit is configured to detect a reduction in the output power demanded by the inverter. The protection circuit is further configured to control an auxiliary load coupled to the fuel cell to utilize the output power at an initial level. The protection circuit is further configured to maintain the power output from the fuel cell at the initial level.
In yet another aspect, a method of controlling an output power of a fuel cell is provided. The method includes controlling a chemical process of the fuel cell to generate the output power at an initial level demanded by a load coupled to the fuel cell. The method includes determining a reduction in power demanded by the load. The method includes controlling an auxiliary load coupled to the fuel cell to utilize the reduction in power demanded by the load. The method includes maintaining the output power from the fuel cell at the initial level.
These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein.
In the following specification and the claims, a number of terms are referenced that have the following meanings.
The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor, processing device, or controller, such as a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field programmable gate array (FPGA), a digital signal processing (DSP) device, and/or any other circuit or processing device capable of executing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processing device, cause the processing device to perform at least a portion of the methods described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the terms processor, processing device, and controller.
In the embodiments described herein, memory may include, but is not limited to, a computer-readable medium, such as a random access memory (RAM), and a computer-readable non-volatile medium, such as flash memory. Alternatively, a floppy disk, a compact disc—read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, an operator interface monitor.
Embodiments of the present disclosure provide a protection circuit for a fuel cell. More specifically, embodiments of the present disclosure describe a protection circuit for controlling power output of a fuel cell during a transition between power levels. Embodiments of the present disclosure facilitate operation of a fuel cell within healthy operating boundaries for the fuel cell's chemical process through transitions between power levels. For example, protection circuits described herein maintain a relatively constant power output for the fuel cell during a rapid change in load, which may occur, for example, and without limitation, during a transient event, a planned ramp-up in output power, and a planned ramp-down in output power. In such embodiments, total power delivered to the load varies according to these events, but fuel cell power output remains relatively constant. Protection circuits described herein control an auxiliary load coupled to the fuel cell during such events to utilize the excess power output from the fuel cell. The auxiliary load may include, for example, and without limitation, load banks, electric heaters, electric steam generators, and other electrical loads.
Fuel cell 110 may include a high-temperature fuel cell system that utilizes electric heaters and electric steam generation to initiate operation. During “steady-state” operation, such components are typically power-off. Protection circuit 120, in certain embodiments, is configured to utilize such electric heaters and electric steam generators as auxiliary load 140 to further manage the chemical process conditions for fuel cell 110, including, for example, and without limitation, temperature and steam-to-carbon ratio, during a transition between power levels. More specifically, for example, a transient event for load 130 may result in a sudden disconnection of load 130 from fuel cell 110. Rather than rapidly ramping down the chemical process of fuel cell 110, protection circuit 120 selectively couples auxiliary load 140 to fuel cell 110 through switch 150, thus preventing alternating of chemical process conditions that can damage fuel cell 110. For example, ramping-down of output power from fuel cell 110 may reduce the water production, which impacts the steam-to-carbon ratio. The chemical process conditions for fuel cell 110 define the ramp-rate limit that fuel cell 110 can support during transitions between power levels. Controller 160, given the ramp-rate limit for fuel cell 110, determines whether a transition between power levels can be achieved, within the ramp-rate limit, or requires auxiliary load 140 to be attached. If the transition is achievable by fuel cell 110, controller 160, in certain embodiments, modifies the chemical process of fuel cell 110 to ramp-up or ramp-down the power output. If the transition exceeds the ramp-rate limit, controller 160 determines which components of auxiliary load 140 should be coupled or decoupled to fuel cell 110 to sink a sufficient amount of output power from fuel cell 110 to facilitate a relatively constant power output from fuel cell 110. In certain embodiments, controller 160 controls switch 150 using a pulse-width modulation (PWM) or pulse density modulation signal to continuously regulate power flow to auxiliary load 140. Auxiliary load 140 may include variable load components such as, for example, and without limitation, load banks, electric heaters, and electric steam generators. Such auxiliary loads 140 generally affect the operation of fuel cell 110. In certain embodiments, auxiliary loads 140 may include components supporting other fuel cells or other power plants that supply power to load 130.
Protection circuit 120 includes switch 150 coupled in series between fuel cell 110 and auxiliary load 140. Switch 150 may be implemented as, for example, and without limitation, an electro-mechanical contactor, a relay, a solid-state contactor, semiconductor switch, or other suitable electrical switch for opening and closing the circuit between fuel cell 110 and auxiliary load 140. Switch 150 is controlled by a control signal transmitted from controller 160 (shown in
Auxiliary load 140 includes an impedance 206 that may be implemented as simple resistance or any other suitable load for sinking current from fuel cell 110. For example, and without limitation, impedance 206 may include electric heaters and electric steam generators to support the chemical process of fuel cell 110.
During operation of protection circuit 120, when load 130 reduces rapidly, i.e., is transitioning to a lower power level, controller 160 compares the reduction to the ramp-rate limit for fuel cell 110. When the reduction exceeds the ramp-rate limit, switch 150 is closed and auxiliary load 140 is coupled to fuel cell 110. Auxiliary load 140 utilizes excess power output from fuel cell 110 that would otherwise be supplied to load 130. The power output from fuel cell 110 remains constant relative to load 130. For example, load 130 may be reduced 100% during a transient event, while the power output from fuel cell 110 fluctuates plus-or-minus 5%. The extent to which fuel cell 110 tolerates fluctuations in output power is a function of the precise chemical process of fuel cell 110 and the associated ramp-rate limit. When load 130 returns to its previous power level, for example, and without limitation, when a transient event clears, or when a planned ramp-up occurs, switch 150 is selectively opened to disconnect auxiliary load 140 and the power output from fuel cell 110 is directed to load 130.
In certain embodiments, auxiliary load 140 includes multiple components that may be prioritized in connecting to fuel cell 110. For example, and without limitation, auxiliary load 140 may include load banks that simply sink power output from fuel cell 110. Auxiliary load 140 may further include electric heaters or electric steam generators that regulate chemical process conditions for fuel cell 110. The load banks are wasteful relative to the electrical equipment that supports the chemical process of fuel cell 110. Accordingly, controller 160, in certain embodiments, may selectively couple the electric heaters and electric steam generators to utilize excess power from fuel cell 110 before coupling a resistive load bank that simply sinks current and dissipates energy in the form of heat. In certain embodiments, controller 160 may adjust a variable load set point for auxiliary load 140 to adjust the amount of power consumed by auxiliary load 140. For example, and without limitation, controller 160 may initially operate a steam generator at 10% capacity. When the power demand of load 130 is reduced, controller 160 increases the load set point of the steam generator to utilize the excess power generated by fuel cell 110.
Leading up to event 420, power output curve 510 illustrates load 130 having a generally flat demand at initial power level 340. When event 420 occurs, load 130 transitions 430 from initial power level 340 to lower power level 520. Transition 430 is illustrated by a dip in power output curve 510. The area above power output curve 510, illustrated by cross-hatching, represents power 530 provided to auxiliary load 140 over the duration of event 420. After a duration of time at lower power level 520, load 130 transitions 450 back up to initial power level 340.
The above described embodiments of protection circuits for fuel cells provide a protection circuit for controlling power output of a fuel cell during a transition between power levels. Embodiments of the present disclosure facilitate operation of a fuel cell within rated operating boundaries for the fuel cell's chemical process through transitions between power levels. For example, protection circuits described herein maintain a relatively constant power output for the fuel cell during a rapid change in load, which may occur, for example, and without limitation, during a transient event, a planned ramp-up in output power, and a planned ramp-down in output power. In such embodiments, total power delivered to the load varies according to these events, but fuel cell power output remains relatively constant. Protection circuits described herein connect an auxiliary load during such events to utilize the excess power output from the fuel cell. The auxiliary load may include, for example, and without limitation, load banks, electric heaters, electric steam generators, and other electrical loads.
An exemplary technical effect of the methods, systems, and apparatus described herein includes at least one of: (a) maintaining operation of fuel cells within rated operating boundaries; (b) maintaining constant power output from fuel cells relative to a varying load; (c) protecting fuel cells from rapid ramping-up and ramping-down of power output; (d) reducing initial costs through installation of auxiliary loads versus energy storage systems; (e) reducing maintenance costs through use of auxiliary loads versus energy storage systems; (0 improving life expectancy of fuel cells through reduced stress during operation; and (g) improving system cost and reliability through reduced component count and component cost.
Exemplary embodiments of methods, systems, and apparatus for controlling output power of fuel cells are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other non-conventional protection circuits for fuel cells, and are not limited to practice with only the systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other applications, equipment, and systems that may benefit from increased efficiency, reduced operational cost, and reduced capital expenditure.
Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
