Systems and methods for using energy storage devices to assist ejectors

Abstract

The present disclosure generally relates to systems and methods for using an energy storage device to assist a venturi or ejector in a fuel cell or fuel stack system.

Description

Technical Field

[0001] The present disclosure relates to systems and methods for using an energy storage device to assist in the operation of a venturi or ejector in a fuel cell or fuel stack system. Background Art

[0002] The vehicle and / or power system uses a fuel cell or fuel cell stack for its power needs. The fuel cell or fuel cell stack can be any type of fuel cell. For example, the fuel cell and / or fuel cell stack can include, but is not limited to, a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a proton exchange membrane fuel cell (also known as a polymer exchange membrane fuel cell (PEMFC)), and a solid oxide fuel cell (SOFC).

[0003] A fuel cell or fuel cell stack can generate electricity in the form of direct current (DC) from the electrochemical reactions that occur in the fuel cell or fuel cell stack. A fuel processor converts the fuel into a form that is usable by the fuel cell or fuel cell stack. If the fuel cell or fuel cell stack is powered by a conventional fuel rich in hydrogen (e.g., methanol, gasoline, diesel, or gasified coal), a reformer can convert the hydrocarbons into a gaseous mixture of hydrogen and carbon compounds, or reformate. The reformate can then be converted into carbon dioxide, purified, and recycled back into the fuel cell or fuel cell stack.

[0004] Fuel, such as hydrogen or hydrocarbons, is directed to the anode on one side of the fuel cell or fuel cell stack through a field flow plate, while oxygen from the air is directed to the cathode on the other side of the fuel cell or fuel cell stack. At the anode, a catalyst, such as a platinum catalyst, splits hydrogen into positive hydrogen ions (protons) and negatively charged electrons. In the case of a polymer exchange membrane fuel cell (PEMFC), a polymer electrolyte membrane (PEM) allows positively charged ions to flow to the cathode through the PEM. Negatively charged electrons are directed to the cathode along an external loop, forming a circuit (current). At the cathode, electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the fuel cell or fuel cell stack.

[0005] The fuel stream is discharged from the fuel cell or fuel cell stack outlet and recirculated back to the anode through the anode inlet. The recirculation of the fuel stream exhaust gas returning to the anode inlet includes both fuel and water. The recirculation rate is based on a specified excess fuel target, such as the excess fuel ratio or entrainment ratio (ER). The entrainment ratio (ER) is defined as the ratio of the mass flow rate of the low-pressure stream (e.g., the secondary mass flow rate) to the mass flow rate of the high-pressure stream (e.g., the primary mass flow rate).

[0006] Based on the operating conditions of the fuel cell or fuel cell stack, the fuel target of the system can be specified as the minimum excess fuel level required for the fuel cell or fuel cell stack. The excess fuel level of the fuel cell or fuel cell stack may be higher than the minimum level defined by the excess fuel target, but reaching this higher level may result in a high parasitic load on the fuel cell or fuel cell stack. For example, an excess fuel level higher than the minimum excess fuel level can be achieved by maintaining a high fuel flow rate at the anode, which may result in a pressure loss in the fuel cell or fuel cell stack. The blower and / or pump can function with a capacity proportional to the pressure loss in the fuel cell or fuel cell stack and / or the volume flow rate through the blower and / or pump. The blower and / or pump can use additional power to compensate for the pressure loss. The use of additional power by the blower and / or pump may result in a high parasitic load on the fuel cell or fuel cell stack.

[0007] The present specification provides systems and methods for using an energy storage device to assist a venturi or ejector in a fuel cell or fuel stack system during transient operation. Summary of the Invention

[0008] In one aspect, the present disclosure relates to a fuel cell stack system comprising an ejector, a blower, a controller, and an energy storage device. The system operates under a transient hysteresis state.

[0009] In one embodiment, the system needs to operate at a first operating current density and the ejector or blower cannot support the first operating current density. In some embodiments, the controller determines a second operating current density for the system, and the second operating current density is higher than the first operating current density.

[0010] In one embodiment, when the system is operating in a transient hysteresis state, the temperature or pressure of the fuel cell stack is decreasing.

[0011] In one embodiment, the system generates excess power when operating at the second operating current density, and the excess power generated is dissipated or stored for a period of time in an energy storage device. In some embodiments, the storage device is a battery having a state of charge. In other embodiments, the storage of the excess power generated depends on the state of charge of the battery. In some embodiments, the excess power generated is stored as kinetic energy, potential energy, chemical energy, electrical energy, electrochemical energy, mechanical energy, or thermal energy.

[0012] In one embodiment, the controller determines a third operating current density for the system, and the third operating current density is lower than the first operating current density. In some embodiments, the system uses energy from the energy storage device when operating at the third operating current density.

[0013] In another aspect, the present disclosure relates to a method for operating a fuel cell stack system including an ejector, a blower, a controller, and an energy storage device. The method includes determining an operating current density of the system and operating the fuel cell stack in a transient hysteresis state.

[0014] In one embodiment of the method, determining the operating current density of the system includes determining a first operating current density such that the ejector or blower cannot support the first operating current density. In some embodiments of the method, the method further includes the controller determining a second operating current density of the system, wherein the second operating current density is higher than the first operating current density.

[0015] In one embodiment of the method, the temperature or pressure of the fuel cell stack is decreasing while the system is operating in the transient hysteresis state.

[0016] In one embodiment of the method, the method further includes generating excess power when the system operates at the second operating current density, and dissipating the generated excess power or storing the generated excess power in an energy storage device for a period of time.

[0017] In some embodiments of the method, the storage device is a battery having a state of charge. In some embodiments of the method, storing the generated excess power depends on the state of charge of the battery. In some embodiments of the method, the generated excess power is stored as kinetic energy, potential energy, chemical energy, electrical energy, electrochemical energy, mechanical energy, or thermal energy.

[0018] In one embodiment of the method, the method further includes the controller determining a third operating current density for the system, and wherein the third operating current density is lower than the first operating current density.

[0019] In some embodiments of the method, the method further includes the system using energy from the energy storage device when operating at the third operating current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] These and other features, aspects, and advantages of the present invention will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout, and in which:

[0021] Figure 1 is a graph showing operating curves of a system including a fuel cell or a fuel cell stack.

[0022] Figure 2 is a schematic diagram showing a mechanical regulator used with a venturi or ejector in a fuel cell stack system.

[0023] Figure 3is a schematic diagram showing a proportional control valve used with a venturi or ejector in a fuel cell stack system.

[0024] Figure 4A is a graph showing operating curves for a system including a venturi or ejector under choked conditions.

[0025] Figure 4B is a graph showing operating curves for a system including a venturi or ejector under choked and unchoked conditions.

[0026] Figure 5 is a graph showing operating curves of a system including blowers in different operating states when the system is in a transient state. DETAILED DESCRIPTION

[0027] The present disclosure relates to systems and methods for enhancing the operation of a venturi or ejector in a fuel cell or fuel stack system. More particularly, it relates to systems and methods for using a battery storage system to assist a venturi or ejector in a fuel cell or fuel stack system during transient operation.

[0028] One embodiment of the present operating system requirements including a fuel cell or fuel cell stack is Figure 1 The operating pressure and the associated operating temperature are shown as a function of current density. A fuel cell or fuel cell stack may require a current density that is known as the anode inlet manifold pressure (P AIM ) pressure range.

[0029] The maximum anode inlet manifold pressure (P AIM_HI ) is represented by 110. The minimum anode inlet manifold pressure (P AIM_LO ) is represented by 120. The range 160 between 110 and 120 represents the target anode inlet manifold pressure range. In some embodiments, the target temperature of the system can be adjusted from the low fuel supply operating temperature (T CV_LO )102 to high fuel supply operating temperature (T CV_HI )104.

[0030] In one embodiment, when the fuel cell or fuel cell stack is at the critical current density (i _LO_CR )130, when operating from about or approximately the maximum anode inlet manifold pressure (P AIM_HI )110 to about or approximately the minimum anode inlet manifold pressure (P AIM_LO )120 is critical to operate a fuel cell or fuel cell stack at a pressure within the range of 120. In some embodiments, the critical current density (i _LO_CR )130 can be about 0.7A / cm 2In other embodiments, the critical current density (i _LO_CR )130 can be about 0.6A / cm 2 In some other embodiments, the critical current density (i _LO_CR )130 can be higher or lower than 0.7A / cm 2 , for example, ranging from about 0.5 A / cm 2 To about 0.9A / cm 2 , including each current density contained therein.

[0031] In one embodiment, the fuel cell or fuel cell stack can be operated in a high current density range, such as from about 1.3 A / cm 2 to about 2.0A / cm 2 , or about 1.3A / cm 2 to about 1.6A / cm 2 , or about 1.0A / cm 2 to about 1.6A / cm 2 In some embodiments, the ionizer is operated at a high current density (e.g., at about 1.6 A / cm2) at a pressure and temperature different from the optimal target operating pressure and temperature. 2 ) may reduce the efficiency of the fuel cell or fuel cell stack. Doing so may also cause damage to the fuel cell or fuel cell stack due to MEA degradation (e.g., due to starvation, flooding, and / or relative humidity effects). In some embodiments, when the fuel cell or fuel cell stack is at the critical current density (i _LO_CR )130 or less, the operating pressure and temperature of the fuel cell or fuel cell stack may have greater flexibility. The present operating system including the fuel cell or fuel cell stack may be operated at the minimum current density (i MIN )132 and the maximum current density (i MAX )134 and run.

[0032] In one embodiment, the system of the present invention including a fuel cell or fuel cell stack can be used in conjunction with a Figure 1 In some embodiments, the system can be operated at a higher pressure (e.g., the maximum anode inlet manifold pressure (P AIM_HI )110) or at a current density as low as the critical current density (i _LO_CR )130. For example, the system can extend steady-state operation to the critical current density (i _LO_CR ) 130. Pressure measurements in bara refer to the absolute pressure in bar.

[0033] In one embodiment, excess fuel can be provided at the anode inlet to avoid fuel shortage towards the anode outlet. The water content of the anode inlet stream or the relative humidity of the inlet stream may affect the performance and health of the fuel cell. For example, low inlet humidity may cause the membrane electrode assembly (MEA) to dry out, thereby reducing performance. Low inlet humidity may also cause stress, which may cause permanent damage to the membrane electrode assembly (MEA). High humidity levels may cause overflow in the fuel cell, which may lead to local shortages and / or other effects that may reduce fuel cell performance and / or damage the membrane electrode assembly (MEA). In some embodiments, there may be an optimal inlet relative humidity range, wherein fuel cell performance is improved and membrane electrode assembly (MEA) degradation rate is minimized. For example, when the anode inlet gas relative humidity level is in the range of about 30% to about 35%, the fuel cell can achieve optimal performance.

[0034] In one embodiment, under normal operating conditions, the source of excess fuel and water content in the fuel cell can come from recirculated anode gas. The composition of the recirculation flow in an operating system depends on the composition of the anode gas outlet. In some embodiments, at a given anode gas outlet temperature and pressure, the anode outlet gas can be saturated with water. Therefore, the composition of the recirculation flow can vary and should be taken into account when determining the required recirculation flow to meet inlet anode gas excess fuel or relative humidity targets.

[0035] The desired recirculation flow rate level can be set based on the need for excess fuel or increased water content, either of which requires a higher recirculation flow. The desired recirculation flow can be expressed as a target entrainment ratio (ER). Alternatively, a target effective excess fuel ratio or minimum required fuel ratio can take into account the need for excess fuel or the inlet anode water content. "Excess fuel ratio" can be used to represent the required composition from the recirculation flow to meet the anode inlet gas requirements. The anode gas requirement can be the more stringent of the excess fuel ratio or relative humidity requirements of the fuel cell system.

[0036] The minimum required excess fuel ratio as a function of current density is indicated by line 140. The excess fuel ratio (λ) or anode stoichiometric ratio is defined as the ratio of the anode inlet fuel flow rate to the fuel consumed in the fuel cell or fuel cell stack. In some embodiments, the system requires a fuel quantity at or above the minimum required fuel ratio level. In other embodiments, a target water or humidity level may be required to operate the system, which may affect the excess fuel ratio (λ). Except at low current densities, for example at or below the excess fuel ratio current density threshold (i _λ_THV )150, the excess fuel ratio (λ) may be flat over the entire system operating range, or the excess fuel ratio (λ) may vary with current density. In some embodiments, above the excess fuel ratio current density threshold (i _λ_THV)150 may be in the range of about 1.3 to about 1.9, including any ratios subsumed therein. In a preferred embodiment, above the excess fuel ratio current density threshold (i _λ_THV )150 may have an excess fuel ratio (λ) of about 1.4 or about 1.6.

[0037] In some embodiments, the excess fuel specific current density threshold (I _λ_THV )150 may be at or about 0.2A / cm 2 In other embodiments, the excess fuel ratio current density threshold (i _λ_THV )150 can be at different current densities. For example, the excess fuel ratio current density threshold (i _λ_THV )150 can be from about 0.05A / cm 2 To about 0.4A / cm 2 In a preferred embodiment, the excess fuel ratio current density threshold (i _λ_THV )150 can be about 0.1A / cm 2 or about 0.2A / cm 2 Excess fuel ratio current density threshold (i _λ_THV )150 may depend on the operating conditions of the fuel cell or fuel cell stack.

[0038] In one embodiment, if the fuel cell or fuel cell stack is below the excess fuel specific current density threshold (i _λ_THV ) 150, a minimum volume flow rate can be maintained through the anode to ensure that any liquid water that may form in the fuel cell or fuel cell stack can be flushed out of the fuel cell or fuel cell stack. In some embodiments, at low flow rates (e.g., less than about 0.2 A / cm 2 or less than about 0.1A / cm 2 ), there may be flooding in the fuel cell. In other embodiments, if the minimum volume flow rate is lower than the excess fuel specific current density threshold (i _λ_THV )150, the rate of degradation of the fuel cell or fuel cell stack may increase.

[0039] In one embodiment, a venturi or ejector may be used in the system. The size of the venturi or ejector may be designed so that the system may not require the assistance of a recirculation pump (e.g., a blower) at certain current densities. The absence of a blower may result in a reduction in parasitic loads, such as by Figure 1As shown in curves 170 and 180, curve 170 shows the partial flow delivered by the blower and / or recirculation pump in the absence of a venturi or ejector. Curve 180 shows the corresponding parasitic load. In some embodiments, the parasitic load can increase with increasing current density, as shown by curve 180, because the blower and / or recirculation pump can operate at a capacity proportional to the pressure loss and the required recirculation flow rate in the fuel cell or fuel cell stack.

[0040] In some embodiments, the fuel cell or fuel cell stack may initially be operated at a high current density, high operating temperature, and high pressure, such that the fuel cell load under these initial operating conditions is high. The fuel cell load is defined as:

[0041] Load = Stack Power = Current x Fuel Cell or Fuel Cell Stack Voltage = Current Density x Fuel Cell Area x Fuel Cell or Fuel Cell Stack Voltage

[0042] In some embodiments, when the load demand for power decreases rapidly or decreases, the fuel cell or fuel cell stack is in a load shedding state, requiring the fuel cell or fuel cell stack to reduce the current delivered.

[0043] In one embodiment, during transient operation in a fuel cell or fuel cell stack, the operating pressure in the fuel cell or fuel cell stack may be varied based on changes in the fuel cell or fuel cell stack temperature indicated by curve 106. For example, during load shedding, the transient operating pressure (P _AIM_TRS ) may be greater than the steady-state operating pressure (P _AIM_SS In some embodiments, even at low current densities, the transient operating pressure (P _AIM_TRS ) can also be equal to the maximum anode inlet manifold pressure (P AIM_HI )110. During the load period, the rate of increase of current density is limited, and the steady-state operating pressure (P _AIM_SS ) may be equal to the anode inlet manifold pressure (P AIM ).

[0044] In one embodiment, the operating pressure of the fuel cell or fuel cell stack indicated by curve 160 can optimize the balance between achieving efficient fuel cell or fuel cell stack operation and the parasitic loads (e.g., parasitic loads of an air compressor, blower, and / or pump) required to operate at the selected operating pressure. In some embodiments, the operating temperature indicated by curve 106, the operating pressure indicated by curve 160, and / or the excess air ratio can maintain a target relative humidity (RH) for the operation of the fuel cell or fuel cell stack. In other embodiments, the operating temperature indicated by curve 106, the operating pressure indicated by curve 160, and / or the excess air ratio can be determined by targeting a specific value for the relative humidity (RH) at the cathode.

[0045] The definition of excess air ratio is similar to that of excess fuel ratio, but refers to the cathode side stream (i.e., excess O2 in air). The combination of excess air ratio, pressure, and temperature are used together to control the humidity on the cathode side (which in turn affects the water content on the anode (H2) side. In one embodiment, the humidity can be controlled using temperature, pressure, and excess air ratio that vary with current density. In some embodiments, the excess air ratio is about 2.0. In other embodiments, the excess air ratio is about 1.7 to about 2.1. In some other embodiments, the excess air ratio is about 1.8 to about 1.9 under pressurized operation. The excess air ratio may be increased below a threshold current to maintain a sufficiently high volumetric flow rate to prevent flooding in the fuel cell or fuel cell stack.

[0046] In some embodiments, a target relative humidity (RH) can be maintained by using a humidifier in conjunction with the operating pressure and operating temperature. For example, a humidifier can be used on the cathode side of a fuel cell or fuel cell stack. In other embodiments, if a target relative humidity (RH) and a target operating pressure for a fuel cell or fuel cell stack are specified, a target temperature for the fuel cell or fuel cell stack operation can be determined.

[0047] In one embodiment, a system including a fuel cell or fuel cell stack may include a control valve. In some embodiments, the control valve may be a mechanical regulator (e.g., a dome-regulated mechanical regulator), a proportional control valve, or an ejector. In other embodiments, the control valve may include an internal valve, a coil, a solenoid, or a different mechanical element that controls the opening or closing of the control valve.

[0048] Figure 2 An embodiment of an operating system 200 is shown, which includes a fuel cell stack 210, a mechanical regulator 250, a recirculation pump or blower 220 connected in series or in parallel with the fuel cell stack 210, an exhaust valve 280, a shutoff valve 270, a pressure transfer valve 290, one or more pressure sensors 240 / 260, and a venturi or ejector 230. In some embodiments, the system 200 may include one or more fuel cell stacks or one or more fuel cells. In other embodiments, one or more valves, sensors, compressors, regulators, blowers, injectors, ejectors, and / or other devices may also be connected in series or in parallel with the fuel cell stack 210.

[0049] In one embodiment of the present system 200, an anode inlet stream 222 flows through the anode 204 end of the fuel cell stack 210. Typically, the anode stream can be a mixture of fresh fuel (e.g., H2) and anode exhaust (e.g., H2 fuel and / or water). Conversely, an oxidant 206 (e.g., air, oxygen, or humidified air) can flow through the cathode end 208 of the fuel cell stack 210.

[0050] In one embodiment, the mechanical regulator 250 can be used to control the flow of fresh fuel 202, also referred to as primary flow, primary mass flow, primary fuel, or power flow, to the anode 204. The pressure difference between the gas flows (e.g., fuel 222 and air 206) at the anode 204 and cathode 208 can provide an input signal to a controller in the mechanical regulator 250. The controller of the mechanical regulator 250 can determine the flow of the fuel 222 through the anode inlet 212 at the anode 204.

[0051] In some embodiments, the input signal from the anode and / or cathode of the fuel cell or fuel cell stack can be a physical signal. In other embodiments, the input signal can be a virtual or electronic signal. In still other embodiments, the signal can be any type of communication or computer signal known in the art.

[0052] In one embodiment, the primary fuel flow rate or primary flow rate can be controlled based on the operating pressure (e.g., anode pressure) used as an intermediate signal to match fuel consumption in the fuel cell stack 210. In some embodiments, assuming all other parameters are equal, the pressure in the anode 204 can be stabilized when fuel consumption is matched to the fresh fuel supply at the anode 204. Since the function of the mechanical regulator 250 is based on the pressure difference between the anode 204 and the cathode 208, it is necessary to maintain a target pressure difference when using the mechanical regulator 250. In some embodiments, the pressure at the cathode 208 is controlled and / or maintained at a target level by cathode-side control.

[0053] In one embodiment, a mechanical regulation method, such as by employing an actuator, can use the pressure signal from the cathode / air inlet 216 to control the air mass flow and maintain the appropriate pressure on the cathode 208 side of the fuel cell stack 210. In some embodiments, the pressure signal from the cathode 208 side is an input to the mechanical regulator 250. In some embodiments, the anode 204 side mass flow and the anode 204 side pressure can be controlled by using the pressure signal from the cathode 208 side and measuring one or more anode 204 side conditions.

[0054] In one embodiment, a pressure signal from the cathode 208 side can change the position of a valve in the mechanical regulator 250 to control mass flow through the mechanical regulator 250 and maintain a target pressure differential between the anode 204 and cathode 208. In other embodiments, the input signal to the mechanical regulator 250 is actually a pressure differential across the diaphragm or other portion of the mechanical regulator 250. No other direct measurement of the pressure differential is required. For example, a single-point pressure at the anode 204 can be calculated as the pressure on the cathode 208 side plus the pressure difference between the gas flows at the anode 204 and cathode 208. The single-point pressure can be either absolute or gauge pressure.

[0055] In one embodiment, a venturi or ejector 230 can extract a secondary flow (entrained flow or recirculated flow) 226 from the anode gas recirculation (AGR) loop 224. In some embodiments, the anode gas recirculation loop 224 can include the venturi or ejector 230, the fuel cell stack 210, a secondary inlet 232 in a suction chamber in the venturi or ejector 230, and / or other pipes, valves, channels, manifolds associated with the venturi or ejector 230 and / or the fuel cell stack 210. In other embodiments, a recirculation pump or blower 220 can increase or decrease the pressure differential across the anode gas recirculation (AGR) loop 224.

[0056] In one embodiment, a venturi or ejector 230 can use the flow pressure across the anode gas recirculation (AGR) loop 224 to extract a secondary flow 226, also referred to as a secondary mass flow, entrained flow, or recirculated flow. In some embodiments, as discussed later, the venturi or ejector 230 can utilize the excess exergy available from the higher pressure primary flow to draw in the secondary flow 226, overcoming pressure losses through the AGR loop 224. In some embodiments, the AGR loop 224 can include the venturi or ejector 230, the fuel cell stack 210, a secondary inlet 232 in the intake chamber of the venturi or ejector 230, and / or other conduits, valves, passages, and manifolds associated with the venturi or ejector 230 and / or the fuel cell stack 210. In other embodiments, a recirculation pump or blower 220 can increase or decrease the pressure differential across the AGR loop 224.

[0057] In one embodiment, the system 200 may require a target water or humidity level that may drive the saturated secondary flow 226. The saturated secondary flow 226 may then drive the primary flow 202 such that a target excess fuel ratio (λ) may depend on the target water or humidity level.

[0058] In one embodiment, a recirculation pump or blower 220 can be used to achieve an excess fuel ratio. In some embodiments, the recirculation pump or blower 220 can operate over the entire operating range (current density) of the fuel cell stack 210. In other embodiments, the parasitic load of the recirculation pump or blower 220 may be very large. In one embodiment, a large recirculation pump or blower 220 may be required to provide power to achieve an excess target fuel ratio. In some embodiments, the use of the recirculation pump or blower 220 may be inefficient and expensive. In some embodiments, the operating characteristics of the recirculation pump or blower 220 may be different from a venturi tube or ejector 230.

[0059] In one embodiment, the pressure increase capability (ΔP _BLWR) is a function of the flow (Q) through the recirculation pump or blower 220, the blower speed (N), and the density (ρ) of the flow components. In some embodiments, the pressure increase 220 (ΔP _BLWR ) can be limited by power draw limitations and / or speed limitations of the system 200 / 300. In one embodiment, the recirculation pump or blower 220 can act as a limiter in the AGR loop when it is not rotating or in other system 200 / 300 stall conditions.

[0060] ΔP _BLWR =f(Q,N,ρ).

[0061] In one embodiment, Figure 3 . A proportional control valve 310 may be used in place of the mechanical regulator 250. The proportional control valve 310 is electronically controlled and may provide greater flexibility in controlling a single point pressure at the anode 204 than the mechanical regulator 250. In one embodiment, the proportional control valve 310 may be used to control the primary flow in the operating system 300. In other embodiments, an ejector (not shown) may be used in place of the proportional control valve 310.

[0062] For example, the proportional control valve 310 can advantageously allow for active management of pressure differentials, can avoid droop issues, and / or provide flexibility in operating the fuel cell stack 210 under different operating conditions. Illustrative operating conditions can include, but are not limited to, operating current density, operating pressure, operating temperature, operating relative humidity, fuel supply pressure, fuel supply temperature, desired secondary flow, entrainment ratio, parasitic load limitations, power demand, pressure loss in the AGR loop 224, performance and / or efficiency of the venturi or ejector 230, performance and / or efficiency of the recirculation pump or blower 220, fuel density, purge flow, and blocked or unblocked (e.g., no blockage) flow conditions.

[0063] The turndown ratio of the system 200 / 300 is defined as the ratio of the maximum capacity of the venturi or ejector 230 to the minimum capacity of the venturi or ejector 230. In one embodiment, the venturi or ejector 230 can use the primary flow exergy to extract the recirculation flow 226. The turndown ratio represents the range over which the venturi or ejector 230 can deliver a desired excess fuel ratio to the fuel cell stack 210. In one embodiment, the operating system 200 / 300 can be designed to maximize the turndown ratio of the venturi or ejector 230. Therefore, maximizing the turndown ratio of the venturi or ejector 230 can also be used to minimize the size and parasitic loads associated with the recirculation pump or blower 220. In some embodiments, the venturi or ejector 230 may need to operate and / or perform robustly to deliver the desired primary flow 202 at the desired excess fuel ratio.

[0064] In one embodiment, the fuel supply system can be operated at a fuel supply pressure (P CV ) and fuel supply temperature (T CV ) is supplied with fuel. In some embodiments, the size pressure (P _CV_MIN ) may be the minimum inlet pressure at a control valve, such as the proportional control valve 310 or the mechanical regulator 250 or the injector. In other embodiments, the fuel size pressure (P _CV_MIN ) can be the pressure at the inlet of the control valve under air pressure conditions (P EMPTY ).

[0065] In one embodiment, the primary flow 202 can be passed through a control valve and at a primary nozzle inlet pressure (P O ) and primary inlet temperature (T O ) through the primary nozzle into the venturi or ejector 230. In other embodiments, the secondary flow 226 may be at a secondary inlet pressure (P S ) and secondary inlet temperature (T S ) enters the venturi or ejector 230 through a secondary inlet 232 in the suction chamber.

[0066] In one embodiment, the venturi or ejector 230 may have available exergy in the primary flow to induce anode gas recirculation flow in the venturi or ejector 230 as the secondary flow 226. In some embodiments, the stack pressure (ΔP STACK ) is the pressure loss through the AGR loop 224. The secondary flow 226 can be boosted to overcome the stack pressure (ΔP STACK ).

[0067] In one embodiment, the pressure increase (ΔP LIFT ) is to overcome the pressure loss (ΔP STACK) required pressure. In some embodiments, the pressure increase (ΔP LIFT ) may be dominated by pressure losses through the fuel cell stack 210 or any other component of the AGR loop 224. In some embodiments, the pressure losses may be proportional to the volumetric flow rate through one or more manifolds and / or passages in the AGR loop 224. In other embodiments, the volumetric flow 222 at the anode inlet 212 may include a mixture of the fresh fuel 202 and the recirculated flow 226.

[0068] In one embodiment, the secondary inlet pressure (P S ) may depend on the anode inlet manifold pressure (P AIM ) and the pressure loss (ΔP STACK ) or required pressure increase (ΔP LIFT )

[0069] P S =P AIM -ΔP LIFT .

[0070] In one embodiment, the amount of secondary flow 226 that can be entrained is determined by the boundary conditions of the system 200 / 300 and the efficiency of the venturi or ejector 230. In some embodiments, the boundary condition can be the primary nozzle inlet pressure (P O ), secondary inlet pressure (P S ), anode inlet manifold pressure (P AIM ), and / or the composition of the secondary stream 226. In some embodiments, the secondary stream 226 from the anode outlet 214 to the venturi or ejector inlet 232 is an adiabatic process. In other embodiments, the primary inlet temperature (T O ) and secondary inlet temperature (T S ) can affect the secondary flow 226.

[0071] In one embodiment, as described above, at a certain critical current density (I _LO_CR )130 above, the system 200 / 300 needs to be Figure 1 In some embodiments, the primary inlet pressure (P O ) is reduced in proportion to the primary fuel demand until the primary nozzle is no longer blocked (unblocked). In other embodiments, if the primary nozzle is unblocked, the primary inlet pressure (P O ) may be non-linear and / or have a negative effect on the downstream pressure, such as the secondary inlet pressure (P S ) is sensitive. In other embodiments, the primary inlet pressure (PO ) can be adjusted with the primary inlet temperature (T O ) decreases and decreases.

[0072] In one embodiment, the primary inlet temperature (T O ) can be equal to the fuel supply temperature (T CV In some embodiments, the primary inlet temperature (T O ) can affect the primary flow 202. In some embodiments, the system 200 / 300 can have a target mass flow rate. In other embodiments, the secondary inlet temperature (T S ) can affect the secondary flow 226 by geometric constraints of the secondary inlet 232 and / or the venturi or ejector 230. In some other embodiments, thermodynamic constraints and / or venturi or ejector 230 efficiency can affect the secondary flow 226.

[0073] In one embodiment, the venturi or ejector 230 controls the primary nozzle inlet pressure (P O ), back pressure and required pressure rise (ΔP LIFT In some embodiments, the back pressure may be the exit pressure (P C ) or anode inlet manifold pressure (P AIM In other embodiments, if there is no pressure loss from the venturi or ejector 230 to the outlet anode inlet manifold, the exit pressure (P C ) can be equal to the anode inlet manifold pressure (P AIM In some embodiments, the primary nozzle inlet pressure (P O ) can be a function of the current density (i) in the system 200 / 300

[0074] P O =f(i).

[0075] In one embodiment, the entrainment ratio (ER) is a measure of the performance and / or capacity of the venturi or ejector 230 and may be a function of the primary nozzle inlet pressure (P O ), back pressure (e.g., P C 、P AIM ) and / or pressure rise (ΔP LIFT ) sensitive. In one embodiment, as the back pressure (e.g., P C 、P AIM) increases, the venturi or ejector 230 may go from being double blocked (with a stable entrainment ratio) to being in a transitional state (with a reduced entrainment ratio) with reverse flow. Reverse flow in the venturi or ejector 230 may be undesirable because reverse flow indicates that no fuel is being recirculated through the AGR loop 224. In some embodiments, the venturi or ejector 230 may need to offset the pressure loss (ΔP) across the fuel cell or fuel cell stack 210. STACK ), while overcoming back pressure (e.g., P C 、P AIM )run.

[0076] In one embodiment, the reversible entrainment ratio (RER) or the reversible portion of the entrainment ratio (ER) is based on thermodynamic constraints and is defined as:

[0077] RER=-Δ χ_M / Δ χ_S

[0078] Δ x_M is the effective energy of power flow, Δ x_S is the effective energy of the entrainment flow.

[0079] In one embodiment, if the minimum and maximum anode inlet manifold pressures (P AIM_LO 120 and P AIM_ HI 110) is known, the minimum anode inlet manifold pressure P can be determined AIM_LO The low breakpoint (i.e. current density) where 120 is located (i _LO_BRK ) and the maximum anode inlet manifold pressure P AIM_HI The high breakpoint (i.e. current density) where 110 is located (i _HI_BRK ).

[0080] Figure 4A shows the operating range of the venturi or ejector 230 under choked conditions, while Figure 4B The operating range of the venturi or ejector 230 is shown in Figure 2 under blocked and unblocked conditions. Figure 4A As shown in FIG. 1 and B, curve 160 indicates the target anode inlet manifold pressure range determined by the fuel cell stack design. Above the critical current density (I _LO_CR ) 130, it may be necessary to operate the system 200 / 300 within a target anode inlet manifold pressure range that is within the range indicated by 160. In the illustrated embodiment, the critical current density (i _LO_CR )130 is about 0.7A / cm 2 The maximum anode inlet manifold pressure (P AIM ) is the maximum ejector pressure (P_AIM_EJCT_MAX ) as a function of current density is shown by curve 410. The maximum injector pressure (P _AIM_EJCT_MAX ) for the primary inlet temperature (T O )sensitive.

[0081] Maximum injector pressure (P _AIM_EJCT_MAX ) may vary depending on the limitations and range of the fuel supply system. In one embodiment, the maximum injector pressure (P _AIM_EJCT_MAX ) curve 410 and the maximum anode inlet manifold pressure (P AIM_HI )110 intersection is defined as the high current density injector threshold (i _HI_THV ) 464. In one embodiment, the maximum injector pressure (P _AIM_EJCT_MAX ) curve 410 and the minimum anode inlet manifold pressure (P AIM_HI )120 The current density at the intersection is defined as the low current density injector threshold (i _LO_THV )460.

[0082] In one embodiment, if the maximum injector pressure (P _AIM_EJCT_MAX ) is greater than the anode inlet manifold pressure (P AIM ), the venturi or ejector 230 can operate in a primary nozzle blocked condition, which is a robust ejector condition. In some embodiments, although if the anode inlet manifold pressure (P AIM ) than the maximum injector pressure (P _AIM_EJCT_MAX ) a larger venturi or ejector 230 can still entrain flow, the venturi or ejector 230 can become more sensitive to boundary conditions. In other embodiments, if the anode inlet manifold pressure (P AIM ) is greater than the maximum injector pressure (P _AIM_EJCT_MAX ), the ability of the venturi or ejector 230 to continue to meet the entrainment ratio (ER) requirement may become dependent on the pressure rise (ΔP_ LIFT ) is more sensitive.

[0083] In one embodiment, the venturi or ejector 230 configuration may be sized to provide a current density at the critical current density (i _LO_CR) 130, while taking into account the pressure difference across the AGR circuit 224. In some embodiments, the venturi or ejector 230 configuration can be sized to fully deliver the recirculation flow 226 without the assistance of the recirculation pump or blower 220. As shown by curves 170 and 440, not using the recirculation pump or blower 220 can result in a reduction in parasitic loads. Curve 170 shows the portion of the recirculation flow delivered by the recirculation pump or blower 220, and curve 440 shows the corresponding parasitic savings. Curve 440, which illustrates the parasitic savings 440, is inversely proportional to curve 170, which illustrates the portion of the recirculation flow delivered by the recirculation pump or blower 220.

[0084] In a preferred embodiment, the venturi or ejector 230 is designed so that the venturi or ejector 230 can continue to robustly meet any entrainment ratio (ER) requirements at low current densities. In some embodiments, at current densities as low as Figure 4A and Figure 4B The excess fuel ratio current density threshold (I _λ_THV ) 150, the venturi or ejector 230 is able to continue to meet the entrainment ratio (ER) requirement. The benefit of a configuration in which the venturi or ejector 230 can continue to meet the entrainment ratio (ER) requirement at such low current densities is illustrated by the curve showing parasitic savings 440. In one embodiment, the venturi or ejector 230 and the recirculation pump or blower 220 can be operated simultaneously. In other embodiments, the recirculation pump or blower 220 can be smaller in size to increase parasitic savings and / or reduce the cost, size, or weight of the system 200 / 300.

[0085] In one embodiment, Figure 2 and 3 As shown in , if the recirculation pump or blower 220 is upstream of the venturi or ejector 230, the flow rate (Q) through the recirculation pump or blower 220 corresponds to the recirculation flow through the anode recirculation loop 224. For example, if the entrainment ratio (ER) is equal to 2.0, the flow (Q) through the recirculation pump or blower 220 is 2 / 3 of the total fuel 222 flow (primary fuel flow 202 + recirculated fuel flow 226).

[0086] In one embodiment, the venturi or ejector 230 and the recirculation pump or blower 220 may be optimally integrated and / or sized to enhance the operation and / or performance of the venturi or ejector 230 in the fuel cell stack 210. In some embodiments, the recirculation pump or blower 220 may be sized to deliver a pressure rise (ΔP LIFT) to offset any pressure losses through the anode recirculation loop 224. In other embodiments, the recirculation pump or blower 220 may be sized to support the operation and / or performance of the venturi or ejector 230 in the fuel cell stack 210 under varying operating conditions. Operating conditions may include, but are not limited to, pseudo-steady-state conditions and transient conditions or conditions.

[0087] In one embodiment, the recirculation pump or blower 220 can exist in different operating states. In one embodiment, the recirculation pump or blower 220 can be in an idle state 484 and the venturi or ejector 230 can operate without the support of the recirculation pump or blower 220.

[0088] In one embodiment, the recirculation pump or blower 220 may be in a blower base state 480, ie, the current density may be below the excess fuel ratio current density threshold (i _λ_THV ). Under such conditions, the performance and / or operation of the venturi or ejector 230 may be challenged, and the venturi or ejector 230 may be operated with the support of the recirculation pump or blower 220. In one embodiment, the recirculation pump or blower 220 may deliver the required recirculation flow primarily through the recirculating anode loop 224. In other embodiments, the blower pressure (ΔP BLWR ) can be adjusted to provide sufficient recirculation stream fuel flow to match the excess fuel requirement of the fuel cell stack 210 in the system 200 / 300.

[0089] In one embodiment, the recirculation pump or blower 220 may be in the ejector support state 482, wherein the venturi or ejector 230 may be pressurized by the recirculation pump or blower 220. The current density may be greater than the excess fuel current density threshold (I _λ_THV ) but less than the minimum anode inlet manifold pressure (P AIM_LO )120 can be set to a low breakpoint current density (i _LO_BRK A recirculation pump or blower 220 may provide a portion of the recirculation flow.

[0090] like Figure 5 As shown in FIG, the venturi or ejector 230 operates at a steady state pressure (P _AIM_SS The lowest current density that is blocked under the condition of _LO_ACT ) 520. When the recirculation pump or blower 220 is in the idle state 484, that is, the operating current density is greater than the minimum blocking current density (i _LO_ACT )520, or when the blower is in the basic state, that is, the operating current density is far lower than the excess fuel ratio current density threshold (i _λ_THV) 150, or when the system 200 / 300 is being blower-pressurized in the injector support state 582, the system 200 / 300 can operate under pseudo-steady-state conditions. When the system 200 / 300 is in the injector support state 582, the system 200 / 300 can operate under pseudo-steady-state conditions when the system 200 / 300 is greater than the excess fuel current density threshold (i _λ_THV )150 but less than the minimum blocking current density (i _LO_ACT )520. In some embodiments, the minimum blocking current density (i _LO_ACT )520 can be equal to the critical current density (i _LO_CR )130.

[0091] In one embodiment, the system 200 / 300 may be operated in a transient state or condition such as a load shedding support state, where the target operating pressure (P AIM ) is greater than the steady-state operating pressure (P _AIM_SS ) so that the primary inlet nozzle is not clogged. In other embodiments, the system 200 / 300 can be operated in a transient state or condition, such as a load-supported state, where the rate of increase of the current density (i) is greater than a certain threshold, such as 0.2 A / cm per second. 2 In some embodiments, the system 200 / 300 can operate during transient conditions such as system 200 / 300 startup or system 200 / 300 shutdown. In one embodiment, the recirculation pump or blower 220 is sized so that the operation and / or performance of the venturi or ejector 230 can be increased when needed. In some embodiments, this increased capacity of the venturi or ejector 230 may impose higher costs and higher parasitic loads on the system 200 / 300.

[0092] In one embodiment, the recirculation pump or blower 220 is sized to support the system 200 / 300 at a minimum level when the recirculation pump or blower 220 is in a base state and during system 200 / 300 startup or system 200 / 300 shutdown when the venturi or ejector 230 is unable to deliver the required fuel flow rate. In other embodiments, the recirculation pump or blower 220 is sized to support the pressure differential across the fuel cell stack 210 when the system 200 / 300 is in a transient state or condition such as a load shedding support state.

[0093] In one embodiment, Figure 5 As shown in FIG, the venturi or ejector 230 can be operated without blower support and at a blower threshold current density (i _BS_THV )522 above, when the system 200 / 300 is not blocked, the turndown ratio (TD) can be managed by the venturi or ejector 230 RATIO )equal:

[0094] TD RATIO =i _BS_THV / i _LO_ACT .

[0095] When the operating pressure (P AIM ) is the maximum operating pressure (P_ AIM_HI )110, the lowest current density threshold at which the venturi or injector 230 is blocked is the high current injector threshold (i _HI_THV ) 464. In one embodiment, if the venturi or ejector 230 needs to be operated at the maximum operating pressure (P_ AIM_HI ), the venturi or ejector 230 may be lowered to a value equal to the high current ejector threshold (i _HI_THV )464. The venturi tube or ejector 230 may not be blocked at this current density. Due to this current density, if the operating pressure (P AIM ) is maintained at the maximum operating pressure (P_ AIM_HI ) 110, the system 200 / 300 may require a recirculation pump or blower 220 to provide blower support. In some embodiments, for the same turndown ratio (TD RATIO ), from equal to the transition blower threshold current density (i _BS_TRNS_THV ) 524 may begin to require support from the recirculation pump or blower 220. In other embodiments, the upper limit of the ejector support state 582 is determined by the transition blower threshold current density (i _BS_TRNS_THV )524 Definition

[0096] i _BS_TRNS_THV =i _BS_THV / i _LO_ACT xi _HI_THV .

[0097] In one embodiment, if the venturi or injector 230 can be operated at a current density equal to the excess fuel specific current density threshold (i _λ_THV )150 blower threshold current (i _BS_THV )522 and above run without blower support,

[0098] i _BS_TRNS_THV =i _λ_THV / i _LO_ACT xi _HI_THV .

[0099] The recirculation pump or blower 220 is sized to provide flow in the event that the venturi or ejector 230 itself cannot provide all the fuel flow. In one embodiment, during operation of the system 200 / 300 when the support of the recirculation pump or blower 220 is not needed, the recirculation pump or blower 220 may act as a restriction and cause a pressure loss in the anode recirculation loop 224. In some embodiments, the recirculation pump or blower 220 may need to be oversized to pass the primary anode inlet manifold pressure (e.g., (P_)) during unloading transients or conditions or when the system 200 / 300 is operating at high primary anode inlet manifold pressures (e.g., (P_)). AIM_HI )110) when running at reduced pressure (ΔP_ LIFT ) is required to support the venturi or ejector 230.

[0100] In one embodiment, the recirculation pump or blower 220 is sized to match the blower threshold current density (i _BS_THV )522 and / or transition blower threshold current density (i _BS_TRNS_THV ) 524. In other embodiments, the size of the recirculation pump or blower 220 may be proportional to the blower threshold current density (i _BS_THV )522 and / or transition blower threshold current density (i _BS_TRNS_THV ) 524 is not linearly proportional. In some embodiments, the size of the recirculation pump or blower 220 may depend on the mass flow rate through the recirculation pump or blower 220.

[0101] In one embodiment, the size of the recirculation pump or blower 220 may depend on variables including, but not limited to, the entrainment ratio (ER) of the system 200 / 300, the excess fuel ratio (λ) of the system 200 / 300, the density of the fuel components flowing through the recirculation pump or blower 220, the density of the fuel components flowing through the fuel cell or fuel cell stack 210, the anode inlet manifold pressure (P AIM ), the operating temperature of the system 200 / 300, the mass flow through the system 200 / 300, and / or the entrained flow through the recirculation pump or blower 220.

[0102] In one embodiment, the venturi or ejector 230 may have a robust entrainment ratio (ER) due to one or more controllers of the venturi or ejector 230 and the recirculation pump or blower 220. In some embodiments, one or more controllers of the venturi or ejector 230 and the recirculation pump or blower 220 may allow the system 200 / 300 to monitor the status of the venturi or ejector 230 and initiate startup and / or increase the speed of the recirculation pump or blower 220 when support is needed.

[0103] In some embodiments, the recirculation pump or blower 220 may be in an idle state 584 / 484, ie, in a high load pseudo steady state, such that the current density is above the low current injector threshold (i _LO_THV ) 460. In some embodiments, when the system 200 / 300 is operating at a current above the low current injector threshold (I _LO_THV ) 460, the venturi or ejector 230 may be able to deliver the desired entrainment ratio (ER).

[0104] In one embodiment, one or more controllers for the venturi or ejector 230 and the recirculation pump or blower 220 may allow the system 200 / 300 to monitor the status of the venturi or ejector 230 and, when support is needed, initiate startup and / or increase the speed of the recirculation pump or blower 220. In some embodiments, during startup and / or shutdown of the recirculation pump or blower 220, there may be a mismatch between the pressure provided by the recirculation pump or blower 220 and the pressure required by the venturi or ejector 230.

[0105] In one embodiment, one or more controllers for monitoring and / or controlling the operation of the venturi or ejector 230 and / or the recirculation pump or blower 220 in the system 200 / 300 may be implemented to communicate, in some cases, with hardware, firmware, software, or any combination thereof, residing on or external to the system 200 / 300 including the fuel cell or fuel cell stack 210. Such communication may be accomplished using any one or more communication technologies (e.g., wired or wireless communication) and associated protocols (e.g., Ethernet, InfiniBand®, Wi-Fi®, Bluetooth®, WiMAX, 3G, 4G LTE, 5G, etc.) to transmit information to the one or more controllers.

[0106] In one embodiment, one or more controllers may be in a computing device. The computing device may be embodied as any type of computing or computer device capable of performing the functions described herein, including but not limited to servers (e.g., standalone, rack-mounted, blade, etc.), network devices (e.g., physical or virtual), high-performance computing devices, network appliances, distributed computing systems, computers, processor-based systems, multi-processor systems, smartphones, tablets, laptops, notebook computers, and mobile computing devices.

[0107] A computing device may include an input / output (I / O) subsystem, a memory, a processor, a data storage device, a communication subsystem, a controller, and a display. In other embodiments, a computing device may include additional and / or alternative components, such as those commonly found in computers (e.g., various input / output devices). In other embodiments, one or more of the illustrative components may be incorporated into another component or otherwise form part of another component. For example, a memory or portion thereof may be incorporated into a processor.

[0108] In one embodiment, the system 200 / 300 can operate in a transient state, such as a load shedding state, a startup state, or a shutdown state. In some embodiments, the system 200 / 300 can operate in a transient hysteresis state, such that the pressure or temperature of the fuel cell or fuel cell stack 210 can lag behind the pressure or temperature of the fuel cell or fuel cell stack 210 in the transient state. For example, in some embodiments, during a transient state, the system 200 / 300 can be in a transient hysteresis state, where the system can support the current density required by the transient state or condition, but the operating temperature of the fuel cell or fuel cell stack 210 may take some time to decrease.

[0109] In one embodiment, the system 200 / 300 can maintain the current density generation above a minimum current density while reducing the fuel cell operating temperature. In some embodiments, the minimum current density can be the current density at the instantaneous break point (i _TRS_BRK Targeting minimum density during transient operation may avoid the need for a large recirculation pump or blower 220.

[0110] In one embodiment, when the system 200 / 300 is in a transient hysteresis state, the system 200 / 300 may enter a region where the venturi or ejector 230, along with the recirculation pump or blower 220, cannot support the desired current density. In some embodiments, one or more controllers of the venturi or ejector 230 and the recirculation pump or blower 220 may select to operate the system 200 / 300 at a current density higher than the desired current density, causing the system 200 / 300 to generate more energy than desired. In other embodiments, one or more controllers of the venturi or ejector 230 and the recirculation pump or blower 220 may select to operate the system 200 / 300 at a current density lower than the desired current density, causing the system 200 / 300 to generate less energy than desired.

[0111] In one embodiment, if the system 200 / 300 is operating at a current density lower than the required current density, the system 200 / 300 can use energy from a storage device such as a battery to provide the required current density. In some embodiments, the system can use energy from a supercapacitor, a superconductor, via a lithium-ion battery, a lead-acid battery, a flywheel, compressed air, or a phase change material.

[0112] In one embodiment, if the system 200 / 300 is operated at a current density higher than the desired current density, the excess power generated while maintaining the current density above the desired current density can be transferred to an energy storage device such as a battery for storage. In some embodiments, the excess power can be stored as potential energy or kinetic energy. For example, the excess power can be stored as electrical energy via supercapacitors and / or superconductors, as electrochemical energy via lithium-ion batteries and / or lead-acid batteries, as mechanical energy via flywheels and / or compressed air, or as thermal energy via phase change materials.

[0113] In one embodiment, the additional power generated can be dissipated by increasing parasitic loads. For example, the vehicle system cooling fan load can be increased by spinning the cooling fan faster, and the air compressor load can be increased by increasing the bypass air flow around the fuel cell or fuel cell stack. In other embodiments, the energy can be dissipated as heat (e.g., through a resistor).

[0114] In one embodiment, if the system includes multiple fuel cell stacks, the system may choose to operate one set of fuel cell stacks at an upper threshold value of the system power demand and operate the remaining fuel cell stacks at a lower threshold value of the system power demand so that the total power generated meets the required power demand. For example, the system may include two stacks of equal size. Under load shedding conditions where the recirculation pump or blower 220 cannot operate, and when the power demand is halfway between the upper and lower threshold values, the system may choose to operate one stack at the lower threshold value and the other stack at the upper threshold value. The net power generated by the system meets the power demand, so there may be no need to store the additional generated power. In some embodiments, if the power generated by the system is greater than the demand, the additional power may be stored. In other embodiments, if the power generated by the system is less than the demand, the system may use the stored power.

[0115] In one embodiment, the system 200 / 300 may include a battery for storing excess power. In other embodiments, the battery for storing excess power may be external to the system 200 / 300. In some embodiments, the generated power may be transmitted via a physical entity such as a wire. In other embodiments, the generated power may be transmitted wirelessly. In some embodiments, the state of charge (SOC) of the battery may determine the ability of the system 200 / 300 to transmit any generated power to the battery and / or to store energy in the battery.

[0116] In one embodiment, the power generated during the transient state or condition is:

[0117] power _TRANSIENT =I _TRANSIENT x V _TRANSIENT

[0118] In one embodiment, the energy generated over a period of time (Δt) is:

[0119] energy _TRANSIENT =I _TRANSIENT x V _TRANSIENT x Δt

[0120] V _TRANSIENT is the total voltage 210 of the fuel cells included in the fuel cell stack, and I _TRANSIENT is the total current density under transient conditions. In one embodiment, the fuel stack 210 of the system 200 / 300 may include about 150 to about 250 fuel cells, about 250 to about 450 fuel cells, or about 350 to about 650 fuel cells, including each number of fuel cells contained therein. In other embodiments, the fuel stack 210 of the system 200 / 300 may include fewer than 150 fuel cells or more than 450 fuel cells.

[0121] In one embodiment, if the voltage of a single fuel cell is about 0.8 V, and the fuel cell stack 210 includes about 320 fuel cells, the total voltage of the fuel cell stack 210 is:

[0122] V _TRANSIENT =0.8 x 320=256V.

[0123] In one embodiment, the total current density (I _TRANSIENT ) depends on the area of ​​the fuel cell stack 210 and the current density in the transient state. The area of ​​the fuel cell stack 210 may depend on various operating conditions and / or power generation requirements of the system 200 / 300. In one embodiment, if the area of ​​the fuel cell stack 210 is about 608 cm 2, then the current density at the instantaneous break point (i _TRS_BRK ) is about 0.25A / cm 2 , the total current density under transient conditions (I _TRANSIENT )yes:

[0124] I _TRANSIENT =0.25 x 608=152A.

[0125] In one embodiment, the fuel cell stack area may be approximately 50 cm 2 to about 1000cm 2 , about 350cm 2 to about 500cm 2 , or about 500cm 2 to about 900cm 2 range, including every size contained therein.

[0126] In one embodiment, the system 200 / 300 may be in a transient state for less than 5 seconds. The power generated during the period when the system is in a transient state or condition (e.g., 5 seconds) is:

[0127] power _TRANSIENT =I _TRANSIENT x V _TRANSIENT =38.9kW

[0128] energy _TRANSIENT =I _TRANSIENT x V _TRANSIENT x Δt=0.54kWh

[0129] In some embodiments, the system 200 / 300 can be in a transient state or state for about 2 seconds to about 5 seconds, from about 5 seconds to about 10 seconds, from about 10 seconds to about 20 seconds, including each duration subsumed therein.

[0130] In one embodiment, if the required current density (i _DEMAND ) is zero, then the current density at the instantaneous break point (i _TRS_BRK ) can be stored in the battery. In some embodiments, if the state of charge (SOC) of the battery allows energy storage, the current density (i _TRS_BRK )The total power generated can be stored in the battery.

[0131] In one embodiment, the primary anode inlet manifold pressure (P AIM ) can be in a transient state or condition for the duration that the system 200 / 300 can be in the transient state or condition. In some embodiments, the current density at the transient break point (i _TRS_BRK ) can be compared with the instantaneous primary anode inlet manifold pressure (P_AIM_TRS ). In some embodiments, the energy generated during a transient state or a transient hysteresis state may depend on the number of fuel cell stacks used. A single fuel cell stack may generate approximately 0.0025 kWh to approximately 2 kWh of energy. A small fuel cell stack may generate approximately 0.0025 kWh to approximately 0.05 kWh of energy. A medium-sized fuel cell stack may generate approximately 0.05 kWh to approximately 1 kWh of energy. A large fuel cell stack may generate approximately 1 kWh to approximately 2 kWh of energy.

[0132] In one embodiment, if the area is about 400 cm 2 There are about 100 fuel cells in the fuel cell stack at 0.6A / cm 2 The energy generated by using a current (i) of 0.004 kWh and a voltage of 0.6 V for 1 second is about 0.004 kWh per fuel pile. In another embodiment, if the area is about 500 cm 2 There are about 420 fuel cells in the fuel cell stack at 0.8A / cm 2 The energy generated is about 0.2 kWh per fuel stack if the current (i) is 0.8 V and the voltage is 0.8 V for 5 seconds. In another embodiment, if the area is about 900 cm 2 There are about 650 fuel cells in the fuel cell stack at 1A / cm 2 The energy generated is about 1.3 kWh per fuel stack when the current (i) is 0.8 V and the voltage is 0.8 V for 10 seconds.

[0133] In one embodiment, the current density at the instantaneous break point (i _TRS_BRK ) can be slowly reduced. In some embodiments, if there is no storage available in the energy storage device in the system 200 / 300, the system 200 / 300 may not be able to deliver the required current because additional storage may not be possible. In some embodiments, electrical energy or waste heat from the fuel cell or fuel cell stack 210 can be transferred to a heater or other heat storage / use device such as a resistor. In other embodiments, heat from a heater, other heat storage / use device, such as resistive heating or a heat exchanger can be used to heat the primary inlet temperature (T O In some embodiments, if the primary inlet temperature (T O ) is heated, the primary nozzle inlet pressure (P O ) may need to be increased to compensate for temperature changes. In some embodiments, compensation can reduce the size of the recirculation pump or blower 220 required for the entrainment ratio (ER). In some embodiments, the flow in the cathode air side can be managed based on the operating current density. For example, when the system 200 / 300 is operating in a transient state or a transient hysteresis state, the air flow can be managed to ensure that the humidification state is maintained at upper and lower operating current densities.

[0134] The following numbered embodiments are contemplated and are non-limiting:

[0135] 1. A fuel cell stack system comprising an ejector, wherein the system operates in a transient hysteresis state and the system needs to operate at a first operating current density that the ejector cannot support, and wherein the system operates at a second operating current density.

[0136] 2. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of the suitable clauses, comprising a blower, wherein the system operates in a transient hysteresis condition and the system is required to operate at a first operating current density that the injector cannot support, and wherein the system operates at a second operating current density.

[0137] 3. The fuel cell stack system of clause 1, any other suitable clause, or any combination of suitable clauses, wherein the temperature or pressure of the fuel cell stack is decreasing while the system is operating in the transient hysteresis condition.

[0138] 4. The fuel cell stack system of clause 1, any other suitable clause, or any combination of the suitable clauses, comprising a controller, wherein the controller determines a second operating current density of the system.

[0139] 5. The fuel cell stack system of clause 4, any other suitable clause, or any combination of suitable clauses, wherein the second operating current density is higher than the first operating current density.

[0140] 6. The fuel cell stack system of clause 4, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power when operated at the second operating current density.

[0141] 7. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power, and wherein the excess power generated is dissipated or stored in an energy storage device for a period of time.

[0142] 8. The fuel cell stack system of clause 7, any other suitable clause, or any combination of the suitable clauses, wherein the energy storage device is a supercapacitor, a superconductor, a lithium-ion battery, a lead-acid battery, a flywheel, compressed air, or a phase change material.

[0143] 9. The fuel cell stack system of clause 7, any other suitable clause, or any combination of suitable clauses, wherein the energy storage device is a battery having a state of charge.

[0144] 10. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power, and wherein storage of the generated excess power is dependent on the state of charge of the battery.

[0145] 11. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power, and wherein the excess power is stored as kinetic energy, potential energy, chemical energy, electrical energy, electrochemical energy, mechanical energy, or thermal energy.

[0146] 12. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, comprising a controller, wherein the controller determines a second operating current density of the system and a third operating current density of the system, and wherein the third operating current density is lower than the first operating current density.

[0147] 13. The fuel cell stack system of clause 12, any other suitable clause, or any combination of suitable clauses, wherein when operating at the third operating current density, the system uses energy from the energy storage device.

[0148] 14. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system operates in a transient hysteresis state after a transient state such as a load shedding support state, wherein the target operating pressure (P AIM ) is greater than the steady-state operating pressure (P _AIM_SS ) so that the primary inlet nozzle will not be blocked.

[0149] 15. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system operates in a transient hysteresis state after a transient state such as a load-supporting state, wherein the rate of increase of the current density (i) is greater than a threshold value, such as 0.2 A / cm2 per second. 2 .

[0150] 16. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system operates in a transient hysteresis state following a transient state such as system startup or system shutdown.

[0151] 17. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system operates at a first current density that is higher than a desired current density such that the system produces more energy than desired.

[0152] 18. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system operates at a first current density that is lower than a desired current density such that the system produces less energy than desired.

[0153] 19. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power and the generated excess power is consumed by an increased parasitic load.

[0154] 20. The fuel cell stack system of clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power and the generated excess power is consumed by a vehicle system cooling fan or air compressor.

[0155] 21. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power and the generated excess power is dissipated as heat.

[0156] 22. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system comprises a plurality of fuel cell stacks.

[0157] 23. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system operates one set of fuel cell stacks at an upper threshold of the system power demand and operates the remaining fuel cell stacks at a lower threshold of the system power demand so that the total power generated meets the required power demand.

[0158] 24. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the power generated in the transient state or in the transient hysteresis state is:

[0159] power _TRANSIENT =I _TRANSIENT x V _TRANSIENT

[0160] V _TRANSIENT is the total voltage of the fuel cells included in the fuel stack system, and I _TRANSIENT is the total current density in the instantaneous state.

[0161] 25. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the energy generated during the time period (Δt) is:

[0162] energy _TRANSIENT =I _TRANSIENT x V_TRANSIENT x Δt

[0163] V _TRANSIENT is the total voltage of the fuel cells included in the fuel stack system, and I _TRANSIENT is the total current density in the instantaneous state.

[0164] 26. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein if the demand current density (i _DEMAND ) is zero, then the current density at the instantaneous break point (i _TRS_BRK )The total power generated can be stored in the battery.

[0165] 27. A fuel cell stack system according to clause 26, any other suitable clause, or any combination of suitable clauses, wherein the current density at the instantaneous break point (i _TRS_BRK ) slowly decreases.

[0166] 28. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system includes an energy storage device, and if the energy storage device has no available storage, the system does not deliver the required current because additional storage is not possible.

[0167] 29. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of the suitable clauses, wherein electrical energy or waste heat from the system is transferred to a heater or other heat storage / use device, such as a resistor.

[0168] 30. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein heat from a heater, other heat storage / use device, such as resistive heating or a heat exchanger, is used to heat the primary inlet temperature (T O ).

[0169] 31. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein if the primary inlet temperature (T O ) is heated, the primary nozzle inlet pressure (P O ) increases to compensate for temperature changes.

[0170] 32. A fuel cell stack system according to clause 31, any other suitable clause, or any combination of suitable clauses, wherein the compensation reduces the size of the blower required for the entrainment ratio (ER).

[0171] 33. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein flow in the cathode side can be managed according to operating current density.

[0172] 34. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein when the system operates in a transient hysteresis condition, air flow is managed to ensure that humidification is maintained at upper and lower operating current densities.

[0173] 35. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the injector is sized to _LO_CR ) to fully convey the recirculation flow.

[0174] 36. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the ejector is sized to deliver complete recirculation without the assistance of a blower.

[0175] 37. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of the suitable clauses, wherein the system further comprises a blower optimally integrated and / or sized to enhance operation and / or performance of the ejector.

[0176] 38. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system further comprises a blower sized to deliver a pressure increase (ΔP LIFT ) to offset any pressure losses through the anode recirculation loop.

[0177] 39. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the transient hysteresis state follows a pseudo-steady state or transient state.

[0178] 40. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of the suitable clauses, wherein the system further comprises a blower operating in an idle state, in a blower base state, or in an ejector support state.

[0179] 41. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein not using a blower results in a reduction in parasitic loads.

[0180] 42. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of suitable clauses, wherein the system comprises a humidification device.

[0181] 43. A fuel cell stack system according to clause 42, any other suitable clause, or any combination of the suitable clauses, wherein a target relative humidity (RH) is maintained by using a humidifying device in conjunction with operating pressure and operating temperature.

[0182] 44. A fuel cell stack system according to clause 1, any other suitable clause, or any combination of the suitable clauses, wherein the system comprises a mechanical regulator, proportional control valve, or injector.

[0183] 45. A method of operating a fuel cell stack system, comprising:

[0184] Operating the fuel cell stack under transient hysteresis,

[0185] determining a first operating current density for the system, the first operating current density being an operating current density required by the system and not supported by the injector,

[0186] Determine the second operating current density of the system,

[0187] The system is operated at a second operating current density.

[0188] 46. ​​The method of clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system further comprises a blower, and wherein the ejector or the blower is unable to support the first operating current density.

[0189] 47. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the temperature or pressure of the fuel cell stack is reduced while the system is operating in the transient hysteresis state.

[0190] 48. The method of clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system further comprises a controller, wherein the controller determines a second operating current density of the system.

[0191] 49. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the second operating current density is higher than the first operating current density.

[0192] 50. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power when operating at the second operating current density.

[0193] 51. A method as recited in clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power, and wherein the excess power generated is dissipated or stored in an energy storage device for a period of time.

[0194] 52. The method of clause 51, any other suitable clause, or any combination of the suitable clauses, wherein the energy storage device is a supercapacitor, a superconductor, a lithium-ion battery, a lead-acid battery, a flywheel, compressed air, or a phase change material.

[0195] 53. The method of clause 51, any other suitable clause, or any combination of suitable clauses, wherein the energy storage device is a battery having a state of charge.

[0196] 54. A method as recited in clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system generates excess power, and wherein storage of the generated excess power is dependent upon a state of charge of the battery.

[0197] 55. A method according to clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system generates excess power, and wherein the excess power is stored as kinetic energy, potential energy, chemical energy, electrical energy, electrochemical energy, mechanical energy, or thermal energy.

[0198] 56. A method of clause 45, any other suitable clause, or any combination of suitable clauses, comprising a controller, wherein the controller determines a second operating current density for the system and a third operating current density for the system, and wherein the third operating current density is lower than the first operating current density.

[0199] 57. The method of clause 56, any other suitable clause, or any combination of the suitable clauses, wherein when operating at the third operating current density, the system uses energy from the energy storage device.

[0200] 58. A method according to clause 45, any other appropriate clause, or any combination of appropriate clauses, wherein the system operates in a transient hysteresis state after a transient state such as a load shedding support state, wherein the target operating pressure (P AIM ) is greater than the steady-state operating pressure (P _AIM_SS ) so that the primary inlet nozzle will not be blocked.

[0201] 59. A method according to clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system operates in a transient hysteresis state after a transient state such as a load-supported state, wherein the rate of increase of the current density (i) is greater than a threshold value, such as 0.2 A / cm2 per second. 2 .

[0202] 60. A method as defined in clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system operates in a transient hysteresis state following a transient state such as system startup or system shutdown.

[0203] 61. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system operates at a first current density that is higher than a desired current density such that the system produces more energy than desired.

[0204] 62. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system operates at a first current density that is lower than a desired current density such that the system produces less energy than desired.

[0205] 63. A method as recited in clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system generates excess power and the excess power generated is consumed by increasing a parasitic load.

[0206] 64. The method of clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system generates excess power and the generated excess power is consumed by a vehicle system cooling fan or air compressor.

[0207] 65. A method as recited in clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system generates excess power and the generated excess power is dissipated as heat.

[0208] 66. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system comprises a plurality of fuel cell stacks.

[0209] 67. A method according to clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system operates one set of fuel cell stacks at an upper threshold value of the system power demand and operates the remaining fuel cell stacks at a lower threshold value of the system power demand such that the total power generated meets the required power demand.

[0210] 68. A method according to clause 45, any other appropriate clause, or any combination of the appropriate clauses, wherein the power generated in the transient state or in the transient delayed state is:

[0211] power _TRANSIENT =I _TRANSIENT x V _TRANSIENT

[0212] V _TRANSIENT is the total voltage of the fuel cells included in the fuel stack system, and I _TRANSIENT is the total current density in the instantaneous state.

[0213] 69. A method according to clause 45, any other appropriate clause, or any combination of the appropriate clauses, wherein the energy generated during the time period (Δt) is:

[0214] energy _TRANSIENT =I _TRANSIENT x V _TRANSIENT x Δt

[0215] V _TRANSIENT is the total voltage of the fuel cells included in the fuel stack system, and I _TRANSIENT is the total current density in the instantaneous state.

[0216] 70. A method according to clause 45, any other appropriate clause, or any combination of appropriate clauses, wherein if the demand current density (i _DEMAND ) is zero, then the current density at the instantaneous break point (i _TRS_BRK ) is stored in the battery.

[0217] 71. A method according to clause 70, any other suitable clause, or any combination of suitable clauses, wherein the current density at the instantaneous break point (i _TRS_BRK ) slowly decreases.

[0218] 72. A method according to clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system includes an energy storage device, and if the energy storage device has no available storage, the system does not deliver the required current because additional storage is not possible.

[0219] 73. A method according to clause 45, any other suitable clause, or any combination of the suitable clauses, wherein electrical energy or waste heat from the system is transferred to a heater or other heat storage / use device such as a resistor.

[0220] 74. A method according to clause 45, any other suitable clause, or any combination of suitable clauses, wherein heat from a heater, other heat storage / use device, such as resistor heating or a heat exchanger is used to heat the primary inlet temperature (T O ).

[0221] 75. Clause 45, any other suitable clause, or any combination of suitable clauses, wherein if the primary inlet temperature (T O ) heating, primary nozzle inlet pressure (P O ) increases to compensate for temperature changes.

[0222] 76. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the compensation reduces the size of the blower required for the entrainment ratio (ER).

[0223] 77. A method as recited in clause 45, any other suitable clause, or any combination of suitable clauses, wherein the flow in the cathode side is managed according to the operating current density.

[0224] 78. A method as recited in clause 45, any other suitable clause, or any combination of the suitable clauses, wherein when the system operates in a transient hysteresis condition, air flow is managed to ensure humidification is maintained at upper and lower operating current densities.

[0225] 79. A method according to clause 45, any other suitable clause, or any combination of suitable clauses, wherein the injector is sized to generate a current at a critical current density (i _LO_CR ) to fully convey the recirculation flow.

[0226] 80. A method according to clause 45, any other suitable clause, or any combination of suitable clauses, wherein the ejector is sized to deliver the recirculation entirely without the assistance of a blower.

[0227] 81. The method of clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system further comprises a blower optimally integrated and / or sized to enhance operation and / or performance of the ejector.

[0228] 82. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system further comprises a blower sized to deliver a pressure increase (ΔP LIFT ) to offset any pressure losses through the anode recirculation loop.

[0229] 83. A method according to clause 45, any other suitable clause, or any combination of suitable clauses, wherein the transient hysteresis state follows a pseudo-steady state or a transient state.

[0230] 84. The method of clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system further comprises a blower operating in an idle state, in a blower base state, or in an ejector support state.

[0231] 85. The method of clause 45, any other suitable clause, or any combination of suitable clauses, wherein not using the blower results in a reduction in parasitic loads.

[0232] 86. A method as defined in clause 45, any other suitable clause, or any combination of suitable clauses, wherein the system comprises a humidifying device.

[0233] 87. A fuel cell stack system as defined in clause 42, any other suitable clause, or any combination of the suitable clauses, wherein a target relative humidity (RH) is maintained by using a humidifying device in conjunction with operating pressure and operating temperature.

[0234] 88. A method according to clause 45, any other suitable clause, or any combination of the suitable clauses, wherein the system comprises a mechanical regulator, a proportional control valve, or an ejector.

[0235] The above embodiments are described in sufficient detail to enable those skilled in the art to practice what is claimed, and it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made without departing from the scope and spirit of the claims. Therefore, the detailed description should not be taken in a limiting sense.

[0236] As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated.

[0237] Furthermore, references to "one embodiment" of the presently described subject matter are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The specified numerical ranges of units, measurements, and / or values ​​include, consist essentially of, or consist of all values, units, measurements, and / or ranges, including or within such ranges and / or endpoints, whether or not such values, units, measurements, and / or ranges are expressly specified in this disclosure.

[0238] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms "first," "second," "third," etc., as used herein, do not denote any order or importance, but are used to distinguish one element from another. The terms "or" and "and / or" are meant to be inclusive and mean one or all of the listed items. Furthermore, the terms "connected" and "coupled" are not limited to physical or mechanical connections or couplings, and may include direct or indirect electrical connections or couplings.

[0239] In addition, unless expressly stated to the contrary, embodiments that "comprise," "include," or "have" one or more elements having a particular property may include additional such elements that do not have that property. The terms "comprise" or "comprising" refer to ingredients, compounds, formulations, or methods that are included and do not exclude additional elements, components, and / or method steps. The term "comprising" also refers to ingredients, compounds, formulations, or method embodiments of the present disclosure that include and do not exclude additional elements, components, or method steps. The phrase "consisting of" or "consisting of" refers to compounds, ingredients, formulations, or methods that exclude the presence of any additional elements, components, or method steps.

[0240] The term "consisting of also refers to compounds, compositions, formulations, or methods of the present disclosure excluding the presence of any additional elements, components, or method steps. The phrase "consisting essentially of" or "consisting essentially of" refers to compositions, compounds, formulations, or methods that include additional elements, components, or method steps that do not materially affect one or more properties of the composition, compound, formulation, or method. The phrase "consisting essentially of" also refers to compositions, compounds, formulations, or methods of the present disclosure that include additional elements, components, or method steps that do not materially affect the properties of the composition, compound, formulation, or method step.

[0241] Approximate language used throughout the specification and claims can be used to modify any quantitative representation that can be permissibly varied without causing a change in the basic function to which it is related. Therefore, a value modified by one or more terms (such as "about" and "substantially") is not limited to the precise value specified. In some cases, approximate language may correspond to the precision of an instrument for measuring a value. Here and throughout the specification and claims, range limitations can be combined and / or interchanged. Unless the context or language indicates otherwise, such ranges are identified and include all subranges contained therein.

[0242] As used herein, the terms "may" and "might be" indicate the possibility of occurring within a set of circumstances; possessing a specified attribute, characteristic, or function; and / or qualifying another verb by expressing one or more of the ability, capacity, or possibility associated with the qualifying verb. Thus, the use of "may" and "might be" indicates that the modified term is clearly suitable, capable, or applicable to the indicated capacity, function, or use, while taking into account that in some circumstances, the modified term may sometimes not be suitable, capable, or applicable.

[0243] It should be understood that the above description is intended to be illustrative and not restrictive. For example, the above embodiments (and / or aspects thereof) can be used alone, together, or in combination with each other. In addition, without departing from its scope, many modifications can be made to adapt specific situations or materials to the teachings of the subject matter set forth herein. Although the size and type of materials described herein are intended to limit the parameters of the disclosed subject matter, they are by no means restrictive and are exemplary embodiments. After reading the above description, many other embodiments will be apparent to those skilled in the art. Therefore, the scope of the subject matter described herein should be determined with reference to the complete scope of the equivalents authorized by the appended claims and these claims.

[0244] This written description uses examples to disclose several embodiments of the subject matter described herein, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of the disclosed subject matter, including making and using devices or systems and performing methods. The patentable scope of the subject matter described herein is defined by the claims, and may include other examples that occur to one of ordinary skill 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.

[0245] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the invention.

Claims

1. A fuel cell stack system comprising: Fuel cell stacks, injectors, blowers and energy storage devices, wherein the fuel cell stack system is configured to operate at a first pressure or a first temperature, respectively, which is higher than a second pressure or a second temperature, in a transient state, in a transient hysteresis state, and wherein the controller is configured to operate the fuel cell stack system at a second operating current density when the fuel cell stack system is required to operate at a first operating current density.

2. The system according to claim 1, wherein: The first operating current density is the current density at the instantaneous break point.

3. The system according to claim 1, wherein: The second operating current density is higher than the first operating current density.

4. The system according to claim 3, wherein: The system generates excess power at the second operating current density, and wherein the excess power generated is dissipated or stored in the energy storage device over a period of time.

5. The system according to claim 4, wherein: The energy storage device is a battery having a state of charge.

6. The system according to claim 5, wherein: The storage of the excess power depends on the state of charge of the battery.

7. The system according to claim 4, wherein: The excess power is stored as kinetic energy, potential energy, chemical energy, electrical energy, electrochemical energy, mechanical energy or thermal energy.

8. The system according to claim 3, wherein: The controller is configured to determine a third operating current density, and the third operating current density is lower than the first operating current density.

9. The system according to claim 8, wherein: The system uses energy from the energy storage device when operating at the third operating current density.

10. A method for operating a fuel cell stack system, comprising: operating the fuel cell stack system including an ejector or blower in the fuel cell stack under transient hysteresis conditions, determining a first operating current density of the system that the ejector or blower cannot support, determining a second operating current density of the system, reducing the temperature or pressure of the system while operating in the transient hysteresis state before the system operates in the transient state, The system is operated at the second operating current density, wherein the second operating current density is higher than the first operating current density.

11. The method according to claim 10, wherein: The first operating current density is the current density at the instantaneous break point.

12. The method of claim 10, further comprising generating excess power by the fuel cell stack system when operating at the second operating current density, and dissipating the excess power or storing the excess power in an energy storage device for a period of time.

13. The method according to claim 12, wherein: The energy storage device is a battery having a state of charge.

14. The method according to claim 13, wherein Storing the excess power depends on the state of charge of the battery.

15. The method according to claim 12, wherein: And the excess power is stored as kinetic energy, potential energy, chemical energy, electrical energy, electrochemical energy, mechanical energy or thermal energy. 16 . The method of claim 10 , further comprising a controller determining a third operating current density for the system, and wherein the third operating current density is lower than the first operating current density. 17 . The method of claim 16 , further comprising using energy from an energy storage device when the fuel cell stack system operates at the third operating current density.

18. The method of claim 10, wherein the first operating current density is higher than a desired operating current density such that the fuel cell stack system produces more energy than desired.

19. The method of claim 10, further comprising operating a plurality of fuel cell stacks based on system power demand.

20. The method of claim 12, further comprising dissipating the excess power by a parasitic load.

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