Patent Description:
A known technique is described in, for example, Patent Literature <NUM>.

<CIT> discloses a solid oxide fuel cell for producing variable power in response to power demand, comprising: a fuel cell module configured to generate electricity using supplied fuel; a fuel supply device configured to supply fuel to the fuel cell module; a generating oxidant gas supply device configured to supply oxidant gas for electrical generation to the fuel cell module; a combustion section configured to burn remaining residual fuel supplied by the fuel supply device and not utilized for electrical generation, and heating the interior of the fuel cell module; a heat storing material configured to accumulate heat generated within the fuel cell module; a power demand detection device configured to detect power demand; a temperature detection device configured to detect the temperature of the fuel cell module; and a control device programmed to control, based on the power demand detected by the power demand detection device, such that the fuel utilization rate is high when generated power is large, and the fuel utilization rate is low when generated power is small, and also for changing the power actually output from the fuel cell module at a delay after changing the fuel supply amount in response to changes in power demand; wherein the control device includes a stored heat estimating circuit configured to estimate amount of stored heat accumulated in the heat storing material based on the detected temperature detected by the temperature detection device, and the control device reduces the fuel supply amount so that the fuel utilization rate increases relative to the same generated power when it is estimated that a usable amount of heat has accumulated in this heat storing material, in comparison with cases in which it is estimated that a usable amount of heat has not accumulated.

<CIT> discloses a solid oxide fuel cell system for producing variable generated power in accordance with power demand, comprising: a fuel cell module that generates power using supplied fuel; a fuel supply device that supplies fuel to the fuel cell module; a generating oxidant gas supply device that supplies oxidant gas for electrical generation to the fuel cell module; a heat storage material that stores heat produced within the fuel cell module; a demand power detection device that detects power demand; and a controller programmed to control the fuel supply device based on the demand power detected by the demand power detection device so that the fuel utilization rate increases when generated power is large and decreases when generated power is small, wherein the controller is programmed to change the electrical power actually output from the fuel cell module with a delay after changing the fuel supply amount based on changes in demand power; wherein the controller comprises a stored heat estimating circuit that estimates the amount of surplus heat based on fuel supplied by the fuel supply device and on the power output at a delay relative to fuel supply, and wherein when the stored heat estimating circuit estimates that a utilizable amount of heat has accumulated in the storage material, the controller reduces the fuel supply amount so that the fuel utilization rate for the same generated power is increased relative to the case when a utilizable amount of heat has not accumulated.

<CIT> discloses an air-cooled fuel cell system comprising: an air-cooled fuel cell having a cell in which a first channel portion for letting an oxidizing gas for cooling flow and a second channel portion for letting an oxidizing gas for power generation flow are formed such that both the oxidizing gas for cooling and the oxidizing gas for power generation flow from a same side; a supplying device for supplying oxidizing gas; and a distributing device for distributing the supplied oxidizing gas into the first channel portion and the second channel portion, as the oxidizing gas for cooling and the oxidizing gas for power generation, respectively, in a variable distribution ratio.

<CIT> discloses a fuel cell system comprising: a controller; a temperature sensor that has a physical presence in a conduit within the system; and a wall temperature sensor for sensing a temperature of a wall of the conduit; the controller operative to iteratively apply a thermal model to calculate a predicted temperature value that is, based on temperature values measured using the temperature sensor in the conduit and the wall temperature sensor, expected to be measured; wherein, when in an iterative step the predicted temperature value does not fulfil an interrupt criterion, an input temperature value used in a next iterative step is altered based on a difference between the temperatures measured by the sensors.

<CIT> discloses a fuel cell stack that is operated with a low air utilization which is very low when the stack is providing low current density, and is operated with air utilization increasing as a function of current density above a predetermined current density.

<CIT> discloses a fuel cell stack assembly comprising: a stack of fuel cells, each fuel cell having a cooling air conduit with an input/output ventilation aperture disposed on a ventilation face of the stack, the ventilation apertures forming an array over said ventilation face of the stack; a first fan configured to direct air flow through a first portion of the ventilation face and a second fan configured to direct air flow through a second portion of the ventilation face; and, a reconfigurable plenum in fluid communication with said first fan and said second fan, the plenum having a first configuration in which air is directed, by the first and second fans, through the first and second portions of the ventilation face in the same direction, and a second configuration in which air is directed, by at least one of the fans, respectively through the first and second portions of the ventilation face in opposing directions.

The present invention provides a fuel cell system according to claim <NUM>. Further embodiments of the present invention are disclosed in the dependent claims.

The objects, features, and advantages of the present disclosure will become more apparent from the following detailed description and the drawings.

A fuel cell system with the structure that forms the basis of a fuel cell system according to one or more embodiments of the present disclosure will be described first.

A known solid oxide fuel cell (SOFC) generates electricity using a fuel gas as a hydrogen-containing gas and air as an oxygen-containing gas. Such a fuel cell may generate electricity using a fuel gas and air supplied in varying amounts to meet the power level requested by an external load, such as a home appliance.

A fuel cell system according to one or more embodiments of the present disclosure will now be described with reference to the drawings. <FIG> is a schematic diagram of the fuel cell system according to one or more embodiments of the present disclosure. <FIG> is a perspective view of the fuel cell system housed in an external case. <FIG> is a graph showing the temperature of a fuel cell in a rated operation mode and in a partial load operation mode. <FIG> is a flowchart showing control for increasing air.

A fuel cell system <NUM> according to one or more embodiments includes a fuel cell <NUM> that generates electricity using a fuel gas and air, an air supply <NUM> that supplies air to the fuel cell <NUM>, a temperature meter TC that measures the temperature of the fuel cell <NUM>, and a controller <NUM>. The fuel cell system <NUM> can operate in multiple operation modes in a manner switchable as appropriate. The operation modes used in the present embodiment include at least a rated operation mode and a partial load operation mode (load-following operation mode). The rated operation mode is used for generating rated power. In the rated operation mode for generating rated power, the fuel cell <NUM> operates with a predetermined amount of fuel gas and a predetermined amount of air supplied to generate a predetermined level of power. The partial load operation mode is used for generating varying levels of output power in accordance with varying power levels requested by an external load. For example, the requested power level varies depending on the types and the number of home appliances to be used. In this operation mode, the fuel cell generates electricity in accordance with the varying requested power level.

As indicated by symbol HC1 in <FIG>, the fuel cell system <NUM> includes a first heat circulation system (heat cycle) as a waste heat recovery system including a first heat exchanger <NUM>, a heat storage tank <NUM>, a refrigerator <NUM>, a heating medium pump P2, and circulation channels connecting these components. As indicated by symbol HC2 in <FIG>, the fuel cell system <NUM> also includes a second heat circulation system as a waste heat recovery system including a second heat exchanger <NUM> (also referred to as a clean water heat exchanger), a circulation pump P3 for circulation of a heating medium from the heat storage tank <NUM>, and channel pipes connecting these components. The high-temperature heating medium stored in the heat storage tank <NUM> is used to heat, with the second heat exchanger <NUM>, water such as tap water supplied from an external source through a supply channel Kin. The heated water is then supplied to a reheater, such as an external water heater, through a feed channel Kout.

A fuel cell module <NUM> includes the fuel cell <NUM> and a reformer <NUM> housed in a housing <NUM>. The fuel cell <NUM> may have any cell structure that generates electricity using a fuel gas and air. For example, the fuel cell <NUM> may be a cell stack structure including multiple unit cells. The fuel cell <NUM> with the cell stack structure includes unit cells having their lower ends fixed to a manifold with an insulating bond such as a glass sealant between them. The fuel gas and air to be used by the fuel cell <NUM> for power generation are supplied through the lower ends of the unit cells. The fuel cell <NUM> includes the unit cells that are vertically arranged prisms having gas channels inside to allow gas to flow in the longitudinal direction. The unit cells are electrically connected in series to one another with a current collector between adj acent unit cells. Among various known unit cells, SOFCs may be used in a fuel cell system with the partial load operation (load-following operation) mode as one of its operation modes.

The fuel cell system <NUM> may include a temperature meter TC to measure the temperature of the fuel cell <NUM>. The temperature meter TC may be a known measurement device such as a thermocouple. In the present embodiment, the temperature at the center position of the fuel cell <NUM> is measured by a thermocouple and used as a representative value of the temperature of the fuel cell <NUM>.

Gas discharged from the fuel cell module <NUM> through power generation performed by the fuel cell <NUM> exchanges heat using a heating medium or a refrigerant such as water flowing through the first heat exchanger <NUM>. The moisture contained in the discharged gas then condenses to produce condensed water. The resultant condensed water is collected through a condensed water channel C and is stored in a reformed water tank <NUM>. Any condensed water exceeding the capacity of the reformed water tank <NUM> overflows and is discharged through a water discharge channel D.

The discharged gas from which the moisture has been removed is discharged out of the fuel cell system through a discharged gas channel E. The reformed water stored in the reformed water tank <NUM> is supplied to the reformer <NUM> included in the fuel cell module <NUM> through a reformed water channel R and a reformed water pump P1, and is used for steam reforming of a raw fuel gas.

Air used for power generation in the fuel cell module <NUM> is supplied into the fuel cell <NUM> by the air supply <NUM>. The air supply <NUM> includes a blower B2 and a pipe F as an air channel. The raw fuel gas, together with the reformed water flowing through the reformed water channel R, is supplied into the reformer <NUM> through a fuel gas pump B1 and a pipe G as a raw fuel gas channel.

The fuel cell system <NUM> may include various other components for, for example, power generation or hot water supply. The components described above are examples. The components other than those associated with the control for increasing air (described later) may have any structure.

The fuel cell system <NUM> may include, as auxiliary devices to assist its power generation operation, a power conditioner <NUM>, the controller <NUM>, an operation board <NUM> including a display and an operation panel, in addition to the fuel cell module <NUM> and other components described above. The fuel cell system <NUM> is housed in a case <NUM> including, for example, frames <NUM> and exterior panels <NUM> as shown in <FIG>.

The fuel cell system <NUM> includes the controller <NUM> including at least one processor and a memory to implement control and processing capability for performing various functions described in detail later.

In various embodiments, the at least one processor may be a single integrated circuit or may include multiple integrated circuits and/or discrete circuits that are connected to one another to allow communication between them. The at least one processor may be implemented with various known techniques.

In one embodiment, the processor includes one or more circuits or units that perform one or more data computation procedures or processes by, for example, executing instructions stored in an associated memory. In some embodiments, the processor may be firmware, or for example, a discrete logic component that performs one or more data computation procedures or processes.

In various embodiments, the processor may be one or more processors, controllers, microprocessors, microcontrollers, application-specific integrated circuits, digital signal processors, programmable logic devices, field programmable gate arrays, or any combination of these devices or configurations or any other known combination of devices and configurations that may perform the functions described later.

The controller <NUM> is connected to a memory and a display (both not shown) and to various components and various sensors included in the fuel cell system <NUM>. The controller <NUM> controls and manages these functional components and thus controls and manages the entire fuel cell system <NUM>. The controller <NUM> obtains a program stored in its memory, and executes the program to implement various functions of the components of the fuel cell system <NUM>.

To transmit control signals or various types of information from the controller <NUM> to other functional components or devices, the controller <NUM> may be connected to the other functional components either with wires or wirelessly. The particular control performed by the controller <NUM> in the present embodiment will be described later. In the present embodiment, the controller <NUM> controls various auxiliary devices, such as the fuel gas pump B1, based on instructions and commands from external devices connected to the fuel cell system or based on instructions and measurements results from various sensors listed above. In the figure, the connections between the controller <NUM> and the components of the fuel cell and the sensors may not be shown.

The memory (not shown) can store programs and data. The memory may be used as a work area to temporarily store the processing results. The memory includes a recording medium. The recording medium may include any non-transitory recording medium, such as a semiconductor memory or a magnetic memory. The memory may include multiple different recording media. The memory may include a combination of a memory reader and a portable recording medium, such as a memory card, an optical disc, or a magneto-optical disk. The memory may include a memory device usable as a temporary storage area, such as a random-access memory (RAM).

The controller <NUM> and the memory in the fuel cell system may be external to the fuel cell system <NUM>, or may be implemented with a control method including particular control steps of the controller <NUM> in one or more embodiments of the present disclosure, or as a control program for causing a computer to execute these steps.

The temperature of the fuel cell <NUM> in the rated operation mode and in the partial load operation mode will now be described briefly. <FIG> is a graph showing the temperature of the fuel cell in the rated operation mode and in the partial load operation mode. The fuel cell <NUM> in the present embodiment is a cell stack structure including vertically arranged prism-like unit cells. The fuel cell <NUM> receives a fuel gas and air supplied through its lower end. In the rated operation mode, larger amounts of fuel gas and air are supplied than in the partial load operation mode, thus causing upper end portions of the vertically arranged unit cells to generate more power and thus have higher temperatures. In other words, the temperature profile shows an increase from the root portions to the upper end portions of the unit cells. In the partial load operation mode, smaller amounts of fuel gas and air are supplied, and the root portions of the vertically arranged unit cells are not cooled with air and thus have higher temperatures than in the rated operation mode. Further, the upper end portions of the unit cells generate less power than in the rated operation mode and thus have lower temperatures. In other words, the temperature profile shows a decrease from the root portions to the upper end portions of the unit cells. This temperature profile causes the temperature at the center position of the fuel cell <NUM> (center temperature) to be higher when the temperature is measured as a representative value of the fuel cell <NUM> in the partial load operation mode, although the output power level is actually lower in the partial load operation mode than in the rated operation mode. Thus, changing the amount of air supplied to cool the fuel cell <NUM> based on a higher center temperature assumingly indicating more power generation can cause either insufficient or excessive cooling or other issues.

When the temperature of the fuel cell <NUM> exceeds a predetermined temperature (threshold temperature) in the fuel cell system <NUM>, the air supply <NUM> is controlled to increase the amount of air supplied to the fuel cell <NUM>. However, the determination using the single threshold temperature can cause the issues described above due to the temperature distribution across the different operation modes. In the present embodiment, multiple threshold temperatures are used for cooling the fuel cell <NUM> appropriately in different operation modes. This reduces the likelihood that the durability of the fuel cell system <NUM> decreases. In the present embodiment, different operation modes are reflected in different levels of output power, which are then detected as the current values each representing the output power level.

<FIG> is a flowchart showing the control for increasing air. In this flowchart, symbol S represents a step, Yes represents a positive result (with a computer flag indicating <NUM>) in the determination, and No represents a negative result (with a computer flag indicating <NUM>) in the determination.

The control in the fuel cell system <NUM> includes, preceding the start of this process, measuring the center temperature of the fuel cell <NUM> continuously with the temperature meter TC. The measured center temperature may be used in control other than the control for increasing air. Once the air increasing control starts in the present embodiment, the controller <NUM> starts monitoring the center temperature of the fuel cell <NUM>.

The fuel cell system <NUM> controls the air supply <NUM> in accordance with an increase or decrease in the level of output power, and changes an air utilization Ua as appropriate. The air utilization Ua is the ratio of the amount of air used by the fuel cell <NUM> for power generation to the amount of air supplied to the fuel cell <NUM>. The air utilization Ua includes a first utilization Ua1 as a reference value used during power generation.

In S1, the determination is performed as to whether the center temperature exceeds a first set temperature H1. The first set temperature H1 is the highest of set temperatures including a second set temperature H2 and a third set temperature H3, and is the upper limit of the operational temperature of the fuel cell <NUM>. The second set temperature H2 is used for a level of output power of the fuel cell <NUM> less than a predetermined level corresponding to the partial load operation mode. The third set temperature H3 is used for a level of output power of the fuel cell <NUM> greater than or equal to a predetermined level corresponding to the rated operation mode, and lower than the second set temperature H2. In the present embodiment, for example, the temperature H1 is <NUM>, the temperature H2 is <NUM>, and the temperature H3 is <NUM>.

For the center temperature exceeding the first set temperature H1 (Yes), the temperature of the fuel cell <NUM> is to be lowered promptly. In S2, the controller <NUM> sets the air utilization Ua to a second utilization Ua2 lower than the first utilization Ua1, which is the reference value. This decreases the air utilization Ua, with the amount of air used for power generation remaining substantially unchanged although a larger amount of air is supplied to the fuel cell <NUM> to cool the fuel cell <NUM>. In S2, the air supply <NUM> is controlled to increase the amount of air supplied to the fuel cell <NUM>.

When the center temperature is lower than or equal to the first set temperature H1 (No), the determination is performed in S3 as to whether the duration for which the center temperature remains lower than or equal to the first set temperature H1 exceeds a predetermined time T. When the duration does not exceed the time T (Yes), the processing returns to S1. When the duration exceeds the time T (No), the controller <NUM> detects the output power level of the fuel cell <NUM> and determines whether the output power level is greater than or equal to a predetermined level. In detail, the current value output from the fuel cell <NUM> is measured as the output power level and is compared with a predetermined current value A1 to determine whether the current value is greater than or equal to the predetermined current value A1. In the present embodiment, the time T may be, for example, two minutes.

When the current value is less than the current value A1 in S4 (No), the controller <NUM> determines whether the center temperature exceeds the second set temperature H2 in S5. When the center temperature exceeds the second set temperature H2 (Yes), the controller <NUM> determines whether the air utilization is the second utilization Ua2 in S9. When the air utilization is not the second utilization Ua2 (No), the air utilization is decreased by one stage in S10 to cause the air utilization to approach the second utilization Ua2. In other words, when the center temperature exceeds the second set temperature H2 in the partial load operation mode, the air supply amount is increased for cooling.

When the current value is greater than or equal to the current value A1 in S4 (Yes), the controller <NUM> determines whether the center temperature exceeds the third set temperature H3 in S6. When the center temperature exceeds the third set temperature H3 (Yes), the controller <NUM> determines whether the air utilization is the second utilization Ua2 in S9. When the air utilization is not the second utilization Ua2 (No), the air utilization is decreased by one stage in S10 to cause the air utilization to approach the second utilization Ua2. In other words, when the center temperature exceeds the third set temperature H3 lower than the second set temperature H2 in the rated operation mode, the air supply amount is increased for cooling.

When the air utilization is the second utilization Ua2 in S9 (Yes), the air utilization is unchanged and maintained. The processing then returns to S1. In other words, the air utilization is controlled to decrease in stages with the second utilization Ua2 as the lower limit.

When the center temperature is lower than or equal to the second set temperature H2 in S5 (No) or when the center temperature is lower than or equal to the third set temperature H3 in S6 (No), the controller <NUM> determines whether the air utilization is the first utilization Ua1, which is the reference value, in S7. When the air utilization is not the first utilization Ua1 (No), the air utilization is increased by one stage in S8. More specifically, when the center temperature is lower than or equal to the threshold temperature and the current air utilization is not the reference value in the partial load operation mode or in the rated operation mode, the controller <NUM> controls the air supply amount to cause the air utilization to approach and return to the reference value. In other words, the air utilization is controlled to increase in stages with the reference value or the first utilization Ua1 as the upper limit.

When the air utilization is the first utilization Ua1 in S7 (Yes), the air utilization is unchanged and maintained. The processing then returns to S1.

The present disclosure may be implemented in the following forms.

A fuel cell system according to one or more aspects of the present disclosure includes a fuel cell that generates electricity using a fuel gas and air, an air supply that supplies air to the fuel cell, a temperature meter that measures a temperature of the fuel cell, and a controller that controls the air supply to increase an amount of air to be supplied to the fuel cell in response to the temperature of the fuel cell exceeding one of a plurality of predetermined temperatures.

Claim 1:
A fuel cell system (<NUM>), comprising:
a fuel cell (<NUM>) configured to generate electricity using a fuel gas and air;
an air supply (<NUM>) configured to supply air to the fuel cell (<NUM>);
a temperature meter (TC) configured to measure a temperature of the fuel cell (<NUM>); and
a controller (<NUM>), wherein
the fuel cell system (<NUM>) is configured to operate in multiple operation modes including a rated operation mode and a partial load operation mode,
the controller (<NUM>) is configured to control the air supply (<NUM>) to increase an amount of air to be supplied to the fuel cell (<NUM>) in response to the temperature of the fuel cell (<NUM>) exceeding one of a plurality of predetermined temperatures,
the controller (<NUM>) is configured to decrease, as an air utilization (Ua), a ratio of an amount of air used for power generation of the fuel cell (<NUM>) to an amount of air supplied to the fuel cell (<NUM>) by increasing an amount of air supplied to the fuel cell (<NUM>), and
the plurality of predetermined temperatures include
a first set temperature (H1) being highest,
a second set temperature (H2) for a power level of the fuel cell (<NUM>) being less than a predetermined level corresponding to the partial load operation mode, and
a third set temperature (H3) lower than the second set temperature (H2) for a power level of the fuel cell (<NUM>) being greater than or equal to the predetermined level corresponding to the rated operation mode.