Patent Description:
A known technique is described in, for example, Patent Literature <NUM>. Patent Literature <NUM> discloses a fuel cell system according to the preamble of claim <NUM>. Patent Literature <NUM> discloses a solid oxide fuel cell having: a fuel cell module; a fuel supply device; a combustion chamber for burning residual fuel and heating; a heat storing material, a power demand detecting sensor; a temperature detection device, and a control device for controlling so that the fuel utilization rate is high when generated power is large, and also for changing output power at a delay to the fuel supply amount; whereby the control device is furnished with a stored heat amount estimating circuit, and when it is estimated that a usable heat amount has accumulated in the heat storing material, the fuel supply amount is reduced so that the fuel utilization rate increases vs. the same generated power.

Patent Literature <NUM>: <CIT>; Patent Literature <NUM>: <CIT>; Patent Literature <NUM>: <CIT>.

The present invention provides a fuel cell system according to claim <NUM>.

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 according to one or more embodiments of the present disclosure will now be described with reference to 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 fuel cell system including solid oxide fuel cells (SOFCs) includes a controller that controls the operations of a raw fuel supply and an oxygen-containing gas supply to supply, to each unit cell, a raw fuel (hydrogen-containing gas) and air (oxygen-containing gas) in amounts intended for power generation. Direct current (DC) resulting from power generation is converted to alternating-current (AC) power by a power level regulator that operates in cooperation with an external electrical grid. The AC power is then fed to an external load as requested from an external device (external load) that is connected to the power level regulator.

Fuel cells are also used in small-scale power generation for applications that use low power (current value), such as homes and small businesses. For fuel cell systems for home use, for example, the level of power requested by an external load varies relatively largely.

To adjust output power levels, a fuel cell system undergoes high air utilization control during a low-current operation (low-output operation) performed for a low power level requested externally (current value of an external load). In the high air utilization control, the air utilization (Ua) increases as the output power level increases.

During a high-current operation (high-output operation) performed for a high current value of an external load, the fuel cell system undergoes constant air utilization control, in which the air utilization (Ua) is maintained at a predetermined high utilization (hereafter, high Ua ratio) to maintain highly efficient power generation.

The high-current operation (high-output operation) may be referred to as an operation involving a rated level of power generation or a near rated level of power generation. The low-current operation (low-output operation) may be referred to as either a partial load operation or a load-following operation.

In response to an increase in the output power level of the fuel cell to meet the power level requested by an external load, the fuel cell system may change the air utilization (Ua) of each unit cell and may continuously undergo the above constant air utilization control, in which the air utilization is maintained at the predetermined high Ua ratio under a high external load (externally requested power level). However, this may increase the temperature of the fuel cell and lower the durability of the unit cell, thus affecting the power generation efficiency.

A fuel cell system according to one or more embodiments will now be described.

A fuel cell system <NUM> according to an embodiment shown in <FIG> includes a fuel cell module <NUM> that generates electricity using a fuel gas and an oxygen-containing gas and auxiliary devices for assisting an independent power generation operation of the fuel cell. The auxiliary devices include an oxygen-containing gas supply <NUM> including an air blower B1 and an air channel F, a raw fuel supply <NUM> including a raw fuel pump B2 and a raw fuel channel G, a reformed water tank <NUM>, and a reformed water pump P1.

The fuel cell system <NUM> further includes a power level regulator (power conditioner <NUM>) as an auxiliary device that feeds power to an external unit and coordinates with the electrical grid, and a controller <NUM> that controls the operation of the auxiliary devices assisting the power generation operation of the fuel cell as described above in cooperation with the power conditioner <NUM>. The power conditioner <NUM> includes an ammeter (in amperes) and a voltmeter (in volts).

The fuel cell system <NUM> according to the embodiment further includes a waste heat recovery system (heat cycle HC1). The waste heat recovery system includes a heat exchanger <NUM>, a heat storage tank <NUM> (also referred to as a hot water tank), a heat dissipater (radiator <NUM>), and channel pipes connecting these components, and a heating medium pump P2.

The fuel cell system <NUM> shown in <FIG> further includes a second heat exchanger <NUM> (also referred to as a clean water heat exchanger) for heating tap water (clean water) to be supplied to an external unit, and a hot water supply system (heat cycle HC2). The hot water supply system includes a heat pump P3 and a circulation pipe for receiving and circulating a high-temperature heating medium from the heat storage tank <NUM>. The fuel cell system may be used as a monogeneration system that does not supply hot water to an external unit.

The fuel cell system <NUM> is housed in a case <NUM> as shown in <FIG>. The case <NUM> includes frames <NUM> and exterior panels <NUM>. The case <NUM> further contains multiple measurement devices, sensors, and other devices on and around the fuel cell module <NUM> and the auxiliary devices, the channels, and the piping.

For example, an air flowmeter FM1 is installed on the air channel F in the oxygen-containing gas supply <NUM>, which supplies air to the fuel cell module <NUM>. The air flowmeter FM1 measures the hourly flow rate (in NL/min, where NL is a normal liter) of air (oxygen-containing gas) that is supplied to a cell stack <NUM>.

Although not shown, a similar gas flowmeter is also installed on the raw fuel channel G in the raw fuel supply <NUM>.

The fuel cell system <NUM> may also include multiple temperature meters or thermometers (not shown), such as temperature sensors and thermistors for measuring the temperature of the components of the fuel cell.

The controller <NUM> that centrally controls the operation of the fuel cell system <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> also 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> specifically controls the operation of the air blower B <NUM> in the oxygen-containing gas supply <NUM> and the raw fuel pump B2 in the raw fuel supply <NUM> that supplies a raw fuel gas to a reformer <NUM> based on the level of output power requested from an external load, instructions and commands from an external unit connected to the fuel cell system (e.g., a water heater), measurement values of, for example, an ammeter indicating the amount of power supply to an external unit and a voltmeter (e.g., apparent power in volt-amperes), or measurement values of various sensors listed above.

More specifically, the controller <NUM> in the fuel cell system <NUM> with the structure described above controls the operations of the raw fuel supply <NUM> and the oxygen-containing gas supply <NUM> to supply, to each unit cell, a fuel gas and an oxygen-containing gas in amounts intended for operation. This causes each unit cell to generate power and a flow of DC through the unit cell. The power generated by the unit cells is converted to AC power by the power level regulator (power conditioner <NUM>) and is fed to an external load.

The air flow rate control for controlling, or specifically increasing or decreasing the air utilization (Ua) representing the air flow rate to meet the output power level (A) will now be described.

The controller <NUM> included in the fuel cell system <NUM> according to the present embodiment controls the air blower B1 in response to the level of power generation (in amperes) controllable by the power level regulator (hereinafter referred to as the power conditioner <NUM>). More specifically, the controller <NUM> controls the oxygen-containing gas utilization (Ua), which is the ratio of the amount of air used by the fuel cell for power generation to the amount of oxygen-containing gas (hereafter, air) supplied to the fuel cell. In detail, the controller <NUM> controls or regulates the air blower B1 to provide an increase-control section in which the oxygen-containing gas utilization (Ua) increases in accordance with an increase in the output power level of the fuel cell and a decrease-control section in which the oxygen-containing gas utilization (Ua) decreases in accordance with an increase in the output power level.

As an example of this control pattern, the graph in <FIG> shows the values of air (oxygen-containing gas) utilization (Ua) and the values of the air flow rate against the current (A) as the output power level.

The air utilization and the output power level may be set as appropriate for, for example, the scale of the fuel cell system (rated output power level). Thus, the graph in <FIG> merely shows a relational expression of the air utilization (Ua) and the output power level. In the graph shown in <FIG>, the solid line indicates the air utilization Ua, the dot-and-dash line indicates the air flow rate, and the dotted lines indicate the boundaries of the different control sections (described later).

The control over the air utilization Ua including the increase-control section and the decrease-control section described above will now be described with reference to the graph in <FIG>. In the graph, a section in which the current value (in amperes) is between <NUM> and a predetermined power generation level is a constant-control section in which the air utilization Ua is maintained constant (hereafter referred to as a second constant-control section in an aspect of the present disclosure).

The second constant-control section allows for efficient operation although the output power level based on the power level requested by an external load, or specifically the current value (A), is low. The air flow rate is set in the second constant-control section either based on the power generation efficiency or based on the lowest (minimum) flow rate determined by the specifications of the air blower B1 being used. The second constant-control section is defined in correspondence with smaller current values (output power levels) than for an increase-control section (described later).

In the graph shown in <FIG>, a section in which the current value (A) is between the second constant-control section and a first constant-control section (described later) is defined as the increase-control section according to an aspect of the present disclosure. In the increase-control section, the air utilization Ua increases in accordance with an increase in the current value (the output power level as well as the power level requested by an external load).

As shown in the graph, the air flow rate is constant in the increase-control section. This suggests that an increase in the air utilization Ua in the increase-control section results from an increase in the supply amount of the corresponding fuel gas (hydrogen-containing gas), an increase in the temperature of each unit cell, and an increase in the power generation efficiency (the rate of reaction or the contribution to power generation).

Similarly to the second constant-control section described above, the air flow rate in this section may also be constant and determined by the specifications of the air blower B <NUM> being used.

In the graph in <FIG>, a section in which the current value (A) is between the increase-control section and the decrease-control section (described below) is defined as a constant-control section in which the air utilization Ua is maintained constant (hereafter referred to as a first constant-control section in an aspect of the present disclosure).

This first constant-control section is defined to maximize the power generation efficiency but to reduce the likelihood of the air utilization Ua increasing excessively and causing insufficient air, possibly causing flame off. In this section, the air utilization Ua is maintained constant. More specifically, the current value and the air flow rate are proportional to each other in the first constant-control section. The first constant-control section is defined to be a section (or range) with the current value (A) or output power level between the increase-control section described above and the decrease-control section described later.

Finally, a section with the highest load current in which the current value (A) is higher than in the first constant-control section in the graph shown in <FIG> is the decrease-control section in an aspect of the present disclosure. In the decrease-control section, the air utilization Ua decreases in accordance with an increase in the current value. This section reduces the likelihood of the fuel cell reaching high temperatures.

As shown in the graph, the degree of increase (gradient) in the air flow rate in the decrease-control section is larger than the degree of increase (gradient) in the air flow rate in the first constant-control section described above. In this section following the first constant-control section in which the air utilization Ua is constant, a larger amount of air is supplied to each unit cell by an amount greater than the corresponding increase in the current value (A). This causes the air utilization Ua to be lower in the decrease-control section than in the preceding section, despite the larger output power level (current value) in the decrease-control section than in the preceding section.

For the fuel cell system with the structure that forms the basis of the fuel cell system according to one or more embodiments of the present disclosure to maintain high current operation (high output operation) in response to a high level of power requested by an external load, as described above, the fuel cell system maintains the air utilization (Ua) at the predetermined high utilization (high Ua ratio) by increasing the amount of air supplied to each unit cell by the same amount as the corresponding increase in the output current amount to maintain high power generation efficiency.

In contrast, the fuel cell system <NUM> according to the present embodiment uses the section in which the air utilization (Ua) starts decreasing during high current operation to supply more air to the unit cells with high operation efficiency. This reduces the likelihood of the fuel cell reaching high temperatures while maintaining power generation efficiency.

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 an oxygen-containing gas, an oxygen-containing gas supply that supplies the oxygen-containing gas to the fuel cell, a power level regulator that regulates a power level of the fuel cell, and a controller that controls the oxygen-containing gas supply and the power level regulator.

The controller controls the oxygen-containing gas supply and the power level regulator to cause the power level of the fuel cell controllable by the power level regulator and an oxygen-containing gas utilization to have an increase-control section in which the oxygen-containing gas utilization increases in accordance with an increase in the power level of the fuel cell and a decrease-control section in which the oxygen-containing gas utilization decreases in accordance with an increase in the power level of the fuel cell. The oxygen-containing gas utilization is a ratio of an amount of the oxygen-containing gas used by the fuel cell for power generation to an amount of the oxygen-containing gas supplied to the fuel cell.

Claim 1:
A fuel cell system (<NUM>), comprising:
a fuel cell (<NUM>) configured to generate electricity using a fuel gas and an oxygen-containing gas;
an oxygen-containing gas supply (<NUM>) configured to supply the oxygen-containing gas to the fuel cell (<NUM>);
a power level regulator (<NUM>) configured to regulate a power level of the fuel cell (<NUM>); and
a controller (<NUM>) configured to control the oxygen-containing gas supply (<NUM>) and the power level regulator (<NUM>),
wherein the controller (<NUM>) controls the oxygen-containing gas supply (<NUM>) and the power level regulator (<NUM>) to cause the power level of the fuel cell (<NUM>) controllable by the power level regulator (<NUM>) and an oxygen-containing gas utilization (Ua) to have an increase-control section in which the oxygen-containing gas utilization (Ua) increases in accordance with an increase in the power level of the fuel cell (<NUM>), a first section in which the oxygen-containing gas utilization (Ua) is constant against an increase in the power level of the fuel cell (<NUM>), and a decrease-control section in which the oxygen-containing gas utilization (Ua) decreases in accordance with an increase in the power level of the fuel cell (<NUM>), in this order, and the oxygen-containing gas utilization (Ua) is a ratio of an amount of the oxygen-containing gas used by the fuel cell (<NUM>) for power generation to an amount of the oxygen-containing gas supplied to the fuel cell (<NUM>).