Fuel cell system

Abstract

To suppress the excessive change of the output power following the change of the target output power in a system which performs feedback control based on the output power and the target output power in the speed type.SOLUTION: A fuel cell system having a fuel cell comprises: a power conversion device which converts the power generation output of the fuel cell into the power that can be supplied to a load to output it; and a control device which sets the target output power of the power conversion device and controls the power conversion device on the basis of an operation amount set by feedback control such that the output power of the power conversion device becomes the target output power. The feedback control is the speed type which calculates a deviation by reducing the target output power from the output power, calculates a change amount including a proportional term obtained by multiplying the difference obtained by reducing the previous value from the current value of the deviation by a proportional gain and sets an operation amount by adding the change amount to the previous value of the operation amount. The control device sets the target output power so as to suppress the change speed of the target output power.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system.

Background Art

[0002] Conventionally, as this type of fuel cell system, there is known one including a fuel cell that generates electricity using fuel gas and air, and a power conversion device that converts the generated output power of the fuel cell into electric power that can be supplied to a load and outputs it. For example, in Patent Document 1, in performing feedback control by determining a target output power so that the output power of the power conversion device becomes power corresponding to the power consumption of the load, the rate of increase of the output power is limited for the protection of the fuel cell. It is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] This disclosure primarily aims to suppress excessive changes in output power associated with changes in target output power in a speed-type feedback control system based on output power and target output power. [Means for solving the problem]

[0006] This disclosure employs the following means to achieve the primary objectives described above.

[0007] The first fuel cell system of this disclosure is A fuel cell system equipped with a fuel cell, A power converter that converts the power output of the fuel cell into electricity that can be supplied to a load and outputs it, A control device that sets a target output power for the power converter and controls the power converter based on an input variable set by feedback control so that the output power of the power converter becomes the target output power, Equipped with, The aforementioned feedback control is a speed-type control that calculates a deviation by subtracting the target output power from the output power, calculates a change amount that includes a proportional term obtained by multiplying the difference between the current value and the previous value of the deviation by a proportional gain, and adds this change amount to the previous value of the manipulated variable to set the manipulated variable. The control device's main function is to set the target output power in such a way that it suppresses the rate of change of the target output power.

[0008] In the first fuel cell system of this disclosure, the deviation is calculated by subtracting the target output power from the output power of the power converter, and the change amount, which includes a proportional term obtained by multiplying the difference between the current value of the deviation and the previous value by a proportional gain, is calculated, and the power converter is controlled based on the set manipulated variable by adding the change amount to the previous value of the manipulated variable. Furthermore, the target output power is set so as to suppress the rate of change of the target output power. This prevents the target output power from changing abruptly and reduces the deviation between the output power and the target output power, thereby preventing the change amount, which includes the proportional term, from changing significantly. For this reason, it is possible to prevent abrupt changes in the manipulated variable and prevent the output power of the power converter from changing excessively.

[0009] In the first fuel cell system of this disclosure, the control device may set the target output power to the smaller of the power consumption of the load and the power obtained by adding a predetermined value to the output power. In this way, the deviation can be kept within the range of a predetermined value, and excessive changes in the output power of the power converter can be prevented with simple processing.

[0010] The second fuel cell system of this disclosure is A fuel cell system equipped with a fuel cell, A power converter that converts the power output of the fuel cell into electricity that can be supplied to a load and outputs it, A control device that sets a target output power of the power converter based on the power consumption of the load, and controls the power converter based on an input variable set by feedback control so that the output power of the power converter becomes the target output power, Equipped with, The aforementioned feedback control is a speed-type control that calculates a deviation by subtracting the target output power from the output power, calculates a change amount that includes a proportional term obtained by multiplying the difference between the current value and the previous value of the deviation by a proportional gain, and adds this change amount to the previous value of the manipulated variable to set the manipulated variable. The gist of the control device is that, when the target output power decreases, it subtracts a value with a smaller absolute value than the actual value from the current value of the deviation, which is the previous value of the deviation.

[0011] In the second fuel cell system of this disclosure, the deviation is calculated by subtracting the target output power from the output power of the power converter, and the change amount, which includes a proportional term obtained by multiplying the difference between the current value of the deviation and the previous value by a proportional gain, is calculated and added to the previous value of the manipulated variable to control the power converter based on the set manipulated variable. Furthermore, if the target output power decreases, the previous value of the deviation is set by subtracting a value with a smaller absolute value than the actual value from the current value of the deviation. This prevents the difference obtained by subtracting the previous value of the deviation from the current value from the previous value from changing significantly even if the target output power decreases. Therefore, it is possible to prevent abrupt changes in the manipulated variable and prevent excessive changes in the output power of the power converter.

[0012] In the second fuel cell system of this disclosure, the control device may set a value of 0 to a value that has an absolute value smaller than the actual value. This ensures that the difference does not change significantly when the target output power decreases, and prevents excessive changes in the output power of the power converter with simple processing. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing the general configuration of the fuel cell system 10. [Figure 2] This is a block diagram showing an example of the functions of the control device 90. [Figure 3] This is an explanatory diagram showing the difference in the rate of increase of output power P depending on whether or not there is an output limit. [Figure 4] This is a flowchart showing an example of the target power setting process. [Figure 5] This is an explanatory diagram showing an example of the changes in power consumption Pcon, target power Ptag, and output power P in this embodiment. [Figure 6] This is an explanatory diagram showing an example of the changes in power consumption Pcon, target power Ptag, and output power P in a comparative example. [Figure 7] This is a flowchart showing an example of proportional term calculation processing. [Modes for carrying out the invention]

[0014] Next, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an outline of the configuration of a fuel cell system 10. As shown in the figure, the fuel cell system 10 of the present embodiment includes a power generation module 20 including a fuel cell stack 21 that generates power by an electrochemical reaction between hydrogen in anode gas and oxygen in cathode gas, a raw fuel gas supply device 30 that supplies a raw fuel gas (for example, natural gas or LP gas) that is a raw material of the anode gas to the power generation module 20, a reformed water supply device 40 that supplies reformed water necessary for reforming (steam reforming) the raw fuel gas into anode gas to the power generation module 20, an air supply device 50 that supplies air as cathode gas to the power generation module 20 (fuel cell stack 21), a waste heat recovery device 60 that recovers waste heat generated in the power generation module 20, and a control device 90 that controls the entire system.

[0015] The power generation module 20 includes a fuel cell stack 21, a vaporizer 22, a reformer 23, a combustor 24, and a plurality (two) of heat exchangers 26 and 27, and these are housed in a module case 29 having heat insulation properties.

[0016] The fuel cell stack 21 includes a plurality of solid oxide type single cells each having an electrolyte such as zirconium oxide and an anode and a cathode sandwiching the electrolyte. An anode gas passage through which anode gas flows is connected to the anode of each single cell. Also, a cathode gas passage through which cathode gas flows is connected to the cathode of each single cell. A temperature sensor <112> is installed near the fuel cell stack 21. The temperature sensor <112> detects a temperature (stack correlation temperature) correlated with the temperature of the fuel cell stack 21.

[0017] The vaporizer 22 and the reformer 23 of the power generation module 20 are arranged at intervals above the fuel cell stack 21 in the module case 29. Also, a combustor 24 that generates heat necessary for the operation of the fuel cell stack 21 and the reactions in the vaporizer 22 and the reformer 23 is arranged between the fuel cell stack 21 and the vaporizer 22 and the reformer 23.

[0018] The vaporizer 22 heats the raw fuel gas from the raw fuel gas supply device 30 and the reformed water from the reformed water supply device 40 using heat from the combustor 24, preheating the raw fuel gas and evaporating the reformed water to generate steam. The raw fuel gas preheated by the vaporizer 22 is mixed with the steam, and this mixed gas flows from the vaporizer 22 into the reformer 23. A temperature sensor 111 is installed near the inlet of the reformer 23 to detect the temperature of the mixed gas flowing into the reformer 23.

[0019] The reformer 23 has a reforming catalyst, such as a Ru-based or Ni-based one, packed inside, and in the presence of heat from the combustor 24, the reformer 23 reacts with the mixed gas from the vaporizer 22 (steam reforming reaction) to produce hydrogen gas and carbon monoxide. Furthermore, the reformer 23 produces hydrogen gas and carbon dioxide through a reaction between the carbon monoxide produced in the steam reforming reaction and water vapor (carbon monoxide shift reaction). As a result, the reformer 23 produces anode gas containing hydrogen, carbon monoxide, carbon dioxide, water vapor, and unreformed raw fuel gas. The anode gas produced by the reformer 23 flows through the anode gas piping 71 into the anode gas passage of each single cell and is supplied to the anode.

[0020] Furthermore, air, acting as the cathode gas, flows into the cathode gas passage of each single cell via the cathode gas piping 72 and is supplied to the cathode. At the cathode of each single cell, oxide ions (O) are present. 2- ) is generated, and electrical energy is obtained when these oxide ions permeate the electrolyte and react with hydrogen and carbon monoxide at the anode.

[0021] Anode gas not used in the electrochemical reaction (power generation) in each single cell (hereinafter referred to as "anode off gas") is supplied to the condenser 62 through the anode off gas piping 73, where it is cooled by the condenser 62, removing at least some of the water vapor contained in the anode off gas, and then supplied to the combustor 24 through the anode off gas piping 74. Heat exchangers 26 are installed in the anode off gas piping 73 and 74, and the anode off gas flowing through the anode off gas piping 74 (anode off gas after passing through the condenser 62) is heated in the heat exchanger 26 by heat exchange with the high-temperature anode off gas flowing from the fuel cell stack 21 through the anode off gas piping 73 (anode off gas before passing through the condenser 62). In addition, cathode gas not used in the electrochemical reaction (power generation) in each single cell (hereinafter referred to as "cathode off gas") is supplied to the combustor 24 through the cathode off gas piping 75.

[0022] The anode-off gas flowing into the combustor 24 is a combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the cathode-off gas containing oxygen that flows into the combustor 24. The combustion of this mixed gas in the combustor 24 generates heat necessary for the operation of the fuel cell stack 21, preheating of the raw fuel gas and generation of steam in the vaporizer 22, and the steam reforming reaction in the reformer 23. In addition, the combustor 24 generates combustion exhaust gas containing unburned fuel, which passes through the combustion exhaust gas piping 76, through the heat exchanger 27 and the combustion catalyst 28, and is discharged to the outside air. The combustion catalyst 28 is an oxidation catalyst for re-combusting the unburned fuel in the combustion exhaust gas.

[0023] The raw fuel gas supply system 30 includes a raw fuel gas supply pipe 31 connecting a raw fuel supply source 1 that supplies raw fuel gas to a vaporizer 22, and on-off valves (double valves) 32, 33, a gas pump 36, and a desulfurizer 38 installed on the raw fuel gas supply pipe 31. The raw fuel gas is pumped (supplied) from the raw fuel supply source 1 to the vaporizer 22 via the desulfurizer 38 by operating the gas pump 36. A flow sensor 39 is also installed on the raw fuel gas supply pipe 31 to detect the flow rate of the raw fuel gas per unit time flowing through the raw fuel gas supply pipe 31.

[0024] The reformed water supply system 40 includes a reformed water tank 42 for storing reformed water, a reformed water supply pipe 41 connecting the reformed water tank 42 and the vaporizer 22, and a reformed water pump 43 installed on the reformed water supply pipe 41. The reformed water in the reformed water tank 42 is pumped (supplied) to the vaporizer 22 by the reformed water pump 43 when the pump 43 is activated. The reformed water supply pipe 41 is equipped with a flow sensor 45 that detects the flow rate of reformed water per unit time flowing through the reformed water supply pipe 41.

[0025] The air supply device 50 includes an air supply pipe 51 connected to a cathode gas pipe 72 installed inside a module case 29, an air filter 52 provided at the inlet of the air supply pipe 51, and an air pump 53 installed on the air supply pipe 51. By operating the air pump 53, air as cathode gas is drawn into the air supply pipe 51 via the air filter 52 and pressurized (supplied) through the cathode gas pipe 72 to the fuel cell stack 21 (cathode). The air flowing through the cathode gas pipe 72 is heated in the heat exchanger 27 by heat exchange with the high-temperature combustion exhaust gas flowing through the combustion exhaust gas pipe 76.

[0026] The waste heat recovery device 60 includes a hot water storage tank 61 for storing hot water, a condenser 62 for exchanging heat between the hot water and the anode off gas flowing from the fuel cell stack 21 through the anode off gas piping 73 to condense the water vapor contained in the anode off gas, a circulation piping 63 connected to the hot water storage tank 61 and the condenser 62, and a circulation pump 64 incorporated into the circulation piping 63. The hot water stored in the hot water storage tank 61 is introduced into the condenser 62 by operating the circulation pump 64, where it is heated by heat exchange with the anode off gas before being returned to the hot water storage tank 61.

[0027] Furthermore, the anode-off gas side passage outlet of the condenser 62 is connected to the condensate pipe 44 and the anode-off gas pipe 74. The condensate obtained by the condensation of water vapor in the anode-off gas through heat exchange with the hot water from the hot water storage tank 61 is introduced into the reformed water tank 42 through the condensate pipe 44. The reformed water tank 42 is equipped with a water purifier (not shown) to purify the condensate that has passed through the condensate pipe 44. As described above, the anode-off gas from which water vapor has been removed in the condenser 62 is supplied to the combustor 24 through the anode-off gas pipe 74.

[0028] The output terminal of the fuel cell stack 21 is connected to the input terminal of the power conditioner 80, and the output terminal of the power conditioner 80 is connected to the power line 3 from the power system 2 to the load 4 via a relay. The power line connected to the fuel cell stack 21 is equipped with a current sensor 113 for detecting the stack current Is output from the fuel cell stack 21 and a voltage sensor 114 for detecting the stack voltage Vs output from the fuel cell stack 21.

[0029] The power conditioner 80 includes a DC / DC converter 81 that converts the DC power output from the fuel cell stack 21 into DC power of a predetermined voltage (e.g., DC 250V to 300V), and an inverter 82 that converts the converted DC power into AC power of a voltage that can be connected to the power grid (e.g., AC 200V). This makes it possible to convert the DC power from the fuel cell stack 21 into AC power and supply it to loads 4 such as household appliances. A power sensor 115 that detects the output power P output from the power conditioner 80 (inverter 82) is installed on the power line connected to the power conditioner 80 (inverter 82). A power supply board 85 is also connected to the power conditioner 80. The power supply board 85 converts DC power from the fuel cell stack 21 and AC power from the power grid 2 into low-voltage DC power and supplies it to auxiliary equipment such as the gas pump 36, reformed water pump 43, air pump 53, and circulation pump 64, sensors such as flow sensors 39 and 45, temperature sensors 111 and 112, current sensor 113, voltage sensor 114, and power sensor 115, and the control device 90. In addition, the auxiliary equipment room where the power conditioner 80 and power supply board 85 are located is equipped with a cooling fan (not shown) and a ventilation fan for cooling the power conditioner 80 and power supply board 85. The cooling fan blows air into the heat-generating parts of the power conditioner 80 and power supply board 85, cooling them through heat exchange with the air. The air that has been cooled and heated is discharged into the atmosphere by the ventilation fan.

[0030] The control device 90 is configured as a microprocessor centered around a CPU 91, and in addition to the CPU 91, it includes a ROM 92 for storing processing programs, a RAM 93 for temporarily storing data, and input / output ports (not shown). Various detection signals from flow sensors 39, 45, temperature sensors 111, 112, current sensor 113, voltage sensor 114, power sensors 115, 116, etc. are input to the control device 90 via input ports. The power sensor 116 is installed on a power line connected to the load 4 and detects the power consumption Pcon consumed by the load 4. Furthermore, various control signals are output from the control device 90 via output ports to the solenoids of the on-off valves 32, 33, the pump motor of the gas pump 36, the pump motor of the reformed water pump 43, the pump motor of the air pump 53, the pump motor of the circulation pump 64, the DC / DC converter 81 and inverter 82 of the power conditioner 80, etc. A remote control (not shown) is connected to the control device 90 via a wireless or wired communication line. The control device 90 performs various controls based on signals from the remote control operated by the user of the fuel cell system 10.

[0031] Here, the control device 90 generates PWM signals for the DC / DC converter 81 and inverter 82 as control signals to the power conditioner 80, and controls the switching elements of the DC / DC converter 81 and inverter 82 (not shown) using the generated PWM signals. Figure 2 is a block diagram showing an example of the functions of the control device 90. In this block diagram, as part of the functions of the control device 90, the function related to calculating the target value of the stack voltage Vs for generating the PWM signal of the DC / DC converter 81 is shown. As shown in the figure, the control device 90 has a target power setting unit 90a, an output power acquisition unit 90b, a subtraction unit 90c, a PI calculation unit 90d, an addition unit 90e, an upper and lower limit processing unit 90f, a delay unit 90g, and a slow change processing unit (rate limit processing unit) 90h. The functions of each unit are described in general below.

[0032] The target power setting unit 90a sets the target power (target output power) Ptag, which is the target value of the output power P of the power conditioner 80, based on the power consumption Pcon of the load 4, and the detailed setting process will be described later. The output power acquisition unit 90b acquires the output power P detected by the power sensor 115. Alternatively, the output current and output voltage output from the power conditioner 80 (inverter 82) may be detected and the output power P calculated as the product of these values ​​may be acquired.

[0033] The subtraction unit 90c calculates the deviation e(n) by subtracting the target power Ptag from the output power P using equation (1). Note that if the target power Ptag is greater than the output power P, the deviation e(n) will be a negative value. The PI calculation unit 90d uses the current deviation e(n) and the previous deviation e(n-1) calculated by the subtraction unit 90c to calculate the proportional term (P term) using equation (2) and the integral term (I term) using equation (3). Note that if the previous deviation e(n-1) is a negative value, subtracting the previous deviation e(n-1) from the deviation e(n) in equation (2) is equivalent to adding the absolute value of the previous deviation e(n-1) to the deviation e(n). The PI calculation unit 90d also calculates the sum of the proportional term and the integral term (PI term) as the change in the manipulated variable u(n) Δu(n) using equation (4). In equations (2) and (3), Kp and Ki are the proportional gain and integral gain, respectively, and Δt is the calculation period (e.g., several msec). Note that the PI calculation unit 90d may be configured as a PID calculation unit that calculates not only the proportional and integral terms but also the differential term. The adder 90e calculates the manipulated variable u(n) by adding the change amount Δu(n) calculated by the PI calculation unit 90d to the previously manipulated variable u(n-1) according to equation (5).

[0034] e(n) = P - Ptag ... (1) P term = Kp(e(n)-e(n-1)) ···(2) Term I = Ki·e(n)·Δt ···(3) Δu(n)=P term+I term...(4) u(n) = u(n-1) + Δu(n) ... (5)

[0035] Thus, in this embodiment, velocity-type PI control is performed to calculate the manipulated variable u(n) by adding the change amount Δu(n) to the previously manipulated variable u(n-1). As will be described later, in this embodiment, since the manipulated variable u(n) is restricted, the time it takes to converge to the target value may be relatively long. In that case, in position-type PI control, the integral term (term I) becomes large, causing so-called wind-up, so it becomes necessary to reset the integral value by defining conditions in advance. To prevent such wind-up and eliminate the need for reset processing, velocity-type PI control is performed.

[0036] The upper and lower limit processing unit 90f performs processing to limit the value calculated by the adder 90e to be less than or equal to a predetermined upper limit and greater than or equal to a predetermined lower limit. The delay unit 90g holds the previous (one-period delayed) manipulated variable u processed by the upper and lower limit processing unit 90f and outputs it to the adder 90e as the previous manipulated variable u(n-1). The slow change processing unit 90h performs rate limit processing to limit the degree of increase or decrease of the current manipulated variable u(n) relative to the previous manipulated variable u(n-1), thereby limiting the manipulated variable u(n) and outputting it.

[0037] From this point onward, block diagrams are omitted as they do not constitute the essence of this disclosure, but the calculated value is processed as the target value of the stack voltage Vs. For example, the control device 90 performs a calculation using feedback control (PI control) based on the deviation between the target value of the stack voltage Vs and the stack voltage Vs detected by the voltage sensor 114, and sets the duty cycle of the DC / DC converter 81 by limiting the calculated value with upper and lower limit processing. The control device 90 then generates a PWM signal for the DC / DC converter 81 based on the duty cycle of the DC / DC converter 81, and controls the switching elements of the DC / DC converter 81 using the generated PWM signal. Note that when the target power Ptag is greater than the output power P and the deviation e(n) remains negative, a value that lowers the target value of the stack voltage Vs is output as the manipulated variable u(n) to increase the output power P.

[0038] Here, Figure 3 is an explanatory diagram showing the difference in the rate of increase of output power P with and without output limiting, where the horizontal axis represents time and the vertical axis represents power. In Figure 3, the case where the target power Ptag (dotted line) corresponds to the power consumption Pcon of load 4 is shown. In addition, the output power P of this embodiment is shown by a solid line, and the output power P' without output limiting such as rate limiting is shown by a double-dotted line. As shown in the figure, the output power P of this embodiment takes a longer time to reach the power consumption Pcon compared to the output power P' without output limiting. Thus, although limiting the rate of increase of output power P can prevent failure and deterioration of the fuel cell stack 21 and provide protection, the time during which the output power P cannot keep up with the target value (power consumption Pcon in Figure 3) increases.

[0039] Next, the processing performed by the CPU 91 of the control device 90 according to the functions described above will be explained. Figure 4 is a flowchart of an example of the target power setting process. In this target power setting process, the CPU 91 obtains the power consumption Pcon of the load 4 detected by the power sensor 115 (S100) and obtains the output power P of the power conditioner 80 detected by the power sensor 116 (S110).

[0040] Next, the CPU 91 sets the smaller of the power consumption Pcon obtained in S100 and the power obtained in S110 plus a predetermined value α (P+α) as the target power Ptag (S120), and terminates the target power setting process. The set target power Ptag is output to the subtraction unit 90c as described above.

[0041] Here, Figure 5 is an explanatory diagram showing an example of the changes in power consumption Pcon, target power Ptag, and output power P in this embodiment. Figure 6 is an explanatory diagram showing an example of the changes in power consumption Pcon, target power Ptag, and output power P in a comparative example. In Figure 5, power consumption Pcon is shown by a dotted line, target power Ptag by a dashed line, and output power P by a solid line. In Figure 6 of the comparative example, the target power Ptag is set according to the power consumption Pcon, and the target power Ptag (power consumption Pcon) is shown by a dashed line, and output power P by a solid line.

[0042] In this embodiment, as described above, the target power Ptag is set to the smaller of the power consumption Pcon and the power obtained by adding a predetermined value α to the output power P (P+α). Therefore, even if the power consumption Pcon rises sharply at time t1, the target power Ptag remains larger than the output power P by a predetermined value α (see Figure 5). As a result, even when there is a large discrepancy between the output power P and the power consumption Pcon, the target power Ptag is set in such a way that the rate of change (rate of increase) of the target power Ptag is suppressed, and the deviation e(n) from the output power P can be kept within the range of the predetermined value α. On the other hand, in the comparative example where the target power Ptag is set according to the power consumption Pcon, a large deviation e(n) occurs. Furthermore, even if the target power Ptag is large, the rate of increase of the output power P is limited, so it does not immediately follow, and the deviation e(n) remains large (see Figure 6). Furthermore, in situations where the target power Ptag is greater than the output power P, and the deviation e(n) remains negative, as described above, the difference between the two deviations e(n) and e(n-1) is calculated by adding the absolute value of the previous negative deviation e(n-1) to the current negative deviation e(n) in equation (2), and the proportional term (P term) is then calculated.

[0043] In this state, consider the case where, at time t2, the power consumption Pcon drops so sharply that it falls below the output power P, and the target power Ptag becomes smaller than the output power P, for example, when the relative magnitudes of output power P and target power Ptag are reversed. In this case, the sign of the current deviation e(n) changes from negative to positive. Therefore, in equation (2) above, the absolute value of the previous negative deviation e(n-1) is added to the current positive deviation e(n), so the original difference between the two deviations e(n) and deviation e(n-1) is not calculated, and instead the sum of the two deviations e(n) and deviation e(n-1) (absolute value) is calculated. Consequently, a large proportional term (P term) is calculated, and the change amount Δu and thus the manipulated variable u become large. In particular, in the comparative example, because the previous deviation e(n-1) was large, its effect is significant, and as a result of calculating an excessively large proportional term, the phenomenon of an excessive decrease in output power P occurs (time t2 in Figure 6). Furthermore, as mentioned above, limiting the rate of increase of the output power P increases the time during which the output power P cannot keep up with the target power Ptag (power consumption Pcon), making such phenomena more likely to occur. Therefore, in this embodiment, by setting the target power Ptag so that the deviation e(n) is kept within the range of a predetermined value α, the influence of the previous deviation e(n-1) is suppressed, and an excessive decrease (drop) in the output power P is prevented (time t2 in Figure 5). The predetermined value α can be set appropriately according to the allowable decrease in output power P. Although not particularly limited, if the rated output of the fuel cell system 10 is 700W, the predetermined value α is set to, for example, 100W.

[0044] Furthermore, in this embodiment, which prevents an excessive decrease in output power P, the output power P can be quickly brought to track the target power Ptag (power consumption Pcon) after time t2. On the other hand, in the comparative example, the output power P continues to deviate from the target power Ptag (power consumption Pcon) even after time t2. Figures 5 and 6 both show that power consumption Pcon rises sharply again at time t3, and then falls sharply at time t4. In the comparative example, an excessive decrease in output power P occurs at time t4, similar to that at time t2. On the other hand, in this embodiment, an excessive decrease in output power P can be prevented, similar to that at time t2. Note that Figures 5 and 6 illustrate the case where the relative magnitudes of target power Ptag and output power P are reversed, but are not limited to this. That is, even if the relative magnitudes of target power Ptag and output power P are not reversed, if the target power Ptag decreases while the output power P is not tracking the target power Ptag, it can result in an excessive decrease in output power P, so the processing of this embodiment should be applied.

[0045] The fuel cell system 10 described above sets the target power Ptag to the smaller of the power consumption Pcon of the load 4 and the power obtained by adding a predetermined value α to the output power P (P+α), thereby keeping the deviation e(n) a small value within the range of the predetermined value α. Therefore, it suppresses the change in the amount Δu and thus the sudden change in the manipulated variable u caused by a rapid change in the target power Ptag, and thus prevents an excessive decrease in output power P with simple processing.

[0046] In the embodiment described above, the smaller of the power consumption Pcon and the power (P+α) was set as the target power Ptag. However, the invention is not limited to this, and other methods may be used, such as setting the target power Ptag in a way that reflects fluctuations in power consumption Pcon while suppressing the rate of increase (rate of change) of the target power Ptag.

[0047] In this embodiment, the target power Ptag was set so that the deviation e(n) falls within a predetermined range α to prevent an excessive decrease in output power P, but this is not the only method. The target power Ptag may be set according to the power consumption Pcon while simultaneously preventing an excessive decrease in output power P. A modified example will be described below. Figure 7 is a flowchart showing the proportional term calculation process.

[0048] In the proportional term calculation process, the CPU 91 first obtains the current deviation e(n), the previous deviation e(n-1), the current target power Ptag(n), and the previous target power Ptag(n-1) (S200). The target power Ptag should be set to the same value as the power consumption Pcon. Next, the CPU 91 determines whether the deviation between the previous target power Ptag(n-1) and the current target power Ptag(n) is greater than or equal to a predetermined value (S210). In S210, it is determined whether the output power target value has decreased. The predetermined value is set to, for example, 5W, although this is not particularly limited.

[0049] In S210, if CPU91 determines that the deviation between the previous target power Ptag(n-1) and the current target power Ptag(n) is greater than or equal to a predetermined value, i.e., that the output power target value has decreased, it changes the deviation e(n-1) to a value of 0 (S220). In other words, CPU91 uniformly sets the deviation e(n-1) to a value of 0 regardless of its actual value. Then, it calculates the proportional term using the above-mentioned equation (2) (S230) and terminates this process. If CPU91 determines in S210 that the output power target value has not decreased, it skips S220 and calculates the proportional term as usual in S230 and terminates this process.

[0050] In this modified example, if the deviation between the previous target power Ptag(n-1) and the current target power Ptag(n) is greater than or equal to a predetermined value, the deviation e(n-1) is set to a smaller value of 0 than the actual value, and subtracted from the current deviation e(n) to calculate the proportional term. Therefore, as described above, when the sign of the current deviation e(n) changes from negative to positive, a large proportional term is calculated because the previous deviation e(n-1) was large, which would cause the feedback control to over-operate and result in an excessive decrease in output power P. This prevents this from happening. In other words, it achieves the same effect as the embodiment described above.

[0051] In the modified example, the deviation e(n-1) is changed to 0 in S220, but this is not the only option; it is sufficient to change it to a value with a smaller absolute value than the actual value of the deviation e(n-1). For example, it can be changed to a predetermined value or to a value with a smaller absolute value than the predetermined value.

[0052] In the embodiments and modifications, excessive reductions in output power P were prevented by setting limits on the target power Ptag or by changing the value of the previous deviation e(n-1), but the invention is not limited to these methods. For example, excessive reductions in output power P may be prevented by limiting the difference obtained by subtracting the previous deviation e(n-1) from the current deviation e(n) if the difference has changed significantly from the previous difference.

[0053] The correspondence between the main elements of the embodiment and the main elements of the disclosure described in the section on the main elements of the embodiment and the means for solving the problems will be explained. In the embodiment, the fuel cell stack 21 corresponds to the "fuel cell" in the disclosure, the power conditioner 80 corresponds to the "power converter", and the control device 90 corresponds to the "control device".

[0054] Furthermore, the correspondence between the main elements of the embodiments and the main elements of the disclosure described in the section on means for solving the problems is merely an example to specifically explain the form in which the embodiments implement the disclosure described in the section on means for solving the problems, and does not limit the elements of the disclosure described in the section on means for solving the problems. In other words, the interpretation of the disclosure described in the section on means for solving the problems should be based on the description in that section, and the embodiments are merely one specific example of the disclosure described in the section on means for solving the problems.

[0055] The above describes the forms for implementing this disclosure, but this disclosure is not limited in any way to these embodiments, and it is of course possible to implement it in various forms without departing from the gist of this disclosure. [Industrial applicability]

[0056] This disclosure can be used in industries such as the manufacturing of fuel cell systems. [Explanation of Symbols]

[0057] 1 Raw fuel source, 2 Power grid, 3 Power line, 4 Load, 10 Fuel cell system, 20 Power generation module, 21 Fuel cell stack, 22 Vaporizer, 23 Reformer, 24 Combustor, 26,27 Heat exchanger, 28 Combustion catalyst, 29 Module case, 30 Raw fuel gas supply device, 31 Raw fuel gas supply pipe, 32,33 On / off valve, 36 Gas pump, 38 Desulfurizer, 39 Flow sensor, 40 Reformed water supply device, 41 Reformed water supply pipe, 42 Reformed water tank, 43 Reformed water pump, 44 Condensate piping, 45 Flow sensor, 50 Air supply device, 51 Air supply pipe, 52 Air filter, 53 Air pump, 60 Waste heat recovery device, 61 Hot water storage tank, 62 Condenser, 63 Circulation piping, 64 Circulation pump, 71 Anode gas piping, 72 Cathode gas piping, 73, 74 Anode off gas piping, 75 Cathode off gas piping, 76 Combustion exhaust gas piping, 80 Power conditioner, 81 DC / DC converter, 82 Inverter, 85 Power supply board, 90 Control device, 90a Target power setting unit, 90b Output power acquisition unit, 90c Subtraction unit, 90d PI calculation unit, 90e Addition unit, 90f Upper and lower limit processing unit, 90g Delay unit, 90h Slow change processing unit, 91 CPU, 92 ROM, 93 RAM, 111, 112 Temperature sensor, 113 Current sensor, 114 Voltage sensor, 115, 116 Power sensor.

Claims

1. A fuel cell system equipped with a fuel cell, A power converter that converts the power output of the fuel cell into electricity that can be supplied to a load and outputs it, A control device that sets a target output power for the power converter and controls the power converter based on an input variable set by feedback control so that the output power of the power converter becomes the target output power, Equipped with, The aforementioned feedback control is a speed-type control that calculates a deviation by subtracting the target output power from the output power, calculates a change amount that includes a proportional term obtained by multiplying the difference between the current value and the previous value of the deviation by a proportional gain, and adds this change amount to the previous value of the manipulated variable to set the manipulated variable. The control device sets the target output power in such a way as to suppress the rate of change of the target output power. Fuel cell system.

2. The control device sets the target output power to the smaller of the power consumed by the load and the power obtained by adding a predetermined value to the output power. The fuel cell system according to claim 1.

3. A fuel cell system equipped with a fuel cell, A power converter that converts the power output of the fuel cell into electricity that can be supplied to a load and outputs it, A control device that sets a target output power of the power converter based on the power consumption of the load, and controls the power converter based on an input variable set by feedback control so that the output power of the power converter becomes the target output power, Equipped with, The aforementioned feedback control is a speed-type control that calculates a deviation by subtracting the target output power from the output power, calculates a change amount that includes a proportional term obtained by multiplying the difference between the current value and the previous value of the deviation by a proportional gain, and adds this change amount to the previous value of the manipulated variable to set the manipulated variable. When the target output power decreases, the control device subtracts a value with a smaller absolute value than the actual value from the current value of the deviation, as the previous value of the deviation. Fuel cell system.

4. The control device sets a value of 0 to a value that is smaller in absolute value than the actual value. The fuel cell system according to claim 3.

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