JP2007012532A - Control device of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel consumption efficiency of a fuel cell system by accurately estimating impurity gas concentration of a hydrogen circulating system to reduce a purge volume and save driving energy of a circulating pump. <P>SOLUTION: A gas composition estimation means 104 is provided with a steady gas mass density estimation calculation part 104a carrying out gas mass density estimation from a steady operation state of the fuel cell system, and an excessive gas mass density estimation calculation part 104b carrying out gas mass density estimation from an excessive operation state, and estimates a gas composition in a fuel circulation channel based on a target generation power decided by a target generation power deciding means 101, an operating state detected by a fuel cell operating state detecting means 102, and an operating state of a circulating device detected by a circulating device operating state detecting means 103. Estimation results of the gas composition are input into an impurity draining means 105 draining outside impurities in the fuel circulation system, a circulation device control means 106 controlling the circulating device, and a fuel supply control means 107 controlling a fuel supply volume, and utilized for an operation control of the fuel cell. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a fuel cell system, and more particularly to a control device for a fuel cell system that recirculates unreacted fuel.

  In general, a fuel cell is a device that directly converts chemical energy of a fuel into electrical energy by electrochemically reacting a fuel gas such as hydrogen with an oxidant such as air. A polymer electrolyte fuel cell using a polymer electrolyte membrane is known.

  In order to perform stable power generation with a fuel cell, it is necessary to supply more hydrogen to the fuel electrode than is necessary for power generation, and excess hydrogen that did not react chemically is discharged from the fuel cell outlet. The Therefore, a fuel cell system is known in which unreacted fuel discharged is circulated again to the supply side by a circulation device such as a circulation pump in order to further increase the utilization efficiency of hydrogen.

  By the way, in the fuel cell system in which hydrogen is circulated, when air is used as an oxidant, impurities such as nitrogen permeate from the oxidant electrode to the fuel electrode through the electrolyte membrane of the fuel cell, and the like. Will be accumulated. As a result, the hydrogen concentration in the fuel cell decreases and the output decreases, or the amount of hydrogen circulated by the circulation device decreases, so that stable power generation cannot be performed.

Therefore, in order to cope with such a problem, a discharge valve is provided in the hydrogen circulation path, and impurities in the circulation path are discharged to the outside. However, since a small fuel cell does not include a hydrogen separation device that separates impurities from hydrogen, hydrogen is discharged together when impurities are discharged. If the discharge valve is opened too much, hydrogen will be discarded excessively and the utilization rate of hydrogen will decrease. Therefore, a fuel cell system that detects the load state of a circulation pump driven by a rotating machine and calculates the impurity gas concentration from the load state is disclosed (for example, Patent Document 1).
Japanese Patent Laying-Open No. 2004-165093 (6th page, FIG. 4)

  Normally, the higher the pressure of the fuel gas and the oxidant gas, the higher the power generation efficiency in the fuel cell body. However, the power consumption of the blower and compressor that supply air as the oxidant gas increases as the air supply pressure increases. For this reason, the operation method of the fuel cell which increases fuel gas and air pressure according to the increase in generated electric power (electric current) is generally performed.

  Due to such changes in the operating pressure of the fuel cell, the gas mass density changes even if the impurity concentration and gas composition in the hydrogen system are constant. In addition, immediately after the start of power generation, the temperature of the fuel cell may be below freezing point. On the other hand, the fuel cell may be used even in a state close to 100 ° C. For this reason, even if the gas composition in the hydrogen system is constant, the influence of the gas mass density due to the expansion and contraction of the gas due to the temperature is also great.

  A change in gas mass density changes the pressure loss generated in the fuel cell and the circulation path. At this time, since the load state at a predetermined rotation speed of the circulation pump changes depending on the head (discharge pressure) necessary for circulating the gas, in the fuel cell system in which the pressure and temperature are likely to change, the impurity gas is changed from the load state. By directly calculating the density, the calculation error becomes large.

  Also, when the rotational speed of the circulation pump is changed according to the target power generation amount, for example, the load increases transiently during acceleration. For example, if estimation is performed using such values, the impurity gas concentration can be accurately determined. Cannot be estimated.

  In order to solve the above problems, the present invention provides a fuel cell configured by laminating a plurality of single cells each having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode, and fuel to the fuel cell. A fuel supply path to be supplied, a fuel circulation path for circulating the residual fuel discharged from the fuel electrode to the fuel supply path, and a booster for circulating the remaining fuel discharged from the fuel electrode provided in the fuel circulation path A circulation device, a circulation pressure detection means for detecting the pressure of the fuel circulation passage, a circulation passage gas temperature detection means for detecting a gas temperature of the fuel circulation passage, and a circulation device operation for detecting an operating state of the circulation device. In the fuel cell system comprising the state detection means, the mass density of the gas circulated by the circulation device is estimated based on the operation state value detected by the circulation device operation state detection means, and the estimated value of the gas mass density , The circuit pressure A fuel cell system comprising gas composition estimation means for estimating a gas composition in the fuel circulation path based on a pressure detection value of a detection means and a temperature detection value of the circulation path gas temperature detection means. It is a control device.

  The present invention utilizes a difference in molecular weight between a fuel gas (for example, hydrogen: molecular weight 2) and an impurity gas (for example, nitrogen: molecular weight 28) that has permeated through the electrolyte membrane from the oxidant electrode to the fuel electrode. The gas composition inside the road is estimated. That is, the reaction received from the gas circulated by the fuel circulation device is proportional to the mass density of the gas. The magnitude of this reaction can be detected as the circulating device operating state, and the mass density of the gas inside the fuel circulation path can be estimated based on this operating state detection value. Then, the gas composition in the fuel circulation path is estimated from the estimated mass density, the pressure in the fuel circulation path, and the temperature in the fuel circulation path. The gas composition estimated in this way can be used for high accuracy of operation control of the fuel cell such as purge control and fuel circulation control.

  According to the present invention, the mass density of the gas in the circulation path is estimated based on the operating state detection value of the circulation device that circulates the unreacted fuel discharged from the fuel electrode to the fuel supply path. Since the gas composition in the fuel circulation path can be estimated based on the estimated value, the circulation path pressure detection value, and the circulation path gas temperature detection value, even when the pressure and temperature in the fuel path change, There is an effect that the gas composition in the fuel circulation path can be accurately estimated.

  Further, by using the estimated gas composition value in the fuel circulation path accurately estimated in this way for operation control of the fuel cell system, the fuel gas at the time of purging can be saved and the driving force of the fuel circulation device can be reduced. There is an effect that the fuel efficiency of the fuel cell system can be improved.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are not particularly limited, but are preferred embodiments for a fuel cell vehicle in which the fuel efficiency of the fuel cell system directly affects the travelable distance.

  FIG. 1 is a diagram showing a basic configuration of the present invention. The target generated power determining means 101 in the figure determines the target generated power of the fuel cell. The fuel cell operating state detection means 102 detects the operating state of the fuel cell system. The circulation device operating state detection means 103 detects the operation state of the circulation device that circulates the fuel gas discharged from the fuel electrode outlet to the fuel electrode inlet.

  The gas composition estimating means 104 is based on the target generated power determined by the target generated power determining means 101, the operating state detected by the fuel cell operating state detecting means 102, and the operating state detected by the circulating device operating state detecting means 103. Estimate the gas composition in the fuel circuit. The gas composition estimation means 104 includes a steady gas mass density estimation calculation unit 104a that performs gas mass density estimation from a steady operation state of the fuel cell system, and a transient gas mass density estimation that performs gas mass density estimation from a transient operation state. A calculation unit 104b is provided. The estimation result of the gas composition estimating means 104 controls the impurity discharge means 105 for releasing impurities in the fuel circulation system to the outside, the circulation device control means 106 for controlling the rotation speed of the circulation device, and the amount of fuel supplied to the fuel cell. Input to each of the fuel supply control means 107 to determine the operation of the fuel cell system.

  FIG. 2 is a system configuration diagram showing the configuration of the fuel cell system to which the first embodiment of the present invention is applied. The fuel cell system 1 includes, for example, a polymer electrolyte fuel cell 2. The fuel cell 2 has a structure in which a plurality of unit cells (cells) in which an electrolyte membrane 3 is sandwiched between an anode (fuel electrode) 4 and a cathode (oxidant electrode) 5 are stacked, but only the unit cell is illustrated. Hydrogen gas is supplied as fuel to the anode 4 and air is supplied as oxidant gas to the cathode 5, and the electrode reaction shown below proceeds to generate electric power.

Anode (fuel electrode): H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode (oxidant electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
At this time, a part of the water generated at the cathode 5 becomes water vapor and permeates the electrolyte membrane 3 and enters the anode 4. Hydrogen as a fuel gas is supplied from the hydrogen tank 6 to the anode 4 through the hydrogen tank main valve 7, the pressure reducing valve 8, and the hydrogen supply valve 9. The high-pressure hydrogen supplied from the hydrogen tank 6 is mechanically reduced to a predetermined pressure by the pressure reducing valve 8 and further reduced by the hydrogen supply valve 9 so that the hydrogen pressure at the inlet of the anode 4 becomes a desired pressure. The hydrogen pressure at the anode inlet is detected by the anode inlet pressure sensor 10 a and input to the controller 30.

  A fuel circulation path 11 is provided for circulating the fuel gas that has not been consumed at the anode from the outlet of the anode 4 to the inlet of the anode 4. The circulation pump 12 is a circulation device that boosts and circulates the fuel gas in the fuel circulation path 11. Circulation pump 12 is driven by an electric motor (not shown), and current of this electric motor is detected by current sensor 13. Air to the cathode 5 is supplied by the compressor 14. An air pressure adjusting valve 24 is provided at the cathode outlet to control the cathode pressure.

  The power manager 15 extracts power from the fuel cell 2 and supplies power to the load device 16 or the battery 17. The battery controller 18 monitors the charging / discharging current of the battery 17 to calculate the state of charge (SOC) of the battery, and transmits the SOC to the controller 30. The voltage sensor 19 measures the voltage of each unit cell of the fuel cell 2 or each unit cell group in which a plurality of unit cells are connected in series. The controller 30 controls each actuator in the system using each sensor signal at the time of starting, stopping, and generating power of the fuel cell system.

  In order to supply air as an oxidant to the cathode 5, non-chemically reacting nitrogen permeates the electrolyte membrane 3 and accumulates in a hydrogen circulation system including the anode 4, the fuel circulation path 11 and the circulation pump 12. If the amount of nitrogen accumulated in the hydrogen circulation system increases too much, the mass density of the gas in the hydrogen circulation system increases and the gas circulation amount by the circulation pump 12 cannot be maintained, so the amount of nitrogen in the hydrogen circulation system must be managed. There is. Therefore, the gas containing nitrogen in the hydrogen circulation system is discharged to the outside by the purge valve 20 so that the circulation performance can be maintained for the amount of nitrogen present in the hydrogen circulation system. The anode outlet pressure sensor 10b is a sensor that measures the pressure at the anode outlet, the anode inlet temperature sensor 21a is a sensor that measures the temperature of the gas at the anode inlet, the anode outlet temperature sensor 21b is a temperature sensor that measures the gas temperature at the anode outlet, and humidity The sensor 22 is a sensor that measures the humidity of the gas in the fuel circulation path 11, and each detected value is input to the controller 30.

  FIG. 3 shows the configuration of the controller 30. Requested power detection unit 31 for detecting the power required for the fuel cell 2, charge state detection unit 32 for detecting the SOC transmitted from the battery controller 18, detection values of the required power detection unit 31 and the charge state detection unit 32 , A fuel cell generated power determining unit 33 that determines target generated power in the fuel cell, and an oxidant supply amount control unit that determines the supply amount of the oxidant based on the target generated power and controls the compressor 14 34, the fuel supply amount is determined based on the target generated power, the fuel supply amount control unit 35 that controls the hydrogen supply valve 9 based on the anode inlet pressure sensor 10a, and the target generated power is stable. Based on the circulation amount control unit 36 that controls the circulation pump 12 and the target generated power so as to realize the hydrogen circulation flow rate that is necessary for power generation, the energy for the required power A supply current control unit 37 that controls power to be supplied or charged by the power manager 15 to charge the battery, a circulation pump current detected by the circulation pump state quantity detection unit 39, and a circulation pump current The gas mass density and the gas composition are estimated based on the rotation speed, and the gas state quantity estimation unit 38 and the gas composition result estimated by the gas state quantity estimation unit 38 are irrelevant to the chemical reaction in the fuel cell. An emission amount control unit 40 for releasing substances from the hydrogen path to the outside, and a fuel cell system activation / deactivation determination unit 41 that determines activation or deactivation of the fuel cell system.

  The required power generation amount detection unit 31 uses the fuel cell 2 directly as an energy supply source like a generator, or indirectly uses a fuel cell as an energy supply source like an energy supply source for driving force of a moving body. The required power to the fuel cell 2 is detected.

  The charge state detection unit 32 receives the SOC from the battery controller 18. The battery controller 18 constantly monitors the temperature, voltage, and charge / discharge current of the battery 17 to calculate the SOC of the battery. The SOC is expressed, for example, as a ratio (%) to the full charge amount of the battery.

  The fuel cell power generation amount determination unit 33 determines the generated power in the fuel cell 2 from the required power transmitted from the required power detection unit 31 and the SOC transmitted from the charge state detection unit 32.

  The oxidant supply amount control unit 34 calculates the supply amount of the oxidant corresponding to the power generation amount based on the target generated power determined by the fuel cell power generation amount determination unit 33 and determines the target rotation speed of the compressor 14. The compressor 14 is provided with a controller for controlling the actual rotational speed in accordance with the target rotational speed.

  Based on the target generated power determined by the fuel cell generated power determining unit 33, the fuel supply amount control unit 35 converts the hydrogen supply necessary for power generation and the conversion efficiency to be achieved so as to satisfy the target generated power. The target opening of the hydrogen supply valve 9 is determined using the anode inlet pressure sensor 10a so as to satisfy the target value. The hydrogen supply valve 9 is provided with a controller for controlling the actual opening degree according to the target opening degree.

  The circulation amount control unit 36 determines the rotation speed of the circulation pump 12 in order to realize the surplus hydrogen circulation amount based on the target generated power determined by the fuel cell generated power determination unit 33. At this time, in order to determine the rotation speed with respect to the target generated power, it is necessary to assume the amount of nitrogen existing in the hydrogen circulation system. The gas density in the hydrogen circulation system when the assumed amount of nitrogen exists is determined as the standard gas density. For example, assuming that the volume of the gas in the hydrogen circulation system is expressed using 0 [° C.] and 1 [atm], which are gas standard states, the volume of nitrogen (nitrogen amount) is, for example, 10 From the range of ˜40 [%], it is set to an arbitrary point with high fuel efficiency obtained experimentally.

  Here, if the generated power of the fuel cell is used for the driving power of the circulation pump, this power cannot be supplied to the external load. Therefore, in the fuel cell efficiency of the fuel cell, the hydrogen discharged simultaneously with the discharge of impurities due to the purge. The quantity and the driving power of the circulation pump are in a reciprocal relationship.

  When the nitrogen amount is set high, the purge amount or the purge frequency is reduced, and the amount of hydrogen discharged at the same time as the impurity discharge can be reduced. However, the mass density of the gas in the hydrogen circulation system is increased, which is a circulation device. The driving power of the circulation pump increases. Conversely, if the nitrogen amount is set low, the mass density of the gas in the hydrogen circulation system is reduced, and the drive power of the circulation pump can be reduced, but the purge amount or purge frequency increases, and the impurities are discharged simultaneously with the impurity discharge. The amount of hydrogen produced increases. In the polymer electrolyte fuel cell, depending on the material, structure, power density, etc. of the fuel cell, there is an optimum nitrogen amount in the range of 10 to 40 [%] where the fuel efficiency becomes the highest. It is preferable to obtain and set.

  The nitrogen amount thus determined is set as a target nitrogen amount to be maintained in the hydrogen circulation system during operation of the fuel cell. The circulation pump 12 is provided with a controller for controlling the actual rotational speed in accordance with the target rotational speed.

  The extraction current control unit 37 determines a target extraction current for the power manager 15 to extract the target generated power from the fuel cell 2 based on the target generated power determined by the fuel cell generated power determination unit 33. The power manager 15 includes a controller for controlling the actual extraction current in accordance with the target extraction current.

  The gas state quantity estimation unit 38 uses the rotational speed of the circulation pump 12 detected by the circulation pump state quantity detection unit 39 and the current flowing in the drive motor of the circulation pump detected by the current sensor 13 in the fuel circulation path 11. Estimate the gas mass density. At this time, the gas mass density estimation method is switched between a steady gas mass density estimation calculation and a transient gas mass density estimation calculation depending on whether the operation state of the fuel cell is a steady state or a transient state. The gas composition is estimated using the estimated gas mass density.

  The discharge amount control unit 40 determines the impurity discharge amount based on the gas composition estimation result estimated by the gas state amount estimation unit 38 and controls the opening degree of the purge valve 20.

  The fuel cell system activation / deactivation determination unit 41 makes a determination that the user is requested to start power generation of the fuel cell or that the power generation request power from the user is reduced and power generation is suspended.

  FIG. 4 is a flowchart for explaining the operation of the controller in the first embodiment.

  First, in step (hereinafter abbreviated as S) 102, the required power to the fuel cell system is detected, and in S104, the SOC of the battery 17 is received from the battery controller 18 to detect the SOC. Next, in S106, the current generated power of the fuel cell 2 (hereinafter simply referred to as generated power) and the target generated power are calculated. The generated power is calculated by the product of the current total voltage of the fuel cell 2 detected by the voltage sensor 19 and the current extraction current notified from the power manager 15. The target generated power is calculated, for example, as power that follows the required power by limiting the change speed of the required power within a certain change speed that the fuel cell can respond to.

  Next, in S108, it is determined whether the generated power is larger than the required power. If the generated power is larger than the required power, the process proceeds to S110, and if not, the process proceeds to S112.

  In S110, it is determined whether the SOC detected in S104 is less than SOC1. Here, the SOC1 may be a predetermined value, but the generated power Pf−the required power Pr = the surplus power Pe is an SOC having a free capacity capable of charging the battery 17 for a predetermined time T1 necessary for steady gas mass density estimation. Is preferred.

(1-SOC1) × Q = (Pe / V) × T1 (3)
Here, the voltage V of the battery, the maximum charge capacity Q of the battery, the SOC, and the SOC1 are numbers from 0 to 1 ([0, 1]).

  If it is determined in S110 that the SOC is less than SOC1, it is determined that there is sufficient free capacity to charge the battery 17 with surplus power, and the process proceeds to S114. If the SOC is SOC1 or more, the process proceeds to S116.

  In S112, it is determined whether or not the SOC detected in S104 is greater than SOC2. Here, the SOC2 may be a predetermined value different from the SOC1, but the charge capacity that can be discharged from the battery 17 during the predetermined time T1 required for the steady gas mass density estimation is calculated as the generated power Pf−the required power Pr = the insufficient power Pu. A certain SOC is preferable.

SOC2 × Q = (Pu / V) × T1 (4)
Here, V is a battery voltage, Q is a battery maximum charge capacity, and SOC and SOC2 are numbers from 0 to 1.

  If it is determined in S112 that the SOC is greater than SOC2, it is determined that there is sufficient charge capacity to discharge the insufficient power from the battery 17, and the process proceeds to S114. If the SOC is SOC2 or less, the process proceeds to S116.

  In S114, the target air flow rate determined by the oxidant supply amount control unit 34, the compressor rotation speed, and the fuel supply amount control unit 35 are determined in order to create a steady operation state of the fuel cell system and estimate the gas composition. The target fuel cell inlet pressure, the circulation pump rotational speed determined by the circulation amount control unit 36, and the target extraction current determined by the extraction current control unit 37 are fixed. That is, the instruction values to the hydrogen supply valve 9, the circulation pump 12, the compressor 14, and the air pressure adjusting valve 24 for controlling the operation parameters of the fuel cell are continued, and the current manager is instructed to continue the current extraction. , Go to S118.

  In S116, it is determined that a steady operation state cannot be performed in S110 or S112. Therefore, the target generated power determined by the fuel cell generated power determination unit 33 is determined based on the required power and the remaining battery capacity. As a result, the oxidant supply amount control unit 34, the fuel supply amount control unit 35, the circulation amount control unit 36, and the extraction current control unit 37 determine the target operation amount of each actuator corresponding to the target power generation amount. That is, the control target values for the hydrogen supply valve 9, the circulation pump 12, the compressor 14, and the air pressure adjusting valve 24 are set by referring to a map of various control values corresponding to the target generated power equivalent value of the fuel cell calculated in S 106. In addition, the power manager 15 is instructed to extract a current corresponding to the target generated power, and the process proceeds to S118.

  In S118, the detected values of the anode inlet pressure sensor 10a, the anode inlet temperature sensor 21a, the anode outlet pressure sensor 10b, the anode outlet temperature sensor 21b, the rotational speed sensor of the circulation pump 12, and the drive motor current sensor 13 of the circulation pump 12 are used as fuel. Read as battery operating status.

  Next, in S120, it is determined whether the operation state of the fuel cell system is a steady operation state and the state continues for a predetermined time or more. Specifically, the target generated power is a constant value for a predetermined time, the extraction current at the anode inlet pressure sensor 10a, the anode outlet pressure sensor 10b, the power manager 15, the rotational speed of the circulation pump 12, and the circulation pump motor current detection value. A constant value is detected for a predetermined time. The predetermined time at this time is set by obtaining in advance the time required for estimating the steady gas mass density by experiment.

  If the steady state duration time is equal to or longer than the predetermined time in S120, the process proceeds to S122, the steady gas mass density calculation is performed, and the process proceeds to S126. If the steady state duration time is less than the predetermined time in S120, the process proceeds to S124, a transient gas mass density calculation is performed, and the process proceeds to S126.

  In S122, a steady gas mass density estimation calculation is performed. Details of this calculation are shown in the steady gas mass density estimation unit 201 of FIG. The steady gas mass density estimation unit 201 includes a map for calculating the gas mass density from the circulation pump rotation speed and the circulation pump drive motor current. This map is obtained by enclosing gas of different gas mass density in the anode and fuel circulation path of the actual fuel cell system, changing the circulation pump rotation speed, and measuring the current of the circulation pump drive motor, or The pressure loss characteristic design value of the fuel circulation path and the fuel cell, the pressure flow characteristic of the pump, and the design value of the rotational speed-torque characteristic of the drive motor at this time are designed.

  FIG. 6 shows the relationship between the pressure flow characteristics of the pump and the pressure loss characteristics of the fuel circuit and the fuel cell anode. In order to increase the gas in the fuel circulation path by the circulation pump and ensure the circulation flow rate, it is necessary to increase the pressure by the pressure loss determined from the configurations of the fuel circulation path and the anode gas flow path of the fuel cell. Therefore, the operating point of the circulation pump when operating at the predetermined rotational speed R1 is obtained as the intersection of the pressure flow characteristic of the pump and the pressure loss characteristic.

  As shown in FIG. 6, the pressure loss characteristic varies depending on the gas mass density. Therefore, the operating point of the circulation pump varies depending on the difference in the gas mass density, that is, the work rate of the pump varies with the gas mass density. Since the power of the motor that drives the circulation pump is the product of the rotation speed and torque, the rotation speed is fixed, and the change in torque from the change in the work efficiency of the circulation pump due to gas mass density makes it possible to Perform density estimation.

  Here, since the pressure and temperature of the fuel cell change depending on the operating state, the change in the gas mass density changes not only in the gas composition but also in the pressure and temperature. Further, as shown in FIG. 7, there are some speed type circulation pumps whose pressure flow characteristics at each rotation speed change depending on the gas mass density. The target to be managed during the operation of the fuel cell is the gas composition of the hydrogen circulation system of the fuel cell, particularly the nitrogen concentration. In order to determine the gas composition, it is necessary to first determine the gas mass density in consideration of the fact that the operating point of the circulation pump varies depending on the gas mass density, and then determine the gas composition taking into account the effects of pressure and temperature. There is.

  Returning to FIG. 4, a transient gas mass density estimation calculation is performed in S124. The transient gas mass density estimation calculation is an estimation method performed when the rotation speed of the circulation pump is not constant, and its principle is shown in FIG. FIG. 8A is an explanatory diagram of mechanical parameters in transient gas mass density estimation, and FIG. 8B is a time chart showing changes in the motor torque of the circulation pump given a constant target rotational speed at different gas mass densities. is there.

In the circulation pump, it is assumed that the rotor part of the drive motor and the impeller part of the circulation pump are connected by a highly rigid shaft, and the inertia (moment of inertia) of this rotating part is J _M. When driving torque τ _M is applied to the motor rotor, the reaction force τ _G (ρ) of the gas boosted by the impeller acts in a direction that prevents rotation. A time change of the rotational speed ω _M of the motor, that is, the impeller, is generated by the combined force of the driving force and the reaction force. This relationship is expressed by the following formula (5). Here, ρ is the mass density of the gas.

τ _M −τ _G (ρ) = J _M × (d (ω _M ) / dt) (5)
Therefore, the gas reaction force τ _G (ρ) can be calculated from the inertia of the rotating portion of the circulation pump, the drive torque (ie, current), and the change in the rotation speed. Specifically, for example, the rotation speed change Δω _M and the drive motor torque τ _M are obtained for each sampling period ΔT, and τ _G (ρ) is calculated for each sampling period ΔT. Next, an average value of τ _G (ρ) in a plurality of sampling periods is obtained. Then, the gas mass density ρ is obtained using the average value of τ _G (ρ) from the map in which the relationship between τ _G (ρ) and the gas mass density ρ has been obtained in advance by experiments.

  After performing the steady gas mass density estimation calculation of S122 or the transient gas mass density calculation of S124, next, in S126, a gas composition estimation calculation is performed based on the estimated gas mass density. The gas composition estimation method is shown in FIG.

  The molar mass calculation unit 202 calculates the molar mass by the equation (6) from the estimated gas mass density value, the circulation path pressure detection value detected by the pressure sensor 10b, and the circulation path temperature detection value detected by the temperature sensor 21b.

Molar mass [g / mol] = (Estimated gas mass density [g / L]) x (Total gas volume 22.4 [L / mol])
× (1atm pressure 101.3 [kPa] / circulation pressure sensor detection value [kPa])
× (1+ (Temperature sensor detection value [K] / 0 [℃] temperature 273.15 [K]))
(6)
The water vapor concentration calculation unit 203 obtains the water vapor concentration from the circuit temperature sensor detection value, the circuit pressure sensor detection value, and the circuit humidity detection value detected by the humidity sensor 22. As this method, the water vapor partial pressure is obtained from the temperature and humidity using the Antoine equation, and the water vapor partial pressure is divided by the total pressure to obtain the water vapor concentration.

  The gas composition calculation unit 204 obtains a hydrogen concentration and a nitrogen concentration. Since M is the molar mass determined by the molar mass calculation unit 202, y is the water vapor concentration determined by the water vapor concentration calculation unit 203, and x is the nitrogen concentration, M and y are expressed as the following equation (7). Since x is known, the hydrogen concentration and the nitrogen concentration are determined.

M = (molecular weight of hydrogen [g / mol]: 2) × (1-x) + (molecular weight of nitrogen [g / mol]: 28) × x
+ (Molecular weight of water vapor [g / mol]: 18) x y (7)
In a fuel cell, if power generation is performed at a low temperature, the water vapor partial pressure is not high, and if the total pressure is high, the water vapor concentration is small, so the water vapor concentration need not be taken into consideration. Further, when it is considered that the water vapor is always in a saturated state as in an internal humidified fuel cell, the humidity sensor is unnecessary because the saturated water vapor pressure can be obtained from the detection value of the temperature sensor.

  Returning to FIG. 4, in S128, the nitrogen amount in the hydrogen circulation system is estimated from the nitrogen concentration obtained in S126, and the estimated nitrogen amount and the target nitrogen amount are compared. As shown in FIG. 6, this is estimated by using the fact that the intersection of the pressure flow rate characteristic at a predetermined rotational speed of the circulation pump and the pressure loss characteristic of the fuel circulation path and the fuel cell anode varies depending on the gas mass density. The circulation flow rate is obtained from the gas mass density and the rotation speed of the circulation pump based on the pressure flow characteristic of the pump.

  Then, the amount of nitrogen in the hydrogen circulation system is obtained from the flow path volume between the fuel circulation path 11 and the anode 4 of the fuel cell, the hydrogen supply amount and the circulation flow rate, and the estimated nitrogen concentration, water vapor concentration, and hydrogen concentration.

  The amount of nitrogen in the fuel circulation path 11 is obtained by multiplying the volume of the fuel circulation path 11 by the estimated nitrogen concentration in the fuel circulation path.

  In order to obtain the nitrogen amount in the anode 4 of the fuel cell, first, the nitrogen concentration at the fuel cell inlet is obtained from the hydrogen supply amount and the circulation flow rate. The hydrogen supply amount is obtained from the opening of the hydrogen supply valve 9 and the differential pressure across it. Then, assuming that the nitrogen concentration distribution in the anode changes linearly from the inlet to the outlet, the average nitrogen concentration is obtained from the anode inlet nitrogen concentration and the circulation channel nitrogen concentration, and this is multiplied by the volume in the anode.

  When the obtained nitrogen amount is converted into the standard state of gas, 0 [° C.], 1 [atm], the sensor value is used to calculate the average value of pressure and temperature, and this is used for conversion. These processes are performed by the gas state quantity estimation unit 38.

  If it is determined in S128 that the estimated nitrogen amount is larger than the target nitrogen amount, the process proceeds to S130. If the estimated nitrogen amount is equal to the target nitrogen amount, the process returns without doing anything. If the estimated nitrogen amount is less than the target nitrogen amount, the process proceeds to S138.

  In S130, the purge valve 20 is controlled so as to increase the nitrogen discharge amount. In the case of the purge valve 20 that opens and closes periodically, the open time is extended or shortened, and in the case of a variable opening valve, the control amount is corrected so as to increase the opening. The correction amount at this time is determined based on at least one of the difference between the estimated nitrogen amount and the target nitrogen amount, or the difference between the actual current value and the current value of the circulation pump at the standard gas density. The larger the difference is, the more the discharge amount is corrected. Then, the process proceeds to S132.

  In S132, it correct | amends so that a target rotational speed may be increased with respect to the target rotational speed of the circulation pump 12 determined by the circulation amount control part 36 of FIG. The correction amount at this time is determined based on the difference between the target nitrogen amount and the estimated nitrogen amount. Then, the process proceeds to S134.

  In S134, it is determined whether the rotation speed reaches the maximum value in the circulation pump performance as a result of increasing the rotation speed in S132. If it is determined that the maximum value is reached, the target rotational speed of the circulation pump is limited to the maximum value, and the process proceeds to S136. If not, the process returns.

  In S136, since the circulating pump rotational speed reaches the maximum value in S134 and the circulating flow rate cannot be increased, it is determined that the amount of hydrogen supplied to the fuel cell is insufficient, and the target value for the normal use of the target value of the fuel cell inlet pressure is determined. Set higher than the value. Here, the target value returns after setting an upper limit in consideration of the pressure resistance of the fuel cell 21. As a result, the opening of the hydrogen supply valve increases, and the amount of hydrogen supplied increases.

  In S138, the purge valve 20 is controlled so as to reduce the nitrogen discharge amount. If the purge valve 20 opens and closes periodically, the opening time is shortened or the closing time is extended. If the valve is a variable opening valve, the control amount is corrected so as to reduce the opening. The correction amount at this time is determined based on at least one of the difference between the estimated nitrogen amount and the target nitrogen amount, or the difference between the actual current value and the current value of the circulation pump at the standard gas density. The larger the difference is, the smaller the discharge amount is corrected. Then, the process proceeds to S140.

  In S140, the target rotation speed of the circulation pump 12 determined by the circulation amount control unit 36 in FIG. 3 is corrected so as to decrease the target rotation speed. The correction amount at this time is determined based on the difference between the target nitrogen amount and the estimated nitrogen amount. Then return.

  In addition, although the example which performs all S130, S132, S136 was shown, you may carry out in any one or the combination of two. When performing S132, it is necessary to perform S134. Moreover, although S138 and S140 showed the example which performs both, neither may be performed or you may make it perform any one.

  The effects of the first embodiment described above include the following.

  The gas mass density estimation means in the hydrogen circuit includes a steady gas mass density estimation calculation for estimating in a steady operation state of the fuel cell system, and a transient for estimating the gas mass density in a transient operation state of the fuel cell system. Since the gas mass density estimation calculation is provided, the steady gas mass density estimation calculation and the transient gas mass density estimation calculation can be properly used according to whether the operation state of the fuel cell system is the transient state or the steady state. Regardless of the operation state, it is possible to always estimate the gas mass density with high accuracy.

  As gas composition estimation means, the gas is a mixed gas of nitrogen and hydrogen, and the gas composition estimation calculation is performed. Therefore, by estimating and managing the amount of nitrogen that has permeated from the oxidant electrode side and accumulated in the fuel path Stable power generation can be performed.

  Estimate the water vapor concentration from the humidity detection value, pressure detection value, and temperature detection value of the hydrogen circulation path, and perform the gas composition estimation calculation using the gas as a mixed gas of nitrogen, hydrogen, and water vapor. By thinking, the gas composition can be estimated with high accuracy, and more stable power generation can be performed.

  Since the gas mass density is estimated on the basis of the deviation between the drive motor current in the standard gas mass density state and the actual current of the circulation pump at a predetermined rotational speed of the circulation pump, no new sensor is required. The gas mass density can be estimated based on the obtained value.

  Further, as another configuration of the circulation device, for example, there is one that drives the circulation device by force from a fluid using an expander, for example. In this case, instead of the driving motor current of the circulation device, the driving force of the circulation device is measured. That is, in order to estimate the gas mass density based on the deviation between the circulator load generated in the standard gas mass density state and the load actually generated in the circulator, the gas mass density is By measuring the difference in load between when it is large and when it is extremely small, the gas mass density can be estimated from the difference in relative load.

  As a transient gas mass density estimation calculation, the reaction force that the circulation device receives from the circuit fluid is estimated, and from this reaction force, the gas mass density is estimated, so the gas mass density is estimated even in the transient state of the fuel cell system. be able to.

  When the amount of energy stored in the power storage means is relatively large relative to the difference between the required power and the generated power of the fuel cell, the fuel cell system is switched to a steady operating state and a steady gas mass density estimation calculation is performed. Therefore, by supplying energy to the required power by the power storage means, the steady operation state can be performed without impairing the amount of energy supplied, and the steady gas density can be estimated.

  When the free capacity of the power storage means is relatively large with respect to the difference between the generated power of the fuel cell and the required power, the fuel cell system is switched to a steady operating state and the steady gas mass density estimation calculation is performed. Since steady operation is performed in a state where surplus generated power obtained by subtracting required power from the generated power of the fuel cell can be stored in the storage means, the fuel cell system can be protected.

  As a steady operation state of the fuel cell system, the target pressure of the fuel circuit, the target operating amount of the circulating device, and the target power generation amount of the fuel cell are given constant values for a predetermined time, so the elements related to the load on the circulating device are constant. It becomes a state and the accuracy of gas density estimation can be raised.

  It has an impurity discharge path that discharges impurities that do not contribute to the electrochemical reaction branched off from the fuel circulation path and an emission control valve that controls the amount of impurities discharged from the impurity discharge path. Impurities accumulated in the fuel path to correct the operation of the emission control valve based on at least one of the difference between the generated circulation device output and the output actually generated in the circulation device or the gas composition estimation result The amount can be controlled so as not to exceed the circulation performance of the circulation device.

  Based on the gas composition estimation result, the target operating amount of the circulation device is corrected with respect to the target power generation amount to the fuel cell, so even if the impurity amount exceeds the normal control amount, the operating amount is increased to increase the fuel By maintaining the amount of circulation, stable power generation can be performed.

  Fuel supply means that changes the amount of fuel supplied to the fuel cell and corrects the fuel supply amount to the fuel cell based on the gas composition estimation result, so even if the circulation performance of the circulation device is insufficient By increasing the amount, stable power generation can be performed.

  Next, a second embodiment of the control device for the fuel cell system according to the present invention will be described. The feature of the second embodiment is that the steady gas mass density estimation calculation and the transient gas mass density calculation are performed in parallel, and the steady gas mass density estimation is performed if the steady state continues for a predetermined time or more as the operation state of the fuel cell system. The result of the calculation is adopted, otherwise, the result of the transient gas mass density estimation calculation is adopted. The basic configuration of this embodiment, the configuration diagram of the fuel cell system to which this embodiment is applied, and the configuration diagram of the controller are the same as those of the first embodiment.

  FIG. 9 shows a control flowchart of the controller in the second embodiment. First, when the flow is started, the processing after S202, the steady gas mass density estimation calculation of S204, and the transient gas mass density estimation calculation of S206 can be processed in parallel.

  The processing contents in S202 to S222 in FIG. 9 are the same as the processing contents in S102 to S118 in FIG.

  Then, when all the processes of S222, S204, and S206 are completed, the process of S224 can be started. In S224, as in S120 of FIG. 4, it is determined whether or not the steady operation state of the fuel cell system has continued for a predetermined time or more. When it is determined that the steady operation state has continued for a predetermined time or longer, the process proceeds to S226, and the estimated value of the steady gas mass density estimation calculation in S204 is set as the gas mass density value. When it cannot be determined in S224 that the steady operating state has continued for a predetermined time or longer, the process proceeds to S228, and the estimated value of the transient gas mass density estimation calculation in S206 is set as the gas mass density value. Thereafter, the same processing as S126 and subsequent steps in FIG. 4 is performed, the gas composition is estimated using the gas mass density value, the nitrogen amount is estimated from the gas composition, and the comparison result between the estimated nitrogen amount and the target nitrogen amount Accordingly, the purge valve 20, the circulation pump 12, and the hydrogen supply valve 9 are controlled.

  According to Example 2 demonstrated above, there exist the following effects. The steady gas mass density estimation calculation and the transient gas mass density estimation calculation are performed in parallel, and the detected values of the circulation path pressure, the circulation device operating state, and the fuel cell power generation amount are observed, respectively, and determined to be the steady operating state. In the case where the steady gas mass density estimation calculation result is selected as the gas mass density estimation result and the gas composition estimation calculation is performed, the number of times the steady gas mass density estimation is performed can be increased. The estimation accuracy can be increased.

  Next, a third embodiment of the control device for the fuel cell system according to the present invention will be described. The feature of the third embodiment is that when the fuel cell system is started, the composition of the gas in the fuel circulation path is estimated based on the current consumption of the circulation pump drive motor, and the hydrogen supply amount is determined according to the estimated gas composition. In the point. The basic configuration of this embodiment, the configuration diagram of the fuel cell system to which this embodiment is applied, and the configuration diagram of the controller are the same as those of the first embodiment.

  FIG. 10 is a control flowchart when the fuel cell system is started in this embodiment. First, in step S302, the fuel cell system activation / deactivation determination unit 41 in FIG. 3 determines whether or not there is a user power generation start request based on the state of the key switch 23 in FIG. If the key switch 23 is turned on, it is determined that there is a power generation start request and the fuel cell is started, and the process proceeds to S304. If not, the process returns without doing anything.

  In S304, the target rotational speed of the circulation pump 12 is set as a predetermined value, and the drive of the circulation pump is started. Here, as described in the steady gas mass density estimation unit 201 in FIG. 5, the predetermined value is a gas flow density that exceeds a certain level, and the gas mass density in the fuel circulation path 11 depends on the value of the current flowing through the circulation pump. Is a rotation speed that can be estimated.

  Next, in S306, the current of the drive motor of the circulation pump 12 is detected by the current sensor 13, and in S308, it is determined whether or not the current change of the drive motor has disappeared and has settled to a constant value. During this period, before the supply of hydrogen and the start of power generation, there is no change in the gas composition in the fuel circuit. The target rotational speed of the circulation pump is set to a predetermined rotational speed in S304, so that immediately after the circulation pump is started, the drive motor current suddenly rises, and when the rotational speed increases to some extent, the drive motor current peaks. Head for decline. Further, when the target rotational speed is approached, the decrease in the drive motor current becomes moderate, and after the circulating pump rotational speed matches the target rotational speed, the current value of the drive motor also becomes a constant value. Therefore, the fact that the drive motor current has become a constant value in S308 is the same as the rotation of the circulation pump 12 being in a steady state.

  Here, instead of determining whether the current has reached a constant value, the time to reach the target rotational speed set in S304 is examined in advance from experiments or design values, and it is determined whether the time has elapsed. Also good. If the determination in S308 is YES, the process proceeds to S310, and if not, the process returns to S306.

  In S310, steady gas density estimation is performed, and in S312, gas composition estimation is performed. These estimation methods are the same as S122 and S126 of the first embodiment, but in this embodiment, the gas composition is estimated as a mixed gas of air and hydrogen. This is because air leaks from the cathode to the anode while the operation of the fuel cell system is stopped.

  In S314, the hydrogen supply amount is determined based on the gas composition in S312. If the hydrogen concentration estimated in S312 is lower than the preset reference hydrogen concentration, hydrogen is supplied so that more hydrogen is supplied according to the concentration difference in order to avoid starting power generation due to insufficient hydrogen. Set supply targets. Conversely, if the estimated hydrogen concentration is higher than the reference hydrogen concentration, the hydrogen supply target is set to decrease.

  Next, in S316, the target pressure for supplying the amount of hydrogen determined in S314 is determined, the hydrogen supply valve 9 is controlled to reach this target pressure, and the process returns.

  According to the third embodiment described above, the target rotational speed of the circulation device is given a constant value for a predetermined time before the fuel supply is started, and the steady gas mass density estimation is performed after the rotational speed detection value becomes a constant value. Therefore, by knowing the composition of the gas present in the fuel circulation path before the fuel cell power generation, the hydrogen supply amount can be made variable and the current extraction can be started in a stable state.

  Next, a fourth embodiment of the control device for the fuel cell system according to the present invention will be described. The feature of the fourth embodiment is that the composition of the gas in the fuel circulation path is estimated based on the consumption current of the circulation pump drive motor when the fuel cell system is stopped (rested). The basic configuration of this embodiment, the configuration diagram of the fuel cell system to which this embodiment is applied, and the configuration diagram of the controller are the same as those of the first embodiment.

  FIG. 11 is a control flowchart when the operation of the fuel cell system in the present embodiment is stopped. First, in step S402, the fuel cell system start / stop determination unit 41 in FIG. 3 determines whether there is a user's power generation stop (stop) request based on the state of the key switch 23 in FIG. If the key switch 23 is turned off, it is determined that there is a power generation stop request and power generation of the fuel cell is stopped. The process proceeds to S404, and if not, the process returns without doing anything.

  In S404, the compressor 14 is stopped, and then in S406, the power manager 15 is instructed to stop current extraction, and current extraction is stopped.

  Next, in S408, a constant value is given to the target value of the anode inlet pressure of the fuel cell 2. Here, a target pressure equal to or lower than the detection value of the anode inlet pressure sensor 10a when the operation stop determination is made in S402 is set.

  Next, in S410, the target rotational speed of the circulation pump 12 is set as a predetermined value, and the drive of the circulation pump is started. Here, as described in the steady gas mass density estimation unit 201 in FIG. 5, the predetermined value is a gas flow density that exceeds a certain level, and the gas mass density in the fuel circulation path 11 depends on the value of the current flowing through the circulation pump. Is a rotation speed that can be estimated.

  Next, in S412, the current of the drive motor of the circulation pump 12 is detected by the current sensor 13, and in S414, it is determined whether or not the current change of the drive motor has disappeared and has settled to a constant value. Here, instead of determining whether the current has reached a constant value, the time to reach the target rotational speed set in S410 is examined in advance from experiments or design values, and it is determined whether the time has elapsed. Also good. If the determination in S414 is YES, the process proceeds to S416, otherwise, the process returns to S412.

  In S416, gas mass density estimation in the steady state of the fuel cell is performed, and in S418, gas composition estimation using the gas mass density is performed. These estimation methods are the same as S122 and S126 of the first embodiment, but in this embodiment, the gas composition is estimated as a mixed gas of hydrogen, nitrogen, and water vapor.

  According to the fourth embodiment described above, from the state where the supply of the oxidant is stopped and the extraction of the current is stopped, the circulation path pressure is maintained at a constant pressure for a predetermined time, and the circulation device is operated at a constant value for a predetermined time. In order to perform gas mass density estimation calculation, the fuel cell power generation is not performed, the gas composition estimation is performed in a stable state, the estimation accuracy is increased, and power extraction can be started in a stable state when power generation is resumed. it can.

1 is a basic configuration diagram of a fuel cell system according to the present invention. 1 is a configuration diagram of a fuel cell system to which the present invention is applied. 1 is a configuration diagram of a controller 30 that is a control device of a fuel cell system according to Embodiment 1. FIG. 2 is a control flowchart according to the first embodiment. It is a calculation block diagram of a gas composition estimation means. It is a figure explaining the pressure loss characteristic of the hydrogen circulation system by the pressure flow characteristic of a circulation pump, and the change of gas mass density. It is explanatory drawing at the time of using the circulation pump from which performance changes with gas mass densities. (A) It is explanatory drawing of the dynamic parameter in transient gas mass density estimation, (b) It is a time chart which shows the motor torque change of the circulation pump which gave the constant target rotational speed in different gas mass density. 10 is a control flowchart in Embodiment 2. 10 is a control flowchart in Embodiment 3. 10 is a control flowchart in Embodiment 4.

Explanation of symbols

101: target generated power determining means 102: fuel cell operating state detecting means 103: circulating device operating state detecting means 104: gas composition estimating means 104a: steady gas mass density estimating calculator 104b: transient gas mass density estimating calculator 105: impurities Discharge means 106: Circulation device control means 107: Fuel supply control means

Claims (16)

A fuel cell configured by stacking a plurality of single cells each having an electrolyte membrane sandwiched between a fuel electrode and an oxidant electrode;
A fuel supply path for supplying fuel to the fuel cell;
A fuel circulation path for circulating the remaining fuel discharged from the fuel electrode to a fuel supply path;
A circulation device provided in the fuel circulation path for boosting and circulating the residual fuel discharged from the fuel electrode;
A circuit pressure detecting means for detecting the pressure of the fuel circuit;
A circuit gas temperature detecting means for detecting a gas temperature of the fuel circuit;
Circulator operating state detecting means for detecting the operating state of the circulating device;
In a fuel cell system comprising:
Calculate an estimated value of the mass density of the gas circulated by the circulation device based on the operation state value detected by the circulation device operation state detection means,
Gas composition estimation means for estimating the gas composition in the fuel circulation path based on the estimated value of the gas mass density, the pressure detection value of the circulation path pressure detection means, and the temperature detection value of the circulation path gas temperature detection means A control apparatus for a fuel cell system, comprising:   The estimation of the gas mass density may be performed by a steady gas mass density estimation calculation that performs mass density estimation in a steady operation state of the fuel cell system, or a transient that performs mass density estimation in a transient operation state of the fuel cell system. 2. The fuel cell system control device according to claim 1, wherein at least one of gas mass density estimation calculation is performed.   3. The control apparatus for a fuel cell system according to claim 1, wherein the gas composition estimation means estimates the gas composition as an object to be estimated as a mixed gas of nitrogen and hydrogen. The circulating device operating state detecting means is
Circuit humidity detecting means for detecting the humidity of the fuel circuit;
Water vapor concentration estimation means for estimating the water vapor concentration based on the humidity detection value detected by the circuit humidity detection means, the pressure detection value, and the temperature detection value;
3. The control apparatus for a fuel cell system according to claim 1, wherein the gas composition estimation unit performs the gas composition estimation when the estimation target is a mixed gas of nitrogen, hydrogen, and water vapor. 4.   The circulation device operating state detection value is a load of the circulation device, and the circulation device load generated when the nitrogen concentration in the fuel circulation path is a standard gas mass density that matches a predetermined control target value, and circulation 2. The control apparatus for a fuel cell system according to claim 1, wherein the mass density is estimated based on a load actually generated in the apparatus.   The circulation device is a circulation device that is rotationally driven by an electric motor to increase the pressure of the gas, and the circulation device operating state detection value is a current of the electric motor and a rotation speed of the circulation device, and at a predetermined rotation speed of the circulation device, the 2. The fuel according to claim 1, wherein the gas mass density is estimated based on an electric motor current when the nitrogen concentration in the fuel circulation path is a predetermined control target value and an actual electric motor current in the circulation device. Battery system control device.   3. The fuel cell system according to claim 2, wherein the transient gas mass density estimation calculation estimates a reaction force that the circulation device receives from a fluid in a fuel circulation path, and estimates a gas mass density from the reaction force. Control device. The fuel cell system includes required power detection means for detecting required power for the fuel cell, and storage means for storing a surplus of the generated power of the fuel cell and discharging the shortage,
A steady operation state in which the generated power of the fuel cell system is constant when the required power exceeds the generated power of the fuel cell and the difference between the required power and the generated power can be supplied from the power storage means for a predetermined time or more. The fuel cell system control device according to claim 2, wherein the steady gas mass density estimation calculation is performed.   When the required power is less than the generated power of the fuel cell and the difference between the required power and the generated power can be stored in the power storage means for a predetermined time or longer, the fuel cell system generates a steady operating state in which the generated power is constant. 9. The control device for a fuel cell system according to claim 8, wherein the steady gas mass density estimation calculation is performed by switching.   As the steady operation state, a constant target value is given to each of the target pressure of the fuel circulation path, the target rotation speed of the circulation device, and the target generated power of the fuel cell for a predetermined time, thereby making the load on the circulation device constant. 10. The fuel cell system control device according to claim 8 or 9, wherein: An impurity discharge path that branches off from the fuel circulation path and discharges fuel gas containing impurities to the outside, and a discharge amount control valve that controls the discharge amount discharged from the impurity discharge path,
The operation of the discharge amount control valve is corrected based on at least one of a difference between a circulation device output generated in the standard gas mass density state and an output actually generated in the circulation device, or a gas composition estimation result. The control apparatus for a fuel cell system according to claim 5.   The fuel cell according to any one of claims 1 to 11, wherein a target rotational speed of the circulation device is corrected with respect to a target generated power of the fuel cell based on an estimation result by the gas composition estimation means. System control unit. A fuel supply means for changing a fuel flow rate supplied to the fuel cell;
The fuel cell system control device according to any one of claims 1 to 12, wherein a flow rate of fuel supplied to the fuel cell is corrected based on an estimation result by the gas composition estimation means.   The steady gas mass density estimation calculation and the transient gas mass density estimation calculation are performed in parallel to detect the pressure of the fuel circulation path, the operating state of the circulation device, and the generated power of the fuel cell, respectively, and these are in the steady state. The result of the steady gas mass density estimation calculation is selected when determined, and the result of the transient gas mass density estimation calculation is selected when not determined as a steady state. The control apparatus of the fuel cell system described.   3. The steady gas mass density estimation is performed after a predetermined value is given as a target rotational speed of the circulation device for a predetermined time before the fuel supply is started, and the rotational speed detection value becomes a constant value. The control apparatus of the fuel cell system of description.   From the state where the supply of oxidant is stopped and the extraction of current is stopped, the circulation path pressure is maintained at a constant pressure for a predetermined time, the circulation device is operated at a constant rotation speed for a predetermined time, and the steady gas mass density estimation calculation is performed. The control device for a fuel cell system according to claim 2.

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