Fuel cell module

Abstract

To suppress the fluctuation of the output power of a fuel cell module when the output power of a DC-DC converter becomes smaller than the power command value due to the power generation limit of a fuel cell stack.SOLUTION: A fuel cell module FCM is configured to include a fuel cell stack FCS, a DCDC converter CNV that converts the output voltage of the fuel cell stack FCS to a predetermined voltage, and a control unit Cm that controls the power generation command value of the fuel cell stack FCS using feedforward control and feedback control such that the output power of the DCDC converter CNV follows the input power command value, and controls the operation of the DCDC converter CNV, and the control unit Cm prohibits feedback control when the power generation command value is limited and the output power of the DCDC converter CNV is not greater than the power generation command value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuel cell module. [Background technology]

[0002] Some fuel cell modules include a DC-DC converter that converts the output voltage of a fuel cell stack into a predetermined voltage, and controls the power generation command value of the fuel cell stack by feedback control so that the output power of the DC-DC converter follows the input power command value. Related technology is disclosed in Patent Document 1.

[0003] However, when the power generation command value of the fuel cell stack is limited to a relatively small value due to an abnormality in the fuel cell stack, and the output power of the DCDC converter becomes smaller than the power command value, the positive integral term of the feedback control (PI control) accumulates excessively, and when the limit on the power generation command value of the fuel cell stack is released, the output power of the DCDC converter overshoots the power command value due to the influence of the excessively accumulated integral term. In other words, when the output power of the DCDC converter becomes smaller than the power command value due to the limit on the power generation command value of the fuel cell stack, the output power of the fuel cell module fluctuates. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-129639 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one aspect of the present invention is to suppress fluctuations in the output power of a fuel cell module when the power generation command value of the fuel cell stack is limited such that the output power of the DCDC converter becomes smaller than the power command value. [Means for solving the problem]

[0006] A fuel cell module according to one embodiment of the present invention includes a fuel cell stack, a DCDC converter that converts an output voltage of the fuel cell stack to a predetermined voltage, and a control unit that controls a power generation command value of the fuel cell stack by feedforward control and feedback control so that the output power of the DCDC converter follows an input power command value, and controls the operation of the DCDC converter. When the power generation command value is limited and the output power of the DCDC converter is not greater than the power generation command value, the control unit prohibits the feedback control.

[0007] As a result, when the power generation command value of the fuel cell stack is limited and the output power of the DCDC converter becomes smaller than the power command value, the integral term of the feedback control is no longer excessively accumulated.Therefore, when the limit on the power generation command value of the fuel cell stack is lifted, the output power of the DCDC converter can be prevented from overshooting the power command value due to the influence of the excessively accumulated integral term, and fluctuations in the output power of the fuel cell module can be suppressed.

[0008] The DCDC converter may also include a high-side diode, a low-side switch, an inductor connected between the connection point of the diode and the switch and the fuel cell stack, and a capacitor connected in parallel to the diode and the switch, and the control unit may be configured to prohibit the feedback control when the power generation command value is limited and the output power of the DCDC converter is not greater than the power generation command value, or when the voltage of the fuel cell stack is higher than the voltage downstream of the DCDC converter when the switch is always off.

[0009] For example, if the voltage of the fuel cell stack becomes higher than the voltage downstream of the DCDC converter when the switch is always off, an unintended current flows from the fuel cell stack to the DCDC converter, causing the output power of the DCDC converter to exceed the power command value. If feedback control is performed in such a case, the power generation command value of the fuel cell stack will decrease, causing a shortage of anode gas and cathode gas supplied to the fuel cell stack, which may cause an abnormality such as water clogging in the fuel cell stack. Therefore, if the voltage of the fuel cell stack is higher than the voltage downstream of the DCDC converter when the switch is always off, the feedback control can be prohibited to suppress the decrease in the power generation command value of the fuel cell stack, thereby suppressing a shortage of the supply of anode gas and cathode gas and suppressing the occurrence of an abnormality such as water clogging in the fuel cell stack.

[0010] The fuel cell module may further include an auxiliary device that causes the fuel cell stack to generate power, and the control unit may be configured to, when the feedback control is not prohibited, obtain a proportional term by multiplying a difference between the output power of the DCDC converter and the power command value by a proportional gain, and obtain an integral term by multiplying the difference by an integral gain, and control the operation of the auxiliary device so that the output power of the fuel cell stack follows the power generation command value obtained by adding together the proportional term, the integral term, and the power command value, and when the feedback control is prohibited, control the operation of the auxiliary device so that the output power of the fuel cell stack follows the power generation command value obtained by adding together the proportional term, which is zero, the integral term obtained at the last control timing in a state in which the feedback control is not prohibited before the feedback control is prohibited, and the power command value.

[0011] For example, when the proportional term calculated at the last control timing before the feedback control is prohibited is continuously used not only for the integral term but also for the proportional term, if the feedback control is prohibited immediately after the DCDC converter outputs a power greater than the power command value when the fuel cell module is started up, the negative proportional term will continue to be used, which may result in a decrease in the power generation command value and the occurrence of an abnormality such as water clogging in the fuel cell stack. Therefore, by setting the proportional term to zero when the feedback control is prohibited, the decrease in the power generation command value can be suppressed even if the feedback control is prohibited immediately after the DCDC converter outputs a power greater than the power command value when the fuel cell module is started up, and therefore the occurrence of an abnormality such as water clogging in the fuel cell stack can be suppressed.

[0012] The control unit may also be configured to limit the power generation of the fuel cell stack to a power generation limit value when the temperature of the fuel cell module is equal to or higher than a temperature threshold value, or when the voltage difference between the target power generation voltage calculated from the power generation command value and the voltage of the fuel cell stack is equal to or higher than a voltage threshold value.

[0013] The power command value may be sent from an external load to which the DC-DC converter supplies power. Effect of the Invention

[0014] According to the present invention, in the case where the output power of the DC-DC converter becomes smaller than the power command value due to the power generation command value of the fuel cell stack being limited, fluctuations in the output power of the fuel cell module can be suppressed. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating an example of a fuel cell module according to an embodiment. [Diagram 2] FIG. 4 illustrates an example of a power generation command value calculation unit. [Diagram 3]FIG. 4 illustrates an example of a PI control unit and a feedback prohibition determination unit. [Figure 4] 4A to 4C are diagrams illustrating an example of an output power, a power command value, and a power generation limit value of a DC-DC converter. [Diagram 5] 5A to 5C are diagrams illustrating an example of an output power, a power command value, a power generation limit value, and a passive step-down flag of a DC-DC converter. [Figure 6] FIG. 13 is a diagram showing a modified example of the fuel cell module of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0017] FIG. 1 is a diagram illustrating an example of a fuel cell module according to an embodiment.

[0018] The fuel cell module FCM shown in FIG. 1 supplies power to an external load Lo.

[0019] For example, the external load Lo is a load mounted on a vehicle such as an industrial vehicle like a forklift or an electric vehicle, and is an inverter that drives a driving motor, a power storage device, etc. In addition, when the fuel cell module FCM is provided in a stationary generator, the external load Lo is a power storage device provided in the stationary generator, etc.

[0020] The external load Lo also includes a higher-level control unit (not shown). For example, the higher-level control unit is configured with a microcomputer or the like, and determines the charging rate [%] of the power storage device (the ratio of the remaining capacity to the full charge capacity of the power storage device) based on the current Ib flowing through the power storage device and the voltage Vb of the power storage device. The higher-level control unit also refers to information indicating the correspondence between the charging rate of the power storage device and the open circuit voltage of the power storage device, and determines the charging rate corresponding to the open circuit voltage determined from the voltage Vb as the current charging rate of the power storage device. Alternatively, the higher-level control unit determines the current charging rate of the power storage device by calculating the charging rate of the power storage device at the start of charging / discharging + (integrated value [Ah] of the current Ib flowing through the power storage device during charging / discharging / full charge capacity [Ah] of the power storage device) / 100. The higher-level control unit also determines a power command value Pc* and a voltage command value based on the power consumption of the inverter, the charging rate of the power storage device, and the like, and sends them to the fuel cell module FCM.

[0021] The fuel cell module FCM includes a fuel cell stack FCS, current sensors Sif, Sic, voltage sensors Svf, Svc, a DC-DC converter CNV, and a control unit Cm. The fuel cell module FCM also includes auxiliary equipment such as an injector (not shown) that supplies anode gas (hydrogen gas, etc.) to the fuel cell stack FCS, which is the main unit, a hydrogen circulation pump (not shown), and an air compressor (not shown) that supplies cathode gas (air, etc.).

[0022] When the supply power corresponding to the difference between the output power Pc of the DC-DC converter CNV and the power supplied to the auxiliary equipment is larger than the power command value Pc* sent from the upper control unit, the power corresponding to the power command value Pc* is supplied to a load such as an inverter, and the remaining power is supplied to a power storage device. When power is supplied from the DC-DC converter CNV to the power storage device, the power storage device is charged and the charging rate of the power storage device increases.

[0023] In addition, when the supply power corresponding to the difference between the output power Pc of the DC-DC converter CNV and the power supplied to the auxiliary equipment is smaller than the power command value Pc*, the supply power is supplied to a load such as an inverter, and the shortage of power is supplied from the power storage device to the load such as the inverter. When power is supplied from the power storage device to the load such as the inverter, the power storage device is discharged and the charging rate of the power storage device is reduced.

[0024] The fuel cell stack FCS is composed of multiple fuel cell units connected in series with each other, and generates electricity through an electrochemical reaction between hydrogen contained in an anode gas supplied from a hydrogen tank (not shown) via an injector and oxygen contained in a cathode gas supplied from an air compressor.

[0025] The current sensor Sif is composed of a shunt resistor, a Hall element, etc., and detects the current If flowing from the fuel cell stack FCS to the DCDC converter CNV, and sends the detected current If to the DCDC converter CNV and the control unit Cm.

[0026] The voltage sensor Svf is composed of a plurality of voltage dividing resistors and the like, detects the voltage Vf output from the fuel cell stack FCS, and sends the detected voltage Vf to the DC-DC converter CNV and the control unit Cm.

[0027] The current sensor Sic is composed of a shunt resistor, a Hall element, etc., detects a current Ic flowing from the DC-DC converter CNV to the auxiliary equipment and the external load Lo, and sends the detected current Ic to the control unit Cm.

[0028] The voltage sensor Svc is configured with a plurality of voltage dividing resistors and the like, detects the voltage Vc output from the DC-DC converter CNV, and sends the detected voltage Vc to the control unit Cm.

[0029] The DC-DC converter CNV is a boost circuit having a U phase, a V phase, and a W phase, and is connected between the fuel cell stack FCS and an external load Lo.

[0030] The DCDC converter CNV also includes high-side switches SHu, SHv, SHw, low-side switches SLu, SLv, SLw, high-side diodes DHu, DHv, DHw, low-side diodes DLu, DLv, DLw, inductors Lu, Lv, Lw, a capacitor C, current sensors Siu, Siv, Siw, and a control unit Cc.

[0031] The switches SHu, SHv, SHw and the switches SLu, SLv, SLw are configured, for example, by MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and the diodes DHu, DHv, DHw and the diodes DLu, DLv, DLw are parasitic diodes of the switches SHu, SHv, SHw and the switches SLu, SLv, SLw.

[0032] Also, on the high side of each phase of the DC-DC converter CNV, the switches SHu, SHv, and SHw may be omitted, and only the diodes DHu, DHv, and DHw may be provided.

[0033] In addition, when the current of the remaining phase is calculated from the difference between the current If detected by the current sensor Sif and the total value of the currents flowing through two of the three phases, the current sensor corresponding to the remaining phase among the current sensors Siu, Siv, and Siw may be omitted.

[0034] In the U phase, a diode DHu is connected in parallel to the switch SHu, a diode DLu is connected in parallel to the switch SLu which is connected in series to the switch SHu, and an inductor Lu is connected between the connection point of the switches SHu and SLU and the fuel cell stack FCS.

[0035] In the V phase, a diode DHv is connected in parallel to the switch SHv, a diode DLv is connected in parallel to the switch SLv which is connected in series to the switch SHv, and an inductor Lv is connected between the connection point of the switch SHv and the switch SLv and the fuel cell stack FCS.

[0036] In the W phase, a diode DHw is connected in parallel to the switch SHw, a diode DLw is connected in parallel to the switch SLw which is connected in series to the switch SHw, and an inductor Lw is connected between the connection point of the switches SHw and SLw and the fuel cell stack FCS.

[0037] The capacitor C is connected in parallel to the switches SHu and SLu, connected in parallel to the switches SHv and SLv, and connected in parallel to the switches SHw and SLw.

[0038] The current sensor Siu is configured with a shunt resistor, a Hall element, etc., detects a current Iu flowing through the U phase, and sends the detected current Iu to the control unit Cc.

[0039] The current sensor Siv is composed of a shunt resistor, a Hall element, etc., detects the current Iv flowing through the V phase, and sends the detected current Iv to the control unit Cc.

[0040] The current sensor Siw is composed of a shunt resistor, a Hall element, etc., detects a current Iw flowing through the W phase, and sends the detected current Iw to the control unit Cc.

[0041] The control section Cc is constituted by a microcomputer or the like, and controls the operations of the switches SHu, SHv, SHw and the switches SLu, SLv, SLw.

[0042] In other words, the control unit Cc controls the operation of the switches SHu, SHv, SHw and the switches SLu, SLv, SLw so that the voltage Vf of the fuel cell stack FCS follows the target output voltage sent from the control unit Cm and the current If flowing from the fuel cell stack FCS to the DCDC converter CNV or the total value of the currents Iu, Iv, Iw follows the current command value sent from the control unit Cm.

[0043] For example, when the current voltage Vf of the fuel cell stack FCS is lower than the target output voltage sent from the control unit Cm, the control unit Cc keeps the switches SHu, SHv, and SHw off at all times, while repeatedly turning the switches SLu, SLv, and SLw on and off to boost the current voltage Vf to the target output voltage.

[0044] Furthermore, when the current voltage Vf is equal to or higher than the target output voltage sent from the control unit Cm, the control unit Cc does not boost the current voltage Vf by keeping the switches SHu, SHv, SHw and the switches SLu, SLv, SLw always off. Note that when the switches SHu, SHv, SHw and the switches SLu, SLv, SLw are always off, if the voltage Vf is higher than the voltage Vc downstream of the DCDC converter CNV, there is a risk that an unintended current will flow from the fuel cell stack FCS to the downstream of the DCDC converter CNV via the diodes DHu, DHv, DHw.

[0045] The control unit Cm is composed of a microcomputer or the like, and controls the operation of the auxiliary equipment to control the generated power of the fuel cell stack FCS at each control timing that occurs every time a certain period of time (e.g., the clock period of the microcomputer) has elapsed, and also controls the operation of the DCDC converter CNV by sending target output voltage and current command values ​​to the control unit Cc.

[0046] The control unit Cm also includes an output power calculation unit 1, a power generation limit value calculation unit 2, a power generation command value calculation unit 3, an auxiliary control unit 4, and a DCDC converter control unit 5. For example, the output power calculation unit 1, the power generation limit value calculation unit 2, the power generation command value calculation unit 3, the auxiliary control unit 4, and the DCDC converter control unit 5 are realized by a microcomputer executing a program stored in a memory (not shown).

[0047] The output power calculation unit 1 determines the multiplication value of the voltage Vf and the current If as the output power of the fuel cell stack FCS, and the multiplication value of the voltage Vc and the current Ic as the output power Pc of the DC-DC converter CNV (the output power of the fuel cell module FCM).

[0048] The power generation limit value calculation unit 2 calculates a power generation limit value for the power generation command value Ps* of the fuel cell stack FCS based on parameters (such as temperature and voltage) obtained from the fuel cell stack FCS. For example, when the temperature of the fuel cell stack FCS detected by a temperature sensor (not shown) is equal to or higher than a temperature threshold value, the power generation limit value calculation unit 2 determines that the fuel cell stack FCS is in an overheated state, and calculates a power generation limit value based on the temperature of the fuel cell stack FCS. Alternatively, when the voltage difference between the target power generation voltage obtained from the power generation command value Ps* of the fuel cell stack FCS and the voltage Vf is equal to or higher than a voltage threshold value, the power generation limit value calculation unit 2 determines that water has accumulated in the fuel cell stack FCS and a power generation failure has occurred, and calculates a power generation limit value based on the voltage difference. For example, the temperature threshold value is set to the minimum value of the temperature of the fuel cell stack FCS when the fuel cell stack FCS is in an overheated state. For example, the voltage threshold value is set to the minimum value of the difference between the target power generation voltage and the voltage Vf when water has accumulated in the fuel cell stack FCS and a power generation failure has occurred.

[0049] The power generation command value calculation unit 3 controls the power generation command value Ps* of the fuel cell stack FCS by feedforward control and feedback control so that the output power Pc of the DCDC converter CNV follows the power command value Pc* sent from the external load Lo. In addition, the power generation command value calculation unit 3 prohibits feedback control when the power generation command value Ps* is limited to the power generation limit value and the output power Pc of the DCDC converter CNV is not larger than the power generation command value Ps*, or when a passive step-down flag described later is on. The power generation command value calculation unit 3 may be configured to include the loss of the DCDC converter CNV in the power command value Pc*. In addition, the passive step-down flag is on when the switches SHu, SHv, SHw and switches SLu, SLv, SLw are always off in the DCDC converter CNV and the voltage Vf is higher than the voltage Vc downstream of the DCDC converter CNV. On the other hand, the passive step-down flag is off when the switches SLu, SLv, and SLw in the DCDC converter CNV are repeatedly turned on and off, or when the switches SHu, SHv, SHw and the switches SLu, SLv, and SLw are always off and the voltage Vf is lower than the voltage Vc downstream of the DCDC converter CNV.

[0050] The auxiliary control unit 4 controls the operation of the auxiliary devices (such as an injector, a hydrogen circulation pump, and an air compressor) so that the output power of the fuel cell stack FCS follows the power generation command value Ps* of the fuel cell stack FCS.

[0051] During power generation by the fuel cell stack FCS, the DCDC converter control unit 5 sends a target output voltage and a current command value to the DCDC converter CNV at each control timing. For example, the DCDC converter control unit 5 sets a current command value to a value obtained by dividing the output power Pc of the DCDC converter CNV by the target output voltage.

[0052] FIG. 2 is a diagram illustrating an example of the power generation command value calculation unit 3. As shown in FIG.

[0053] The power generation command value calculation unit 3 shown in FIG. 2 includes a subtraction unit 21, a PI control unit 22, an addition unit 23, a limit arbitration unit 24, an upper and lower limit guard unit 25, and a feedback prohibition determination unit .

[0054] The subtraction unit 21 obtains the difference e between the power command value Pc* sent from the external load Lo and the output power Pc of the DC-DC converter CNV.

[0055] When a feedback prohibition flag, which will be described later, is off, the PI control unit 22 outputs a control amount u for controlling the power generation command value Ps* so that the difference e approaches zero. The feedback prohibition flag is off when the power generation of the fuel cell stack FCS is limited to the power generation limit value and the output power Pc of the DCDC converter CNV is not larger (smaller) than the power generation command value Ps* of the fuel cell stack FCS, or when the passive step-down flag is on. The feedback prohibition flag is on when the power generation of the fuel cell stack FCS is not limited, or when the passive step-down flag is off. The passive step-down is a state in which the power generated in the fuel cell stack when power generation is stopped can be charged to a power storage device (load) through a path using a diode provided in the DCDC converter. This makes it possible to avoid a high potential of the fuel cell stack by a passive step-down operation without operating the boost converter, while ensuring a necessary and sufficient number of fuel cell cells and optimizing the output of the fuel cell stack.

[0056] Here, FIG. 3( a ) is a diagram illustrating an example of the PI control unit 22 .

[0057] The PI control unit 22 shown in FIG. 3( a ) includes a proportional term calculation unit 221 , an integral term calculation unit 222 , selection switches 223 and 224 , a holding unit 225 , and an adding unit 226 .

[0058] The proportional term calculation unit 221 outputs a value obtained by multiplying the difference e by a proportional gain at each control timing as a proportional term. Note that the proportional gain is an arbitrary value determined in advance through experiments or simulations.

[0059] The integral term calculation unit 222 outputs a value obtained by multiplying the difference e by an integral gain at each control timing as an integral term. Note that the integral gain is an arbitrary value determined in advance through experiments or simulations.

[0060] When the feedback prohibition flag is off, selection switch 223 selects and outputs the proportional term output from proportional term calculation unit 221 from the proportional term output from proportional term calculation unit 221 and the proportional term that is zero, for each control timing. Also, when the feedback prohibition flag is on, selection switch 223 selects and outputs the proportional term that is zero from the proportional term output from proportional term calculation unit 221 and the proportional term that is zero, for each control timing.

[0061] When the feedback prohibition flag is off, the selection switch 224 selects and outputs the integral term output from the integral term calculation unit 222 from the integral term output from the integral term calculation unit 222 and the integral term held by the holding unit 225 at each control timing. Also, when the feedback prohibition flag is on, the selection switch 224 selects and outputs the integral term held by the holding unit 225 from the integral term output from the integral term calculation unit 222 and the integral term held by the holding unit 225 at each control timing.

[0062] At the current control timing, the holding unit 225 holds the integral term output from the selection switch 224 until the next control timing. For example, when the feedback prohibition flag switches from off to on, the holding unit 225 holds the integral term calculated at the last control timing in a state in which the feedback prohibition flag is not off (a state in which feedback control is not prohibited) before the feedback prohibition flag is turned on (before feedback control is prohibited).

[0063] The adder 226 adds the proportional term output from the selection switch 223 and the integral term output from the selection switch 224, and outputs the result as a control amount u.

[0064] That is, when the feedback prohibition flag is off (when feedback control is not prohibited), the PI control unit 22 multiplies the difference e by a proportional gain to obtain a proportional term, multiplies the difference e by an integral gain to obtain an integral term, and adds the proportional term and the integrated term to obtain a controlled variable u. When the feedback prohibition flag is on (when feedback control is prohibited), the PI control unit 22 adds the proportional term, which is zero, to the integral term obtained at the last control timing in a state in which feedback control is not prohibited before the feedback control is prohibited to obtain the controlled variable u. The function of the PI control unit 22 corresponds to "controlling the power generation command value Ps* of the fuel cell stack FCS by feedback control so that the output power Pc of the DC-DC converter CNV follows the power command value Pc*". The PI control unit 22 may also be configured to continue to use the proportional term obtained at the last control timing before the feedback control is prohibited.

[0065] 2 adds the control amount u and the power command value Pc* to obtain a power generation command value Ps*' of the fuel cell stack FCS. The function of the adder 23 corresponds to "controlling the power generation command value Ps* of the fuel cell stack FCS by feedforward control so that the output power Pc of the DC-DC converter CNV follows the power command value Pc*."

[0066] The limit arbitration unit 24 outputs the smaller of the power generation command value Ps*' output from the adder 23 and the power generation limit value sent from the power generation limit value calculation unit 2 as the arbitrated power generation command value Ps*". When the power generation command value Ps*' and the power generation limit value are the same value, the limit arbitration unit 24 outputs the power generation command value Ps*' or the power generation limit value as the arbitrated power generation command value Ps*". For example, when the power generation limit value is smaller than the power generation command value Ps*', that is, when the power generation command value Ps* is limited to the power generation limit value, the limit arbitration unit 24 outputs the power generation limit value as the power generation command value Ps*". In this case, the arbitrated power generation command value Ps*' output from the limit arbitration unit 24 is smaller than the power generation command value Ps*' before arbitration.

[0067] The upper and lower limit guard unit 25 outputs the upper limit value as the power generation command value Ps* when the power generation command value Ps*'' is equal to or greater than the upper limit value, outputs the lower limit value as the power generation command value Ps* when the power generation command value Ps*'' is equal to or less than the lower limit value, and outputs the power generation command value Ps*'' as the power generation command value Ps* when the power generation command value Ps*'' is smaller than the upper limit value and larger than the lower limit value. For example, the upper limit value is the rated power of the fuel cell stack FCS, and the lower limit value is zero.

[0068] The feedback prohibition determination unit 26 compares the power generation command value Ps*' before arbitration by the limit arbitration unit 24 with the power generation command value Ps* after arbitration by the limit arbitration unit 24 to determine whether the power generation command value Ps* is limited to the power generation limit value.

[0069] Further, the feedback inhibition determination unit 26 determines whether or not the output power Pc of the DC-DC converter CNV is greater than the power generation command value Ps*.

[0070] Furthermore, the feedback inhibition determination unit 26 determines whether or not the passive step-down flag is on.

[0071] Furthermore, when the power generation command value Ps* is limited to the power generation limit value and the output power Pc of the DC-DC converter CNV is not greater than the power generation command value Ps*, or when the passive step-down flag is on, the feedback prohibition determination unit 26 turns on the feedback prohibition flag. Furthermore, when the power generation command value Ps* is not limited, or when the passive step-down flag is off, the feedback prohibition determination unit 26 turns off the feedback prohibition flag.

[0072] Here, FIG. 3(b) is a diagram showing an example of the feedback prohibition determination unit 26. As shown in FIG.

[0073] The feedback prohibition determination unit 26 shown in FIG. 3( b ) includes comparison circuits 261 and 262 , a logical AND circuit 263 , and a logical OR circuit 264 .

[0074] The comparison circuit 261 outputs “true” when the power generation command value Ps*′ is greater than the power generation command value Ps*, i.e., when the power generation command value Ps* is limited to the power generation limit value, and outputs “false” when the power generation command value Ps*′ is less than or equal to the power generation command value Ps*, i.e., when the power generation command value Ps* is not limited.

[0075] The comparison circuit 262 outputs "true" when the output power Pc of the DCDC converter CNV is smaller than the power generation command value Ps*, that is, when the output power Pc of the DCDC converter CNV is not greater than the power generation command value Ps*, and outputs "false" when the output power Pc of the DCDC converter CNV is greater than the power generation command value Ps*.

[0076] The logical AND circuit 263 outputs "true" when the comparison circuits 261, 262 each output "true", and outputs "false" when at least one of the comparison circuits 261, 262 outputs "false".

[0077] If the AND circuit 263 outputs “true” or if the passive step-down flag is on, the OR circuit 264 turns on the feedback prohibition flag, and if the AND circuit 263 outputs “false” and the passive step-down flag is off, the OR circuit 264 turns off the feedback prohibition flag.

[0078] That is, when the power generation command value Ps* is not limited, and when the switches SLi, SLv, and SLw are repeatedly turned on and off, or when the switches SHu, SHv, and SHw and the switches SLi, SLv, and SLw are always off, and the voltage Vf is lower than the voltage Vc downstream of the DCDC converter CNV, the feedback prohibition determination unit 26 does not prohibit the feedback control. Also, when the power generation command value Ps* is limited to the power generation limit value, and the output power Pc of the DCDC converter CNV is not greater than the power generation command value Ps* of the fuel cell stack FCS, or when the switches SLi, SLv, and SLw are always off and the voltage of the fuel cell stack FCS is higher than the voltage downstream of the DCDC converter CNV, the feedback prohibition determination unit 26 prohibits the feedback control.

[0079] Here, as shown in FIG. 4(a) and FIG. 4(b), assume that the power generation command value Ps* is limited to the power generation limit value due to overheating of the fuel cell stack FCS between time t11 and time t12, and the output power Pc of the DCDC converter CNV becomes smaller than the power command value Pc*. Note that the horizontal axis of the two-dimensional coordinate system shown in FIG. 4(a) and FIG. 4(b) indicates time, and the vertical axis indicates power. Also, the solid line shown in FIG. 4(a) and FIG. 4(b) indicates the output power Pc of the DCDC converter CNV, the dashed line shown in FIG. 4(a) and FIG. 4(b) indicates the power command value Pc*, and the dashed line shown in FIG. 4(a) and FIG. 4(b) indicates the power generation limit value. Also, it is assumed that feedback control is not prohibited between time t11 and time t12 in FIG. 4(a), and that feedback control is prohibited between time t11 and time t12 in FIG. 4(b).

[0080] In this case, if the power generation command value Ps* is controlled by feedback control between time t11 and time t12 in Figure 4(a), the integral term of the feedback control will accumulate excessively. Therefore, when the limit on the power generation command value Ps* is released at time t12, the output power Pc of the DCDC converter CNV will overshoot the power command value Pc* due to the influence of the excessively accumulated integral term.

[0081] Therefore, in the fuel cell module FCM of the embodiment, the integral term is prevented from accumulating excessively by holding the integral term calculated at the last control timing before time t11 between time t11 and time t12. That is, in the fuel cell module FCM of the embodiment, feedback control is prohibited between time t11 and time t12, and only feedforward control is performed. Note that in FIG. 4(b), feedback control is permitted and feedforward control and feedback control are performed during periods other than the period between time t11 and time t12.

[0082] In this way, even if the power generation command value Ps* of the fuel cell stack FCS is limited to the power generation limit value between time t11 and time t12 and the output power Pc of the DCDC converter CNV becomes smaller than the power command value Pc*, the integral term of the feedback control is not excessively accumulated, so that when the limit on the power generation command value Ps* is lifted at time t12, as shown in Figure 4(b), the output power Pc of the DCDC converter CNV can be prevented from overshooting the power command value Pc*, and fluctuations in the output power of the fuel cell module FCM can be suppressed.

[0083] Also, as shown in Fig. 5(a), assume that the power generation command value Ps* is smaller than the power generation limit value between time t21 and time t22. The horizontal axis of the two-dimensional coordinate system shown in Fig. 5(a) indicates time, and the vertical axis indicates power. The solid line shown in Fig. 5(a) indicates the output power Pc of the DC-DC converter CNV, the dashed line shown in Fig. 5(a) indicates the power command value Pc*, and the dashed line shown in Fig. 5(a) indicates the power generation limit value.

[0084] In this case, if feedback control is prohibited between time t21 and time t22, the output power Pc will become larger than the power generation command value Ps*, and the output power Pc of the DCDC converter CNV will no longer follow the power command value Pc*, which may result in the desired power not being supplied from the DCDC converter CNV to the external load Lo.

[0085] Therefore, in the fuel cell module FCM of the embodiment, when the output power Pc of the DCDC converter CNV is larger than the power generation command value Ps*, the feedback control is permitted and feedforward control and feedback control are performed.

[0086] As a result, as shown in Figure 5 (a), even if the output power Pc temporarily becomes larger than the power generation command value Ps* between time t21 and time t22, the output power Pc of the DCDC converter CNV can be immediately made to follow the power command value Pc*, so that the desired power can be supplied from the DCDC converter CNV to the external load Lo.

[0087] Also, as shown in Fig. 5(b), at time t22, the passive step-down flag is switched from off to on, and after time t22, an unintended current flows from the fuel cell stack FCS to the DCDC converter CNV, causing the output power Pc of the DCDC converter CNV to become larger than the power command value Pc*, as shown in Fig. 5(a). Note that the solid line in Fig. 5(b) indicates the passive step-down flag.

[0088] In this case, if feedback control is performed after time t22, a negative integral term will accumulate, causing the power generation command value Ps* to decrease and resulting in a shortage of anode gas and cathode gas supplied to the fuel cell stack FCS, which may lead to an abnormality such as water clogging in the fuel cell stack FCS.

[0089] Therefore, in the fuel cell module FCM of this embodiment, when the passive step-down flag is on, the feedback control is prohibited and only the feedforward control is performed.

[0090] As a result, from time t22 onwards, the influence of the integral term can be eliminated, thereby suppressing the decrease in the power generation command value Ps*, thereby preventing a shortage of anode gas and cathode gas supply and suppressing the occurrence of abnormalities such as water clogging in the fuel cell stack FCS.

[0091] In addition, when the feedback control is prohibited, it is assumed that not only the integral term but also the proportional term calculated at the last control timing before the feedback control is prohibited continues to be used.

[0092] In this case, if the passive step-down flag is turned on immediately after the DCDC converter CNV outputs power greater than the power command value Pc* when the fuel cell module FCM is started, the negative proportional term will continue to be used, causing the power generation command value Ps* to decrease, which may lead to an abnormality such as water clogging in the fuel cell stack FCS.

[0093] Therefore, in the fuel cell module FCM of this embodiment, when feedback control is prohibited, the proportional term is set to zero.

[0094] As a result, even if the passive step-down flag is turned on immediately after a power greater than the power command value Pc* is output from the DCDC converter CNV when the fuel cell module FCM is started, the power generation command value Ps* can be prevented from decreasing, thereby preventing abnormalities such as water clogging in the fuel cell stack FCS.

[0095] The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the gist of the present invention.

[0096] <Variation 1> Fig. 6 is a diagram showing a modified example of the fuel cell module of the embodiment. In the configuration shown in Fig. 6, the same components as those shown in Fig. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

[0097] The fuel cell module FCM' shown in FIG. 6 differs from the fuel cell module FCM shown in FIG. 1 in that a DC-DC converter CNV' is configured by only one phase (for example, the U phase shown in FIG. 1).

[0098] The operation of the control unit Cm shown in Fig. 6 is the same as the operation of the control unit Cm shown in Fig. 1. That is, the power generation command value calculation unit 3 of the control unit Cm shown in Fig. 6 prohibits feedback control when the power generation command value Ps* is limited to the power generation limit value and when the output power Pc of the DC-DC converter CNV is not greater than the power generation command value Ps* or when the passive step-down flag is on.

[0099] Also, in the DC-DC converter CNV', the high-side switch SHu may be omitted, and only the high-side diode DHu may be provided.

[0100] Even with this configuration, when the limit on the power generation command value Ps* is lifted, the output power Pc of the DCDC converter CNV can be prevented from overshooting the power command value Pc*, thereby suppressing fluctuations in the output power of the fuel cell module FCM.

[0101] In addition, when the passive step-down flag is on, the decrease in the power generation command value Ps* can be suppressed, thereby preventing a shortage of anode gas or cathode gas and preventing abnormalities such as water clogging in the fuel cell stack FCS.

[0102] <Variation 2> The above-mentioned DCDC converters CNV and CNV' are configured with a non-isolated boost circuit having a diode on the high side, but may also be configured with an isolated boost circuit having a bridge circuit consisting of multiple switches on the primary side of the transformer (fuel cell stack FCS side) and a rectifier circuit on the secondary side of the transformer (external load Lo side).

[0103] When configured in this manner, no unintended current flows from the fuel cell stack FCS to the DCDC converters CNV, CNV', so the power generation command value calculation unit 3 prohibits feedback control only when the power generation command value Ps* is limited to the power generation limit value and the output power Pc of the DCDC converter CNV is not greater than the power generation command value Ps*.

[0104] This makes it possible to prevent the output power Pc of the DCDC converter CNV from overshooting the power command value Pc* when the limit on the power generation command value Ps* is lifted, thereby suppressing fluctuations in the output power of the fuel cell module FCM. [Explanation of symbols]

[0105] FCM Fuel Cell Module FCS Fuel Cell Stack Svf voltage sensor Sif current sensor Svc Voltage Sensor SiC Current Sensor CNV DC / DC Converter Cm control section 1 Output power calculation section 2. Power generation limit value calculation section 3. Power generation command value calculation section 4 Auxiliary control unit 5 DC / DC converter control section SHu, SHv, SHw switches SLu, SLv, SLw Switches DHu, DHv, DHw Diodes DLu, DLv, DLw Diodes Lu, Lv, Lw Inductors C Capacitor Siu, Siv, Siw Current Sensors Cc control section Lo External Load

Claims

1. A fuel cell stack; a DC-DC converter that converts the output voltage of the fuel cell stack into a predetermined voltage; a control unit that controls a power generation command value of the fuel cell stack by feedforward control and feedback control so that the output power of the DCDC converter follows an input power command value, and controls the operation of the DCDC converter; Equipped with The control unit prohibits the feedback control when the power generation command value is limited and the output power of the DC-DC converter is not greater than the power generation command value. Fuel cell module.

2. 2. The fuel cell module of claim 1, The DC-DC converter comprises: The high side diode, A low-side switch and an inductor connected between the junction of the diode and the switch and the fuel cell stack; a capacitor connected in parallel to the diode and the switch; Equipped with The control unit prohibits the feedback control when the power generation command value is limited and the output power of the DC-DC converter is not greater than the power generation command value, or when the voltage of the fuel cell stack is higher than the voltage downstream of the DC-DC converter when the switch is always off. Fuel cell module.

3. 3. The fuel cell module according to claim 1, an auxiliary device that generates power from the fuel cell stack; The control unit is When the feedback control is not prohibited, a proportional term is obtained by multiplying a difference between the output power of the DCDC converter and the power command value by a proportional gain, and an integral term is obtained by multiplying the difference by an integral gain, and controlling operation of the auxiliary equipment so that the output power of the fuel cell stack follows the power generation command value obtained by adding the proportional term, the integral term, and the power command value; When the feedback control is prohibited, the operation of the auxiliary is controlled so that the output power of the fuel cell stack follows the power generation command value obtained by adding the proportional term, which is zero, the integral term calculated at the last control timing in a state in which the feedback control is not prohibited before the feedback control is prohibited, and the power command value. Fuel cell module.

4. 2. The fuel cell module of claim 1, The control unit limits the power generation of the fuel cell stack to a power generation limit value when the temperature of the fuel cell module is equal to or higher than a temperature threshold value, or when a voltage difference between a target power generation voltage calculated from the power generation command value and a voltage of the fuel cell stack is equal to or higher than a voltage threshold value. Fuel cell module.

5. 2. The fuel cell module of claim 1, The power command value is sent from an external load to which the DCDC converter supplies power. Fuel cell module.

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