Fuel cell module

Abstract

This invention provides a fuel cell module that enables the easy and highly accurate acquisition of reactor temperature. [Solution] The system comprises a fuel cell that generates electricity using fuel and an oxidizer, a switching module having a switching element and a capacitor, a reactor having a core and a coil, a DC-DC converter that converts the voltage of the electricity generated by the fuel cell, a temperature sensor that detects the temperature of the switching module, and a control unit that estimates the temperature of the reactor based on the temperature detected by the temperature sensor.

Description

Technical Field

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

Background Art

[0002] Conventionally, Patent Document 1 describes a fuel cell module for an electric vehicle. In this prior art, the electric power taken out from the fuel cell is boosted by a boost chopper circuit and supplied to a load side such as a power storage device. The boost chopper circuit has a reactor, a diode, and a switching element. A reactor temperature sensor for detecting the temperature of the reactor is provided near the reactor.

Prior Art Documents

Patent Documents

[0003] <U+ <U+

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above prior art, when the reactor becomes too hot, magnetic saturation occurs and the characteristic values deteriorate. Therefore, it is necessary to monitor the temperature of the reactor to protect the reactor. However, in the above prior art, since the reactor temperature sensor is arranged near the reactor, it is difficult to appropriately monitor the temperature of the reactor. [[ID=3?]]

[0005] That is, the temperature of the core of the reactor is the highest, but the temperature of the surface of the reactor is significantly lower than the temperature of the core of the reactor. Therefore, the reactor temperature sensor arranged near the reactor cannot accurately obtain the temperature of the reactor. If the reactor temperature sensor is arranged near the core of the reactor, it becomes possible to accurately obtain the temperature of the reactor. However, it is structurally difficult to arrange the reactor temperature sensor near the core of the reactor.

[0006] It should be noted that there seems to be an encoding issue with the character "<U+ " etc. in the original text which might cause some display problems. But I have translated it as is according to the rules. If this is an incorrect character encoding, it may need to be corrected for a more accurate interpretation. Furthermore, the conventional technology described above requires a dedicated temperature sensor to detect the reactor temperature, which increases the number of components and sensor signals, leading to increased complexity of the configuration.

[0007] This invention was made in view of the above background, and aims to provide a fuel cell module that can easily and accurately obtain the temperature of a reactor. [Means for solving the problem]

[0008] A first aspect of the present invention is: A fuel cell that generates electricity using fuel and an oxidizer, A DC-DC converter having a switching module with switching elements and capacitors, and a reactor with a core and coil, which converts the voltage of the power generated by the fuel cell, A temperature sensor for detecting the temperature of the switching module, The fuel cell module includes a control unit that estimates the temperature of the reactor based on the temperature detected by the temperature sensor.

[0009] According to this method, the reactor temperature is estimated based on the temperature of a switching module, which is correlated with the reactor temperature, thus enabling high-precision acquisition of the reactor temperature. Furthermore, since the reactor temperature is acquired using an existing temperature sensor that detects the temperature of the switching module, the reactor temperature can be easily obtained. [Effects of the Invention]

[0010] According to the fuel cell module in the first aspect of the present invention, the temperature of the reactor can be obtained with high accuracy and easily. [Brief explanation of the drawing]

[0011] [Figure 1] An overall configuration diagram showing the fuel cell module in the first embodiment. [Figure 2] Current-voltage characteristic diagram of the fuel cell in the first embodiment. [Figure 3] A schematic diagram showing the internal layout of the fuel cell module in the first embodiment. [Figure 4] A schematic exploded perspective view of the switching module in the first embodiment. [Figure 5] A diagram showing an image of the control map used to determine the first corrected temperature in the first embodiment. [Figure 6] A diagram showing an image of the control map used to determine the second correction temperature in the first embodiment. [Figure 7] A block diagram showing the reactor temperature estimation process in the second embodiment. [Figure 8] A graph showing an example of reactor temperature estimation in the second embodiment. [Figure 9] An overall configuration diagram showing a fuel cell module in another embodiment. [Modes for carrying out the invention]

[0012] The fuel cell module comprises a fuel cell that generates electricity using fuel and an oxidizer, a switching module having a switching element and a capacitor, a reactor having a core and a coil, a DC-DC converter that converts the voltage of the electricity generated by the fuel cell, a temperature sensor that detects the temperature of the switching module, and a control unit that estimates the temperature of the reactor based on the temperature detected by the temperature sensor.

[0013] In a fuel cell module, the switching module has a switching substrate on which the switching elements are arranged, and the temperature sensor may be arranged on the switching substrate. Since the temperature of the reactor is estimated based on the temperature of the switching substrate that has a correlation with the temperature of the reactor, the temperature of the reactor can be obtained with high accuracy. Since the temperature of the reactor is obtained by using an existing temperature sensor that detects the temperature of the switching substrate, the temperature of the reactor can be easily obtained.

[0014] In a fuel cell module, the switching substrate may be formed of a material mainly composed of metal. The temperature of the switching element has a high correlation with the temperature of the reactor. Since the thermal conductivity from the switching element to the switching substrate is high, the correlation between the temperature of the reactor and the temperature of the switching substrate also becomes high. Therefore, the temperature of the reactor can be obtained with even higher accuracy.

[0015] In a fuel cell module, the switching module has a capacitor substrate on which the capacitors are arranged, and the temperature sensor may be arranged on the capacitor substrate. Since the temperature of the reactor is estimated based on the temperature of the capacitor substrate that has a correlation with the temperature of the reactor, the temperature of the reactor can be obtained with high accuracy. Since the temperature of the reactor is obtained by using an existing temperature sensor that detects the temperature of the capacitor substrate, the temperature of the reactor can be easily obtained.

[0016] In a fuel cell module, the switching module has a control substrate on which a control circuit for controlling the switching elements is arranged, and the temperature sensor may be arranged on the control substrate. Since the temperature of the reactor is estimated based on the temperature of the control substrate that has a correlation with the temperature of the reactor, the temperature of the reactor can be obtained with high accuracy. Since the temperature of the reactor is obtained by using an existing temperature sensor that detects the temperature of the control substrate, the temperature of the reactor can be easily obtained.

[0017] In a fuel cell module, the control unit may estimate the temperature of the reactor by correcting the temperature detected by the temperature sensor using at least one of the value of the current input from the fuel cell to the DCDC converter and the input-output voltage difference of the DCDC converter. Since both the value of the current input from the fuel cell to the DCDC converter and the input-output voltage difference of the DCDC converter have a correlation with the temperature of the reactor, the temperature detected by the temperature sensor can be corrected with high precision to obtain the temperature of the reactor with high precision.

[0018] In a fuel cell module, the control unit may estimate the temperature of the reactor by correcting the temperature detected by the temperature sensor using the temperature of the cooling water that cools the fuel cell. Since the temperature of the cooling water that cools the fuel cell has a correlation with the temperature of the reactor, the temperature detected by the temperature sensor can be corrected with high precision to obtain the temperature of the reactor with high precision.

[0019] In a fuel cell module, the control unit may estimate the temperature of the reactor based on the temperature detected by the temperature sensor and execute protection control or stop control of the switching module based on the temperature detected by the temperature sensor. The protection control or stop control of the switching module can be executed simply and with high precision.

[0020] In a fuel cell module, when the input-side voltage of the DCDC converter is smaller than the output-side voltage of the DCDC converter, the DCDC converter functions as a boost circuit by the switching operation of the switching element, and when the input-side voltage of the DCDC converter is larger than the output-side voltage of the DCDC converter, it may function as a buck circuit due to the voltage drop by the circuit elements constituting the DCDC converter. The circuit elements are, for example, a reactor and a diode. In a fuel cell module having such characteristics, the temperature of the reactor can be obtained simply and with high precision.

[0021] A fuel cell module includes a radiator that exchanges heat between cooling water and air to cool the fuel cell, and a cooling fan that generates an airflow that is blown to the radiator. The switching module and the reactor may be arranged in series with each other along the path of the airflow generated by the cooling fan. For example, in the path of the airflow generated by the cooling fan, the switching module may be located upstream of the reactor. In such an arrangement, the temperature of the reactor has a strong correlation with the temperature of the switching module, so the temperature of the reactor can be obtained with even greater accuracy.

[0022] In a fuel cell module, the DC-DC converter may have multiple circuits in parallel, each including the switching element and the reactor. In a DC-DC converter, the current flowing from the fuel cell can be distributed to multiple circuits, thus preventing the DC-DC converter from becoming overcurrent (in other words, overloaded).

[0023] In a fuel cell module, the control unit includes a first temperature estimation unit that estimates the temperature of the reactor based on the temperature detected by the temperature sensor, and a second temperature estimation unit that estimates the temperature of the reactor based on the heat generation and heat dissipation of the reactor. The temperature of the reactor estimated by the first temperature estimation unit is designated as the first estimated temperature, and the temperature of the reactor estimated by the second temperature estimation unit is designated as the second estimated temperature. When power is supplied to the DC-DC converter, the second estimated temperature may be used as the estimated temperature of the reactor during the first period, and the first estimated temperature may be used as the estimated temperature of the reactor during the second period following the first period. Since the second temperature estimation unit estimates the temperature of the reactor based on the heat generation and heat dissipation of the reactor, the temperature of the reactor can be estimated with accuracy during the transient period from when power is supplied to the DC-DC converter until the temperature of the reactor and the temperature of the switching module approach the saturation temperature. Furthermore, immediately after the DC-DC converter is energized, the second estimated temperature is used as the estimated temperature of the reactor, thus improving the accuracy of the reactor temperature estimation during the transient period.

[0024] In a fuel cell module, the control unit includes a first temperature estimation unit that estimates the temperature of the reactor based on the temperature detected by the temperature sensor, and a second temperature estimation unit that estimates the temperature of the reactor based on the heat generation and heat dissipation of the reactor. The temperature of the reactor estimated by the first temperature estimation unit may be designated as the first estimated temperature, and the temperature of the reactor estimated by the second temperature estimation unit may be designated as the second estimated temperature. The lower of the first and second estimated temperatures may be adopted as the estimated temperature of the reactor. Since the second temperature estimation unit estimates the temperature of the reactor based on the heat generation and heat dissipation of the reactor, it can accurately estimate the temperature of the reactor during the transient period from when the DC-DC converter is energized until the temperature of the reactor and the temperature of the switching module approach the saturation temperature. Furthermore, since the second estimated temperature is adopted as the estimated temperature of the reactor immediately after the DC-DC converter is energized, the accuracy of the reactor temperature estimation during the transient period can be improved.

[0025] In a fuel cell module, the second temperature estimation unit may include a heat generation estimation unit that estimates the heat generation amount based on the amount of current flowing through the DC-DC converter, and a heat dissipation estimation unit that estimates the heat dissipation amount based on the ambient temperature and the heat capacity of the reactor. This allows for accurate estimation of the heat generation and heat dissipation amount of the reactor during the transient period.

[0026] In a fuel cell module, the heat generation estimation unit may estimate the heat generation based on the current and the DC resistance of the coil. This allows for easy estimation of the heat generation of the reactor. Furthermore, it allows for accurate estimation of the reactor temperature, which tends to generate more heat as the current increases and to rise in temperature as the current flows for a longer period.

[0027] In a fuel cell module, the heat dissipation estimation unit may estimate the amount of heat that the reactor can dissipate in a forced convection state as the heat dissipation amount. This allows for easy estimation of the amount of heat dissipated by the reactor.

[0028] In a fuel cell module, the second temperature estimation unit may include an ambient temperature correction unit that calculates the second estimated temperature by correcting the temperature of the reactor, which is estimated based on the heat generation amount estimated by the heat generation amount estimated by the heat generation amount estimated by the heat generation amount estimated by the heat generation amount estimation unit, and the heat generation amount estimated by the heat generation amount estimation unit, based on the ambient temperature. The second estimated temperature can be calculated with high accuracy during the transient period.

[0029] In a fuel cell module, the switching module includes a substrate on which the temperature sensor is arranged, and a heat sink on which the substrate is stacked to promote heat dissipation. In such a configuration, the first estimated temperature deviates significantly from the actual reactor temperature during the transient period. Therefore, by calculating a second estimated temperature, the accuracy of estimating the reactor temperature during the transient period can be significantly improved.

[0030] (First Embodiment) 1. Overall configuration of the fuel cell module The fuel cell module 1 shown in Figure 1 is installed in vehicles Ve such as industrial vehicles like forklifts or electric vehicles, and supplies power to load Lo. Load Lo includes power sources for the drive motor, electrical components, computers, memory, etc. In addition to vehicles, the fuel cell module 1 can also be applied to stationary emergency generators and other applications.

[0031] The fuel cell module 1 comprises a fuel cell FC, a current detection unit Si0, voltage detection units V1 and V2, a DC-DC unit Unt, and a control unit Cnt. The DC-DC unit Unt comprises a DC-DC converter Cnv and a control board Cnb.

[0032] The DC-DC converter Cnv is connected between the fuel cell FC and the energy storage device S. The DC-DC converter Cnv comprises reactors Re1, Re2, and Re3, current sensing units Si1, Si2, and Si3, six switching elements Q1 to Q6, six diodes D1 to D6, and a capacitor Co.

[0033] The fuel cell FC is connected to six switching elements Q1-Q6 and six diodes D1-D6 via reactors Re1, Re2, Re3 and current sensing units Si1, Si2, Si3. The current sensing unit Si0 is connected between the fuel cell FC and reactors Re1, Re2, Re3.

[0034] MOSFETs (metal-oxide-semiconductor field-effect transistors) are used as switching elements Q1 to Q6. IGBTs (Insulated Gate Bipolar Transistors) may also be used as switching elements. The six diodes D1 to D6 are parasitic diodes for the six switching elements (MOSFETs) Q1 to Q6.

[0035] A switching element Q1 constituting the u-phase upper arm and a switching element Q2 constituting the u-phase lower arm are connected in series between the positive busbar Lp and the negative busbar Ln. A switching element Q3 constituting the v-phase upper arm and a switching element Q4 constituting the v-phase lower arm are connected in series between the positive busbar Lp and the negative busbar Ln. A switching element Q5 constituting the w-phase upper arm and a switching element Q6 constituting the w-phase lower arm are connected in series between the positive busbar Lp and the negative busbar Ln.

[0036] A power storage device S is connected to the positive busbar Lp and the negative busbar Ln via a capacitor Co.

[0037] By constructing the DC-DC converter Cnv using a MOSFET and a parasitic diode of the MOSFET, the DC-DC converter Cnv can be made with a simpler configuration than if it were constructed using a mechanical switch, thereby enabling miniaturization of the fuel cell module 1.

[0038] The path through which power supplied from the fuel cell (FC) passes through diodes D1, D3, D5, or D2, D4, D6 will be referred to as the "first path" below. The path through which power supplied from the fuel cell (FC) passes through switching elements Q1, Q3, Q5, or switching elements Q2, Q4, Q6 will be referred to as the "second path" below.

[0039] Switching elements Q1, Q3, and Q5 constituting the u-phase upper arm and the v-phase upper arm are connected to the load Lo via a positive bus Lp. Switching elements Q2, Q4, and Q6 constituting the u-phase lower arm and the v-phase lower arm are connected to the load Lo via a negative bus Ln.

[0040] The switching operation of the switching elements Q1 to Q6 that make up the upper and lower arms allows the DC voltage, which is the voltage of the energy storage device S, to be supplied to the load Lo. The load Lo is, for example, a vehicle drive motor or a cargo handling motor.

[0041] A control board Cnb is connected to the gate terminals of each switching element Q1 to Q6. The control board Cnb switches the switching elements Q1 to Q6 of the DC-DC converter Cnv based on a pulse pattern, which is a control signal.

[0042] The DC-DC converter Cnv converts the voltage of the fuel cell FC into a constant voltage by switching elements Q1 to Q6 on and off according to the input control signal, and outputs it to the load Lo or the energy storage device S.

[0043] Reactor Re1 is connected between the current detection unit Si0 and the switching element Q1 and switching element Q2. Reactor Re2 is connected between the current detection unit Si0 and the switching element Q3 and switching element Q4. Reactor Re3 is connected between the current detection unit Si0 and the switching element Q5 and switching element Q6.

[0044] The current detection unit Si1 is connected between the reactor Re1 and the switching element Q1 and switching element Q2. The current detection unit Si2 is connected between the reactor Re2 and the switching element Q3 and switching element Q4. The current detection unit Si3 is connected between the reactor Re3 and the switching element Q5 and switching element Q6.

[0045] A fuel cell (FC) is a fuel cell composed of multiple fuel cell cells connected in series with each other, and generates electricity by utilizing the electrochemical reaction between a supplied fuel (e.g., hydrogen) and an oxidizer (e.g., oxygen) based on the control of a control unit (Cnt). The energy storage device (S) is composed of a lithium-ion capacitor or the like and is connected between a DC-DC converter (Cnv) and a load (Lo).

[0046] If the power output from the DC-DC converter Cnv is greater than the power required by the load Lo, the surplus power is supplied to the energy storage device S, and the energy storage device S is charged. If the power output from the DC-DC converter Cnv is less than the power required by the load Lo, the deficit power is supplied from the energy storage device S to the load Lo. When regenerative power is supplied from the load Lo to the energy storage device S, the energy storage device S is charged. The energy storage device S is not limited to lithium-ion capacitors, as long as it is an energy storage device (such as a lithium-ion battery) that can be charged and discharged.

[0047] The current detection unit Si0 is composed of an ammeter and the like, and detects the current flowing from the fuel cell FC to the DC-DC converter Cnv, and outputs the detected current to the control unit Cnt.

[0048] The current detection unit Si1 is composed of an ammeter or the like, and detects the current flowing through the DC-DC converter Cnv via the switching element Q1 or the switching element Q2, and outputs the detected current to the control unit Cnt.

[0049] The current detection unit Si2 is composed of an ammeter or the like, and detects the current flowing through the DC-DC converter Cnv via the switching element Q3 or the switching element Q4, and outputs the detected current to the control unit Cnt.

[0050] The current detection unit Si3 is composed of an ammeter and the like, and detects the current flowing through the DC-DC converter Cnv via the switching element Q5 or the switching element Q6, and outputs the detected current to the control unit Cnt.

[0051] The voltage detection unit V1 is composed of a voltmeter or the like, detects the voltage of the fuel cell FC, and outputs the detected voltage to the control unit Cnt. The voltage detection unit V2 is composed of a voltmeter or the like, detects the voltage of the energy storage device S, and outputs the detected voltage to the control unit Cnt.

[0052] The method for detecting the voltage of a fuel cell (FC) can be to directly measure the voltage across the fuel cell FC, or to measure the voltage of one representative fuel cell among those constituting the fuel cell FC and multiply that voltage by the number of stacked fuel cell cells. Alternatively, the voltage of one representative cell itself can be used. In other words, the method is not limited as long as the voltage of the fuel cell can be measured with sufficient accuracy. The same applies to detecting the voltage of the energy storage device S.

[0053] The control board Cnb and control unit Cnt are composed of a CPU (Central Processing Unit) or programmable devices (such as an FPGA (Field Programmable Gate Array) or PLD (Programmable Logic Device)) and output control signals. The control board Cnb and control unit Cnt control the operation of the DC-DC converter Cnv.

[0054] The control unit Cnt controls the amount of electricity generated by the fuel cell FC by controlling the amount of fuel (hydrogen) and air (oxygen) supplied to the fuel cell FC. In other words, the more fuel and air supplied to the fuel cell FC increases, the more electricity is generated, and the less fuel and air supplied to the fuel cell FC decreases, the less electricity is generated. The control unit Cnt may also gradually increase or decrease the amount of fuel and air supplied to the fuel cell FC.

[0055] When the control unit Cnt reduces the amount of fuel and air supplied to the fuel cell FC to zero, the power generation of the fuel cell FC stops after a predetermined time has elapsed, and the amount of power generated by the fuel cell FC becomes zero. The current-voltage characteristics of the fuel cell FC are shown in Figure 2. As can be seen from this characteristic diagram, the voltage of the fuel cell FC (fuel cell) decreases as the current output from the fuel cell FC increases, and the voltage of the fuel cell FC (fuel cell) increases as the current output from the fuel cell FC decreases.

[0056] The control board Cnb and control unit Cnt control the operation of the DC-DC converter Cnv so that the fuel cell FC outputs a current corresponding to the power required by the load Lo and the energy storage device S, and so that the voltage of the fuel cell FC does not exceed a threshold. The process of adjusting the current flowing through the DC-DC converter Cnv to prevent the fuel cell FC from degrading due to its voltage exceeding a threshold is called high-potential avoidance processing. Furthermore, the duty cycle of the control signal increases as the power required by the load Lo and the energy storage device S increases, and decreases as the power required by the load Lo and the energy storage device S decreases. The threshold is the voltage of the fuel cell FC when there is a risk of degradation of the fuel cell FC, and when the voltage of the fuel cell FC is about to exceed the threshold, the reduction in the duty cycle of the control signal is restricted. In fuel cell module 1, in order to perform high-potential avoidance, the voltage per cell of the fuel cell FC is set so that it does not exceed a first threshold. This first threshold voltage is hereinafter referred to as the "high-potential avoidance voltage".

[0057] In this embodiment, in order to create a low-cost fuel cell module 1, the number of cells constituting the fuel cell FC is reduced, and the voltage of the fuel cell FC is boosted by a boost-type DC-DC converter Cnv. The voltage of the fuel cell FC is set to satisfy the following equation F1. In the following equation F1, "voltage of the fuel cell FC" refers to the voltage across the fuel cell FC.

[0058] Fuel cell (FC) voltage ≤ high potential avoidance voltage × number of cells…(F1)

[0059] Since the DC-DC converter Cnv is a boost type, during normal operation, i.e., when current is drawn due to the load Lo, the number of cells is adjusted so that the voltage of the fuel cell FC is lower than the voltage of the energy storage device S, so that the voltage of the fuel cell FC does not overlap with the voltage of the energy storage device S. However, if the voltage of the fuel cell FC is made too low, the number of cells will be too low. As a result, the output of the fuel cell FC will be insufficient, and the fuel cell system will not function properly.

[0060] Therefore, in this embodiment, in order to avoid high potential and improve the output of the fuel cell module 1, the fuel cell module 1 is configured such that when power generation by the fuel cell FC is stopped, the voltage of the fuel cell FC becomes higher than the voltage of the energy storage device S. Specifically, power generation by the fuel cell FC is stopped when there is no load Lo or power demand from the energy storage device S, and the number of cells is determined so that the value of high potential avoidance voltage × number of cells becomes higher than the voltage of the energy storage device S. In addition, the fuel cell module 1 is configured so that the voltage of the fuel cell FC is lower than the voltage of the energy storage device S while power generation by the fuel cell FC is in progress. This clarifies the timing at which the DC-DC converter Cnv should operate, making it easier to control the DC-DC converter Cnv.

[0061] The control board Cnb and the control unit Cnt ensure that when power generation is stopped, the electricity generated by the fuel cell FC can be used to charge the energy storage device via at least one of the first paths D1, D3, D5 or the second paths Q1, Q3, Q5.

[0062] In this embodiment, the electricity generated by the fuel cell FC when power generation is stopped refers to the electricity generated by the reaction of hydrogen and oxygen remaining in the fuel cell module 1 from the hydrogen and oxygen whose supply has been reduced to zero based on the control of the control unit Cnt. Furthermore, stopping power generation by the fuel cell FC includes not only cases where the amount of power generated by the fuel cell FC becomes completely zero, but also cases where power generation by the fuel cell FC is suppressed and the amount of power generated by the fuel cell FC approaches zero. Therefore, when power generation is stopped, the current of the fuel cell FC can be charged by the energy storage device S by flowing current through the first path (diodes D1, D3, D5).

[0063] Furthermore, in the fuel cell module 1, the voltage of the fuel cell FC is set not to exceed a second threshold to prevent the energy storage device S from overcharging. This second threshold voltage is hereinafter referred to as the "power generation stop voltage". The power generation stop voltage is a value unique to the fuel cell module 1. For example, the voltage at a predetermined percentage (remaining energy storage capacity) of the State of Charge (SOC) of the energy storage device S is used as the power generation stop voltage. When the voltage of the energy storage device S exceeds the power generation stop voltage, power generation by the fuel cell FC is stopped. The number of cells in the fuel cell FC is determined by the following formula F2. In the following formula F2, the "high potential avoidance voltage" is the voltage across the fuel cell FC.

[0064] Number of cells × High potential avoidance voltage = Power generation stop voltage + Vf…(F2)

[0065] Vf is the threshold voltage (turn-on voltage) that accounts for the losses due to diodes D1, D3, and D5.

[0066] By setting the number of cells in the fuel cell FC such that equation F2 holds true, it is possible to set a larger number of cells in the fuel cell FC and, as a result, increase the output of the fuel cell FC. Furthermore, in voltage (region) where the voltage of the fuel cell FC is lower than the voltage of the energy storage device S, simply allowing the current to flow naturally will prevent high potential and lower the voltage of the fuel cell FC.

[0067] When current is drawn due to the load (Lo), the voltage of the fuel cell (FC) drops, so the DC-DC converter (Cnv) boosts the voltage of the fuel cell (FC) to output the desired voltage. When boosting the voltage, the DC-DC converter (Cnv) turns off all of the switching elements Q1, Q3, and Q5 on the upper arm, and switches the switching elements Q2, Q4, and Q6 on the lower arm on and off by shifting their phases.

[0068] If no current is drawn due to the load Lo, the control unit Cnt stops power generation by the fuel cell FC. However, even if power generation by the fuel cell FC is stopped, if no power is drawn due to the load Lo, the voltage of the fuel cell FC will rise due to the power generated by the reaction of the remaining fuel (hydrogen) and air (oxygen). Then, when the following equation F3 is satisfied and the voltage of the fuel cell FC becomes higher than the voltage of the energy storage device S, the DC-DC converter Cnv will no longer be able to boost the voltage. In the following equation F3, "voltage of the fuel cell FC" refers to the voltage across the fuel cell FC.

[0069] Fuel cell FC voltage > Energy storage device S voltage... (F3)

[0070] Even if the state of equation F3 occurs when power generation is stopped, by setting the number of cells to the number set in equation F2, the current in the fuel cell FC can be charged by the energy storage device S so that the current flows to the first path by default, and the state in which the fuel cell FC cells are below the high potential avoidance voltage can be maintained. When the current flows by default, the DC-DC converter Cnv turns OFF all of the switching elements Q1, Q3, Q5 on the upper arm and the switching elements Q2, Q4, Q6 on the lower arm. When the relationship in equation F3 is true, the current generated in the fuel cell FC flows to the energy storage device S through the diodes D1, D3, D5 on the upper arm.

[0071] Therefore, by utilizing the characteristics of the parasitic diodes D1, D3, and D5 in the upper arm, high potential can be avoided by default. Furthermore, since an overlap between the voltage of the fuel cell FC and the voltage of the energy storage device S can be tolerated, the number of cells in the fuel cell FC can be increased, thereby increasing the output of the fuel cell FC.

[0072] Furthermore, by selecting a number of cells that satisfies equation F2, it becomes possible to avoid high potential without operating (i.e., without controlling) the boost DC-DC converter Cnv, while simultaneously determining a state in which the output of the fuel cell FC is optimized. Therefore, the number of cells can be optimized without complicating the control of the fuel cell module 1.

[0073] Thus, in the fuel cell module 1 of this embodiment, when power generation by the fuel cell FC is stopped, the voltage of the fuel cell FC becomes higher than the voltage of the energy storage device S. The fuel cell module 1 is configured such that when power generation by the fuel cell FC is stopped, the power generated by the fuel cell FC is made available for charging the energy storage device S by at least one of the diodes D1, D3, D5 (first path) or the switching elements Q1, Q3, Q5 (second path).

[0074] As a result, if no current is drawn due to the load Lo, the control unit Cnt can determine the number of cells so that current flows to the first path even if power generation by the fuel cell FC is stopped, thereby allowing the fuel cell FC to be charged by the energy storage device S. This makes it possible to avoid high potential and improve the output of the fuel cell system.

[0075] Furthermore, the control unit Cnt controls the DC-DC converter Cnv so that the voltage of the fuel cell FC is lower than the voltage of the energy storage device S while power generation is being carried out by the fuel cell FC. Specifically, when a load Lo from the load or a power request from the energy storage device S occurs, power generation by the fuel cell FC is started, and the control unit Cnt controls the DC-DC converter Cnv to achieve a target current corresponding to the power request. This clarifies the timing at which the DC-DC converter Cnv should operate, making it easier to control the DC-DC converter Cnv.

[0076] Furthermore, the control unit Cnt sets the lowest voltage within the fuel cell FC's power generation voltage range (the range of lower and upper voltage limits in the control of the fuel cell FC) to a voltage lower than the lowest voltage within the energy storage device S's usable voltage range (the range of voltages set from the lower and upper SOC limits of the energy storage device S). This allows the energy storage device S's performance to be utilized to the greatest extent possible.

[0077] Furthermore, the switching element of the DC-DC converter Cnv is configured with a MOSFET, and the diode is configured with a parasitic diode of the MOSFET. This makes it possible to create the DC-DC converter Cnv with a simpler configuration than if it were configured with a mechanical switch, and thus enables miniaturization of the fuel cell module 1.

[0078] 2. Internal layout of the fuel cell module Figure 3 is a schematic diagram showing the internal layout of the fuel cell module 1. In Figure 3, the up and down arrows indicate the up and down directions in the direction of gravity. The fuel cell FC, control unit Cnt, energy storage device S, reactor module Rem, switching module Swm, fuel tank Hc, radiator Rd, and cooling fan Fn are mounted on the vehicle Ve in the arrangement shown in Figure 3.

[0079] The radiator Rd is a heat exchanger through which coolant circulates to cool the fuel cell FC. The cooling fan Fn is an electric fan that blows air into the radiator Rd. In the radiator Rd, heat exchange occurs between the air blown by the cooling fan Fn and the coolant that has cooled the fuel cell FC, and heat is dissipated from the coolant to the air.

[0080] The Reactor Module Rem is a modularized version of the Reactors Re1, Re2, and Re3 from the DCDC Unit Unt. The Switching Module Swm is a modularized version of the Switching Elements Q1-Q6, Diodes D1-D6, Capacitor Co, and Control Board Cnb from the DCDC Unit Unt.

[0081] The reactor module Rem and the switching module Swm are arranged in series along the path of the airflow created by the cooling fan Fn. In Figure 3, the thick solid arrows indicate the direction of the airflow created by the cooling fan Fn. In the example in Figure 3, the switching module Swm is located upstream and the reactor module Rem is located downstream in the airflow created by the cooling fan Fn. Alternatively, the reactor module Rem may be located upstream and the switching module Swm downstream in the airflow created by the cooling fan Fn. The fuel tank Hc is a tank for storing fuel (hydrogen).

[0082] 3. Protection and shutdown control of fuel cell modules Figure 4 is a schematic exploded perspective view of a switching module Swm. The switching module Swm includes a control board Cnb, a capacitor board Cob, a switching board Swb, and a heat sink Hs. Capacitors Co are placed on the capacitor board Cob. Switching elements Q1 to Q6 and diodes D1 to D6 are placed on the switching board Swb. The switching board Swb, capacitor board Cob, and control board Cnb are stacked on the heat sink Hs in this order. Specifically, the switching board Swb is stacked on the heat sink Hs, the capacitor board Cob is further stacked on the switching board Swb, and the control board Cnb is further stacked on the capacitor board Cob. The control board Cnb, capacitor board Cob, and switching board Swb are insulating metal substrates, glass epoxy substrates, etc. In this example, the switching board Swb is an insulating metal substrate (i.e., a substrate made of a metal-based material in which the most abundant atoms constituting the material are metal atoms).

[0083] As temperature sensors to detect the temperature of the switching module Swm, a control board temperature sensor Scn is located on the control board Cnb, a capacitor board temperature sensor Sco is located on the capacitor board Cob, and a switching board temperature sensor Ssw is located on the switching board Swb. The control board temperature sensor Scn is a temperature sensor that detects the temperature of the control board Cnb. The capacitor board temperature sensor Sco is a temperature sensor that detects the temperature of the capacitor board Cob. The switching board temperature sensor Ssw is a temperature sensor that detects the temperature of the switching board Swb.

[0084] In this example, since the switching substrate Swb is an insulating metal substrate with high thermal conductivity, the temperature of the switching substrate Swb detected by the switching substrate temperature sensor Ssw has a high correlation with the temperatures of the switching elements Q1 to Q6.

[0085] The detection signals from the control board temperature sensor (Scn), the capacitor board temperature sensor (Sco), and the switching board temperature sensor (Ssw) are input to the control unit (Cnt). Based on the detection signals (in other words, the detected temperatures) from these temperature sensors, the control unit (Cnt) performs protection control and shutdown control. Specifically, to protect the switching module (Swm), the control unit (Cnt) performs protection control and shutdown control when the detected temperatures from these temperature sensors exceed a predetermined temperature.

[0086] The protection control is a control that suppresses power generation by the fuel cell FC in order to suppress the temperature rise of the control board Cnb, capacitor board Cob, switching board Swb, and reactors Re1, Re2, and Re3. The shutdown control is a control that stops power generation by the fuel cell FC in order to prevent the temperature rise of the control board Cnb, capacitor board Cob, switching board Swb, and reactors Re1, Re2, and Re3.

[0087] In other words, the control unit Cnt monitors the temperature of the control board Cnb, capacitor board Cob, switching board Swb, and reactors Re1, Re2, and Re3, and performs protective control and shutdown control when their temperatures exceed a predetermined temperature.

[0088] The control unit Cnt monitors the temperature detected by the control board temperature sensor Scn as the temperature of the control board Cnb, the temperature detected by the capacitor board temperature sensor Sco as the temperature of the capacitor board Cob, and the temperature detected by the switching board temperature sensor Ssw as the temperature of the switching board Swb.

[0089] The control unit Cnt estimates and monitors the temperatures of reactors Re1, Re2, and Re3 based on the temperature detected by the control board temperature sensor Scn, the capacitor board temperature sensor Sco, and the switching board temperature sensor Ssw.

[0090] The control unit Cnt executes protection control when the temperature of the switching board Swb (hereinafter referred to as the switching board temperature) exceeds the switching board protection temperature, when the temperature of the capacitor board Cob (hereinafter referred to as the capacitor board temperature) exceeds the capacitor board protection temperature, when the temperature of the control board Cnb (hereinafter referred to as the control board temperature) exceeds the control board protection temperature, or when the temperatures of reactors Re1, Re2, and Re3 (hereinafter referred to as the reactor temperatures) exceed the reactor protection temperature.

[0091] The control unit Cnt executes a stop control if the switching board temperature exceeds the switching board stop temperature, the capacitor board temperature exceeds the capacitor board stop temperature, the control board temperature exceeds the control board stop temperature, or the reactor temperature exceeds the reactor stop temperature.

[0092] In this example, the switching board shutdown temperature is set higher than the switching board protection temperature, the capacitor board shutdown temperature is set higher than the capacitor board protection temperature, the control board shutdown temperature is set higher than the control board protection temperature, and the reactor shutdown temperature is set higher than the reactor protection temperature.

[0093] The control unit Cnt estimates the reactor temperature by correcting the temperature of the switching module Swm (specifically, one of the temperatures of the switching board, capacitor board, and control board).

[0094] First, we will explain an example of estimating the reactor temperature by correcting the switching substrate temperature. The reactor temperature is estimated by correcting the switching substrate temperature with a first correction temperature and a second correction temperature. Specifically, the reactor temperature is calculated using the following formula F4.

[0095] Reactor temperature = Switching board temperature + First correction temperature + Second correction temperature ... (F4)

[0096] Since reactors Re1, Re2, and Re3 are located in the same cooling air path as the switching board Swb, the reactor temperatures are correlated with the temperature of the switching board Swb. Therefore, the reactor temperatures are calculated based on the switching board temperature.

[0097] The first correction temperature is determined using the control map shown in Figure 5. The first correction temperature is determined based on the boost amount by the DC-DC converter Cnv and the current value of the fuel cell FC. In other words, the first correction temperature is determined based on the input-output voltage difference of the DC-DC converter Cnv and the value of the current input to the DC-DC converter Cnv. Figure 5 shows an image illustrating the relative magnitudes of the boost amount by the DC-DC converter Cnv, the current value of the fuel cell FC, and the first correction temperature, and specific numerical values ​​are omitted.

[0098] Since the reactor temperature increases with increasing voltage boost from the DC-DC converter (Cnv), the first correction temperature is determined to be a larger value as the voltage boost from the DC-DC converter (Cnv) increases. Similarly, since the reactor temperature increases with increasing current value from the fuel cell (FC), the first correction temperature is determined to be a larger value as the current value from the fuel cell (FC) increases.

[0099] The second correction temperature is determined using the control map shown in Figure 6. The second correction temperature is determined based on the temperature of the cooling water that cools the fuel cell (FC). Figure 6 shows an image illustrating the relative magnitudes of the cooling water temperature and the second correction temperature, and specific numerical values ​​are omitted.

[0100] As the temperature of the fuel cell (FC) increases, the temperature of the cooling water used to cool the FC also increases. Therefore, the higher the temperature of the cooling water used to cool the fuel cell (FC), the larger the second correction temperature will be determined to be.

[0101] By estimating the reactor temperature in this way, the reactor temperature can be obtained without using dedicated temperature sensors to detect the temperatures of reactors Re1, Re2, and Re3.

[0102] The reactor temperature may be estimated by correcting the capacitor substrate temperature with a first correction temperature and a second correction temperature. Specifically, the reactor temperature may be calculated using the following formula F5.

[0103] Reactor temperature = Capacitor substrate temperature + First correction temperature + Second correction temperature ... (F5)

[0104] In other words, since the reactor temperature is correlated with the capacitor substrate temperature, the reactor temperature may be calculated based on the capacitor substrate temperature.

[0105] The reactor temperature may be estimated by correcting the control board temperature with a first correction temperature and a second correction temperature. Specifically, the reactor temperature may be calculated using the following formula F6.

[0106] Reactor temperature = Control board temperature + First correction temperature + Second correction temperature ... (F6)

[0107] In other words, since the reactor temperature is correlated with the control substrate temperature, the reactor temperature may be calculated based on the control substrate temperature.

[0108] 4. Effects In this embodiment, the control unit Cnt estimates the temperatures of reactors Re1, Re2, and Re3 based on the temperatures detected by temperature sensors (specifically, the control board temperature sensor Scrn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw) that detect the temperature of the switching module Swm.

[0109] According to this method, the temperatures of reactors Re1, Re2, and Re3 are estimated based on the temperature of the switching module Swm, which is correlated with the temperatures of reactors Re1, Re2, and Re3, thus enabling high-precision acquisition of the temperatures of reactors Re1, Re2, and Re3. Furthermore, since the temperatures of reactors Re1, Re2, and Re3 are acquired using an existing temperature sensor that detects the temperature of the switching module Swm, the temperatures of reactors Re1, Re2, and Re3 can be easily acquired.

[0110] If the temperature sensor used to detect the temperature of the switching module Swm is a switching board temperature sensor Ssw located on the switching board Swb, the temperatures of reactors Re1, Re2, and Re3 can be estimated based on the temperature of the switching board Swb, which is correlated with the reactor temperature. Therefore, the temperatures of reactors Re1, Re2, and Re3 can be obtained with high accuracy. Since the temperatures of reactors Re1, Re2, and Re3 are obtained using the existing switching board temperature sensor Ssw, the temperatures of reactors Re1, Re2, and Re3 can be obtained easily.

[0111] The temperatures of the switching elements Q1 to Q6 have a high correlation with the temperatures of the reactors Re1, Re2, and Re3. In this embodiment, the switching substrate Swb is an insulating metal substrate formed from a material mainly composed of metal, so the thermal conductivity from the switching elements Q1 to Q6 to the switching substrate Swb is high. Therefore, the correlation between the temperatures of the reactors Re1, Re2, and Re3 and the temperature of the switching substrate Swb is also high, so the temperatures of the reactors Re1, Re2, and Re3 can be obtained with even greater accuracy.

[0112] If the temperature sensor used to detect the temperature of the switching module Swm is a capacitor board temperature sensor Sco located on the capacitor board Cob, the temperatures of reactors Re1, Re2, and Re3 can be estimated based on the temperature of the capacitor board Cob, which is correlated with the temperatures of reactors Re1, Re2, and Re3. Therefore, the temperatures of reactors Re1, Re2, and Re3 can be obtained with high accuracy. Since the temperatures of reactors Re1, Re2, and Re3 are obtained using the existing capacitor board temperature sensor Sco, the temperatures of reactors Re1, Re2, and Re3 can be obtained easily.

[0113] If the temperature sensor used to detect the temperature of the switching module Swm is the control board temperature sensor Scn located on the control board Cnb, the temperatures of reactors Re1, Re2, and Re3 can be estimated based on the temperature of the control board Cnb, which is correlated with the temperatures of reactors Re1, Re2, and Re3. Therefore, the temperatures of reactors Re1, Re2, and Re3 can be obtained with high accuracy. Since the temperatures of reactors Re1, Re2, and Re3 are obtained using the existing control board temperature sensor Scn, the temperatures of reactors Re1, Re2, and Re3 can be obtained easily.

[0114] In this embodiment, the control unit Cnt estimates the temperatures of reactors Re1, Re2, and Re3 by correcting the temperature detected by the control board temperature sensor Scrn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw using the value of the current input from the fuel cell FC to the DC-DC converter Cnv and the input / output voltage difference of the DC-DC converter Cnv. Since both the value of the current input from the fuel cell FC to the DC-DC converter Cnv and the input / output voltage difference of the DC-DC converter Cnv are correlated with the temperatures of reactors Re1, Re2, and Re3, the temperatures detected by the control board temperature sensor Scrn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw can be corrected with high accuracy, and the temperatures of reactors Re1, Re2, and Re3 can be obtained with high accuracy.

[0115] In this embodiment, the control unit Cnt may estimate the temperatures of reactors Re1, Re2, and Re3 by correcting the temperatures detected by the control board temperature sensor Scrn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw using the temperature of the cooling water that cools the fuel cell FC. Since the temperature of the cooling water that cools the fuel cell FC is correlated with the temperatures of reactors Re1, Re2, and Re3, the temperatures of reactors Re1, Re2, and Re3 can be obtained with high accuracy by correcting the temperatures detected by the control board temperature sensor Scrn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw with high accuracy.

[0116] In this embodiment, the control unit Cnt estimates the temperatures of reactors Re1, Re2, and Re3 based on the temperatures detected by the control board temperature sensor Scn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw, and also performs protection control or shutdown control of the switching module Swm based on the temperatures detected by the control board temperature sensor Scn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw. This makes it possible to perform protection control or shutdown control of the switching module simply and with high accuracy.

[0117] In this embodiment, the DC-DC converter Cnv functions as a boost circuit when the input voltage of the DC-DC converter Cnv is lower than the output voltage of the DC-DC converter Cnv, through the switching operation of switching elements Q1 to Q6. When the input voltage of the DC-DC converter Cnv is higher than the output voltage of the DC-DC converter Cnv, it functions as a step-down circuit due to the voltage drop caused by the circuit elements constituting the DC-DC converter Cnv. The circuit elements are, for example, reactors Re1, Re2, Re3 and diodes D1 to D6. In a fuel cell module 1 having such characteristics, the temperatures of reactors Re1, Re2, and Re3 can be obtained easily and with high accuracy.

[0118] In this embodiment, the switching module Swm and reactors Re1, Re2, and Re3 may be arranged in series with each other along the path of the airflow generated by the cooling fan Fn. Specifically, in the path of the airflow generated by the cooling fan Fn, the switching module Swm is located upstream of the reactors Re1, Re2, and Re3. In such an arrangement, the temperatures of reactors Re1, Re2, and Re3 have a strong correlation with the temperature of the switching module Swm, so the temperatures of reactors Re1, Re2, and Re3 can be obtained with even greater accuracy.

[0119] In this embodiment, the DC-DC converter Cnv has three circuits in parallel, each containing a switching element and a reactor. In the DC-DC converter Cnv, the current flowing from the fuel cell FC can be distributed to multiple circuits, thus preventing the DC-DC converter Cnv from entering an overcurrent state (in other words, an overload state). In the DC-DC converter Cnv, the number of circuits in parallel containing switching elements and reactors is not limited to three, but may be more than three.

[0120] (Second Embodiment) In the above embodiment, the control unit Cnt estimates the reactor temperature by correcting the temperature of the switching module Swm. That is, in the above embodiment, the control unit Cnt estimates the reactor temperature using one estimation method. In contrast, in this embodiment, the control unit Cnt estimates the reactor temperature using two estimation methods.

[0121] As shown in Figure 7, the control unit Cnt of this embodiment includes a first temperature estimation unit 101, a second temperature estimation unit 102, and an estimated temperature comparison unit 103. The first temperature estimation unit 101 estimates the reactor temperature based on the temperature of the switching module Swm, similar to the embodiment described above. The second temperature estimation unit 102 estimates the reactor temperature based on the heat generated by reactors Re1, Re2, and Re3 and the heat dissipated by reactors Re1, Re2, and Re3. Hereinafter, the reactor temperature estimated by the first temperature estimation unit 101 will be referred to as the first estimated temperature, and the reactor temperature estimated by the second temperature estimation unit 102 will be referred to as the second estimated temperature.

[0122] In this embodiment, the first estimated temperature is calculated using the following formula F4. First estimated temperature = Switching board temperature + First corrected temperature + Second corrected temperature + Third corrected temperature ... (F4)

[0123] The first corrected temperature is the same as the first corrected temperature in the above embodiment and is determined using the first control map 101a, which is the same as the control map shown in Figure 5. The second corrected temperature is the same as the second corrected temperature in the above embodiment and is determined using the second control map 101b, which is the same as the control map shown in Figure 6. The third corrected temperature is a corrected temperature determined based on the ambient temperature and is determined using the third control map 101c.

[0124] The second temperature estimation unit 102 includes a heat generation estimation unit 102a, a heat dissipation estimation unit 102b, an integration unit 102c, and an ambient temperature correction unit 102d.

[0125] The heat generation estimation unit 102a estimates the heat generation of reactors Re1, Re2, and Re3. The heat dissipation estimation unit 102b estimates the heat dissipation of reactors Re1, Re2, and Re3. The integration unit 102c integrates the heat generation and heat dissipation of reactors Re1, Re2, and Re3 and converts it into the temperatures of reactors Re1, Re2, and Re3. The ambient temperature correction unit 102d corrects the temperatures of reactors Re1, Re2, and Re3 converted by the integration unit 102c using the ambient temperature.

[0126] The heat generation estimation unit 102a estimates the heat generation of reactors Re1, Re2, and Re3 based on the amount of current flowing through the DC-DC converter Cnv. Specifically, the heat generation estimation unit 102a estimates the heat generation of reactors Re1, Re2, and Re3 from the amount of current flowing through the DC-DC converter Cnv and the DC resistance values ​​of the coils of reactors Re1, Re2, and Re3.

[0127] In other words, the current flowing through the coils of reactors Re1, Re2, and Re3 can be estimated from the current flowing through the DC converter Cnv, and the amount of heat generated by the coils of reactors Re1, Re2, and Re3 can be calculated from the current flowing through the coils of reactors Re1, Re2, and Re3 and the DC resistance values ​​of the coils of reactors Re1, Re2, and Re3. To put it another way, the losses of the coils of reactors Re1, Re2, and Re3 are estimated as the amount of heat generated by the coils. Then, the amount of heat generated by reactors Re1, Re2, and Re3 can be estimated from the amount of heat generated by the coils of reactors Re1, Re2, and Re3.

[0128] The heat dissipation estimation unit 102b estimates the amount of heat dissipated by reactors Re1, Re2, and Re3 based on the ambient temperature and the heat capacities of reactors Re1, Re2, and Re3. For example, the heat dissipation estimation unit 102b estimates the amount of heat that reactors Re1, Re2, and Re3 can dissipate under forced convection conditions as the amount of heat dissipated by reactors Re1, Re2, and Re3. For example, the heat dissipation estimation unit 102b estimates the amount of heat dissipated by reactors Re1, Re2, and Re3 using the heat capacities and heat dissipation coefficients of reactors Re1, Re2, and Re3.

[0129] The integration unit 102c estimates the reactor temperature by integrating the heat generation amounts of reactors Re1, Re2, and Re3 estimated by the heat generation amount estimation unit 102a with the heat dissipation amounts of reactors Re1, Re2, and Re3 estimated by the heat dissipation amount estimation unit 102b and converting the results into temperature.

[0130] The ambient temperature correction unit 102d corrects the reactor temperature converted by the integration unit 102c using the ambient temperature. In other words, the ambient temperature correction unit 102d corrects the error caused by the difference between the ambient temperature assumed by the heat generation estimation unit 102a and the heat dissipation estimation unit 102b and the actual ambient temperature.

[0131] The second temperature estimation unit 102 uses the reactor temperature corrected by the ambient temperature correction unit 102d as the second estimated temperature.

[0132] The control unit Cnt compares the first estimated temperature estimated by the first temperature estimation unit 101 with the second estimated temperature estimated by the second temperature estimation unit 102, and determines the smaller value as the estimated reactor temperature. Hereafter, the estimated reactor temperature determined by the control unit Cnt by comparing the first estimated temperature and the second estimated temperature will be referred to as the estimated reactor temperature.

[0133] If the first estimated temperature is greater than the second estimated temperature, the second estimated temperature will be set to the same temperature as the first estimated temperature.

[0134] Figure 8 shows an example of reactor temperature estimation according to this embodiment. In Figure 8, the solid line represents the actual reactor temperature. In Figure 8, the temperature detected by the switching substrate temperature sensor Ssw (i.e., the switching substrate temperature in the above formula F4) is shown by a dashed line, the first estimated temperature is shown by a dashed line, and the second estimated temperature is shown by a double dashed line.

[0135] Immediately after the fuel cell module 1 is started up and power is supplied to the DC-DC converter Cnv, the actual reactor temperature rises more rapidly than the temperature of the switching board Swb. This is because, due to the structure of the DC-DC converter Cnv in this embodiment, the heat dissipation capacity of reactors Re1, Re2, and Re3 is lower than that of the switching board Swb.

[0136] Immediately after fuel cell module 1 is started and power is supplied to the DC-DC converter Cnv, the second estimated temperature is closer to the actual reactor temperature than the first estimated temperature. The reason for this is explained below.

[0137] As explained in the above formula F4, the first estimated temperature is obtained by correcting the temperature of the switching board Swb. The difference between the first estimated temperature and the temperature of the switching board Swb is the sum of the first, second, and third corrected temperatures. The first estimated temperature will be higher than the temperature of the switching board Swb, but it will basically fluctuate in the same way as the temperature of the switching board Swb. Therefore, the first estimated temperature will rise more rapidly than the actual reactor temperature.

[0138] On the other hand, since the second estimated temperature is calculated based on the estimated heat generation and heat dissipation of reactors Re1, Re2, and Re3, the second estimated temperature will be close to the actual reactor temperature immediately after the fuel cell module 1 is started up and power is supplied to the DC-DC converter Cnv.

[0139] After a certain amount of time has passed since the fuel cell module 1 was started up, the actual reactor temperature and the temperature of the switching substrate Swb both begin to rise more slowly and approach their saturation temperatures. In the following, the period from the start-up of the fuel cell module 1 until the actual reactor temperature and the temperature of the switching substrate Swb approach their saturation temperatures will be referred to as the transition period.

[0140] During the transition period, the first estimated temperature will be closer to the actual reactor temperature than the second estimated temperature. This is because the first control map 101a, the second control map 101b, and the third control map 101c are set so that the first estimated temperature will be closer to the actual reactor temperature when the actual reactor temperature and the temperature of the switching substrate Swb approach the saturation temperature.

[0141] On the other hand, since the second estimated temperature is calculated using an estimation method that is close to the actual reactor temperature during the transient period, the second estimated temperature deviates significantly from the actual reactor temperature after a certain amount of time has passed since the fuel cell module 1 was started up.

[0142] Since the smaller of the first estimated temperature and the second estimated temperature is adopted as the estimated reactor temperature, the second estimated temperature is adopted as the estimated reactor temperature until the first time T1, which is the time when the first estimated temperature and the second estimated temperature coincide. After the first time T1, the first estimated temperature is adopted as the estimated reactor temperature.

[0143] In other words, during the first period from when the fuel cell module 1 is started up until the first time T1, the second estimated temperature is used as the estimated reactor temperature, and during the second period after the first time T1, the first estimated temperature is used as the estimated reactor temperature.

[0144] Therefore, the reactor temperature can be estimated with high accuracy relative to the actual reactor temperature.

[0145] The second time point T2 shown in Figure 8 is the time when power is cut off to the DC-DC converter Cnv. From the first time point T1 to the second time point T2, the first estimated temperature is used as the estimated reactor temperature. From the first time point T1 to the second time point T2, the second estimated temperature is set to the same temperature as the first estimated temperature.

[0146] When power is cut off to the DC-DC converter Cnv, the first estimated temperature decreases discontinuously from the first estimated temperature immediately before the second time T2, because the first corrected temperature becomes 0. The estimation of the second estimated temperature resumes from the second estimated temperature immediately before the second time point T2 (i.e., the first estimated temperature immediately before the second time point T2). At this point, the first estimated temperature is smaller than the second estimated temperature, so the first estimated temperature is adopted as the estimated reactor temperature.

[0147] The decrease in the second estimated temperature is more rapid than the decrease in the first estimated temperature, so after some time has passed from the second time T2, the first and second estimated temperatures coincide. From the third time T3 onward, when the first and second estimated temperatures coincide, the second estimated temperature becomes smaller than the first estimated temperature, so the second estimated temperature is adopted as the estimated reactor temperature.

[0148] Although not shown in the diagram, when power is restored to the DC-DC converter Cnv after the third time step T3, both the first and second estimated temperatures begin to rise. However, as with the period up to the first time step T1, the rise in the second estimated temperature is more rapid than the rise in the second estimated temperature. Therefore, after some time has passed since power was restored to the DC-DC converter Cnv, the first and second estimated temperatures coincide.

[0149] If the power supply to the DC-DC converter Cnv is repeatedly stopped and restarted in this manner, the estimation of the first estimated temperature and the second estimated temperature as described above will be repeated.

[0150] In this embodiment, the first temperature estimation unit 101 of the control unit Cnt estimates a first estimated temperature based on the switching substrate temperature, and the second temperature estimation unit 102 of the control unit Cnt estimates a second estimated temperature based on the heat generation and heat dissipation of the reactors Re1, Re2, and Re3. When power is supplied to the DC-DC converter Cnv, the second estimated temperature is adopted as the estimated reactor temperature during the first period, and the first estimated temperature is adopted as the estimated reactor temperature during the second period following the first period.

[0151] According to this, the second temperature estimation unit 102 estimates the second estimated temperature based on the heat generation and heat dissipation of the reactors Re1, Re2, and Re3, so that the reactor temperature can be estimated accurately during the transient period. Furthermore, since the second estimated temperature is adopted as the estimated reactor temperature immediately after the DC-DC converter Cnv is powered on, the accuracy of the reactor temperature estimation during the transient period from when the DC-DC converter Cnv is powered on until the reactor temperature and switching substrate temperature approach the saturation temperature can be improved.

[0152] In this embodiment, the control unit Cnt adopts the lower of the first estimated temperature and the second estimated temperature as the estimated reactor temperature. As a result, immediately after the DCDC converter Cnv is energized, the second estimated temperature is adopted as the estimated reactor temperature, which improves the accuracy of reactor temperature estimation during the transient period.

[0153] In this embodiment, the heat generation estimation unit 102a of the second temperature estimation unit 102 estimates the heat generation of reactors Re1, Re2, and Re3 based on the amount of current flowing through the DC-DC converter Cnv, and the heat dissipation estimation unit 102b of the second temperature estimation unit 102 estimates the heat dissipation of reactors Re1, Re2, and Re3 based on the ambient temperature and the heat capacities of reactors Re1, Re2, and Re3. This makes it possible to accurately estimate the heat generation and heat dissipation of reactors Re1, Re2, and Re3 during the transient period.

[0154] In this embodiment, the heat generation estimation unit 102a estimates the heat generation of reactors Re1, Re2, and Re3 based on the amount of current flowing through the DC-DC converter Cnv and the DC resistance values ​​of the coils of reactors Re1, Re2, and Re3.

[0155] According to this method, the amount of heat generated by reactors Re1, Re2, and Re3 can be easily estimated. Furthermore, the temperatures of reactors Re1, Re2, and Re3, which tend to generate more heat as the current increases and whose temperature rises as the current flows for a longer period of time, can be estimated with high accuracy.

[0156] Furthermore, since the heat generation estimation unit 102a uses the DC component rather than impedance in estimating the heat generation, it is possible to easily estimate the heat generation in a fuel cell module where a DC current flows as a surplus current when the voltage of the fuel cell FC is higher than the voltage of the energy storage device S, as in this embodiment.

[0157] In this embodiment, the heat dissipation estimation unit 102b estimates the amount of heat that reactors Re1, Re2, and Re3 can dissipate in a forced convection state as the heat dissipation amount of reactors Re1, Re2, and Re3. This makes it easy to estimate the heat dissipation amount of reactors Re1, Re2, and Re3.

[0158] In this embodiment, the ambient temperature correction unit 102d of the second temperature estimation unit 102 calculates the second estimated temperature by correcting the temperature of the reactors, which was estimated based on the heat generation amount of reactors Re1, Re2, and Re3 estimated by the heat generation amount estimation unit 102a and the heat generation amount of reactors Re1, Re2, and Re3 estimated by the heat generation amount estimation unit 102b, based on the ambient temperature. This allows for accurate calculation of the second estimated temperature during the transient period.

[0159] In this embodiment, the switching substrate Swb is laminated on the heat sink Hs in the switching module Swm. In such a configuration, the first estimated temperature deviates significantly from the actual reactor temperature during the transient period. Therefore, by calculating the second estimated temperature, the accuracy of estimating the reactor temperature during the transient period can be significantly improved.

[0160] (Other embodiments) In the above embodiment, the first corrected temperature is determined using the input-output voltage difference of the DC-DC converter Cnv and the value of the current input to the DC-DC converter Cnv, but it may also be determined using at least one of the input-output voltage difference of the DC-DC converter Cnv and the value of the current input to the DC-DC converter Cnv. Since both the value of the current input from the fuel cell FC to the DC-DC converter Cnv and the input-output voltage difference of the DC-DC converter Cnv are correlated with the temperatures of reactors Re1, Re2, and Re3, the temperatures detected by the control board temperature sensor Scrn, the capacitor board temperature sensor Sco, or the switching board temperature sensor Ssw can be corrected with high accuracy to obtain the temperatures of reactors Re1, Re2, and Re3 with high accuracy.

[0161] In the above embodiment, the second correction temperature is determined based on the temperature of the cooling water that cools the fuel cell FC. However, if the control unit Cnt controls the cooling fan Fn to increase its rotational speed as the temperature of the cooling water that cools the fuel cell FC increases, the second correction temperature may be determined based on the rotational speed of the cooling fan Fn. If the second correction temperature is determined to be a larger value as the rotational speed of the cooling fan Fn increases, then the second correction temperature can be determined to be a larger value as the temperature of the fuel cell FC increases and the temperature of the cooling water that cools the fuel cell FC increases.

[0162] In the above embodiment, the switching module Swm is positioned upstream of the reactors Re1, Re2, and Re3 in the airflow path generated by the cooling fan Fn. However, conversely, the switching module Swm may be positioned downstream of the reactors Re1, Re2, and Re3. In this arrangement as well, a strong correlation exists between the temperatures of the reactors Re1, Re2, and Re3 and the temperature of the switching module Swm, allowing for more accurate acquisition of the temperatures of the reactors Re1, Re2, and Re3.

[0163] The fuel cell module 1 may be a DC-DC converter as shown in Figure 9. In this case, there is no second path with a switching element, but when the boost operation by the DC-DC converter is stopped, current flows through the first path with a diode, preventing the fuel cell FC from becoming high-potential.

[0164] Furthermore, in the above-described embodiment, the number of cells in the fuel cell FC is determined by formula F2, but this is not limited to this. For example, the voltage of the fuel cell FC may be set to be higher than the voltage obtained by adding the threshold voltage (start-up voltage) of the diode to the voltage of the energy storage device S. In this case, the number of cells in the fuel cell FC is determined by the following formula F7. In the following formula F6, "high potential avoidance voltage" refers to the voltage across the fuel cell FC.

[0165] Number of cells × High potential avoidance voltage = Power generation stop voltage…(F7)

[0166] Furthermore, in the above embodiment, when current is allowed to flow naturally, current is supplied to diodes D1, D3, and D5 on the upper arm, but this is not limited to this.

[0167] The control unit Cnt may turn on (close) the switching elements Q1, Q3, and Q5 when it detects that the voltage of the fuel cell FC detected by the voltage detection unit V1 is higher than the voltage of the energy storage device S detected by the voltage detection unit V2. As a result, even when the voltage of the fuel cell FC is higher than the voltage of the energy storage device S (the state in equation F3 above), the current generated by the fuel cell FC flows to the energy storage device S through the switching elements Q1, Q3, and Q5. This eliminates power loss due to the diodes, and the power output by the fuel cell FC can be used to efficiently charge the energy storage device S.

[0168] Furthermore, the control unit Cnt may be capable of detecting the ON-OFF state (open / closed state) of the switching elements Q1 to Q6. When the control unit Cnt detects that current is flowing through the first or second path when the ON-OFF operation of the switching elements Q1 to Q6 is not being performed, it sets the switching elements Q1 to Q6 to the OFF state (closed state). As a result, even when the voltage of the fuel cell FC is greater than the voltage of the energy storage device S (the state of equation F3 above), the current generated by the fuel cell FC flows to the energy storage device S through the switching elements Q1, Q3, and Q5. This eliminates power loss due to the diodes, and the power output by the fuel cell FC can be used to efficiently charge the energy storage device S. [Explanation of Symbols]

[0169] 1 Fuel cell module Cnb control board Cnt Control Unit CNV DC-DC Converter Co capacitor Cob capacitor board D1~D6 Diodes FC fuel cell Fn Cooling Fan Rd radiator Re1, Re2, Re3 Reactors S Power storage device SCN control board temperature sensor Sco capacitor board temperature sensor Ssw Switching Board Temperature Sensor Swb switching board Swm switching module Q1-Q6 Switching elements

Claims

1. A fuel cell that generates electricity using fuel and an oxidizer, A switching module having switching elements and capacitors, and a reactor having a core and coil, and a DC-DC converter that converts the voltage of the power generated by the fuel cell, A temperature sensor for detecting the temperature of the switching module, A fuel cell module comprising: a control unit that estimates the temperature of the reactor based on the temperature detected by the temperature sensor.

2. The fuel cell module according to claim 1, wherein the control unit estimates the temperature of the reactor by correcting the temperature detected by the temperature sensor using at least one of the value of the current input from the fuel cell to the DC-DC converter and the input / output voltage difference of the DC-DC converter.

3. The fuel cell module according to claim 1 or 2, wherein the control unit estimates the temperature of the reactor by correcting the temperature detected by the temperature sensor using the temperature of the cooling water that cools the fuel cell.

4. The fuel cell module according to claim 1 or 2, wherein the control unit estimates the temperature of the reactor based on the temperature detected by the temperature sensor and performs protection control or shutdown control of the switching module based on the temperature detected by the temperature sensor.

5. The DCDC converter is When the input voltage of the DC-DC converter is lower than the output voltage of the DC-DC converter, the switching operation of the switching element functions as a boost circuit. The fuel cell module according to claim 1 or 2, wherein when the input voltage of the DC-DC converter is greater than the output voltage of the DC-DC converter, it functions as a step-down circuit due to the voltage drop by the circuit elements constituting the DC-DC converter.

6. A radiator that exchanges heat between cooling water and air to cool the aforementioned fuel cell, The radiator is equipped with a cooling fan that generates an airflow that is blown onto the radiator, The fuel cell module according to claim 1, wherein the switching module and the reactor are arranged in series with respect to each other along the path of the airflow generated by the cooling fan.

7. The fuel cell module according to claim 1 or 2, wherein the DC-DC converter has a plurality of circuits including the switching element and the reactor arranged in parallel.

8. The control unit, A first temperature estimation unit estimates the temperature of the reactor based on the temperature detected by the temperature sensor, It includes a second temperature estimation unit that estimates the temperature of the reactor based on the amount of heat generated and the amount of heat dissipated by the reactor, The temperature of the reactor estimated by the first temperature estimation unit is set as the first estimated temperature, and the temperature of the reactor estimated by the second temperature estimation unit is set as the second estimated temperature. The fuel cell module according to claim 1, wherein when power is supplied to the DC-DC converter, the second estimated temperature is adopted as the estimated temperature of the reactor during the first period, and the first estimated temperature is adopted as the estimated temperature of the reactor during the second period following the first period.

9. The control unit, A first temperature estimation unit estimates the temperature of the reactor based on the temperature detected by the temperature sensor, It includes a second temperature estimation unit that estimates the temperature of the reactor based on the amount of heat generated and the amount of heat dissipated by the reactor, The temperature of the reactor estimated by the first temperature estimation unit is set as the first estimated temperature, and the temperature of the reactor estimated by the second temperature estimation unit is set as the second estimated temperature. The fuel cell module according to claim 1, wherein the lower of the first estimated temperature and the second estimated temperature is adopted as the estimated temperature of the reactor.

10. The second temperature estimation unit is, A heat generation estimation unit that estimates the amount of heat generated based on the amount of current flowing through the DC-DC converter, A fuel cell module according to claim 8 or 9, comprising a heat dissipation estimation unit that estimates the amount of heat dissipation based on the ambient temperature and the heat capacity of the reactor.

11. The fuel cell module according to claim 10, wherein the heat generation estimation unit estimates the heat generation based on the current and the DC resistance value of the coil.

12. The fuel cell module according to claim 10, wherein the heat dissipation amount estimation unit estimates the amount of heat that the reactor can dissipate in a forced convection state as the heat dissipation amount.

13. The fuel cell module according to claim 10, wherein the second temperature estimation unit has an ambient temperature correction unit that calculates the second estimated temperature by correcting the temperature of the reactor, which has been estimated based on the heat generation amount estimated by the heat generation amount estimated by the heat generation amount estimated by the heat generation amount estimated by the heat generation amount estimation unit, and the heat generation amount estimated by the heat generation amount estimation unit, based on the ambient temperature.

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