Patent Publication Number: US-8541120-B2

Title: Fuel cell system and operation method for fuel cell system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application of International Application No. PCT/IB2007/000659, filed Mar. 16, 2007, and claims the priority of Japanese Application No. 2006-078817, filed Mar. 22, 2006, the contents of both of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a fuel cell system, and an operation method for the fuel cell system. Particularly, the invention relates to a failure detection regarding a circulation pump for circulating the fuel gas. 
     2. Description of the Related Art 
     In recent years, fuel cell that generates electric power through the use of a fuel gas containing hydrogen and an oxidizing gas containing oxygen are drawing attention. A fuel cell system having such a fuel cell includes a fuel gas supply channel that supplies the fuel gas to the fuel cell, a fuel gas circulation channel that circulates the fuel gas discharged from the fuel cell by returning it to a fuel gas supply channel for reuse, a circulation pump provided on the fuel gas circulation channel so as to circulate the fuel gas, etc. Among these gas channels, the channels in which the fuel gas circulates are called circulation system channels as well. 
     A fuel cell system as described above, at the time of startup, performs a pump driving detection in which the driving of the circulation pump is attempted and it is detected whether or not the circulation pump is driven (Japanese Patent Application Publication No JP-A-2004-172025). In this pump driving detection, if it is detected that the circulation pump fails to be driven, it is determined that the circulation pump has a breakdown, and a measure, for example, stopping the power generation, is taken. 
     In the fuel cell, water is produced by an electrochemical reaction during power generation, and the reaction-produced water circulates in a circulation system channel, and sometimes remains in the circulation pump. If, with water remaining, the outside air temperature falls below freezing point and the operation of the fuel cell system is stopped for a certain amount of time, the water remaining in the circulation pump freezes. In that case, there is risk of the circulation pump failing to be driven. 
     Therefore, if, at the time of starting the fuel cell system, the pump driving detection is performed and the circulation pump fails to be driven, a case is conceivable in which the circulation pump fails to be driven because of the freezing as well as a case where the circulation pump fails to be driven because of a breakdown. Hence, as for the pump driving detection, there is risk of falsely determining that the circulation pump has a breakdown in the case where the circulation pump fails to be driven due to freezing, and actually does not have a breakdown. In consequence, there is risk of bringing about an inconvenience in which the power generation has to be stopped although the circulation pump actually does not have a breakdown. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a technology of accurately determining whether the circulation pump is normal or broken, at the time of start of a fuel cell system. 
     A fuel cell system in accordance with one aspect of the invention includes: a fuel cell; a fuel gas supply portion; a fuel gas supply channel that supplies a fuel gas from the fuel gas supply portion to the fuel cell; a fuel gas circulation channel that is connected to the fuel cell and to the fuel gas supply channel and that circulates the fuel gas discharged from the fuel cell by returning the fuel gas to the fuel gas supply channel for reuse; a circulation pump provided on the fuel gas circulation channel so as to circulate the fuel gas; a temperature detection portion that detects a temperature of the fuel cell system; a pump control portion that drives the circulation pump; and a breakdown determination portion that determines whether the circulation pump has broken. In the fuel cell system, the pump control portion drives the circulation pump, and the breakdown determination portion determines that the circulation pump has broken if the temperature of the fuel cell system detected by the temperature detection portion is higher than or equal to a melting point of water and a rotation speed of the circulation pump is less than a predetermined rotation speed. 
     The fuel cell system of this aspect may further include a warmup portion that warms up the circulation pump. When fuel cell system is started, the warmup portion may warm the circulation pump if the temperature of the fuel cell system detected by the temperature detection portion is less than the melting point of water. 
     According to the fuel cell system constituted as described above, it can be accurately determined whether the circulation pump is normal or is actually broken, even when the circulation pump is frozen. 
     The fuel cell system of this aspect may further include an oxidizing gas supply portion that supplies an oxidizing gas to the fuel cell. If the temperature of the fuel cell system detected by the temperature detection portion is less than the melting point of water, the warmup portion may cause the fuel gas supply portion and the oxidizing gas supply portion to supply the fuel gas and the oxidizing gas, respectively, to the fuel cell so as to cause the fuel cell to perform power generation so that the circulation pump is warmed by heat produced by the power generation. 
     Therefore, the circulation pump can be warmed by using devices provided in the fuel cell system, and the number of component parts of the fuel cell system can be minimized. 
     In the fuel cell system of this aspect, the circulation pump may be disposed near the fuel cell. Furthermore the circulation pump may be disposed integrally with the fuel cell. 
     Therefore, heat produced in the fuel cell is quickly transferred to the circulation pump, and the circulation pump can be rapidly warmed up. 
     The fuel cell system of this aspect may further include: a purge channel that discharges the fuel gas to outside the fuel cell system from the fuel gas circulation channel upstream of a position where the circulation pump is provided, in a circulating direction of the fuel gas; a shut-off valve provided on the purge channel; a valve control portion that performs a control of opening and closing the shut-off valve; and an oxidizing gas adjustment portion that adjusts a supply amount of the oxidizing gas supplied by the oxidizing gas supply portion to the fuel cell. The warmup portion, when causing the fuel cell to perform the power generation, may increase an amount of power generation of the fuel cell by causing the valve control portion to open the shut-off valve so as to increase the supply amount of the fuel gas supplied to the fuel cell and causing the oxidizing gas adjustment portion to increase the supply amount of the oxidizing gas corresponding to the supply amount of the fuel gas. 
     Therefore, the circulation pump can be quickly warmed since the heat produced by the power generation increases as the amount of power generation of the fuel cell is increased. 
     An operation method for a fuel cell system in accordance with an aspect of the invention is an operation method for a fuel cell system including a fuel cell, a fuel gas supply portion, a fuel gas supply channel that supplies a fuel gas from the fuel gas supply portion to the fuel cell, a fuel gas circulation channel that is connected to the fuel cell and to the fuel gas supply channel and that circulates the fuel gas discharged from the fuel cell by returning the fuel gas to the fuel gas supply channel for reuse, and a circulation pump provided on the fuel gas circulation channel so as to circulate the fuel gas, the operation method including: (A) the step of detecting a temperature of the fuel cell system when the fuel cell system is started; (B) the step of warming the circulation pump and driving the circulation pump if the detected temperature of the fuel cell system is less than a melting point of water; (C) the step of determining that the circulation pump has broken if the temperature of the fuel cell system is higher than or equal to the melting point of water and a rotation speed of the circulation pump is less than a predetermined rotation speed. 
     According to the operation method for the fuel cell system as described above, it can be accurately determined whether the circulation pump is normal or is actually broken, even when the circulation pump is frozen. 
     The invention is not limited to the aspects of a device, such as the above-described fuel cell system, an operation method for a fuel cell system, or the like, but can also be carried out in various other aspects, for example, an aspect as a computer program that constructs such methods or devices, or an aspect as a recording medium in which such a computer program is recorded, an aspect as a data signal that includes the computer program and is embodied in a carrier wave, etc. 
     If the invention is constituted as a computer program, a recording medium in which the program is recorded, or the like, the invention may be provided in a form that includes the entire program that controls the operation of the aforementioned device, or may also be provided in a form that includes only a portion that performs the functions of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: 
         FIG. 1  is a block diagram showing a constitution of a fuel cell system  100  of an embodiment of the invention; and 
         FIG. 2  is a flowchart of a pump breakdown detection process performed by the fuel cell system  100  of the embodiment shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the invention will be described hereinafter in the following procedure. 
     A. Embodiment: 
     A1. Constitution of Fuel Cell System: 
     A2. Pump Breakdown Detection Process: 
     B. Modifications: 
     A. Embodiment 
     A1. Constitution of Fuel Cell System 
       FIG. 1  is a block diagram showing a constitution of a fuel cell system  100  as an embodiment of the invention. This fuel cell system  100  includes a fuel cell  10 , a hydrogen tank  20 , a blower  30 , a circulation pump  50 , a diluter  60 , a temperature sensor  70 , a hydrogen shut-off valve  200 , a pressure regulating valve  220 , a gas discharge valve  240 , and a control circuit  400 . 
     The fuel cell  10  is a solid polymer type fuel cell, and has a stack structure in which a plurality of unit cells that are constitution units (hereinafter, referred to simply as “cells”) are stacked. Each cell has a constitution in which an electrolyte membrane (not shown) is sandwiched between an anode (not shown) and a cathode (not shown). The fuel cell  10  causes electrochemical reactions to progress to produce electromotive force by supplying a hydrogen-containing fuel gas to the anode side of each cell, and supplying an oxygen-containing oxidizing gas to the cathode side of each cell. The fuel cell  10  supplies produced electric power to predetermined loads (e.g., an electric motor, a storage battery) that are connected to the fuel cell  10 . As the fuel cell  10 , various types of fuel cell besides the aforementioned solid polymer fuel cell may be also be used, for example, a hydrogen separation membrane type fuel cell, an alkaline aqueous solution electrolyte type fuel cell, phosphoric acid electrolyte type fuel cell, a molten carbonate electrolyte type fuel cell, etc. In the following description, a channel in the fuel cell  10  in which the fuel gas flows is referred to as “anode channel  25 ”, and a channel in which the oxidizing gas flows is referred to as “cathode channel  35 ”. 
     The hydrogen tank  20  is a storage device in which a high-pressure hydrogen gas is stored. The hydrogen tank  20  is connected to the anode channel  25  of the fuel cell  10  via a fuel gas supply channel  24 . The hydrogen shut-off valve  200  and the pressure regulating valve  220  are provided on the fuel gas supply channel  24  in that order from the side of the hydrogen tank  20 . By opening the hydrogen shut-off valve  200 , the hydrogen gas is supplied as a fuel gas to the fuel cell  10 . Instead of the hydrogen tank  20 , a device that produces hydrogen through a reforming reaction of a raw material, such as alcohol, hydrocarbon, aldehyde, etc., and supplies hydrogen to the anode side may also be employed. 
     An outlet side of the anode channel  25  and the fuel gas supply channel  24  are connected by a gas circulation channel  27 . The circulation pump  50  is provided on the gas circulation channel  27 . By driving the circulation pump  50 , the fuel gas that has been used in the electrochemical reaction in the anodes of the fuel cell  10  is supplied again to the anode channel  25  (anodes) of the fuel cell  10  via the gas circulation channel  27  and the fuel gas supply channel  24 , and thus is re-used for the power generation. Hereinafter, the channel in which the fuel gas circulates, that is, the channel formed by the gas circulation channel  27 , the fuel gas supply channel  24  and the anode channel  25  is referred to as “hydrogen circulation system channel” as well. 
     The circulation pump  50  may be disposed in contact with the fuel cell  10  so as to be integrated with the fuel cell  10 , via a support post  55 . 
     The fuel cell system  100  is provided with a temperature sensor  70  that detects the temperature of a pump chamber (not shown) of the circulation pump  50 . 
     A purge channel  28  connected to the diluter  60  is branched from the gas circulation channel  27  at the point between the fuel cell  10  and the circulation pump  50 . The gas discharge valve  240  is provided on the purge channel  28 . While the fuel gas is circulating in the hydrogen circulation system channel, an impurity gas (nitrogen or the like) other than hydrogen mixes into the fuel gas, so that the hydrogen concentration gradually declines. As a result, the performance of the fuel cell  10  declines. Therefore, the fuel cell system  100  periodically opens the gas discharge valve  240 . Then, the fuel gas is discharged into the purge channel  28 . Details regarding the fuel gas discharged into the purge channel  28  will be described later. 
     The blower  30  is a device that supplies air as an oxidizing gas to the cathodes (not shown) of the fuel cell  10 . The blower  30  is connected to the cathode channel  35  of the fuel cell  10  via an oxidizing gas supply channel  34 . 
     The cathode channel  35  of the fuel cell  10  is also connected (at its outlet side) to an oxidizing gas discharge channel  36 . The oxidizing gas after being used in the electrochemical reaction at the cathodes is discharged into the oxidizing gas discharge channel  36 . 
     The diluter  60  is a device that dilutes the hydrogen contained in the fuel gas by mixing it with the oxidizing gas. The diluter  60  is connected to the oxidizing gas discharge channel  36 , the purge channel  28 , and a mixture gas discharge channel  45 . The diluter  60  is divided into two chambers by a flow plate  61  that is made of a porous ceramic, that is, the diluter  60  has a residence chamber  62  that the fuel gas from the purge channel  28  flows into and resides in, and a dilution chamber  63  that the oxidizing gas from the oxidizing gas discharge channel  36  flows into. 
     When the gas discharge valve  240  is opened, the fuel gas flowing in the gas circulation channel  27  flows through the purge channel  28  into the residence chamber  62  of the diluter  60 , and resides therein. On the other hand, the oxidizing gas that has flown into the dilution chamber  63  of the diluter  60  passes directly through the dilution chamber  63 , and is discharged to the outside via the mixture gas discharge channel  45 . At this time, the fuel gas residing in the residence chamber  62  is gradually drawn into the dilution chamber  63  via the porous flow plate  61  due to the passage of the oxidizing gas, and mixes with the oxidizing gas in the dilution chamber  63 . In consequence, a mixture gas of the fuel gas and the oxidizing gas flows out of the dilution chamber  63  of the diluter  60 , and is discharged to the outside of the fuel cell system  100  via the mixture gas discharge channel  45 . In this manner, the hydrogen in the fuel gas circulating in the hydrogen circulation system channel is diluted with the oxidizing gas, and is discharged to the outside of the fuel cell system  100 . 
     The control circuit  400  is constituted as a logic circuit that includes a microcomputer as a main component. Specifically, the control circuit  400  includes a CPU (not shown) that executes predetermined computations and the like following pre-set control programs, a ROM (not shown) in which control programs, control data, etc. that are needed in order for the CPU to execute various computation processes are pre-stored, a RAM (not shown) in which various data needed for the CPU to perform various computation processes is written and read on a temporary basis, an input/output port (not shown) that inputs and outputs various signals, etc. The control circuit  400  performs various controls regarding the fuel cell system  100 , concretely, regarding the blower  30 , the circulation pump  50 , the hydrogen shut-off valve  200 , the gas discharge valve  240 , etc. 
     The control circuit  400  functions as a pump control portion  410 , a temperature detection portion  420 , a valve control portion  430 , a blower control portion  440 , and a breakdown determination portion  450 , and executes a pump breakdown detection process described later. The temperature detection portion  420  detects the temperature of the circulation pump  50  (the pump chamber thereof) from the temperature sensor  70 . 
     The fuel cell system  100  of this embodiment executes the pump breakdown detection process that detects a breakdown of the circulation pump  50 , when the system is started. This process will be described hereinafter. 
     A2. Pump Breakdown Detection Process 
       FIG. 2  is a flowchart of the pump breakdown detection process performed by the fuel cell system  100  of the embodiment. A precondition at the time of starting the pump breakdown detection process is that the hydrogen shut-off valve  200  and the gas discharge valve  240  are both closed, and the blower  30  and the circulation pump  50  are not being driven, that is, the fuel cell  10  is not in a power generating state. 
     Firstly, the pump control portion  410  sends a drive signal V that drives the circulation pump  50 , to the circulation pump  50  (step S 10 ). Upon receiving the drive signal V, the circulation pump  50  is driven on the basis of the signal, if the circulation pump  50  is normal. 
     Next, the pump control portion  410  judges whether or not the circulation pump  50  is driven, concretely, whether or not the circulation pump  50  is rotating at or above a predetermined rotation speed a (step S 20 ). The predetermined rotation speed a is determined on the basis of a concrete design of the fuel cell system  100 , and may be, for example, “1”. 
     If the pump control portion  410  judges that the circulation pump  50  is rotating at or above the predetermined rotation speed a (YES in step S 20 ), the breakdown determination portion  450  determines that the circulation pump  50  is being driven normally (step S 200 ), and then ends this process. Incidentally, after this, the control circuit  400  may, for example, start power generation by driving the blower  30  and opening the hydrogen shut-off valve  200 . 
     On the other hand, if the pump control portion  410  judges that the circulation pump  50  is not rotating at or above the predetermined rotation speed a (NO in step S 20 ), the temperature detection portion  420  detects the temperature of the circulation pump  50  (the pump chamber thereof) (hereinafter, referred to as “circulation pump temperature Tp 1 ”) from the temperature sensor  70  (step S 30 ). On this occasion, the pump control portion  410  stops sending the drive signal V. 
     Then, the temperature detection portion  420  judges whether or not the circulation pump temperature Tp 1  is below the melting point of water (about 0° C.) (step S 40 ). The indication of the melting point of water being “about 0° C.” is based on consideration of the fact that the melting point changes depending on the pressure state. 
     If the temperature detection portion  420  judges that the circulation pump temperature Tp 1  is not below the melting point of water (about 0° C.) (NO in step S 40 ), the breakdown determination portion  450  determines that the circulation pump  50  has a breakdown (step S 100 ) since the circulation pump  50  fails to be driven although the circulation pump  50  (the pump chamber thereof) is not frozen. Then, the process ends. After that, the control circuit  400  may, for example, perform a process of prohibiting the power generation of the fuel cell  10 , or the like. 
     On the other hand, if the temperature detection portion  420  judges that the circulation pump temperature Tp 1  is below the melting point of water (about 0° C.) (YES in step S 40 ), the control circuit  400  judges that the circulation pump  50  is frozen and cannot be driven, and causes the power generation by the fuel cell  10  (step S 50 ). Concretely, the valve control portion  430  opens the hydrogen shut-off valve  200 , and performs the open-close control of the gas discharge valve  240  so that the supply amount of the fuel gas supplied to the anode channel  25  does not become less than or equal to a predetermined value β. Furthermore, the blower control portion  440  drives the blower  30  so as to supply an amount of the oxidizing gas that corresponds to the supply amount of the fuel gas, to the cathodes of the fuel cell  10 . In this manner, the power generation by the fuel cell  10  is performed. Therefore, as the power generation progresses, the temperature of the fuel cell  10  heightens, and the circulation pump  50  (the pump chamber thereof) disposed in contact with the fuel cell  10  is warmed up to relatively high temperature. On this occasion, the fuel gas discharged from the purge channel  28  is diluted by the diluter  60 , and is discharged to the outside of the fuel cell system  100 . It is appropriate if the predetermined value β be set at a numerical value that allows the fuel cell  10  to sufficiently warm up the circulation pump  50 . The predetermined value β is determined on the basis of a concrete design of the fuel cell system  100 . Furthermore, the frequency of opening the gas discharge valve  240  is also determined on the basis of the predetermined value β. 
     Thus, when power generation is performed by the fuel cell  10 , the amount of the fuel gas supplied to the anodes of the fuel cell  10  is increased by opening the hydrogen shut-off valve  200 , and the oxidizing gas is supplied to the cathodes of the fuel cell  10  corresponding to the supply amount of the fuel gas. In this manner, the amount of power generation of the fuel cell  10  can be increased, and the circulation pump  50  can be quickly warmed up. 
     When the power generation of the fuel cell  10  is started, the temperature detection portion  420  detects the temperature of the circulation pump  50  (the pump chamber thereof) (hereinafter, referred to as “circulation pump temperature Tp 2 ”) from the temperature sensor  70  (step S 60 ), and judges whether or not the circulation pump temperature Tp 2  is higher than or equal to the melting point of water (about 0° C.) (step S 70 ). If the temperature detection portion  420  judges that the detected circulation pump temperature Tp 2  is not higher than or equal to the melting point of water (about 0° C.) (NO in step S 70 ), the process returns to step S 60 . 
     If the temperature detection portion  420  judges that the circulation pump temperature Tp 2  is higher than or equal to the melting point of water (about 0° C.) (YES in step S 70 ), the pump control portion  410  sends the drive signal V that drives the circulation pump  50 , to the circulation pump  50  again (step S 80 ). 
     Then, the pump control portion  410  judges whether or not the circulation pump  50  has been driven, concretely, whether or not the circulation pump  50  is rotating at or above the predetermined rotation speed a (step S 90 ). 
     If the pump control portion  410  judges that the circulation pump  50  is rotating at or above the predetermined rotation speed a (YES in step S 90 ), the breakdown determination portion  450  determines that the reason why the circulation pump  50  was not be driven (NO in step S 20 ) although the pump control portion  410  sent the drive signal V (step S 10 ) to attempt to drive the circulation pump  50  is that the circulation pump  50  was frozen, and determines that the circulation pump  50  is normally drivable (step S 200 ). After that, this process ends. Then, for example, the control circuit  400  may start power generation by the fuel cell  10 . 
     On the other hand, if the pump control portion  410  judges that the circulation pump  50  is not rotating at or above the predetermined rotation speed a (NO in step S 90 ), the breakdown determination portion  450  determines that the circulation pump  50  has a breakdown since the circulation pump  50  fails to be driven although the circulation pump  50  (the pump chamber thereof) is not frozen due to the warmup (step S 100 ). Then, this process ends. Incidentally, at the end of the process, the power generation may be stopped in the case where the power generation of the fuel cell  10  was performed in the process of step S 50 . On this occasion, the pump control portion  410  stops sending the drive signal V. 
     As described above, in the fuel cell system  100 , if the circulation pump  50  fails to be driven and the temperature of the circulation pump  50  (the pump chamber thereof), that is, the circulation pump temperature Tp 1 , is below the melting point of water (about 0° C.), the power generation by the fuel cell  10  is started to warm up the circulation pump  50  so that the temperature of the circulation pump  50  (the pump chamber thereof) becomes higher than or equal to the melting point of water (about 0° C.), and after that, the driving of the circulation pump  50  is attempted again. This makes it possible to accurately determine whether the circulation pump  50  is normal, or actually has a breakdown, even in the case where the circulation pump  50  is frozen. 
     Furthermore, in the fuel cell system  100 , the circulation pump  50  is disposed so as to contact the fuel cell  10 . During the pump breakdown detection process, power generation is performed by the fuel cell  10  so that heat produced thereby warms up the circulation pump  50 . This makes it possible to warm up the circulation pump  50  by using a device provided in the fuel cell system  100 . Therefore, the number of component parts of the fuel cell system  100  can be minimized. Furthermore, since the circulation pump  50  is in contact with the fuel cell  10 , heat produced in the fuel cell  10  is quickly transferred to the circulation pump  50 , and therefore the circulation pump can be rapidly warmed up. 
     In the invention, the hydrogen tank  20  corresponds to a fuel gas supply portion, and the gas circulation channel  27  corresponds to a fuel gas circulation channel. Furthermore, the gas discharge valve  240  corresponds to a shut-off valve. The pump control portion  410  corresponds to a pump control portion. The temperature detection portion  420  corresponds to a temperature detection portion. The valve control portion  430  corresponds to a valve control portion. The blower control portion  440  corresponds to an oxidizing gas adjustment portion. The breakdown determination portion  450  corresponds to a breakdown determination portion. The blower  30  corresponds to an oxidizing gas supply portion. Still further, the blower  30 , the hydrogen tank  20 , the hydrogen shut-off valve  200 , the control circuit  400  and the fuel cell  10  correspond to warmup portion. 
     B. Modifications 
     The invention is not limited to the foregoing embodiment, but can be carried out in various manners without departing from the spirit of the invention. 
     B1. Modification 1 
     Although in the fuel cell system  100  of the foregoing embodiment, the circulation pump  50  is disposed so as to be in contact with the fuel cell  10 , this does not limit the invention. The circulation pump  50  does not need to be disposed in contact with the fuel cell  10 , but the circulation pump  50  may be disposed at a predetermined distance from the fuel cell  10  if the distance is such that the circulation pump  50  can be warmed up by the power generation of the fuel cell  10 . This modification can achieve substantially the same effects as those of the foregoing embodiment. 
     B2. Modification 2 
     Although in the fuel cell system  100  of the foregoing embodiment, the circulation pump  50  is disposed so as to be in contact with the fuel cell  10  and the circulation pump  50  is warmed up through the use of heat produced by the power generation of the fuel cell  10 , this does not limit the invention. For example, the circulation pump  50  may be provided with a heat source, such as a heater or the like, whereby the circulation pump  50  will be warmed up. In this modification, it is not necessary to dispose the circulation pump  50  in contact with the fuel cell  10 , and thus the degree of freedom in disposing the circulation pump  50  increases. 
     B3. Modification 3 
     Although, in the pump breakdown detection process ( FIG. 2 ) performed by the fuel cell system  100  of the foregoing embodiment, the temperature detection portion  420  detects the circulation pump temperature Tp 1  directly from the circulation pump  50  in the process of step S 30 , this does not limit the invention. For example, the temperature detection portion  420  may detect the atmospheric temperature outside the fuel cell system  100 , and may estimate the temperature of the circulation pump  50  from the atmospheric temperature. Furthermore, the temperature detection portion  420  may estimate the temperature of the circulation pump  50  from the temperature of a predetermined portion (e.g., the fuel cell  10 ) within the fuel cell system  100 . 
     Furthermore, for example, the temperature detection portion  420  detects the circulation pump temperature Tp 2  directly from the circulation pump  50  in the process of step S 60 . However, this does not limit the invention. For example, the temperature detection portion  420  may detect the duration of power generation of the fuel cell  10 , and may estimate the temperature of the circulation pump  50  by taking into account the power generation duration together with the supply amount of the fuel gas, the atmospheric temperature outside the fuel cell system  100 , etc. This modification eliminates the need to provide the temperature sensor  70 , and therefore can reduce the number of component parts. 
     B4. Modification 4 
     The fuel cell system  100  of the foregoing embodiment, during the pump breakdown detection process ( FIG. 2 ), sends the drive signal V to the circulation pump  50  (step S 80 ) after the circulation pump temperature Tp 2  becomes higher than or equal to the melting point of water due to the power generation of the fuel cell  10  (YES in step S 70 ). In that case, if the circulation pump  50  is not rotating at or above the predetermined rotation speed α, it is determined that the circulation pump  50  has a breakdown. However, this does not limit the invention. For example, in the pump breakdown detection process of  FIG. 2 , the process of step S 60  to step S 90  may be omitted, and the following process may be performed instead. 
     That is, after the control circuit  400  starts the power generation by the fuel cell  10  (step S 50 ), the pump control portion  410  sends the drive signal V to the circulation pump  50  (step S 60 A). Next, the pump control portion  410  judges whether or not the circulation pump  50  has been driven, concretely, whether or not the circulation pump  50  is rotating at or above the predetermined rotation speed a (step S 70 A). If the pump control portion  410  judges that the circulation pump  50  is rotating at or above the predetermined rotation speed a (YES in step S 70 A), the breakdown determination portion  450  determines that the circulation pump  50  is normally drivable (step S 200 ). 
     On the other hand, if the pump control portion  410  judges that the circulation pump  50  is not rotating at or above the predetermined rotation speed a (NO in step S 70 A), the temperature detection portion  420  subsequently detects the circulation pump temperature Tp 2  (step S 80 A), and judges whether or not the circulation pump temperature Tp 2  is higher than or equal to the melting point of water (about 0° C.) (step S 90 A). If the temperature detection portion  420  judges that the detected circulation pump temperature Tp 2  is not higher than or equal to the melting point of water (about 0° C.) (NO in step S 90 A), the process returns to step S 60 A. 
     If the temperature detection portion  420  judges that the circulation pump temperature Tp 2  is higher than or equal to the melting point of water (about 0° C.) (YES in step S 90 A), the breakdown determination portion  450  determines that the circulation pump  50  has a breakdown (step S 100 ) since the circulation pump  50  fails to be driven although the circulation pump  50  (the pump chamber thereof) is not frozen due to the warmup. Then, this process ends. The modification as described above also achieves substantially the same effects as those of the foregoing embodiment. 
     B5. Modification 5 
     Although in the foregoing embodiment, the various portions of the control circuit  400  are provided as software, they may be provided as hardware. Furthermore, portions provided as hardware in the foregoing embodiment may be provided as software.