Abstract:
A method for controlling a fuel cell system is provided. In this method, the operation of a fuel cell system is divided into several modes, and the operation mode of the fuel cell system is determined according to voltage signals, current signals, and temperature signals of the fuel cell system. Moreover, a fuel cell system using the control method is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a method for controlling a fuel cell system and a fuel cell system using the control method, in which the operation of the fuel cell system is divided into several modes, and the operation mode of the fuel cell system is determined according to voltage signals, current signals, and temperature signals of the fuel cell system. 
         [0003]    2. Related Art 
         [0004]    To cope with problems of increasingly exhausted petroleum and global warming, each country increasingly attaches importance to research and development, and application of alternative energy sources, in which the development of hydrogen energy is most important. Having high energy conversion efficiency and a by-product of clean and pollution-free water, the fuel cell is critical to the development of the hydrogen energy. 
         [0005]    A power supply process of a fuel cell system involves cooperation of sub-systems for heat management, water management, fuel supply, and power adjustment and control, and the fuel cell itself concerns reaction temperature, reactant concentration, output voltage, and output current. Due to effective management of power energy sources, a longer using time and a stable power supply of an electronic devices using electricity (for example, a notebook computer or a mobile phone) may be improved. Therefore, when the fuel cell is applied, it is to be solved in the prior art how to effectively manage the operation of the fuel cell system, so that the system is controlled and is always operated in an optimal state, thereby enhancing the system performance, reliability, and service life. 
         [0006]    Generally, the output voltage and the output current of the fuel cell are greatly effected by a load, and according to a polarization curve of the fuel cell, when the demand on the output current is raised, the output voltage is lowered; on the contrary, when the demand on the output current is lowered, the output voltage is raised. Moreover, when the fuel cell is applied to a dynamic load, if a load change time is too short, the fuel cell is limited to a reaction mechanism, and it is difficult to supply sufficient power to the load for an instant, so that the power is insufficient or unstable. Therefore, in the prior art, at least one auxiliary cell (secondary cell) is used in combination in the fuel cell system, so as to solve the problem of insufficient or unstable power. However, if an operation voltage has an excessively great swing or is too frequently changed, the fuel cell and the auxiliary cell may be easily deteriorated. 
         [0007]    In view of the disadvantages of the conventional fuel cell system and the increasingly growing importance of the management of power energy sources of the fuel cell system, it is necessary to provide a method for controlling a fuel cell system and a fuel cell system using the control method. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is mainly directed to a method for controlling a fuel cell system, in which the operation of the fuel cell system is divided into several modes, and the operation mode of the fuel cell system is determined according to voltage signals, current signals, and temperature signals of the fuel cell system. 
         [0009]    In order to achieve the above objective, the present invention is further directed to a fuel cell system that implements the method for controlling the fuel cell system according to the present invention. 
         [0010]    In order to make the characteristics, objectives, and efficacies of the present invention comprehensible to the examiner, related processes, detailed structures, and design concepts of the present invention are described below through embodiments with the accompanying drawings, so that the examiner may better understand the features of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
           [0012]      FIG. 1  is a flow chart of switching operation modes in a method for controlling a fuel cell system according to the present invention; and 
           [0013]      FIG. 2  is a structural view of a fuel cell system for implementing the method for controlling the fuel cell system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    In a method for controlling a fuel cell system according to the present invention, the operation of the fuel cell system is divided into several modes, which includes four operations modes of the fuel cell system. The fuel cell system at least includes a fuel cell stack, a balance of plant (BOP), a first voltage regulating circuit, a second voltage regulating circuit, an auxiliary cell, and a system load connected in parallel with the auxiliary cell. Here, the first voltage regulating circuit regulates an output voltage of the fuel cell stack to be a voltage capable of being used by the auxiliary cell and the system load. The second voltage regulating circuit is used during booting, so that a power voltage of the auxiliary cell is converted through the first voltage regulating circuit and the second voltage regulating circuit, and is supplied to the BOP for operation. The BOP includes components capable of supplying air and fuel required by the fuel cell and assisting the operation, for example, a pump, a fan, an energy management system (EMS), and a central processing unit (CPU), and a detection unit. The detection unit detects a using current of the system load, a working voltage of the auxiliary cell, a current output by the fuel cell stack through the first voltage regulating circuit, a temperature of the fuel cell stack, and an environmental temperature, and provides detection data to the CPU for performing a logical judgment. The CPU at least includes a timer. In the following, the several operation modes are described with a working process. 
         [0015]    (1) Starting: for an initial action, a switching device of a booting device of the fuel cell system is started, so that the system is in an ON state, and during the startup process, firstly, it is judged whether the system uses the load and whether the power of the auxiliary cell is sufficient. When the using current (hereinafter referred to as I load ) of the system load is smaller than a minimum working current of the system load, a working voltage (hereinafter referred to as V 1 ) of the auxiliary cell is greater than a discharging set value, and the environmental temperature (hereinafter referred to as T en ) is higher than 0° C., the fuel cell stack enters a sleep mode. If any condition is unsatisfied, the fuel cell system enters a boot mode. Here, the minimum working current of the system load is defined to be a minimum current threshold of the system load set by the system. When the current of the system load is smaller than the threshold, the system load does not operate, and the fuel cell stack in the fuel cell system stops outputting a power. 
         [0016]    (2) Sleep mode: in the sleep mode, the BOP is set to stop working, so that the fuel cell stack in the fuel cell system stops outputting the power. At this time, only the CPU in the entire system continues to operate (the power is supplied by the auxiliary cell), and continuously measures I load , V 1 , and T en . When I load  is greater than the minimum working current of the system load, or V 1  is smaller than the discharging set value, or T en  is lower than 0° C., the fuel cell system enters the boot mode. 
         [0017]    (3) Boot mode: after the system enters the boot mode, the system performs the judgment according to the measured temperature (hereinafter referred to as T fc ) of the fuel cell stack, if T fc  is lower than an initial working temperature of the fuel cell stack, the fuel cell stack enters a heating-up step, and the system continuously judges T fc . When T fc  is higher than the initial working temperature, the fuel cell system enters a stable mode. Here, the initial working temperature of the fuel cell stack is defined to be a lowest temperature at which an electrochemical reaction is performed in the fuel cell stack and the current is stably output. 
         [0018]    (4) Stable mode: in the stable mode of the fuel cell system, the power generated by the fuel cell stack is entirely supplied to the auxiliary cell and the system load. In the stable mode, it is necessary to continuously observe whether V 1  is smaller than the discharging set value or greater than a charging set value, and whether the current (hereinafter referred to as I out ) output by the fuel cell stack through the first voltage regulating circuit is smaller than a minimum output current. Here, the minimum output current is a set output current threshold of the system, and when the output current of the system is smaller than the threshold, it is defmed that power supply demands of the load are reduced. When I out  is smaller than the minimum output current, and V 1  is greater than the charging set value, the fuel cell system enters a stand-by mode. If any condition is unsatisfied, the fuel cell system maintains the stable mode. 
         [0019]    (5) Stand-by mode: after the fuel cell system enters the stand-by mode, the system only supplies the power of the fuel cell to the BOP for operation, and continuously observes I load  and V 1 . When I load  is smaller than the minimum working current of the system load, and V 1  is greater than the discharging set value, the timer of the CPU starts timing. If any condition is unsatisfied, the fuel cell system returns to the stable mode. If the timer of the CPU starts timing and a counted time of the timer is longer than a time set for entering the sleep mode, and the environmental temperature is higher than 0° C., the fuel cell system enters the sleep mode. If the counted time of the timer of the CPU is shorter than the time set for entering the sleep mode, the fuel cell system maintains the stand-by mode. 
         [0020]    In the following, the implementation of the method for controlling the fuel cell system according to the present invention is described with an embodiment. 
         [0021]      FIG. 1  is a flow chart of switching operation modes in a method for controlling a fuel cell system according to the present invention. Referring to  FIG. 1 , the method includes the following steps. 
         [0022]    In Step ( 1 ), the system is started. 
         [0023]    In Step ( 2 ), it is judged whether I load  is greater than a minimum working current of a system load, or whether V 1  is smaller than a discharging set value, or whether T fc  is higher than an initial working temperature of a fuel cell stack, if any condition is positive, the system enters next Step ( 3 ), and if all the conditions are negative, the system does not enter next Step ( 3 ), but continuously measures I load , V 1 , and T fc  for performing a judgment of the conditions. 
         [0024]    In Step ( 3 ), the fuel cell system enters a system stable mode, in which the system performs the following steps. 
         [0025]    In Step ( 31 ), the fuel cell stack operates in the stable mode. 
         [0026]    In Step ( 32 ), it is judged whether I out  of the fuel cell stack is smaller than a minimum output current, and whether V 1  is greater than a charging set value, if all the conditions are positive, next Step ( 4 ) is performed, and if any condition is negative, the system returns to Step ( 31 ). 
         [0027]    In Step ( 4 ), the fuel cell system exits from the system stable mode. 
         [0028]    In this embodiment, Step ( 2 ) further includes the following steps. 
         [0029]    In Step ( 21 ), the fuel cell system enters a system sleep mode, in which the system performs the following steps. 
         [0030]    In Step ( 211 ), it is judged whether I load  is smaller than the minimum working current of the system load, whether V 1  is greater than the discharging set value, and whether T en  is higher than 0° C., if any condition is negative, the system enters Step ( 22 ), and if all the conditions are positive, the system enters Step ( 212 ). 
         [0031]    In Step ( 212 ), the fuel cell stack enters the sleep mode, and I load , V 1 , and T en  are continuously measured for performing the judgment in Step ( 211 ). 
         [0032]    In Step ( 22 ), the fuel cell system enters a system boot mode, in which the system performs the following steps. 
         [0033]    In Step ( 221 ), it is judged whether T fc  is higher than an initial working temperature of the fuel cell stack, and if yes, the system enters Step ( 3 ); while if not, the system enters Step ( 222 ). 
         [0034]    In Step ( 222 ), a heating-up step of the fuel cell stack is performed, and T fc  is continuously measured for performing the judgment in Step ( 221 ). 
         [0035]    In this embodiment, Step ( 4 ) further includes the following steps. 
         [0036]    In Step ( 41 ), the system enters a fuel cell stack stand-by mode, and performs next Step ( 42 ). 
         [0037]    In Step ( 42 ), it is judged whether I load  is smaller than the minimum working current of the system load, and whether V 1  is greater than the discharging set value, if any condition is negative, the system returns to Step ( 31 ), and if all the conditions are positive, the system enters next Step ( 43 ). 
         [0038]    In Step ( 43 ), a timer of a CPU starts timing, it is judged whether a counted time of the timer is longer than a time set for entering the sleep mode, and whether T en  is higher than 0° C., if all the conditions are positive, the system returns to Step ( 2 ), and if any condition is negative, the system returns to Step ( 41 ). 
         [0039]      FIG. 2  is a structural view of a fuel cell system for implementing a method for controlling a fuel cell system according to the present invention. Referring to  FIG. 2 , the fuel cell system  100  includes a fuel cell stack  1001 , a BOP  1002 , a first voltage regulating circuit  1003 , a second voltage regulating circuit  1004 , an auxiliary cell  1005 , a system load  1006  connected in parallel with the auxiliary cell  1005 , and at least two switching devices SW 1  and SW 2 . The first voltage regulating circuit  1003  regulates an output voltage of the fuel cell stack  1001  to be a voltage capable of being used by the auxiliary cell  1005  and the system load  1006 . The second voltage regulating circuit  1004  is used during booting, so that a power voltage of the auxiliary cell  105  is converted through the first voltage regulating circuit  1003  and the second voltage regulating circuit  1004 , and is supplied to the BOP  1002  for operation. The BOP  1002  at least includes components capable of supplying air and fuel required by the fuel cell and assisting the operation, for example, a pump, a fan, an EMS, a CPU  1002   a,  and a detection unit  1002   c  (in which the pump, the fan, and the EMS are not shown), the functions and operation manner of which are disclosed in the prior art and will not be given herein again. The detection unit  1002   c  detects I load , V 1 , I out , T fc , and T en , and provides detection data to the CPU  1002   a  for performing a logical judgment. The CPU  1002   a  further includes a timer  1002   b.  The at least two switching devices SW 1  and SW 2  are used to start the system, turn off the system, and perform a conduction switching on lines of the system when switching the operation modes of the system, in which the switching device SW 1  is a booting device of the system. 
         [0040]    In the following, an operation manner of the fuel cell system  100  is described with the switching flow chart of  FIG. 1 . 
         [0041]    In Step ( 1 ), after the switching device SW 1  is conducted, the system is in the ON state, and here the fuel cell system  100  is started. 
         [0042]    In Step ( 3 ), after the switching device SW 2  is conducted, the fuel cell system  100  enters the system stable mode. 
         [0043]    In Step ( 41 ), after the switching device SW 2  is not conducted, the fuel cell system  100  enters the fuel cell stack stand-by mode. 
         [0044]    The fuel cell system  100  of the present invention further includes at least three diodes D 1  to D 3 , used to limit a direction of the current. As shown in  FIG. 2 , the diode D 1  is used to limit that the power of the fuel cell stack  1001  may only be output to the outside, so the power of the auxiliary cell  1005  cannot be inversely supplied to the fuel cell stack  1001  due to the limit of the diode D 1 . The diode D 2  limits that the power of the auxiliary cell  1005  is sent to the first voltage regulating circuit  1003  through the second voltage regulating circuit  1004 , and is supplied to the BOP  1002  for operation, and thus the power of the fuel cell stack  1001  cannot be inversely sent to the second voltage regulating circuit  1004  due to the limit of the diode D 2 . The power of the fuel cell stack  1001  is supplied through the diode D 3  to the auxiliary cell  1005  and the system load  1006  through the first voltage regulating circuit  1003 , and the diode D 3  limits that the power of the auxiliary cell  1005  is sent to the BOP  1002  through the first voltage regulating circuit  1003 . 
         [0045]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.