JP2006310246A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system without any possibility of deterioration in a service life of a fuel cell. <P>SOLUTION: A fuel cell system is built as a system in which a fuel cell stack 1 and a rechargeable battery 3 are provided in parallel, and includes the fuel cell stack 1, a fuel feeder 2 feeding the fuel to the fuel cell stack 1, the electric storage device 3, and a DC/DC converter 4 converting the output voltage of the rechargeable battery 3 into a predetermined voltage and outputting it. This predetermined voltage is equal to or higher than the output voltage of the fuel cell stack 1 as obtained when the fuel cell stack 1 outputs the maximum output electric power. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system that is a parallel system of a fuel cell and an electricity storage device.

  In recent years, various fuel cell systems that are parallel systems of fuel cells and power storage devices have been developed (see, for example, Patent Document 1). Here, FIG. 14 shows a configuration example of a conventional fuel cell system.

The fuel cell system shown in FIG. 14 is a parallel system of a fuel cell and an electricity storage device, and includes a fuel cell stack 1, a fuel supply unit 2, a secondary battery 3 as an electricity storage device, a DC / DC converter 4, And a backflow prevention diode 5. The fuel supply unit 2 periodically supplies a predetermined amount of fuel to the fuel cell stack 1 and collects fuel that has not been used in the fuel cell stack 1. The output terminal of the fuel cell stack 1 is connected to the anode of the backflow prevention diode 5, and the positive electrode of the secondary battery 3 is connected to the input terminal of the DC / DC converter 4. Further, the cathode of the backflow prevention diode 5 and the output terminal of the DC / DC converter 4 are connected in common and connected to the load 6.
JP 2004-71260 A JP-A-2005-123110

Since the fuel supply unit 2 periodically supplies a predetermined amount of fuel to the fuel cell stack 1, the current-voltage characteristics and current-power characteristics of the fuel cell stack 1 are as shown in FIG. T _IV in FIG. 15, T _IP output current respectively the fuel cell stack 1 - output voltage characteristics curve, of the output current fuel cell stack 1 - shows the output power characteristic curve.

  The output voltage of the fuel cell stack 1 changes according to the output current, and the output voltage decreases as the output current increases. The value Ipmax of the output current when the output power is maximum is determined by the amount of fuel supplied from the fuel supply unit 2 to the fuel cell stack 1. The operation of the fuel cell stack 1 is unstable in the current region larger than Ipmax, and if the fuel cell stack 1 continues to operate in the current region larger than Ipmax, the life of the fuel cell stack 1 is reduced. In the conventional fuel cell system, the fuel cell stack 1 may continue to operate in a current region larger than Ipmax depending on the state of the load 6.

  In view of the above problems, an object of the present invention is to provide a fuel cell system in which there is no risk of a decrease in the life of the fuel cell.

  In order to achieve the above object, a fuel cell system according to the present invention converts a fuel cell, a fuel supply unit that supplies fuel to the fuel cell, an electricity storage device, and an output voltage of the electricity storage device into a predetermined voltage. A fuel cell system that is a parallel system of the fuel cell and the power storage device, wherein the fuel is output when the output power of the fuel cell is maximum. The battery output voltage is exceeded. Examples of the electricity storage device include a secondary battery and an electric double layer capacitor.

  According to such a configuration, when the predetermined voltage is equal to or higher than the output voltage of the fuel cell when the output power of the fuel cell is maximum, the output power of the fuel cell is maximum. The fuel cell does not operate in a voltage range smaller than the output voltage value of the fuel cell. Thereby, there is no possibility that the life of the fuel cell is reduced.

  In addition, the fuel supply unit may periodically supply a predetermined amount of fuel to the fuel cell and collect fuel that has not been used in the fuel cell. Thereby, unused fuel can be reused.

  The fuel supply unit may use electric power based on the output of the fuel cell system as an operation power source. This eliminates the need for a separate power supply for the fuel supply unit.

  Further, from the viewpoint of improving the efficiency of the fuel cell system, the output terminal of the fuel cell and the DC / DC converter may be directly connected. According to such a configuration, since the backflow prevention diode is not connected to the output side of the fuel cell, the efficiency of the fuel cell system can be improved by the amount of power loss in the backflow prevention diode.

  Further, an ON / OFF control circuit for ON / OFF control of the operation of the DC / DC converter is provided, and if the output voltage of the fuel cell is larger than a predetermined value, the operation of the DC / DC converter is controlled. If the output voltage of the fuel cell is not larger than the predetermined value, the operation of the DC / DC converter may be turned on. The predetermined value is set to a value slightly larger than the predetermined voltage.

  According to such a configuration, the DC / DC converter operates only when the DC / DC converter supplies power to the external load. Therefore, when the DC / DC converter does not supply power to the external load, the DC / DC converter operates. Wasteful power is not consumed in the DC converter, and the efficiency of the fuel cell system can be improved.

  A load power detection unit that detects load power that is required by the external load for the fuel cell system; and output power that determines whether or not power is being supplied from the DC / DC converter to the external load. The determination unit, the detection result of the load power detection unit and the determination result of the output power determination unit are input, and power is supplied from the DC / DC converter to the external load even though the load power is less than a threshold value. If so, a fuel supply amount control unit that controls the fuel supply unit to supply fuel to the fuel cell may be provided.

  According to such a configuration, fuel is supplied to the fuel cell as long as power is supplied from the DC / DC converter to the external load even though the load power is less than a threshold value. The shortage of fuel can be resolved.

  In order to achieve the above object, a fuel cell system according to the present invention is a fuel cell system which is a parallel system of a fuel cell and a power storage device, and limits the output current of the fuel cell to a limit value or less. Current limiting means, and the limit value is the maximum output power in the stable operation state of the fuel cell when the output in the stable operation state elapses for a predetermined time and the output is reduced compared to the initial state. It is made to be below the value of the output current of the fuel cell at the time. Examples of the electricity storage device include a secondary battery and an electric double layer capacitor.

  Since the limit value is set to be equal to or less than the output current value of the fuel cell when the output power in the stable operation state of the fuel cell is the maximum, the output power in the stable operation state of the fuel cell is the maximum. The fuel cell does not operate in a current region larger than the value of the output current of the fuel cell. Thereby, there is no possibility that the life of the fuel cell is reduced. Further, the fuel cell when the output power in the stable operation state of the fuel cell is maximum when the limit value is used in the stable operation state and the output is reduced compared to the initial state after a predetermined time has elapsed. Therefore, the fuel cell can be operated in the stable region even when the use in the stable operation state has elapsed for a predetermined time and the output is reduced compared to the initial state.

  In order to achieve the above object, a fuel cell system according to the present invention is a fuel cell system which is a parallel system of a fuel cell and a power storage device, and limits the output voltage of the fuel cell to a limit value or more. Voltage limiting means is provided, and the limit value is equal to or greater than the value of the output voltage of the fuel cell when the output power in the stable operation state of the fuel cell is maximum. Examples of the electricity storage device include a secondary battery and an electric double layer capacitor.

  Since the limit value is set to be equal to or higher than the output voltage value of the fuel cell when the output power in the stable operation state of the fuel cell is maximum, the output power in the stable operation state of the fuel cell is maximum. The fuel cell does not operate in a voltage region smaller than the value of the output voltage of the fuel cell when Thereby, there is no possibility that the life of the fuel cell is reduced. Further, the fuel cell can be operated in the stable region even when the use in the stable operation state elapses for a predetermined time and the output is reduced as compared with the initial state.

  In order to achieve the above object, a fuel cell system according to the present invention is a fuel cell system that is a parallel system of a fuel cell and an electricity storage device, and the output current of the fuel cell is limited to a first limit value or less. And a fuel cell voltage limiting means for limiting the output voltage of the fuel cell to a second limit value or more, wherein the first limit value is predetermined for use in a stable operating state. When the output is reduced compared to the initial state after a lapse of time, the output power is less than or equal to the output current of the fuel cell when the output power in the stable operation state of the fuel cell is maximum, and the second limit value However, the output voltage of the fuel cell is equal to or greater than the value of the output voltage when the output power in the stable operation state of the fuel cell is maximum. Examples of the electricity storage device include a secondary battery and an electric double layer capacitor.

  According to such a configuration, before the use in the stable operation state elapses for a predetermined time and the output decreases compared to the initial state, the use in the stable operation state elapses for the predetermined time and the output decreases compared to the initial state. After the occurrence, there is no possibility that the life of the fuel cell will be reduced. Furthermore, it is possible to sufficiently extract the power of the fuel cell even in the initial state, and it is possible to prevent the output power of the fuel cell from being significantly reduced even after long-time use.

  In order to achieve the above object, a fuel cell system according to the present invention is a fuel cell system that is a parallel system of a fuel cell and an electricity storage device, the fuel cell, the electricity storage device, and an output of the electricity storage device. A DC / DC converter that converts voltage, a charging circuit that charges the power storage device using the output of the fuel cell, and a maximum output of the operating point of the fuel cell by power control of the DC / DC converter and the charging circuit And a control unit as a power operating point. Examples of the electricity storage device include a secondary battery and an electric double layer capacitor.

  According to such a configuration, the fuel cell always outputs the maximum power, so that the capacity of the fuel cell can be maximized and the fuel cell can always be operated in a stable region.

  According to the present invention, it is possible to realize a fuel cell system that does not cause a decrease in the life of the fuel cell.

  Embodiments of the present invention will be described below with reference to the drawings. A configuration example of the fuel cell system according to the present invention is shown in FIG. In FIG. 1, the same parts as those in FIG. 14 are denoted by the same reference numerals.

  The fuel cell system according to the present invention shown in FIG. 1 is a parallel system of a fuel cell and an electricity storage device, which is a fuel cell stack 1, a fuel supply unit 2, a secondary battery 3 that is an electricity storage device, and a DC / DC. And a converter 4. The fuel supply unit 2 periodically supplies a predetermined amount of fuel to the fuel cell stack 1 and collects fuel that has not been used in the fuel cell stack 1. Further, the positive electrode of the secondary battery 3 is connected to the input terminal of the DC / DC converter 4. Further, the output end of the fuel cell stack 1 and the output end of the DC / DC converter 4 are connected in common and connected to the load 6.

  The fuel supply unit 2 uses power based on the output of the fuel cell system as an operating power source. That is, in FIG. 1, for convenience of explanation, the fuel supply unit 2 and the load 6 are illustrated separately, but the fuel supply unit 2 actually constitutes a part of the load 6.

  Here, the relationship between the output voltage set value Vop of the DC / DC converter 4 and the output voltage of the fuel cell stack 1 will be described with reference to FIG. 2 that are the same as those in FIG. 15 are given the same reference numerals, and detailed descriptions thereof are omitted. In the fuel cell system according to the present invention, the output voltage set value Vop of the DC / DC converter 4 is set to be equal to or higher than the output voltage value Vmin of the fuel cell stack 1 when the output power of the fuel cell stack 1 is maximum. Yes.

  Since the fuel cell system according to the present invention shown in FIG. 1 is a parallel system of a fuel cell and a secondary battery as an electricity storage device, the load is applied only from the fuel cell stack 1 and the DC / DC converter 4 whose output voltage is higher. 6 is supplied with power, and when the output voltages of the fuel cell stack 1 and the DC / DC converter 4 are equal, power is supplied to the load 6 from both the fuel cell stack 1 and the DC / DC converter 4.

  In the fuel cell system according to the present invention, when the load 6 is a light load, the output voltage of the fuel cell stack 1 is higher than the output voltage of the DC / DC converter 4, and power is supplied from only the fuel cell stack 1 to the load 6. Supplied. When the load of the load 6 increases and the power required from the load 6 increases, the output power of the fuel cell stack 1 also increases accordingly, so the output voltage of the fuel cell stack 1 decreases. When the load of the load 6 increases and the output voltage of the fuel cell stack 1 becomes equal to the output voltage set value Vop of the DC / DC converter 4, both the fuel cell stack 1 and the DC / DC converter 4 supply the load 6 to the load 6. Power is supplied. Then, even if the load of the load 6 further increases and the power required from the load 6 increases, the output voltage of the fuel cell stack 1 does not become smaller than the output voltage set value Vop of the DC / DC converter 4, and the load The shortage of the output power of the fuel cell stack 1 with respect to the power required from 6 is compensated by the output power of the secondary battery 3.

  Thus, in the fuel cell system according to the present invention, the output voltage setting value Vop of the DC / DC converter 4 is equal to or higher than the output voltage value Vmin of the fuel cell stack 1 when the output power of the fuel cell stack 1 is maximum. Therefore, the fuel cell stack 1 does not operate in a voltage region smaller than Vmin (= current region larger than Ipmax). Thereby, there is no possibility that the life of the fuel cell stack 1 is reduced.

  Also, from the viewpoint of improving the efficiency of the fuel cell system, the fuel cell system according to the present invention shown in FIG. 1 is configured not to include the backflow prevention diode 5 unlike the conventional fuel cell system shown in FIG. Since the fuel cell stack 1 is not reversely charged (charging from a battery having a high voltage to a battery having a low voltage) unlike a secondary battery, no problem arises even if the backflow prevention diode 5 is not provided. By not providing the backflow prevention diode 5, the efficiency of the fuel cell system can be improved by the amount of power loss in the backflow prevention diode 5.

  As described above, it is desirable that the fuel cell system has no backflow prevention diode, but the present invention can also be applied to a fuel cell system having a backflow prevention diode. In the fuel cell system having the backflow prevention diode shown in FIG. 14, the output voltage set value Vop of the DC / DC converter 4 is set to the output voltage of the fuel cell stack 1 when the output power of the fuel cell stack 1 is maximum. Since the output voltage of the fuel cell stack 1 does not become less than the sum of the output voltage setting value Vop of the DC / DC converter 4 and the forward voltage Vf of the backflow prevention diode, the voltage less than Vmin is set. The fuel cell stack 1 does not operate in the region (= current region greater than Ipmax). Therefore, there is no possibility that the life of the fuel cell stack 1 is reduced.

  Next, another configuration example of the fuel cell system according to the present invention is shown in FIG. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. Further, in the fuel cell system shown in FIG. 3, as in the fuel cell system shown in FIG. 1, the output voltage set value Vop of the DC / DC converter 4 is used as the fuel cell when the output power of the fuel cell stack 1 is maximum. The output voltage value Vmin of the stack 1 is set to be equal to or higher.

  The fuel cell system shown in FIG. 3 has a configuration in which an ON / OFF control circuit 7 is newly provided in the fuel cell system shown in FIG. The ON / OFF control circuit 7 detects the output voltage of the fuel cell stack 1 and determines whether or not the output voltage of the fuel cell stack 1 is greater than a predetermined value. The ON / OFF control circuit 7 causes the DC / DC converter 4 to stop the voltage conversion operation if the output voltage of the fuel cell stack 1 is larger than a predetermined value, and if the output voltage of the fuel cell stack 1 is not larger than the predetermined value. The DC / DC converter 4 is caused to perform a voltage conversion operation. Here, the predetermined value is set to a value slightly larger than the output voltage set value Vop of the DC / DC converter 4.

  Thus, since the DC / DC converter 4 operates only when the DC / DC converter 4 supplies power to the load 6, the DC / DC converter 4 wastes when the DC / DC converter 4 does not supply power to the load 6. Power is not consumed, and the efficiency of the fuel cell system can be improved.

  Even in a fuel cell system having a backflow prevention diode, by providing the ON / OFF control circuit 7 as described above, when the DC / DC converter 4 does not supply power to the load 6, Wasteful power is not consumed in the DC converter 4, and the efficiency of the fuel cell system can be improved. However, from the viewpoint of improving the efficiency of the fuel cell system, a configuration in which no backflow prevention diode as shown in FIG. 3 is provided is desirable.

  In the fuel cell system shown in FIG. 3, the output voltage setting value Vop of the DC / DC converter 4 is set to be equal to or higher than the output voltage value Vmin of the fuel cell stack 1 when the output power of the fuel cell stack 1 is maximum. Otherwise, the object of the present invention, which eliminates the risk of a decrease in the life of the fuel cell, cannot be achieved. However, since the ON / OFF control circuit 7 is provided, the efficiency of the fuel cell system can be improved. If the fuel cell system is a parallel system of a fuel cell and an electricity storage device, the efficiency of the fuel cell system can be improved by providing the ON / OFF control circuit 7 without being limited to the configuration shown in FIG. it can.

  Next, still another configuration example of the fuel cell system according to the present invention is shown in FIG. 4 that are the same as those in FIG. 1 are assigned the same reference numerals and detailed descriptions thereof are omitted. Further, in the fuel cell system shown in FIG. 4, similarly to the fuel cell system shown in FIG. 1, the output voltage set value Vop of the DC / DC converter 4 is set to the fuel cell when the output power of the fuel cell stack 1 is maximum. The output voltage value Vmin of the stack 1 is set to be equal to or higher.

Moreover, the current-voltage characteristic and the current-power characteristic of the fuel cell stack 1 are shown in FIG. In FIG. 5, the same parts as those in FIG. 2 are denoted by the same reference numerals. Even if a predetermined amount of fuel is regularly supplied to the fuel cell stack 1, the fuel concentration changes due to a recovery loss of unused fuel, evaporation due to a rise in ambient temperature, and the like. When the fuel concentration decreases, the output current-output voltage characteristic curve of the fuel cell stack 1 and the output current-output power characteristic curve of the fuel cell stack 1 become T _IV ′ and T _IP ′, respectively, and are taken out from the fuel cell stack 1. Less power is obtained than the design specs. Such a condition is called fuel shortage.

  The fuel cell system shown in FIG. 4 has a configuration in which a load power detection unit 8, an output power determination unit 9, and a supply fuel amount control unit 10 are newly provided in the fuel cell system shown in FIG.

  The load power detection unit 8 detects power required by the load 6 for the fuel cell system (hereinafter referred to as load power), and outputs the detection result to the supply fuel amount control unit 10. For example, when the load 6 is a DC / DC converter, the output voltage of the DC / DC converter is fixed to a predetermined setting value, so that the load power detection unit 8 detects the output current of the DC / DC converter. The load power can be detected.

  The output power determination unit 9 determines whether or not power is supplied from the DC / DC converter 4 to the load 6 and outputs the determination result to the supply fuel amount control unit 10. The output power determination unit 9 detects the input current or output current of the DC / DC converter 4 and determines that power is supplied from the DC / DC converter 4 to the load 6 unless the detected current value is zero. If the detected current value is zero, it is determined that power is not supplied from the DC / DC converter 4 to the load 6.

The supplied fuel amount control unit 10 determines that the fuel cell is short of fuel if power is supplied from the DC / DC converter 4 to the load 6 even though the load power is less than the threshold value Pth. Even so, the fuel supply unit 2 is controlled to supply the fuel to the fuel cell stack 1. In the current region of I ₀ or more and less than Iop, power is supplied from the DC / DC converter 4 to the load 6 even though the load power is less than the threshold value Pth. Moreover, since the fuel shortage amount of the fuel cell is larger as the load power when the power supply from the DC / DC converter 4 to the load 6 is started is smaller, it is desirable to increase the amount of fuel supplied.

  When the supplied fuel amount control unit 10 supplies power to the load 6 from the DC / DC converter 4 even though the load power is less than the threshold value Pth, the supply fuel amount control unit 10 determines that the fuel cell is short of fuel. Since the fuel supply unit 2 is controlled so as to supply fuel to the fuel cell stack 1 even at regular intervals, the fuel shortage of the fuel cell can be solved.

  Even in a fuel cell system having a backflow prevention diode, the load power detection unit 8, the output power determination unit 9, and the supply fuel amount control unit 10 are provided as described above, so that the fuel of the fuel cell is provided. The shortage can be resolved. However, from the viewpoint of improving the efficiency of the fuel cell system, a configuration in which no backflow prevention diode as shown in FIG. 4 is provided is desirable.

  In the fuel cell system shown in FIG. 4, the output voltage set value Vop of the DC / DC converter 4 is set to be equal to or higher than the output voltage value Vmin of the fuel cell stack 1 when the output power of the fuel cell stack 1 is maximum. Otherwise, the object of the present invention, which eliminates the risk of a decrease in the life of the fuel cell, cannot be achieved, but the load power detection unit 8, the output power determination unit 9, and the supply fuel amount control unit 10 are provided. The fuel shortage of the fuel cell can be solved. A fuel cell system that is a parallel system of a fuel cell and an electricity storage device is not limited to the configuration shown in FIG. 4, and a load power detection unit 8, an output power determination unit 9, and a supply fuel amount control unit 10 are provided. As a result, the shortage of fuel in the fuel cell can be resolved.

  The scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. For example, a fuel cell system that combines the configuration shown in FIG. 3 and the configuration shown in FIG. 4 is configured, and the output voltage set value Vop of the DC / DC converter 4 is used as the fuel when the output power of the fuel cell stack 1 is maximum. You may make it set to the value Vmin or more of the output voltage of the battery stack 1.

  Next, FIG. 6 shows a configuration example of a fuel cell system according to the present invention of a type including a DC / DC converter for a fuel cell.

  The fuel cell system according to the present invention shown in FIG. 6 is a parallel system of a fuel cell and an electricity storage device, and includes a fuel cell stack 11, a fuel supply unit 12, a secondary battery 13 as an electricity storage device, and a fuel cell system. A DC / DC converter 14, a secondary battery DC / DC converter 15, a secondary battery charging circuit 16, a system output terminal 17, a current detection circuit 18, and a microcomputer 19 are provided. The system output terminal 17 is a DC output terminal composed of a positive terminal and a negative terminal.

  The fuel supply unit 12 periodically supplies a predetermined amount of fuel to the fuel cell stack 11 and collects fuel that has not been used in the fuel cell stack 11. The fuel cell stack 11 is connected to the input end of the fuel cell DC / DC converter 14 via a current detection circuit 18 that detects the output current of the fuel cell stack 11, and the positive output end of the fuel cell DC / DC converter 14 is Connected to the positive terminal of the system output terminal 17. The secondary battery 13 is connected to the input terminal of the secondary battery DC / DC converter 15 and the output terminal of the secondary battery charging circuit 16, respectively, and the positive electrode output terminal of the secondary battery DC / DC converter 15 and the secondary battery charging. The positive input terminal of the circuit 16 is connected to the positive terminal of the system output terminal 17. The negative output terminal of the fuel cell DC / DC converter 14, the negative output terminal of the secondary battery DC / DC converter 15, and the negative input terminal of the secondary battery charging circuit 16 are respectively connected to the negative terminal of the system output terminal 17. Connected. The microcomputer 19 controls the fuel cell DC / DC converter 14 based on the detection result of the current detection circuit 18. The fuel cell system according to the present invention shown in FIG. 6 uses electric power based on the output of the fuel cell system as an operating power source of the fuel supply unit 12, and the fuel supply unit uses the electric power based on the output of the secondary battery 13 when the system is activated. 12 is operating.

  By connecting the system output terminal 17 to the DC input terminal of the electric device (load), electric power is supplied to the electric device from the fuel cell system according to the present invention shown in FIG.

  The DC / DC converter 14 for the fuel cell boosts the DC voltage output from the fuel cell stack 11 to a DC voltage of a predetermined value (PV1) in principle, and outputs it, and the DC / DC converter 15 for the secondary battery 15 The DC voltage output from 13 is boosted to a predetermined value (PV2) DC voltage and output. The output voltage value (PV1) of the fuel cell DC / DC converter 14 is set to be larger than the output voltage value (PV2) of the secondary battery DC / DC converter 15. Thus, in principle, only the output power of the fuel cell DC / DC converter 14 is supplied to the electrical device via the system output terminal 17.

However, when the output current of the fuel cell stack 11 increases due to an increase in power required by the electric equipment and reaches the limit value I _LIM , the microcomputer 19 fixes the boost ratio of the DC / DC converter 14 for the fuel cell. As a result, the output voltage of the fuel cell DC / DC converter 14 decreases to a predetermined value (PV2). Thus, when the output current of the fuel cell stack 11 reaches the limit value I _LIM , both the output voltage value of the fuel cell DC / DC converter 14 and the output voltage value of the secondary battery DC / DC converter 15 are predetermined values. (PV2), the output power of the fuel cell DC / DC converter 14 and the output power of the secondary battery DC / DC converter 15 are supplied to the electric device via the system output terminal 17, and the output of the fuel cell stack 11 is supplied. The current is clamped at the limit value I _LIM .

Here, the limit value I _LIM is set to be equal to or less than the value Ipmax of the output current of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum in the initial state (see FIG. 7). As a result, the fuel cell stack 11 does not operate in a current region larger than Ipmax, so that there is no possibility that the life of the fuel cell stack 11 is reduced in the initial state.

The fuel cell stack 11 has a feature that the output decreases with use time. Therefore, the current-voltage characteristics and current-power characteristics of the fuel cell stack 11 are as shown in FIG. In FIG. 7, T _IV, T _IP output current of the initial states of the fuel cell stack 11 - output voltage characteristic curve, the output current of the initial state of the fuel cell stack 11 - shows the output power characteristic curve, T _IV ' , T _IP ′ respectively indicate an output current-output voltage characteristic curve of the fuel cell stack 11 after A time use, and an output current-output power characteristic curve of the fuel cell stack 11 after A time use, and T _IV ′ “ , T _IP '' are output current-output voltage characteristic curves of the fuel cell stack 11 after use of B (> A) time, and output current-output power characteristics curves of the fuel cell stack 11 after use of B (> A) time, respectively. Is shown.

Since the fuel cell stack 11 has the above-described characteristics, in order to always operate the fuel cell stack 11 in the stable region, the fuel cell stack 11 is used even when the longest use time (the set life of the fuel cell system) is reached. In order to operate in the stable region, it is necessary to set the limit value I _LIM to be equal to or less than the value of the output current of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum when the longest usage time has elapsed. . For example, assuming that the B time is the longest use time and the limit value I _LIM is set as shown in FIG. 7, the operation point in the initial state, the operation point after the A time use, and the operation point after the B time use are OP1. , OP2 and OP3, and the fuel cell stack 11 can always be operated in the stable region. However, if the limit value I _LIM is set below the value of the output current of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum when the longest usage time has elapsed, the fuel cell stack 11 has in the initial state. There is a problem that it is not possible to draw out enough abilities.

  The secondary battery charging circuit 16 has a surplus power when the output power of the fuel cell stack 11 is greater than the power required by the electric device (= output power of the fuel cell stack 11−power consumption in the fuel cell system−request of the electric device). The secondary battery 13 is charged using the output power of the fuel cell stack 11 when the electric device as the load is not operating.

  Next, FIG. 8 shows another configuration example of the fuel cell system according to the present invention of a type including a DC / DC converter for a fuel cell. In FIG. 8, the same parts as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The fuel cell system according to the present invention shown in FIG. 8 removes the current detection circuit 18 and the microcomputer 19 from the fuel cell system according to the present invention shown in FIG. 6, and the fuel cell DC / DC converter 14 is replaced with a DC / DC for fuel cell. In this configuration, the DC converter 20 is replaced.

  The fuel cell DC / DC converter 20 boosts and outputs the DC voltage output from the fuel cell stack 11 to a DC voltage of a predetermined value (PV1) in principle. Thus, in principle, only the output power of the fuel cell DC / DC converter 20 is supplied to the electrical equipment via the system output terminal 17.

However, the boost ratio of the fuel cell DC / DC converter 20 has an upper limit, and when the output voltage of the fuel cell stack 11 decreases and reaches the limit value V _LIM due to an increase in power required by the electrical equipment, The step-up ratio of the DC / DC converter 20 reaches the upper limit, and the output voltage of the fuel cell DC / DC converter 20 falls to a predetermined value (PV2). As a result, the output power of the fuel cell DC / DC converter 20 and the output power of the secondary battery DC / DC converter 15 are supplied to the electric device via the system output terminal 17, and the output voltage of the fuel cell stack 11 is limited. _Clamped with value V _LIM .

Here, the limit value V _LIM is set to be equal to or higher than the output voltage value Vmin of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum in the initial state (see FIG. 9). As a result, the fuel cell stack 11 does not operate in a voltage region smaller than Vmin (= current region larger than Ipmax), so that there is no possibility that the life of the fuel cell stack 11 is reduced in the initial state.

The fuel cell stack 11 has a feature that the output decreases with use time. For this reason, the current-voltage characteristic and the current-power characteristic of the fuel cell stack 11 are as shown in FIG. In Figure 9, T _IV, T _IP output current of the initial states of the fuel cell stack 11 - output voltage characteristic curve, the output current of the initial state of the fuel cell stack 11 - shows the output power characteristic curve, T _IV ' , T _IP ′ respectively indicate an output current-output voltage characteristic curve of the fuel cell stack 11 after A time use, and an output current-output power characteristic curve of the fuel cell stack 11 after A time use, and T _IV ′ “ , T _IP '' are output current-output voltage characteristic curves of the fuel cell stack 11 after use of B (> A) time, and output current-output power characteristics curves of the fuel cell stack 11 after use of B (> A) time, respectively. Is shown.

Since the fuel cell stack 11 has the characteristics as described above, in order to always operate the fuel cell stack 11 in the stable region, in the initial state, the fuel cell stack 11 operates in the stable region. It is necessary to set the limit value V _LIM above the value of the output voltage of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum. For example, when the B time is the longest use time and the limit value V _LIM is set as shown in FIG. 9, the operating point in the initial state, the operating point after using the A time, and the operating point after using the B time are OP4. , OP5, OP6, and the fuel cell stack 11 can always be operated in the stable region. However, if the limit value V _LIM is set to be equal to or higher than the value of the output voltage of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum in the initial state, the output of the fuel cell stack 11 is increased as the usage time elapses. There is a problem of a significant drop.

  Next, FIG. 10 shows still another configuration example of a fuel cell system according to the present invention of a type including a DC / DC converter for a fuel cell. 10, the same parts as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

The fuel cell stack 11 has a feature that the output decreases with use time. Therefore, the current-voltage characteristics and current-power characteristics of the fuel cell stack 11 are as shown in FIG. In Figure 11, T _IV, T _IP output current of the initial states of the fuel cell stack 11 - output voltage characteristic curve, the output current of the initial state of the fuel cell stack 11 - shows the output power characteristic curve, T _IV ' , T _IP ′ respectively indicate an output current-output voltage characteristic curve of the fuel cell stack 11 after A time use, and an output current-output power characteristic curve of the fuel cell stack 11 after A time use, and T _IV ′ “ , T _IP '' are output current-output voltage characteristic curves of the fuel cell stack 11 after use of B (> A) time, and output current-output power characteristics curves of the fuel cell stack 11 after use of B (> A) time, respectively. Is shown.

  The fuel cell system according to the present invention shown in FIG. 10 has a configuration in which the fuel cell DC / DC converter 14 is replaced with a fuel cell DC / DC converter 21 in the fuel cell system according to the present invention shown in FIG.

  The fuel cell DC / DC converter 21 boosts and outputs the DC voltage output from the fuel cell stack 11 to a DC voltage of a predetermined value (PV1) in principle. The output voltage value (PV1) of the fuel cell DC / DC converter 21 is set to be larger than the output voltage value (PV2) of the secondary battery DC / DC converter 15. Thus, in principle, only the output power of the fuel cell DC / DC converter 21 is supplied to the electrical equipment via the system output terminal 17.

However, when the output current of the fuel cell stack 11 increases due to the increase in power required by the electrical equipment and reaches the limit value I ′ _LIM , the microcomputer 19 fixes the boost ratio of the fuel cell DC / DC converter 21, As a result, the output voltage of the fuel cell DC / DC converter 21 decreases to a predetermined value (PV2). As a result, when the output current of the fuel cell stack 11 reaches the limit value I ′ _LIM , the output voltage value of the fuel cell DC / DC converter 21 and the output voltage value of the secondary battery DC / DC converter 15 are both predetermined. Value (PV2), the output power of the fuel cell DC / DC converter 21 and the output power of the secondary battery DC / DC converter 15 are supplied to the electrical equipment via the system output terminal 17, and the fuel cell stack 11 The output current is clamped at the limit value I ′ _LIM .

The boost ratio of the fuel cell DC / DC converter 21 has an upper limit. When the output voltage of the fuel cell stack 11 decreases and reaches the limit value V ′ _LIM due to an increase in electric power required by the electric device, the fuel cell. The step-up ratio of the DC / DC converter 21 for the fuel reaches the upper limit, and the output voltage of the DC / DC converter 21 for the fuel cell decreases to a predetermined value (PV2). As a result, the output power of the fuel cell DC / DC converter 21 and the output power of the secondary battery DC / DC converter 15 are supplied to the electric device via the system output terminal 17, and the output voltage of the fuel cell stack 11 is limited. _Clamped with the value V ' _LIM .

Here, for example, the limit value I ′ _LIM is set to the same value as the value I′pmax of the output current of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum when the usage time is A time, The limit value V ′ _LIM is set to the same value as the value V ′ min of the output voltage of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum when the usage time is A time. Thereby, when the usage time is A hour or less, the limit value I ′ _LIM prevents the fuel cell stack 11 from operating in a current region larger than I′pmax. When the usage time is longer than A hours, the limit value V ′ _LIM prevents the fuel cell stack 11 from operating in a voltage region smaller than V ′ min. When the usage time is longer than A hours, there is no possibility that the life of the fuel cell stack 11 is reduced.

  Since the fuel cell DC / DC converter 21 performs the above-described operation, the fuel cell system according to the present invention shown in FIG. 10 can sufficiently extract the power of the fuel cell stack 11 even in the initial state, and can be used for a long time. Even after use, the output power of the fuel cell stack 11 can be prevented from being greatly reduced.

A function for measuring the usage time of the fuel cell system is added to the microcomputer 19 of the fuel cell system according to the present invention shown in FIG. 6, and the limit value I _LIM is reduced with an increase in the usage time. By setting the limit value I _LIM below the value of the output current of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum, the same effect as the fuel cell system according to the present invention shown in FIG. Can be obtained.

Further, a function for measuring the usage time of the fuel cell system is added to the fuel cell DC / DC converter 20 of the fuel cell system according to the present invention shown in FIG. 8, and the upper limit of the step-up ratio increases as the usage time increases. Then, the limit value V _LIM is reduced, and the limit value V _LIM is set to be equal to or higher than the output voltage value of the fuel cell stack 11 when the output power of the fuel cell stack 11 is maximum in each usage time. The same effects as those of the fuel cell system according to the present invention shown in FIG.

  Next, still another configuration example of a fuel cell system according to the present invention of a type including a fuel cell DC / DC converter is shown in FIG. In FIG. 12, the same parts as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The fuel cell system according to the present invention shown in FIG. 12 includes a fuel cell DC / DC converter 14, a secondary battery DC / DC converter 15, and a secondary battery charging circuit 16 in the fuel cell system according to the present invention shown in FIG. The current detection circuit 18 and the microcomputer 19 are replaced with a fuel cell DC / DC converter 22, a secondary battery DC / DC converter 23, a secondary battery charging circuit 24, a power detection circuit 25, and a microcomputer 26, respectively. It is a configuration.

  The fuel cell DC / DC converter 22 is a DC / DC converter that boosts and outputs a DC voltage output from the fuel cell stack 11 to a DC voltage of a predetermined value (PV). The DC / DC converter 23 for the secondary battery boosts the DC voltage output from the secondary battery 13 to a DC voltage of a predetermined value (PV) and outputs the boosted DC power to the system output terminal 17. DC / DC converter supplied to The secondary battery charging circuit 24 is a charging circuit that charges the secondary battery 13 with a current value instructed from the microcomputer 26. The power detection circuit 25 is a detection circuit that detects the output power of the fuel cell stack 11 and sends the detection result to the microcomputer 26.

  The microcomputer 26 controls the secondary battery DC / DC converter 23 and the secondary battery charging circuit 24 so that the fuel cell stack 11 always operates at the power peak point. An example of the power peak point is shown in FIG. In FIG. 13, the same parts as those in FIG. 7 are denoted by the same reference numerals, and detailed description thereof is omitted. P1 to P3 in FIG. 13 are power peak points. When the microcomputer 26 performs the above-described control, even if the fuel cell stack 11 runs out of fuel or the output of the fuel cell stack 11 decreases with time of use, the capacity of the fuel cell stack 11 is always maximized. The fuel cell stack 11 can be pulled out and the life of the fuel cell stack 11 can be reduced.

  Hereinafter, an operation example of the microcomputer 26 will be described. While the microcomputer 26 gradually increases the current value instructed to the secondary battery charging circuit 24, the output power of the fuel cell stack 11 increases as the current value instructed to the secondary battery charging circuit 24 increases. When the output power of the fuel cell stack 11 turns from an increase to a decrease, the current value instructed to the secondary battery charging circuit 24 is returned to the value just before the output power of the fuel cell stack 11 turns to a decrease. The output power of the battery stack 11 is stored in the built-in memory. Thereby, the output power of the fuel cell stack 11 at the power peak point is stored in the built-in memory of the microcomputer 26.

  The microcomputer 26 always or periodically performs the storage operation of the output power of the fuel cell stack 11 at the power peak point described above, and periodically updates the output power of the fuel cell stack 11 at the power peak point.

  When the fuel cell system according to the present invention shown in FIG. 12 supplies electric power to the electrical equipment connected to the system output terminal 17, the microcomputer 26 performs the following operation. The microcomputer 26 calculates the maximum power that can be supplied by the load by subtracting the power consumed by the fuel cell system (such as the operating power of the fuel supply unit 12) from the output power of the fuel cell stack 11 at the power peak point stored in the built-in memory. It is calculated and it is determined whether or not the load power is greater than the maximum power that can be supplied.

  When the load power is less than or equal to the maximum load supplyable power, the microcomputer 26 charges the secondary battery charging circuit 24 so that the secondary battery 13 is charged with the power obtained by subtracting the load power from the maximum load supplyable power. Control the value. When the load power is less than or equal to the maximum load supplyable power, the microcomputer 26 prevents power from being supplied from the secondary battery DC / DC converter 23 to the system output terminal 17.

  On the other hand, when the load power is larger than the maximum load supplyable power, the microcomputer 26 causes the secondary battery DC / DC converter 23 to output the amount of power obtained by subtracting the maximum load supplyable power from the load power. If the load power is greater than the maximum power that can be supplied to the load, the microcomputer 26 sets the charging current of the secondary battery charging circuit 24 to zero.

  As in the above example of operation, the microcomputer 26 detects the load power and gives an indication of the amount of discharge of the DC / DC converter 23 for the secondary battery and the amount of charge of the secondary battery charging circuit 24, so that the fuel cell stack 11 The followability of the power peak point operation can be improved. Note that the microcomputer 26 can control the secondary battery DC / DC converter 23 and the secondary battery charging circuit 24 so that the fuel cell stack 11 always operates at the power peak point without detecting the load power. Therefore, if there is no problem in the followability of the power peak point operation of the fuel cell stack 11, the load power need not be detected.

  In the above-described embodiment, the secondary battery (secondary battery 3 or secondary battery 13) is used as the power storage device, but another power storage device (for example, an electric double layer capacitor) is used instead of the secondary battery. It doesn't matter.

  2, 5, 7, 9, 11, 13, and 15 show the current-voltage characteristics and current-power characteristics of the fuel cell stack in a stable operation state. Here, the stable operation state means that the fuel cell is not in an operation state immediately after the start-up of the fuel cell.

These are figures which show the example of 1 structure of the fuel cell system based on this invention. These are figures which show the relationship between the output voltage setting value of a DC / DC converter, and the output voltage of a fuel cell stack. These are figures which show the other structural example of the fuel cell system which concerns on this invention. These are figures which show the further another structural example of the fuel cell system which concerns on this invention. These are figures which show the current-voltage characteristic and current-power characteristic of a fuel cell stack. These are figures which show the example of 1 structure of the fuel cell system which concerns on this invention of the type which comprises DC / DC converter for fuel cells. These are figures which show the current-voltage characteristic and current-power characteristic of a fuel cell stack. These are figures which show the other structural example of the fuel cell system which concerns on this invention of the type which comprises DC / DC converter for fuel cells. These are figures which show the current-voltage characteristic and current-power characteristic of a fuel cell stack. These are figures which show the further another structural example of the fuel cell system which concerns on this invention of the type which comprises DC / DC converter for fuel cells. These are figures which show the current-voltage characteristic and current-power characteristic of a fuel cell stack. These are figures which show the further another structural example of the fuel cell system which concerns on this invention of the type which comprises DC / DC converter for fuel cells. These are figures which show the current-voltage characteristic and current-power characteristic of a fuel cell stack. These are figures which show the example of 1 structure of the conventional fuel cell system. These are figures which show the current-voltage characteristic and current-power characteristic of a fuel cell stack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Fuel cell stack 2,12 Fuel supply part 3,13 Secondary battery 4 DC / DC converter 5 Backflow prevention diode 6 Load 7 ON / OFF control circuit 8 Load power detection part 9 Output power determination part 10 Supply fuel quantity control Part 14, 20, 21, 22 Fuel cell DC / DC converter 15, 23 Secondary battery DC / DC converter 16, 24 Secondary battery charging circuit 17 System output terminal 18 Current detection circuit 19, 26 Microcomputer 25 Power detection circuit

Claims (10)

A fuel cell; a fuel supply unit that supplies fuel to the fuel cell; a power storage device; and a DC / DC converter that converts an output voltage of the power storage device into a predetermined voltage and outputs the voltage. In a fuel cell system that is a parallel system of power storage devices,
The fuel cell system, wherein the predetermined voltage is equal to or greater than a value of the output voltage of the fuel cell when the output power of the fuel cell is maximum.   The fuel cell system according to claim 1, wherein the fuel supply unit periodically supplies a predetermined amount of fuel to the fuel cell and collects fuel that has not been used in the fuel cell.   The fuel cell system according to claim 1, wherein the fuel supply unit uses electric power based on an output of the fuel cell system as an operation power source.   The fuel cell system according to any one of claims 1 to 3, wherein an output terminal of the fuel cell and the DC / DC converter are directly connected. An ON / OFF control circuit for ON / OFF control of the operation of the DC / DC converter;
The ON / OFF control circuit turns off the operation of the DC / DC converter if the output voltage of the fuel cell is greater than a predetermined value, and the DC / DC converter if the output voltage of the fuel cell is not greater than the predetermined value. The fuel cell system according to claim 1, wherein the operation is turned on. A load power detection unit that detects load power that is required by the external load for the fuel cell system;
An output power determination unit that determines whether power is supplied from the DC / DC converter to the external load;
If the detection result of the load power detection unit and the determination result of the output power determination unit are input and power is supplied from the DC / DC converter to the external load even though the load power is less than a threshold value The fuel cell system according to claim 1, further comprising: a supply fuel amount control unit that controls the fuel supply unit so as to supply fuel to the fuel cell. A fuel cell system that is a parallel system of a fuel cell and an electricity storage device,
A fuel cell current limiting means for limiting the output current of the fuel cell to a limit value or less;
The limit value is a value of the fuel cell when the output power in the stable operation state of the fuel cell is maximum when the use in the stable operation state elapses for a predetermined time and the output decreases compared to the initial state. A fuel cell system having an output current value or less. A fuel cell system that is a parallel system of a fuel cell and an electricity storage device,
A fuel cell voltage limiting means for limiting the output voltage of the fuel cell to a limit value or more;
The fuel cell system, wherein the limit value is equal to or greater than a value of an output voltage of the fuel cell when the output power in a stable operation state of the fuel cell is maximum. A fuel cell system that is a parallel system of a fuel cell and an electricity storage device,
Fuel cell current limiting means for limiting the output current of the fuel cell to a first limit value or less; and fuel cell voltage limiting means for limiting the output voltage of the fuel cell to a second limit value or more,
The first limit value is obtained when the output power in the stable operation state of the fuel cell is maximum when the use in the stable operation state has elapsed for a predetermined time and the output is reduced compared to the initial state. It is below the value of the output current of the fuel cell,
The fuel cell system, wherein the second limit value is equal to or greater than the value of the output voltage of the fuel cell when the output power in the stable operation state of the fuel cell is maximum. A fuel cell system that is a parallel system of a fuel cell and an electricity storage device,
The fuel cell, the power storage device, a DC / DC converter that converts an output voltage of the power storage device, a charging circuit that charges the power storage device using the output of the fuel cell, the DC / DC converter, and the A fuel cell system comprising: a control unit configured to set the operating point of the fuel cell as a maximum output power operating point by power control of a charging circuit.

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