JP2013168224A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably generate power in a fuel cell system capable of realizing a system interconnection operation and an autonomous operation.SOLUTION: A fuel cell system 1 comprises an SOFC 11 for generating power using hydrogen-containing fuel; a PCS 12 and a signal input circuit 13 controlling an operation of the SOFC 11; and a power storage unit 20 for storing power. The SOFC 11 is configured switchable between a system interconnection operation interconnected with power of an external power system CE and supplying power to an indoor distribution panel EI, and an autonomous operation interconnected with power of the power storage unit 20 and supplying power to the indoor distribution panel EI. The PCS 12 has an individual operation prevention function of a frequency shift system for making the SOFC 11 parallel-off when detecting that the power interconnected with the SOFC 11 stopped. Here, only while the SOFC 11 is autonomously operated, the PCS 12 makes the individual operation prevention function to a stop state, and thereby, variation of a frequency due to the individual operation prevention function during the autonomous operation is restrained.

Description

  The present invention relates to a fuel cell system.

  As a conventional fuel cell system, for example, as described in Patent Document 1, a fuel cell unit (fuel cell stack) that generates power using a hydrogen-containing fuel, and a control unit (micro) that controls the operation of the fuel cell A computer including a computer and a power storage unit (secondary battery) that stores electric power is known. In this fuel cell system, it is possible to charge the power storage unit without stopping the external power load.

Japanese Patent No. 4799026

  By the way, in the fuel cell system as described above, there is a case where the fuel cell unit performs grid connection operation for supplying power to the external power load in linkage with the power of the external power system. In this case, as specified in the grid connection regulations, for example, from the viewpoint of security, the fuel cell unit should not continue to operate independently when the power of the external power system is stopped (power failure) It is necessary to disconnect the output of the unit from the external power system. Therefore, the control unit normally outputs the output of the fuel cell unit from the interconnection target when the stop of the electric power of the interconnection target connected to the fuel cell unit (hereinafter also simply referred to as “interconnection power”) is detected. It has a function to prevent isolated operation.

  Here, in recent years, in such a fuel cell system, for example, in the event of a power failure, it has been attempted to further perform a self-sustained operation in which the fuel cell unit supplies power to an external power load in conjunction with the power of the power storage unit. However, in this case, when the fuel cell unit is operating independently, the fuel cell unit may be unintentionally disconnected, and it may be difficult to perform stable power generation.

  This invention is made | formed in view of the said situation, and makes it a subject to perform the stable electric power generation in the fuel cell system in which a grid connection operation and a self-sustained operation are possible.

  In order to solve the above problems, it has been found that when the fuel cell unit is operating independently, the isolated operation prevention function of the control unit adversely affects the operation of the fuel cell unit and makes the operation of the fuel cell unit unstable. It was. Specifically, the isolated operation prevention function is active such as a frequency shift method in which the frequency of the power generated by the fuel cell unit is changed and the system power is detected based on the frequency change. Has a method. Therefore, even if the isolated operation prevention function functions normally during grid-connected operation, the isolated operation prevention function may erroneously detect the stoppage of the connected power and misinterpret the fuel cell unit during independent operation. There was found. Accordingly, the inventors have conceived that stable power generation can be performed if such erroneous detection can be suppressed, and the present invention has been completed.

  That is, the fuel cell system of the present invention includes a fuel cell unit that generates power using hydrogen-containing fuel, a control unit that controls the operation of the fuel cell, and a power storage unit that stores electric power. The system can be switched between grid-connected operation that supplies power to the external power load linked to the power of the external power system and independent operation that supplies power to the external power load linked to the power of the power storage unit. The control unit has an active isolated operation prevention function that disconnects the output of the fuel cell from the connection target when the stop of the power of the connection target connected to the fuel cell unit is detected. The isolated operation prevention function is stopped only while the fuel cell unit is operating independently.

  In the fuel cell system of the present invention, when the fuel cell unit is operating independently, the isolated operation preventing function can be stopped (masking the isolated operation preventing function), and the above-described isolated operation preventing function has an adverse effect. Can be suppressed. Therefore, according to the present invention, stable power generation can be performed in a fuel cell system capable of grid interconnection operation and independent operation. The active method may be a frequency shift method.

  Moreover, it is preferable that the fuel cell unit is switched to a self-sustained operation when the power of the external power system is stopped. In this case, when the power of the external power system is stopped, the fuel cell unit can be operated independently to stably supply power to the external power load.

  In addition, the fuel cell unit continues the self-sustained operation until a predetermined time elapses after the power of the external power system is restored, and the control unit performs a predetermined time from the time when the power of the external power system is restored. Until the time elapses, it is preferable to maintain the standstill state of the isolated operation prevention function. In this case, for the predetermined time after power recovery, the independent operation is continued and the stop state of the independent operation prevention function is maintained for ensuring safety.

  Here, as a configuration that favorably achieves the above-described effects, specifically, the power storage unit outputs a command signal to the control unit, and the control unit operates alone only while the command signal is input from the power storage unit. The structure which makes a prevention function a stop state is mentioned.

  In addition, the control unit has an undervoltage detection function for disconnecting the output of the fuel cell unit from the connection target when the voltage shortage of the power connected to the fuel cell unit is detected, and the power connected to the fuel cell unit. And an insufficient frequency detection function for disconnecting the output of the fuel cell unit from the interconnection target when an insufficient frequency is detected. In this case, during the self-sustained operation of the fuel cell unit, when the power of the power storage unit becomes equal to or lower than a predetermined value, the output of the fuel cell unit is disconnected from the power storage unit by the undervoltage detection function and the underfrequency detection function.

  According to the present invention, stable power generation can be performed in a fuel cell system capable of grid interconnection operation and independent operation.

1 is a schematic block diagram showing a fuel cell system according to an embodiment. It is a circuit diagram which shows the interface of the mask command signal in the fuel cell system of FIG. 2 is a time chart for explaining the operation of the fuel cell system of FIG. 1. It is a graph which shows the confirmation test result about the response of the mask command signal in the fuel cell system of FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic block diagram showing a fuel cell system according to an embodiment of the present invention. As shown in FIG. 1, the fuel cell system 1 is used as, for example, a household power supply source, and includes a fuel cell unit 10, a power storage unit 20, and a switch 30. The fuel cell system 1 links the power generated by the fuel cell unit 10 with the grid power of the external power grid CE and supplies power to the indoor distribution board EI as an external power load (hereinafter referred to as “grid grid operation”). Called). Further, the fuel cell system 1 links the generated power of the fuel cell unit 10 with the stored power of the power storage unit 20 and supplies power to the indoor distribution board EI (hereinafter referred to as “self-sustained operation”).

  The fuel cell unit 10 includes an SOFC (fuel cell unit) 11 that is a solid oxide fuel cell (SOFC) fuel cell, and a PCS (Power Conditioning System, power conditioner) 12 that controls the operation of the SOFC 11. And a signal input circuit 13 that receives a mask command signal (command signal) described later, and is connected to the indoor distribution board EI via an electric circuit 50.

  The SOFC 11 generates power using a hydrogen-containing fuel and an oxidant, and outputs, for example, 0.7 kW. The type of the fuel cell is not limited to the solid oxide type. For example, the polymer electrolyte fuel cell (PEFC), the phosphoric acid fuel cell (PAFC), and the molten carbonate. A type fuel cell (MCFC: Molten Carbonate Fuel Cell) and other types can be adopted.

  As the hydrogen-containing fuel, for example, a hydrocarbon fuel is used. As the hydrocarbon fuel, a compound containing carbon and hydrogen in the molecule (which may contain other elements such as oxygen) or a mixture thereof is used. Examples of hydrocarbon fuels include hydrocarbons, alcohols, ethers, and biofuels. These hydrocarbon fuels are derived from conventional fossil fuels such as petroleum and coal, and synthesized from syngas. A fuel-derived one or a biomass-derived one can be used as appropriate.

  Specific examples of hydrocarbons include methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, town gas, gasoline, naphtha, kerosene, and light oil. Examples of alcohols include methanol and ethanol. Examples of ethers include dimethyl ether. Examples of biofuels include biogas, bioethanol, biodiesel, and biojet. As the oxidizing agent, for example, air, pure oxygen gas (which may contain impurities that are difficult to remove by a normal removal method), or oxygen-enriched air is used.

  The PCS 12 has a power adjustment function for adjusting the power generated in the SOFC 11. Specifically, the PCS 12 includes a DC / DC converter that transforms the voltage of the DC power output from the SOFC 11, an inverter that converts the transformed power from DC to AC, and the like. The PCS 12 has at least an undervoltage detection function, an underfrequency detection function, and an isolated operation prevention function. Therefore, these functions will be described in detail below.

  The undervoltage detection function connects the output of the fuel cell unit 10 when a voltage shortage (decrease with respect to a predetermined voltage) of power to be connected to the SOFC 11 (hereinafter also referred to as “linkage power”) is detected. The system is disconnected from the system target, and an undervoltage relay (UVR) is used. The insufficient frequency detection function is to disconnect the output of the fuel cell unit 10 from the connection target when a frequency shortage of the interconnection power (decrease with respect to a predetermined frequency) is detected, and a frequency reduction relay (UFR) is used. It has been.

  The isolated operation prevention function is a function that disconnects the output of the SOFC 11 from the connection target so that the SOFC 11 does not operate independently when the stop of the connected power is detected. In particular, this isolated operation prevention function can comply with the regulations that during grid connection operation, power must not be generated from work security in the event of a power failure when the power of the external power system CE is stopped. This is because, for example, if the fuel cell unit 10 continues the single operation without being disconnected from the external power system CE, the external power system CE that should be essentially non-voltage is charged. Therefore, there is a risk that the operator may be more likely to receive an electric shock, or in the event of an accident, power will continue to be supplied to the point of the accident, resulting in increased damage.

  As this isolated operation prevention function, an active type is used, and here, a frequency shift type is used. In this independent operation prevention function, first, the generated power is actively varied constantly at a current frequency according to the external power load by an inverter control system or the like. Subsequently, for example, a change in the frequency of the voltage is detected near the exit of the PCS 12. Then, based on the detected frequency change, it is detected whether or not the grid power is stopped. When the power stop is detected, the output of the SOFC 11 is disconnected from the grid target. The active method is a method in which the inverter applies some disturbance to the output current, and determines whether or not a power failure has occurred depending on whether the disturbance causes a disturbance in the AC voltage. As the active method, in addition to the frequency shift method, a reactive power fluctuation method, an active power fluctuation method, a synchronous harmonic injection method, a phase shift method, an inter-order harmonic injection method, and the like can be exemplified.

  The PCS 11 is connected to the signal input circuit 13 and masks the isolated operation preventing function according to the input of the mask command signal from the signal input circuit 13, thereby the isolated operation preventing function during the independent operation. Is set to a stop state (details will be described later). As shown in FIG. 2, the signal input circuit 13 includes a photocoupler 12a that operates in response to an input of a mask command signal, and resistors R1 and R2.

  As shown in FIG. 1, the power storage unit 20 constitutes a power storage unit for storing power, and includes a battery 21, an inverter 22, a signal output circuit 23, and a power failure detector 27. The battery 21 constitutes a DC secondary power supply having a predetermined capacity (for example, 3 kW). When a battery 21 having a capacity that can secure the energy required for starting the fuel cell unit 10 is used as the battery 21, the fuel cell unit 10 can be operated independently by a cold start during a power failure.

  The inverter 22 converts the power of the battery 21 from direct current to alternating current. Further, the inverter 22 supplies a DC 5V DC voltage serving as a mask command signal to the signal output circuit 23. The signal output circuit 23 outputs a mask command signal, which is an analog signal of a DC voltage of DC 5 V, to the signal input circuit 13 during the independent operation. As shown in FIG. 2, the signal output circuit 23 includes an off-delay timer 23a and a filter circuit 26 (resistor R3 and capacitor C), and is connected to the signal input circuit 13 via a wiring 25. ing. The inverter 22 includes a switch 24 that controls connection of the battery 21 to the external power system CE and the fuel cell unit 10.

  The off-delay timer 23a turns on the output at the same time as the input from the power failure detector 27 is turned on, and elapses a predetermined time t1 (here, t1 = 300 s) after the input from the power failure detector 27 is turned off. The output is turned off later. As the off-delay timer 23a here, for example, model H3CR-H8L manufactured by OMRON can be used. The filter circuit 26 is an element for noise reduction, makes the rising / falling edge of the mask command signal steep and enables the output of the mask command signal with high accuracy.

  As shown in FIG. 1, the power failure detector 27 is always energized when receiving power from the external power system CE and is connected to the external power system CE via the electric circuit 51 and is turned off by opening the b contact. The input to the delay timer 23a is turned off. On the other hand, at the time of a power failure, the system power is not applied, so that it is de-energized, disconnected from the external power system CE, and the b contact is closed to turn on the input to the off-delay timer 23a.

  The switch 30 is operated when it is desired to bypass the operation of the power storage unit 20 for maintenance or the like. Specifically, the switch 30 connects the electric circuit 50 to the electric circuit 52 connected to the power storage unit 20 while connecting the electric circuit 50 to the electric circuit 52 connected to the external power system CE. At least a part of the switch 30 and the electric circuits 50 to 53 are disposed on the outdoor interconnection panel.

  Next, the operation of the fuel cell system 1 described above will be illustrated with reference to FIG.

  FIG. 3 is a time chart for explaining the operation of the battery system of FIG. In FIG. 3, the horizontal axis represents time. In the fuel cell system 1, when receiving, for example, AC 200V system power from the external power system CE, the electric circuits 50 and 53 are connected to each other by the switch 30, and the fuel cell unit 10 and the external power system CE are connected to the indoor power distribution system. The battery 21 of the power storage unit 20 is charged by the external power system CE while being connected to the panel EI.

  At this time, the b-contact of the power failure detector 27 is opened, and the input to the off-delay timer 23a is turned off, so that the mask command signal is not output from the signal output circuit 23 (becomes 0V). The driving prevention function is activated.

  Subsequently, when the power failure occurs and the power reception from the external power system CE is stopped (t = tc in the figure when AC 200V becomes 0V), the switch 24 inside the inverter 22 is switched, and the fuel cell unit 10 and the discharge output of the power storage unit 20 are connected to the indoor distribution board EI. Thereby, an operation | movement is switched to the electric power supply to the indoor distribution board EI by a self-supporting operation. Immediately after starting the self-sustained operation, the SOFC 11 once enters the idling mode, but is connected again after a predetermined time t0 seconds and sends the power generation output to the indoor distribution board EI. The power storage unit 20 secures an external load for a predetermined time t0 seconds.

  At the same time, the power failure detector 27 is de-energized, and the switch 24 inside the inverter 22 is disconnected from the external power system CE. At this time, the b-contact of the power failure detector 27 is closed and the input to the off-delay timer 23a is turned on, so that the mask command signal is output as DC 5V via the wiring 25, and the mask command signal is output from the fuel cell. The signal is input to the signal input circuit 13 of the unit 10. As a result, in the PCS 12, the isolated operation prevention function is masked according to the input of the mask command signal, and the isolated operation prevention function is stopped.

  Subsequently, when the external power system CE recovers and receives power from the external power system CE again (t = tr in the figure when 0V is changed to AC200V), the switch 24 is not yet switched, so that it can operate independently. Will continue to supply electricity. At the same time, the power failure detector 27 is excited, the b contact of the power failure detector 27 is opened, and the input to the off-delay timer 23a is turned off. The signal is maintained and output as DC 5 V, and the mask command signal is input to the signal input circuit 13 of the fuel cell unit 10. As a result, in the PCS 12, the masking of the isolated operation preventing function is continued in response to the input of the mask command signal, and the stopped state of the isolated operation preventing function is continued.

  When the predetermined time t1 elapses after power recovery of the external power system CE (t = tr + t1 in the figure), the switch 24 is switched, and the battery 21 of the power storage unit 20 is charged by the external power system CE. Thereby, the power supply to the indoor distribution board EI in the grid connection operation is performed again. At the same time, the delay function of the off-delay timer 23a is terminated, the mask command signal is reset and not output from the signal output circuit 23 (becomes 0V), and the isolated operation prevention function is again activated.

  By the way, the above-mentioned isolated operation prevention function of the PCS 12 erroneously detects the stop of the stored power from the power storage unit 20 and misunderstands the SOFC 11 during the independent operation even if it functions normally during the grid connection operation. It is found that they are queued up. This is because active frequency fluctuations due to the isolated operation prevention function are absorbed by the capacity of the external power system CE, but cannot be absorbed by the capacity of the battery 21 which is smaller than the capacity of the external power system CE. This is probably because an error factor is included in the frequency change.

  In this regard, according to the present embodiment, the isolated operation prevention function can be stopped by the mask command signal from the power storage unit 20 only during a power failure, and the isolated operation prevention function can be normally activated after power recovery. As a result, at the time of system power reception, it is possible to avoid the safety problem caused by the independent operation of the SOFC 11 by reliably operating the isolated operation prevention function, and to appropriately carry out the grid interconnection operation. On the other hand, at the time of a power failure, the SOFC 11 can be operated independently to continue power generation, and the power can be stably supplied to the indoor distribution board EI connected to the household load. The frequency fluctuation due to the above can be suppressed and the SOFC 11 can be prevented from being unintentionally disconnected.

  Therefore, according to the present embodiment, stable power generation can be performed in the fuel cell system 1 capable of grid interconnection operation and independent operation. Note that, in the present embodiment, it is possible to generate power by operating the SOFC 11 stably even during a self-sustained operation linked to any other power storage unit. Furthermore, in the present embodiment, for example, in the event of a failure (excluding welding of the b contact), the isolated operation prevention function is activated (returns), which is suitable for the fail-safe concept. Can be made.

  In the present embodiment, as described above, the self-sustaining operation is continued and the stop state of the independent operation prevention function by the PCS 12 is maintained until the predetermined time t1 elapses from the time tr when the power is restored. As a result, the fuel cell unit 10 can be stably operated even during the predetermined time t1 immediately after the power recovery.

  In this embodiment, as described above, the mask command signal is output from the power storage unit 20 to the signal input circuit 13, and the PCS 12 stops the isolated operation prevention function only while the mask command signal is input. ing. By comprising in this way, the said effect | action which stops an independent operation function is suitably realizable.

  Moreover, in this embodiment, the isolated operation prevention function of the SOFC 11 can be secured by the undervoltage detection function and the underfrequency detection function of the PCS 12. In particular, during the self-sustaining operation, the undervoltage detection function and the underfrequency detection function cause the SOFC 11 to be disconnected when the stored power of the power storage unit 20 falls below a predetermined value. . Therefore, electric power for idling mode operation or the like at the time of disconnection necessary for the SOFC 11 that is operated at a high temperature can be reliably ensured during the independent operation.

  Here, the fuel cell system 1 was subjected to a confirmation test for confirming that the mask command signal surely responded during a power failure. A part of the result is shown in FIG. In the confirmation test here, the commercial power source used as the external power system was continuously opened and closed 100 times, and whether or not the mask command signal was output and stopped according to the opening and closing was confirmed by the voltage waveform.

  As shown in FIG. 4, a mask command signal is output in response to the commercial power source being switched from open to closed, and the mask command signal is stopped in response to the commercial power source being switched from closed to open. ing. Therefore, it can be confirmed that the mask command signal is reliably output during a power failure. Further, in the confirmation test, the mask command signal is surely responded in all 100 times when the commercial power source is opened and closed, and thus the durability of the fuel cell system 1 related to the mask command signal can also be confirmed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. The present invention is modified without departing from the scope described in the claims or applied to others. It may be.

  For example, in the above embodiment, the grid interconnection operation and the self-sustained operation are switched between when the external power system CE receives power and when there is a power failure. However, the present invention is not limited to this. The grid interconnection operation and the independent operation may be switched. In the above, the PCS 12 and the signal input circuit 13 constitute a control unit.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 10 ... Fuel cell unit, 11 ... SOFC (fuel cell part), 12 ... PCS (control part), 13 ... Signal input circuit (control part), 20 ... Power storage unit (power storage part), CE ... External power system, EI ... external power load, t1 ... predetermined time.

Claims (6)

A fuel cell unit that generates power using hydrogen-containing fuel;
A control unit for controlling the operation of the fuel cell;
A power storage unit for storing electric power,
The fuel cell unit is
Switchable between grid-connected operation for supplying power to an external power load linked to power from an external power system, and independent operation for supplying power to the external power load linked to power from the power storage unit Has been
The controller is
In addition to having an active isolated operation preventing function that disconnects the output of the fuel cell from the interconnection target when a stop of the power of the interconnection target connected to the fuel cell unit is detected,
The fuel cell system is characterized in that the isolated operation prevention function is stopped only while the fuel cell unit is operating independently.   The fuel cell system according to claim 1, wherein the active method is a frequency shift method.   3. The fuel cell system according to claim 1, wherein the fuel cell unit is switched to the self-sustained operation when power of the external power system is stopped. The fuel cell unit continues the self-sustained operation until a predetermined time elapses after the power of the external power system is restored,
4. The fuel cell according to claim 3, wherein the control unit maintains the stop state of the islanding prevention function until a predetermined time elapses after the power of the external power system is restored. system. The power storage unit outputs a command signal to the control unit,
5. The fuel cell according to claim 1, wherein the control unit stops the isolated operation prevention function only while the command signal is input from the power storage unit. system.   The controller includes an undervoltage detection function that disconnects an output of the fuel cell unit from the interconnection target when a voltage shortage of power connected to the fuel cell unit is detected, and the fuel cell unit is connected. 6. A deficiency frequency detection function for disconnecting the output of the fuel cell unit from the interconnection target when a deficiency in frequency of power to be connected is detected. 6. The fuel cell system according to item.

Images