JP2010192256A - Fuel cell power generation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell power generation system that does not generate excessive inrush current at startup of a fuel cell device, and is excellent in respect of reliability and cost, while eliminating a relay circuit for limiting the inrush current. <P>SOLUTION: In the fuel cell power generation system 1 provided with a fuel cell device 2 generating power by dint of a fuel gas supply means (a reformer 22) and an oxidant gas supply means (a cathode air pump 23), a power conversion device 3 for converting modes of direct-current output power outputted from the fuel cell device 2, and a control device 4 for controlling operation of the fuel cell device 2 and the power conversion device 3, the control device 4 is provided with a startup control means 5 for controlling the fuel gas supply means 22 for supplying fuel gas after the finish of generation preparation of the fuel cell device 2, and then, controlling the oxidant gas supply means 23 to gradually supply the oxidant gas so that an output current I of the direct-current output power may not go beyond a specified startup current value at startup control for supplying the oxidant gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell power generation system, and more particularly to an improvement in a start control method for a fuel cell device.

  In recent years, the development of distributed power generation systems aimed at saving energy and reducing carbon dioxide emissions has been promoted, and fuel cell power generation systems also belong to this category. The fuel cell power generation system converts a fuel cell main body that generates power by electrochemically reacting a fuel gas including hydrogen and an oxidant gas having oxygen, and converts the output DC output power into AC power having a predetermined frequency. In general, it is provided with a power conversion device, and further includes an auxiliary device necessary for operation of the fuel cell main body, a control device for controlling the operation, and the like.

  In the inverter device disclosed in Patent Document 1, a power supply and a booster circuit are connected using a relay circuit, and an inverter (power converter) is connected to the output side of the booster circuit. A fuel cell is exemplified as the power source, and a fuel cell power generation system is configured as a whole. The relay circuit limits an inrush current, and is configured by connecting a circuit in which a resistor and an inrush current preventing relay are connected in series and a main relay circuit in parallel. Then, when starting the power supply, only the inrush current prevention relay is closed and a current limiting action is caused as a circuit configuration via a resistor, and the main relay circuit is closed when the inrush current is settled.

  Furthermore, the inverter device of Patent Document 1 is characterized in that the welding of the relay circuit is determined by causing the booster circuit to function while the relay circuit is broken. In other words, when the booster circuit is functioned by breaking the relay circuit, the output voltage of the booster circuit does not increase because the power supply is disconnected if it is normal, and if the output voltage rises, the power supply to the booster circuit is not increased. Since it is supplied, it is possible to judge the welding of the relay. As exemplified in Patent Document 1, when a noise removing or smoothing capacitor is used in a booster circuit or an inverter, an excessive charging current tends to flow as an inrush current when the power supply is started. Therefore, it is highly necessary to provide a relay circuit, and it is difficult to eliminate the possibility of welding failure due to an excessive charging current.

JP 2005-261040 A

  By the way, in the apparatus of patent document 1, in order to judge the welding failure of a relay circuit, it was necessary to provide a special circuit structure and to perform special operation. Further, even when proper maintenance is performed when the welding failure is detected, the function can be recovered, but the welding failure itself cannot be prevented. Furthermore, as long as the relay circuit is provided and controlled to open and close, there is a possibility of malfunction and other problems as well as welding, which is disadvantageous in terms of reliability. In addition, since the relay circuit increases the device cost, it is desirable if it can be omitted. However, if the relay circuit is omitted, an excessive inrush current may flow, so it is considered that an alternative measure for limiting the inrush current and ensuring reliability is necessary.

  The present invention has been made in view of the above problems, and an excessive inrush current does not flow when the fuel cell device is started, and a relay circuit for limiting the inrush current is unnecessary, and the fuel cell is excellent in terms of reliability and cost. Providing a power generation system is an issue to be solved.

  The invention of a fuel cell power generation system according to claim 1 that solves the above-described problems includes a fuel cell apparatus that generates power by having a fuel gas supply means for supplying fuel gas and an oxidant gas supply means for supplying oxidant gas A fuel cell power generation system comprising: a power conversion device that converts the form of DC output power output from the fuel cell device; and a control device that controls the operation of the fuel cell device and the power conversion device, The control device supplies one of the fuel gas and the oxidant gas after completing preparation for power generation of the fuel cell device, and then performs a start control for supplying the other of the fuel gas and the oxidant gas. And a start control means for gradually supplying the other of the fuel gas and the oxidant gas so that the output current of the DC output power does not exceed a specified current value.

  The invention according to claim 2 is characterized in that, in claim 1, the start control means gradually increases the supply amount per unit time of the other of the fuel gas and the oxidant gas after the start.

  According to a third aspect of the present invention, in the first or second aspect, the power conversion device includes a capacitor in parallel on an input side thereof, and the start control means outputs an output voltage of the DC output power applied to the capacitor. Is increased in proportion to the elapsed time after start-up, and the rate of increase is controlled to match the voltage determined by the capacitance value of the capacitor and the specified current value.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the control device includes at least one of a voltmeter that detects an output voltage of the DC output power and an ammeter that detects the output current. The start control means holds in advance time transition data of at least one of the output voltage and output current when the power converter is started without load and the output current does not exceed the specified current value. In the starting control, at least one of the output voltage and the output current is detected, and compared with the time transition data, the oxidant gas supply means or the fuel gas supply means is feedback-controlled. .

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the fuel cell device and the power conversion device are directly electrically connected.

  In the invention according to claim 1, during the start control of the fuel cell device, the start control means of the control device first supplies one of the fuel gas and the oxidant gas, and then gradually supplies the other of the fuel gas and the oxidant gas. To supply. Furthermore, in the invention according to claim 2, the start control means gradually increases the supply amount per unit time of the other of the fuel gas and the oxidant gas after the start. According to these start-up controls, the electrochemical reaction inside the fuel cell device progresses gradually and the output voltage gradually increases. Therefore, the specified current is determined depending on the initial amount of fuel to be supplied and the amount of oxidant gas. Inrush current exceeding the value does not occur. Therefore, a conventional relay circuit that limits an excessive inrush current is not required, and there is no risk of problems such as welding or malfunction, and the system can be excellent in terms of reliability.

  In the invention according to claim 3, in the electric circuit configuration in which the capacitor is disposed in parallel on the input side of the power conversion device, the start control means matches the output voltage of the fuel cell device with a voltage having an appropriate increase rate. Can be controlled. Therefore, in an electric circuit configuration in which an excessive inrush current tends to flow to charge the capacitor, the output voltage can be raised in a short time while maintaining the output current below the specified current value, and the startup time is prolonged. Absent.

  In the invention according to claim 4, the start control means compares the detected output voltage and / or output current with appropriate time transition data, and feedback-controls the oxidant gas supply means or the fuel gas supply means. Therefore, when the output voltage or output current deviates from the time transition data, the supply amount of the oxidant gas or the fuel gas can be quickly adjusted, and the reliability of the start control is improved.

  In the invention which concerns on Claim 5, the fuel cell apparatus and the power converter device can be directly electrically connected without a relay circuit, and the cost of a relay circuit can be reduced.

It is a block block diagram explaining the structure of the fuel cell power generation system of embodiment of this invention. FIG. 2 is a diagram schematically illustrating a start control method for controlling an air supply amount with output time transition data as a target in the configuration of FIG. 1. It is a figure which illustrates typically an example of the starting control method in the conventional system. It is a block block diagram explaining the structure of the conventional fuel cell power generation system which has a relay circuit.

  An embodiment for carrying out the present invention will be described with reference to FIG. 1 and FIG. FIG. 1 is a block diagram illustrating the configuration of a fuel cell power generation system 1 according to an embodiment of the present invention. The fuel cell power generation system 1 includes a fuel cell device 2, a power conversion device 3, and a control device 4, and converts DC output power generated by the fuel cell device 2 into AC power having a commercial frequency by the power conversion device 3. And sent to the power system 9.

  The fuel cell device 2 includes a solid polymer fuel cell body 21, a reformer 22 corresponding to fuel gas supply means, and a cathode air pump 23 corresponding to oxidant gas supply means. The fuel cell main body 21 is mainly composed of a cell stack formed by structurally stacking a number of cell batteries (not shown) and electrically connecting them in series. Both ends of the cell stack are drawn to the outside of the apparatus to be positive and negative output terminals 2P and 2N, and a DC stack voltage, that is, an output voltage V is output between the output terminals 2P and 2N. Yes. The reformer 22 steam-reforms a source gas such as city gas to generate a hydrogen-rich fuel gas and supplies it to the fuel electrode of each cell. The cathode air pump 23 supplies air containing oxygen as an oxidant gas to the cathode (air electrode) of each cell.

  The power converter 3 is also called a power conditioner, and as shown in the figure, a protective fuse 31, a noise removing capacitor 32, a DC / DC converter unit 33, a smoothing capacitor 34, and a DC / AC inverter unit 35 are sequentially arranged. Connected and configured. The positive and negative input terminals 3P and 3N of the power converter 3 are directly electrically connected to the positive and negative output terminals 2P and 2N of the fuel cell device 2, respectively. The protection fuse 31 is connected to the subsequent stage of the positive input terminal 3P, and when the excessive current flows, the fuel cell device 2 and the power conversion device 3 are electrically disconnected to protect both 2 and 3 have. The noise removing capacitor 32 is connected between the positive and negative stages of the protective fuse 31 and removes noise that enters between the positive and negative lines.

  The DC / DC converter unit 33 is connected to the subsequent stage of the noise removing capacitor 32 and converts the voltage level of the direct-current output voltage V of the fuel cell device 2. The smoothing capacitor 34 is connected to the subsequent stage of the DC / DC converter unit 33, and smoothes the pulsation contained in the direct current. The DC / AC inverter unit 35 is connected to the subsequent stage of the smoothing capacitor 34, and converts DC power into single-phase AC power of commercial frequency and outputs it. The output end of the DC / AC inverter unit 35 is drawn out of the apparatus to form single-phase three-wire output terminals 3X, 3Y, and 3Z, which are connected to the power system 9.

  The DC / DC converter unit 33 and the DC / AC inverter unit 35 employ a well-known circuit configuration in which power semiconductors capable of phase control are combined. A control unit 36 is provided to perform phase control of the power semiconductor.

  The control device 4 controls the operation of the entire system 1, controls the reformer 22 and the cathode air pump 23 of the fuel cell device 2, and performs control in cooperation with the control unit 36 of the power conversion device 3. . The control device 4 can be constituted by, for example, an electronic control device that incorporates a computer and operates by software.

  In addition, a voltmeter 41 for detecting the output voltage V of the fuel cell device 2 is provided between the output terminals 2P and 2N. The output line of the voltmeter 41 is connected to the control device 4 so that information on the detected output voltage V is directly transmitted. Further, an ammeter 42 for detecting the output current I of the fuel cell device 2 is provided in series between the protective fuse 31 of the power conversion device 3 and the noise removing capacitor 32. An output line of the ammeter 42 is connected to the control unit 36, and information on the detected output current I is transmitted to the control device 4 via the control unit 36.

  The start control means 5 is realized by start control software 51 and output time transition data 52 incorporated in the control device 4. The start control software 51 is activated when starting the fuel cell device 2. The output time transition data 52 is a waveform of a preferable change in time of the output voltage V and the output current I detected when the fuel cell device 2 is started with the power conversion device 3 unloaded and the output current I is not excessive. Data, that is, data that is a control target. The output time transition data 52 can be obtained by, for example, a development test of the system 1 or an inspection before product shipment, and can be held in a storage unit in the control device 4. The start control software 51 monitors the output voltage V detected by the voltmeter 41 and the output current I detected by the ammeter 42 when starting the fuel cell device 2, and compares it with the output time transition data 52. The cathode air pump 23 or the reformer 22 is feedback-controlled to adjust the supply amount of air or fuel gas.

  Next, a start control method of the fuel cell device 2 in the fuel cell power generation system 1 of the embodiment will be described with reference to FIG. FIG. 2 is a diagram schematically illustrating a start control method for controlling the air supply amount with the output time transition data as a target. The horizontal axis in the figure is a common time axis, and the vertical axis is (1) the output voltage V of the fuel cell device 2, (2) the output current I of the fuel cell device 2, and (3) the cathode of the fuel cell main body 21. Air concentration D, (4) The air supply amount F per unit time of the cathode air pump 23 is shown. The waveforms of (1) the output voltage V and (2) the output current I show the output time transition data 52 held in the storage unit of the control device 4 as described above, but when the start control is performed well. It also shows the measured changes.

  At time T0 in FIG. 2, the fuel cell device 2 finishes preparation for power generation, and fuel gas of an initial fuel amount necessary for start-up has already been supplied from the reformer 22, and power is generated if air is supplied from the cathode air pump 23. It is in a state to be started. On the other hand, the power conversion device 3 is disconnected from the power system 9 and has no load, and the DC / DC converter unit 33 and the DC / AC inverter unit 35 are not operating. That is, the load viewed from the fuel cell device 2 is only the noise removing capacitor 32.

  First, the specified current value I0 will be described. When starting the fuel cell device 2, a preferable initial fuel amount can be determined from the performance characteristics, and the initial power P0 obtained when sufficient air is supplied can be determined. At this time, if the no-load output voltage output from the cell stack is V0, the maximum current IP allowed for the fuel cell device 2 can be obtained by IP = P0 / V0. Therefore, if an excessive load with a small impedance is connected, an output current I exceeding the maximum current IP is required, which puts a burden on the fuel cell device 2 and is not preferable. At this time, it is preferable to slow the rise of the output voltage V by limiting the supply amount of air and to maintain the output current I below the maximum current IP. Practically, the specified current value I0 is set with a margin for the maximum current IP.

  Next, the waveforms of FIG. 2 (1) output voltage V and (2) output current I will be described. In this embodiment, the start control means 5 sets a voltage increasing at a constant increase rate A (slope) from 0 (zero) at time T0 to the no-load output voltage V0 at time T1 as a target of the output voltage V. Control. Then, an output current I flows in order to charge the noise removing capacitor 32 having the capacitance C to the no-load output voltage V0. That is, if the output current I during the starting time TS from the time T0 to the time T1 is integrated, the charge charge amount Q (= C × V0) having a constant value is obtained. Therefore, if the increase rate A of the output voltage V is increased to shorten the start time TS, the output current I increases. Conversely, if the increase rate A is decreased to increase the start time TS, the output current I decreases. Here, the starting time TS can be determined so that the peak of the output current I coincides with the specified current value I0.

  The actual waveform of the output current I is not the simple triangular wave shown in the figure, but can be obtained by the transient phenomenon theory in consideration of the conductor resistance and inductance in addition to the capacitance C, or can be obtained experimentally. . In any case, it is possible to determine the shortest starting time TS for matching the peak of the output current I to the specified current value I0, that is, to determine the voltage increase rate A.

  Although the target of the output voltage V can be determined as described above, the start control means 5 cannot directly control the output voltage V. Instead, the output voltage V can be indirectly controlled by controlling the air supply amount F per unit time of the cathode air pump 23, which will be described in detail later. The magnitude of the output voltage V depends on the activity of the electrochemical reaction in the fuel cell main body 21. In the present embodiment, since the initial amount of fuel gas is supplied in advance, the activity of the electrochemical reaction depends on the amount of air supplied to the cathode. Therefore, the start control means 5 controls the cathode air concentration D similarly to the waveform of the output voltage V, as shown in FIG. That is, the air concentration D is increased from 0 to the predetermined concentration D0 at a constant increase rate during the starting time TS from time T0 to time T1. In order to realize this, the air supply amount F per unit time of the cathode air pump 23 is gradually increased. In the example of FIG. 2 (4), the air supply amount F per unit time is linearly increased from 0 to the predetermined supply amount F0. Then, since the integrated supply amount increases in a quadratic function and a part is consumed for power generation, the waveform of the air concentration D increases linearly as shown in FIG.

  Note that the waveform of the air supply amount F per unit time in FIG. 2 (4) is an example, and is not limited to this. In order to finally set the output current I to the specified current value I0 or less, It is preferable to use a control method that matches the characteristics of the fuel cell device 2.

  Further, the start control means 5 monitors the detected values of the output voltage V and the output current I during the start control, and confirms the presence or absence of deviation compared with the output time transition data. When the deviation occurs, the cathode air pump 23 is feedback-controlled so as to cancel the deviation. Therefore, the output current I is set to the specified current value I0 or less, and is reliably maintained below the maximum current IP.

  Further, after the output voltage V reaches the no-load output voltage V0, there is no load and the output current I becomes a small value I1, so that the air supply amount F can also be set to a small amount F1. After the power converter 3 is connected to the power system 9 and the load is connected, the control device 4 controls the reformer 22 to add fuel gas, and further controls the anode air pump 23 to supply air. to add. As a result, the DC output power of the fuel cell device 2 increases, and single-phase AC power can be sent from the power conversion device 3 to the power system 9.

  On the other hand, in the conventional fuel cell power generation system, control for gradually supplying air has not been performed at the time of starting control. FIG. 3 is a diagram schematically illustrating an example of a start control method in a conventional system. The horizontal axis in the figure is a common time axis, and the vertical axis is (1) the output voltage v detection value of the fuel cell device 2, (2) the output current i detection value of the fuel cell device 2, and (3) the fuel cell body. 21 shows an air concentration d of the cathode 21 and (4) an air supply amount f per unit time of the cathode air pump 23. As shown in FIG. 3 (4), in the conventional example, the air supply amount f per unit time is set to a substantially constant value F6 during the start time TS. For this reason, (3) the cathode air concentration d increased steeply, and (1) the output voltage v also increased steeply. Therefore, (2) the output current i also has a steep rising inrush current waveform, and the peak I6 exceeds the maximum current IP. Therefore, countermeasures are required. In order to limit the peak I6, a current limiting circuit has been conventionally provided. In the current limiting circuit, for example, as shown in the conventional system configuration of FIG. 4, a relay circuit configured by connecting a limiting resistor 81 and an inrush current preventing relay 82 in series with a main relay 83 in parallel. 8 was used.

  In the present embodiment, the start control means 5 of the control device 4 is improved, so that the relay circuit 8 is not required while maintaining the output current I below the maximum current IP. Is excellent.

  In the embodiment, the start control method of controlling the output voltage V and the output current I by first supplying the initial fuel amount and then adjusting the air supply amount F per unit time is illustrated. In the normal operation mode, since the fuel gas generally remains in the fuel cell device 2 at the time of stoppage, the above-described start control method is efficient. However, a second control method is also conceivable in which the supply order is reversed and the oxidant gas is supplied first and then the supply amount of the fuel gas is adjusted. For example, when the inside of the fuel cell device 2 is purged with an inert gas and stopped, the second control method may be used.

  Furthermore, although the fuel cell main body 21 of this embodiment is a solid polymer type, the present invention can also be applied to other types of fuel cells such as a solid oxide type. Moreover, although the power converter device 3 shall be connected with the electric power grid | system 9, the structure which supplies electric power to a specific load without connecting may be sufficient. In addition, it can be applied to cogeneration systems that use not only electrical energy but also thermal energy, and has a wide range of applications.

1: Fuel cell power generation system 2: Fuel cell device 21: Fuel cell body 22: Reformer 23: Cathode air pump 3: Power converter 31: Protection fuse 32: Noise removal capacitor 33: DC / DC converter unit 34: Smooth Capacitor 35: DC / AC inverter 36: Controller 4: Controller 41: Voltmeter 42: Ammeter 5: Start control means 51: Start control software 52: Output time transition data 8: Relay circuit 9: Power system V : Output voltage I: Output current

Claims (5)

A fuel cell device having a fuel gas supply means for supplying fuel gas and an oxidant gas supply means for supplying oxidant gas to generate power, and electric power for converting the form of DC output power output from the fuel cell device A fuel cell power generation system comprising a conversion device, and a control device that controls the operation of the fuel cell device and the power conversion device,
The control device supplies one of the fuel gas and the oxidant gas after completing preparation for power generation of the fuel cell device, and then performs a start control for supplying the other of the fuel gas and the oxidant gas. The fuel cell power generation system further comprises start control means for gradually supplying the other of the fuel gas and the oxidant gas so that the output current of the DC output power does not exceed a specified current value.   2. The fuel cell power generation system according to claim 1, wherein the start control means gradually increases the supply amount per unit time of the other of the fuel gas and the oxidant gas after the start.   3. The power conversion device according to claim 1, wherein the power converter has a capacitor in parallel on an input side thereof, and the start control means sets the output voltage of the DC output power applied to the capacitor to an elapsed time after the start. A fuel cell power generation system, wherein the fuel cell power generation system is controlled so as to increase in proportion and the rate of increase to a voltage determined by the capacitance value of the capacitor and the specified current value.   4. The control device according to claim 1, wherein the control device includes at least one of a voltmeter that detects an output voltage of the DC output power and an ammeter that detects the output current. The power conversion device holds in advance time transition data of at least one of the output voltage and the output current when the output current starts without exceeding the specified current value with no load, and in starting control A fuel cell power generation system, wherein at least one of the output voltage and the output current is detected and compared with the time transition data to feedback control the oxidant gas supply means or the fuel gas supply means.   The fuel cell power generation system according to any one of claims 1 to 4, wherein the fuel cell device and the power converter are directly electrically connected.

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