JP2004193063A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which reduction of cost can be realized by decreasing the maximum voltage in fluctuating power consumption of auxiliary machineries and by reducing a voltage-withstanding nature of a variety of parts. <P>SOLUTION: Upon the start-up of the fuel cell system, a relay 24a to connect or cut off a fuel cell stack 1 and a driving motor 21 is cut off under the control of a controller 11, and the auxiliary machineries 22 are actuated by setting a directive voltage to a DC/DC converter 27 for high voltage to control a direct current voltage between the fuel cell stack 1 and the driving motor 21 to be of a smaller value than an open voltage of the fuel cell stack 1, and after the directive voltage to the DC/DC converter 27 for high voltage is controlled to be in the vicinity of the open voltage of the fuel cell stack 1, the relay 24a is connected. By this, the fuel cell system can set the instruction voltage to the DC/DC converter 27 for high voltage low at the start-up, and as a result, reduction of cost can be realized by decreasing the voltage-withstanding nature of the variety of parts. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system mounted on, for example, a fuel cell vehicle to generate electric power for generating a driving force of the fuel cell vehicle.
[0002]
[Prior art]
In recent years, a fuel gas containing a large amount of hydrogen has been supplied to a fuel electrode (hydrogen electrode) of a fuel cell, and air has been supplied to an air electrode, and the hydrogen and oxygen have been electrochemically reacted via an electrolyte membrane. 2. Description of the Related Art A fuel cell system that obtains generated power is known. Such fuel cell systems are expected to be put to practical use, for example, as power sources for vehicles, and research and development for practical use are being actively conducted.
[0003]
Such a fuel cell system is usually provided with a DC / DC (Direct Current to Direct Current) converter, and in order to supply power to a power supply destination of the fuel cell stack, a DC voltage of power generated by the secondary battery is supplied. To increase the DC voltage of the power generated by the fuel cell stack, while reducing the DC voltage of the power generated by the fuel cell stack to the DC voltage of the power generated by the secondary battery in order to charge the secondary battery Has been done.
[0004]
As such a fuel cell system, there is a technique in which a secondary battery is connected in parallel to a fuel cell stack via a DC / DC converter, and the fuel cell stack and the DC / DC converter are connected via a diode. It has been proposed (see Patent Document 1).
[0005]
In this fuel cell system, the target value of the output voltage during the step-up operation of the DC / DC converter is smaller than the value obtained by subtracting the value of the on-voltage of the diode from the value of the open voltage of the fuel cell stack, and Is set to a value larger than the output voltage of the fuel cell stack at the time of equilibrium when all the electric power necessary for starting the fuel cell is supplied from the fuel cell stack.
[0006]
As described above, this fuel cell system performs the connection between the fuel cell stack and the load through the diode, despite the simple control, by performing the connection between the fuel cell stack and the load via the diode. It is possible to prevent occurrence of overcurrent due to voltage mismatch with the converter.
[0007]
[Patent Document 1]
JP 2001-229943 A
[0008]
[Problems to be solved by the invention]
By the way, in the fuel cell system described in Patent Document 1 described above, at the time of startup, the operation of the diode suppresses the extraction of power from the fuel cell stack, so that the target value of the output voltage of the DC / DC converter is set to the fuel cell. It is necessary to set a high voltage near the open voltage of the stack.
[0009]
Further, in this fuel cell system, if it is intended to completely suppress the extraction of power from the fuel cell stack at the time of startup, the target value of the output voltage of the DC / DC converter is set to a higher voltage than the open voltage of the fuel cell stack. Must be set. Therefore, in the fuel cell system, the operation of the accessories is started using such a high voltage.
[0010]
However, in the conventional fuel cell system, a small error caused by a response delay of the DC / DC converter with respect to fluctuations in the power consumption of the auxiliary devices during the start of the operation of the auxiliary devices while the power consumption is not stable is caused. However, there is a risk that the voltage may fluctuate greatly and greatly exceed the open voltage of the fuel cell stack.
[0011]
Therefore, in the conventional fuel cell system, in order to increase the resistance to the voltage greatly exceeding the open voltage of the fuel cell stack, for example, various parts including the diode are required to have high withstand voltage and high cost is required. There was a problem.
[0012]
In view of the above, the present invention has been proposed in view of the above-described circumstances, and it is possible to reduce the withstand voltage of various parts by lowering the maximum voltage when the power consumption of the auxiliary devices fluctuates, thereby reducing costs. It is intended to provide a fuel cell system capable of achieving the following.
[0013]
[Means for Solving the Problems]
According to the present invention, at the time of startup, the relay unit is operated so as to cut off the fuel cell stack and the load by the control of the control unit, and the voltage conversion unit controls the DC voltage from the fuel cell stack to the load. The command voltage is set to a value smaller than the open-circuit voltage of the fuel cell stack, the accessories are operated, and thereafter, the command voltage to the voltage conversion unit is controlled to be close to the open-circuit voltage of the fuel cell stack, and then the relay unit is connected. This solves the above-mentioned problem.
[0014]
【The invention's effect】
According to the fuel cell system of the present invention, at the time of startup, by setting the command voltage to the voltage conversion means to be low, it is possible to reduce the maximum voltage when the power consumption of the auxiliary devices fluctuates. The withstand voltage of the component can be reduced, and the cost can be reduced.
[0015]
Also, according to the fuel cell system of the present invention, the relay connection between the fuel cell stack and the load is performed after controlling the command voltage to the voltage conversion means to around the open voltage of the fuel cell stack. As a result, the electric power is not suddenly started to be taken out from the fuel cell stack, and the connection between the fuel cell stack and the load can be performed via the diode. This makes it possible to start taking out power from the fuel cell stack. Therefore, according to the fuel cell system of the present invention, it is possible to prevent the occurrence of an overcurrent due to a voltage mismatch between the voltage converting unit and the fuel cell stack when the fuel cell stack is connected to the load, despite the simple control. it can.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.
[0017]
[Configuration of fuel cell system]
The present invention is applied to a fuel cell system configured as shown in FIGS. 1 and 2, for example. This fuel cell system is mounted on, for example, a vehicle and generates electric power serving as a drive source of the vehicle.
[0018]
As shown in FIG. 1, this fuel cell system includes a fuel cell stack 1 that generates power by supplying a fuel gas containing a large amount of hydrogen and an oxidizing gas containing oxygen for generating a power generation reaction. In this fuel cell stack 1, a fuel cell structure in which an air electrode 1a to which an oxidizing gas is supplied and a hydrogen electrode 1b to which a fuel gas is supplied is sandwiched by a separator with a solid polymer electrolyte membrane interposed therebetween. It is configured by stacking a plurality of cell structures. That is, in the power generation by the fuel cell stack 1, in the hydrogen electrode 1b, hydrogen emits electrons and is ionized, and the generated hydrogen ions (H +) pass through the polymer electrolyte membrane and reach the air electrode 1a. The hydrogen ions combine with oxygen at the air electrode 1a to form water (H ₂ O).
[0019]
Further, the fuel cell system includes a controller 11 that controls the operation of each unit to control the power generation reaction of the fuel cell stack 1. The controller 11 stores a fuel cell start-up program describing a series of processing procedures for starting up the fuel cell system and supplying power to a load in a storage unit such as a ROM (Read Only Memory) not shown, By executing the fuel cell start-up program by a CPU (Central Processing Unit) (not shown) or the like, each unit described later is controlled.
[0020]
In this fuel cell system, air as an oxidant gas is supplied to the fuel cell stack 1 by being pumped from an air supply system 2 such as an air compressor driven by a compressor motor to take in outside air. At this time, the controller 11 controls the driving amount of the air compressor in the air supply system 2 in response to a power generation request from the fuel cell stack 1 from the outside, and controls the air flow rate and the air pressure. Then, the air is used for the power generation reaction of the fuel cell stack 1, and a surplus is discharged from the fuel cell stack 1.
[0021]
In the fuel cell system, an air pressure regulating valve 4 is provided on a pipe for exhaust from the air electrode 1a. The controller 11 reads a sensor signal from the pressure sensor 3 provided near the entrance of the air electrode 1a, and adjusts the air pressure at the air electrode 1a according to this value so that the air pressure at the air electrode 1a becomes a pressure corresponding to the power generation request. The opening of the pressure valve 4 is controlled.
[0022]
On the other hand, the fuel gas is accumulated in a hydrogen supply system 5 such as a high-pressure hydrogen storage tank, and the pressure is adjusted by a hydrogen pressure regulating valve 6 under the control of a controller 11 to be supplied to the fuel cell stack 1. At this time, the controller 11 reads a sensor signal from the pressure sensor 8 provided near the entrance of the hydrogen electrode 1b, and according to this value, sets the hydrogen pressure at the hydrogen electrode 1b to a pressure according to the power generation request. The opening degree of the hydrogen pressure regulating valve 6 is controlled to control the fuel gas flow rate and the fuel gas pressure. The fuel gas is used together with the air for the power generation reaction of the fuel cell stack 1, and the surplus is discharged from the fuel cell stack 1.
[0023]
In the fuel cell system, a purge valve 9 is provided on a pipe for exhaust from the hydrogen electrode 1b. Normally, the fuel gas discharged from the hydrogen electrode 1b is provided on the downstream side of the hydrogen pressure regulating valve 6 through the recirculation pipe 10 connected upstream of the purge valve 9 when the purge valve 9 is closed. The ejected fuel is supplied to the ejector 7, where it is combined with the fuel gas from the hydrogen storage tank 2 and supplied again to the fuel cell stack 1. This is to supply the unconsumed fuel gas to the hydrogen electrode 1b again in order to set the stoichiometric ratio of hydrogen (supply flow rate / consumption flow rate) to 1 or more for the purpose of stabilizing the cell voltage. When detecting a decrease in cell voltage due to, for example, water in the fuel cell stack 1 due to impurities, the controller 11 opens the purge valve 9 to discharge moisture along with hydrogen.
[0024]
Next, the configuration of the electric system of the fuel cell system constituting such a gas system will be described.
[0025]
As shown in FIG. 2, when driving the drive motor 21, the fuel cell system drives the auxiliary devices 22 and the weak electric auxiliary devices 23 to cause the fuel cell stack 1 to perform a power generation reaction. The generated power is supplied to the drive motor 21 via the relay box 24 and the inverter 25.
[0026]
The accessories 22 are various devices necessary for power generation of the fuel cell stack 1 and operation of the vehicle, and include, for example, the compressor motor in the air supply system 2 described above. The accessories 22 are driven by electric power supplied from the fuel cell stack 1 and the high-voltage battery 26 via the high-voltage DC / DC converter 27.
[0027]
The high-voltage battery 26 is provided to accumulate surplus power generated by the fuel cell stack 1 and regenerative power by the drive motor 21 when the fuel cell vehicle decelerates. The high-voltage battery 26 is used when the fuel cell stack 1 does not generate enough power to cover the traveling power consumed by the drive motor 21 and the auxiliary power consumed by the auxiliary equipment 22 and the like. Discharges and supplies power to the drive motor 21 and the auxiliary devices 22 to compensate for the insufficient power.
[0028]
The high-voltage DC / DC converter 27 converts the DC voltage of the power generated by the high-voltage battery 26 into the DC voltage of the power generated by the fuel cell stack 1 in order to supply power to the power supply destination of the fuel cell stack 1. In order to charge the high-voltage battery 26 while increasing the voltage, the DC voltage of the power generated by the fuel cell stack 1 is reduced to the DC voltage of the power generated by the high-voltage battery 26. At this time, the high-voltage DC / DC converter 27 sets the high voltage based on the value of the voltage sensor 28 such that the voltage between the stack DC / DC converter 24 and the inverter 25 becomes the command voltage given from the controller 11. The voltage is controlled by charging or discharging the voltage battery 26.
[0029]
Here, in order to specifically describe the operation of the high-voltage DC / DC converter 27, if a current-voltage (power) characteristic of the fuel cell stack 1 is expressed, for example, a tendency shown in FIG. 3 is obtained. That is, as shown by a curve a in FIG. 3, as the current of the fuel cell stack 1 increases, the voltage of the fuel cell 1 rapidly drops from a predetermined open voltage V0, and then becomes a substantially constant value. In particular, when the current value exceeds a predetermined current value, the current value drops sharply. Further, as shown by a curve b in FIG. 3, the electric power of the fuel cell 1 has a characteristic that it monotonically increases as the current of the fuel cell stack 1 increases. Therefore, from FIG. 3, in the fuel cell system, for example, when it is desired to output 20 kW of power from the fuel cell stack 1, 300 V is supplied to the high-voltage DC / DC converter 27 under the control of the controller 11. It is understood that it is sufficient to instruct. At this time, if the power consumption of the drive motor 21 is 30 kW, the high-voltage DC / DC converter 27 sets the voltage between the stack DC / DC converter 24 and the inverter 25 to 300 V. Is controlled so as to discharge 10 kW of power to the high-voltage battery 26.
[0030]
The relay box 24 is connected to a power supply line from the fuel cell stack 1 to the drive motor 21. The relay box 24 is provided with a relay 24a that connects or disconnects the fuel cell stack 1 and the drive motor 21 by performing an on / off operation under the control of the controller 11. In order to prevent current from flowing from the drive motor 21 to the fuel cell stack 1, a diode 24 b is provided in the relay box 24 between the relay 24 a and the connection part of the high-voltage DC / DC converter 27. And are provided integrally.
[0031]
The inverter 25 controls the drive motor 21 by converting DC power supplied from the fuel cell stack 1 into AC and supplying the converted power to the drive motor 21. At this time, the inverter 25 controls the drive motor 21 so that the drive motor 21 generates a command torque given from the controller 11. As will be described later, the inverter 25 is provided with, for example, a capacitor 25a in order to absorb an error between a response of the high-voltage DC / DC converter 27 and a fluctuation in power consumption of the accessories 22.
[0032]
The voltage sensor 28 measures a voltage between the relay box 24 and the inverter 25. The voltage value measured by the voltage sensor 28 is used for controlling the high-voltage battery 26 for voltage conversion by the high-voltage DC / DC converter 27, as described above.
[0033]
The low-voltage auxiliary devices 23 include low-voltage auxiliary devices such as a 14 V system, and are connected between the high-voltage DC / DC converter 27 for the stack and the inverter 25 via the low-voltage DC / DC converter 29. .
[0034]
The low-voltage DC / DC converter 29 reduces the DC voltage of the power generated by the fuel cell stack 1 to the DC voltage of the power generated by the low-voltage battery 30 in order to charge the low-voltage battery 30. Yes, under the control of the controller 11, converts a high voltage of, for example, 200V to 14V, and supplies the stepped-down power to the lightly-powered auxiliary equipment 23 and the low-voltage battery 30.
[0035]
The low-voltage battery 30 is, for example, a low-voltage secondary battery such as a 14 V system, and is connected between the low-voltage auxiliary equipment 23 and the low-voltage DC / DC converter 29. When the fuel cell stack 1 does not generate enough power to supply the auxiliary power consumed by the weak electrical accessories 23, the low voltage battery 30 discharges and supplies power to the weak electrical accessories 23. And make up for the lack of power.
[0036]
The fuel cell system including such components controls the command voltage to the high-voltage DC / DC converter 27 by performing the following operations.
[0037]
[Startup control process of fuel cell system]
Next, an activation control process executed by the controller 11 when the above-described fuel cell system is activated will be described with reference to FIG.
[0038]
In the controller 11, as shown in FIG. 4, when a start switch (not shown) is turned on, in step S1, the relay 24a in the relay box 24 is turned off to shut off the fuel cell stack 1 and the drive motor 21. Then, the activation of the high-voltage DC / DC converter 27 is started. At this time, the controller 11 sets the command voltage to the high-voltage DC / DC converter 27 to be lower than the open-circuit voltage of the fuel cell stack 1 and higher than the lower limit voltage at which the accessories in the accessories 22 can operate. Specify the value.
[0039]
Subsequently, in step S2, the controller 11 determines whether the activation of the high-voltage DC / DC converter 27 has been completed. This determination is made, for example, based on whether the difference between the voltage commanded in step S1 and the actual voltage measured by the voltage sensor 28 is within a predetermined value. If the controller 11 determines that the activation of the high-voltage DC / DC converter 27 has not been completed, the controller 11 repeats the process of step S2 until it determines that the activation of the high-voltage DC / DC converter 27 has been completed.
[0040]
On the other hand, if the controller 11 determines in step S2 that the activation of the high-voltage DC / DC converter 27 has been completed, the controller 11 shifts the processing to step S3, where the auxiliary equipment necessary for the power generation of the fuel cell stack 1 is performed. The operation of class 22 is started. Specifically, in the fuel cell system, for example, the operation of a compressor motor for supplying air to the fuel cell stack 1 and a water pump for circulating cooling water through the fuel cell stack 1 are started.
[0041]
Subsequently, in step S4, the controller 11 determines whether a predetermined time, for example, several seconds to several tens of seconds has elapsed from the start of the operation of the accessories 22 in step S3. As the predetermined time, it is desirable to measure in advance the time when the auxiliary equipment 22 starts operating and the power consumption is sufficiently stabilized, and set this time. If the controller 11 determines that the predetermined time has not elapsed from the start of the operation of the auxiliary devices 22, the controller 11 repeats the process of step S4 until it determines that the predetermined time has elapsed.
[0042]
On the other hand, if the controller 11 determines in step S4 that the predetermined time has elapsed from the start of the operation of the accessories 22, the process proceeds to step S5, and the voltage of the fuel cell stack 1, that is, the open voltage Is greater than or equal to a predetermined value. When the controller 11 determines that the voltage of the fuel cell stack 1 is lower than the predetermined value, the controller 11 repeats the process of step S5 until it determines that the voltage is higher than the predetermined value.
[0043]
If the controller 11 determines in step S5 that the voltage of the fuel cell stack 1 is equal to or higher than the predetermined value, in step S6, the controller 11 sends the command voltage to the high-voltage DC / DC converter 27 to the fuel cell stack 1 The voltage is increased to a value near the open voltage, that is, a voltage value corresponding to the predetermined value + α in step S5.
[0044]
Subsequently, in step S7, the controller 11 determines whether the deviation between the command voltage (predetermined value + α) commanded in step S6 and the actual voltage measured by the voltage sensor 28 is within the predetermined deviation. Determine whether or not. If the controller 11 determines that the deviation is larger than the predetermined deviation, the controller 11 repeats the process of step S7 until it determines that the deviation is within the predetermined deviation.
[0045]
If the controller 11 determines in step S7 that the deviation is within the predetermined deviation, the controller 11 turns on the relay 24a and connects the fuel cell stack 1 and the drive motor 21 in step S8.
[0046]
The fuel cell system completes startup by going through such a series of steps.
[0047]
After the relay 24 a is turned on in this manner, the output voltage of the high-voltage DC / DC converter 27 is lower than the output voltage of the fuel cell stack 1 under the control of the controller 11. Thus, the command voltage to the high-voltage DC / DC converter 27 is gradually changed. Therefore, the fuel cell system can smoothly start supplying power from the fuel cell stack 1 to the drive motor 21 by the action of the diode 24b.
[0048]
Here, in the fuel cell system, before the command voltage to the high-voltage DC / DC converter 27 by the controller 11 is increased to near the open voltage of the fuel cell stack 1 in step S5, under the control of the controller 11 Then, the operation of the low-voltage DC / DC converter 29 dedicated to step-down is stopped, and thereafter, until the relay 24a is turned on in step S8, the power of the low-voltage auxiliary equipment 23 is reduced to the low-voltage battery 30. Only supply from.
[0049]
This allows the fuel cell system to suppress power fluctuations on the high-power system formed by each unit between the relay box 24 and the inverter 25. As a result, the maximum The voltage can be reduced.
[0050]
In the fuel cell system, in step S4, the necessity of stabilizing the power consumption of the accessories 22 is estimated using the elapsed time from the start of the operation of the accessories 22. As a method of estimating whether power consumption is stable or not, for example, a method in which predetermined power fluctuation detection means calculates power from the voltage and current of the high-voltage battery 26 and the power fluctuation is within a predetermined value When the determination is made, the method may shift to step S5.
[0051]
In the fuel cell system, it is possible to more accurately detect that the power consumption of the auxiliary equipment 22 has been stabilized by using this method. Can be shifted, and the start-up time can be minimized.
[0052]
[Effects of Embodiment]
In the above-described fuel cell system, as shown in FIG. 5 (a), the power consumption of the auxiliary equipment 22 varies over time without activation, as shown in FIG. Here, an air compressor and a water pump are taken as the auxiliary devices 22, and the power consumption characteristics of the air compressor are indicated by a curve a, and the power consumption characteristics of the water pump are indicated by a curve b. From these characteristics, in the fuel cell system, assuming that the activation time of the high-pressure DC / DC converter 27 is T1 and the time at which the supply of hydrogen is started is T2, immediately after the time T2, both the air compressor and the water pump are used. Power consumption fluctuates greatly. Here, in the fuel cell system, as described above, as a countermeasure for absorbing a slight error caused by a response delay of the high-voltage DC / DC converter 27 with respect to the fluctuation of the power consumption of the auxiliary equipment 22, usually, a measure is taken. , Only the capacitor 25 a provided inside the inverter 25.
[0053]
Therefore, as shown by a curve c in FIG. 5B showing a time change of the voltage as a comparative example with the present invention, it is caused by a response delay of the high-voltage DC / DC converter 27 with respect to the fluctuation of the power consumption of the accessories 22. Due to a slight error, the voltage between the high-voltage DC / DC converter 27 and the inverter 25 greatly fluctuates.
[0054]
In this comparative example, as shown by the voltage level d in FIG. 5B, at the time of startup, the command voltage to the high-voltage DC / DC converter 27 by the controller 11 is changed to a curve e in FIG. 5B. This is a case where the voltage is set to be higher than the open-circuit voltage of the fuel cell stack 1 indicated by.
[0055]
As described above, in the comparative example, since the original operating voltage is high, the open circuit voltage of the fuel cell stack 1 may greatly exceed due to the fluctuation. Therefore, in the comparative example, in order to be able to withstand a voltage that greatly exceeds the open-circuit voltage of the fuel cell stack 1, for example, various parts including the relay 24a and the diode 24b are required to have high withstand voltage, and the cost is inevitably reduced. Will be higher.
[0056]
On the other hand, in the above-described fuel cell system, as shown by a curve f in FIG. 5B, the controller 11 controls the high voltage from the start to the time when the power consumption of the accessories 22 is stabilized. Command voltage to the DC / DC converter 27 is set low.
[0057]
As a result, in the fuel cell system, the voltage between the relay box 24 and the inverter 25 when the power consumption of the accessories 22 fluctuates is changed as shown by a curve g in FIG. 5B. Even if this voltage fluctuates, the maximum voltage can be reduced. As a result, in the fuel cell system, the withstand voltage of various components including, for example, the relay 24a and the diode 24b can be reduced to about the open voltage of the fuel cell stack 1, and the cost can be reduced. .
[0058]
In the above-described fuel cell system, after the command voltage to the high-voltage DC / DC converter 27 by the controller 11 is set low until the power consumption of the auxiliary equipment 22 is stabilized, the high-voltage After the command voltage to the DC / DC converter 27 is controlled near the open voltage of the fuel cell stack 1, a relay connection is made between the fuel cell stack 1 and the drive motor 21. That is, in the fuel cell system, the predetermined value + α (in FIG. 5B), which is a voltage near the predetermined value (the voltage level h in FIG. 5B) described in steps S5 and S6 in FIG. At the voltage level i), and thereafter at time T ₃ Then, a relay connection is made between the fuel cell stack 1 and the drive motor 21.
[0059]
Therefore, in the fuel cell system, the power is not suddenly started to be taken out of the fuel cell stack 1 and the connection between the fuel cell stack 1 and the drive motor 21 is made via the diode 24b. 1 can be started, and despite the simple control, the overcurrent caused by the voltage mismatch between the high-voltage DC / DC converter 27 and the connection between the fuel cell stack 1 and the drive motor 21 Can be prevented from occurring.
[0060]
Further, in the fuel cell system, the stability of the power consumption of the auxiliary equipment 22 can be determined based on the power fluctuation of the high-voltage battery 26. In this case, the power consumption of the auxiliary equipment 22 can be more accurately determined. Since it is possible to detect that the power consumption is stable, the startup time can be reduced.
[0061]
Furthermore, in the fuel cell system, until the relay 24a is turned on, the electric power of the weak electric auxiliary equipment 23 is supplied only from the low-voltage battery 30 so that the electric power from the relay box 24 to the inverter 25 is maintained. It is possible to suppress power fluctuations applied to the high-power system constituted by the respective sections between them, and as a result, it is possible to reduce the maximum voltage between the high-voltage DC / DC converter for stack 27 and the inverter 25.
[0062]
Further, in the fuel cell system, after the relay 24a of the high voltage DC / DC converter 27 for the stack is turned on, the output voltage of the high voltage DC / DC converter 27 is controlled under the control of the controller 11. By gradually changing the command voltage so as to be lower than the output voltage of the battery stack 1, the power supply from the fuel cell stack 1 to the drive motor 21 can be started smoothly by the action of the diode 24b. .
[0063]
The above embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and even if it is in a form other than this embodiment, as long as it does not deviate from the technical idea according to the present invention, Of course, various changes are possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a gas system of a fuel cell system shown as an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an electric system of the fuel cell system.
FIG. 3 is a diagram illustrating an example of current-voltage (power) characteristics of a fuel cell stack in the fuel cell system.
FIG. 4 is a flowchart showing a series of steps when controlling a command voltage to a DC / DC converter in the fuel cell system.
FIG. 5 is a diagram showing a change over time in power consumption of accessories and a change over time in voltage in the fuel cell system.
[Explanation of symbols]
1 Fuel cell stack
1a Air electrode
1b Hydrogen electrode
2 Air supply system
3 Pressure sensor
4 Air pressure regulating valve
5 Hydrogen supply system
6 Hydrogen pressure regulating valve
7 Ejector
8 Pressure sensor
9 Purge valve
10 Pipe for reflux
11 Controller
21 Drive motor
22 Auxiliary equipment
23 Light Electric Auxiliary Equipment
24 relay box
24a relay
24b diode
25 Inverter
25a capacitor
26 Battery for high voltage
27 DC / DC converter for high voltage
28 Voltage sensor
29 DC / DC Converter for Low Voltage
30 Battery for low voltage

Claims (4)

A fuel cell system that drives auxiliary equipment when starting a fuel cell stack that generates power using fuel gas and air, and supplies power generated by the fuel cell stack to a load,
Voltage conversion means for controlling a DC voltage between the fuel cell stack and the load,
A secondary battery connected to the load and the accessories in parallel with the fuel cell stack via the voltage conversion means;
Relay means provided between the fuel cell stack and the connection portion of the voltage conversion means, for connecting or disconnecting the fuel cell stack and the load,
A diode provided between the relay means and the connection portion, for preventing a current from flowing from the load to the fuel cell stack;
At the time of start-up, the relay unit is shut off, the command voltage to the voltage conversion unit is set to a value smaller than the open-circuit voltage of the fuel cell stack, the accessories are operated, and then the command voltage to the voltage conversion unit is turned on. And a control unit for connecting the relay unit after controlling the voltage around the open voltage of the fuel cell stack. Further comprising a power fluctuation detecting means for detecting power fluctuation of the secondary battery,
The control means controls the command voltage to the voltage conversion means to be close to the open voltage of the fuel cell stack when the power fluctuation detection means determines that the power fluctuation of the secondary battery is within a predetermined value. The fuel cell system according to claim 1, wherein: Weak electric auxiliary machines operating at a lower voltage than the auxiliary machines;
A low-voltage secondary battery with a lower voltage than the secondary battery,
Step-down voltage conversion means for stepping down a DC voltage of electric power generated by the fuel cell stack and supplying the stepped-down power supply to the weak electric auxiliary devices and the weak electric secondary battery,
The control means stops the operation of the step-down voltage conversion means at the time of start-up, and supplies power to the weak electricity auxiliary devices only from the weak electricity secondary battery. Item 3. The fuel cell system according to Item 2. The control means changes a command voltage such that an output voltage of the voltage conversion means becomes lower than an output voltage of the fuel cell stack after connection of the relay means. Item 4. The fuel cell system according to any one of Items 3.

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